WO2020105598A1 - Composite carbon particles, method for producing same, and lithium ion secondary battery - Google Patents

Abstract

The present invention provides composite carbon particles, each of which comprises a carbon particle (A) and a carbonaceous cover layer (B) that covers the surface of the carbon particle (A), and which is configured such that the carbonaceous cover layer (B) is composed of single-walled graphene or multi-walled graphene having a thickness of from 0.1 nm to 30.0 nm (inclusive). The R value of the particles is preferably 0.10-0.40; and the variation coefficient of the R value is preferably 0.30 or less. The composite carbon particles according to the present invention enable the achievement of a lithium ion secondary battery which is excellent in terms of low-temperature charge and discharge rate characteristics, high-temperature storage characteristics and high-temperature cycle characteristics, while having low internal resistance and high coulombic efficiency.

Description

COMPOSITE CARBON PARTICLE, METHOD FOR PRODUCING THE SAME, AND LITHIUM ION SECONDARY BATTERY

The present invention relates to a composite carbon particle, a method for producing the same, a negative electrode active material containing the particle, a negative electrode containing the negative electrode active material, and a lithium ion secondary battery using the negative electrode.

A lithium-ion secondary battery is used as a power source for portable electronic devices. Initially, lithium ion batteries had many problems such as insufficient battery capacity and short charge / discharge cycle life. Nowadays, such problems have been overcome, and the applications of lithium-ion secondary batteries have changed from low-power devices such as mobile phones, notebook computers and digital cameras to high-power devices that require power such as power tools and electric bicycles. The application is spreading. Further, the lithium-ion secondary battery is particularly expected to be used as a power source for automobiles, and research and development of electrode materials, cell structures, etc. have been actively promoted.

Lithium-ion secondary batteries used as power sources for automobiles are required to have excellent low-temperature charge / discharge rate characteristics, high-temperature storage characteristics, high-temperature cycle characteristics, low internal resistance, and high Coulombic efficiency. On the other hand, various methods have been taken.

A carbon material is used as the negative electrode active material of the lithium ion secondary battery. Further, it has been proposed to form a coating layer on the surface in order to repair the surface defects of the carbon material or to impart a characteristic different from that of the carbon material as the core material.

Patent Document 1 describes composite carbon particles in which an amorphous carbon layer is formed on the surface using petroleum pitch as a coating material.

Patent Document 2 describes composite carbon particles having a pyrolytic carbon layer formed on the surface by a CVD process.

Patent Document 3 describes composite carbon particles in which graphene is attached to the surface by using graphene as a coating material.

Patent Document 4 describes carbon composite silicon in which a graphene sheet is attached to the surface of silicon.

Patent Document 5 describes a method of manufacturing a graphene shell having a graphene film as a shell structure.

Non-Patent Document 1 describes multilayer graphene, and Non-Patent Document 2 describes bilayer graphene.

Japanese Patent No. 4531174 Japanese Patent No. 5898628 (European Patent No. 2650955) WO2017 / 169882 Japanese Patent Laid-Open No. 2013-60355 (US Pat. No. 9815691) Japanese Patent No. 5749418 (European Patent No. 0973698)

With the conventional technology of forming a coating layer using pitch, it is possible to produce composite carbon particles in which an amorphous carbon layer is formed on the surface of carbon particles. However, the high temperature characteristics of the amorphous carbon layer are insufficient, and it is difficult to control the thickness of the amorphous carbon layer uniformly. Therefore, the electronic conductivity becomes non-uniform, so that the internal resistance is high and the rate characteristics are insufficient. Met.

When forming a carbonaceous coating layer by a CVD process, it is difficult to form a thin and uniform layer on a core material having large irregularities such as carbon particles. To form a uniform layer, the coating layer should be thick or It was necessary to form a buffer layer inside, and as a result, high temperature cycle characteristics and high temperature storage characteristics were insufficient.

In the technique of coating graphene described in Patent Document 3, amorphous carbon is used for binding the core material and graphene, and the high temperature characteristics are insufficient.

The technique of coating graphene described in Patent Document 4 is to attach a coating layer using an electrophoretic method, and it is not possible to form a graphene layer on the surface of carbon particles.

The graphene shell using the graphene film described in Patent Document 5 as a shell is a technique that uses a catalytic metal inside, and the graphene layer cannot be coated on the surface of carbon particles.

An object of the present invention is to provide composite carbon particles for a lithium-ion secondary battery, which have excellent low-temperature charge / discharge rate characteristics, high-temperature storage characteristics, high-temperature cycle characteristics, low internal resistance, and high Coulombic efficiency.

The present invention has the following configurations.
[1] A composite carbon particle comprising carbon particles (A) and a carbonaceous coating layer (B) coating the surface thereof, wherein the carbonaceous coating layer (B) is a single layer having a thickness of 0.1 nm to 30.0 nm. Composite carbon particles that are graphene or multilayer graphene.
[2] The variation coefficient of the R values obtained from the Raman spectra by Raman spectroscopy (ratio (ID / IG) of 1350 cm ^-1 vicinity of the peak intensity (ID) and 1580 cm ^-1 vicinity of the peak intensity (IG)) is The composite carbon particle as described in 1 above, which is 0.30 or less.
[3] The composite carbon particles as described in 1 or 2 above, wherein the R value measured by Raman spectroscopy is 0.10 or more and 0.40 or less.
[4] The composite carbon particles as described in any one of the above items 1 to 3, wherein an average interplanar spacing d002 of (002) planes measured by an X-ray diffraction method is 0.3354 nm or more and 0.3370 nm or less.
[5] The 50% particle diameter (D50) in the volume-based cumulative particle size distribution measured by the laser diffraction method is 1.0 μm or more and 30.0 μm or less, and the 400 times tapping density is 0.30 g / cm ³ or more and 1.50 g / cm ³ 5. The composite carbon particle according to any one of items 1 to 4 below, which is as follows.
[6] The composite carbon particles as described in any one of the above items 1 to 5, which has a BET specific surface area of 1.0 m ² / g or more and 10.0 m ² / g or less.
[7] The composite carbon particles as described in any one of the above items 1 to 6, wherein the carbon particles (A) are graphite particles.
[8] The composite carbon particles as described in any one of 1 to 7 above, wherein (BET specific surface area of composite carbon particles) / (BET specific surface area of carbon particles (A)) is 0.30 or more and 0.90 or less. ..
[9] The composite carbon particles as described in any one of 1 to 8 above, wherein (Raman R value of composite carbon particles) / (Raman R value of carbon particles (A)) is 1.50 or more and 10.00 or less. ..
[10] A negative electrode active material containing the composite carbon particles according to any one of items 1 to 9 above.
[11] A negative electrode including the negative electrode active material and the current collector described in the above item 11.
[12] A lithium ion secondary battery using the negative electrode described in 11 above.
[13] An all-solid-state lithium ion secondary battery using the negative electrode described in 11 above.
[14] A method for producing composite carbon particles, wherein the carbon particles (A) and a carboxylic acid compound having at least one carboxy group and one hydroxy group are added to the total mass of the carbon particles (A) and the carboxylic acid compound. On the other hand, the carbon particles (A) are mixed in an amount of 80.0% by mass or more and 99.9% by mass or less and the carboxylic acid compound is 0.1% by mass or more and 20.0% by mass or less, and the resulting mixture is heat treated A method for producing composite carbon particles, comprising:
[15] A method for producing composite carbon particles, comprising: carbon particles (A) and a carboxylic acid compound having two or more carboxy groups, based on the total mass of the carbon particles (A) and the carboxylic acid compound. (A) is mixed so that 80.0 mass% or more and 99.9 mass% or less and a carboxylic acid compound is 0.1 mass% or more and 20.0 mass% or less, and the obtained mixture is heat-treated. And a method for producing composite carbon particles.
[16] A method for producing composite carbon particles, comprising carbon particles (A), a carboxylic acid compound having one or more carboxy groups and one or more hydroxy groups, and a carboxylic acid compound having two or more carboxy groups. The carbon particles (A) are 80.0 mass% or more and 99.90 mass% or less and the carboxylic acid compound is 0.1 mass% or more and 20.0 mass% or less with respect to the total mass of (A) and the carboxylic acid compound. A method for producing composite carbon particles, which comprises:

