WO2024024446A1 - Carbon nanotube dispersed liquid, slurry for nonaqueous secondary battery negative electrodes, negative electrode for nonaqueous secondary batteries, and nonaqueous secondary battery - Google Patents

Carbon nanotube dispersed liquid, slurry for nonaqueous secondary battery negative electrodes, negative electrode for nonaqueous secondary batteries, and nonaqueous secondary battery Download PDF

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WO2024024446A1
WO2024024446A1 PCT/JP2023/025180 JP2023025180W WO2024024446A1 WO 2024024446 A1 WO2024024446 A1 WO 2024024446A1 JP 2023025180 W JP2023025180 W JP 2023025180W WO 2024024446 A1 WO2024024446 A1 WO 2024024446A1
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negative electrode
secondary battery
water
slurry
mass
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PCT/JP2023/025180
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French (fr)
Japanese (ja)
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晃平 居城
弘樹 大島
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日本ゼオン株式会社
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a carbon nanotube dispersion, a slurry for a non-aqueous secondary battery negative electrode, a negative electrode for a non-aqueous secondary battery, and a non-aqueous secondary battery.
  • Carbon nanotubes have excellent properties such as mechanical strength, optical properties, electrical properties, thermal properties, and molecular adsorption ability, so they are used in electronic circuits such as logic circuits.
  • memories such as DRAM, SRAM, and NRAM
  • electronic components such as semiconductor devices, interconnects, complementary MOS, and bipolar transistors
  • chemical sensors such as trace gas detectors
  • biosensors such as DNA and protein measuring instruments; etc. It is used in various electronic products.
  • secondary battery electrodes used to form electrode mixture layers included in electrodes of non-aqueous secondary batteries such as lithium ion secondary batteries
  • CNTs are also used as a conductive material for slurry.
  • the electrodes of secondary batteries expand and contract significantly during charging and discharging, which reduces the conductivity of the electrodes and reduces the cycle characteristics of the secondary battery.
  • CNTs are used as a conductive material in the slurry for secondary battery electrodes, A secondary battery can be obtained in which a decrease in conductivity is suppressed and excellent cycle characteristics are achieved.
  • CNTs are first dispersed in an N-methylpyrrolidone (NMP) solution of an acrylic binder to prepare a dispersion solution, and then the obtained dispersion solution is mixed with a positive electrode active material, etc.
  • NMP N-methylpyrrolidone
  • a positive electrode mixture slurry is prepared using the following steps.
  • CNT dispersions containing water that have excellent dispersibility of CNTs have been developed.
  • a CNT dispersion for example, in Patent Document 2, the average outer diameter of the carbon nanotubes is more than 3 nm and 25 nm or less, the BET specific surface area of the carbon nanotubes is 150 to 800 m 2 /g, and, A carbon nanotube dispersion using carbon nanotubes in which the fiber length of the carbon nanotubes in the carbon nanotube dispersion is 0.8 to 3.5 ⁇ m has been proposed.
  • Patent Document 3 discloses an aqueous carbon nanotube using multi-walled carbon nanotubes having a length of 2 ⁇ m or more and an aspect ratio of length to diameter within a range of 200 to 1000. Dispersions have been proposed.
  • an object of the present invention is to provide a carbon nanotube dispersion liquid that can prepare a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties, and also allows a non-aqueous secondary battery to exhibit excellent cycle characteristics.
  • Another object of the present invention is to provide a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties and can exhibit excellent cycle characteristics in a non-aqueous secondary battery.
  • Another object of the present invention is to provide a negative electrode for a non-aqueous secondary battery that allows the non-aqueous secondary battery to exhibit excellent cycle characteristics.
  • Another object of the present invention is to provide a non-aqueous secondary battery that can exhibit excellent cycle characteristics.
  • the present inventor conducted extensive studies with the aim of solving the above problems.
  • the present inventor has found that a CNT dispersion containing CNTs whose average length and average diameter are within predetermined ranges, a water-soluble polymer, and water is a non-aqueous type that has excellent thickening suppressing properties.
  • the present invention aims to advantageously solve the above problems, and the present invention provides [1] a carbon nanotube dispersion containing carbon nanotubes, a water-soluble polymer, and water
  • the carbon nanotubes are a carbon nanotube dispersion having an average length of 5 ⁇ m or more and 100 ⁇ m or less, and an average diameter of 20 nm or more and 100 nm or less.
  • a carbon nanotube dispersion containing CNTs whose average length and average diameter are within predetermined ranges, a water-soluble polymer, and water can be used as a non-aqueous secondary material with excellent viscosity-inhibiting properties.
  • a slurry for a battery negative electrode can be prepared, and a non-aqueous secondary battery including a negative electrode produced using the slurry for a negative electrode can exhibit excellent cycle characteristics.
  • the average length and average diameter of CNTs can be measured using the method described in the Examples of this specification.
  • a polymer is "water-soluble" it means that when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25°C, the insoluble content is less than 1.0% by mass. .
  • the water-soluble polymer has an acid functional group. If a water-soluble polymer having an acid functional group is used, the dispersibility and storage stability of the CNT dispersion can be improved.
  • the acid functional groups of the water-soluble polymer be an alkali metal base or an ammonium base. If at least a part of the acid functional groups of the water-soluble polymer are in the form of either an alkali metal salt or an ammonium salt, the dispersibility and storage stability of the CNT dispersion can be improved, and the CNT It is possible to further improve the viscosity increase suppressing property of a slurry for a negative electrode containing a dispersion liquid and the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for a negative electrode.
  • the mass ratio of the carbon nanotubes to the water-soluble polymer is preferably 0.1 or more and 10 or less. If the mass ratio of CNT to water-soluble polymer (CNT/water-soluble polymer) in the CNT dispersion is within the above-mentioned predetermined range, the storage stability of the CNT dispersion can be improved.
  • the carbon nanotube dispersion liquid according to any one of [1] to [4] above preferably has a pH of 6 or more and 10 or less. If the pH of the CNT dispersion liquid is within the above-mentioned predetermined range, the thickening suppressing property of the negative electrode slurry containing the CNT dispersion liquid will be further improved, and a secondary battery equipped with a negative electrode prepared using the negative electrode slurry will be improved. Cycle characteristics can be further improved.
  • a slurry for a non-aqueous secondary battery negative electrode comprising: As described above, a non-aqueous secondary battery negative electrode slurry containing a negative electrode active material and the above-mentioned CNT dispersion has excellent viscosity-inhibiting properties, and a non-aqueous secondary battery negative electrode slurry containing a negative electrode slurry prepared using the negative electrode slurry has excellent viscosity-inhibiting properties.
  • a water-based secondary battery can exhibit excellent cycle characteristics.
  • the negative electrode active material contains a silicon-based negative electrode active material. If a silicon-based negative electrode active material (negative electrode active material containing silicon) is used as the negative electrode active material, it is possible to increase the capacity of a non-aqueous secondary battery equipped with a negative electrode prepared using a slurry for a non-aqueous secondary battery negative electrode. can.
  • the silicon-based negative electrode active material has particularly large expansion and contraction upon charging and discharging, and the slurry for the non-aqueous secondary battery negative electrode of the present invention is prepared using the above-mentioned carbon nanotube dispersion of the present invention. Therefore, even when a silicon-based negative electrode active material is used as the negative electrode active material, the decrease in conductivity of the electrode composite layer is suppressed, forming a negative electrode that can exhibit excellent cycle characteristics in non-aqueous secondary batteries. can do.
  • a polymer when a polymer "contains a monomer unit", it means that "a repeating unit derived from the monomer is contained in the polymer obtained using the monomer”. means.
  • the content ratio of the carboxylic acid group-containing monomer unit in the particulate polymer exceeds all repeating units contained in the particulate polymer. As 100% by mass, it is preferably 3% by mass or more and 30% by mass or less. If the content ratio of the carboxylic acid group-containing monomer unit in the particulate polymer is within the above-mentioned predetermined range, the cycle of a non-aqueous secondary battery including a negative electrode prepared using the slurry for a non-aqueous secondary battery negative electrode. The characteristics can be further improved.
  • the content of repeating units (monomeric units) in the polymer can be measured using nuclear magnetic resonance (NMR) methods such as 1 H-NMR and 13 C-NMR.
  • the present invention aims to advantageously solve the above problems, and the present invention provides a slurry for a non-aqueous secondary battery negative electrode according to any one of [10] [6] to [9] above.
  • This is a negative electrode for a non-aqueous secondary battery, including a negative electrode composite material layer formed using the above-mentioned method.
  • a negative electrode for a non-aqueous secondary battery comprising a negative electrode composite layer formed using the slurry for a non-aqueous secondary battery negative electrode described above can exhibit excellent cycle characteristics in a non-aqueous secondary battery. Can be done.
  • the present invention aims to advantageously solve the above problems, and the present invention provides a non-aqueous secondary battery comprising the negative electrode for a non-aqueous secondary battery according to [11] above [10]. be.
  • a non-aqueous secondary battery equipped with the above-described negative electrode for a non-aqueous secondary battery can exhibit excellent cycle characteristics.
  • a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties, and to provide a carbon nanotube dispersion that can exhibit excellent cycle characteristics in a non-aqueous secondary battery. Can be done. Further, according to the present invention, it is possible to provide a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties and can also cause a non-aqueous secondary battery to exhibit excellent cycle characteristics. Further, according to the present invention, it is possible to provide a negative electrode for a non-aqueous secondary battery that allows a non-aqueous secondary battery to exhibit excellent cycle characteristics. Further, according to the present invention, it is possible to provide a non-aqueous secondary battery that can exhibit excellent cycle characteristics.
  • the CNT dispersion of the present invention is not particularly limited, and can be used, for example, as a material for producing a non-aqueous secondary battery negative electrode slurry (hereinafter sometimes simply referred to as "negative electrode slurry"). Can be used.
  • the negative electrode slurry of the present invention is prepared using the CNT dispersion of the present invention.
  • the negative electrode for non-aqueous secondary batteries of the present invention (hereinafter sometimes simply referred to as "negative electrode”) is characterized by comprising a negative electrode composite layer formed using the negative electrode slurry of the present invention. shall be.
  • non-aqueous secondary battery of the present invention is characterized by comprising the negative electrode of the present invention.
  • the CNT dispersion of the present invention can be used as a raw material for composite materials containing resin and CNTs, and in the production of electronic products.
  • the CNT dispersion of the present invention contains CNTs whose average length and average diameter are each within predetermined ranges, a water-soluble polymer, and water, and optionally contains other components. Note that the CNT dispersion usually does not contain electrode active materials (positive electrode active material, negative electrode active material).
  • the CNT dispersion of the present invention it is possible to prepare a slurry for a negative electrode that is excellent in suppressing thickening, and also exhibits excellent cycle characteristics in a secondary battery equipped with a negative electrode prepared using the slurry for a negative electrode. can be done.
  • the CNTs may be single-walled CNTs or multi-walled CNTs. Furthermore, as the CNTs, single-walled CNTs and multi-walled CNTs may be used in combination at any ratio. From the viewpoint of improving the dispersibility and storage stability of the CNT dispersion, it is preferable to use multi-walled CNTs as the CNTs.
  • CNTs are not particularly limited, and those synthesized using known CNT synthesis methods such as arc discharge method, laser ablation method, and chemical vapor deposition method (CVD method) can be used. Furthermore, after the CNTs have been synthesized by the above-described synthesis method, they may be subjected to dispersion processing, as necessary, in order to adjust the average length within a predetermined range, which will be described later. By performing the dispersion treatment on the CNTs, some of the CNT fibers are cut, so that the average length of the CNTs after the dispersion treatment can be adjusted within the above-mentioned predetermined range. Details of the dispersion treatment will be described later in the section "Preparation of CNT dispersion".
  • the average length of the CNTs in the CNT dispersion liquid needs to be 5 ⁇ m or more, preferably 6 ⁇ m or more, more preferably 7 ⁇ m or more, even more preferably 8 ⁇ m or more, and 100 ⁇ m or less. It is preferably 80 ⁇ m or less, more preferably 60 ⁇ m or less, even more preferably 40 ⁇ m or less, and even more preferably 20 ⁇ m or less.
  • the average length of the CNTs in the CNT dispersion is 5 ⁇ m or more, a good conductive path can be formed in the negative electrode composite layer of the negative electrode prepared using the negative electrode slurry containing the CNT dispersion.
  • the cycle characteristics of the included secondary battery can be sufficiently improved.
  • the peel strength of the negative electrode can be improved.
  • the average length of the CNTs in the CNT dispersion is 100 ⁇ m or less, the thickening suppressing properties of the negative electrode slurry containing the CNT dispersion can be sufficiently improved.
  • the average length of CNTs in the CNT dispersion may be 10 ⁇ m or more or 10 ⁇ m or less. Note that the average length of the CNTs can be controlled by the CNT synthesis method, the dispersion processing of the CNTs after synthesis, and the like.
  • the average diameter of the CNTs in the CNT dispersion needs to be 20 nm or more, preferably 30 nm or more, more preferably 40 nm or more, and needs to be 100 nm or less, and 80 nm or less. It is preferable that it is, and it is more preferable that it is 60 nm or less. When the average diameter of the CNTs in the CNT dispersion is 20 nm or more, it is possible to sufficiently improve the viscosity-inhibiting properties of the negative electrode slurry containing the CNT dispersion.
  • the average diameter of CNTs in the CNT dispersion is 100 nm or less, the number of CNTs per unit mass can be sufficiently increased. Since a good conductive path can be formed in the composite material layer, the cycle characteristics of a secondary battery including the negative electrode can be sufficiently improved. Moreover, if the average diameter of the CNTs in the CNT dispersion liquid is the above-mentioned upper limit, the number of CNTs per unit mass can be sufficiently increased, so that the peel strength of the negative electrode can be improved. Further, the average diameter of CNTs in the CNT dispersion may be 50 nm or more or 50 nm or less. Note that the average diameter of the CNTs can be controlled by the CNT synthesis method.
  • the ratio of the G band peak intensity to the D band peak intensity (G/D ratio) in the Raman spectrum is preferably 0.4 or more, more preferably 0.5 or more, and 0.6 or more. It is even more preferable that there be. If the G/D ratio of CNT is equal to or higher than the above lower limit, the cycle characteristics of the secondary battery can be further improved. Note that the upper limit of the G/D ratio of CNT is not particularly limited, but is, for example, 200 or less.
  • the "G/D ratio" of CNT is the Raman spectrum obtained by measuring the Raman spectrum of CNT using a microlaser Raman spectrophotometer (Nicolet Almega XR manufactured by Thermo Fisher Scientific Co., Ltd.).
  • the intensity of the G-band peak observed near 1590 cm ⁇ 1 and the intensity of the D-band peak observed near 1340 cm ⁇ 1 can be calculated as a ratio of these.
  • the content ratio of CNTs in the CNT dispersion is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and 0.1% by mass or more, more preferably 0.2% by mass or more, based on the mass of the entire CNT dispersion as 100% by mass. It is more preferably 3% by mass or more, preferably 10.0% by mass or less, more preferably 5.0% by mass or less, even more preferably 2.0% by mass or less, 1 It is more preferable that the amount is .0% by mass or less. If the content of CNT in the CNT dispersion is equal to or higher than the above lower limit, the productivity of products such as negative electrode slurry prepared using the CNT dispersion can be improved. On the other hand, if the content of CNT in the CNT dispersion is below the above upper limit, sufficiently high dispersibility and storage stability of the CNT dispersion can be ensured.
  • the water-soluble polymer is a component that can function as a dispersant in the CNT dispersion.
  • a natural polymer compound may be used, a semi-synthetic polymer compound obtained by modifying the natural polymer compound using a chemical reaction, or a semi-synthetic polymer compound obtained by modifying the natural polymer compound using a chemical reaction.
  • An artificially produced synthetic polymer compound may also be used.
  • specific examples of the natural polymer compound and the semi-synthetic polymer compound include those described in JP-A-2017-010822.
  • the synthetic polymer compound for example, a water-soluble polymer obtained by polymerizing one or more types of monomers by a polymerization reaction can be used.
  • a water-soluble polymer having an acid functional group as the water-soluble polymer. Further, it is more preferable to use a cellulose derivative having an acid functional group such as carboxymethylcellulose and its salt, and it is particularly preferable to use a water-soluble polymer having an acid functional group.
  • Examples of the acid functional groups possessed by water-soluble polymers such as the above-mentioned water-soluble polymers and cellulose derivatives include carboxylic acid groups, sulfonic acid groups, and phosphoric acid groups. Note that the water-soluble polymer and cellulose derivative may have only one type of these acid functional groups, or may have two or more types in combination in any ratio.
  • the above-mentioned “acid functional group” that the water-soluble polymer has includes a salt neutralized with a base. That is, at least a portion of the above-mentioned “acid functional groups” that the water-soluble polymer has may be in the form of a salt.
  • the acid functional group includes not only the carboxylic acid group (-COOH) but also a neutralized type such as a lithium carboxylate group (-COO - Li + ).
  • the dispersibility and storage stability of the CNT dispersion we further evaluated the dispersibility and storage stability of the CNT dispersion, the viscosity-inhibiting properties of a negative electrode slurry containing the CNT dispersion, and the cycle characteristics of a secondary battery equipped with a negative electrode prepared using the negative electrode slurry.
  • the acid functional groups of the water-soluble polymer are an alkali metal base or an ammonium base. That is, at least a portion of the acid functional groups of the water-soluble polymer are preferably in the form of either an alkali metal salt or an ammonium salt. Note that all of the acid functional groups may be an alkali metal base or an ammonium base.
  • alkali metal base examples include lithium metal base, sodium metal base, potassium metal base, and the like.
  • water-soluble polymer may have only one type of these alkali metal bases and ammonium bases as an acid functional group, or a combination of two or more types in any ratio. Good too.
  • the water-soluble polymer as the water-soluble polymer preferably has a carboxylic acid group as the acid functional group. If the acid functional group of the water-soluble polymer is a carboxylic acid group, the dispersibility and storage stability of the CNT dispersion, the thickening suppressing property of the negative electrode slurry containing the CNT dispersion, and the negative electrode slurry The cycle characteristics of a secondary battery including a negative electrode produced using the method can be further improved. In addition, the dispersibility and storage stability of the CNT dispersion can be maintained well regardless of the type of CNT.
  • the water-soluble polymer as the water-soluble polymer preferably has a sulfonic acid group as the acid functional group. If the acid functional group that the water-soluble polymer has is a sulfonic acid group, the dispersibility and storage stability of the CNT dispersion, the thickening suppressing property of the negative electrode slurry containing the CNT dispersion, and the negative electrode slurry. The cycle characteristics of a secondary battery including a negative electrode produced using the method can be further improved.
  • the water-soluble polymer that can be preferably used as the water-soluble polymer preferably contains an ether group.
  • the "ether group” here is a group represented by "-R'OR-”.
  • R and R' represent a linear or branched hydrocarbon group having 1 to 10 carbon atoms, preferably an alkyl group, and each may be the same or different.
  • the number of carbon atoms in R and R' is preferably 2 or more and 5 or less, preferably 2 or 3, and more preferably 2. If the water-soluble polymer contains an ether group, the dispersibility and storage stability of the CNT dispersion, the ability to suppress thickening of the negative electrode slurry containing the CNT dispersion, and the negative electrode prepared using the negative electrode slurry are improved.
  • the cycle characteristics of the included secondary battery can be further improved.
  • the water-soluble polymer as the water-soluble polymer contained in the CNT dispersion of the present invention will be explained by illustrating the first form and the second form, but the water-soluble polymer is limited to these. It's not a thing.
  • the water-soluble polymer of the first form contains a carboxylic acid group-containing monomer unit and a conjugated diene monomer unit. Note that the water-soluble polymer of the first form may contain repeating units (other repeating units) other than the carboxylic acid group-containing monomer unit and the conjugated diene monomer unit.
  • the carboxylic acid group-containing monomer unit is a repeating unit containing a carboxylic acid group (-COOH).
  • some or all of the carboxylic acid groups of the carboxylic acid group-containing monomer units are sodium carboxylate groups (-COO - Na + ), lithium carboxylate groups (-COO - Li + ). It is preferably in at least one of the following states: , and ammonium carboxylate group (-COO - NH 4 + ).
  • the carboxylic acid group takes the form of at least one of the above-mentioned carboxylic acid groups, the dispersibility and storage stability of the CNT dispersion, the thickening suppressing property of a slurry for a negative electrode containing the CNT dispersion, and the negative electrode
  • the cycle characteristics of a secondary battery including a negative electrode produced using the slurry can be further improved.
  • Examples of the carboxylic acid group-containing monomer that can form the carboxylic acid group-containing monomer unit of the water-soluble polymer of the first form include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their Examples include derivatives.
  • Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid.
  • Examples of monocarboxylic acid derivatives include 2-ethyl acrylic acid, isocrotonic acid, ⁇ -acetoxyacrylic acid, ⁇ -trans-aryloxyacrylic acid, ⁇ -chloro- ⁇ -E-methoxyacrylic acid, and the like.
  • Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.
  • dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoro maleate.
  • examples include alkyl and other maleic acid monoesters.
  • dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methylmaleic anhydride, dimethylmaleic anhydride, and the like.
  • carboxylic acid group-containing monomer acid anhydrides that generate carboxylic acid groups by hydrolysis can also be used.
  • carboxylic acid group-containing monomer may be used alone, or two or more types may be used in combination.
  • carboxylic acid group-containing monomer acrylic acid and methacrylic acid are preferable from the viewpoint of further improving the cycle characteristics of the secondary battery. That is, the water-soluble polymer of the first form preferably contains at least one of an acrylic acid unit and a methacrylic acid unit as the carboxylic acid group-containing monomer unit.
  • the content of the carboxylic acid group-containing monomer unit in the water-soluble polymer of the first form is 30% by mass or more, based on 100% by mass of all repeating units contained in the water-soluble polymer of the first form. It is preferably 40% by mass or more, even more preferably 50% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, and 80% by mass. It is more preferably at most 70% by mass, even more preferably at most 70% by mass. Further, the content of the carboxylic acid group-containing monomer unit in the water-soluble polymer of the first form is 30 mol% or more, with the total repeating units contained in the water-soluble polymer of the first form being 100 mol%.
  • the content of the carboxylic acid group-containing monomer unit in the water-soluble polymer of the first form is within the above-mentioned predetermined range, the dispersibility and storage stability of the CNT dispersion, and the negative electrode containing the CNT dispersion are improved. It is possible to further improve the viscosity increase suppressing property of the slurry for use as well as the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for negative electrode.
  • conjugated diene monomer unit examples include 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2 , 3-dimethyl-1,3-butadiene, and 1,3-pentadiene. These may be used alone or in combination of two or more. Among these, 1,3-butadiene and isoprene are preferred, and isoprene is more preferred.
  • the water-soluble polymer of the first form preferably contains at least one of a 1,3-butadiene unit and an isoprene unit, and preferably contains an isoprene unit as the conjugated diene monomer unit of the first form. More preferred.
  • the content of conjugated diene monomer units in the water-soluble polymer of the first form may be 5% by mass or more, with the total repeating units contained in the water-soluble polymer of the first form being 100% by mass. It is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, preferably 70% by mass or less, and 60% by mass or less. It is more preferable that the amount is at least 50% by mass, and even more preferably 50% by mass or less. Further, the content ratio of the conjugated diene monomer unit in the water-soluble polymer of the first form is 10 mol% or more, with the total repeating units included in the water-soluble polymer of the first form being 100 mol%.
  • the content is preferably 20 mol% or more, further preferably 30 mol% or more, even more preferably 40 mol% or more, preferably 70 mol% or less, and 60 mol%. It is more preferably at most 50 mol%, even more preferably at most 50 mol%. If the content ratio of the conjugated diene monomer units in the water-soluble polymer of the first form is within the above-mentioned predetermined range, the dispersibility and storage stability of the CNT dispersion, and the negative electrode slurry containing the CNT dispersion are improved. It is possible to further improve the viscosity-inhibiting properties of the slurry and the cycle characteristics of a secondary battery including a negative electrode produced using the negative electrode slurry.
  • repeating units that the water-soluble polymer of the first form may contain other than the above-mentioned carboxylic acid group-containing monomer units and conjugated diene monomer units are not particularly limited. Examples include monomer units derived from known monomers (other monomers) copolymerizable with the monomer and the conjugated diene monomer. The other monomers may be used alone or in combination of two or more.
  • the content ratio of other repeating units in the water-soluble polymer of the first form should be adjusted to the total repeating units contained in the water-soluble polymer of the first form. is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 1% by mass or less, and 0 Particularly preferred is mass %. Further, the content ratio of other repeating units in the water-soluble polymer of the first form may be 20 mol% or less, with the total repeating units contained in the water-soluble polymer of the first form being 100 mol%.
  • the total content of carboxylic acid group-containing monomer units and conjugated diene monomer units in the water-soluble polymer of the first form is equal to the total content of all repeating units contained in the water-soluble polymer of the first form.
  • 100% by mass it is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 99% by mass or more, and 100% by mass. % is particularly preferred.
  • the total content ratio of carboxylic acid group-containing monomer units and conjugated diene monomer units in the water-soluble polymer of the first form is 100% of all repeating units contained in the water-soluble polymer of the first form.
  • mol% it is preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, even more preferably 99 mol% or more, and 100 mol%. It is particularly preferable that
  • the water-soluble polymer of the second form contains a sulfonic acid group-containing monomer unit and an alkylene oxide structure-containing monomer unit. Note that the water-soluble polymer of the second form may contain repeating units (other repeating units) other than the sulfonic acid group-containing monomer unit and the alkylene oxide structure-containing monomer unit.
  • the sulfonic acid group-containing monomer unit is a repeating unit containing a sulfonic acid group (-SO 3 H).
  • some or all of the sulfonic acid groups of the sulfonic acid group-containing monomer units are sodium sulfonate groups (-SO 3 - Na + ), lithium sulfonate groups (-SO 3 - Li + ), and ammonium sulfonate group (-SO 3 - NH 4 + ).
  • the sulfonic acid group take the form of at least one of the above-mentioned sulfonic acid groups, the dispersibility and storage stability of the CNT dispersion, the thickening suppressing property of a slurry for a negative electrode containing the CNT dispersion, and the negative electrode
  • the cycle characteristics of a secondary battery including a negative electrode produced using the slurry can be further improved.
  • Examples of the sulfonic acid group-containing monomer that can form the sulfonic acid group-containing monomer unit of the water-soluble polymer of the second form include vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, Examples include styrenesulfonic acid, ethyl (meth)acrylate-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and salts thereof.
  • (meth)allyl means allyl and/or methallyl.
  • the sulfonic acid group-containing monomers may be used alone or in combination of two or more.
  • styrene sulfonic acid is preferable from the viewpoint of further improving the cycle characteristics of the secondary battery. That is, the water-soluble polymer of the second form preferably contains a styrene sulfonic acid unit as the sulfonic acid group-containing monomer unit.
  • the content of the sulfonic acid group-containing monomer unit in the water-soluble polymer of the second form is 40% by mass or more, based on 100% by mass of all repeating units contained in the water-soluble polymer of the second form. It is preferably 50% by mass or more, even more preferably 55% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, and 80% by mass. It is more preferably at most 70% by mass, even more preferably at most 70% by mass. Further, the content of the sulfonic acid group-containing monomer unit in the water-soluble polymer of the second form is 40 mol% or more, with the total repeating units contained in the water-soluble polymer of the second form being 100 mol%.
  • the content ratio of the sulfonic acid group-containing monomer unit in the water-soluble polymer of the second form is within the above-mentioned predetermined range, the dispersibility and storage stability of the CNT dispersion, and the negative electrode containing the CNT dispersion are improved. It is possible to further improve the viscosity increase suppressing property of the slurry for use as well as the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for negative electrode.
  • alkylene oxide structure-containing monomer unit The alkylene oxide structure-containing monomer unit of the water-soluble polymer of the second form is a monomer unit containing a structure that can be represented by the following general formula (I). [In formula (I), m is an integer of 1 or more, and n is an integer of 1 or more. ]
  • the alkylene oxide structure-containing monomer unit By incorporating the alkylene oxide structure-containing monomer unit into the second form of the water-soluble polymer, the dispersibility and storage stability of the CNT dispersion, the ability to suppress thickening of the negative electrode slurry containing the CNT dispersion, In addition, the cycle characteristics of a secondary battery including a negative electrode produced using the negative electrode slurry can be further improved.
  • the integer m is preferably 2 or more and 5 or less, more preferably 2 or 3, and even more preferably 2.
  • the monomer unit containing the structural unit represented by general formula (I) is referred to as an ethylene oxide structure-containing monomer unit.
  • the monomer unit containing the structural unit represented by the general formula (I) is referred to as a propylene oxide structure-containing monomer unit.
  • the integer m is less than or equal to the above upper limit, the dispersibility and storage stability of the CNT dispersion, the thickening suppressing property of the negative electrode slurry containing the CNT dispersion, and the negative electrode produced using the negative electrode slurry are improved.
  • the cycle characteristics of the included secondary battery can be further improved.
  • the integer m is 2, that is, when the water-soluble polymer of the second form contains an ethylene oxide structure-containing monomer unit, the water-soluble polymer of the second form has appropriate hydrophilicity.
  • the water-soluble polymer of the second form can have an increased affinity for water.
  • the water-soluble polymer of the second form contains an ethylene oxide structure-containing monomer unit, the dispersibility and storage stability of the CNT dispersion, and the improvement of the negative electrode slurry containing the CNT dispersion are improved.
  • the viscosity control property and the cycle characteristics of a secondary battery including a negative electrode produced using the negative electrode slurry can be particularly improved.
  • the water-soluble polymer of the second form may contain a plurality of types of alkylene oxide structure-containing monomer units.
  • both the ethylene oxide structure-containing monomer unit and the propylene oxide structure-containing monomer unit may be contained in the water-soluble polymer of the second form.
  • the integer n that defines the repeating number of the monomer unit containing the structure that can be represented by the above formula (I) is preferably 10 or less, more preferably 5 or less, and still more preferably 3 or less. Preferably, the number is 2 or more. That is, the alkylene oxide structure-containing monomer unit contained in the water-soluble polymer of the second form preferably includes a polyalkylene oxide structural unit in which the alkylene oxide structural unit is repeated n times. Further, in the alkylene oxide structural unit, some or all of the hydrogen atoms may be substituted with an arbitrary substituent.
  • the repeating number n for each alkylene oxide structure-containing monomer unit may be the same or different.
  • the number average value of all the repetition numbers n is within the above-mentioned suitable range, and it is more preferable that all the repetition numbers n are within the above-mentioned suitable range.
  • alkylene oxide structure-containing monomer that can form the alkylene oxide structure-containing monomer unit of the water-soluble polymer of the second form include monomers represented by the following general formula (II).
  • R 1 is a (meth)acryloyl group
  • R 2 represents a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms.
  • the number of carbon atoms in the alkyl group is preferably 2 or more and 5 or less, preferably 2 or 3, and more preferably 2.
  • m and n in general formula (II) are the same as m and n in general formula (I).
  • examples of the linear or branched alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, and a propyl group.
