JP2008010224A - Manufacturing method of carbon material, negative electrode material for secondary battery, and the secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phenol resin composition for carbon material, capable of obtaining a carbon material with high efficiency and high capacity used for a secondary battery that can be applied for a lithium ion secondary battery negative electrode material and a carbon material made by carbonization treatment of the same, and to provide its manufacturing method. <P>SOLUTION: A resol-type phenol resin 1,000 parts available in the market is heat treated for 3 hours at 80°C in electric furnace and methanol is volatilized; then it is increased in temperature upto 400°C at 100°C/h; and after retaining for 3 hours at 400°C, annealed up to room temperature and thereby, carbon precursor is obtained; thereafter, it is pulverized, until the average grain size becomes about 20 μm and a powder-like carbon precursor is obtained. The powder-like carbon precursor obtained is increased in temperature at 100°C/h, in an atmosphere of hydrogen:nitrogen=3:97 (volume ratio), and after reaching 1,100°C, retained for 3 hours to obtain the carbon material. The obtained carbon material, when used for the lithium ion secondary battery negative electrode material, can provide a secondary battery, having a high charge and discharge efficiency and high charge and discharge capacity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a carbon material production method, a negative electrode material for a secondary battery, and a secondary battery.

Currently, materials used for the negative electrode of lithium ion secondary batteries mainly include natural graphite and artificial graphite. The characteristics of this material include a theoretical charge / discharge capacity of 372 mAh / g, a charge / discharge efficiency as high as 90% or higher, and a higher density than a non-graphitizable carbon material.
With respect to graphite, various studies have been made to improve the electrode density, and studies have been made to give various shapes such as flakes, milleds, and spheres. Furthermore, although studies such as increasing the charge / discharge efficiency have been made (for example, see Patent Document 1 and Non-Patent Document 1), further studies are required.

  In addition to carbon materials such as graphite, non-graphitizing materials using phenolic resin as a starting material have been studied in the same way. However, since the manufacturing method differs depending on the starting material, it is appropriate for the starting material. It is difficult to obtain a good quality carbon material without heat treatment.

Japanese Patent Laid-Open No. 10-284061 J. et al. Electrochem. Soc. , Wt. 142, no. 8, 1995

  The present invention has been made in order to solve such problems in non-graphitizable materials, and the object of the present invention is to provide a carbon material obtained by carbonizing a phenol resin composition with a lithium ion secondary battery. The present invention provides a method for producing a carbon material that can realize a high charge / discharge efficiency and a high charge / discharge capacity when used in a negative electrode material.

Such an object is achieved by the present invention described in the following [1] to [6].
[1] A method for producing a carbon material obtained by heat-treating a phenol resin composition, wherein the heat treatment atmosphere contains 1 to 5% by volume of hydrogen gas.
[2] The method for producing a carbon material according to [1], wherein the amount of hydrogen gas relative to the phenol resin composition is 1 to 5% by volume.
[3] The method for producing a carbon material according to [1] or [2], wherein the heat treatment temperature is 900 to 1400 ° C.
[4] A carbon material obtained by the method for producing a carbon material according to any one of [1] to [3].
[5] A negative electrode material for a secondary battery comprising the carbon material according to the item [4].
[6] A secondary battery using the negative electrode material for a secondary battery as described in the item [5].

  According to the present invention, particularly when used as a negative electrode material for a secondary battery, a high-quality carbon material having a high charge / discharge capacity and a high charge / discharge efficiency can be obtained.

  First, a method for producing a carbon material of the present invention (hereinafter sometimes simply referred to as “manufacturing method”) will be described in detail.

  The phenol resin composition used in the production method of the present invention is obtained by reacting phenols and aldehydes by a known method, for example, a novolak type phenol obtained by reacting in the presence of an acidic catalyst. Resins, resol type phenol resins obtained by reacting in the presence of a basic catalyst, and the like can be mentioned, and these can be used alone or in combination.

  Although it does not specifically limit as phenols used for the synthesis | combination of the said phenol resin, For example, cresol, such as a phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2, 5-xylenol, 2,6-xylenol, 3,4-xylenol, xylenol such as 3,5-xylenol, ethylphenol such as o-ethylphenol, m-ethylphenol, p-ethylphenol, isopropylphenol, butylphenol, p -Alkylphenols such as butylphenol such as tert-butylphenol, p-tert-amylphenol, p-octylphenol, p-nonylphenol, p-cumylphenol, fluorophenol, chlorophenol, bromophenol, Halogenated phenols such as dephenol, monovalent phenol substitutes such as p-phenylphenol, aminophenol, nitrophenol, dinitrophenol and trinitrophenol, and monovalent phenols such as 1-naphthol and 2-naphthol, resorcin And polyhydric phenols such as alkylresorcin, pyrogallol, catechol, alkylcatechol, hydroquinone, alkylhydroquinone, phloroglucin, bisphenol A, bisphenol F, bisphenol S, dihydroxynaphthalene, and isomers thereof. These can be used alone or in combination of two or more.