According to the present invention, a thin, uniform carbonaceous coating layer is formed on the surface of carbon particles, which has excellent low-temperature charge / discharge rate characteristics, high-temperature storage characteristics, high-temperature cycle characteristics, low internal resistance, and high coulombic efficiency. Carbon particles can be provided.

1 is a transmission electron micrograph of the composite carbon particles produced in Example 1. 6 is a transmission electron micrograph of the composite carbon particles produced in Example 5. 5 is a transmission electron micrograph of the composite carbon particles produced in Comparative Example 3. 13 is a transmission electron micrograph of the composite carbon particles produced in Comparative Example 13. 9 is an R value imaging result of the composite carbon particles manufactured in Example 5. 5 is an R value imaging result of the carbon particles manufactured in Comparative Example 1. 5 is an R value imaging result of the composite carbon particles manufactured in Comparative Example 3. 9 is an R value imaging result of the composite carbon particles produced in Comparative Example 26. It is a schematic diagram showing an example of composition of all-solid-state type lithium ion battery 1 concerning one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail.

[1] Composite Carbon Particles The composite carbon particles in one embodiment of the present invention include carbon particles (A) and a carbonaceous coating layer (B) that covers the surface thereof, and the carbon coating layer is single-layer graphene or multilayer graphene. (Hereinafter, it may be simply referred to as a graphene layer.).
The carbon particles (A) are not particularly limited, and graphite particles, carbon particles such as soft carbon and hard carbon, graphene, and the like can be used, and a composite material in which a metal, a metal oxide, or an alloy is compounded can also be used. .. Examples of the metal include silicon, tin, zinc and the like, and examples of the metal oxide include oxides thereof. The particle shape is not limited, and examples thereof include spherical shape, lump shape, scale shape, and fibrous shape, and the particle shape is preferable. Specific examples of the fibrous material include nanowires, vapor grown carbon fibers and carbon nanotubes. Of these, it is particularly preferable to use graphite particles. Since graphite particles have high crystallinity, they are excellent in discharge capacity, high temperature cycle characteristics, and high temperature storage characteristics. The carbon particles (A) also include those whose surface is partially or wholly coated with amorphous carbon.
Among the graphite particles, artificial graphite particles are preferable, and artificial graphite particles having a solid structure are more preferable. When the inside has a solid structure, intra-particle peeling hardly occurs even after repeated expansion and contraction due to charge and discharge, and high temperature cycle characteristics and high temperature storage characteristics are excellent.
The graphene contained in the carbonaceous coating layer (B) is a two-dimensional sheet-like material in which carbon particles are continuous in a honeycomb shape, and is superior in conductivity, chemical stability, and mechanical strength to amorphous carbon. Have strength. By covering the surface of the carbon particles with graphene, it is possible to suppress the volume change of the carbon particles and improve the conductivity, and obtain a negative electrode material for a lithium ion secondary battery having excellent durability and charge / discharge characteristics. .. The graphene is preferably formed as a graphene layer along the surface of the carbon particles (A), and more preferably formed almost entirely or partially along the surface of the carbon particles (A) as a graphene layer. It is more preferable that the graphene layer is formed so as to cover almost the entire surface of the carbon particles (A). Further, it is more preferable that the surface of the carbon particles (A) is directly covered with the single-layer graphene or the multilayer graphene layer. Note that graphene including one layer is referred to as single-layer graphene and graphene including two or more layers is referred to as multilayer graphene, and graphene includes graphene oxide. Graphene having a thickness exceeding 30 nm is graphite and is excluded from the graphene layer forming the carbonaceous coating layer (B).

The thickness of the carbonaceous coating layer (B) is 0.1 nm or more. 0.1 nm corresponds to the thickness of a single layer of graphene. The thickness of the carbonaceous coating layer (B) is preferably 1.0 nm or more, and more preferably 2.0 nm or more from the viewpoint of having a certain level of conductivity, chemical stability, and mechanical strength. The carbonaceous coating layer (B) has a thickness of 30.0 nm or less. When the thickness of the carbonaceous coating layer (B) is 30.0 nm or less, the excessive formation of the carbonaceous coating layer (B) is suppressed, and the high temperature storability and the high temperature cycle characteristics can be kept good. From the same viewpoint, 20.0 nm or less is more preferable, 10.0 nm or less is still more preferable, and 5.0 nm or less is most preferable.

The thickness of the carbon coating layer (B) is measured by observation with a transmission electron microscope (TEM). From the viewpoint of measurement accuracy, the number of measurement points is preferably 30 or more, more preferably 60 or more. Let the average be the thickness of the carbonaceous coating layer (B). Specifically, it can be measured by the method described in Examples.

The R value of the composite carbon particles in one embodiment of the present invention is preferably 0.10. When the R value is 0.10 or more, the electric resistance on the surface of the composite carbon particles is reduced, and a lithium ion secondary battery having good low temperature charge / discharge characteristics can be obtained. From the same viewpoint, the R value is more preferably 0.15 or more and most preferably 0.20 or more. The R value of the composite carbon particles is preferably 0.40 or less. This is because when the R value is 0.40 or less, the crystallinity of the surface is not too low, and good high temperature storage and high temperature cycle characteristics can be maintained. From the same viewpoint, the R value is more preferably 0.35 or less, and further preferably 0.30 or less.
The R value means the intensity ratio (ID / IG) of the peak intensity (ID) near 1350 cm ^{−1 and} the peak intensity (IG) near 1580 cm ⁻¹ observed by Raman spectroscopy. The state of the surface of the composite carbon particles can be evaluated by the R value. The smaller the R value, the higher the crystallinity of the surface of the composite carbon particles.