  • the monomer represented by general formula (II) is not particularly limited, and examples include ethoxypolyethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, etc. Examples include acrylate, polypropylene glycol mono(meth)acrylate, and methoxypolypropylene glycol (meth)acrylate.
  • ethoxypolyethylene glycol (meth)acrylate is preferred, ethoxydiethylene glycol (meth)acrylate is more preferred, and ethoxydiethylene glycol acrylate is particularly preferred.
  • (meth)acrylate means acrylate or methacrylate, and "(meth)acryloyl” means acryloyl or methacryloyl.
  • the content of the alkylene oxide structure-containing monomer unit in the water-soluble polymer of the second form is 5% by mass or more, based on 100% by mass of all repeating units contained in the water-soluble polymer of the second form. It is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, preferably 60% by mass or less, and 50% by mass. It is more preferably at most 45% by mass, even more preferably at most 45% by mass. Further, the content ratio of the alkylene oxide structure-containing monomer unit in the water-soluble polymer of the second form is 5 mol% or more, with the total repeating units included in the water-soluble polymer of the second form being 100 mol%.
  • the content ratio of the alkylene oxide structure-containing monomer unit in the water-soluble polymer of the second form is within the above-mentioned predetermined range, the dispersibility and storage stability of the CNT dispersion, and the negative electrode containing the CNT dispersion are improved. It is possible to further improve the viscosity increase suppressing property of the slurry for use as well as the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for negative electrode.
  • repeating units that the water-soluble polymer of the second form may contain other than the above-mentioned sulfonic acid group-containing monomer units and alkylene oxide structure-containing monomer units are not particularly limited, and include the above-mentioned sulfonic acid groups. Examples include monomer units derived from known monomers (other monomers) copolymerizable with group-containing monomer units and alkylene oxide structure-containing monomer units. The other monomers may be used alone or in combination of two or more.
  • the content ratio of other repeating units in the water-soluble polymer of the second form is lower than that of all repeating units contained in the water-soluble polymer of the second form. is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 1% by mass or less, and 0 Particularly preferred is mass %.
  • the content ratio of other repeating units in the water-soluble polymer of the second form is preferably 20 mol% or less, assuming that the total repeating units contained in the water-soluble polymer of the second form is 100 mol%.
  • the total content ratio of the sulfonic acid group-containing monomer unit and the alkylene oxide structure-containing monomer unit in the water-soluble polymer of the second form is equal to the total content of the monomer unit containing the sulfonic acid group in the water-soluble polymer of the second form.
  • the unit is 100% by mass, it is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 99% by mass or more, Particularly preferred is 100% by mass.
  • the total content ratio of the sulfonic acid group-containing monomer unit and the alkylene oxide structure-containing monomer unit in the water-soluble polymer of the second form is the total repeating unit contained in the water-soluble polymer of the second form. is preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, even more preferably 99 mol% or more, and 100 mol% or more. Particularly preferred is mole %.
  • the method for preparing the water-soluble polymer is not particularly limited.
  • the water-soluble polymer can be obtained, for example, by polymerizing a monomer composition containing one or more types of monomers in an aqueous solvent.
  • the resulting polymer may optionally be hydrogenated.
  • the content ratio of each monomer in the monomer composition can be determined according to the content ratio of desired repeating units (monomer units) in the polymer.
  • the polymerization method is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used.
  • any reaction such as ionic polymerization, radical polymerization, living radical polymerization, various condensation polymerizations, and addition polymerization can be used.
  • known emulsifiers and polymerization initiators can be used as necessary.
  • hydrogenation can be performed by a known method.
  • neutralization may be performed with an aqueous sodium hydroxide solution, an aqueous lithium hydroxide solution, aqueous ammonia, etc. to prepare a water-soluble polymer having a neutralized acid functional group as described above. good.
  • the content ratio of the water-soluble polymer in the CNT dispersion is not particularly limited, but it is preferably 0.1% by mass or more, and 0.2% by mass or more, based on the mass of the entire CNT dispersion as 100% by mass. It is more preferable that the content is 0.3% by mass or more, even more preferably 5.0% by mass or less, more preferably 2.0% by mass or less, and 1.0% by mass or less. It is more preferable that it is, and even more preferable that it is 0.8% by mass or less. If the content of the water-soluble polymer in the CNT dispersion is equal to or higher than the above lower limit, the dispersibility of the CNT dispersion can be improved. On the other hand, if the content of the water-soluble polymer in the CNT dispersion is below the above upper limit, the storage stability of the CNT dispersion can be improved.
  • the mass ratio of CNT to water-soluble polymer (CNT/water-soluble polymer) in the CNT dispersion is preferably 0.1 or more, more preferably 0.3 or more, and 0.5 or more. It is more preferably 0.7 or more, more preferably 10 or less, more preferably 8 or less, even more preferably 5 or less, even more preferably 3 or less. preferable. If the mass ratio of CNT to water-soluble polymer (CNT/water-soluble polymer) in the CNT dispersion is within the above-mentioned predetermined range, the storage stability of the CNT dispersion can be improved.
  • CNT dispersion may contain other than CNTs, water-soluble polymers, and water are not particularly limited, but include conductive materials other than CNTs, dispersion media other than water, and "slurry for non-aqueous secondary battery negative electrodes.” Components other than the negative electrode active material, which will be described later in the section, are included.
  • the conductive material other than CNT is not particularly limited, and for example, carbon black (acetylene black, Ketjen Black (registered trademark), furnace black, etc.), graphite, carbon flakes, and carbon nanofibers can be used.
  • dispersion medium other than water known organic solvents that are compatible with water can be used.
  • one type of other components may be used alone, or two or more types may be used in combination.
  • a CNT dispersion liquid can be prepared by mixing CNTs, a water-soluble polymer, water, and other components used as necessary.
  • known mixing devices such as a disper, a homo mixer, a planetary mixer, and a kneader can be used for mixing.
  • the CNTs used for preparing the CNT dispersion liquid can be subjected to a dispersion treatment in order to adjust the average length within the above-mentioned predetermined range.
  • a dispersion treatment apparatus such as a ball mill, bead mill, jet mill, etc. can be used.
  • these dispersion processing apparatuses may be of a wet type or a dry type. From the viewpoint of easily adjusting the length of the CNTs within the above-mentioned predetermined range, it is preferable to use a wet jet mill for the dispersion treatment.
  • a CNT dispersion may be prepared by mixing the CNTs after the temperature adjustment with other components such as a water-soluble polymer and water, or as a process that also serves as the preparation of the CNT dispersion itself, A dispersion treatment may be performed on a mixed liquid such as molecules and water.
  • the latter that is, a process that also serves as the preparation of the CNT dispersion itself, involves performing a dispersion treatment on a mixed liquid of CNTs, a water-soluble polymer, water, etc. is preferred.
  • the CNT dispersion liquid can be prepared, for example, according to the following procedure and conditions.
  • CNTs before dispersion treatment a water-soluble polymer, water, and other components used as necessary are mixed to obtain a liquid mixture.
  • the above-mentioned mixing device can be used.
  • the average length of the CNTs before dispersion treatment is, for example, 500 ⁇ m or more and 2000 ⁇ m or less. Note that the average diameter of the CNTs before the dispersion treatment is within the same range as the preferable range of the average diameter of the CNTs described above in the "CNT" section.
  • the obtained mixed liquid is subjected to a dispersion treatment using a wet jet mill, and the liquid after the dispersion treatment is obtained as a CNT dispersion liquid.
  • the pressure applied during the dispersion treatment of the mixed liquid using a wet jet mill is preferably 100 MPa or more, more preferably 125 MPa or more, and preferably 200 MPa or less, more preferably 175 MPa or less.
  • the number of times of dispersion treatment using a wet jet mill (number of passes) is 1 or more, preferably 5 or more and 20 or less.
  • the temperature during the dispersion treatment is preferably 0°C or higher and 80°C or lower.
  • the minimum flow path diameter of the wet jet mill is preferably 100 ⁇ m or more from the viewpoint of clogging prevention, and preferably 500 ⁇ m or less, more preferably 300 ⁇ m or less from the viewpoint of effective pressurized dispersion.
  • wet jet mills that can be used in dispersion processing include "Nano Veita (registered trademark)" (manufactured by Yoshida Kikai Kogyo Co., Ltd.), “BERYU SYSTEM PRO” (manufactured by Bijutsu Co., Ltd.), and ultra-high pressure wet atomization equipment ( (manufactured by Yoshida Kogyo Co., Ltd.), “Nanomizer (registered trademark)” (manufactured by Nanomizer Co., Ltd.), and “Starburst (registered trademark)” (manufactured by Sugino Machine Co., Ltd.).
  • the pH of the CNT dispersion is preferably 6 or higher, more preferably 7 or higher, even more preferably 7.5 or higher, preferably 10 or lower, and more preferably 9 or lower. It is preferably 8.5 or less, and more preferably 8.5 or less. If the pH of the CNT dispersion liquid is within the above-mentioned predetermined range, the thickening suppressing properties of the negative electrode slurry containing the CNT dispersion liquid will be further improved, and a secondary battery equipped with a negative electrode prepared using the negative electrode slurry will be improved. Cycle characteristics can be further improved.
  • the negative electrode slurry of the present invention contains the above-described CNT dispersion liquid and a negative electrode active material, and optionally contains optional components such as a binder.
  • the slurry for a negative electrode of the present invention contains CNTs whose average length and average diameter are within the above-mentioned predetermined ranges, a water-soluble polymer, and water, and optionally contains a binder or the like. Contains optional ingredients. In this way, the slurry for a negative electrode containing the above-mentioned CNT dispersion liquid can form a negative electrode that is excellent in suppressing thickening and can exhibit excellent cycle characteristics in a secondary battery.
  • the negative electrode active material to be added to the negative electrode slurry is not particularly limited, and any known negative electrode active material can be used.
  • negative electrode active materials used in lithium ion secondary batteries include, but are not particularly limited to, carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that are combinations thereof.
  • the carbon-based negative electrode active material refers to an active material whose main skeleton is carbon and into which lithium can be inserted (also referred to as "doping").
  • Carbon-based negative electrode active materials include, for example, carbonaceous materials and graphite. Examples include quality materials.
  • Examples of the carbonaceous material include graphitizable carbon and non-graphitic carbon having a structure close to an amorphous structure represented by glassy carbon.
  • graphitizable carbon include carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers, and pyrolytic vapor growth carbon fibers.
  • examples of the non-graphitic carbon include phenolic resin fired products, polyacrylonitrile carbon fibers, pseudo-isotropic carbon, furfuryl alcohol resin fired products (PFA), hard carbon, and the like.
  • examples of the graphite material include natural graphite, artificial graphite, and the like.
  • the artificial graphite includes, for example, artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800°C or higher, graphitized MCMB obtained by heat-treating MCMB at 2000°C or higher, mesophase pitch carbon fiber at 2000°C or higher.
  • examples include graphitized mesophase pitch carbon fibers heat-treated as described above.
  • a metal-based negative electrode active material is an active material that contains metal, and usually contains an element in its structure that allows insertion of lithium, and has a theoretical electric capacity per unit mass of 500 mAh/m when lithium is inserted. It refers to an active material that is more than 100 g.
  • metal-based active materials include lithium metal, single metals that can form lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn). , Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like.
  • a silicon-based negative electrode active material (a negative electrode active material containing silicon) is preferable. This is because by using a silicon-based negative electrode active material, the capacity of the secondary battery can be increased.
  • silicon-based negative electrode active materials have particularly large expansion and contraction upon charging and discharging, but since the slurry for negative electrodes of the present invention is prepared using the above-mentioned CNT dispersion of the present invention, it can be used as a negative electrode active material. Even when a silicon-based negative electrode active material is used, a decrease in the conductivity of the negative electrode composite layer is suppressed, and a negative electrode that can exhibit excellent cycle characteristics in a secondary battery can be formed.
  • silicon-based negative electrode active materials include silicon (Si), silicon-containing alloys, SiO, SiO x , and composites of Si-containing materials and conductive carbon, which are obtained by coating or compounding Si-containing materials with conductive carbon. etc.
  • the proportion of the silicon-based negative electrode active material in the negative electrode active material is preferably 1% by mass or more, more preferably 3% by mass or more, and 20% by mass or more, based on 100% by mass of the entire negative electrode active material. It is preferably at most 15% by mass, more preferably at most 15% by mass. If the proportion of the silicon-based negative electrode active material is 1% by mass or more, the capacity of the secondary battery can be sufficiently increased, and if the proportion is 20% by mass or less, the cycle characteristics of the secondary battery can be further improved.
  • the particle size of the negative electrode active material is not particularly limited, and may be the same as that of conventionally used negative electrode active materials. Further, the amount of the negative electrode active material in the negative electrode slurry is not particularly limited, and can be within the conventionally used range.
  • the negative electrode active material may be used alone or in combination of two or more types, but from the viewpoint of further improving the cycle characteristics while increasing the capacity of the secondary battery sufficiently,
  • the slurry preferably contains both a carbon-based negative electrode active material made of a graphite material and a silicon-based negative electrode active material.
  • the above-mentioned CNT dispersion of the present invention can be used.
  • the content of CNT in the negative electrode slurry is preferably 0.01 parts by mass or more, and preferably 0.05 parts by mass or more, when the content of the negative electrode active material is 100 parts by mass. is more preferably 0.08 parts by mass or more, still more preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, and 0.15 parts by mass or less. More preferably.
  • the content of the water-soluble polymer in the negative electrode slurry is preferably 0.01 parts by mass or more, and 0.05 parts by mass or more, when the content of the negative electrode active material is 100 parts by mass. More preferably, the amount is 0.08 parts by mass or more, still more preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, and 0.15 parts by mass or less. It is more preferable that
  • the negative electrode slurry examples include a binder, a viscosity modifier, a reinforcing material, an antioxidant, and an electrolyte additive having a function of suppressing decomposition of the electrolyte. These optional components may be used alone or in combination of two or more.
  • the negative electrode slurry preferably contains a binder from the viewpoint of improving the cycle characteristics of the secondary battery.
  • the binder is not particularly limited, and any binder that can be used as a binder for a negative electrode can be used.
  • a binder a carboxylic acid group-containing monomer unit, an aromatic vinyl monomer, etc. It is preferable to use a particulate polymer containing at least a unit and a conjugated diene monomer unit. Note that a particulate polymer that can be used as a binder can be prepared by a known method.
  • carboxylic acid group-containing monomer unit examples of the carboxylic acid group-containing monomer that can form the carboxylic acid group-containing monomer unit of the particulate polymer include the carboxylic acid group-containing monomers mentioned above in the section of "Water-soluble polymer of the first form" The same thing can be mentioned.
  • One type of carboxylic acid group-containing monomer may be used alone, or two or more types may be used in combination.
  • the content of the carboxylic acid group-containing monomer unit in the particulate polymer is preferably 3% by mass or more, and 5% by mass, based on 100% by mass of all repeating units contained in the particulate polymer. It is more preferably at least 30% by mass, more preferably at most 20% by mass. If the content of the carboxylic acid group-containing monomer unit in the particulate polymer is within the above-described predetermined range, the cycle characteristics of a secondary battery including a negative electrode prepared using the negative electrode slurry can be further improved.
  • aromatic vinyl monomer unit examples include styrene, styrene sulfonic acid and its salts, ⁇ -methylstyrene, pt-butylstyrene, and butoxystyrene. , vinyltoluene, chlorostyrene, and vinylnaphthalene.
  • One type of aromatic vinyl monomer may be used alone, or two or more types may be used in combination.
  • styrene is preferable from the viewpoint of further improving the cycle characteristics of a secondary battery including a negative electrode produced using the negative electrode slurry. That is, the particulate polymer preferably contains styrene units as aromatic vinyl monomer units.
  • the content ratio of aromatic vinyl monomer units in the particulate polymer is preferably 20% by mass or more, and 25% by mass or more, with the total repeating units included in the particulate polymer being 100% by mass. It is more preferable that it is, it is preferable that it is 80 mass % or less, and it is more preferable that it is 75 mass % or less. If the content ratio of aromatic vinyl monomer units in the particulate polymer is within the above-determined range, the cycle characteristics of a secondary battery equipped with a negative electrode prepared using the negative electrode slurry can be further improved. .
  • conjugated diene monomer unit examples include those similar to the conjugated diene monomers described above in the section of "first form of water-soluble polymer". It will be done.
  • the conjugated diene monomers may be used alone or in combination of two or more.
  • 1,3-butadiene is preferable from the viewpoint of further improving the cycle characteristics of a secondary battery including a negative electrode prepared using the negative electrode slurry. That is, the particulate polymer preferably contains 1,3-butadiene units as conjugated diene monomer units.
  • the content of the conjugated diene monomer unit in the particulate polymer is preferably 15% by mass or more, and 20% by mass or more, based on 100% by mass of all repeating units contained in the particulate polymer. It is more preferable that the amount is at most 50% by mass, more preferably at most 45% by mass. If the content of the conjugated diene monomer unit in the particulate polymer is within the above range, the cycle characteristics of a secondary battery including a negative electrode produced using the negative electrode slurry can be further improved.
  • repeating units that the above-mentioned particulate polymer may contain other than the carboxylic acid group-containing monomer unit, the aromatic vinyl monomer unit, and the conjugated diene monomer unit are not particularly limited, and include the above-mentioned repeating units. Examples include monomer units derived from known monomers (other monomers) copolymerizable with carboxylic acid group-containing monomers, aromatic vinyl monomers, and conjugated diene monomers. The other monomers may be used alone or in combination of two or more.
  • the content of other repeating units in the particulate polymer is preferably 10% by mass or less, more preferably 5% by mass or less, based on 100% by mass of all repeating units contained in the particulate polymer. , more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0% by mass.
  • the content of the particulate polymer in the negative electrode slurry is preferably 0.1 part by mass or more, and 0.5 parts by mass or more, when the content of the negative electrode active material is 100 parts by mass. It is more preferably 0.8 parts by mass or more, still more preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and 1.5 parts by mass or less. is even more preferable. If the content of the particulate polymer is within the above-mentioned predetermined range, the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for negative electrode can be further improved.
  • the content of the particulate polymer in the negative electrode slurry is preferably 100 parts by mass or more, more preferably 500 parts by mass or more, and 5000 parts by mass or less per 100 parts by mass of CNTs. is preferable, and more preferably 2000 parts by mass or less. If the content of the particulate polymer is within the above-mentioned predetermined range, the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for negative electrode can be further improved.
  • the pH of the negative electrode slurry is preferably 6 or higher, more preferably 7 or higher, preferably 10 or lower, and more preferably 9 or lower. If the pH of the negative electrode slurry is within the above-mentioned predetermined range, it is possible to further improve the thickening suppressing properties of the negative electrode slurry and the cycle characteristics of a secondary battery equipped with a negative electrode prepared using the negative electrode slurry. can.
  • the negative electrode of the present invention includes a negative electrode composite layer formed using the above-mentioned negative electrode slurry.
  • the negative electrode of the present invention typically includes a current collector and a negative electrode composite layer formed on the current collector using the negative electrode slurry.
  • the negative electrode composite layer includes a negative electrode active material, CNTs whose average length and average diameter are within the above-mentioned predetermined ranges, and a water-soluble polymer, and optionally includes a binder or the like. include. Since the negative electrode of the present invention includes the negative electrode composite material layer formed using the above-described slurry for negative electrodes of the present invention, it is possible to make the secondary battery exhibit excellent cycle characteristics.
  • the current collector is made of an electrically conductive and electrochemically durable material.
  • a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. can be used.
  • copper foil is preferable as the current collector used for the negative electrode of a lithium ion secondary battery from the viewpoint of improving the peel strength of the negative electrode. Note that the above-mentioned materials constituting the current collector may be used alone or in combination of two or more.
  • the method for manufacturing the negative electrode of the present invention is not particularly limited.
  • the negative electrode of the present invention can be manufactured by applying the above-described slurry for a negative electrode of the present invention to at least one surface of a current collector and drying it to form a negative electrode composite layer.
  • the manufacturing method includes a step of applying a negative electrode slurry to at least one surface of a current collector (coating step), and drying the negative electrode slurry applied to at least one surface of the current collector. and a step (drying step) of forming a negative electrode composite material layer on the current collector.
  • the method for applying the negative electrode slurry onto the current collector is not particularly limited, and any known method can be used. Specifically, as a coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, etc. can be used. At this time, the negative electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after coating and before drying can be appropriately set depending on the thickness of the negative electrode composite material layer obtained by drying.
  • the method of drying the negative electrode slurry on the current collector is not particularly limited and any known method can be used, such as drying with hot air, hot air, low humidity air, vacuum drying, irradiation with infrared rays, electron beams, etc.
  • An example is a drying method.
  • the negative electrode composite material layer may be subjected to pressure treatment using a mold press, a roll press, or the like.
  • the pressure treatment allows the negative electrode composite material layer to be brought into good contact with the current collector.
  • the negative electrode composite material layer contains a curable polymer
  • the polymer may be cured after forming the negative electrode composite material layer.
  • the secondary battery of the present invention includes the negative electrode of the present invention described above. Since the secondary battery of the present invention includes the negative electrode of the present invention, it has excellent cycle characteristics. In addition, it is preferable that the secondary battery of this invention is a lithium ion secondary battery, for example.
  • This lithium ion secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator.
  • the negative electrode is the above-mentioned negative electrode for a non-aqueous secondary battery of the present invention.
  • the positive electrode is not particularly limited, and any known positive electrode can be used.
  • an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used.
  • the supporting electrolyte for example, lithium salt is used.
  • lithium salts include LiPF 6 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlCl 4 , LiClO 4 , CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) 2 NLi. , (CF 3 SO 2 ) 2 NLi, (C 2 F 5 SO 2 ) NLi, and the like.
  • LiPF 6 , LiClO 4 , and CF 3 SO 3 Li are preferred, and LiPF 6 is particularly preferred since they are easily soluble in solvents and exhibit a high degree of dissociation.
  • one type of electrolyte may be used alone, or two or more types may be used in combination in any ratio.
  • the lithium ion conductivity tends to increase as a supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted depending on the type of supporting electrolyte.
  • the organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte, but examples include dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), Carbonates such as butylene carbonate (BC) and methyl ethyl carbonate (EMC); Esters such as ⁇ -butyrolactone and methyl formate; Ethers such as 1,2-dimethoxyethane and tetrahydrofuran; Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide etc. are preferably used. Alternatively, a mixture of these solvents may be used.
  • DMC dimethyl carbonate
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • PC propylene carbonate
  • Carbonates such as butylene carbonate (BC) and methyl ethyl carbonate (EMC)
  • Esters such as ⁇ -butyrolactone and methyl format
  • carbonates because they have a high dielectric constant and a wide stable potential range, and it is more preferable to use a mixture of ethylene carbonate and ethyl methyl carbonate.
  • concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate, for example, preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and 5 to 10% by mass. is even more preferable.
  • known additives such as fluoroethylene carbonate and ethylmethylsulfone may be added to the electrolyte.
  • the separator is not particularly limited, and for example, those described in JP-A No. 2012-204303 can be used. Among these, polyolefins are preferred because they can reduce the overall film thickness of the separator, thereby increasing the ratio of the electrode active material in the lithium ion secondary battery and increasing the capacity per volume.
  • a microporous membrane made of a resin of the type (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred.
  • the lithium ion secondary battery according to the present invention can be produced by, for example, stacking a positive electrode and a negative electrode with a separator interposed therebetween, and rolling or folding them according to the shape of the battery as necessary and placing them in a battery container. It can be manufactured by injecting an electrolyte into the container and sealing it. In order to prevent an increase in pressure inside the secondary battery, overcharging and discharging, etc., a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary.
  • the shape of the secondary battery may be, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, or the like.
  • the average length and average diameter of CNTs, the dispersibility and storage stability of CNT dispersion, the thickening suppressing property of negative electrode slurry, the peel strength of negative electrode composite layer, and the secondary The cycle characteristics of the batteries were evaluated using the following methods.
  • ⁇ Average length and average diameter of CNT> A coating film formed by applying a CNT dispersion liquid as a measurement sample onto a copper foil was observed using a scanning electron microscope (SEM). 100 CNTs were randomly selected from the obtained SEM images and their lengths and diameters (outer diameters) were measured. Then, the respective average values of the length and diameter (outer diameter) of the 100 CNTs were taken as the average length and average diameter of the CNTs in the CNT dispersion (that is, after the dispersion treatment).
  • SEM scanning electron microscope
  • the measurement was performed in the same manner as above, except that instead of the CNT dispersion liquid, a mixed liquid obtained by mixing CNTs before dispersion treatment with a wet jet mill with an appropriate amount of ion-exchanged water was used as the measurement sample. The average length and average diameter of the CNTs before dispersion treatment were determined.
  • volume average particle diameter D50 of the CNT dispersion liquid was wet-measured in accordance with JIS Z8825:2013 using a laser diffraction/scattering particle size distribution analyzer (Microtrac MT-3300EXII, manufactured by Microtrac Bell Co., Ltd.). The smaller the value of the volume average particle diameter D50, the better the dispersibility.
  • B Volume average particle diameter D50 is 15 ⁇ m or more and less than 50 ⁇ m
  • C Volume average particle diameter D50 is 50 ⁇ m or more
  • ⁇ Storage stability of CNT dispersion The viscosity ⁇ 1 of the CNT dispersion liquid immediately after preparation was measured using a B-type viscometer at a temperature of 25° C. and a spindle rotation speed of 60 rpm, 60 seconds after the start of spindle rotation. After measuring ⁇ 1, the CNT dispersion was stored at 25° C. for 10 days, and the viscosity ⁇ 2 after storage was measured in the same manner as the viscosity ⁇ 1. The ratio of ⁇ 2 to ⁇ 1 ( ⁇ 2/ ⁇ 1) was taken as the viscosity ratio of the dispersion liquid, and evaluation was made according to the following criteria.
  • the ratio of ⁇ 4 to ⁇ 3 ( ⁇ 4/ ⁇ 3) was defined as the slurry viscosity ratio, and evaluation was made according to the following criteria. The closer the value of the slurry viscosity ratio is to 1.0, the more suppressed is the increase in the viscosity of the negative electrode slurry due to the addition of the CNT dispersion, indicating that the negative electrode slurry is excellent in suppressing thickening.
  • B Slurry viscosity ratio is 1.5 or more and less than 3
  • Slurry viscosity ratio is 3 or more
  • ⁇ Peel strength of negative electrode> The produced negative electrode was cut into a rectangle with a length of 100 mm and a width of 10 mm to prepare a test piece. Cellophane tape was attached to the surface of the negative electrode composite material layer of this test piece with the surface of the negative electrode composite material layer facing down. At this time, the cellophane tape specified in JIS Z1522 was used. In addition, cellophane tape was fixed to the test stand. Thereafter, one end of the current collector was pulled vertically upward at a pulling speed of 150 mm/min and the stress was measured when it was peeled off. This measurement was performed three times, the average value was determined, and the average value was used as the peel strength of the negative electrode and evaluated according to the following criteria.
  • peel strength is 8 N/m or more
  • B Peel strength is 5 N/m or more and less than 8 N/m
  • C Peel strength is less than 5 N/m
  • Example 1 Preparation of water-soluble polymer (dispersant)>
  • a reactor 473 parts of ion-exchanged water, 58 parts of methacrylic acid (carboxylic acid group-containing monomer), 0.6 parts of t-dodecyl mercaptan, and diluted with ion-exchanged water to a solid concentration of 10% were added. 3.0 parts of sodium dodecylbenzenesulfonate were charged.
  • the inside of the reactor was sealed, and nitrogen substitution was performed twice while stirring with a stirring blade. After completing the nitrogen substitution, 42 parts of nitrogen-substituted isoprene (conjugated diene monomer) was charged into the reactor.
  • Multiwalled CNT (1) (average length before dispersion treatment: 1000 ⁇ m, average diameter before dispersion treatment: 50 nm, G / D ratio: 2.8) 0.4 part and water-soluble as a dispersant prepared above 0.4 parts of polymer (equivalent to solid content) and an appropriate amount of ion-exchanged water are stirred with a disper (3000 rpm, 60 minutes), and then wet jet mill (manufactured by Yoshida Kikai Kogyo Co., Ltd., product name: Nano Veita) is used. ”) was used to perform distributed processing.
  • ⁇ Preparation of particulate polymer (binder)> In a 5 MPa pressure-resistant container A equipped with a stirrer, 3.15 parts of styrene, 1.66 parts of 1,3-butadiene, 0.2 parts of sodium lauryl sulfate as an emulsifier, 20 parts of ion-exchanged water, and persulfuric acid as a polymerization initiator. After adding 0.03 part of potassium and stirring thoroughly, the mixture was heated to 60° C. to initiate polymerization, and reacted for 6 hours to obtain seed particles.
  • the mixture was heated to 75°C, containing 53.85 parts of styrene, 31.34 parts of 1,3-butadiene, 10.0 parts of acrylic acid, 0.25 parts of tert-dodecylmercaptan as a chain transfer agent, and an emulsifier.
  • the second stage of polymerization was started by starting the addition of .
  • the total monomer composition used was 57 parts of styrene, 33 parts of 1,3-butadiene, and 10 parts of acrylic acid.
  • Five and a half hours after the start of the second stage polymerization addition of the entire amount of the mixture containing these monomer compositions was completed, and then the mixture was further heated to 85° C. and reacted for 6 hours.
  • the reaction was stopped by cooling.
  • a 5% aqueous sodium hydroxide solution was added to the mixture containing this polymer to adjust the pH to 8. Thereafter, unreacted monomers were removed by heating and vacuum distillation. Thereafter, the mixture was cooled to obtain an aqueous dispersion of a water-insoluble particulate polymer.
  • the CNT dispersion obtained as described above was added to the planetary mixer so that the amount of multi-walled CNTs was 0.1 part (equivalent to solid content), and mixed.
  • the solid content concentration was adjusted to 50% with ion-exchanged water, and 1.0 part (solid content equivalent) of the aqueous dispersion of the particulate polymer (binder) obtained as described above was added.
  • a mixed solution was obtained.
  • the resulting mixed solution was defoamed under reduced pressure to obtain a slurry for a negative electrode with good fluidity.
  • the pH of the obtained negative electrode slurry was measured, it was found to be pH 8.
  • the obtained negative electrode slurry was evaluated for its ability to suppress thickening. The results are shown in Table 1.
  • the aluminum foil coated with this positive electrode slurry was transported at a speed of 0.5 m/min in an oven at a temperature of 60°C for 2 minutes and then in an oven at a temperature of 120°C for 2 minutes.
  • the positive electrode slurry was dried to obtain a positive electrode material.
  • This positive electrode original fabric was rolled with a roll press to obtain a positive electrode with a positive electrode composite layer having a thickness of 70 ⁇ m.
  • a single-layer polypropylene separator (manufactured by a dry method, width 65 mm, length 500 mm, thickness 25 ⁇ m, porosity 55%) was prepared. This separator was cut into a 5 cm x 5 cm square and used for manufacturing a secondary battery.
  • An aluminum packaging material exterior was prepared as the battery exterior.