  The aldehydes used for the synthesis of the phenol resin are not particularly limited. For example, formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, polyoxymethylene, chloral, hexamethylenetetramine, furfural, glyoxal, n-butyl. Examples include aldehyde, caproaldehyde, allyl aldehyde, benzaldehyde, crotonaldehyde, acrolein, tetraoxymethylene, phenylacetaldehyde, o-tolualdehyde, salicylaldehyde and the like. These can be used alone or in combination of two or more.

  When a novolac type phenol resin is used, a curing agent can be used together with the resin. Although it does not specifically limit as a hardening | curing agent, For example, aldehyde sources, such as a hexamethylenetetramine, a trioxane, and paraformaldehyde, a resole resin, an acid catalyst, an amine type hardening | curing agent, an imidazole type hardening | curing agent, an epoxy resin etc. are mentioned.

Although the usage-amount of a hardening | curing agent is not specifically limited, Usually, 0.1-20 weight part can be used with respect to 100 weight part of phenol resins. Since phenol resins are basically thermosetting resins, a solid state is mainly maintained during the first heat treatment due to a three-dimensional crosslinking reaction when the curing treatment is performed. Specifically, when a novolak type phenol resin is used as the phenol resin, first, a curing reaction is performed by adding hexamethylenetetramine as a curing agent to the novolak type phenol resin. In the production method of the present invention, the phenol resin to be used may be completely cured, or the curing agent may be consciously reduced so that a part of the phenol resin is melted during the heat treatment. Moreover, it is not necessary to add a hardening | curing agent.
Moreover, when using a self-hardening resol type phenol resin, an acid or a hardening accelerator may be added to the resol type phenol resin, or a novolac type phenol resin may be added to reduce the degree of hardening. . Moreover, they can also be used in combination.

  In the production method of the present invention, a mixture comprising the above phenol resins, a curing agent, a curing accelerator and the like is used as the phenol resin composition.

Moreover, the manufacturing method of the carbon material of this invention heat-processes the phenol resin composition in the atmosphere which contains 1-5 volume% of hydrogen gas.
The atmosphere for performing the heat treatment of the present invention is not particularly limited as long as the hydrogen gas is 1 to 5% by volume, but the remaining 95 to 99% by weight of the atmosphere is air, argon, nitrogen, helium, neon, An inert gas such as carbon dioxide may be used, and a heat treatment atmosphere condition in which two or more of these are combined may be used.

Moreover, it is preferable that the quantity with respect to the phenol resin composition of the hydrogen gas in heat processing atmosphere is 1-5 volume%. More preferably, it is 2-4 volume%. When the atmospheric hydrogen volume with respect to the phenol resin composition is within the above range, aromatics generated from the phenol resin composition during the heat treatment, and hydrocarbon-based volatiles efficiently react with hydrogen in the atmosphere. Decomposition of volatile matter is promoted, and it becomes easy to remove volatile matter outside the furnace system. The volatile matter is easily removed, so that the pore structure of the carbon material made of the phenol resin composition is developed. When the obtained carbon material is used in a lithium ion secondary battery, lithium ions can be intercalated. Since the formation of pores is promoted, high charge / discharge efficiency and discharge capacity can be obtained when the obtained carbon material is used as a negative electrode of a lithium ion secondary battery. Moreover, since carbon atoms contained in the phenol resin are efficiently removed by carbonizing in a small amount of hydrogen atmosphere, the carbon content of the obtained carbon material can be improved. By improving the carbon content in the carbon material, when the obtained carbon material is used in a lithium ion secondary battery, it is possible to suppress the decomposition reaction of the electrolytic solution, etc. Can be improved. Conversely, if heat treatment is performed in an atmosphere where the hydrogen gas is less than the above lower limit value, the decomposition and removal of volatile components will not be performed smoothly, so the pore structure of the carbon material tends to be underdeveloped, and the resulting carbon material Is used for a lithium ion secondary battery, the number of pores through which lithium ions can be intercalated decreases, resulting in a decrease in discharge capacity. In addition, when heat treatment is performed in an atmosphere in which hydrogen gas exceeds the above upper limit value, the volatile matter is completely decomposed, but the carbon material surface carbon having a phenol resin composition as a precursor reacts with hydrogen, and lithium Many carbon material surface pores that do not contribute to ion intercalation are generated. As a result, a decrease in charge / discharge efficiency of the secondary battery and a decrease in the carbon material yield are not preferable.

  Although it does not specifically limit as time to perform this heat processing, Usually, it is preferable to perform in 1 to 50 hours to the final heat processing temperature. Moreover, it is preferable that the final heat processing temperature is 900 to 1400 degreeC, More preferably, it is 1000 to 1300 degreeC. In this final heat treatment temperature range, the heat treatment time can be usually 1 to 15 hours, but is not particularly limited.

  By setting the final heat treatment temperature within the above-described temperature range, a preferable specific surface area and pore structure can be obtained when the obtained carbon material is a lithium ion secondary battery negative electrode material. When the heat treatment is performed at a temperature higher than the above temperature, the pore structure develops too much, the pore diameter is reduced due to ring condensation, and many pores having a size that does not contain lithium ions are generated. Therefore, when it is set as a lithium ion secondary battery negative electrode, since a charge capacity falls remarkably and a weight energy density falls, it is unpreferable.