The variation coefficient of the R value (ID / IG) of the composite carbon particles in one embodiment of the present invention is preferably 0.30 or less. When the coefficient of variation of the R value is 0.30 or less, the variation in the coating state is small, so that the effect of reducing the resistance is large, and the high temperature cycle characteristics and the low temperature rate characteristics are improved. From the same viewpoint, the coefficient of variation is more preferably 0.25 or less, still more preferably 0.20 or less.
The coefficient of variation of the R value is obtained by measuring the R value at a plurality of points by the microscopic Raman spectroscopy and dividing the standard deviation value by the average value of the R values. The variation of the coating state can be evaluated by obtaining the coefficient of variation. The larger the coefficient of variation, the lower the uniformity of the R value, and the larger the variation in the coating state.
In the microscopic Raman spectroscopic measurement method, a microscopic laser Raman spectroscope having a high spatial resolution is used and R values are measured at a plurality of points for the same sample. From the viewpoint of measurement accuracy, 50 points or more are preferable, and 100 points or more are more preferable. Typically, the measurement is performed by shifting the laser irradiation position after the end of each measurement so that the position is different each time. When the spatial resolution is too low (that is, when the irradiation positions overlap too much), variations between particles are difficult to be reflected in the R value, and the accuracy of the evaluation result may be reduced.

In the composite carbon particles according to one embodiment of the present invention, (Raman R value of composite carbon particles) / (Raman R value of carbon particles (A)) is preferably 1.50 or more. When the ratio is 1.50 or more, the carbonaceous coating layer is formed on the surface of the carbon particles (A), the effect of lowering the resistance is large, and the low temperature rate characteristics are improved. From the same viewpoint, the ratio is more preferably 1.80 or more, and most preferably 2.10 or more. On the other hand, (Raman R value of composite carbon particles) / (Raman R value of carbon particles (A)) is preferably 10.00 or less. When the ratio is 10.00 or less, the excessive formation of the carbonaceous coating layer (B) can be suppressed, and thereby the high temperature storability and the high temperature cycle characteristics can be kept good. From the same viewpoint, the ratio is more preferably 6.00 or less and most preferably 4.00 or less.

The average interplanar spacing d002 of (002) planes of the composite carbon particles in one embodiment of the present invention is 0.3354 nm or more. This is the theoretical lower limit of graphite. d002 is 0.3370 nm or less. When d002 is 0.3370 nm or less, the discharge capacity becomes large, and a battery satisfying the energy density required for a large battery can be obtained. From the same viewpoint, d002 is preferably 0.3367 nm or less, and more preferably 0.3364 nm or less.

The 50% particle diameter (D50) of the composite carbon particles in one embodiment of the present invention is preferably 1.0 μm or more. When D50 is 1.0 μm or more, aggregation of particles is suppressed, and a slurry for electrode coating is easily prepared. From the same viewpoint, D50 is more preferably 3.0 μm or more, and most preferably 5.0 μm or more. D50 is preferably 50.0 μm or less. This is because when D50 is 50.0 μm or less, the electrical resistance of the electrode is reduced and the rate characteristics are improved. From the same viewpoint, 30.0 μm or less is more preferable, and 10.0 μm or less is most preferable.
In the present specification, the “50% particle size (D50)” means a particle size that is cumulative 50% in a volume-based particle size distribution obtained by a laser diffraction / scattering method.

The 400 times tapping density of the composite carbon particles in one embodiment of the present invention is preferably 0.30 g / cm ³ or more. When the tapping density is 0.30 g / cm ³ or more, the electrode density reached during pressing can be made sufficiently high, and a battery with high energy density can be obtained. From the same viewpoint, the tapping density is more preferably 0.40 g / cm ³ or more, most preferably 0.50 g / cm ³ or more. The 400 times tapping density is preferably 1.50 g / cm ³ or less. When the tapping density is 1.50 g / cm ³ or less, the contact density between the materials in the obtained electrode can be sufficiently improved, and a battery having high input / output characteristics can be obtained. From the same viewpoint, the tapping density is more preferably 1.20 g / cm ³ or less, 0.90 g / cm ³ or less is most preferred.

The BET specific surface area of the composite carbon particles in one embodiment of the present invention is preferably 0.1 m ² / g or more. When the BET specific surface area is 0.1 m ² / g or more, high-speed charging / discharging becomes possible. From the same viewpoint, BET specific surface area is more preferably equal to or greater than ^{1.0m 2 / g, 3.0m 2 /} g or more is most preferred. The BET specific surface area is preferably 10.0 m ² / g or less. When it is 10.0 m ² / g or less, aggregation is suppressed, so that a slurry is easily prepared, and side reactions when used as a battery are suppressed, and Coulomb efficiency, high-temperature storability and high-temperature cycle characteristics are excellent. From the same viewpoint, it is preferably 8.0 m ² / g or less, more preferably 5.0 m ² / g or less.

The d002, D50, 400 times tapping density and BET specific surface area described in this specification are measured by the methods described in the examples.

[2] Method for producing composite carbon particles A method for producing composite carbon particles in one embodiment of the present invention comprises a mixing step of mixing carbon particles and a carboxylic acid compound to obtain a mixture, and a mixture obtained in the mixing step. And a heat treatment step of heat treatment at 500 ° C. or more and 2000 ° C. or less.

[2-1] Mixing Step In the mixing step, the carbon particles (A) and the carboxylic acid compound are mixed to obtain a mixture.

The carboxylic acid compound used in one embodiment of the present invention is a compound containing two or more carboxy groups in one molecule (referred to as “polycarboxylic acid compound”), or one carboxylic xyl group and one hydroxy group in one molecule. It is a compound containing the above (referred to as “hydroxycarboxylic acid compound”). Examples of such polycarboxylic acid compounds include succinic acid (melting point 185 ° C), glutaric acid (95 ° C), maleic acid (131 ° C), phthalic acid (210 ° C), oxaloacetic acid (161 ° C). ) And malonic acid (at the same temperature of 135 ° C.). Examples of the hydroxycarboxylic acid include malic acid (130 ° C.), citric acid (153 ° C.), tartaric acid (168 ° C. (L form), 151 ° C. (meso form), 206 ° C. (racemic form)). , Gallic acid (at the same temperature of 250 ° C.) and salicylic acid (at the same temperature of 159 ° C.). By using such a carboxylic acid compound, in the heat treatment step described later, dehydration between molecules, a denser network structure is formed, and the carboxylic acid compound can cover the carbon particles more broadly and thinly. it can.
Of these, compounds containing two or more carboxy groups and one or more hydroxy groups in one molecule are more preferable, and malic acid (melting point: 130 ° C), citric acid (153 ° C: 168 ° C) and tartaric acid (168 ° C: L form). ) Is particularly preferable.
The carboxylic acid compound may be used alone or in combination of two or more. That is, two or more polycarboxylic acid compounds may be used, two or more hydroxycarboxylic acid compounds may be used, or a polycarboxylic acid compound and a hydroxycarboxylic acid compound may be used in combination. Further, the carboxylic acid compound may be used in combination with a compound containing one carboxy group in one molecule.

The melting point of the carboxylic acid compound is preferably 300 ° C or lower. When the melting point is within this range, thermal decomposition of the carboxylic acid compound is small and the coating effect is high. From the same viewpoint, the melting point is more preferably 250 ° C. or lower, further preferably 200 ° C. or lower. The melting point of the carboxylic acid compound is preferably 90 ° C. or higher. When the melting point is in this range, the carboxylic acid compound can be easily handled and the yield after the mixing treatment is high. From the same viewpoint, the melting point is more preferably 110 ° C. or higher, further preferably 130 ° C. or higher.