  • the above positive electrode was cut into a square of 4 cm x 4 cm and placed so that the surface on the current collector side was in contact with the exterior of the aluminum packaging material.
  • the square separator was placed on the surface of the positive electrode composite layer of the positive electrode.
  • the negative electrode was cut into a square of 4.2 cm x 4.2 cm, and this was placed on a separator so that the surface on the negative electrode composite layer side faced the separator.
  • Example 2 Example 1 was repeated, except that 0.4 parts of sodium carboxymethylcellulose (sodium salt of carboxymethylcellulose) was used as a dispersant instead of 0.4 parts of the water-soluble polymer when preparing the CNT dispersion. Various operations, measurements, and evaluations were performed in the same manner. The results are shown in Table 1.
  • Example 3 When preparing a CNT dispersion, by changing the number of treatments from 10 to 20 under the dispersion treatment conditions using a wet jet mill, the average length of CNTs in the resulting CNT dispersion was increased from 10 ⁇ m to 5 ⁇ m. Various operations, measurements, and evaluations were performed in the same manner as in Example 1 except for the adjustments. The results are shown in Table 1.
  • Example 4 When preparing a CNT dispersion, the number of treatments was changed from 10 to 5 under the conditions of dispersion treatment using a wet jet mill, thereby increasing the average CNT in the resulting CNT dispersion (i.e., after dispersion treatment). Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the length was adjusted from 10 ⁇ m to 100 ⁇ m. The results are shown in Table 1.
  • Example 5 When preparing the CNT dispersion, instead of multiwall CNT (1) (average length before dispersion treatment: 1000 ⁇ m, average diameter before dispersion treatment: 50 nm, G/D ratio: 2.8), multiwall CNT ( 2) By using (average length before dispersion treatment: 1000 ⁇ m, average diameter before dispersion treatment: 20 nm, G/D ratio: 2.8), the average diameter of CNTs in the obtained CNT dispersion can be changed from 50 nm to 50 nm. Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the wavelength was adjusted to 20 nm. The results are shown in Table 1.
  • Example 6 When preparing a CNT dispersion, instead of multiwall CNT (1) (average length before dispersion treatment: 1000 ⁇ m, average diameter before dispersion treatment: 50 nm, G/D ratio: 2.8), multiwall CNT ( 3) By using (average length before dispersion treatment: 1000 ⁇ m, average diameter before dispersion treatment: 100 nm, G/D ratio: 2.8), the average diameter of CNTs in the obtained CNT dispersion can be changed from 50 nm to 50 nm. Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the wavelength was adjusted to 100 nm. The results are shown in Table 1.
  • Example 7 In the preparation of the water-soluble polymer and the CNT dispersion, various procedures were carried out in the same manner as in Example 1, except that the pH was adjusted using a 5% lithium hydroxide aqueous solution instead of a 5% sodium hydroxide aqueous solution. Operations, measurements and evaluations were performed. The results are shown in Table 1.
  • Example 8 In the preparation of the water-soluble polymer, 59 parts of sodium styrene sulfonate (monomer containing a sulfonic acid group) and 41 parts of ethoxydiethylene glycol acrylate (monomer containing an alkylene oxide structure) were used in place of isoprene and methacrylic acid. Other than that, various operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
  • Example 1 In the same manner as in Example 1, except that the average length of the CNTs in the resulting CNT dispersion was adjusted from 10 ⁇ m to 5 ⁇ m, and the average diameter was adjusted from 50 nm to 12 nm by changing from to 5 times, Various operations, measurements, and evaluations were performed. The results are shown in Table 1.
  • IP indicates an isoprene unit
  • MAA indicates a methacrylic acid unit
  • CMC indicates sodium salt of carboxymethyl cellulose
  • SS represents sodium styrene sulfonate unit
  • EC-A represents an ethoxydiethylene glycol acrylate unit
  • Li indicates lithium salt
  • Na indicates sodium salt.
  • the CNT dispersions of Examples 1 to 8 containing CNTs whose average length and average diameter are within the predetermined ranges, a water-soluble polymer, and water have excellent thickening suppressing properties. It can be seen that it is possible to prepare a slurry for a negative electrode of a non-aqueous secondary battery, and also to make the non-aqueous secondary battery exhibit excellent cycle characteristics. On the other hand, in the case of the CNT dispersion liquids of Comparative Examples 1 and 3 containing CNTs whose average length and average diameter are both less than the predetermined ranges, the prepared slurries for non-aqueous secondary battery negative electrodes have poor thickening suppressing properties. I understand that.
  • the prepared slurry for a nonaqueous secondary battery negative electrode has a thickened viscosity. It can be seen that the suppressive properties are inferior. Furthermore, in the case of the CNT dispersion of Comparative Example 6 containing CNTs whose average diameter is within a predetermined range but whose average length exceeds a predetermined range, the prepared slurry for a non-aqueous secondary battery negative electrode is inhibited from thickening. It turns out that they are inferior in gender.
  • a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties, and to provide a carbon nanotube dispersion that can exhibit excellent cycle characteristics in a non-aqueous secondary battery. Can be done. Further, according to the present invention, it is possible to provide a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties and can allow a non-aqueous secondary battery to exhibit excellent cycle characteristics. Further, according to the present invention, it is possible to provide a negative electrode for a non-aqueous secondary battery that allows a non-aqueous secondary battery to exhibit excellent cycle characteristics. Further, according to the present invention, it is possible to provide a non-aqueous secondary battery that can exhibit excellent cycle characteristics.

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Abstract

The purpose of the present invention is to provide a carbon nanotube dispersed liquid which is capable of preparing a slurry for nonaqueous secondary battery negative electrodes, the slurry having excellent thickening inhibition properties, and which enables a nonaqueous secondary battery to exhibit excellent cycle characteristics. The present invention provides a carbon nanotube dispersed liquid which contains carbon nanotubes, a water-soluble polymer and water, wherein the carbon nanotubes have an average length of 5 µm to 100 µm, while having an average diameter of 20 nm to 100 nm.

Description

カーボンナノチューブ分散液、非水系二次電池負極用スラリー、非水系二次電池用負極及び非水系二次電池Carbon nanotube dispersion, slurry for nonaqueous secondary battery negative electrodes, negative electrodes for nonaqueous secondary batteries, and nonaqueous secondary batteries
　本発明は、カーボンナノチューブ分散液、非水系二次電池負極用スラリー、非水系二次電池用負極及び非水系二次電池に関する。 The present invention relates to a carbon nanotube dispersion, a slurry for a non-aqueous secondary battery negative electrode, a negative electrode for a non-aqueous secondary battery, and a non-aqueous secondary battery.
　カーボンナノチューブ（以下、「ＣＮＴ」と称する場合がある。）は、力学的強度、光学特性、電気特性、熱特性、分子吸着能等の各種特性に優れていることから、ロジック回路等の電子回路、ＤＲＡＭ、ＳＲＡＭ、ＮＲＡＭ等のメモリ、半導体装置、インターコネクト、相補型ＭＯＳ、バイポーラトランジスタ等の電子部品；微量ガス等の検出器等の化学センサー；ＤＮＡ、タンパク質等の測定器等のバイオセンサー；等の様々な電子工学品に用いられている。 Carbon nanotubes (hereinafter sometimes referred to as "CNTs") have excellent properties such as mechanical strength, optical properties, electrical properties, thermal properties, and molecular adsorption ability, so they are used in electronic circuits such as logic circuits. , memories such as DRAM, SRAM, and NRAM; electronic components such as semiconductor devices, interconnects, complementary MOS, and bipolar transistors; chemical sensors such as trace gas detectors; biosensors such as DNA and protein measuring instruments; etc. It is used in various electronic products.
　また、近年では、リチウムイオン二次電池等の非水系二次電池（以下、単に「二次電池」と称する場合がある。）の電極が備える電極合材層の形成に用いられる二次電池電極用スラリーの導電材としてもＣＮＴが用いられている。二次電池の電極は充放電による膨張収縮が大きく、これによって電極の導電性が低下し、二次電池のサイクル特性が低下するところ、二次電池電極用スラリーの導電材としてＣＮＴを用いると、導電性の低下が抑制され、サイクル特性に優れる二次電池を得ることができる。 In addition, in recent years, secondary battery electrodes used to form electrode mixture layers included in electrodes of non-aqueous secondary batteries (hereinafter sometimes simply referred to as "secondary batteries") such as lithium ion secondary batteries CNTs are also used as a conductive material for slurry. The electrodes of secondary batteries expand and contract significantly during charging and discharging, which reduces the conductivity of the electrodes and reduces the cycle characteristics of the secondary battery. However, when CNTs are used as a conductive material in the slurry for secondary battery electrodes, A secondary battery can be obtained in which a decrease in conductivity is suppressed and excellent cycle characteristics are achieved.
　ここで、ＣＮＴの使用にあたっては、その特性を十分に発揮させる観点から、溶媒に分散させる必要があり、ＣＮＴを含む分散液が提案されている。例えば特許文献１では、予め、ＣＮＴをアクリル系結着剤のＮ－メチルピロリドン（ＮＭＰ）溶液中に分散させて分散溶液を作製した後に、得られた分散溶液を正極活物質等と混合することにより、正極合剤スラリーを調製している。 Here, when using CNT, it is necessary to disperse it in a solvent from the viewpoint of fully exhibiting its characteristics, and a dispersion containing CNT has been proposed. For example, in Patent Document 1, CNTs are first dispersed in an N-methylpyrrolidone (NMP) solution of an acrylic binder to prepare a dispersion solution, and then the obtained dispersion solution is mixed with a positive electrode active material, etc. A positive electrode mixture slurry is prepared using the following steps.
　一方、環境負荷及び操作性の観点からは、ＣＮＴを分散させる分散媒として、上述したＮＭＰ等の有機溶媒の代わりに水を使用することが望まれている。しかしながら、ＣＮＴは水との親和性が低いため、ＣＮＴを水に分散させたＣＮＴ分散液を得ることは非常に困難である。 On the other hand, from the viewpoint of environmental impact and operability, it is desired to use water as a dispersion medium for dispersing CNTs instead of the above-mentioned organic solvent such as NMP. However, since CNT has a low affinity for water, it is very difficult to obtain a CNT dispersion in which CNT is dispersed in water.
　そこで、近年では、水を含むＣＮＴ分散液において、ＣＮＴの分散性に優れるＣＮＴ分散液の開発が進められている。このようなＣＮＴ分散液として、例えば特許文献２では、カーボンナノチューブの平均外径が、３ｎｍを超えて２５ｎｍ以下であり、カーボンナノチューブのＢＥＴ比表面積が、１５０～８００ｍ２／ｇであり、且つ、カーボンナノチューブ分散液中のカーボンナノチューブの繊維長が、０．８～３．５μｍであるカーボンナノチューブを用いたカーボンナノチューブ分散液が提案されている。また、特許文献３では、２μｍ以上の長さを有し、且つ、２００～１０００の範囲内の長さ対直径のアスペクト比を有していること等を特徴とする多層カーボンナノチューブを用いた水性分散液が提案されている。 Therefore, in recent years, CNT dispersions containing water that have excellent dispersibility of CNTs have been developed. As such a CNT dispersion, for example, in Patent Document 2, the average outer diameter of the carbon nanotubes is more than 3 nm and 25 nm or less, the BET specific surface area of the carbon nanotubes is 150 to 800 m 2 /g, and, A carbon nanotube dispersion using carbon nanotubes in which the fiber length of the carbon nanotubes in the carbon nanotube dispersion is 0.8 to 3.5 μm has been proposed. Further, Patent Document 3 discloses an aqueous carbon nanotube using multi-walled carbon nanotubes having a length of 2 μm or more and an aspect ratio of length to diameter within a range of 200 to 1000. Dispersions have been proposed.
特開２０１４－２３８９４４号公報JP2014-238944A 特開２０２１－０７２２７９号公報Japanese Patent Application Publication No. 2021-072279 特表２０２２－５２７７０７号公報Special Publication No. 2022-527707
　しかしながら、上記従来技術のＣＮＴ分散液を用いて負極用スラリーを調製した場合、当該負極用スラリーの粘度上昇を抑制すること、即ち、負極用スラリーの増粘抑制性に改善の余地があった。
　また、上記従来技術のＣＮＴ分散液を用いて負極用スラリーを調製した場合、当該負極用スラリーを用いて形成された負極を備える二次電池に優れたサイクル特性を発揮させる点にも改善の余地があった。 However, when a negative electrode slurry is prepared using the CNT dispersion liquid of the prior art, there is room for improvement in suppressing the increase in viscosity of the negative electrode slurry, that is, in suppressing the increase in viscosity of the negative electrode slurry.
In addition, when a slurry for a negative electrode is prepared using the CNT dispersion liquid of the above-mentioned conventional technology, there is also room for improvement in ensuring that a secondary battery equipped with a negative electrode formed using the slurry for a negative electrode exhibits excellent cycle characteristics. was there.
　そこで、本発明は、増粘抑制性に優れた非水系二次電池負極用スラリーを調製可能であると共に、非水系二次電池に優れたサイクル特性を発揮させ得るカーボンナノチューブ分散液を提供することを目的とする。
　また、本発明は、増粘抑制性に優れると共に、非水系二次電池に優れたサイクル特性を発揮させ得る非水系二次電池負極用スラリーを提供することを目的とする。
　また、本発明は、非水系二次電池に優れたサイクル特性を発揮させ得る非水系二次電池用負極を提供することを目的とする。
　また、本発明は、優れたサイクル特性を発揮し得る非水系二次電池を提供することを目的とする。 Therefore, an object of the present invention is to provide a carbon nanotube dispersion liquid that can prepare a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties, and also allows a non-aqueous secondary battery to exhibit excellent cycle characteristics. With the goal.
Another object of the present invention is to provide a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties and can exhibit excellent cycle characteristics in a non-aqueous secondary battery.
Another object of the present invention is to provide a negative electrode for a non-aqueous secondary battery that allows the non-aqueous secondary battery to exhibit excellent cycle characteristics.
Another object of the present invention is to provide a non-aqueous secondary battery that can exhibit excellent cycle characteristics.
　本発明者は、上記課題を解決することを目的として鋭意検討を行った。そして、本発明者は、平均長さ及び平均直径がそれぞれ所定の範囲内であるＣＮＴと、水溶性高分子と、水とを含むＣＮＴ分散液であれば、増粘抑制性に優れた非水系二次電池負極用スラリーを調製可能であると共に、当該負極用スラリーを用いて作製した負極を備える非水系二次電池に優れたサイクル特性を発揮させ得ることを新たに見出し、本発明を完成させた。 The present inventor conducted extensive studies with the aim of solving the above problems. The present inventor has found that a CNT dispersion containing CNTs whose average length and average diameter are within predetermined ranges, a water-soluble polymer, and water is a non-aqueous type that has excellent thickening suppressing properties. We have newly discovered that it is possible to prepare a slurry for a secondary battery negative electrode, and that a non-aqueous secondary battery equipped with a negative electrode prepared using the slurry for a negative electrode can exhibit excellent cycle characteristics, and have completed the present invention. Ta.
　即ち、この発明は、上記課題を有利に解決することを目的とするものであり、本発明は［１］カーボンナノチューブと、水溶性高分子と、水とを含むカーボンナノチューブ分散液であって、前記カーボンナノチューブは、平均長さが５μｍ以上１００μｍ以下であり、且つ、平均直径が２０ｎｍ以上１００ｎｍ以下である、カーボンナノチューブ分散液である。
　このように、平均長さ及び平均直径がそれぞれ所定の範囲内であるＣＮＴと、水溶性高分子と、水とを含むカーボンナノチューブ分散液であれば、増粘抑制性に優れた非水系二次電池負極用スラリーを調製可能であると共に、当該負極用スラリーを用いて作製した負極を備える非水系二次電池に優れたサイクル特性を発揮させることができる。
　なお、本発明において、ＣＮＴの平均長さおよび平均直径は、本明細書の実施例に記載の方法を用いて測定することができる。
　本発明において、高分子が「水溶性」であるとは、温度２５℃において高分子０．５ｇを１００ｇの水に溶解した際に、不溶分が１．０質量％未満となることを意味する。 That is, the present invention aims to advantageously solve the above problems, and the present invention provides [1] a carbon nanotube dispersion containing carbon nanotubes, a water-soluble polymer, and water, The carbon nanotubes are a carbon nanotube dispersion having an average length of 5 μm or more and 100 μm or less, and an average diameter of 20 nm or more and 100 nm or less.
In this way, a carbon nanotube dispersion containing CNTs whose average length and average diameter are within predetermined ranges, a water-soluble polymer, and water can be used as a non-aqueous secondary material with excellent viscosity-inhibiting properties. A slurry for a battery negative electrode can be prepared, and a non-aqueous secondary battery including a negative electrode produced using the slurry for a negative electrode can exhibit excellent cycle characteristics.
Note that in the present invention, the average length and average diameter of CNTs can be measured using the method described in the Examples of this specification.
In the present invention, when a polymer is "water-soluble", it means that when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25°C, the insoluble content is less than 1.0% by mass. .
　［２］上記［１］のカーボンナノチューブ分散液において、前記水溶性高分子が酸官能基を有することが好ましい。
　酸官能基を有する水溶性高分子を用いれば、ＣＮＴ分散液の分散性および保存安定性を向上させることができる。 [2] In the carbon nanotube dispersion liquid of [1] above, it is preferable that the water-soluble polymer has an acid functional group.
If a water-soluble polymer having an acid functional group is used, the dispersibility and storage stability of the CNT dispersion can be improved.
　［３］上記［１］又は［２］のカーボンナノチューブ分散液において、前記水溶性高分子の酸官能基の少なくとも一部が、アルカリ金属塩基又はアンモニウム塩基であることが好ましい。
　水溶性高分子が有する酸官能基の少なくとも一部が、アルカリ金属塩又はアンモニウム塩のいずれかの塩の状態であれば、ＣＮＴ分散液の分散性及び保存安定性を向上させ得ると共に、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、及び、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させることができる。 [3] In the carbon nanotube dispersion liquid of [1] or [2] above, it is preferable that at least a part of the acid functional groups of the water-soluble polymer be an alkali metal base or an ammonium base.
If at least a part of the acid functional groups of the water-soluble polymer are in the form of either an alkali metal salt or an ammonium salt, the dispersibility and storage stability of the CNT dispersion can be improved, and the CNT It is possible to further improve the viscosity increase suppressing property of a slurry for a negative electrode containing a dispersion liquid and the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for a negative electrode.
　［４］上記［１］～［３］の何れかのカーボンナノチューブ分散液において、前記水溶性高分子に対する前記カーボンナノチューブの質量比が、０．１以上１０以下であることが好ましい。
　ＣＮＴ分散液中における水溶性高分子に対するＣＮＴの質量比（ＣＮＴ／水溶性高分子）が上記所定の範囲内であれば、ＣＮＴ分散液の保存安定性を向上させることができる。 [4] In the carbon nanotube dispersion according to any one of [1] to [3] above, the mass ratio of the carbon nanotubes to the water-soluble polymer is preferably 0.1 or more and 10 or less.
If the mass ratio of CNT to water-soluble polymer (CNT/water-soluble polymer) in the CNT dispersion is within the above-mentioned predetermined range, the storage stability of the CNT dispersion can be improved.
　［５］上記［１］～［４］の何れかのカーボンナノチューブ分散液は、ｐＨが６以上１０以下であることが好ましい。
　ＣＮＴ分散液のｐＨが上記所定の範囲内であれば、ＣＮＴ分散液を含む負極用スラリーの増粘抑制性を更に向上させると共に、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させることができる。 [5] The carbon nanotube dispersion liquid according to any one of [1] to [4] above preferably has a pH of 6 or more and 10 or less.
If the pH of the CNT dispersion liquid is within the above-mentioned predetermined range, the thickening suppressing property of the negative electrode slurry containing the CNT dispersion liquid will be further improved, and a secondary battery equipped with a negative electrode prepared using the negative electrode slurry will be improved. Cycle characteristics can be further improved.
　また、この発明は、上記課題を有利に解決することを目的とするものであり、本発明は、［６］負極活物質と、上記［１］～［５］の何れかのカーボンナノチューブ分散液とを含む、非水系二次電池負極用スラリーである。
　このように、負極活物質と、上述したＣＮＴ分散液とを含む非水系二次電池負極用スラリーであれば、増粘抑制性に優れると共に、当該負極用スラリーを用いて作製した負極を備える非水系二次電池に優れたサイクル特性を発揮させることができる。 Further, the present invention aims to advantageously solve the above-mentioned problems, and the present invention provides a carbon nanotube dispersion containing [6] a negative electrode active material and any one of the above-mentioned [1] to [5]. A slurry for a non-aqueous secondary battery negative electrode, comprising:
As described above, a non-aqueous secondary battery negative electrode slurry containing a negative electrode active material and the above-mentioned CNT dispersion has excellent viscosity-inhibiting properties, and a non-aqueous secondary battery negative electrode slurry containing a negative electrode slurry prepared using the negative electrode slurry has excellent viscosity-inhibiting properties. A water-based secondary battery can exhibit excellent cycle characteristics.
　［７］上記［６］の非水系二次電池負極用スラリーにおいて、前記負極活物質がシリコン系負極活物質を含むことが好ましい。
　負極活物質としてシリコン系負極活物質（ケイ素を含有する負極活物質）を用いれば、非水系二次電池負極用スラリーを用いて作製した負極を備える非水系二次電池を高容量化することができる。なお、シリコン系負極活物質は、充放電に伴う膨張及び収縮が特に大きいところ、本発明の非水系二次電池負極用スラリーは、上述した本発明のカーボンナノチューブ分散液を用いて調製されているため、負極活物質としてシリコン系負極活物質を用いた場合であっても、電極合材層の導電性の低下が抑制され、非水系二次電池に優れたサイクル特性を発揮させ得る負極を形成することができる。 [7] In the non-aqueous secondary battery negative electrode slurry of [6] above, it is preferable that the negative electrode active material contains a silicon-based negative electrode active material.
If a silicon-based negative electrode active material (negative electrode active material containing silicon) is used as the negative electrode active material, it is possible to increase the capacity of a non-aqueous secondary battery equipped with a negative electrode prepared using a slurry for a non-aqueous secondary battery negative electrode. can. Note that the silicon-based negative electrode active material has particularly large expansion and contraction upon charging and discharging, and the slurry for the non-aqueous secondary battery negative electrode of the present invention is prepared using the above-mentioned carbon nanotube dispersion of the present invention. Therefore, even when a silicon-based negative electrode active material is used as the negative electrode active material, the decrease in conductivity of the electrode composite layer is suppressed, forming a negative electrode that can exhibit excellent cycle characteristics in non-aqueous secondary batteries. can do.
　［８］上記［６］又は［７］の非水系二次電池負極用スラリーにおいて、粒子状重合体を更に含み、前記粒子状重合体が、カルボン酸基含有単量体単位、芳香族ビニル単量体単位及び共役ジエン単量体単位を含むことが好ましい。
　非水系二次電池負極用スラリーが上記所定の粒子状重合体を更に含めば、当該負極用スラリーを用いて作製した負極を備える非水系二次電池のサイクル特性を更に向上させることができる。
　なお、本発明において、重合体が「単量体単位を含む」とは、「その単量体を用いて得た重合体中に当該単量体由来の繰り返し単位が含まれている」ことを意味する。 [8] The slurry for a non-aqueous secondary battery negative electrode according to [6] or [7] above, further comprising a particulate polymer, wherein the particulate polymer contains a carboxylic acid group-containing monomer unit, an aromatic vinyl unit, It is preferable to include a mer unit and a conjugated diene monomer unit.
If the slurry for a non-aqueous secondary battery negative electrode further contains the above-mentioned predetermined particulate polymer, the cycle characteristics of a non-aqueous secondary battery including a negative electrode produced using the slurry for a negative electrode can be further improved.
In the present invention, when a polymer "contains a monomer unit", it means that "a repeating unit derived from the monomer is contained in the polymer obtained using the monomer". means.
　［９］上記［８］の非水系二次電池負極用スラリーにおいて、前記粒子状重合体中における前記カルボン酸基含有単量体単位の含有割合が、前記粒子状重合体が含む全繰り返し単位を１００質量％として、３質量％以上３０質量％以下であることが好ましい。
　粒子状重合体中におけるカルボン酸基含有単量体単位の含有割合が上記所定の範囲内であれば、非水系二次電池負極用スラリーを用いて作製した負極を備える非水系二次電池のサイクル特性を一層向上させることができる。
　なお、本発明において、重合体中の繰り返し単位（単量体単位）の含有割合は、１Ｈ－ＮＭＲ及び１３Ｃ－ＮＭＲ等の核磁気共鳴（ＮＭＲ）法を用いて測定できる。 [9] In the slurry for a non-aqueous secondary battery negative electrode according to [8] above, the content ratio of the carboxylic acid group-containing monomer unit in the particulate polymer exceeds all repeating units contained in the particulate polymer. As 100% by mass, it is preferably 3% by mass or more and 30% by mass or less.
If the content ratio of the carboxylic acid group-containing monomer unit in the particulate polymer is within the above-mentioned predetermined range, the cycle of a non-aqueous secondary battery including a negative electrode prepared using the slurry for a non-aqueous secondary battery negative electrode. The characteristics can be further improved.
In the present invention, the content of repeating units (monomeric units) in the polymer can be measured using nuclear magnetic resonance (NMR) methods such as 1 H-NMR and 13 C-NMR.
　また、この発明は、上記課題を有利に解決することを目的とするものであり、本発明は、［１０］上記［６］から［９］の何れかの非水系二次電池負極用スラリーを用いて形成した負極合材層を備える、非水系二次電池用負極である。
　このように、上述した非水系二次電池負極用スラリーを用いて形成した負極合材層を備える非水系二次電池用負極であれば、非水系二次電池に優れたサイクル特性を発揮させることができる。 Further, the present invention aims to advantageously solve the above problems, and the present invention provides a slurry for a non-aqueous secondary battery negative electrode according to any one of [10] [6] to [9] above. This is a negative electrode for a non-aqueous secondary battery, including a negative electrode composite material layer formed using the above-mentioned method.
In this way, a negative electrode for a non-aqueous secondary battery comprising a negative electrode composite layer formed using the slurry for a non-aqueous secondary battery negative electrode described above can exhibit excellent cycle characteristics in a non-aqueous secondary battery. Can be done.
　さらに、この発明は、上記課題を有利に解決することを目的とするものであり、本発明は、［１１］上記［１０］の非水系二次電池用負極を備える、非水系二次電池である。
　このように、上述した非水系二次電池用負極を備える非水系二次電池であれば、優れたサイクル特性を発揮することができる。 Furthermore, the present invention aims to advantageously solve the above problems, and the present invention provides a non-aqueous secondary battery comprising the negative electrode for a non-aqueous secondary battery according to [11] above [10]. be.
In this way, a non-aqueous secondary battery equipped with the above-described negative electrode for a non-aqueous secondary battery can exhibit excellent cycle characteristics.
　本発明によれば、増粘抑制性に優れた非水系二次電池負極用スラリーを調製可能であると共に、非水系二次電池に優れたサイクル特性を発揮させ得るカーボンナノチューブ分散液を提供することができる。
　また、本発明によれば、増粘抑制性に優れると共に、非水系二次電池に優れたサイクル特性を発揮させ得る非水系二次電池負極用スラリーを提供することができる。
　また、本発明によれば、非水系二次電池に優れたサイクル特性を発揮させ得る非水系二次電池用負極を提供することができる。
　また、本発明によれば、優れたサイクル特性を発揮し得る非水系二次電池を提供することができる。 According to the present invention, it is possible to prepare a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties, and to provide a carbon nanotube dispersion that can exhibit excellent cycle characteristics in a non-aqueous secondary battery. Can be done.
Further, according to the present invention, it is possible to provide a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties and can also cause a non-aqueous secondary battery to exhibit excellent cycle characteristics.
Further, according to the present invention, it is possible to provide a negative electrode for a non-aqueous secondary battery that allows a non-aqueous secondary battery to exhibit excellent cycle characteristics.
Further, according to the present invention, it is possible to provide a non-aqueous secondary battery that can exhibit excellent cycle characteristics.
　以下、本発明の実施形態について詳細に説明する。
　ここで、本発明のＣＮＴ分散液は、特に限定されることなく、例えば非水系二次電池負極用スラリー（以下、単に「負極用スラリー」と称する場合がある。）を製造する際の材料として用いることができる。そして、本発明の負極用スラリーは、本発明のＣＮＴ分散液を用いて調製される。加えて、本発明の非水系二次電池用負極（以下、単に「負極」と称する場合がある。）は、本発明の負極用スラリーを用いて形成された負極合材層を備えることを特徴とする。また、本発明の非水系二次電池は、本発明の負極を備えることを特徴とする。なお、本発明のＣＮＴ分散液は、樹脂とＣＮＴとを含む複合材料の原料や、電子工学品等の製造に用いることができる。 Embodiments of the present invention will be described in detail below.
Here, the CNT dispersion of the present invention is not particularly limited, and can be used, for example, as a material for producing a non-aqueous secondary battery negative electrode slurry (hereinafter sometimes simply referred to as "negative electrode slurry"). Can be used. The negative electrode slurry of the present invention is prepared using the CNT dispersion of the present invention. In addition, the negative electrode for non-aqueous secondary batteries of the present invention (hereinafter sometimes simply referred to as "negative electrode") is characterized by comprising a negative electrode composite layer formed using the negative electrode slurry of the present invention. shall be. Further, the non-aqueous secondary battery of the present invention is characterized by comprising the negative electrode of the present invention. The CNT dispersion of the present invention can be used as a raw material for composite materials containing resin and CNTs, and in the production of electronic products.
（ＣＮＴ分散液）
　本発明のＣＮＴ分散液は、平均長さおよび平均直径がそれぞれ所定の範囲内であるＣＮＴと、水溶性高分子と、水とを含み、任意に、その他の成分を含有する。なお、ＣＮＴ分散液には、通常、電極活物質（正極活物質、負極活物質）は含まれない。 (CNT dispersion)
The CNT dispersion of the present invention contains CNTs whose average length and average diameter are each within predetermined ranges, a water-soluble polymer, and water, and optionally contains other components. Note that the CNT dispersion usually does not contain electrode active materials (positive electrode active material, negative electrode active material).
　そして、本発明のＣＮＴ分散液によれば、増粘抑制性に優れた負極用スラリーを調製し得ると共に、当該負極用スラリーを用いて作製した負極を備える二次電池に優れたサイクル特性を発揮させることができる。 According to the CNT dispersion of the present invention, it is possible to prepare a slurry for a negative electrode that is excellent in suppressing thickening, and also exhibits excellent cycle characteristics in a secondary battery equipped with a negative electrode prepared using the slurry for a negative electrode. can be done.