The mixture obtained in the mixing step may contain materials other than carbon particles and a carboxylic acid compound, but the mixture is preferably composed of carbon particles and a carboxylic acid compound. It is preferable to use the carboxylic acid compound in a powder state. The mixing method is preferably dry mixing, and a commercially available mixer or stirrer can be used. Specific examples include mixers such as ribbon mixers, V-type mixers, W-type mixers, one-blade mixers, and Nauta mixers.

The blending amount of the carbon particles (A) and the carboxylic acid compound is such that the carbon particles (A) are 80.0% by mass or more and 99.9% by mass or less, and the carboxylic acid is based on the total mass of the carbon particles (A) and the carboxylic acid compound. The compound content is preferably 0.1% by mass or more and 20.0% by mass or less. The reason why the blending amount of the carboxylic acid compound is 0.1% by mass or more is to sufficiently coat the carbon particles with the carboxylic acid compound. From this viewpoint, the amount of the carboxylic acid compound is more preferably 0.5% by mass or more, and further preferably 1.0% by mass or more. The reason for setting the amount of the carboxylic acid compound to be 20.0% by mass or less is to suppress the formation of an excessive carbonaceous coating layer (B), thereby maintaining good high-temperature storability and high-temperature cycle characteristics. From this viewpoint, the amount of the carboxylic acid compound is more preferably 15.0% by mass or less, and further preferably 10.0% by mass or less.

[2-2] Heat Treatment Step The heat treatment step of the mixture can be performed using a heat treatment apparatus such as a rotary kiln, a roller hearth kiln, or an electric tubular furnace. By the heat treatment step, composite carbon particles in which the surfaces of the carbon particles are covered with the carbonaceous coating layer (B) are obtained.

The heat treatment temperature in the heat treatment step is preferably 500 ° C. or higher, more preferably 700 ° C. or higher, in order to sufficiently promote carbonization, suppress the retention of hydrogen and oxygen, and improve the battery characteristics. Most preferably, the temperature is at least ° C. Further, in order to suppress graphitization and maintain good charge / discharge rate characteristics, the heat treatment temperature is preferably 2000 ° C. or lower, more preferably 1500 ° C. or lower, and most preferably 1200 ° C. or lower. The treatment time is not particularly limited as long as carbonization has progressed sufficiently, but is preferably 10 minutes or longer, more preferably 30 minutes or longer, and further preferably 50 minutes or longer.

The heat treatment step is preferably performed in an inert gas atmosphere. Examples of the inert gas for the inert gas atmosphere include argon gas and nitrogen gas.

(BET specific surface area of composite carbon particles) / (BET specific surface area of carbon particles (A)) is preferably 0.90 or less. When the ratio is 0.90 or less, the surface of the carbon particles (A) is sufficiently covered and the effect of lowering the resistance is large, so that the charge / discharge characteristics are improved. From the same viewpoint, the ratio is more preferably 0.80 or less, and most preferably 0.70 or less. The ratio is preferably 0.30 or more. When the ratio is 0.30 or more, the coating amount does not become excessive and the cycle characteristics and the high temperature storage characteristics are kept good. From the same viewpoint, the ratio is more preferably 0.50 or more, and most preferably 0.60 or more.

[3] Negative Electrode Active Material for Lithium Ion Secondary Battery A negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention contains the composite carbon particles.

The negative electrode active material is composed of the above composite carbon particles, or further contains another carbon material or a conductivity imparting agent. When another carbon material or a conductivity-imparting agent is included, 0.01 to 200 parts by mass, preferably 0.01 to 100 parts by mass of spherical natural graphite or artificial graphite is mixed with 100 parts by mass of the composite carbon particles. Can be used. By mixing and using another graphite material, it is possible to obtain a negative electrode active material that also has the excellent characteristics of other graphite materials while maintaining the excellent characteristics of the composite carbon particles.
Such a negative electrode active material can be obtained by mixing the composite carbon particles with another carbon material or the like. Upon mixing, it is possible to appropriately select a mixing material and determine the mixing amount according to required battery characteristics.

Also, carbon fiber can be mixed with the negative electrode active material. The blending amount is preferably 0.01 to 20 parts by mass and more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the negative electrode active material.

Examples of carbon fibers include PAN-based carbon fibers, pitch-based carbon fibers, organic carbon fibers such as rayon-based carbon fibers, and vapor grown carbon fibers. Of these, vapor grown carbon fiber having high crystallinity and high thermal conductivity is particularly preferable. When the carbon fiber is adhered to the surface of the composite carbon particle, the vapor grown carbon fiber is particularly preferable.

As a device for mixing the composite carbon particles and other materials, a commercially available mixer or stirrer can be used. Specific examples include mixers such as ribbon mixers, V-type mixers, W-type mixers, one-blade mixers, and Nauta mixers.

[4] Electrode Paste The electrode paste in one embodiment of the present invention contains the above-mentioned negative electrode active material, a binder and a solvent. The electrode paste is obtained by kneading the negative electrode active material and the binder. For kneading, a device such as a ribbon mixer, a screw type kneader, a Spartan Luzer, a Loedige mixer, a planetary mixer, a universal mixer or the like can be used. The electrode paste can be formed into a sheet shape, a pellet shape, or the like.

As the binder used for the electrode paste, a fluorine-based polymer such as polyvinylidene fluoride or polytetrafluoroethylene, a rubber-based material such as SBR (styrene butadiene rubber), etc. may be mentioned.

The amount of the binder used is preferably 1 to 30 parts by mass, and more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material.

Solvents used for kneading include those suitable for each binder, such as toluene and N-methylpyrrolidone in the case of fluoropolymers; water and the like in the case of SBR; and dimethylformamide, isopropanol and the like. In the case of a binder using water as a solvent, it is preferable to use a thickening agent such as carboxymethyl cellulose (CMC) together. The amounts of the solvent and the thickener are adjusted so that the electrode paste has a viscosity that makes it easy to apply the current collector.

[5] Negative Electrode for Lithium Ion Secondary Battery The negative electrode for a lithium ion secondary battery in one embodiment of the present invention comprises a current collector and a negative electrode active material on the current collector. The negative electrode can be obtained by applying the above-mentioned electrode paste on a current collector, drying and press-molding.

As the current collector, for example, aluminum, nickel, copper, stainless steel foil, mesh, or the like can be used. The applied thickness of the paste is preferably 50 to 200 μm. The method of applying the paste is not particularly limited, and examples thereof include a method of applying with a doctor blade or a bar coater and thereafter forming with a roll press or the like.

Examples of the pressure molding method include a roll pressing method and a press pressing method. The pressure during pressure molding is preferably 1 × 10 ³ to 3 × 10 ³ kg / cm ² .

[6] Lithium Ion Secondary Battery A lithium ion secondary battery has a structure in which a positive electrode and a negative electrode are immersed in an electrolytic solution or an electrolyte. The lithium ion secondary battery in one embodiment of the present invention comprises the negative electrode as the negative electrode.