＜ＣＮＴ＞
　ＣＮＴは、単層ＣＮＴであってもよいし、多層ＣＮＴであってもよい。また、ＣＮＴとしては、単層ＣＮＴと多層ＣＮＴとを任意の比率で組み合わせて使用してもよい。そして、ＣＮＴ分散液の分散性及び保存安定性を向上させる観点から、ＣＮＴとしては、多層ＣＮＴを用いることが好ましい。 <CNT>
The CNTs may be single-walled CNTs or multi-walled CNTs. Furthermore, as the CNTs, single-walled CNTs and multi-walled CNTs may be used in combination at any ratio. From the viewpoint of improving the dispersibility and storage stability of the CNT dispersion, it is preferable to use multi-walled CNTs as the CNTs.
　ＣＮＴは、特に限定されることなく、アーク放電法、レーザーアブレーション法、化学的気相成長法（ＣＶＤ法）等の既知のＣＮＴの合成方法を用いて合成したものを使用できる。また、ＣＮＴは、上述した合成方法により合成された後、平均長さを後述する所定の範囲内に調整するために、必要に応じて、分散処理が施されていてもよいものとする。ＣＮＴに対して分散処理を施すことにより、ＣＮＴの繊維の一部が切断されるため、分散処理後のＣＮＴの平均長さを上述した所定の範囲内に調整することができる。分散処理の詳細については、「ＣＮＴ分散液の調製」の項で後述する。 CNTs are not particularly limited, and those synthesized using known CNT synthesis methods such as arc discharge method, laser ablation method, and chemical vapor deposition method (CVD method) can be used. Furthermore, after the CNTs have been synthesized by the above-described synthesis method, they may be subjected to dispersion processing, as necessary, in order to adjust the average length within a predetermined range, which will be described later. By performing the dispersion treatment on the CNTs, some of the CNT fibers are cut, so that the average length of the CNTs after the dispersion treatment can be adjusted within the above-mentioned predetermined range. Details of the dispersion treatment will be described later in the section "Preparation of CNT dispersion".
＜＜平均長さ＞＞
　ＣＮＴ分散液中におけるＣＮＴの平均長さは、５μｍ以上であることが必要であり、６μｍ以上であることが好ましく、７μｍ以上であることがより好ましく、８μｍ以上であることが更に好ましく、１００μｍ以下であることが必要であり、８０μｍ以下であることが好ましく、６０μｍ以下であることがより好ましく、４０μｍ以下であることが更に好ましく、２０μｍ以下であることが一層好ましい。ＣＮＴ分散液中におけるＣＮＴの平均長さが５μｍ以上であると、ＣＮＴ分散液を含む負極用スラリーを用いて作製した負極の負極合材層中に良好な導電パスを形成できるため、当該負極を備える二次電池のサイクル特性を十分に向上させることができる。また、ＣＮＴ分散液中におけるＣＮＴの平均長さが上記下限以上であれば、当該負極のピール強度を向上させることができる。一方、ＣＮＴ分散液中におけるＣＮＴの平均長さが１００μｍ以下であると、ＣＮＴ分散液を含む負極用スラリーの増粘抑制性を十分に向上させることができる。
　また、ＣＮＴ分散液中におけるＣＮＴの平均長さは、１０μｍ以上であってもよいし、１０μｍ以下であってもよい。
　なお、ＣＮＴの平均長さは、ＣＮＴの合成方法、及び、合成後のＣＮＴに対する分散処理などにより制御することができる。 <<Average length>>
The average length of the CNTs in the CNT dispersion liquid needs to be 5 μm or more, preferably 6 μm or more, more preferably 7 μm or more, even more preferably 8 μm or more, and 100 μm or less. It is preferably 80 μm or less, more preferably 60 μm or less, even more preferably 40 μm or less, and even more preferably 20 μm or less. When the average length of the CNTs in the CNT dispersion is 5 μm or more, a good conductive path can be formed in the negative electrode composite layer of the negative electrode prepared using the negative electrode slurry containing the CNT dispersion. The cycle characteristics of the included secondary battery can be sufficiently improved. Furthermore, if the average length of CNTs in the CNT dispersion is equal to or greater than the above lower limit, the peel strength of the negative electrode can be improved. On the other hand, when the average length of the CNTs in the CNT dispersion is 100 μm or less, the thickening suppressing properties of the negative electrode slurry containing the CNT dispersion can be sufficiently improved.
Further, the average length of CNTs in the CNT dispersion may be 10 μm or more or 10 μm or less.
Note that the average length of the CNTs can be controlled by the CNT synthesis method, the dispersion processing of the CNTs after synthesis, and the like.
＜＜平均直径＞＞
　ＣＮＴ分散液中におけるＣＮＴの平均直径は、２０ｎｍ以上であることが必要であり、３０ｎｍ以上であることが好ましく、４０ｎｍ以上であることがより好ましく、１００ｎｍ以下であることが必要であり、８０ｎｍ以下であることが好ましく、６０ｎｍ以下であることがより好ましい。ＣＮＴ分散液中におけるＣＮＴの平均直径が２０ｎｍ以上であると、ＣＮＴ分散液を含む負極用スラリーの増粘抑制性を十分に向上させることができる。一方、ＣＮＴ分散液中におけるＣＮＴの平均直径が１００ｎｍ以下であると、ＣＮＴの単位質量当たりの本数が十分に増加し得ることから、ＣＮＴ分散液を含む負極用スラリーを用いて作製した負極の負極合材層中に良好な導電パスを形成できるため、当該負極を備える二次電池のサイクル特性を十分に向上させることができる。また、ＣＮＴ分散液中におけるＣＮＴの平均直径が上記上限であれば、ＣＮＴの単位質量当たりの本数が十分に増加し得ることから、当該負極のピール強度を向上させることができる。
　また、ＣＮＴ分散液中におけるＣＮＴの平均直径は、５０ｎｍ以上であってもよいし、５０ｎｍ以下であってもよい。
　なお、ＣＮＴの平均直径は、ＣＮＴの合成方法などにより制御することができる。 <<Average diameter>>
The average diameter of the CNTs in the CNT dispersion needs to be 20 nm or more, preferably 30 nm or more, more preferably 40 nm or more, and needs to be 100 nm or less, and 80 nm or less. It is preferable that it is, and it is more preferable that it is 60 nm or less. When the average diameter of the CNTs in the CNT dispersion is 20 nm or more, it is possible to sufficiently improve the viscosity-inhibiting properties of the negative electrode slurry containing the CNT dispersion. On the other hand, if the average diameter of CNTs in the CNT dispersion is 100 nm or less, the number of CNTs per unit mass can be sufficiently increased. Since a good conductive path can be formed in the composite material layer, the cycle characteristics of a secondary battery including the negative electrode can be sufficiently improved. Moreover, if the average diameter of the CNTs in the CNT dispersion liquid is the above-mentioned upper limit, the number of CNTs per unit mass can be sufficiently increased, so that the peel strength of the negative electrode can be improved.
Further, the average diameter of CNTs in the CNT dispersion may be 50 nm or more or 50 nm or less.
Note that the average diameter of the CNTs can be controlled by the CNT synthesis method.
＜＜Ｇ／Ｄ比＞＞
　ＣＮＴは、ラマンスペクトルにおけるＤバンドピーク強度に対するＧバンドピーク強度の比（Ｇ／Ｄ比）が０．４以上であることが好ましく、０．５以上であることがより好ましく、０．６以上であることが更に好ましい。
　ＣＮＴのＧ／Ｄ比が上記下限以上であれば、二次電池のサイクル特性を更に向上させることができる。
　なお、ＣＮＴのＧ／Ｄ比の上限は、特に限定されないが、例えば２００以下である。
　本明細書において、ＣＮＴの「Ｇ／Ｄ比」は、顕微レーザラマン分光光度計（サーモフィッシャーサイエンティフィック（株）製Ｎｉｃｏｌｅｔ　Ａｌｍｅｇａ　ＸＲ）を用いてＣＮＴのラマンスペクトルを計測し、得られたラマンスペクトルについて、１５９０ｃｍ－１近傍で観察されたＧバンドピークの強度と、１３４０ｃｍ－１近傍で観察されたＤバンドピークの強度とを求めた上で、これらの比として算出できる。 <<G/D ratio>>
In the CNT, the ratio of the G band peak intensity to the D band peak intensity (G/D ratio) in the Raman spectrum is preferably 0.4 or more, more preferably 0.5 or more, and 0.6 or more. It is even more preferable that there be.
If the G/D ratio of CNT is equal to or higher than the above lower limit, the cycle characteristics of the secondary battery can be further improved.
Note that the upper limit of the G/D ratio of CNT is not particularly limited, but is, for example, 200 or less.
In this specification, the "G/D ratio" of CNT is the Raman spectrum obtained by measuring the Raman spectrum of CNT using a microlaser Raman spectrophotometer (Nicolet Almega XR manufactured by Thermo Fisher Scientific Co., Ltd.). The intensity of the G-band peak observed near 1590 cm −1 and the intensity of the D-band peak observed near 1340 cm −1 can be calculated as a ratio of these.
＜＜ＣＮＴ分散液中の含有割合＞＞
　ＣＮＴ分散液中のＣＮＴの含有割合は、ＣＮＴ分散液全体の質量を１００質量％として、０．１質量％以上であることが好ましく、０．２質量％以上であることがより好ましく、０．３質量％以上であることが更に好ましく、１０．０質量％以下であることが好ましく、５．０質量％以下であることがより好ましく、２．０質量％以下であることが更に好ましく、１．０質量％以下であることが一層好ましい。ＣＮＴ分散液中のＣＮＴの含有割合が上記下限以上であれば、ＣＮＴ分散液を用いて調製される負極用スラリー等の製品の生産性を向上させることができる。一方、ＣＮＴ分散液中のＣＮＴの含有割合が上記上限以下であれば、ＣＮＴ分散液の分散性および保存安定性を十分に高く確保することができる。 <<Content ratio in CNT dispersion>>
The content ratio of CNTs in the CNT dispersion is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and 0.1% by mass or more, more preferably 0.2% by mass or more, based on the mass of the entire CNT dispersion as 100% by mass. It is more preferably 3% by mass or more, preferably 10.0% by mass or less, more preferably 5.0% by mass or less, even more preferably 2.0% by mass or less, 1 It is more preferable that the amount is .0% by mass or less. If the content of CNT in the CNT dispersion is equal to or higher than the above lower limit, the productivity of products such as negative electrode slurry prepared using the CNT dispersion can be improved. On the other hand, if the content of CNT in the CNT dispersion is below the above upper limit, sufficiently high dispersibility and storage stability of the CNT dispersion can be ensured.
＜水溶性高分子＞
　水溶性高分子は、ＣＮＴ分散液において分散剤として機能し得る成分である。
　水溶性高分子としては、天然高分子化合物を用いてもよいし、化学反応を用いて当該天然高分子化合物を変性させてなる半合成高分子化合物を用いてもよいし、また、化学反応を用いて人工的に作られた合成高分子化合物を用いてもよい。
　なお、天然高分子化合物および半合成高分子化合物の具体例としては、特開２０１７－０１０８２２号公報に記載のものが挙げられる。
　また、合成高分子化合物としては、例えば、１種または２種以上の単量体を重合反応により重合して得られる水溶性重合体を用いることができる。 <Water-soluble polymer>
The water-soluble polymer is a component that can function as a dispersant in the CNT dispersion.
As the water-soluble polymer, a natural polymer compound may be used, a semi-synthetic polymer compound obtained by modifying the natural polymer compound using a chemical reaction, or a semi-synthetic polymer compound obtained by modifying the natural polymer compound using a chemical reaction. An artificially produced synthetic polymer compound may also be used.
Note that specific examples of the natural polymer compound and the semi-synthetic polymer compound include those described in JP-A-2017-010822.
Further, as the synthetic polymer compound, for example, a water-soluble polymer obtained by polymerizing one or more types of monomers by a polymerization reaction can be used.
　そして、ＣＮＴ分散液の分散性および保存安定性を向上させる観点から、水溶性高分子としては、酸官能基を有する水溶性高分子を用いることが好ましく、酸官能基を有する水溶性重合体、並びに、カルボキシメチルセルロースおよびその塩等の酸官能基を有するセルロース誘導体を用いることがより好ましく、酸官能基を有する水溶性重合体を用いることが特に好ましい。 From the viewpoint of improving the dispersibility and storage stability of the CNT dispersion, it is preferable to use a water-soluble polymer having an acid functional group as the water-soluble polymer. Further, it is more preferable to use a cellulose derivative having an acid functional group such as carboxymethylcellulose and its salt, and it is particularly preferable to use a water-soluble polymer having an acid functional group.
　上述した水溶性重合体及びセルロース誘導体などの水溶性高分子が有する酸官能基としては、例えば、カルボン酸基、スルホン酸基、リン酸基等が挙げられる。なお、水溶性重合体及びセルロース誘導体は、これらの酸官能基のうち、１種のみを有していてもよいし、２種以上を任意の比率で組み合わせて有していてもよい。 Examples of the acid functional groups possessed by water-soluble polymers such as the above-mentioned water-soluble polymers and cellulose derivatives include carboxylic acid groups, sulfonic acid groups, and phosphoric acid groups. Note that the water-soluble polymer and cellulose derivative may have only one type of these acid functional groups, or may have two or more types in combination in any ratio.
　なお、水溶性高分子が有する上記「酸官能基」には、塩基により中和された塩が含まれる。即ち、水溶性高分子が有する上記「酸官能基」の少なくとも一部は、塩の形態であってもよい。例えば、カルボン酸基（－ＣＯＯＨ）の場合、酸官能基には、カルボン酸基（－ＣＯＯＨ）の他に、カルボン酸リチウム基（－ＣＯＯ－Ｌｉ＋）等の中和型も含まれる。
　そして、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させる観点から、水溶性高分子が有する酸官能基の少なくとも一部が、アルカリ金属塩基又はアンモニウム塩基であることが好ましい。即ち、水溶性高分子が有する酸官能基の少なくとも一部は、アルカリ金属塩又はアンモニウム塩のいずれかの塩の形態であることが好ましい。なお、当該酸官能基の全部が、アルカリ金属塩基又はアンモニウム塩基であってもよい。
　アルカリ金属塩基としては、例えば、リチウム金属塩基、ナトリウム金属塩基、カリウム金属塩基等が挙げられる。
　なお、水溶性高分子は、酸官能基として、これらのアルカリ金属塩基およびアンモニウム塩基のうち、１種のみを有していてもよいし、２種以上を任意の比率で組み合わせて有していてもよい。 Note that the above-mentioned "acid functional group" that the water-soluble polymer has includes a salt neutralized with a base. That is, at least a portion of the above-mentioned "acid functional groups" that the water-soluble polymer has may be in the form of a salt. For example, in the case of a carboxylic acid group (-COOH), the acid functional group includes not only the carboxylic acid group (-COOH) but also a neutralized type such as a lithium carboxylate group (-COO - Li + ).
Furthermore, we further evaluated the dispersibility and storage stability of the CNT dispersion, the viscosity-inhibiting properties of a negative electrode slurry containing the CNT dispersion, and the cycle characteristics of a secondary battery equipped with a negative electrode prepared using the negative electrode slurry. From the viewpoint of improving the performance, it is preferable that at least a part of the acid functional groups of the water-soluble polymer are an alkali metal base or an ammonium base. That is, at least a portion of the acid functional groups of the water-soluble polymer are preferably in the form of either an alkali metal salt or an ammonium salt. Note that all of the acid functional groups may be an alkali metal base or an ammonium base.
Examples of the alkali metal base include lithium metal base, sodium metal base, potassium metal base, and the like.
Note that the water-soluble polymer may have only one type of these alkali metal bases and ammonium bases as an acid functional group, or a combination of two or more types in any ratio. Good too.
＜＜酸官能基を有する水溶性重合体＞＞
　一実施形態において、水溶性高分子としての水溶性重合体は、酸官能基としてカルボン酸基を有することが好ましい。水溶性重合体が有する酸官能基がカルボン酸基であれば、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させることができる。加えて、ＣＮＴの種類によらず、ＣＮＴ分散液の分散性及び保存安定性を良好に維持することができる。
　別の実施形態において、水溶性高分子としての水溶性重合体は、酸官能基としてスルホン酸基を有することが好ましい。水溶性重合体が有する酸官能基がスルホン酸基であれば、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させることができる。 <<Water-soluble polymer having acid functional group>>
In one embodiment, the water-soluble polymer as the water-soluble polymer preferably has a carboxylic acid group as the acid functional group. If the acid functional group of the water-soluble polymer is a carboxylic acid group, the dispersibility and storage stability of the CNT dispersion, the thickening suppressing property of the negative electrode slurry containing the CNT dispersion, and the negative electrode slurry The cycle characteristics of a secondary battery including a negative electrode produced using the method can be further improved. In addition, the dispersibility and storage stability of the CNT dispersion can be maintained well regardless of the type of CNT.
In another embodiment, the water-soluble polymer as the water-soluble polymer preferably has a sulfonic acid group as the acid functional group. If the acid functional group that the water-soluble polymer has is a sulfonic acid group, the dispersibility and storage stability of the CNT dispersion, the thickening suppressing property of the negative electrode slurry containing the CNT dispersion, and the negative electrode slurry. The cycle characteristics of a secondary battery including a negative electrode produced using the method can be further improved.
　また、水溶性高分子として好ましく用い得る水溶性重合体は、エーテル基を含むことが好ましい。ここでいう「エーテル基」とは、「－Ｒ’ＯＲ－」で表される基である。また、Ｒ及びＲ’は、炭素数が１個以上１０個以下の直鎖若しくは分岐状の炭化水素基、好ましくはアルキル基を表し、それぞれ、同一でも、異なってもよい。Ｒ及びＲ’の炭素数は、２個以上５個以下であることが好ましく、２個又は３個であることが好ましく、２個であることが更に好ましい。
　水溶性重合体がエーテル基を含めば、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させることができる。 Furthermore, the water-soluble polymer that can be preferably used as the water-soluble polymer preferably contains an ether group. The "ether group" here is a group represented by "-R'OR-". Further, R and R' represent a linear or branched hydrocarbon group having 1 to 10 carbon atoms, preferably an alkyl group, and each may be the same or different. The number of carbon atoms in R and R' is preferably 2 or more and 5 or less, preferably 2 or 3, and more preferably 2.
If the water-soluble polymer contains an ether group, the dispersibility and storage stability of the CNT dispersion, the ability to suppress thickening of the negative electrode slurry containing the CNT dispersion, and the negative electrode prepared using the negative electrode slurry are improved. The cycle characteristics of the included secondary battery can be further improved.
　以下、本発明のＣＮＴ分散液に含まれる水溶性高分子としての水溶性重合体について、第１の形態及び第２の形態を例示して説明するが、水溶性重合体はこれらに限定されるものではない。 Hereinafter, the water-soluble polymer as the water-soluble polymer contained in the CNT dispersion of the present invention will be explained by illustrating the first form and the second form, but the water-soluble polymer is limited to these. It's not a thing.
〔第１の形態の水溶性重合体〕
　第１の形態の水溶性重合体は、カルボン酸基含有単量体単位及び共役ジエン単量体単位を含む。なお、第１の形態の水溶性重合体は、カルボン酸基含有単量体単位及び共役ジエン単量体単位以外の繰り返し単位（その他の繰り返し単位）を含んでいてもよい。 [First form of water-soluble polymer]
The water-soluble polymer of the first form contains a carboxylic acid group-containing monomer unit and a conjugated diene monomer unit. Note that the water-soluble polymer of the first form may contain repeating units (other repeating units) other than the carboxylic acid group-containing monomer unit and the conjugated diene monomer unit.
［カルボン酸基含有単量体単位］
　カルボン酸基含有単量体単位は、カルボン酸基（－ＣＯＯＨ）を含む繰り返し単位である。なお、ＣＮＴ分散液中において、カルボン酸基含有単量体単位のカルボン酸基の一部又は全部が、カルボン酸ナトリウム基（－ＣＯＯ－Ｎａ＋）、カルボン酸リチウム基（－ＣＯＯ－Ｌｉ＋）、及びカルボン酸アンモニウム基（－ＣＯＯ－ＮＨ４ ＋）の少なくとも何れかの状態であることが好ましい。カルボン酸基が上述した少なくとも何れかのカルボン酸塩基の形態をとることにより、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を一層向上させることができる。 [Carboxylic acid group-containing monomer unit]
The carboxylic acid group-containing monomer unit is a repeating unit containing a carboxylic acid group (-COOH). In addition, in the CNT dispersion, some or all of the carboxylic acid groups of the carboxylic acid group-containing monomer units are sodium carboxylate groups (-COO - Na + ), lithium carboxylate groups (-COO - Li + ). It is preferably in at least one of the following states: , and ammonium carboxylate group (-COO - NH 4 + ). When the carboxylic acid group takes the form of at least one of the above-mentioned carboxylic acid groups, the dispersibility and storage stability of the CNT dispersion, the thickening suppressing property of a slurry for a negative electrode containing the CNT dispersion, and the negative electrode The cycle characteristics of a secondary battery including a negative electrode produced using the slurry can be further improved.
　第１の形態の水溶性重合体のカルボン酸基含有単量体単位を形成し得るカルボン酸基含有単量体としては、モノカルボン酸及びその誘導体や、ジカルボン酸及びその酸無水物並びにそれらの誘導体等が挙げられる。
　モノカルボン酸としては、アクリル酸、メタクリル酸、クロトン酸等が挙げられる。
　モノカルボン酸誘導体としては、２－エチルアクリル酸、イソクロトン酸、α－アセトキシアクリル酸、β－ｔｒａｎｓ－アリールオキシアクリル酸、α－クロロ－β－Ｅ－メトキシアクリル酸等が挙げられる。
　ジカルボン酸としては、マレイン酸、フマル酸、イタコン酸等が挙げられる。
　ジカルボン酸誘導体としては、メチルマレイン酸、ジメチルマレイン酸、フェニルマレイン酸、クロロマレイン酸、ジクロロマレイン酸、フルオロマレイン酸や、マレイン酸ノニル、マレイン酸デシル、マレイン酸ドデシル、マレイン酸オクタデシル、マレイン酸フルオロアルキル等のマレイン酸モノエステルが挙げられる。
　ジカルボン酸の酸無水物としては、無水マレイン酸、アクリル酸無水物、メチル無水マレイン酸、ジメチル無水マレイン酸等が挙げられる。
　また、カルボン酸基含有単量体としては、加水分解によりカルボン酸基を生成する酸無水物も使用できる。 Examples of the carboxylic acid group-containing monomer that can form the carboxylic acid group-containing monomer unit of the water-soluble polymer of the first form include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their Examples include derivatives.
Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid.
Examples of monocarboxylic acid derivatives include 2-ethyl acrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and the like.
Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.
Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoro maleate. Examples include alkyl and other maleic acid monoesters.
Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methylmaleic anhydride, dimethylmaleic anhydride, and the like.
Furthermore, as the carboxylic acid group-containing monomer, acid anhydrides that generate carboxylic acid groups by hydrolysis can also be used.
　カルボン酸基含有単量体は１種を単独で用いてもよく、２種以上を組み合わせて用いてもよい。そしてカルボン酸基含有単量体としては、二次電池のサイクル特性を更に向上させる観点から、アクリル酸、メタクリル酸が好ましい。即ち、第１の形態の水溶性重合体は、カルボン酸基含有単量体単位として、アクリル酸単位及びメタクリル酸単位の少なくとも一方を含むことが好ましい。 One type of carboxylic acid group-containing monomer may be used alone, or two or more types may be used in combination. As the carboxylic acid group-containing monomer, acrylic acid and methacrylic acid are preferable from the viewpoint of further improving the cycle characteristics of the secondary battery. That is, the water-soluble polymer of the first form preferably contains at least one of an acrylic acid unit and a methacrylic acid unit as the carboxylic acid group-containing monomer unit.
　第１の形態の水溶性重合体中におけるカルボン酸基含有単量体単位の含有割合は、第１の形態の水溶性重合体が含む全繰り返し単位を１００質量％として、３０質量％以上であることが好ましく、４０質量％以上であることがより好ましく、５０質量％以上であることが更に好ましく、９５質量％以下であることが好ましく、９０質量％以下であることがより好ましく、８０質量％以下であることが更に好ましく、７０質量％以下であることが一層好ましい。
　また、第１の形態の水溶性重合体中におけるカルボン酸基含有単量体単位の含有割合は、第１の形態の水溶性重合体が含む全繰り返し単位を１００モル％として、３０モル％以上であることが好ましく、４０モル％以上であることがより好ましく、５０モル％以上であることが更に好ましく、９０モル％以下であることが好ましく、８０モル％以下であることがより好ましく、７０モル％以下であることが更に好ましく、６０モル％以下であることが一層好ましい。
　第１の形態の水溶性重合体中におけるカルボン酸基含有単量体単位の含有割合が上記所定の範囲内であれば、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を一層向上させることができる。 The content of the carboxylic acid group-containing monomer unit in the water-soluble polymer of the first form is 30% by mass or more, based on 100% by mass of all repeating units contained in the water-soluble polymer of the first form. It is preferably 40% by mass or more, even more preferably 50% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, and 80% by mass. It is more preferably at most 70% by mass, even more preferably at most 70% by mass.
Further, the content of the carboxylic acid group-containing monomer unit in the water-soluble polymer of the first form is 30 mol% or more, with the total repeating units contained in the water-soluble polymer of the first form being 100 mol%. It is preferably 40 mol% or more, even more preferably 50 mol% or more, preferably 90 mol% or less, more preferably 80 mol% or less, and 70 mol% or more. It is more preferably at most mol%, even more preferably at most 60 mol%.
If the content of the carboxylic acid group-containing monomer unit in the water-soluble polymer of the first form is within the above-mentioned predetermined range, the dispersibility and storage stability of the CNT dispersion, and the negative electrode containing the CNT dispersion are improved. It is possible to further improve the viscosity increase suppressing property of the slurry for use as well as the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for negative electrode.
［共役ジエン単量体単位］
　第１の形態の水溶性重合体の共役ジエン単量体単位を形成し得る共役ジエン単量体としては、例えば、１，３－ブタジエン、イソプレン（２－メチル－１，３－ブタジエン）、２，３－ジメチル－１，３－ブタジエン、１，３－ペンタジエンが挙げられる。これらは一種を単独で用いてもよく、二種以上を組み合わせて用いてもよい。そしてこれらの中でも、１，３－ブタジエン、イソプレンが好ましく、イソプレンがより好ましい。即ち、第１の形態の水溶性重合体は、第１の形態の共役ジエン単量体単位として、１，３－ブタジエン単位とイソプレン単位の少なくとも一方を含むことが好ましく、イソプレン単位を含むことがより好ましい。 [Conjugated diene monomer unit]
Examples of the conjugated diene monomer that can form the conjugated diene monomer unit of the water-soluble polymer of the first form include 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2 , 3-dimethyl-1,3-butadiene, and 1,3-pentadiene. These may be used alone or in combination of two or more. Among these, 1,3-butadiene and isoprene are preferred, and isoprene is more preferred. That is, the water-soluble polymer of the first form preferably contains at least one of a 1,3-butadiene unit and an isoprene unit, and preferably contains an isoprene unit as the conjugated diene monomer unit of the first form. More preferred.
　第１の形態の水溶性重合体中における共役ジエン単量体単位の含有割合は、第１の形態の水溶性重合体が含む全繰り返し単位を１００質量％として、５質量％以上であることが好ましく、１０質量％以上であることがより好ましく、２０質量％以上であることが更に好ましく、３０質量％以上であることが一層好ましく、７０質量％以下であることが好ましく、６０質量％以下であることがより好ましく、５０質量％以下であることが更に好ましい。
　また、第１の形態の水溶性重合体中における共役ジエン単量体単位の含有割合は、第１の形態の水溶性重合体が含む全繰り返し単位を１００モル％として、１０モル％以上であることが好ましく、２０モル％以上であることがより好ましく、３０モル％以上であることが更に好ましく、４０モル％以上であることが一層好ましく、７０モル％以下であることが好ましく、６０モル％以下であることがより好ましく、５０モル％以下であることが更に好ましい。
　第１の形態の水溶性重合体中における共役ジエン単量体単位の含有割合が上記所定の範囲内であれば、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を一層向上させることができる。 The content of conjugated diene monomer units in the water-soluble polymer of the first form may be 5% by mass or more, with the total repeating units contained in the water-soluble polymer of the first form being 100% by mass. It is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, preferably 70% by mass or less, and 60% by mass or less. It is more preferable that the amount is at least 50% by mass, and even more preferably 50% by mass or less.
Further, the content ratio of the conjugated diene monomer unit in the water-soluble polymer of the first form is 10 mol% or more, with the total repeating units included in the water-soluble polymer of the first form being 100 mol%. The content is preferably 20 mol% or more, further preferably 30 mol% or more, even more preferably 40 mol% or more, preferably 70 mol% or less, and 60 mol%. It is more preferably at most 50 mol%, even more preferably at most 50 mol%.
If the content ratio of the conjugated diene monomer units in the water-soluble polymer of the first form is within the above-mentioned predetermined range, the dispersibility and storage stability of the CNT dispersion, and the negative electrode slurry containing the CNT dispersion are improved. It is possible to further improve the viscosity-inhibiting properties of the slurry and the cycle characteristics of a secondary battery including a negative electrode produced using the negative electrode slurry.
［その他の繰り返し単位］
　第１の形態の水溶性重合体が上述したカルボン酸基含有単量体単位及び共役ジエン単量体単位以外に含有し得るその他の繰り返し単位としては、特に限定されず、上述したカルボン酸基含有単量体及び共役ジエン単量体と共重合可能な既知の単量体（その他の単量体）に由来する単量体単位が挙げられる。その他の単量体は、一種を単独で用いてもよく、二種以上を組み合わせて用いてもよい。 [Other repeat units]
Other repeating units that the water-soluble polymer of the first form may contain other than the above-mentioned carboxylic acid group-containing monomer units and conjugated diene monomer units are not particularly limited. Examples include monomer units derived from known monomers (other monomers) copolymerizable with the monomer and the conjugated diene monomer. The other monomers may be used alone or in combination of two or more.
　しかしながら、二次電池のサイクル特性を一層向上させる観点からは、第１の形態の水溶性重合体中におけるその他の繰り返し単位の含有割合は、第１の形態の水溶性重合体が含む全繰り返し単位を１００質量％として、２０質量％以下であることが好ましく、１０質量％以下であることがより好ましく、５質量％以下であることが更に好ましく、１質量％以下であることが一層好ましく、０質量％であることが特に好ましい。また、第１の形態の水溶性重合体中におけるその他の繰り返し単位の含有割合は、第１の形態の水溶性重合体が含む全繰り返し単位を１００モル％として、２０モル％以下であることが好ましく、１０モル％以下であることがより好ましく、５モル％以下であることが更に好ましく、１モル％以下であることが一層好ましく、０モル％であることが特に好ましい。
　換言すると、第１の形態の水溶性重合体中におけるカルボン酸基含有単量体単位と共役ジエン単量体単位の含有割合合計は、第１の形態の水溶性重合体が含む全繰り返し単位を１００質量％として、８０質量％以上であることが好ましく、９０質量％以上であることがより好ましく、９５質量％以上であることが更に好ましく、９９質量％以上であることが一層好ましく、１００質量％であることが特に好ましい。また、第１の形態の水溶性重合体中におけるカルボン酸基含有単量体単位と共役ジエン単量体単位の含有割合合計は、第１の形態の水溶性重合体が含む全繰り返し単位を１００モル％として、８０モル％以上であることが好ましく、９０モル％以上であることがより好ましく、９５モル％以上であることが更に好ましく、９９モル％以上であることが一層好ましく、１００モル％であることが特に好ましい。 However, from the viewpoint of further improving the cycle characteristics of the secondary battery, the content ratio of other repeating units in the water-soluble polymer of the first form should be adjusted to the total repeating units contained in the water-soluble polymer of the first form. is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 1% by mass or less, and 0 Particularly preferred is mass %. Further, the content ratio of other repeating units in the water-soluble polymer of the first form may be 20 mol% or less, with the total repeating units contained in the water-soluble polymer of the first form being 100 mol%. It is preferably 10 mol% or less, more preferably 5 mol% or less, even more preferably 1 mol% or less, and particularly preferably 0 mol%.
In other words, the total content of carboxylic acid group-containing monomer units and conjugated diene monomer units in the water-soluble polymer of the first form is equal to the total content of all repeating units contained in the water-soluble polymer of the first form. As 100% by mass, it is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 99% by mass or more, and 100% by mass. % is particularly preferred. Further, the total content ratio of carboxylic acid group-containing monomer units and conjugated diene monomer units in the water-soluble polymer of the first form is 100% of all repeating units contained in the water-soluble polymer of the first form. In terms of mol%, it is preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, even more preferably 99 mol% or more, and 100 mol%. It is particularly preferable that
〔第２の形態の水溶性重合体〕
　第２の形態の水溶性重合体は、スルホン酸基含有単量体単位及びアルキレンオキサイド構造含有単量体単位を含む。なお、第２の形態の水溶性重合体は、スルホン酸基含有単量体単位及びアルキレンオキサイド構造含有単量体単位以外の繰り返し単位（その他の繰り返し単位）を含んでいてもよい。 [Second form of water-soluble polymer]
The water-soluble polymer of the second form contains a sulfonic acid group-containing monomer unit and an alkylene oxide structure-containing monomer unit. Note that the water-soluble polymer of the second form may contain repeating units (other repeating units) other than the sulfonic acid group-containing monomer unit and the alkylene oxide structure-containing monomer unit.
［スルホン酸基含有単量体単位］
　スルホン酸基含有単量体単位は、スルホン酸基（－ＳＯ３Ｈ）を含む繰り返し単位である。なお、ＣＮＴ分散液中において、スルホン酸基含有単量体単位のスルホン酸基の一部又は全部が、スルホン酸ナトリウム基（－ＳＯ３ －Ｎａ＋）、スルホン酸リチウム基（－ＳＯ３ －Ｌｉ＋）、及びスルホン酸アンモニウム基（－ＳＯ３ －ＮＨ４ ＋）の少なくとも何れかの状態であることが好ましい。スルホン酸基が上述した少なくとも何れかのスルホン酸塩基の形態をとることにより、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を一層向上させることができる。 [Sulfonic acid group-containing monomer unit]
The sulfonic acid group-containing monomer unit is a repeating unit containing a sulfonic acid group (-SO 3 H). In addition, in the CNT dispersion, some or all of the sulfonic acid groups of the sulfonic acid group-containing monomer units are sodium sulfonate groups (-SO 3 - Na + ), lithium sulfonate groups (-SO 3 - Li + ), and ammonium sulfonate group (-SO 3 - NH 4 + ). By having the sulfonic acid group take the form of at least one of the above-mentioned sulfonic acid groups, the dispersibility and storage stability of the CNT dispersion, the thickening suppressing property of a slurry for a negative electrode containing the CNT dispersion, and the negative electrode The cycle characteristics of a secondary battery including a negative electrode produced using the slurry can be further improved.
　第２の形態の水溶性重合体のスルホン酸基含有単量体単位を形成し得るスルホン酸基含有単量体としては、例えば、ビニルスルホン酸、メチルビニルスルホン酸、（メタ）アリルスルホン酸、スチレンスルホン酸、（メタ）アクリル酸－２－スルホン酸エチル、２－アクリルアミド－２－メチルプロパンスルホン酸、３－アリロキシ－２－ヒドロキシプロパンスルホン酸、及びこれらの塩等が挙げられる。
　なお、本明細書において、「（メタ）アリル」とは、アリル及び／又はメタリルを意味する。 Examples of the sulfonic acid group-containing monomer that can form the sulfonic acid group-containing monomer unit of the water-soluble polymer of the second form include vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, Examples include styrenesulfonic acid, ethyl (meth)acrylate-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and salts thereof.
In addition, in this specification, "(meth)allyl" means allyl and/or methallyl.
　スルホン酸基含有単量体は１種を単独で用いてもよく、２種以上を組み合わせて用いてもよい。そしてスルホン酸基含有単量体としては、二次電池のサイクル特性を一層向上させる観点から、スチレンスルホン酸が好ましい。即ち、第２の形態の水溶性重合体は、スルホン酸基含有単量体単位として、スチレンスルホン酸単位を含むことが好ましい。 The sulfonic acid group-containing monomers may be used alone or in combination of two or more. As the sulfonic acid group-containing monomer, styrene sulfonic acid is preferable from the viewpoint of further improving the cycle characteristics of the secondary battery. That is, the water-soluble polymer of the second form preferably contains a styrene sulfonic acid unit as the sulfonic acid group-containing monomer unit.
　第２の形態の水溶性重合体中におけるスルホン酸基含有単量体単位の含有割合は、第２の形態の水溶性重合体が含む全繰り返し単位を１００質量％として、４０質量％以上であることが好ましく、５０質量％以上であることがより好ましく、５５質量％以上であることが更に好ましく、９５質量％以下であることが好ましく、９０質量％以下であることがより好ましく、８０質量％以下であることが更に好ましく、７０質量％以下であることが一層好ましい。
　また、第２の形態の水溶性重合体中におけるスルホン酸基含有単量体単位の含有割合は、第２の形態の水溶性重合体が含む全繰り返し単位を１００モル％として、４０モル％以上であることが好ましく、５０モル％以上であることがより好ましく、５５モル％以上であることが更に好ましく、９５モル％以下であることが好ましく、９０モル％以下であることがより好ましく、８０モル％以下であることが更に好ましく、７０モル％以下であることが一層好ましい。
　第２の形態の水溶性重合体中におけるスルホン酸基含有単量体単位の含有割合が上記所定の範囲内であれば、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を一層向上させることができる。 The content of the sulfonic acid group-containing monomer unit in the water-soluble polymer of the second form is 40% by mass or more, based on 100% by mass of all repeating units contained in the water-soluble polymer of the second form. It is preferably 50% by mass or more, even more preferably 55% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, and 80% by mass. It is more preferably at most 70% by mass, even more preferably at most 70% by mass.
Further, the content of the sulfonic acid group-containing monomer unit in the water-soluble polymer of the second form is 40 mol% or more, with the total repeating units contained in the water-soluble polymer of the second form being 100 mol%. It is preferably 50 mol% or more, even more preferably 55 mol% or more, preferably 95 mol% or less, more preferably 90 mol% or less, and 80 mol% or more. It is more preferably at most mol%, even more preferably at most 70 mol%.
If the content ratio of the sulfonic acid group-containing monomer unit in the water-soluble polymer of the second form is within the above-mentioned predetermined range, the dispersibility and storage stability of the CNT dispersion, and the negative electrode containing the CNT dispersion are improved. It is possible to further improve the viscosity increase suppressing property of the slurry for use as well as the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for negative electrode.
［アルキレンオキサイド構造含有単量体単位］
　第２の形態の水溶性重合体のアルキレンオキサイド構造含有単量体単位は、下記一般式（Ｉ）で表され得る構造を含む単量体単位である。
Figure JPOXMLDOC01-appb-C000001
 [式（Ｉ）中、ｍは１以上の整数であり、ｎは１以上の整数である。] [Alkylene oxide structure-containing monomer unit]
The alkylene oxide structure-containing monomer unit of the water-soluble polymer of the second form is a monomer unit containing a structure that can be represented by the following general formula (I).
Figure JPOXMLDOC01-appb-C000001
 [In formula (I), m is an integer of 1 or more, and n is an integer of 1 or more. ]
　アルキレンオキサイド構造含有単量体単位を第２の形態の水溶性重合体に含有させることで、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を一層向上させることができる。上記式（Ｉ）中、整数ｍは２以上５以下であることが好ましく、整数ｍが２又は３であることがより好ましく、整数ｍが２であることが更に好ましい。整数ｍが２の場合には、一般式（Ｉ）で表される構造単位を含む単量体単位はエチレンオキサイド構造含有単量体単位と称する。また、整数ｍが３の場合には、一般式（Ｉ）で表される構造単位を含む単量体単位はプロピレンオキサイド構造含有単量体単位と称する。整数ｍが上記上限値以下であれば、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性をより一層向上させることができる。特に、整数ｍが２である場合、即ち、第２の形態の水溶性重合体にエチレンオキサイド構造含有単量体単位を含有させた場合に、第２の形態の水溶性重合体に適度な親水性を付与することができ、第２の形態の水溶性重合体の水に対する親和性を高めることができる。その結果、第２の形態の水溶性重合体にエチレンオキサイド構造含有単量体単位を含有させた場合に、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を特に向上させることができる。 By incorporating the alkylene oxide structure-containing monomer unit into the second form of the water-soluble polymer, the dispersibility and storage stability of the CNT dispersion, the ability to suppress thickening of the negative electrode slurry containing the CNT dispersion, In addition, the cycle characteristics of a secondary battery including a negative electrode produced using the negative electrode slurry can be further improved. In the above formula (I), the integer m is preferably 2 or more and 5 or less, more preferably 2 or 3, and even more preferably 2. When the integer m is 2, the monomer unit containing the structural unit represented by general formula (I) is referred to as an ethylene oxide structure-containing monomer unit. Further, when the integer m is 3, the monomer unit containing the structural unit represented by the general formula (I) is referred to as a propylene oxide structure-containing monomer unit. If the integer m is less than or equal to the above upper limit, the dispersibility and storage stability of the CNT dispersion, the thickening suppressing property of the negative electrode slurry containing the CNT dispersion, and the negative electrode produced using the negative electrode slurry are improved. The cycle characteristics of the included secondary battery can be further improved. In particular, when the integer m is 2, that is, when the water-soluble polymer of the second form contains an ethylene oxide structure-containing monomer unit, the water-soluble polymer of the second form has appropriate hydrophilicity. The water-soluble polymer of the second form can have an increased affinity for water. As a result, when the water-soluble polymer of the second form contains an ethylene oxide structure-containing monomer unit, the dispersibility and storage stability of the CNT dispersion, and the improvement of the negative electrode slurry containing the CNT dispersion are improved. The viscosity control property and the cycle characteristics of a secondary battery including a negative electrode produced using the negative electrode slurry can be particularly improved.
　なお、第２の形態の水溶性重合体が、複数種のアルキレンオキサイド構造含有単量体単位を含んでいてもよい。換言すれば、例えば、第２の形態の水溶性重合体中に、エチレンオキサイド構造含有単量体単位及びプロピレンオキサイド構造含有単量体単位の双方が含有されていてもよい。 Note that the water-soluble polymer of the second form may contain a plurality of types of alkylene oxide structure-containing monomer units. In other words, for example, both the ethylene oxide structure-containing monomer unit and the propylene oxide structure-containing monomer unit may be contained in the water-soluble polymer of the second form.
　上記式（Ｉ）で表され得る構造を含む単量体単位の繰り返し数を規定する整数ｎは、１０以下であることが好ましく、５以下であることがより好ましく、３以下であることが更に好ましく、２以上であることが好ましい。即ち、第２の形態の水溶性重合体に含まれるアルキレンオキサイド構造含有単量体単位は、アルキレンオキサイド構造単位がｎ回繰り返されてなる、ポリアルキレンオキサイド構造単位を含むことが好ましい。また、アルキレンオキサイド構造単位は、一部又は全部の水素原子が任意の置換基により置換されていてもよい。 The integer n that defines the repeating number of the monomer unit containing the structure that can be represented by the above formula (I) is preferably 10 or less, more preferably 5 or less, and still more preferably 3 or less. Preferably, the number is 2 or more. That is, the alkylene oxide structure-containing monomer unit contained in the water-soluble polymer of the second form preferably includes a polyalkylene oxide structural unit in which the alkylene oxide structural unit is repeated n times. Further, in the alkylene oxide structural unit, some or all of the hydrogen atoms may be substituted with an arbitrary substituent.
　第２の形態の水溶性重合体が、複数のアルキレンオキサイド構造含有単量体単位を含む場合において、各アルキレンオキサイド構造含有単量体単位についての上記繰り返し数ｎは、同一でも、異なってもよい。この場合には、全ての繰り返し数ｎの数平均値が上述した好適範囲内であることが好ましく、全ての繰り返し数ｎが上述した好適範囲内であることより好ましい。 When the water-soluble polymer of the second form contains a plurality of alkylene oxide structure-containing monomer units, the repeating number n for each alkylene oxide structure-containing monomer unit may be the same or different. . In this case, it is preferable that the number average value of all the repetition numbers n is within the above-mentioned suitable range, and it is more preferable that all the repetition numbers n are within the above-mentioned suitable range.
　第２の形態の水溶性重合体のアルキレンオキサイド構造含有単量体単位を形成し得るアルキレンオキサイド構造含有単量体としては、例えば、下記一般式（ＩＩ）で表される単量体が挙げられる。
Figure JPOXMLDOC01-appb-C000002
 [一般式（ＩＩ）中、Ｒ１は（メタ）アクリロイル基であり、Ｒ２は、水素原子又は炭素数が１個以上１０個以下の直鎖若しくは分岐状のアルキル基を示す。該アルキル基の炭素数は、２個以上５個以下であることが好ましく、２個又は３個であることが好ましく、２個であることが更に好ましい。なお、一般式（ＩＩ）中、ｍ及びｎは、一般式（Ｉ）のｍ及びｎと同様である。]
　ここで、炭素数が１個以上１０個以下の直鎖又は分岐状のアルキル基としては、例えば、メチル基、エチル基、及びプロピル基等が挙げられる。
　より具体的には、一般式（ＩＩ）で表される単量体としては、特に限定されることなく、メトキシポリエチレングリコール（メタ）アクリレート、エトキシジエチレングリコール（メタ）アクリレート等のエトキシポリエチレングリコール（メタ）アクリレート、ポリプロピレングリコールモノ（メタ）アクリレート、メトキシポリプロピレングリコール（メタ）アクリレート等が挙げられる。中でも、一般式（ＩＩ）で表される単量体としては、エトキシポリエチレングリコール（メタ）アクリレートが好ましく、エトキシジエチレングリコール（メタ）アクリレートがより好ましく、エトキシジエチレングリコールアクリレートが特に好ましい。
　なお、本明細書において「（メタ）アクリレート」とは、アクリレート又はメタクリレートを意味し、「（メタ）アクリロイル」とはアクリロイル又はメタクリロイルを意味する。 Examples of the alkylene oxide structure-containing monomer that can form the alkylene oxide structure-containing monomer unit of the water-soluble polymer of the second form include monomers represented by the following general formula (II). .
Figure JPOXMLDOC01-appb-C000002
 [In general formula (II), R 1 is a (meth)acryloyl group, and R 2 represents a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the alkyl group is preferably 2 or more and 5 or less, preferably 2 or 3, and more preferably 2. In addition, m and n in general formula (II) are the same as m and n in general formula (I). ]
Here, examples of the linear or branched alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, and a propyl group.
More specifically, the monomer represented by general formula (II) is not particularly limited, and examples include ethoxypolyethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, etc. Examples include acrylate, polypropylene glycol mono(meth)acrylate, and methoxypolypropylene glycol (meth)acrylate. Among these, as the monomer represented by general formula (II), ethoxypolyethylene glycol (meth)acrylate is preferred, ethoxydiethylene glycol (meth)acrylate is more preferred, and ethoxydiethylene glycol acrylate is particularly preferred.
In this specification, "(meth)acrylate" means acrylate or methacrylate, and "(meth)acryloyl" means acryloyl or methacryloyl.
　第２の形態の水溶性重合体中におけるアルキレンオキサイド構造含有単量体単位の含有割合は、第２の形態の水溶性重合体が含む全繰り返し単位を１００質量％として、５質量％以上であることが好ましく、１０質量％以上であることがより好ましく、２０質量％以上であることが更に好ましく、３０質量％以上であることが一層好ましく、６０質量％以下であることが好ましく、５０質量％以下であることがより好ましく、４５質量％以下であることが更に好ましい。
　また、第２の形態の水溶性重合体中におけるアルキレンオキサイド構造含有単量体単位の含有割合は、第２の形態の水溶性重合体が含む全繰り返し単位を１００モル％として、５モル％以上であることが好ましく、１０モル％以上であることがより好ましく、２０モル％以上であることが更に好ましく、３０モル％以上であることが一層好ましく、６０モル％以下であることが好ましく、５０モル％以下であることがより好ましく、４５モル％以下であることが更に好ましい。
　第２の形態の水溶性重合体中におけるアルキレンオキサイド構造含有単量体単位の含有割合が上記所定の範囲内であれば、ＣＮＴ分散液の分散性及び保存安定性、当該ＣＮＴ分散液を含む負極用スラリーの増粘抑制性、並びに、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を一層向上させることができる。 The content of the alkylene oxide structure-containing monomer unit in the water-soluble polymer of the second form is 5% by mass or more, based on 100% by mass of all repeating units contained in the water-soluble polymer of the second form. It is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, preferably 60% by mass or less, and 50% by mass. It is more preferably at most 45% by mass, even more preferably at most 45% by mass.
Further, the content ratio of the alkylene oxide structure-containing monomer unit in the water-soluble polymer of the second form is 5 mol% or more, with the total repeating units included in the water-soluble polymer of the second form being 100 mol%. It is preferably 10 mol% or more, even more preferably 20 mol% or more, even more preferably 30 mol% or more, preferably 60 mol% or less, and 50 mol% or more. It is more preferably mol % or less, and even more preferably 45 mol % or less.
If the content ratio of the alkylene oxide structure-containing monomer unit in the water-soluble polymer of the second form is within the above-mentioned predetermined range, the dispersibility and storage stability of the CNT dispersion, and the negative electrode containing the CNT dispersion are improved. It is possible to further improve the viscosity increase suppressing property of the slurry for use as well as the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for negative electrode.
［その他の繰り返し単位］
　第２の形態の水溶性重合体が上述したスルホン酸基含有単量体単位及びアルキレンオキサイド構造含有単量体単位以外に含有し得るその他の繰り返し単位としては、特に限定されず、上述したスルホン酸基含有単量体単位及びアルキレンオキサイド構造含有単量体単位と共重合可能な既知の単量体（その他の単量体）に由来する単量体単位が挙げられる。その他の単量体は、１種を単独で用いてもよく、２種以上を組み合わせて用いてもよい。 [Other repeat units]
Other repeating units that the water-soluble polymer of the second form may contain other than the above-mentioned sulfonic acid group-containing monomer units and alkylene oxide structure-containing monomer units are not particularly limited, and include the above-mentioned sulfonic acid groups. Examples include monomer units derived from known monomers (other monomers) copolymerizable with group-containing monomer units and alkylene oxide structure-containing monomer units. The other monomers may be used alone or in combination of two or more.
　しかしながら、二次電池のサイクル特性を一層向上させる観点からは、第２の形態の水溶性重合体中におけるその他の繰り返し単位の含有割合は、第２の形態の水溶性重合体が含む全繰り返し単位を１００質量％として、２０質量％以下であることが好ましく、１０質量％以下であることがより好ましく、５質量％以下であることが更に好ましく、１質量％以下であることが一層好ましく、０質量％であることが特に好ましい。
　第２の形態の水溶性重合体中におけるその他の繰り返し単位の含有割合は、第２の形態の水溶性重合体が含む全繰り返し単位を１００モル％としては、２０モル％以下であることが好ましく、１０モル％以下であることがより好ましく、５モル％以下であることが更に好ましく、１モル％以下であることが一層好ましく、０モル％であることが特に好ましい。
　換言すると、第２の形態の水溶性重合体中におけるスルホン酸基含有単量体単位とアルキレンオキサイド構造含有単量体単位の含有割合合計は、第２の形態の水溶性重合体が含む全繰り返し単位を１００質量％として、８０質量％以上であることが好ましく、９０質量％以上であることがより好ましく、９５質量％以上であることが更に好ましく、９９質量％以上であることが一層好ましく、１００質量％であることが特に好ましい。また、第２の形態の水溶性重合体中におけるスルホン酸基含有単量体単位とアルキレンオキサイド構造含有単量体単位の含有割合合計は、第２の形態の水溶性重合体が含む全繰り返し単位を１００モル％として、８０モル％以上であることが好ましく、９０モル％以上であることがより好ましく、９５モル％以上であることが更に好ましく、９９モル％以上であることが一層好ましく、１００モル％であることが特に好ましい。 However, from the viewpoint of further improving the cycle characteristics of the secondary battery, the content ratio of other repeating units in the water-soluble polymer of the second form is lower than that of all repeating units contained in the water-soluble polymer of the second form. is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 1% by mass or less, and 0 Particularly preferred is mass %.
The content ratio of other repeating units in the water-soluble polymer of the second form is preferably 20 mol% or less, assuming that the total repeating units contained in the water-soluble polymer of the second form is 100 mol%. , more preferably 10 mol% or less, even more preferably 5 mol% or less, even more preferably 1 mol% or less, and particularly preferably 0 mol%.
In other words, the total content ratio of the sulfonic acid group-containing monomer unit and the alkylene oxide structure-containing monomer unit in the water-soluble polymer of the second form is equal to the total content of the monomer unit containing the sulfonic acid group in the water-soluble polymer of the second form. When the unit is 100% by mass, it is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 99% by mass or more, Particularly preferred is 100% by mass. In addition, the total content ratio of the sulfonic acid group-containing monomer unit and the alkylene oxide structure-containing monomer unit in the water-soluble polymer of the second form is the total repeating unit contained in the water-soluble polymer of the second form. is preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, even more preferably 99 mol% or more, and 100 mol% or more. Particularly preferred is mole %.
〔調製方法〕
　水溶性重合体の調製方法は特に限定されない。水溶性重合体は、例えば、一種類又は二種類以上の単量体を含む単量体組成物を水系溶媒中で重合することにより得ることができる。得られた重合体を任意に水素化してもよい。なお、単量体組成物中の各単量体の含有割合は、重合体中の所望の繰り返し単位（単量体単位）の含有割合に準じて定めることができる。
　重合様式は、特に制限なく、溶液重合法、懸濁重合法、塊状重合法、乳化重合法等のいずれの方法も用いることができる。また、重合反応としては、イオン重合、ラジカル重合、リビングラジカル重合、各種縮合重合、付加重合等いずれの反応も用いることができる。そして、重合に際しては、必要に応じて既知の乳化剤や重合開始剤を使用することができる。また、水素化は、既知の方法により行うことができる。
　また、重合の後、必要に応じて、水酸化ナトリウム水溶液、水酸化リチウム水溶液、アンモニア水等により中和を行い、上述した中和型の酸官能基を有する水溶性重合体を調製してもよい。 [Preparation method]
The method for preparing the water-soluble polymer is not particularly limited. The water-soluble polymer can be obtained, for example, by polymerizing a monomer composition containing one or more types of monomers in an aqueous solvent. The resulting polymer may optionally be hydrogenated. Note that the content ratio of each monomer in the monomer composition can be determined according to the content ratio of desired repeating units (monomer units) in the polymer.
The polymerization method is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. Further, as the polymerization reaction, any reaction such as ionic polymerization, radical polymerization, living radical polymerization, various condensation polymerizations, and addition polymerization can be used. In the polymerization, known emulsifiers and polymerization initiators can be used as necessary. Moreover, hydrogenation can be performed by a known method.
Alternatively, after polymerization, if necessary, neutralization may be performed with an aqueous sodium hydroxide solution, an aqueous lithium hydroxide solution, aqueous ammonia, etc. to prepare a water-soluble polymer having a neutralized acid functional group as described above. good.
＜＜含有割合＞＞
　ＣＮＴ分散液中の水溶性高分子の含有割合は、特に限定されないが、ＣＮＴ分散液全体の質量を１００質量％として、０．１質量％以上であることが好ましく、０．２質量％以上であることがより好ましく、０．３質量％以上であることが更に好ましく、５．０質量％以下であることが好ましく、２．０質量％以下であることがより好ましく、１．０質量％以下であることが更に好ましく、０．８質量％以下であることが一層好ましい。ＣＮＴ分散液中の水溶性高分子の含有割合が上記下限以上であれば、ＣＮＴ分散液の分散性を向上させることができる。一方、ＣＮＴ分散液中の水溶性高分子の含有割合が上記上限以下であれば、ＣＮＴ分散液の保存安定性を向上させることができる。 <<Content ratio>>
The content ratio of the water-soluble polymer in the CNT dispersion is not particularly limited, but it is preferably 0.1% by mass or more, and 0.2% by mass or more, based on the mass of the entire CNT dispersion as 100% by mass. It is more preferable that the content is 0.3% by mass or more, even more preferably 5.0% by mass or less, more preferably 2.0% by mass or less, and 1.0% by mass or less. It is more preferable that it is, and even more preferable that it is 0.8% by mass or less. If the content of the water-soluble polymer in the CNT dispersion is equal to or higher than the above lower limit, the dispersibility of the CNT dispersion can be improved. On the other hand, if the content of the water-soluble polymer in the CNT dispersion is below the above upper limit, the storage stability of the CNT dispersion can be improved.
＜＜質量比（ＣＮＴ／水溶性高分子）＞＞
　ＣＮＴ分散液中における水溶性高分子に対するＣＮＴの質量比（ＣＮＴ／水溶性高分子）が、０．１以上であることが好ましく、０．３以上であることがより好ましく、０．５以上であることが更に好ましく、０．７以上であることが一層好ましく、１０以下であることが好ましく、８以下であることがより好ましく、５以下であることが更に好ましく、３以下であることが一層好ましい。
　ＣＮＴ分散液中における水溶性高分子に対するＣＮＴの質量比（ＣＮＴ／水溶性高分子）が上記所定の範囲内であれば、ＣＮＴ分散液の保存安定性を向上させることができる。 <<Mass ratio (CNT/water-soluble polymer)>>
The mass ratio of CNT to water-soluble polymer (CNT/water-soluble polymer) in the CNT dispersion is preferably 0.1 or more, more preferably 0.3 or more, and 0.5 or more. It is more preferably 0.7 or more, more preferably 10 or less, more preferably 8 or less, even more preferably 5 or less, even more preferably 3 or less. preferable.
If the mass ratio of CNT to water-soluble polymer (CNT/water-soluble polymer) in the CNT dispersion is within the above-mentioned predetermined range, the storage stability of the CNT dispersion can be improved.
＜その他の成分＞
　ＣＮＴ分散液が、ＣＮＴ、水溶性高分子及び水以外に含み得るその他の成分としては、特に限定されないが、ＣＮＴ以外の導電材、水以外の分散媒、「非水系二次電池負極用スラリー」の項で後述する負極活物質以外の成分が挙げられる。
　ＣＮＴ以外の導電材としては、特に限定されないが、例えば、カーボンブラック（アセチレンブラック、ケッチェンブラック（登録商標）、ファーネスブラック等）、グラファイト、カーボンフレーク、カーボンナノファイバーを用いることができる。
　水以外の分散媒としては、水と相溶し得る既知の有機溶媒を用いることができる。
　なお、その他の成分は、一種を単独で用いてもよく、二種以上を組み合わせて用いてもよい。 <Other ingredients>
Other components that the CNT dispersion may contain other than CNTs, water-soluble polymers, and water are not particularly limited, but include conductive materials other than CNTs, dispersion media other than water, and "slurry for non-aqueous secondary battery negative electrodes." Components other than the negative electrode active material, which will be described later in the section, are included.
The conductive material other than CNT is not particularly limited, and for example, carbon black (acetylene black, Ketjen Black (registered trademark), furnace black, etc.), graphite, carbon flakes, and carbon nanofibers can be used.
As the dispersion medium other than water, known organic solvents that are compatible with water can be used.
In addition, one type of other components may be used alone, or two or more types may be used in combination.
＜ＣＮＴ分散液の調製方法＞
　ＣＮＴ分散液を調製する方法は、特に限定されない。ＣＮＴ分散液は、ＣＮＴ、水溶性高分子、水、及び必要に応じて用いられるその他の成分を混合することで調製することができる。なお、混合には、ディスパー、ホモミキサー、プラネタリーミキサー、ニーダー等の既知の混合装置を用いることができる。 <Method for preparing CNT dispersion>
The method for preparing the CNT dispersion is not particularly limited. A CNT dispersion liquid can be prepared by mixing CNTs, a water-soluble polymer, water, and other components used as necessary. In addition, known mixing devices such as a disper, a homo mixer, a planetary mixer, and a kneader can be used for mixing.
　なお、ＣＮＴ分散液の調製に用いるＣＮＴは、平均長さを上述した所定の範囲内に調整するために、分散処理を行うことができる。ＣＮＴに対して分散処理を施すことにより、ＣＮＴの繊維の一部が切断されるため、分散処理後のＣＮＴの平均長さを上述した所定の範囲内に調整することができる。
　分散処理には、例えば、ボールミル、ビーズミル、ジェットミル等の分散処理装置を用いることができる。なお、これらの分散処理装置の方式は、湿式であってもよいし、乾式であってもよい。そして、ＣＮＴの長さを上述した所定の範囲内に容易に調整する観点から、分散処理には、湿式ジェットミルを用いることが好ましい。 Note that the CNTs used for preparing the CNT dispersion liquid can be subjected to a dispersion treatment in order to adjust the average length within the above-mentioned predetermined range. By performing the dispersion treatment on the CNTs, some of the CNT fibers are cut, so that the average length of the CNTs after the dispersion treatment can be adjusted within the above-mentioned predetermined range.
For the dispersion treatment, for example, a dispersion treatment apparatus such as a ball mill, bead mill, jet mill, etc. can be used. Note that these dispersion processing apparatuses may be of a wet type or a dry type. From the viewpoint of easily adjusting the length of the CNTs within the above-mentioned predetermined range, it is preferable to use a wet jet mill for the dispersion treatment.
　ＣＮＴの平均長さを調整するための分散処理を行う場合、事前処理として、ＣＮＴ単独、又はＣＮＴと水等の分散媒との混合液に対して分散処理を行った後、得られた平均長さ調整後のＣＮＴと、水溶性高分子及び水等の他の成分とを混合してＣＮＴ分散液を調製してもよいし、ＣＮＴ分散液の調製自体を兼ねる処理として、ＣＮＴ、水溶性高分子、および水などの混合液に対して分散処理を行ってもよい。そして、ＣＮＴ分散液の製造効率を向上させる観点から、後者、即ち、ＣＮＴ分散液の調製自体を兼ねる処理として、ＣＮＴ、水溶性高分子、および水などの混合液に対して分散処理を行うことが好ましい。 When performing dispersion treatment to adjust the average length of CNTs, as a pretreatment, perform dispersion treatment on CNTs alone or a mixture of CNTs and a dispersion medium such as water, and then adjust the average length obtained. A CNT dispersion may be prepared by mixing the CNTs after the temperature adjustment with other components such as a water-soluble polymer and water, or as a process that also serves as the preparation of the CNT dispersion itself, A dispersion treatment may be performed on a mixed liquid such as molecules and water. From the perspective of improving the production efficiency of CNT dispersions, the latter, that is, a process that also serves as the preparation of the CNT dispersion itself, involves performing a dispersion treatment on a mixed liquid of CNTs, a water-soluble polymer, water, etc. is preferred.