In the positive electrode of the lithium ion secondary battery, a lithium-containing transition metal oxide is usually used as the positive electrode active material, and preferably at least selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo and W. An oxide mainly containing one kind of transition metal element and lithium, in which a compound having a molar ratio of lithium to the transition metal element of 0.3 to 2.2 is used, more preferably V, Cr, Mn, A compound which is an oxide mainly containing at least one transition metal element selected from Fe, Co and Ni and lithium, and whose molar ratio of lithium to the transition metal is 0.3 to 2.2 is used. In addition, you may contain Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B etc. in the range of less than 30 mol% with respect to the mainly existing transition metal. Among the above positive electrode active materials, the general formula Li _x MO ₂ (M is at least one of Co, Ni, Fe and Mn, x = 0.02 to 1.2) or Li _y N ₂ O ₄ (N Contains at least Mn, and it is preferable to use at least one material having a spinel structure represented by y = 0.02-2).

In a lithium-ion secondary battery, a separator may be provided between the positive electrode and the negative electrode. Examples of the separator include a nonwoven fabric containing polyolefin such as polyethylene and polypropylene as a main component, a cloth, a microporous film, or a combination thereof.

Known electrolytes, inorganic solid electrolytes, and polymer solid electrolytes can be used as the electrolyte and the electrolyte that compose the lithium-ion secondary battery in the preferred embodiment of the present invention, but the organic electrolyte is from the viewpoint of electrical conductivity. preferable.

[7] All-solid-state lithium-ion secondary battery The all-solid-state lithium-ion secondary battery has a structure in which the positive electrode and the negative electrode are in contact with the solid electrolyte layer. FIG. 9 is a schematic diagram showing an example of the configuration of the all-solid-state lithium-ion secondary battery 1 according to this embodiment. The all-solid-state lithium-ion secondary battery 1 includes a positive electrode layer 11, a solid electrolyte layer 12, and a negative electrode layer 13.

The positive electrode 11 has a positive electrode current collector 111 and a positive electrode mixture layer 112. The positive electrode current collector 111 is connected to a positive electrode lead 111a for exchanging electric charges with an external circuit. The positive electrode current collector 111 is preferably a metal foil, and an aluminum foil is preferably used as the metal foil.

The positive electrode mixture layer 112 contains a positive electrode active material, and may further contain a solid electrolyte, a conductive additive, a binder, and the like. Examples of the positive electrode active material include rock salt type layered active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and spinel type active materials such as LiMn ₂ O _4. , can be used _{LiFePO 4, LiMnPO 4, LiNiPO 4} , LiCuPO 4 olivine active material such as, sulfide Monokatsu substance such Li ₂ S and the like. Further, these active materials may be coated with LTO (Lithium Tin Oxide), carbon or the like.

As the solid electrolyte that may be contained in the positive electrode mixture layer 112, the materials mentioned in the solid electrolyte layer 12 described later can be used, but a material different from the material contained in the solid electrolyte layer 12 can be used. You may use. The content of the solid electrolyte in the positive electrode mixture layer 112 is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, and 80 parts by mass or more with respect to 100 parts by mass of the positive electrode active material. Is more preferable. The content of the solid electrolyte in the positive electrode mixture layer 112 is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and more preferably 125 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. Is more preferable.

As the conduction aid, it is preferable to use a particulate carbonaceous conduction aid or a fibrous carbonaceous conduction aid. As the particulate carbonaceous conductive aid, Denka Black (registered trademark) (manufactured by Denki Kagaku Kogyo Co., Ltd.), Ketjen Black (registered trademark) (manufactured by Lion Corporation), graphite fine powder SFG series (manufactured by Timcal), graphene Particulate carbon such as can be used. As the fibrous carbonaceous conductive additive, vapor phase carbon fibers (VGCF (registered trademark), VGCF (registered trademark) -H (manufactured by Showa Denko KK)), carbon nanotubes, carbon nanohorns and the like can be used. .. Vapor grown carbon fiber "VGCF (registered trademark) -H" (manufactured by Showa Denko KK) is most preferable because it has excellent cycle characteristics. The content of the conductive additive in the positive electrode mixture layer 112 is preferably 0.1 part by mass or more, and more preferably 0.3 part by mass or more, with respect to 100 parts by mass of the positive electrode active material. The content of the conductive additive in the positive electrode mixture layer 112 is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less with respect to 100 parts by mass of the positive electrode active material.

Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene oxide, polyvinyl acetate, polymethacrylate, polyacrylate, polyacrylonitrile, polyvinyl alcohol, styrene-butadiene rubber, carboxymethyl cellulose and the like.

In the positive electrode mixture layer 112, the content of the binder with respect to 100 parts by mass of the positive electrode active material is preferably 1 part by mass or more and 10 parts by mass or less, and more preferably 1 part by mass or more and 7 parts by mass or less.

The solid electrolyte layer 12 is interposed between the positive electrode layer 11 and the negative electrode layer 13, and serves as a medium for moving lithium ions between the positive electrode layer 11 and the negative electrode layer 13. The solid electrolyte layer 12 preferably contains at least one selected from the group consisting of a sulfide solid electrolyte and an oxide solid electrolyte, and more preferably contains a sulfide solid electrolyte.

Examples of the sulfide solid electrolyte include sulfide glass, sulfide glass ceramics, Thio-LISICON type sulfide, and the like. More specifically, for example, Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -LiI, Li ₂ S-P ₂ S ₅ -LiCl, Li ₂ S-P ₂ S ₅ -LiBr, Li ₂ S-P ₂ S ₅ -Li ₂ O, Li ₂ S-P ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS _{2 -LiBr, Li 2 S-SiS 2} -LiCl, Li 2 S-SiS 2 -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3, Li ₂ S—P ₂ S ₅ —Z _m S _n (where m and n are positive numbers, Z represents any one of Ge, Zn, and Ga), Li ₂ S—GeS ₂ , and Li ₂ S— SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (where x and y are positive numbers, M is P, Si, Ge, B, Al, Ga or In) , Li ₁₀ GeP ₂ S ₁₂ , Li _3.25 Ge _0.25 P _0.75 S ₄ , 30Li ₂ S.26B ₂ S ₃ .44LiI, 63Li ₂ S.36SiS ₂ .1Li ₃ PO ₄ , 57Li ₂ S.38SiS ₂ .. 5Li ₄ SiO ₄ , 70Li ₂ S · 30P ₂ S ₅ , 50LiS ₂ · 50GeS ₂ , Li ₇ P ₃ S ₁₁ , Li _3.25 P _0.95 S ₄ , Li ₃ PS ₄ , Li ₂ S · P ₂ S ₃ · P ₂ S _{5 and the} like can be mentioned. The sulfide solid electrolyte material may be amorphous, crystalline, or glass ceramics.

Examples of the oxide solid electrolyte include perovskite, garnet, and LISICON type oxide. More specifically, for example, La _0.51 Li _0.34 TiO _2.94 , Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ , 50Li ₄ SiO ₄ .50Li ₃ BO ₃ , Li _2.9 PO _{3.3. N 0.46 (LIPON), Li 3.6} Si 0.6 P 0.4 O 4, Li 1.07 Al 0.69 Ti 1.46 (PO 4) 3, Li 1.5 Al 0.5 Ge 1.5 (PO 4) may be mentioned ₃ or the like. The oxide solid electrolyte material may be amorphous, crystalline, or glass ceramics.