　ＣＮＴ分散液の調製自体を兼ねる処理として湿式ジェットミルを用いた分散処理を行う場合、ＣＮＴ分散液の調製は、例えば、以下の手順及び条件で行うことができる。
　まず、分散処理前のＣＮＴ、水溶性高分子、水、及び必要に応じて用いられるその他の成分を混合して混合液を得る。混合には、上述した混合装置を用いることができる。分散処理前のＣＮＴの平均長さは、例えば、５００μｍ以上２０００μｍ以下である。なお、分散処理前のＣＮＴの平均直径は、「ＣＮＴ」の項で上述したＣＮＴの平均直径の好ましい範囲と同じ範囲内である。
　次に、得られた混合液に対して、湿式ジェットミルを用いて分散処理を行い、分散処理後の液体をＣＮＴ分散液として得る。湿式ジェットミルによる混合液の分散処理にあたり印加する圧力は、１００ＭＰａ以上であることが好ましく、１２５ＭＰａ以上であることがより好ましく、また、２００ＭＰａ以下であることが好ましく、１７５ＭＰａ以下であることがより好ましい。また、湿式ジェットミルによる分散処理の回数（パス回数）は１回以上であり、５回以上２０回以下であることが好ましい。分散処理の際の温度は、０℃以上８０℃以下であることが好ましい。さらに、湿式ジェットミルの最小流路径は、目詰まり抑制の観点から、好ましくは１００μｍ以上であり、効果的に加圧分散する観点から、好ましくは５００μｍ以下、より好ましくは３００μｍ以下である。なお、分散処理において使用可能な湿式ジェットミルとしては、「ナノヴェイタ（登録商標）」（吉田機械興業株式会社製）、「ＢＥＲＹＵ　ＳＹＳＴＥＭ　ＰＲＯ」（株式会社美粒製）、超高圧湿式微粒化装置（吉田工業株式会社製）、「ナノマイザー（登録商標）」（ナノマイザー株式会社製）、および「スターバースト（登録商標）」（株式会社スギノマシン製）等が挙げられる。 When performing a dispersion process using a wet jet mill as a process that also serves as the process for preparing the CNT dispersion liquid, the CNT dispersion liquid can be prepared, for example, according to the following procedure and conditions.
First, CNTs before dispersion treatment, a water-soluble polymer, water, and other components used as necessary are mixed to obtain a liquid mixture. For mixing, the above-mentioned mixing device can be used. The average length of the CNTs before dispersion treatment is, for example, 500 μm or more and 2000 μm or less. Note that the average diameter of the CNTs before the dispersion treatment is within the same range as the preferable range of the average diameter of the CNTs described above in the "CNT" section.
Next, the obtained mixed liquid is subjected to a dispersion treatment using a wet jet mill, and the liquid after the dispersion treatment is obtained as a CNT dispersion liquid. The pressure applied during the dispersion treatment of the mixed liquid using a wet jet mill is preferably 100 MPa or more, more preferably 125 MPa or more, and preferably 200 MPa or less, more preferably 175 MPa or less. . Further, the number of times of dispersion treatment using a wet jet mill (number of passes) is 1 or more, preferably 5 or more and 20 or less. The temperature during the dispersion treatment is preferably 0°C or higher and 80°C or lower. Furthermore, the minimum flow path diameter of the wet jet mill is preferably 100 μm or more from the viewpoint of clogging prevention, and preferably 500 μm or less, more preferably 300 μm or less from the viewpoint of effective pressurized dispersion. In addition, wet jet mills that can be used in dispersion processing include "Nano Veita (registered trademark)" (manufactured by Yoshida Kikai Kogyo Co., Ltd.), "BERYU SYSTEM PRO" (manufactured by Bijutsu Co., Ltd.), and ultra-high pressure wet atomization equipment ( (manufactured by Yoshida Kogyo Co., Ltd.), "Nanomizer (registered trademark)" (manufactured by Nanomizer Co., Ltd.), and "Starburst (registered trademark)" (manufactured by Sugino Machine Co., Ltd.).
＜ＣＮＴ分散液のｐＨ＞
　ＣＮＴ分散液のｐＨは、６以上であることが好ましく、７以上であることがより好ましく、７．５以上であることが更に好ましく、１０以下であることが好ましく、９以下であることがより好ましく、８．５以下であることが更に好ましい。ＣＮＴ分散液のｐＨが上記所定の範囲内であれば、ＣＮＴ分散液を含む負極用スラリーの増粘抑制性を更に向上させると共に、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させることができる。 <pH of CNT dispersion>
The pH of the CNT dispersion is preferably 6 or higher, more preferably 7 or higher, even more preferably 7.5 or higher, preferably 10 or lower, and more preferably 9 or lower. It is preferably 8.5 or less, and more preferably 8.5 or less. If the pH of the CNT dispersion liquid is within the above-mentioned predetermined range, the thickening suppressing properties of the negative electrode slurry containing the CNT dispersion liquid will be further improved, and a secondary battery equipped with a negative electrode prepared using the negative electrode slurry will be improved. Cycle characteristics can be further improved.
（非水系二次電池負極用スラリー）
　本発明の負極用スラリーは、上述したＣＮＴ分散液と、負極活物質とを含み、必要に応じて結着材等の任意成分を含む。換言すると、本発明の負極用スラリーは、平均長さ及び平均直径がそれぞれ上述した所定の範囲内であるＣＮＴと、水溶性重合体と、水とを含み、必要に応じて結着材等の任意成分を含む。
　このように、上述したＣＮＴ分散液を含む負極用スラリーは、増粘抑制性に優れると共に、二次電池に優れたサイクル特性を発揮させ得る負極を形成可能である。 (Non-aqueous secondary battery negative electrode slurry)
The negative electrode slurry of the present invention contains the above-described CNT dispersion liquid and a negative electrode active material, and optionally contains optional components such as a binder. In other words, the slurry for a negative electrode of the present invention contains CNTs whose average length and average diameter are within the above-mentioned predetermined ranges, a water-soluble polymer, and water, and optionally contains a binder or the like. Contains optional ingredients.
In this way, the slurry for a negative electrode containing the above-mentioned CNT dispersion liquid can form a negative electrode that is excellent in suppressing thickening and can exhibit excellent cycle characteristics in a secondary battery.
＜負極活物質＞
　負極用スラリーに配合する負極活物質としては、特に限定されることなく、既知の負極活物質を用いることができる。 <Negative electrode active material>
The negative electrode active material to be added to the negative electrode slurry is not particularly limited, and any known negative electrode active material can be used.
　例えば、リチウムイオン二次電池に用いられる負極活物質としては、特に限定されないが、炭素系負極活物質、金属系負極活物質、及びこれらを組み合わせた負極活物質等が挙げられる。 For example, negative electrode active materials used in lithium ion secondary batteries include, but are not particularly limited to, carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that are combinations thereof.
　ここで、炭素系負極活物質とは、リチウムを挿入（「ドープ」ともいう。）可能な、炭素を主骨格とする活物質をいい、炭素系負極活物質としては、例えば炭素質材料と黒鉛質材料とが挙げられる。 Here, the carbon-based negative electrode active material refers to an active material whose main skeleton is carbon and into which lithium can be inserted (also referred to as "doping"). Carbon-based negative electrode active materials include, for example, carbonaceous materials and graphite. Examples include quality materials.
　そして、炭素質材料としては、例えば、易黒鉛性炭素や、ガラス状炭素に代表される非晶質構造に近い構造を持つ難黒鉛性炭素等が挙げられる。
　ここで、易黒鉛性炭素としては、例えば、石油又は石炭から得られるタールピッチを原料とした炭素材料が挙げられる。具体例を挙げると、コークス、メソカーボンマイクロビーズ（ＭＣＭＢ）、メソフェーズピッチ系炭素繊維、熱分解気相成長炭素繊維等が挙げられる。
　また、難黒鉛性炭素としては、例えば、フェノール樹脂焼成体、ポリアクリロニトリル系炭素繊維、擬等方性炭素、フルフリルアルコール樹脂焼成体（ＰＦＡ）、ハードカーボン等が挙げられる。
　更に、黒鉛質材料としては、例えば、天然黒鉛、人造黒鉛等が挙げられる。
　ここで、人造黒鉛としては、例えば、易黒鉛性炭素を含んだ炭素を主に２８００℃以上で熱処理した人造黒鉛、ＭＣＭＢを２０００℃以上で熱処理した黒鉛化ＭＣＭＢ、メソフェーズピッチ系炭素繊維を２０００℃以上で熱処理した黒鉛化メソフェーズピッチ系炭素繊維等が挙げられる。 Examples of the carbonaceous material include graphitizable carbon and non-graphitic carbon having a structure close to an amorphous structure represented by glassy carbon.
Here, examples of graphitizable carbon include carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers, and pyrolytic vapor growth carbon fibers.
Furthermore, examples of the non-graphitic carbon include phenolic resin fired products, polyacrylonitrile carbon fibers, pseudo-isotropic carbon, furfuryl alcohol resin fired products (PFA), hard carbon, and the like.
Furthermore, examples of the graphite material include natural graphite, artificial graphite, and the like.
Here, the artificial graphite includes, for example, artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800°C or higher, graphitized MCMB obtained by heat-treating MCMB at 2000°C or higher, mesophase pitch carbon fiber at 2000°C or higher. Examples include graphitized mesophase pitch carbon fibers heat-treated as described above.
　また、金属系負極活物質とは、金属を含む活物質であり、通常は、リチウムの挿入が可能な元素を構造に含み、リチウムが挿入された場合の単位質量当たりの理論電気容量が５００ｍＡｈ／ｇ以上である活物質をいう。金属系活物質としては、例えば、リチウム金属、リチウム合金を形成し得る単体金属（例えば、Ａｇ、Ａｌ、Ｂａ、Ｂｉ、Ｃｕ、Ｇａ、Ｇｅ、Ｉｎ、Ｎｉ、Ｐ、Ｐｂ、Ｓｂ、Ｓｉ、Ｓｎ、Ｓｒ、Ｚｎ、Ｔｉ等）及びその合金、並びに、それらの酸化物、硫化物、窒化物、ケイ化物、炭化物、燐化物等が用いられる。これらの中でも、金属系負極活物質としては、シリコン系負極活物質（ケイ素を含有する負極活物質）が好ましい。シリコン系負極活物質を用いることにより、二次電池を高容量化することができるからである。なお、シリコン系負極活物質は、充放電に伴う膨張及び収縮が特に大きいところ、本発明の負極用スラリーは、上述した本発明のＣＮＴ分散液を用いて調製されているため、負極活物質としてシリコン系負極活物質を用いた場合であっても、負極合材層の導電性の低下が抑制され、二次電池に優れたサイクル特性を発揮させ得る負極を形成することができる。 In addition, a metal-based negative electrode active material is an active material that contains metal, and usually contains an element in its structure that allows insertion of lithium, and has a theoretical electric capacity per unit mass of 500 mAh/m when lithium is inserted. It refers to an active material that is more than 100 g. Examples of metal-based active materials include lithium metal, single metals that can form lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn). , Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like. Among these, as the metal-based negative electrode active material, a silicon-based negative electrode active material (a negative electrode active material containing silicon) is preferable. This is because by using a silicon-based negative electrode active material, the capacity of the secondary battery can be increased. Note that silicon-based negative electrode active materials have particularly large expansion and contraction upon charging and discharging, but since the slurry for negative electrodes of the present invention is prepared using the above-mentioned CNT dispersion of the present invention, it can be used as a negative electrode active material. Even when a silicon-based negative electrode active material is used, a decrease in the conductivity of the negative electrode composite layer is suppressed, and a negative electrode that can exhibit excellent cycle characteristics in a secondary battery can be formed.
　シリコン系負極活物質としては、例えば、ケイ素（Ｓｉ）、ケイ素を含む合金、ＳｉＯ、ＳｉＯｘ、Ｓｉ含有材料を導電性カーボンで被覆又は複合化してなるＳｉ含有材料と導電性カーボンとの複合化物等が挙げられる。 Examples of silicon-based negative electrode active materials include silicon (Si), silicon-containing alloys, SiO, SiO x , and composites of Si-containing materials and conductive carbon, which are obtained by coating or compounding Si-containing materials with conductive carbon. etc.
　そして、シリコン系負極活物質が、負極活物質中に占める割合は、負極活物質全体を１００質量％として、１質量％以上であることが好ましく、３質量％以上であることがより好ましく、２０質量％以下であることが好ましく、１５質量％以下であることがより好ましい。シリコン系負極活物質の割合が１質量％以上であれば二次電池の容量を十分に高めることができ、２０質量％以下であれば二次電池のサイクル特性を更に向上させることができる。 The proportion of the silicon-based negative electrode active material in the negative electrode active material is preferably 1% by mass or more, more preferably 3% by mass or more, and 20% by mass or more, based on 100% by mass of the entire negative electrode active material. It is preferably at most 15% by mass, more preferably at most 15% by mass. If the proportion of the silicon-based negative electrode active material is 1% by mass or more, the capacity of the secondary battery can be sufficiently increased, and if the proportion is 20% by mass or less, the cycle characteristics of the secondary battery can be further improved.
　なお、負極活物質の粒径は、特に限定されることなく、従来使用されている負極活物質と同様とすることができる。
　また、負極用スラリー中の負極活物質の量も、特に限定されず、従来使用されている範囲内とすることができる。
　そして、負極活物質は、１種を単独で用いてもよく、２種以上を組み合わせて用いてもよいが、二次電池を十分に高容量化しつつサイクル特性を更に向上させる観点から、負極用スラリーは、黒鉛質材料からなる炭素系負極活物質と、シリコン系負極活物質との双方を含むことが好ましい。 Note that the particle size of the negative electrode active material is not particularly limited, and may be the same as that of conventionally used negative electrode active materials.
Further, the amount of the negative electrode active material in the negative electrode slurry is not particularly limited, and can be within the conventionally used range.
The negative electrode active material may be used alone or in combination of two or more types, but from the viewpoint of further improving the cycle characteristics while increasing the capacity of the secondary battery sufficiently, The slurry preferably contains both a carbon-based negative electrode active material made of a graphite material and a silicon-based negative electrode active material.
＜ＣＮＴ分散液＞
　ＣＮＴ分散液としては、上述した本発明のＣＮＴ分散液を用いることができる。
　ここで、負極用スラリー中におけるＣＮＴの含有量は、負極活物質の含有量を１００質量部とした場合に、０．０１質量部以上であることが好ましく、０．０５質量部以上であることがより好ましく、０．０８質量部以上であることが更に好ましく、０．５質量部以下であることが好ましく、０．３質量部以下であることがより好ましく、０．１５質量部以下であることが更に好ましい。
　また、負極用スラリー中における水溶性重合体の含有量は、負極活物質の含有量を１００質量部とした場合に、０．０１質量部以上であることが好ましく、０．０５質量部以上であることがより好ましく、０．０８質量部以上であることが更に好ましく、０．５質量部以下であることが好ましく、０．３質量部以下であることがより好ましく、０．１５質量部以下であることが更に好ましい。 <CNT dispersion>
As the CNT dispersion, the above-mentioned CNT dispersion of the present invention can be used.
Here, the content of CNT in the negative electrode slurry is preferably 0.01 parts by mass or more, and preferably 0.05 parts by mass or more, when the content of the negative electrode active material is 100 parts by mass. is more preferably 0.08 parts by mass or more, still more preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, and 0.15 parts by mass or less. More preferably.
Further, the content of the water-soluble polymer in the negative electrode slurry is preferably 0.01 parts by mass or more, and 0.05 parts by mass or more, when the content of the negative electrode active material is 100 parts by mass. More preferably, the amount is 0.08 parts by mass or more, still more preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, and 0.15 parts by mass or less. It is more preferable that
＜任意成分＞
　負極用スラリーに含まれ得る任意成分としては、例えば、結着材、粘度調整剤、補強材、酸化防止剤、電解液の分解を抑制する機能を有する電解液添加剤が挙げられる。これらの任意成分は、１種を単独で用いてもよく、２種以上を組み合わせて用いてもよい。
　上述した任意成分の中でも、負極用スラリーは、二次電池のサイクル特性を向上させる観点から、結着材を含むことが好ましい。 <Optional ingredients>
Examples of optional components that may be included in the negative electrode slurry include a binder, a viscosity modifier, a reinforcing material, an antioxidant, and an electrolyte additive having a function of suppressing decomposition of the electrolyte. These optional components may be used alone or in combination of two or more.
Among the above-mentioned optional components, the negative electrode slurry preferably contains a binder from the viewpoint of improving the cycle characteristics of the secondary battery.
〔結着材〕
　結着材としては、特に限定されず、負極用の結着材として使用し得る任意の結着材を用いることができる。
　そして本発明において、結着材としては、負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させる観点から、カルボン酸基含有単量体単位、芳香族ビニル単量体単位、及び共役ジエン単量体単位を少なくとも含む粒子状重合体を用いることが好ましい。
　なお、結着材として用い得る粒子状重合体は、既知の方法で調製することができる。 [Binding material]
The binder is not particularly limited, and any binder that can be used as a binder for a negative electrode can be used.
In the present invention, as the binder, a carboxylic acid group-containing monomer unit, an aromatic vinyl monomer, etc. It is preferable to use a particulate polymer containing at least a unit and a conjugated diene monomer unit.
Note that a particulate polymer that can be used as a binder can be prepared by a known method.
［カルボン酸基含有単量体単位］
　粒子状重合体のカルボン酸基含有単量体単位を形成し得るカルボン酸基含有単量体としては、「第１の形態の水溶性重合体」の項で上述したカルボン酸基含有単量体と同様のものが挙げられる。
　カルボン酸基含有単量体は１種を単独で用いてもよく、２種以上を組み合わせて用いてもよい。 [Carboxylic acid group-containing monomer unit]
Examples of the carboxylic acid group-containing monomer that can form the carboxylic acid group-containing monomer unit of the particulate polymer include the carboxylic acid group-containing monomers mentioned above in the section of "Water-soluble polymer of the first form" The same thing can be mentioned.
One type of carboxylic acid group-containing monomer may be used alone, or two or more types may be used in combination.
　ここで、粒子状重合体中におけるカルボン酸基含有単量体単位の含有割合は、粒子状重合体が含む全繰り返し単位を１００質量％として、３質量％以上であることが好ましく、５質量％以上であることがより好ましく、３０質量％以下であることが好ましく、２０質量％以下であることがより好ましい。
　粒子状重合体中におけるカルボン酸基含有単量体単位の含有割合が上記所定の範囲内であれば、負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上できる。 Here, the content of the carboxylic acid group-containing monomer unit in the particulate polymer is preferably 3% by mass or more, and 5% by mass, based on 100% by mass of all repeating units contained in the particulate polymer. It is more preferably at least 30% by mass, more preferably at most 20% by mass.
If the content of the carboxylic acid group-containing monomer unit in the particulate polymer is within the above-described predetermined range, the cycle characteristics of a secondary battery including a negative electrode prepared using the negative electrode slurry can be further improved.
［芳香族ビニル単量体単位］
　粒子状重合体の芳香族ビニル単量体単位を形成し得る芳香族ビニル単量体としては、例えば、スチレン、スチレンスルホン酸及びその塩、α－メチルスチレン、ｐ－ｔ－ブチルスチレン、ブトキシスチレン、ビニルトルエン、クロロスチレン、並びに、ビニルナフタレンが挙げられる。芳香族ビニル単量体は一種を単独で用いてもよく、二種以上を組み合わせて用いてもよい。そして芳香族ビニル単量体としては、負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させる観点から、スチレンが好ましい。即ち、粒子状重合体は、芳香族ビニル単量体単位として、スチレン単位を含むことが好ましい。 [Aromatic vinyl monomer unit]
Examples of the aromatic vinyl monomer that can form the aromatic vinyl monomer unit of the particulate polymer include styrene, styrene sulfonic acid and its salts, α-methylstyrene, pt-butylstyrene, and butoxystyrene. , vinyltoluene, chlorostyrene, and vinylnaphthalene. One type of aromatic vinyl monomer may be used alone, or two or more types may be used in combination. As the aromatic vinyl monomer, styrene is preferable from the viewpoint of further improving the cycle characteristics of a secondary battery including a negative electrode produced using the negative electrode slurry. That is, the particulate polymer preferably contains styrene units as aromatic vinyl monomer units.
　ここで、粒子状重合体中における芳香族ビニル単量体単位の含有割合は、粒子状重合体が含む全繰り返し単位を１００質量％として、２０質量％以上であることが好ましく、２５質量％以上であることがより好ましく、８０質量％以下であることが好ましく、７５質量％以下であることがより好ましい。粒子状重合体中における芳香族ビニル単量体単位の含有割合が上記所定の範囲内であれば、負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させることができる。 Here, the content ratio of aromatic vinyl monomer units in the particulate polymer is preferably 20% by mass or more, and 25% by mass or more, with the total repeating units included in the particulate polymer being 100% by mass. It is more preferable that it is, it is preferable that it is 80 mass % or less, and it is more preferable that it is 75 mass % or less. If the content ratio of aromatic vinyl monomer units in the particulate polymer is within the above-determined range, the cycle characteristics of a secondary battery equipped with a negative electrode prepared using the negative electrode slurry can be further improved. .
［共役ジエン単量体単位］
　粒子状重合体の共役ジエン単量体単位を形成し得る共役ジエン単量体としては、「第１の形態の水溶性重合体」の項で上述した共役ジエン単量体と同様のものが挙げられる。
　共役ジエン単量体は１種を単独で用いてもよく、２種以上を組み合わせて用いてもよい。そして共役ジエン単量体としては、負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させる観点から、１，３－ブタジエンが好ましい。即ち、粒子状重合体は、共役ジエン単量体単位として、１，３－ブタジエン単位を含むことが好ましい。 [Conjugated diene monomer unit]
Examples of the conjugated diene monomer that can form the conjugated diene monomer unit of the particulate polymer include those similar to the conjugated diene monomers described above in the section of "first form of water-soluble polymer". It will be done.
The conjugated diene monomers may be used alone or in combination of two or more. As the conjugated diene monomer, 1,3-butadiene is preferable from the viewpoint of further improving the cycle characteristics of a secondary battery including a negative electrode prepared using the negative electrode slurry. That is, the particulate polymer preferably contains 1,3-butadiene units as conjugated diene monomer units.
　ここで、粒子状重合体中における共役ジエン単量体単位の含有割合は、粒子状重合体が含む全繰り返し単位を１００質量％として、１５質量％以上であることが好ましく、２０質量％以上であることがより好ましく、５０質量％以下であることが好ましく、４５質量％以下であることがより好ましい。粒子状重合体中における共役ジエン単量体単位の含有割合が上記範囲内であれば、負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させることができる。 Here, the content of the conjugated diene monomer unit in the particulate polymer is preferably 15% by mass or more, and 20% by mass or more, based on 100% by mass of all repeating units contained in the particulate polymer. It is more preferable that the amount is at most 50% by mass, more preferably at most 45% by mass. If the content of the conjugated diene monomer unit in the particulate polymer is within the above range, the cycle characteristics of a secondary battery including a negative electrode produced using the negative electrode slurry can be further improved.
[その他の繰り返し単位]
　上述した粒子状重合体が、カルボン酸基含有単量体単位、芳香族ビニル単量体単位、及び共役ジエン単量体単位以外に含有し得るその他の繰り返し単位としては、特に限定されず、上述したカルボン酸基含有単量体、芳香族ビニル単量体、及び共役ジエン単量体と共重合可能な既知の単量体（その他の単量体）に由来する単量体単位が挙げられる。その他の単量体は、１種を単独で用いてもよく、２種以上を組み合わせて用いてもよい。 [Other repeat units]
Other repeating units that the above-mentioned particulate polymer may contain other than the carboxylic acid group-containing monomer unit, the aromatic vinyl monomer unit, and the conjugated diene monomer unit are not particularly limited, and include the above-mentioned repeating units. Examples include monomer units derived from known monomers (other monomers) copolymerizable with carboxylic acid group-containing monomers, aromatic vinyl monomers, and conjugated diene monomers. The other monomers may be used alone or in combination of two or more.
　粒子状重合体中におけるその他の繰り返し単位の含有割合は、粒子状重合体が含む全繰り返し単位を１００質量％として、１０質量％以下であることが好ましく、５質量％以下であることがより好ましく、３質量％以下であることが更に好ましく、１質量％以下であることが一層好ましく、０質量％であることが特に好ましい。 The content of other repeating units in the particulate polymer is preferably 10% by mass or less, more preferably 5% by mass or less, based on 100% by mass of all repeating units contained in the particulate polymer. , more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0% by mass.
　なお、負極用スラリー中における上記粒子状重合体の含有量は、負極活物質の含有量を１００質量部とした場合に、０．１質量部以上であることが好ましく、０．５質量部以上であることがより好ましく、０．８質量部以上であることが更に好ましく、５質量部以下であることが好ましく、３質量部以下であることがより好ましく、１.５質量部以下であることが更に好ましい。粒子状重合体の含有量が上記所定の範囲内であれば、負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させることができる。
　また、負極用スラリー中における上記粒子状重合体の含有量は、ＣＮＴ１００質量部当たり、１００質量部以上であることが好ましく、５００質量部以上であることがより好ましく、５０００質量部以下であることが好ましく、２０００質量部以下であることがより好ましい。粒子状重合体の含有量が上記所定の範囲内であれば、負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させることができる。 In addition, the content of the particulate polymer in the negative electrode slurry is preferably 0.1 part by mass or more, and 0.5 parts by mass or more, when the content of the negative electrode active material is 100 parts by mass. It is more preferably 0.8 parts by mass or more, still more preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and 1.5 parts by mass or less. is even more preferable. If the content of the particulate polymer is within the above-mentioned predetermined range, the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for negative electrode can be further improved.
Further, the content of the particulate polymer in the negative electrode slurry is preferably 100 parts by mass or more, more preferably 500 parts by mass or more, and 5000 parts by mass or less per 100 parts by mass of CNTs. is preferable, and more preferably 2000 parts by mass or less. If the content of the particulate polymer is within the above-mentioned predetermined range, the cycle characteristics of a secondary battery including a negative electrode produced using the slurry for negative electrode can be further improved.
＜負極用スラリーの調製方法＞
　上述した成分を混合して負極用スラリーを得るに際し、混合方法には特に制限は無く、「ＣＮＴ分散液の調製方法」で上述した既知の混合装置を用いることができる。 <Method for preparing slurry for negative electrode>
When mixing the above-mentioned components to obtain a slurry for a negative electrode, there is no particular restriction on the mixing method, and the known mixing device described above in the "CNT dispersion preparation method" can be used.
＜負極用スラリーのｐＨ＞
　負極用スラリーのｐＨは、６以上であることが好ましく、７以上であることがより好ましく、１０以下であることが好ましく、９以下であることがより好ましい。
　負極用スラリーのｐＨが上記所定の範囲内であれば、負極用スラリーの増粘抑制性、及び、当該負極用スラリーを用いて作製した負極を備える二次電池のサイクル特性を更に向上させることができる。 <pH of negative electrode slurry>
The pH of the negative electrode slurry is preferably 6 or higher, more preferably 7 or higher, preferably 10 or lower, and more preferably 9 or lower.
If the pH of the negative electrode slurry is within the above-mentioned predetermined range, it is possible to further improve the thickening suppressing properties of the negative electrode slurry and the cycle characteristics of a secondary battery equipped with a negative electrode prepared using the negative electrode slurry. can.
（非水系二次電池用負極）
　本発明の負極は、上述した負極用スラリーを用いて形成した負極合材層を備える。そして、本発明の負極は、通常、集電体と、前記集電体上に、上記負極用スラリーを用いて形成した負極合材層と、を備える。ここで、負極合材層には、負極活物質と、平均長さ及び平均直径がそれぞれ上述した所定の範囲内であるＣＮＴと、水溶性高分子とが含まれ、任意に結着材等が含まれている。そして、本発明の負極は、上述した本発明の負極用スラリーを用いて形成した負極合材層を備えているので、二次電池に優れたサイクル特性を発揮させることができる。 (Negative electrode for non-aqueous secondary batteries)
The negative electrode of the present invention includes a negative electrode composite layer formed using the above-mentioned negative electrode slurry. The negative electrode of the present invention typically includes a current collector and a negative electrode composite layer formed on the current collector using the negative electrode slurry. Here, the negative electrode composite layer includes a negative electrode active material, CNTs whose average length and average diameter are within the above-mentioned predetermined ranges, and a water-soluble polymer, and optionally includes a binder or the like. include. Since the negative electrode of the present invention includes the negative electrode composite material layer formed using the above-described slurry for negative electrodes of the present invention, it is possible to make the secondary battery exhibit excellent cycle characteristics.
＜集電体＞
　集電体は、電気導電性を有し、かつ、電気化学的に耐久性のある材料からなる。具体的には、集電体としては、例えば、鉄、銅、アルミニウム、ニッケル、ステンレス鋼、チタン、タンタル、金、白金等からなる集電体を用い得る。中でも、リチウムイオン二次電池の負極に用いる集電体としては、負極のピール強度を向上させる観点から、銅箔が好ましい。なお、集電体を構成する上記の材質は、１種を単独で用いてもよく、２種以上を組み合わせて用いてもよい。 <Current collector>
The current collector is made of an electrically conductive and electrochemically durable material. Specifically, as the current collector, for example, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. can be used. Among these, copper foil is preferable as the current collector used for the negative electrode of a lithium ion secondary battery from the viewpoint of improving the peel strength of the negative electrode. Note that the above-mentioned materials constituting the current collector may be used alone or in combination of two or more.
＜負極の製造方法＞
　本発明の負極を製造する方法は特に限定されない。例えば、本発明の負極は、上述した本発明の負極用スラリーを、集電体の少なくとも一方の面に塗布し、乾燥して負極合材層を形成することで製造することができる。より詳細には、当該製造方法は、負極用スラリーを集電体の少なくとも一方の面に塗布する工程（塗布工程）と、集電体の少なくとも一方の面に塗布された負極用スラリーを乾燥して集電体上に負極合材層を形成する工程（乾燥工程）とを含む。 <Manufacturing method of negative electrode>
The method for manufacturing the negative electrode of the present invention is not particularly limited. For example, the negative electrode of the present invention can be manufactured by applying the above-described slurry for a negative electrode of the present invention to at least one surface of a current collector and drying it to form a negative electrode composite layer. More specifically, the manufacturing method includes a step of applying a negative electrode slurry to at least one surface of a current collector (coating step), and drying the negative electrode slurry applied to at least one surface of the current collector. and a step (drying step) of forming a negative electrode composite material layer on the current collector.
〔塗布工程〕
　負極用スラリーを集電体上に塗布する方法としては、特に限定されず公知の方法を用いることができる。具体的には、塗布方法としては、ドクターブレード法、ディップ法、リバースロール法、ダイレクトロール法、グラビア法、エクストルージョン法、ハケ塗り法等を用いることができる。この際、負極用スラリーを集電体の片面だけに塗布してもよいし、両面に塗布してもよい。塗布後乾燥前の集電体上のスラリー膜の厚みは、乾燥して得られる負極合材層の厚みに応じて適宜に設定し得る。 [Coating process]
The method for applying the negative electrode slurry onto the current collector is not particularly limited, and any known method can be used. Specifically, as a coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, etc. can be used. At this time, the negative electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after coating and before drying can be appropriately set depending on the thickness of the negative electrode composite material layer obtained by drying.
〔乾燥工程〕
　集電体上の負極用スラリーを乾燥する方法としては、特に限定されず公知の方法を用いることができ、例えば温風、熱風、低湿風による乾燥、真空乾燥、赤外線や電子線等の照射による乾燥法が挙げられる。このように集電体上の負極用スラリーを乾燥することで、集電体上に負極合材層を形成し、集電体と負極合材層とを備える負極を得ることができる。 [Drying process]
The method of drying the negative electrode slurry on the current collector is not particularly limited and any known method can be used, such as drying with hot air, hot air, low humidity air, vacuum drying, irradiation with infrared rays, electron beams, etc. An example is a drying method. By drying the negative electrode slurry on the current collector in this way, a negative electrode composite layer can be formed on the current collector, and a negative electrode including the current collector and the negative electrode composite layer can be obtained.
　なお、乾燥工程の後、金型プレス又はロールプレス等を用い、負極合材層に加圧処理を施してもよい。加圧処理により、負極合材層を集電体に良好に密着させることができる。
　更に、負極合材層が硬化性の重合体を含む場合は、負極合材層の形成後に前記重合体を硬化させてもよい。 Note that after the drying step, the negative electrode composite material layer may be subjected to pressure treatment using a mold press, a roll press, or the like. The pressure treatment allows the negative electrode composite material layer to be brought into good contact with the current collector.
Furthermore, when the negative electrode composite material layer contains a curable polymer, the polymer may be cured after forming the negative electrode composite material layer.
（非水系二次電池）
　本発明の二次電池は、上述した本発明の負極を備える。そして、本発明の二次電池は、本発明の負極を備えているため、サイクル特性に優れている。なお、本発明の二次電池は、例えば、リチウムイオン二次電池であることが好ましい。 (Non-aqueous secondary battery)
The secondary battery of the present invention includes the negative electrode of the present invention described above. Since the secondary battery of the present invention includes the negative electrode of the present invention, it has excellent cycle characteristics. In addition, it is preferable that the secondary battery of this invention is a lithium ion secondary battery, for example.
　ここで、以下では、本発明の二次電池の一例としてのリチウムイオン二次電池の構成について説明する。このリチウムイオン二次電池は、正極、負極、電解液、セパレータを備える。そして負極が、上述した本発明の非水系二次電池用負極である。 Here, the configuration of a lithium ion secondary battery as an example of the secondary battery of the present invention will be described below. This lithium ion secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode is the above-mentioned negative electrode for a non-aqueous secondary battery of the present invention.
＜正極＞
　正極としては、特に限定されず既知の正極を用いることができる。 <Positive electrode>
The positive electrode is not particularly limited, and any known positive electrode can be used.
＜電解液＞
　電解液としては、通常、有機溶媒に支持電解質を溶解した有機電解液が用いられる。支持電解質としては、例えば、リチウム塩が用いられる。リチウム塩としては、例えば、ＬｉＰＦ６、ＬｉＡｓＦ６、ＬｉＢＦ４、ＬｉＳｂＦ６、ＬｉＡｌＣｌ４、ＬｉＣｌＯ４、ＣＦ３ＳＯ３Ｌｉ、Ｃ４Ｆ９ＳＯ３Ｌｉ、ＣＦ３ＣＯＯＬｉ、（ＣＦ３ＣＯ）２ＮＬｉ、（ＣＦ３ＳＯ２）２ＮＬｉ、（Ｃ２Ｆ５ＳＯ２）ＮＬｉ等が挙げられる。なかでも、溶媒に溶けやすく高い解離度を示すので、ＬｉＰＦ６、ＬｉＣｌＯ４、ＣＦ３ＳＯ３Ｌｉが好ましく、ＬｉＰＦ６が特に好ましい。なお、電解質は１種類を単独で用いてもよく、２種類以上を任意の比率で組み合わせて用いてもよい。通常は、解離度の高い支持電解質を用いるほどリチウムイオン伝導度が高くなる傾向があるので、支持電解質の種類によりリチウムイオン伝導度を調節することができる。 <Electrolyte>
As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte, for example, lithium salt is used. Examples of lithium salts include LiPF 6 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlCl 4 , LiClO 4 , CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) 2 NLi. , (CF 3 SO 2 ) 2 NLi, (C 2 F 5 SO 2 ) NLi, and the like. Among these, LiPF 6 , LiClO 4 , and CF 3 SO 3 Li are preferred, and LiPF 6 is particularly preferred since they are easily soluble in solvents and exhibit a high degree of dissociation. Note that one type of electrolyte may be used alone, or two or more types may be used in combination in any ratio. Usually, the lithium ion conductivity tends to increase as a supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted depending on the type of supporting electrolyte.
　電解液に使用する有機溶媒としては、支持電解質を溶解できるものであれば特に限定されないが、例えば、ジメチルカーボネート（ＤＭＣ）、エチレンカーボネート（ＥＣ）、ジエチルカーボネート（ＤＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、メチルエチルカーボネート（ＥＭＣ）等のカーボネート類；γ－ブチロラクトン、ギ酸メチル等のエステル類；１，２－ジメトキシエタン、テトラヒドロフラン等のエーテル類；スルホラン、ジメチルスルホキシド等の含硫黄化合物類；等が好適に用いられる。またこれらの溶媒の混合液を用いてもよい。中でも、誘電率が高く、安定な電位領域が広いのでカーボネート類を用いることが好ましく、エチレンカーボネートとエチルメチルカーボネートとの混合物を用いることが更に好ましい。
　なお、電解液中の電解質の濃度は適宜調整することができ、例えば０．５～１５質量％することが好ましく、２～１３質量％とすることがより好ましく、５～１０質量％とすることが更に好ましい。また、電解液には、既知の添加剤、例えばフルオロエチレンカーボネートやエチルメチルスルホン等を添加してもよい。 The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte, but examples include dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), Carbonates such as butylene carbonate (BC) and methyl ethyl carbonate (EMC); Esters such as γ-butyrolactone and methyl formate; Ethers such as 1,2-dimethoxyethane and tetrahydrofuran; Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide etc. are preferably used. Alternatively, a mixture of these solvents may be used. Among them, it is preferable to use carbonates because they have a high dielectric constant and a wide stable potential range, and it is more preferable to use a mixture of ethylene carbonate and ethyl methyl carbonate.
The concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate, for example, preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and 5 to 10% by mass. is even more preferable. Additionally, known additives such as fluoroethylene carbonate and ethylmethylsulfone may be added to the electrolyte.
＜セパレータ＞
　セパレータとしては、特に限定されることなく、例えば特開２０１２－２０４３０３号公報に記載のものを用いることができる。これらの中でも、セパレータ全体の膜厚を薄くすることができ、これにより、リチウムイオン二次電池内の電極活物質の比率を高くして体積あたりの容量を高くすることができるという点より、ポリオレフィン系（ポリエチレン、ポリプロピレン、ポリブテン、ポリ塩化ビニル）の樹脂からなる微多孔膜が好ましい。 <Separator>
The separator is not particularly limited, and for example, those described in JP-A No. 2012-204303 can be used. Among these, polyolefins are preferred because they can reduce the overall film thickness of the separator, thereby increasing the ratio of the electrode active material in the lithium ion secondary battery and increasing the capacity per volume. A microporous membrane made of a resin of the type (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred.
＜リチウムイオン二次電池の製造方法＞
　本発明に従うリチウムイオン二次電池は、例えば、正極と、負極とを、セパレータを介して重ね合わせ、これを必要に応じて電池形状に応じて巻く、折る等して電池容器に入れ、電池容器に電解液を注入して封口することにより製造することができる。二次電池の内部の圧力上昇、過充放電等の発生を防止するために、必要に応じて、ヒューズ、ＰＴＣ素子等の過電流防止素子、エキスパンドメタル、リード板等を設けてもよい。二次電池の形状は、例えば、コイン型、ボタン型、シート型、円筒型、角形、扁平型等、何れであってもよい。 <Method for manufacturing lithium ion secondary battery>
The lithium ion secondary battery according to the present invention can be produced by, for example, stacking a positive electrode and a negative electrode with a separator interposed therebetween, and rolling or folding them according to the shape of the battery as necessary and placing them in a battery container. It can be manufactured by injecting an electrolyte into the container and sealing it. In order to prevent an increase in pressure inside the secondary battery, overcharging and discharging, etc., a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. The shape of the secondary battery may be, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, or the like.
　以下、本発明について実施例に基づき具体的に説明するが、本発明はこれら実施例に限定されるものではない。なお、以下の説明において、量を表す「％」及び「部」は、特に断らない限り、質量基準である。
　また、複数種類の単量体を共重合して製造される重合体において、ある単量体を重合して形成される単量体単位の前記重合体における割合は、別に断らない限り、通常は、その重合体の重合に用いる全単量体に占める当該ある単量体の比率（仕込み比）と一致する。
　そして、実施例及び比較例において、ＣＮＴの平均長さ及び平均直径、ＣＮＴ分散液の分散性及び保存安定性、負極用スラリーの増粘抑制性、負極合材層のピール強度、並びに、二次電池のサイクル特性は、それぞれ以下の方法を使用して評価した。 Hereinafter, the present invention will be specifically explained based on Examples, but the present invention is not limited to these Examples. In the following description, "%" and "part" representing amounts are based on mass unless otherwise specified.
In addition, in a polymer produced by copolymerizing multiple types of monomers, the proportion of monomer units formed by polymerizing a certain monomer in the polymer is usually the same unless otherwise specified. , corresponds to the ratio of the certain monomer to the total monomers used for polymerization of the polymer (feeding ratio).
In Examples and Comparative Examples, the average length and average diameter of CNTs, the dispersibility and storage stability of CNT dispersion, the thickening suppressing property of negative electrode slurry, the peel strength of negative electrode composite layer, and the secondary The cycle characteristics of the batteries were evaluated using the following methods.
＜ＣＮＴの平均長さ及び平均直径＞
　測定用試料としてのＣＮＴ分散液を銅箔上に塗布することで形成した塗膜を、走査型電子顕微鏡（ＳＥＭ）を用いて観察した。得られたＳＥＭ画像から無作為に１００本のＣＮＴを選択して長さ及び直径（外径）を測定した。そして、当該１００本のＣＮＴの長さ及び直径（外径）のそれぞれの平均値を、ＣＮＴ分散液中（即ち、分散処理後）におけるＣＮＴの平均長さ及び平均直径とした。
　また、測定試料として、ＣＮＴ分散液に代えて、湿式ジェットミルによる分散処理前のＣＮＴを適量のイオン交換水と混合して得られた混合液を用いたこと以外は、上記と同じ方法により測定を行い、ＣＮＴの分散処理前の平均長さ及び平均直径を求めた。 <Average length and average diameter of CNT>
A coating film formed by applying a CNT dispersion liquid as a measurement sample onto a copper foil was observed using a scanning electron microscope (SEM). 100 CNTs were randomly selected from the obtained SEM images and their lengths and diameters (outer diameters) were measured. Then, the respective average values of the length and diameter (outer diameter) of the 100 CNTs were taken as the average length and average diameter of the CNTs in the CNT dispersion (that is, after the dispersion treatment).
In addition, the measurement was performed in the same manner as above, except that instead of the CNT dispersion liquid, a mixed liquid obtained by mixing CNTs before dispersion treatment with a wet jet mill with an appropriate amount of ion-exchanged water was used as the measurement sample. The average length and average diameter of the CNTs before dispersion treatment were determined.
＜ＣＮＴ分散液の分散性＞
　ＣＮＴ分散液について、ＪＩＳ　Ｚ８８２５：２０１３に準拠し、レーザー回析・散乱式粒度分布測定装置（マイクロトラックベル社製、マイクロトラックＭＴ－３３００ＥＸＩＩ）を用いて、体積平均粒子径Ｄ５０を湿式測定した。体積平均粒子径Ｄ５０の値が小さいほど分散性が良いことを示す。
　Ａ：体積平均粒子径Ｄ５０が１５μｍ未満
　Ｂ：体積平均粒子径Ｄ５０が１５μｍ以上５０μｍ未満
　Ｃ：体積平均粒子径Ｄ５０が５０μｍ以上 <Dispersibility of CNT dispersion>
The volume average particle diameter D50 of the CNT dispersion liquid was wet-measured in accordance with JIS Z8825:2013 using a laser diffraction/scattering particle size distribution analyzer (Microtrac MT-3300EXII, manufactured by Microtrac Bell Co., Ltd.). The smaller the value of the volume average particle diameter D50, the better the dispersibility.
A: Volume average particle diameter D50 is less than 15 μm B: Volume average particle diameter D50 is 15 μm or more and less than 50 μm C: Volume average particle diameter D50 is 50 μm or more
＜ＣＮＴ分散液の保存安定性＞
　ＣＮＴ分散液の作製直後の粘度η１を、Ｂ型粘度計を用いて、温度２５℃、スピンドル回転速度６０ｒｐｍの条件で、スピンドル回転開始後６０秒間経過時に測定した。η１測定後のＣＮＴ分散液を２５℃で１０日間静置条件で保管し、粘度η１と同様にして保管後の粘度η２を測定した。η１に対するη２の比（η２／η１）を分散液の粘度比とし、下記基準で評価した。分散液の粘度比の値が１．０に近い程、ＣＮＴ分散液の粘度上昇が抑制され、保存安定性が良いことを示す。
　Ａ：分散液の粘度比が１．１５未満
　Ｂ：分散液の粘度比が１．１５以上１．６未満
　Ｃ：分散液の粘度比が１．６以上 <Storage stability of CNT dispersion>
The viscosity η1 of the CNT dispersion liquid immediately after preparation was measured using a B-type viscometer at a temperature of 25° C. and a spindle rotation speed of 60 rpm, 60 seconds after the start of spindle rotation. After measuring η1, the CNT dispersion was stored at 25° C. for 10 days, and the viscosity η2 after storage was measured in the same manner as the viscosity η1. The ratio of η2 to η1 (η2/η1) was taken as the viscosity ratio of the dispersion liquid, and evaluation was made according to the following criteria. The closer the viscosity ratio value of the dispersion liquid is to 1.0, the more suppressed the increase in viscosity of the CNT dispersion liquid is, indicating that the storage stability is better.
A: The viscosity ratio of the dispersion liquid is less than 1.15 B: The viscosity ratio of the dispersion liquid is 1.15 or more and less than 1.6 C: The viscosity ratio of the dispersion liquid is 1.6 or more
＜負極用スラリーの増粘抑制性＞
　測定用試料として、負極用スラリーと、ＣＮＴ分散液を添加しなかったこと以外は当該負極用スラリーの調製と同様にして得られた対照用スラリーとを準備した。
　対照用スラリーの作製直後の粘度η３を、Ｂ型粘度計を用いて、温度２５℃、スピンドル回転速度６０ｒｐｍの条件で、スピンドル回転開始後６０秒間経過時に測定した。
　上記と同じ操作及び条件で、負極用スラリーの作製直後の粘度η４を測定した。
　そして、η３に対するη４の比（η４／η３）をスラリー粘度比とし、下記基準で評価した。スラリー粘度比の値が１．０に近い程、ＣＮＴ分散液を添加したことによる負極用スラリーの粘度上昇が抑制され、当該負極用スラリーが増粘抑制性に優れていることを示す。
　Ａ：スラリー粘度比が１．５未満
　Ｂ：スラリー粘度比が１．５以上３未満
　Ｃ：スラリー粘度比が３以上 <Inhibition of thickening of slurry for negative electrode>
As samples for measurement, a slurry for a negative electrode and a control slurry obtained in the same manner as the slurry for a negative electrode except that no CNT dispersion liquid was added were prepared.
The viscosity η3 of the control slurry immediately after preparation was measured using a B-type viscometer at a temperature of 25° C. and a spindle rotation speed of 60 rpm, 60 seconds after the start of spindle rotation.
The viscosity η4 of the negative electrode slurry immediately after preparation was measured under the same operation and conditions as above.
Then, the ratio of η4 to η3 (η4/η3) was defined as the slurry viscosity ratio, and evaluation was made according to the following criteria. The closer the value of the slurry viscosity ratio is to 1.0, the more suppressed is the increase in the viscosity of the negative electrode slurry due to the addition of the CNT dispersion, indicating that the negative electrode slurry is excellent in suppressing thickening.
A: Slurry viscosity ratio is less than 1.5 B: Slurry viscosity ratio is 1.5 or more and less than 3 C: Slurry viscosity ratio is 3 or more
＜負極のピール強度＞
　作製した負極を長さ１００ｍｍ、幅１０ｍｍの長方形に切り出して試験片とした。この試験片を、負極合材層の表面を下にして、負極合材層の表面にセロハンテープを貼り付けた。この際、セロハンテープとしてはＪＩＳ　Ｚ１５２２に規定されるものを用いた。また、セロハンテープは試験台に固定しておいた。その後、集電体の一端を鉛直上方に引張り速度１５０ｍｍ／分で引っ張って剥がしたときの応力を測定した。この測定を３回行い、その平均値を求め、当該平均値を負極のピール強度として、下記の基準で評価した。負極のピール強度が大きいほど、負極合材層の集電体への結着力が大きいこと、即ち、密着強度が大きいことを示す。
　Ａ：ピール強度が８Ｎ／ｍ以上
　Ｂ：ピール強度が５Ｎ／ｍ以上８Ｎ／ｍ未満
　Ｃ：ピール強度が５Ｎ／ｍ未満 <Peel strength of negative electrode>
The produced negative electrode was cut into a rectangle with a length of 100 mm and a width of 10 mm to prepare a test piece. Cellophane tape was attached to the surface of the negative electrode composite material layer of this test piece with the surface of the negative electrode composite material layer facing down. At this time, the cellophane tape specified in JIS Z1522 was used. In addition, cellophane tape was fixed to the test stand. Thereafter, one end of the current collector was pulled vertically upward at a pulling speed of 150 mm/min and the stress was measured when it was peeled off. This measurement was performed three times, the average value was determined, and the average value was used as the peel strength of the negative electrode and evaluated according to the following criteria. The greater the peel strength of the negative electrode, the greater the binding force of the negative electrode composite material layer to the current collector, that is, the greater the adhesion strength.
A: Peel strength is 8 N/m or more B: Peel strength is 5 N/m or more and less than 8 N/m C: Peel strength is less than 5 N/m
＜二次電池のサイクル特性＞
　二次電池を、電解液注液後、２５℃の環境下で２４時間静置させた。次いで、０．２Ｃの定電流－定電圧充電（カットオフ０．０２Ｃ）によりセル電圧４．３５Ｖまで充電し、セル電圧２．７５Ｖまで定電流放電する充放電の操作を行い、初期容量Ｃ０を測定した。更に、２５℃の環境下で１．０Ｃの定電流－定電圧充電（カットオフ０．０２Ｃ）によってセル電圧４．３５Ｖまで充電し、セル電圧２．７５Ｖまで定電流法で放電する充放電を繰り返し、５０サイクル後の容量Ｃ１を測定した。そして、容量維持率（％）＝Ｃ１／Ｃ０×１００を算出し、下記基準で評価した。容量維持率が高いほど、二次電池がサイクル特性に優れることを示す。
　Ａ：容量維持率が９０％以上
　Ｂ：容量維持率が８５％以上９０％未満
　Ｃ：容量維持率が８５％未満 <Cycle characteristics of secondary batteries>
After injecting the electrolyte, the secondary battery was allowed to stand for 24 hours in an environment of 25°C. Next, a charge/discharge operation was performed in which the cell voltage was charged to 4.35V by constant current-constant voltage charging (cutoff 0.02C) at 0.2C, and constant current discharged to a cell voltage of 2.75V, and the initial capacity C0 was It was measured. Furthermore, the cell was charged to a cell voltage of 4.35V by constant current-constant voltage charging (cutoff 0.02C) at 1.0C in an environment of 25°C, and then discharged by a constant current method to a cell voltage of 2.75V. The capacity C1 after 50 cycles was repeatedly measured. Then, capacity retention rate (%)=C1/C0×100 was calculated and evaluated based on the following criteria. The higher the capacity retention rate, the better the cycle characteristics of the secondary battery.
A: Capacity retention rate is 90% or more B: Capacity retention rate is 85% or more and less than 90% C: Capacity retention rate is less than 85%
（実施例１）
＜水溶性重合体（分散剤）の調製＞
　リアクターに、４７３部のイオン交換水と、５８部のメタクリル酸（カルボン酸基含有単量体）と、０．６部のｔ－ドデシルメルカプタンと、イオン交換水で固形分濃度１０％に希釈したドデシルベンゼンスルホン酸ナトリウム３．０部とを仕込んだ。次いで、リアクター内を密閉し、撹拌翼で撹拌しながら窒素置換を２回実施した。窒素置換終了後、窒素置換したイソプレン（共役ジエン単量体）４２部をリアクターに仕込んだ。その後、リアクター内を５℃に制御した。リアクター内が５℃に制御されていることを確認した後、ハイドロサルファイト０．０１部をイオン交換水で溶解してリアクター内に添加した。ハイドロサルファイト添加５分後、クメンハイドロパーオキサイドを０．１部（１回目）添加した。更に別の容器を用い、イオン交換水９．０部にナトリウムホルムアルデヒドスルホキシレート（三菱ガス化学社製、製品名「ＳＦＳ」）０．０４部（１回目）、硫酸第一鉄（中部キレスト社製、製品名「フロストＦｅ」）０．００３部（１回目）、及びエチレンジアミン四酢酸（中部キレスト社製、製品名「キレスト４００Ｇ」）０．０３部を溶解したものを、リアクター内に添加した。
　重合転化率が４０％に到達したところでリアクター内を１０℃に昇温した。その後、重合転化率が６０％に到達した後、リアクター内を１８℃に昇温した。その後、重合転化率７０％に到達時、クメンハイドロパーオキサイド０．０９部（２回目）をリアクター内に添加した。更に別の容器を用い、イオン交換水９．０部にナトリウムホルムアルデヒドスルホキシレート（三菱ガス化学社製、製品名「ＳＦＳ」）０．０４部（２回目）、硫酸第一鉄（中部キレスト社製、製品名「フロストＦｅ」）０．００３部（２回目）、及びエチレンジアミン四酢酸（中部キレスト社製、製品名「キレスト４００Ｇ」）０．０３部を溶解したものをリアクター内に添加した。
　重合転化率が９３％に到達した後、２，２，６，６－テトラメチルピペリジン－１－オキシル０．１２部を１０．３５部のイオン交換水で希釈したものをリアクター内に添加し、反応を停止した。反応停止後、エバポレータで残留イソプレンが３００ｐｐｍ以下となるまで脱臭した。脱臭完了後、５％水酸化ナトリウム水溶液でｐＨが８となるように撹拌しながら調整して、水溶性重合体（分散剤）の水溶液を得た。 (Example 1)
<Preparation of water-soluble polymer (dispersant)>
In a reactor, 473 parts of ion-exchanged water, 58 parts of methacrylic acid (carboxylic acid group-containing monomer), 0.6 parts of t-dodecyl mercaptan, and diluted with ion-exchanged water to a solid concentration of 10% were added. 3.0 parts of sodium dodecylbenzenesulfonate were charged. Next, the inside of the reactor was sealed, and nitrogen substitution was performed twice while stirring with a stirring blade. After completing the nitrogen substitution, 42 parts of nitrogen-substituted isoprene (conjugated diene monomer) was charged into the reactor. Thereafter, the inside of the reactor was controlled at 5°C. After confirming that the inside of the reactor was controlled at 5° C., 0.01 part of hydrosulfite was dissolved in ion-exchanged water and added to the reactor. Five minutes after the addition of hydrosulfite, 0.1 part of cumene hydroperoxide (first time) was added. Using another container, add 9.0 parts of ion-exchanged water, 0.04 part of sodium formaldehyde sulfoxylate (manufactured by Mitsubishi Gas Chemical Co., Ltd., product name "SFS") (first time), and ferrous sulfate (Chubu Chrest Co., Ltd.). A solution of 0.003 parts of ethylenediaminetetraacetic acid (manufactured by Chubu Chrest Co., Ltd., product name ``Frost Fe'') (first time) and 0.03 parts of ethylenediaminetetraacetic acid (manufactured by Chubu Chrest Co., Ltd., product name ``Chrest 400G'') was added to the reactor. .
When the polymerization conversion rate reached 40%, the temperature inside the reactor was raised to 10°C. Thereafter, after the polymerization conversion rate reached 60%, the temperature inside the reactor was raised to 18°C. Thereafter, when the polymerization conversion rate reached 70%, 0.09 part of cumene hydroperoxide (second time) was added into the reactor. Using another container, add 9.0 parts of ion-exchanged water, 0.04 part of sodium formaldehyde sulfoxylate (manufactured by Mitsubishi Gas Chemical Co., Ltd., product name "SFS") (second time), and ferrous sulfate (Chubu Chrest Co., Ltd.). A solution of 0.003 parts of ethylenediaminetetraacetic acid (manufactured by Chubu Chrest Co., Ltd., product name "Frost Fe") (second time) and 0.03 parts of ethylenediaminetetraacetic acid (manufactured by Chubu Chrest Co., Ltd., product name "Chrest 400G") was added to the reactor.
After the polymerization conversion rate reached 93%, 0.12 parts of 2,2,6,6-tetramethylpiperidine-1-oxyl diluted with 10.35 parts of ion-exchanged water was added into the reactor. The reaction was stopped. After the reaction was stopped, deodorization was performed using an evaporator until the residual isoprene became 300 ppm or less. After the deodorization was completed, the pH was adjusted to 8 with a 5% aqueous sodium hydroxide solution while stirring to obtain an aqueous solution of a water-soluble polymer (dispersant).
＜ＣＮＴ分散液の調製＞
　多層ＣＮＴ（１）（分散処理前の平均長さ：１０００μｍ、分散処理前の平均直径：５０ｎｍ、Ｇ／Ｄ比：２．８）０．４部と、上記で調製した分散剤としての水溶性重合体０．４部（固形分相当量）と、適量のイオン交換水とを、ディスパーにて撹拌（３０００ｒｐｍ、６０分）し、次いで、湿式ジェットミル（吉田機械興業社製、製品名「ナノヴェイタ」）を用いて分散処理を行った。なお、湿式ジェットミルによる分散処理の条件は、圧力を１５０ＭＰａとし、処理回数を１０回とした。そして、５％水酸化ナトリウム水溶液を用いてｐＨを８に調整して、ＣＮＴ分散液（ＣＮＴの含有割合＝０．４％、水溶性重合体の含有割合＝０．４％）を製造した。
　得られたＣＮＴ分散液中（即ち、分散処理後）におけるＣＮＴの平均長さ及び平均直径を測定したところ、ＣＮＴの平均長さは１０μｍであり、平均直径は５０ｎｍであった。
　また、得られたＣＮＴ分散液について、分散性及び保存安定性を評価した。結果を表１に示す。 <Preparation of CNT dispersion>
Multiwalled CNT (1) (average length before dispersion treatment: 1000 μm, average diameter before dispersion treatment: 50 nm, G / D ratio: 2.8) 0.4 part and water-soluble as a dispersant prepared above 0.4 parts of polymer (equivalent to solid content) and an appropriate amount of ion-exchanged water are stirred with a disper (3000 rpm, 60 minutes), and then wet jet mill (manufactured by Yoshida Kikai Kogyo Co., Ltd., product name: Nano Veita) is used. ”) was used to perform distributed processing. The conditions for the dispersion treatment using a wet jet mill were such that the pressure was 150 MPa and the number of times the treatment was 10 times. Then, the pH was adjusted to 8 using a 5% aqueous sodium hydroxide solution to produce a CNT dispersion (CNT content = 0.4%, water-soluble polymer content = 0.4%).
When the average length and average diameter of CNTs in the obtained CNT dispersion liquid (ie, after dispersion treatment) were measured, the average length and average diameter of CNTs were 10 μm and 50 nm.
Furthermore, the dispersibility and storage stability of the obtained CNT dispersion were evaluated. The results are shown in Table 1.
＜粒子状重合体（結着材）の調製＞
　撹拌機付き５ＭＰａ耐圧容器Ａに、スチレン３．１５部、１，３－ブタジエン１．６６部、乳化剤としてのラウリル硫酸ナトリウム０．２部、イオン交換水２０部、及び重合開始剤としての過硫酸カリウム０．０３部を入れ、十分に撹拌した後、６０℃に加温して重合を開始させ、６時間反応させてシード粒子を得た。
　上記の反応後、７５℃に加温し、スチレン５３．８５部、１，３－ブタジエン３１．３４部、アクリル酸１０．０部、連鎖移動剤としてのｔｅｒｔ－ドデシルメルカプタン０．２５部、乳化剤としてのラウリル硫酸ナトリウム０．３５部を入れた別の容器Ｂから、これらの混合物の耐圧容器Ａへの添加を開始し、これと同時に、重合開始剤として過硫酸カリウム１部の耐圧容器Ａへの添加を開始することで２段目の重合を開始した。
　即ち、単量体組成物全体としては、スチレン５７部、１，３－ブタジエン３３部、アクリル酸１０部を用いた。
　２段目の重合開始から５時間半後、これら単量体組成物を含む混合物の全量添加が完了し、その後、更に８５℃に加温して６時間反応させた。重合転化率が９７％になった時点で冷却し反応を停止した。この重合物を含む混合物に、５％水酸化ナトリウム水溶液を添加して、ｐＨ８に調整した。その後、加熱減圧蒸留によって未反応単量体の除去を行った。更にその後冷却し、非水溶性である粒子状重合体の水分散液を得た。 <Preparation of particulate polymer (binder)>
In a 5 MPa pressure-resistant container A equipped with a stirrer, 3.15 parts of styrene, 1.66 parts of 1,3-butadiene, 0.2 parts of sodium lauryl sulfate as an emulsifier, 20 parts of ion-exchanged water, and persulfuric acid as a polymerization initiator. After adding 0.03 part of potassium and stirring thoroughly, the mixture was heated to 60° C. to initiate polymerization, and reacted for 6 hours to obtain seed particles.