The negative electrode layer 13 includes a negative electrode current collector 131 and a negative electrode mixture layer 132. The negative electrode current collector 131 is connected to a negative electrode lead 131a for exchanging charges with an external circuit. The negative electrode current collector 131 is preferably a metal foil, and a stainless foil, a copper foil, or an aluminum foil is preferably used as the metal foil. The surface of the current collector may be coated with carbon or the like.

The negative electrode mixture layer 132 contains a negative electrode active material, and may also contain a solid electrolyte, a binder, a conductive auxiliary agent, and the like. The composite carbon particles are used as the negative electrode active material.

As the solid electrolyte that may be included in the negative electrode mixture layer 132, the materials described in the solid electrolyte layer 12 may be used, but the solid electrolyte included in the solid electrolyte layer 12 or the positive electrode mixture layer may be included. A material different from the existing solid electrolyte may be used. The content of the solid electrolyte in the negative electrode mixture layer 132 is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, and 80 parts by mass or more with respect to 100 parts by mass of the negative electrode active material. Is more preferable. The content of the solid electrolyte in the negative electrode mixture layer 132 is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and 125 parts by mass or less with respect to 100 parts by mass of the negative electrode active material. Is more preferable.

As the conductive auxiliary agent that may be contained in the negative electrode mixture layer 132, the conductive auxiliary agents mentioned in the description of the positive electrode mixture layer 112 can be used. Different materials may be used. The content of the conductive additive in the negative electrode mixture layer 132 is preferably 0.1 part by mass or more, and more preferably 0.3 part by mass or more, with respect to 100 parts by mass of the negative electrode active material. The content of the conductive additive in the negative electrode mixture layer 132 is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less with respect to 100 parts by mass of the negative electrode active material.

As the binder, for example, the materials mentioned in the description of the positive electrode mixture layer 112 can be used, but the binder is not limited thereto. In the negative electrode mixture layer 132, the content of the binder with respect to 100 parts by mass of the negative electrode active material is preferably 0.3 parts by mass or more and 10 parts by mass or less, and 0.5 parts by mass or more and 5 parts by mass or less. More preferable.

Note that there is no restriction on the selection of the necessary members for battery configuration other than the above.

Hereinafter, examples of the present invention will be specifically described. It should be noted that these are merely examples for explanation and do not limit the present invention.
The carbon particle evaluation methods, battery production methods, battery characteristic measurement methods, and raw materials used in each example of Examples and Comparative Examples are as follows.

[1] Evaluation of carbon particles [1-1] 50% particle diameter (D50)
Using a Malvern Mastersizer 2000 (Mastersizer; registered trademark) as a particle size measuring device, a 5 mg sample was placed in a container, 10 g of water containing 0.04% by mass of a surfactant was added, and ultrasonic treatment was performed for 5 minutes. After that, the measurement was performed.

[1-2] Tapping Density Using Autotap manufactured by Quantachrome as a tap density measuring device, 50 g of a sample was put into a 250 mL glass cylinder, and the volume after 400 taps was measured to calculate the density. This is a measuring method based on ASTM B527 and JIS K5101-12-2, but the drop height of the auto tap was 5 mm.

[1-3] BET Specific Surface Area Using NOVA2200e manufactured by Quantachrome as a BET specific surface area measuring device, 3 g of a sample was put in a sample cell (9 mm × 135 mm), and dried at 300 ° C. for 1 hour under a vacuum condition. , Measurement was performed. N ₂ was used as the gas for measuring the BET specific surface area.

[1-4] Surface spacing d002
A mixture of composite carbon particles and standard silicon particles (manufactured by NIST) in a mass ratio of 9: 1 was filled in a glass sample plate (sample plate window 18 × 20 mm, depth 0.2 mm). The measurement was performed under such conditions.
XRD device: Rigaku's SmartLab (registered trademark)
X-ray type: Cu-Kα ray Kβ ray removal method: Ni filter X-ray output: 45 kV, 200 mA
Measuring range: 24.0 to 30.0 deg.
Scan speed: 2.0 deg. / Min.
The Gakushin method was applied to the obtained waveform to determine the value of the surface spacing d002.

[1-5] R value and coefficient of variation of R value JASCO Corporation NRS-5100 was used as a microscopic laser Raman spectroscope, and measurement was performed at an excitation wavelength of 532.36 nm.
The R value (ID / IG) is defined as the ratio of the peak intensity (ID) near 1350 cm ^{-1 and} the peak intensity (IG) near 1580 cm ^-1 in the Raman spectrum.
Microscopic laser Raman spectroscopic imaging was performed on the composite carbon particles in the following region.
Measurement point: 22 × 28 places Measurement step: 0.32 μm
Measurement area: 7.0 × 9.0 μm
Of the above measurements, 100 points were randomly extracted from the region corresponding to the carbon particles, and the standard deviation of the obtained R value was divided by the average value of the R values to obtain the coefficient of variation.
Moreover, the average value of the R values was taken as the R value of the composite carbon particles.

[1-6] State and Thickness of Carbonaceous Coating Layer (B) Observed by Transmission Electron Microscope (TEM) The composite carbon particles are dispersed in ethanol, collected on a microgrid mesh, and measured under the following conditions. went.
Transmission electron microscope device: Hitachi H-9500
Accelerating voltage: 300kV
Observation magnification: 30,000 times The state of the carbon coating layer (B) was observed from the measurement. Next, one carbon particle was arbitrarily selected, and the coating layer on the surface of the carbon particle was observed in 5 fields of view at the above-mentioned magnification, and the thickness of the coating layer at 2 locations per field of view was measured. The thickness of the coating layer at each location was the average value of the coating layer length of 10 nm. This measurement was performed on three arbitrarily selected carbon particles, data of 30 points in total were obtained, and the average thereof was used as the thickness of the coating layer. Further, the layer structure such as the graphene layer and the amorphous carbon layer was determined by evaluating the FFT (Fast Fourier Transform) pattern.

[2] Preparation of Battery [2-1] Preparation of Electrode Paste 96.5 g of carbon particles obtained in each of Examples and Comparative Examples described later and 0.5 g of carbon black (manufactured by TIMCAL, C65) as a conduction aid. An aqueous solution in which 1.5 g of carboxymethyl cellulose (CMC) as a thickener and 8 to 12 g of water are appropriately added to adjust the viscosity, and fine particles of an aqueous binder (Polysol (registered trademark) manufactured by Showa Denko KK) are dispersed. 5 g was added and stirred and mixed to prepare a slurry-like dispersion having sufficient fluidity, which was used as an electrode paste.

[2-2] Preparation of Negative Electrode 1 The electrode paste was applied on a high-purity copper foil with a doctor blade to a thickness of 150 μm, and vacuum dried at 70 ° C. for 12 hours. After punching using a punching machine so that the coated part would be 4.2 × 4.2 cm ² , it was sandwiched between press plates made of super steel, and pressed so that the electrode density was 1.3 g / cm ^3, and the negative electrode 1 Was produced. The thickness of the active material layer after pressing is 65 μm.

[2-3] Preparation of Negative Electrode 2 The copper foil coated with the above electrode paste was punched out into a circle of 16 mmφ, and then pressed in the same manner as in Negative Electrode 1 so that the electrode density was 1.3 g / cm ^3. Then, the negative electrode 2 was produced. The thickness of the active material layer after pressing is 65 μm.