After the above reaction, the mixture was heated to 75°C, containing 53.85 parts of styrene, 31.34 parts of 1,3-butadiene, 10.0 parts of acrylic acid, 0.25 parts of tert-dodecylmercaptan as a chain transfer agent, and an emulsifier. Start adding these mixtures to pressure vessel A from another vessel B containing 0.35 parts of sodium lauryl sulfate as a polymerization initiator, and at the same time add 1 part of potassium persulfate as a polymerization initiator to pressure vessel A. The second stage of polymerization was started by starting the addition of .
That is, the total monomer composition used was 57 parts of styrene, 33 parts of 1,3-butadiene, and 10 parts of acrylic acid.
Five and a half hours after the start of the second stage polymerization, addition of the entire amount of the mixture containing these monomer compositions was completed, and then the mixture was further heated to 85° C. and reacted for 6 hours. When the polymerization conversion rate reached 97%, the reaction was stopped by cooling. A 5% aqueous sodium hydroxide solution was added to the mixture containing this polymer to adjust the pH to 8. Thereafter, unreacted monomers were removed by heating and vacuum distillation. Thereafter, the mixture was cooled to obtain an aqueous dispersion of a water-insoluble particulate polymer.
＜負極用スラリーの調製＞
　ディスパー付きのプラネタリーミキサーに、炭素系負極活物質としての人造黒鉛（体積平均粒子径：２４．５μｍ、比表面積：３．５ｍ２／ｇ）９０部と、シリコン系負極活物質としてのＳｉＯｘ１０部と、粘度調整剤としてのカルボキシメチルセルロースの水溶液２．０部（固形分相当量）を加え、イオン交換水で固形分濃度５８％に調整し、室温下で６０分混合した。混合後、当該プラネタリーミキサーに、上記のようにして得られたＣＮＴ分散液を、多層ＣＮＴが０．１部（固形分相当量）となるように添加し、混合した。次いでイオン交換水で固形分濃度５０％に調整し、更に上記のようにして得られた粒子状重合体（結着材）の水分散液を１．０部（固形分相当量）添加して混合液を得た。得られた混合液を減圧下で脱泡処理して、流動性の良い負極用スラリーを得た。得られた負極用スラリーのｐＨを測定したところ、ｐＨ８であった。
　得られた負極用スラリーについて、増粘抑制性を評価した。結果を表１に示す。 <Preparation of slurry for negative electrode>
In a planetary mixer equipped with a disperser, 90 parts of artificial graphite (volume average particle diameter: 24.5 μm, specific surface area: 3.5 m 2 /g) as a carbon-based negative electrode active material and SiO x as a silicon-based negative electrode active material were placed. 10 parts and 2.0 parts (equivalent to solid content) of an aqueous solution of carboxymethyl cellulose as a viscosity modifier were added, the solid content concentration was adjusted to 58% with ion-exchanged water, and the mixture was mixed for 60 minutes at room temperature. After mixing, the CNT dispersion obtained as described above was added to the planetary mixer so that the amount of multi-walled CNTs was 0.1 part (equivalent to solid content), and mixed. Next, the solid content concentration was adjusted to 50% with ion-exchanged water, and 1.0 part (solid content equivalent) of the aqueous dispersion of the particulate polymer (binder) obtained as described above was added. A mixed solution was obtained. The resulting mixed solution was defoamed under reduced pressure to obtain a slurry for a negative electrode with good fluidity. When the pH of the obtained negative electrode slurry was measured, it was found to be pH 8.
The obtained negative electrode slurry was evaluated for its ability to suppress thickening. The results are shown in Table 1.
＜負極の製造＞
　上記のようにして得られた負極用スラリーを、コンマコーターで、集電体としての厚さ１６μｍの銅箔の上に、乾燥後の膜厚が１０５μｍ、塗布量が１０ｍｇ／ｃｍ２になるように塗布した。この負極用スラリーが塗布された銅箔を、０．５ｍ／分の速度で温度１００℃のオーブン内を２分間、更に温度１２０℃のオーブン内を２分間かけて搬送することにより、銅箔上の負極用スラリーを乾燥させ、負極原反を得た。この負極原反をロールプレスで圧延して、負極合材層の厚みが８０μｍの負極を得た。
　得られた負極について、ピール強度を評価した。結果を表１に示す。 <Manufacture of negative electrode>
Using a comma coater, the slurry for the negative electrode obtained as described above was coated onto a 16 μm thick copper foil as a current collector so that the film thickness after drying was 105 μm and the coating amount was 10 mg/ cm2 . It was applied to. The copper foil coated with this negative electrode slurry was transported at a speed of 0.5 m/min in an oven at a temperature of 100°C for 2 minutes, and then in an oven at a temperature of 120°C for 2 minutes. The negative electrode slurry was dried to obtain a negative electrode material. This negative electrode original fabric was rolled with a roll press to obtain a negative electrode with a negative electrode composite material layer thickness of 80 μm.
The peel strength of the obtained negative electrode was evaluated. The results are shown in Table 1.
＜正極の製造＞
　プラネタリーミキサーに、正極活物質としてのスピネル構造を有するＬｉＣｏＯ２を９５部、結着材としてのＰＶＤＦ（ポリフッ化ビニリデン）を固形分相当量で３部、導電材としてのアセチレンブラックを２部、及び溶媒としてのＮ－メチルピロリドンを２０部加えて混合し、正極用スラリーを得た。
　得られた正極用スラリーを、コンマコーターで、厚さ２０μｍのアルミニウム箔（集電体）上に、乾燥後の膜厚が１００μｍ程度になるように塗布した。この正極用スラリーが塗布されたアルミニウム箔を、０．５ｍ／分の速度で温度６０℃のオーブン内を２分間、更に温度１２０℃のオーブン内を２分間かけて搬送することにより、アルミニウム箔上の正極用スラリーを乾燥させ、正極原反を得た。この正極原反をロールプレスで圧延して、正極合材層の厚みが７０μｍの正極を得た。 <Manufacture of positive electrode>
In a planetary mixer, 95 parts of LiCoO 2 having a spinel structure as a positive electrode active material, 3 parts of PVDF (polyvinylidene fluoride) as a binder in a solid content equivalent amount, 2 parts of acetylene black as a conductive material, and 20 parts of N-methylpyrrolidone as a solvent were added and mixed to obtain a positive electrode slurry.
The obtained positive electrode slurry was coated on a 20 μm thick aluminum foil (current collector) using a comma coater so that the film thickness after drying was about 100 μm. The aluminum foil coated with this positive electrode slurry was transported at a speed of 0.5 m/min in an oven at a temperature of 60°C for 2 minutes and then in an oven at a temperature of 120°C for 2 minutes. The positive electrode slurry was dried to obtain a positive electrode material. This positive electrode original fabric was rolled with a roll press to obtain a positive electrode with a positive electrode composite layer having a thickness of 70 μm.
＜セパレータの用意＞
　単層のポリプロピレン製セパレータ（乾式法により製造、幅６５ｍｍ、長さ５００ｍｍ、厚さ２５μｍ、気孔率５５％）を用意した。このセパレータを、５ｃｍ×５ｃｍの正方形に切り抜いて、二次電池の製造に使用した。 <Preparation of separator>
A single-layer polypropylene separator (manufactured by a dry method, width 65 mm, length 500 mm, thickness 25 μm, porosity 55%) was prepared. This separator was cut into a 5 cm x 5 cm square and used for manufacturing a secondary battery.
＜二次電池の製造＞
　電池の外装として、アルミニウム包材外装を用意した。上記正極を、４ｃｍ×４ｃｍの正方形に切り出して、集電体側の表面がアルミニウム包材外装に接するように配置した。次に、正極の正極合材層の面上に、上記正方形のセパレータを配置した。更に、上記負極を、４．２ｃｍ×４．２ｃｍの正方形に切り出して、これをセパレータ上に、負極合材層側の表面がセパレータに向かい合うよう配置した。その後、電解液として濃度１．０ＭのＬｉＰＦ６溶液（溶媒はエチレンカーボネート／ジエチルカーボネート＝１／２（体積比）の混合溶媒、添加剤としてフルオロエチレンカーボネート及びビニレンカーボネートをそれぞれ２体積％（溶媒比）含有）を充填した。更に、アルミニウム包材の開口を密封するために、１５０℃のヒートシールをしてアルミニウム包材外装を閉口し、ラミネートセル型のリチウムイオン二次電池を製造した。
　得られたリチウムイオン二次電池を用いて、サイクル特性を評価した。結果を表１に示す。 <Manufacture of secondary batteries>
An aluminum packaging material exterior was prepared as the battery exterior. The above positive electrode was cut into a square of 4 cm x 4 cm and placed so that the surface on the current collector side was in contact with the exterior of the aluminum packaging material. Next, the square separator was placed on the surface of the positive electrode composite layer of the positive electrode. Further, the negative electrode was cut into a square of 4.2 cm x 4.2 cm, and this was placed on a separator so that the surface on the negative electrode composite layer side faced the separator. After that, a LiPF 6 solution with a concentration of 1.0 M was used as an electrolyte (the solvent was a mixed solvent of ethylene carbonate/diethyl carbonate = 1/2 (volume ratio), and fluoroethylene carbonate and vinylene carbonate were added as additives at 2 volume % each (solvent ratio). ) containing). Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing was performed at 150° C. to close the aluminum packaging material exterior to produce a laminate cell type lithium ion secondary battery.
Cycle characteristics were evaluated using the obtained lithium ion secondary battery. The results are shown in Table 1.
（実施例２）
　ＣＮＴ分散液の調製の際に、分散剤として、水溶性重合体０．４部に代えて、カルボキシメチルセルロースナトリウム（カルボキシメチルセルロースのナトリウム塩）０．４部を用いたこと以外は、実施例１と同様にして、各種操作、測定及び評価を行った。結果を表１に示す。 (Example 2)
Example 1 was repeated, except that 0.4 parts of sodium carboxymethylcellulose (sodium salt of carboxymethylcellulose) was used as a dispersant instead of 0.4 parts of the water-soluble polymer when preparing the CNT dispersion. Various operations, measurements, and evaluations were performed in the same manner. The results are shown in Table 1.
（実施例３）
　ＣＮＴ分散液の調製の際に、湿式ジェットミルによる分散処理の条件において、処理回数を１０回から２０回に変更することで、得られるＣＮＴ分散液中におけるＣＮＴの平均長さを１０μｍから５μｍに調整したこと以外は、実施例１と同様にして、各種操作、測定及び評価を行った。結果を表１に示す。 (Example 3)
When preparing a CNT dispersion, by changing the number of treatments from 10 to 20 under the dispersion treatment conditions using a wet jet mill, the average length of CNTs in the resulting CNT dispersion was increased from 10 μm to 5 μm. Various operations, measurements, and evaluations were performed in the same manner as in Example 1 except for the adjustments. The results are shown in Table 1.
（実施例４）
　ＣＮＴ分散液の調製の際に、湿式ジェットミルによる分散処理の条件において、処理回数を１０回から５回に変更することで、得られるＣＮＴ分散液中（即ち、分散処理後）におけるＣＮＴの平均長さを１０μｍから１００μｍに調整したこと以外は、実施例１と同様にして、各種操作、測定及び評価を行った。結果を表１に示す。 (Example 4)
When preparing a CNT dispersion, the number of treatments was changed from 10 to 5 under the conditions of dispersion treatment using a wet jet mill, thereby increasing the average CNT in the resulting CNT dispersion (i.e., after dispersion treatment). Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the length was adjusted from 10 μm to 100 μm. The results are shown in Table 1.
（実施例５）
　ＣＮＴ分散液の調製の際に、多層ＣＮＴ（１）（分散処理前の平均長さ：１０００μｍ、分散処理前の平均直径：５０ｎｍ、Ｇ／Ｄ比：２．８）に代えて、多層ＣＮＴ（２）（分散処理前の平均長さ：１０００μｍ、分散処理前の平均直径：２０ｎｍ、Ｇ／Ｄ比：２．８）を用いることで、得られるＣＮＴ分散液中におけるＣＮＴの平均直径を５０ｎｍから２０ｎｍに調整したこと以外は、実施例１と同様にして、各種操作、測定及び評価を行った。結果を表１に示す。 (Example 5)
When preparing the CNT dispersion, instead of multiwall CNT (1) (average length before dispersion treatment: 1000 μm, average diameter before dispersion treatment: 50 nm, G/D ratio: 2.8), multiwall CNT ( 2) By using (average length before dispersion treatment: 1000 μm, average diameter before dispersion treatment: 20 nm, G/D ratio: 2.8), the average diameter of CNTs in the obtained CNT dispersion can be changed from 50 nm to 50 nm. Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the wavelength was adjusted to 20 nm. The results are shown in Table 1.
（実施例６）
　ＣＮＴ分散液の調製の際に、多層ＣＮＴ（１）（分散処理前の平均長さ：１０００μｍ、分散処理前の平均直径：５０ｎｍ、Ｇ／Ｄ比：２．８）に代えて、多層ＣＮＴ（３）（分散処理前の平均長さ：１０００μｍ、分散処理前の平均直径：１００ｎｍ、Ｇ／Ｄ比：２．８）を用いることで、得られるＣＮＴ分散液中におけるＣＮＴの平均直径を５０ｎｍから１００ｎｍに調整したこと以外は、実施例１と同様にして、各種操作、測定及び評価を行った。結果を表１に示す。 (Example 6)
When preparing a CNT dispersion, instead of multiwall CNT (1) (average length before dispersion treatment: 1000 μm, average diameter before dispersion treatment: 50 nm, G/D ratio: 2.8), multiwall CNT ( 3) By using (average length before dispersion treatment: 1000 μm, average diameter before dispersion treatment: 100 nm, G/D ratio: 2.8), the average diameter of CNTs in the obtained CNT dispersion can be changed from 50 nm to 50 nm. Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the wavelength was adjusted to 100 nm. The results are shown in Table 1.
（実施例７）
　水溶性重合体の調製及びＣＮＴ分散液の調製において、５％水酸化ナトリウム水溶液に代えて、５％水酸化リチウム水溶液を用いてｐＨ調整を行ったこと以外は、実施例１と同様にして各種操作、測定及び評価を行った。結果を表１に示す。 (Example 7)
In the preparation of the water-soluble polymer and the CNT dispersion, various procedures were carried out in the same manner as in Example 1, except that the pH was adjusted using a 5% lithium hydroxide aqueous solution instead of a 5% sodium hydroxide aqueous solution. Operations, measurements and evaluations were performed. The results are shown in Table 1.
（実施例８）
　水溶性重合体の調製において、イソプレン及びメタクリル酸に代えて、スチレンスルホン酸ナトリウム（スルホン酸基含有単量体）５９部及びエトキシジエチレングリコールアクリレート（アルキレンオキサイド構造含有単量体）４１部を用いたこと以外は、実施例１と同様にして各種操作、測定及び評価を行った。結果を表１に示す。 (Example 8)
In the preparation of the water-soluble polymer, 59 parts of sodium styrene sulfonate (monomer containing a sulfonic acid group) and 41 parts of ethoxydiethylene glycol acrylate (monomer containing an alkylene oxide structure) were used in place of isoprene and methacrylic acid. Other than that, various operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
（比較例１）
　ＣＮＴ分散液の調製の際に、多層ＣＮＴ（１）（分散処理前の平均長さ：１０００μｍ、分散処理前の平均直径：５０ｎｍ、Ｇ／Ｄ比：２．８）に代えて、多層ＣＮＴ（４）（分散処理前の平均長さ：６０μｍ、分散処理前の平均直径：１２ｎｍ、Ｇ／Ｄ比：１．３）を用いることで、得られるＣＮＴ分散液中におけるＣＮＴの平均長さを１０μｍから１μｍに調整し、平均直径を５０ｎｍから１２ｎｍに調整したこと以外は、実施例１と同様にして、各種操作、測定及び評価を行った。結果を表１に示す。 (Comparative example 1)
When preparing the CNT dispersion, instead of multiwall CNT (1) (average length before dispersion treatment: 1000 μm, average diameter before dispersion treatment: 50 nm, G/D ratio: 2.8), multiwall CNT ( 4) By using (average length before dispersion treatment: 60 μm, average diameter before dispersion treatment: 12 nm, G/D ratio: 1.3), the average length of CNTs in the obtained CNT dispersion liquid was set to 10 μm. Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the average diameter was adjusted from 50 nm to 1 μm and the average diameter was adjusted from 50 nm to 12 nm. The results are shown in Table 1.
（比較例２）
　ＣＮＴ分散液の調製の際に、多層ＣＮＴ（１）（分散処理前の平均長さ：１０００μｍ、分散処理前の平均直径：５０ｎｍ、Ｇ／Ｄ比：２．８）に代えて、多層ＣＮＴ（３）（分散処理前の平均長さ：１００μｍ、分散処理前の平均直径：５０ｎｍ、Ｇ／Ｄ比：２．８）を用いることで、得られるＣＮＴ分散液中におけるＣＮＴの平均長さを１０μｍから１μｍに調整したこと以外は、実施例１と同様にして、各種操作、測定及び評価を行った。結果を表１に示す。 (Comparative example 2)
When preparing a CNT dispersion, instead of multiwall CNT (1) (average length before dispersion treatment: 1000 μm, average diameter before dispersion treatment: 50 nm, G/D ratio: 2.8), multiwall CNT ( 3) By using (average length before dispersion treatment: 100 μm, average diameter before dispersion treatment: 50 nm, G/D ratio: 2.8), the average length of CNTs in the obtained CNT dispersion liquid was set to 10 μm. Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the thickness was adjusted from 1 μm to 1 μm. The results are shown in Table 1.
（比較例３）
　ＣＮＴ分散液の調製の際に、多層ＣＮＴ（１）（分散処理前の平均長さ：１０００μｍ、分散処理前の平均直径：５０ｎｍ、Ｇ／Ｄ比：２．８）に代えて、単層ＣＮＴ（分散処理前の平均長さ：５μｍ、分散処理前の平均直径：２ｎｍ、Ｇ／Ｄ比：８４）を用いることで、得られるＣＮＴ分散液中におけるＣＮＴの平均長さを１０μｍから１．２μｍに調整し、平均直径を５０ｎｍから２ｎｍに調整したこと以外は、実施例１と同様にして、各種操作、測定及び評価を行った。結果を表１に示す。 (Comparative example 3)
When preparing a CNT dispersion liquid, instead of multi-walled CNTs (1) (average length before dispersion treatment: 1000 μm, average diameter before dispersion treatment: 50 nm, G/D ratio: 2.8), single-walled CNTs were used. By using (average length before dispersion treatment: 5 μm, average diameter before dispersion treatment: 2 nm, G/D ratio: 84), the average length of CNTs in the obtained CNT dispersion was changed from 10 μm to 1.2 μm. Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the average diameter was adjusted from 50 nm to 2 nm. The results are shown in Table 1.
（比較例４）
　ＣＮＴ分散液の調製の際に、多層ＣＮＴ（１）（分散処理前の平均長さ：１０００μｍ、分散処理前の平均直径：５０ｎｍ、Ｇ／Ｄ比：２．８）に代えて、多層ＣＮＴ（５）（分散処理前の平均長さ：１０００μｍ、分散処理前の平均直径：１５０ｎｍ、Ｇ／Ｄ比：２．８）を用いることで、得られるＣＮＴ分散液中におけるＣＮＴの平均直径を５０ｎｍから１５０ｎｍに調整したこと以外は、実施例１と同様にして、各種操作、測定及び評価を行った。結果を表１に示す。 (Comparative example 4)
When preparing the CNT dispersion, instead of multiwall CNT (1) (average length before dispersion treatment: 1000 μm, average diameter before dispersion treatment: 50 nm, G/D ratio: 2.8), multiwall CNT ( 5) By using (average length before dispersion treatment: 1000 μm, average diameter before dispersion treatment: 150 nm, G/D ratio: 2.8), the average diameter of CNTs in the obtained CNT dispersion can be changed from 50 nm to 50 nm. Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the wavelength was adjusted to 150 nm. The results are shown in Table 1.
（比較例５）
　ＣＮＴ分散液の調製の際に、多層ＣＮＴ（１）（分散処理前の平均長さ：１０００μｍ、分散処理前の平均直径：５０ｎｍ、Ｇ／Ｄ比：２．８）に代えて、多層ＣＮＴ（４）（分散処理前の平均長さ：６０μｍ、分散処理前の平均直径：１２ｎｍ、Ｇ／Ｄ比：１．３）を用いると共に、湿式ジェットミルによる分散処理の条件において、処理回数を１０回から５回に変更することで、得られるＣＮＴ分散液中におけるＣＮＴの平均長さを１０μｍから５μｍに調整し、平均直径を５０ｎｍから１２ｎｍに調整したこと以外は、実施例１と同様にして、各種操作、測定及び評価を行った。結果を表１に示す。 (Comparative example 5)
When preparing the CNT dispersion, instead of multiwall CNT (1) (average length before dispersion treatment: 1000 μm, average diameter before dispersion treatment: 50 nm, G/D ratio: 2.8), multiwall CNT ( 4) Using (average length before dispersion treatment: 60 μm, average diameter before dispersion treatment: 12 nm, G/D ratio: 1.3), and under the conditions of dispersion treatment using a wet jet mill, the number of treatments was 10 times. In the same manner as in Example 1, except that the average length of the CNTs in the resulting CNT dispersion was adjusted from 10 μm to 5 μm, and the average diameter was adjusted from 50 nm to 12 nm by changing from to 5 times, Various operations, measurements, and evaluations were performed. The results are shown in Table 1.
（比較例６）
　ＣＮＴ分散液の調製の際に、湿式ジェットミルによる分散処理の条件において、処理回数を１０回から３回に変更することで、得られるＣＮＴ分散液中におけるＣＮＴの平均長さを１０μｍから２００μｍに調整したこと以外は、実施例１と同様にして、各種操作、測定及び評価を行った。結果を表１に示す。 (Comparative example 6)
When preparing a CNT dispersion, the average length of CNTs in the resulting CNT dispersion was increased from 10 μm to 200 μm by changing the number of treatments from 10 to 3 under the conditions of dispersion treatment using a wet jet mill. Various operations, measurements, and evaluations were performed in the same manner as in Example 1 except for the adjustments. The results are shown in Table 1.
　なお、表１中、
「ＩＰ」は、イソプレン単位を示し、
「ＭＡＡ」は、メタクリル酸単位を示し、
「ＣＭＣ」は、カルボキシメチルセルロースのナトリウム塩を示し、
「ＳＳ」は、スチレンスルホン酸ナトリウム単位を示し、
「ＥＣ－Ａ」は、エトキシジエチレングリコールアクリレート単位を示し、
「Ｌｉ」は、リチウム塩を示し、
「Ｎａ」は、ナトリウム塩を示す。 In addition, in Table 1,
"IP" indicates an isoprene unit,
"MAA" indicates a methacrylic acid unit,
"CMC" indicates sodium salt of carboxymethyl cellulose,
"SS" represents sodium styrene sulfonate unit,
"EC-A" represents an ethoxydiethylene glycol acrylate unit,
"Li" indicates lithium salt,
"Na" indicates sodium salt.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表１より、平均長さ及び平均直径がそれぞれ所定の範囲内であるＣＮＴと、水溶性高分子と、水とを含む実施例１～８のＣＮＴ分散液であれば、増粘抑制性に優れた非水系二次電池負極用スラリーを調製可能であると共に、非水系二次電池に優れたサイクル特性を発揮させ得ることが分かる。
　一方、平均長さ及び平均直径のいずれも所定の範囲に満たないＣＮＴを含む比較例１及び３のＣＮＴ分散液の場合、調製される非水系二次電池負極用スラリーは増粘抑制性に劣ることが分かる。
　また、平均直径は所定の範囲内であるものの、平均長さが所定の範囲に満たないＣＮＴを含む比較例２のＣＮＴ分散液の場合、非水系二次電池はサイクル特性に劣ることが分かる。
　さらに、平均長さは所定の範囲内であるものの、平均直径が所定の範囲を超えるＣＮＴを含む比較例４のＣＮＴ分散液の場合、非水系二次電池はサイクル特性に劣ることが分かる。
　また、平均長さは所定の範囲内であるものの、平均直径が所定の範囲に満たないＣＮＴを含む比較例５のＣＮＴ分散液の場合、調製される非水系二次電池負極用スラリーは増粘抑制性に劣ることが分かる。
　さらに、平均直径は所定の範囲内であるものの、平均長さが所定の範囲を超えるＣＮＴを含む比較例６のＣＮＴ分散液の場合、調製される非水系二次電池負極用スラリーは増粘抑制性に劣ることが分かる。 From Table 1, the CNT dispersions of Examples 1 to 8 containing CNTs whose average length and average diameter are within the predetermined ranges, a water-soluble polymer, and water have excellent thickening suppressing properties. It can be seen that it is possible to prepare a slurry for a negative electrode of a non-aqueous secondary battery, and also to make the non-aqueous secondary battery exhibit excellent cycle characteristics.
On the other hand, in the case of the CNT dispersion liquids of Comparative Examples 1 and 3 containing CNTs whose average length and average diameter are both less than the predetermined ranges, the prepared slurries for non-aqueous secondary battery negative electrodes have poor thickening suppressing properties. I understand that.
Furthermore, in the case of the CNT dispersion of Comparative Example 2 containing CNTs whose average diameter is within a predetermined range but whose average length is less than the predetermined range, it can be seen that the non-aqueous secondary battery has poor cycle characteristics.
Furthermore, in the case of the CNT dispersion liquid of Comparative Example 4 containing CNTs whose average length is within a predetermined range but whose average diameter exceeds a predetermined range, it can be seen that the non-aqueous secondary battery has poor cycle characteristics.
In addition, in the case of the CNT dispersion of Comparative Example 5 containing CNTs whose average length is within a predetermined range but whose average diameter is less than the predetermined range, the prepared slurry for a nonaqueous secondary battery negative electrode has a thickened viscosity. It can be seen that the suppressive properties are inferior.
Furthermore, in the case of the CNT dispersion of Comparative Example 6 containing CNTs whose average diameter is within a predetermined range but whose average length exceeds a predetermined range, the prepared slurry for a non-aqueous secondary battery negative electrode is inhibited from thickening. It turns out that they are inferior in gender.
　本発明によれば、増粘抑制性に優れた非水系二次電池負極用スラリーを調製可能であると共に、非水系二次電池に優れたサイクル特性を発揮させ得るカーボンナノチューブ分散液を提供することができる。
　また、本発明によれば、増粘抑制性に優れると共に、非水系二次電池に優れたサイクル特性を発揮させ得る非水系二次電池負極用スラリーを提供することができる。
　さらに、本発明によれば、非水系二次電池に優れたサイクル特性を発揮させ得る非水系二次電池用負極を提供することができる。
　また、本発明によれば、優れたサイクル特性を発揮し得る非水系二次電池を提供することができる。 According to the present invention, it is possible to prepare a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties, and to provide a carbon nanotube dispersion that can exhibit excellent cycle characteristics in a non-aqueous secondary battery. Can be done.
Further, according to the present invention, it is possible to provide a slurry for a negative electrode of a non-aqueous secondary battery that has excellent viscosity-inhibiting properties and can allow a non-aqueous secondary battery to exhibit excellent cycle characteristics.
Further, according to the present invention, it is possible to provide a negative electrode for a non-aqueous secondary battery that allows a non-aqueous secondary battery to exhibit excellent cycle characteristics.
Further, according to the present invention, it is possible to provide a non-aqueous secondary battery that can exhibit excellent cycle characteristics.

Claims (11)

  1. 　カーボンナノチューブと、水溶性高分子と、水とを含むカーボンナノチューブ分散液であって、
    　前記カーボンナノチューブは、平均長さが５μｍ以上１００μｍ以下であり、且つ、平均直径が２０ｎｍ以上１００ｎｍ以下である、カーボンナノチューブ分散液。     A carbon nanotube dispersion containing carbon nanotubes, a water-soluble polymer, and water,
    The carbon nanotube dispersion liquid has an average length of 5 μm or more and 100 μm or less, and an average diameter of 20 nm or more and 100 nm or less.
  2. 　前記水溶性高分子が酸官能基を有する、請求項１に記載のカーボンナノチューブ分散液。 The carbon nanotube dispersion according to claim 1, wherein the water-soluble polymer has an acid functional group.
  3. 　前記水溶性高分子の酸官能基の少なくとも一部が、アルカリ金属塩基又はアンモニウム塩基である、請求項２に記載のカーボンナノチューブ分散液。 The carbon nanotube dispersion according to claim 2, wherein at least a portion of the acid functional groups of the water-soluble polymer are an alkali metal base or an ammonium base.
  4. 　前記水溶性高分子に対する前記カーボンナノチューブの質量比が、０．１以上１０以下である、請求項１～３の何れかに記載のカーボンナノチューブ分散液。 The carbon nanotube dispersion according to any one of claims 1 to 3, wherein the mass ratio of the carbon nanotubes to the water-soluble polymer is 0.1 or more and 10 or less.
  5. 　ｐＨが６以上１０以下である、請求項１～４の何れかに記載のカーボンナノチューブ分散液。 The carbon nanotube dispersion according to any one of claims 1 to 4, which has a pH of 6 or more and 10 or less.
  6. 　負極活物質と、請求項１～５の何れかに記載のカーボンナノチューブ分散液とを含む、非水系二次電池負極用スラリー。 A slurry for a non-aqueous secondary battery negative electrode, comprising a negative electrode active material and the carbon nanotube dispersion according to any one of claims 1 to 5.
  7. 　前記負極活物質がシリコン系負極活物質を含む、請求項６に記載の非水系二次電池負極用スラリー。 The slurry for a non-aqueous secondary battery negative electrode according to claim 6, wherein the negative electrode active material includes a silicon-based negative electrode active material.
  8. 　粒子状重合体を更に含み、
    　前記粒子状重合体が、カルボン酸基含有単量体単位、芳香族ビニル単量体単位及び共役ジエン単量体単位を含む、請求項６又は７に記載の非水系二次電池負極用スラリー。     further comprising a particulate polymer;
    The slurry for a nonaqueous secondary battery negative electrode according to claim 6 or 7, wherein the particulate polymer contains a carboxylic acid group-containing monomer unit, an aromatic vinyl monomer unit, and a conjugated diene monomer unit.
  9. 　前記粒子状重合体中における前記カルボン酸基含有単量体単位の含有割合が、前記粒子状重合体が含む全繰り返し単位を１００質量％として、３質量％以上３０質量％以下である、請求項８に記載の非水系二次電池負極用スラリー。 A content ratio of the carboxylic acid group-containing monomer unit in the particulate polymer is 3% by mass or more and 30% by mass or less, based on 100% by mass of all repeating units contained in the particulate polymer. 8. The slurry for a non-aqueous secondary battery negative electrode as described in 8.
  10. 　請求項６～９の何れかに記載の非水系二次電池負極用スラリーを用いて形成した負極合材層を備える、非水系二次電池用負極。 A negative electrode for a non-aqueous secondary battery, comprising a negative electrode composite layer formed using the slurry for a negative electrode for a non-aqueous secondary battery according to any one of claims 6 to 9.
  11. 　請求項１０に記載の非水系二次電池用負極を備える、非水系二次電池。
          A non-aqueous secondary battery comprising the negative electrode for a non-aqueous secondary battery according to claim 10.
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