[2-4] Preparation of Positive Electrode 95 g of LiFe ₂ PO ₄ (D50: 7 μm), 1.2 g of carbon black (manufactured by TIMCAL, C65) as a conduction aid, vapor grown carbon fiber (manufactured by Showa Denko KK) , VGCF (registered trademark) -H), 0.3 g of polyvinylidene fluoride (PVdF) as a binder, and N-methyl-pyrrolidone were appropriately added and stirred to prepare a positive electrode slurry.
This positive electrode slurry was applied on an aluminum foil having a thickness of 20 μm by a roll coater so as to have a uniform thickness, dried and then roll-pressed, and punched out so that the applied portion was 4.2 × 4.2 cm ² . A positive electrode was obtained. The thickness of the active material layer after pressing is 65 μm.

[2-5] Preparation of electrolytic solution In a mixed solution of 3 parts by mass of EC (ethylene carbonate), 2 parts by mass of DMC (dimethyl carbonate) and 5 parts by mass of EMC (ethyl methyl carbonate), 1.2 mol of LiPF ₆ was used as an electrolyte. / Liter was dissolved and 1 part by mass of VC (vinylene carbonate) was added as an additive to prepare an electrolytic solution.

[2-6] Battery assembly (bipolar cell)
An ultrasonic welding machine was used to attach a nickel tab to the copper foil portion of the negative electrode 1 and an aluminum tab to the aluminum foil portion of the positive electrode. A negative electrode 1 and a positive electrode are laminated so as to face each other via a polypropylene film microporous film, packed with an aluminum laminate film, and after pouring an electrolyte solution, the opening is sealed by heat fusion to form a bipolar cell. It was made.

(Counter electrode lithium cell (half cell))
In a polypropylene cell with a screw-in lid (internal diameter of about 18 mm), a separator (polypropylene microporous film (Cell Guard 2400)) was sandwiched and laminated between the negative electrode 2 and a 16 mmφ metal lithium foil to form an electrolytic solution. Then, a counter electrode lithium cell was produced by adding and caulking with a caulking machine.

[3] Evaluation of Battery [3-1] Measurement of Initial Coulombic Efficiency A test was conducted in a constant temperature bath set at 25 ° C. using a counter electrode lithium cell. Constant current charging was performed at 0.02 mA from the rest potential to 0.005V. Next, switching to constant voltage charging was carried out at 0.005 V, charging was carried out for 40 hours including constant current charging and constant voltage charging, and the initial charge capacity (a) was measured.
Constant current discharge was performed at 0.2 mA with an upper limit voltage of 1.5 V, and the initial discharge capacity (b) was measured.
The initial discharge capacity (b) / initial charge capacity (a) was expressed as a percentage, that is, 100 × (b) / (a) was defined as the initial Coulombic efficiency.

[3-2] Measurement of Reference Capacity Using a bipolar cell, a test was conducted in a constant temperature bath set at 25 ° C. After the cell was charged with a constant current of 0.2 V (the current value for discharging a fully charged battery in 1 hour is 1 C, the same applies below) with the upper limit voltage of 4 V, the cutoff current value was 0.85 mA and a constant voltage was 4 V. Charged. After that, constant current discharge was performed at a lower limit voltage of 2 V and 0.2 C. The above operation was repeated four times in total, and the discharge capacity at the fourth time was used as the reference capacity (c) of the bipolar cell.

[3-3] Measurement of high temperature cycle characteristics Using a bipolar cell, a test was conducted in a constant temperature bath set at 55 ° C. Regarding charging, constant current charging was performed at a constant current value of 85 mA (corresponding to 5 C) from the rest potential with an upper limit voltage of 4 V, and then constant voltage charging was performed at a cutoff current value of 0.34 mA and 4 V.
After that, constant current discharge was performed at 85 mA with a lower limit voltage of 2V.
Under the above conditions, 500 cycles of charge and discharge were repeated to measure the high temperature cycle discharge capacity (d). The high temperature cycle discharge capacity (d) measured under the above conditions / the reference capacity (c) of the bipolar cell was expressed as a percentage, that is, 100 × (d) / (c) was taken as the high temperature cycle capacity retention rate.

[3-4] Measurement of internal resistance (DC-IR) The test was conducted in a constant temperature bath set at 25 ° C. Constant current discharge was performed at 0.1 C from the fully charged state to 50% of the fully charged capacity. After 30 minutes of rest, the internal resistance (DC-IR) (e) of the bipolar cell was obtained from Ohm's law (R = ΔV / 0.017) from the amount of voltage drop when 17 mA was discharged for 5 seconds.

[3-5] High temperature storage / recovery characteristics measurement test:
Using a bipolar cell, the test was carried out in a constant temperature bath set at 25 ° C. for both charging and discharging. The cell was charged at a constant current of 0.2 C with an upper limit voltage of 4 V, and then at a constant voltage of 4 V with a cutoff current value of 0.34 mA. The charged cell was allowed to stand in a constant temperature bath set at 60 ° C. for 4 weeks and then discharged at a constant current of 0.2 C at a lower limit voltage of 2 V to measure the discharge capacity. This discharge capacity was defined as the high temperature storage capacity (f). The high temperature storage capacity (f) with respect to the reference capacity (c) of the bipolar cell was expressed as a percentage, that is, 100 × (f) / (c) was taken as the value of the high temperature retention characteristic.

After measuring the storage capacity, the cell was charged with a constant current of 0.2 C with an upper limit voltage of 4 V and then with a cut-off current value of 0.34 mA. Then, constant current discharge was performed at a lower limit voltage of 2 V and 0.2 C, and the discharge capacity was measured. This discharge capacity was defined as the high temperature recovery capacity (g). The high temperature recovery capacity (g) with respect to the reference capacity (c) of the bipolar cell was expressed as a percentage, that is, 100 × (g) / (c) was taken as the value of the high temperature recovery characteristic.

[3-6] Low Temperature Charge / Discharge Rate Measurement A test was conducted using a bipolar cell. The cell was charged at a constant current of 0.2 C with an upper limit voltage of 4 V in a constant temperature bath set at 25 ° C., and then at a constant voltage of 4 V with a cutoff current value of 0.34 mA. The charged cell was subjected to constant current discharge at a lower limit voltage of 2 V and 1 C in a constant temperature bath set at -20 ° C, and the discharge capacity was measured. This discharge capacity was defined as the low temperature discharge capacity (h). The low temperature discharge capacity (h) with respect to the reference capacity (c) of the bipolar cell was expressed as a percentage, that is, 100 × (h) / (c) was taken as the value of the low temperature discharge rate characteristic.

After measuring the low temperature discharge capacity, the temperature inside the constant temperature bath was returned to 25 ° C, and constant current discharge was performed at a lower limit voltage of 2V and 0.2C. The cell was subjected to constant current charging at 1 C with an upper limit voltage of 4 V in a constant temperature bath set at −20 ° C., and then constant voltage charging at 4 V with a cut-off current value of 0.34 mA to measure the charge capacity. This charge capacity was defined as the low temperature charge capacity (i). The low temperature charge capacity (i) with respect to the reference capacity (c) of the bipolar cell was expressed as a percentage, that is, 100 × (i) / (c) was taken as the value of the low temperature charge rate characteristic.

[4] Raw material Carbon particles (A): artificial graphite (SCMG (registered trademark) manufactured by Showa Denko KK), 50% particle diameter (D50): 6.0 μm, BET specific surface area: 5.9 m ² / g.
Raw materials for carbonaceous coating layer: Materials shown in Tables 1 and 2.

Examples 1 to 24, Comparative Examples 1 to 23:
In each Example and each Comparative Example, the raw materials and proportions shown in Tables 1 and 2 were put into a V-type mixer (VM-10, manufactured by Dalton Co., Ltd.), and dry mixing was performed at room temperature for 10 minutes. The mixture was heat-treated under an atmosphere of nitrogen gas at a temperature shown in Tables 1 and 2 in an electric tubular furnace for 1 hour to obtain composite carbon particles or carbon particles. In Tables 1 and 2, “none” in the heat treatment step column means that the corresponding heat treatment step has not been performed.
Various physical properties of the obtained carbon particles were measured. Further, a battery was produced using the obtained carbon particles and evaluated. The results are shown in Tables 1 to 4.
TEM photographs of the carbon particles obtained in Examples 1 and 5 and Comparative Examples 3 and 13 are shown in FIGS. 1 to 4, respectively. The R value imaging results of the carbon particles obtained in Example 5 and Comparative Examples 1 and 3 are shown in FIGS. 5 to 7, respectively. In the R value imaging, there is less variation in the R value (the coefficient of variation is smaller) when there is no shading.

Comparative Examples 24-26:
Nitrogen gas containing 0.05 g / L of benzene was introduced into a fluidized reactor at 1 L / min, and carbon particles (A) were in a fluidized state at 900 ° C. for a time shown in Table 2 by chemical vapor deposition (Chemical Vapor Deposition: CVD). ) Treated. The amount of benzene used in the CVD process was 1 to 5 mass%.
Various physical properties of the obtained carbon particles were measured in the same manner as in Examples to prepare a battery. The results are shown in Tables 2 and 4.
The R value imaging result of the carbon particles obtained in Comparative Example 26 is shown in FIG.

From the table and the figures, it is understood that in the composite carbon particles of the examples, the graphene layer is thinly and uniformly formed on the surface of the carbon particles, and all the evaluation results of each battery are improved. On the other hand, the composite carbon particles having the amorphous carbonaceous layer formed on the surface of the carbon particles have lower DC-IR, better initial Coulombic efficiency, and lower temperature rate characteristics than the carbon particles having no carbonaceous layer formed on the surface. Although effective, the battery characteristics at high temperature are deteriorated (Comparative Examples 3 to 5 and Comparative Examples 12 to 17). Further, since the coefficient of variation of the R value is large, the coating is non-uniform, and the effect of coating is not sufficiently obtained.
Further, if the amount of the carboxylic acid compound used is too small, the coating layer is not formed and almost no effect is seen on all the battery characteristics (Comparative Examples 6, 8, 10). When the amount of the carboxylic acid compound is too large, the low DC-IR and the low temperature rate characteristics are improved, but d002 is increased and the tap density is decreased, and the R value and BET are excessively increased, and the initial Coulombic efficiency is decreased. This leads to deterioration of battery characteristics at high temperatures (Comparative Examples 7, 9, 11).
When the coating is performed by the CVD process, it is difficult to control the graphene layer thinly for particles having large irregularities such as carbon particles, and in order to reduce the variation coefficient of the R value to 0.20 or less, Results in an excessively thick graphene layer and an excessively high R value, resulting in deterioration of battery characteristics at high temperatures (Comparative Examples 24 to 26, FIG. 8).

Claims (16)

1. A composite carbon particle comprising carbon particles (A) and a carbonaceous coating layer (B) coating the surface thereof, wherein the carbonaceous coating layer (B) is 0.1 nm or more and 30.0 nm or less single layer graphene or multilayer. Composite carbon particles that are graphene.
2. Coefficient of variation of R values obtained from the Raman spectra by Raman spectroscopy (ratio (ID / IG) of 1350 cm ^-1 vicinity of the peak intensity (ID) and 1580 cm ^-1 vicinity of the peak intensity (IG)) is 0.30 The composite carbon particles according to claim 1, which are as follows.
3. The composite carbon particle according to claim 1 or 2, wherein the R value measured by Raman spectroscopy is 0.10 or more and 0.40 or less.
4. The composite carbon particles according to any one of claims 1 to 3, wherein the average interplanar spacing d002 of the (002) plane measured by X-ray diffraction is 0.3354 nm or more and 0.3370 nm or less.
5. Is 50% particle size (D50) of the 1.0μm or 30.0μm or less in volume-based cumulative particle size distribution by laser diffraction method, it is 400 times the tapping density of 0.30 g / cm ³ or more 1.50 g / cm ³ or less The composite carbon particle according to any one of claims 1 to 4.
6. The composite carbon particles according to any one of claims 1 to 5, which has a BET specific surface area of 1.0 m ² / g or more and 10.0 m ² / g or less.
7. The composite carbon particles according to any one of claims 1 to 6, wherein the carbon particles (A) are graphite particles.
8. The composite carbon particle according to any one of claims 1 to 7, wherein (BET specific surface area of composite carbon particle) / (BET specific surface area of carbon particle (A)) is 0.30 or more and 0.90 or less.
9. The composite carbon particle according to any one of claims 1 to 8, wherein (Raman R value of composite carbon particle) / (Raman R value of carbon particle (A)) is 1.50 or more and 10.00 or less.
10. A negative electrode active material containing the composite carbon particles according to any one of claims 1 to 9.
11. A negative electrode including the negative electrode active material according to claim 10 and a current collector.
12. A lithium-ion secondary battery using the negative electrode according to claim 11.
13. All-solid-state lithium-ion secondary battery using the negative electrode according to claim 11.
14. A method for producing composite carbon particles, comprising: forming carbon particles (A) and a carboxylic acid compound having at least one carboxy group and one hydroxy group based on the total mass of the carbon particles (A) and the carboxylic acid compound. The particles (A) are mixed so as to be 80.0% by mass or more and 99.9% by mass or less, and the carboxylic acid compound is 0.1% by mass or more and 20.0% by mass or less, and the resulting mixture is heat-treated. A method for producing composite carbon particles, which is characterized.
15. A method for producing composite carbon particles, comprising: carbon particles (A) and a carboxylic acid compound having two or more carboxy groups, based on the total mass of the carbon particles (A) and the carboxylic acid compound. Of 80.0 mass% or more and 99.9 mass% or less and the carboxylic acid compound are mixed so as to be 0.1 mass% or more and 20.0 mass% or less, and the resulting mixture is heat-treated. Method for producing carbon particles.
16. A method for producing composite carbon particles, comprising: carbon particles (A), a carboxylic acid compound having at least one carboxy group and a hydroxy group, and a carboxylic acid compound having at least two carboxy groups. And carbon particles (A) are mixed in an amount of 80.0 mass% to 99.90 mass% and a carboxylic acid compound of 0.1 mass% to 20.0 mass% with respect to the total mass of the carboxylic acid compound. And heat-treating the obtained mixture, the manufacturing method of the composite carbon particle characterized by the above-mentioned.

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