If the final heat treatment temperature range is less than or equal to the above lower limit value, the pore size of the carbon material is too large relative to lithium ions, so the lithium ions stored in a cluster state in the carbon material increase, and the charge capacity increases. However, it is not preferable because the charge / discharge efficiency is lowered. In addition, by performing the heat treatment below the lower limit value, a large amount of hydrogen atoms and oxygen atoms remain in the carbon material, resulting in a decrease in cycle performance. Similarly, since the pore volume is large and the pore diameter is large, the true density of the carbon material is lowered, so that the volume energy density of the lithium ion secondary battery is lowered, which is not preferable.
Further, in accordance with the phenol resin composition as a starting material, the treatment time may be delayed in the middle temperature range, or conversely. In a temperature range where many volatile components are generated, the processing conditions may be held in order to completely remove volatile components.

  Moreover, although the temperature increase rate of heat processing is not specifically limited, It is preferable to heat up normally at 50-200 degreeC / hour. Although the cooling rate is not particularly limited, it is usually preferable to perform cooling at 50 to 400 ° C./hour.

  In addition, the temperature which open | releases an inert atmosphere can be made into room temperature-100 degreeC.

Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the examples. In the examples and comparative examples, “parts” and “%” are all “parts by weight” and “% by weight”.
(Example 1)
After 1000 parts of commercially available resol type phenolic resin (manufactured by Sumitomo Bakelite Co., Ltd., “PR-50087”) was heat-treated in an electric furnace at 80 ° C. for 3 hours, the methanol was volatilized and removed up to 400 ° C. at 100 ° C. / The temperature was raised with time, held at 400 ° C. for 3 hours, cooled to room temperature to obtain a carbon precursor, and then pulverized until the average particle size became about 20 μm to obtain a powdery carbon precursor.
The obtained powdery carbon precursor was heated at 100 ° C./hour in an atmosphere of hydrogen: nitrogen = 3: 97 (volume ratio), reached 1100 ° C., and maintained for 3 hours to obtain a carbon material. Got.

(Example 2)
After 1000 parts of commercially available resol type phenolic resin (manufactured by Sumitomo Bakelite Co., Ltd., “PR-50087”) was heat-treated in an electric furnace at 80 ° C. for 3 hours, the methanol was volatilized and removed up to 400 ° C. at 100 ° C. / The temperature was raised with time, held at 400 ° C. for 3 hours, cooled to room temperature to obtain a carbon precursor, and then pulverized until the average particle size became about 20 μm to obtain a powdery carbon precursor.
The obtained powdery carbon precursor was heated at 100 ° C./hour in an atmosphere of hydrogen: nitrogen = 3: 97 (volume ratio), reached 1100 ° C., and then maintained for 1 hour. Got.

(Example 3)
After 1000 parts of commercially available resol type phenolic resin (manufactured by Sumitomo Bakelite Co., Ltd., “PR-50087”) was heat-treated in an electric furnace at 80 ° C. for 3 hours, the methanol was volatilized and removed up to 400 ° C. at 100 ° C. / The temperature was raised with time, held at 400 ° C. for 3 hours, cooled to room temperature to obtain a carbon precursor, and then pulverized until the average particle size became about 20 μm to obtain a powdery carbon precursor.
The obtained powdery carbon precursor was heated at 100 ° C./hour in an atmosphere of hydrogen: argon: nitrogen = 2: 1: 97 (volume ratio), reached 1100 ° C., and maintained for 3 hours. To obtain a carbon material.

Example 4
After pulverizing and mixing 900 parts of a commercially available novolac-type phenolic resin Sumitomo Bakelite Co., Ltd. “PR-50731”) and 100 parts of hexamethylenetetramine, the temperature was raised to 400 ° C. at 100 ° C./hour, and 3 times at 400 ° C. After maintaining the time, the mixture was cooled to room temperature to obtain a carbon precursor, and then pulverized until the average particle size became about 20 μm to obtain a powdery carbon precursor.
The obtained powdery carbon precursor was heated at 100 ° C./hour in an atmosphere of hydrogen: nitrogen = 3: 97 (volume ratio), reached 1100 ° C., and maintained for 3 hours to obtain a carbon material. Got.

(Comparative Example 1)
After 1000 parts of commercially available resol type phenolic resin (manufactured by Sumitomo Bakelite Co., Ltd., “PR-50087”) was heat-treated in an electric furnace at 80 ° C. for 3 hours, the methanol was volatilized and removed up to 400 ° C. at 100 ° C. / The temperature was raised with time, held at 400 ° C. for 3 hours, cooled to room temperature to obtain a carbon precursor, and then pulverized until the average particle size became about 20 μm to obtain a powdery carbon precursor.
The obtained powdery carbon precursor was heated at 100 ° C./hour in an atmosphere of hydrogen: nitrogen = 7: 93 (volume ratio), reached 1100 ° C., and maintained for 3 hours to obtain a carbon material. Got.

(Comparative Example 2)
After pulverizing and mixing 900 parts of a commercially available novolac-type phenolic resin Sumitomo Bakelite Co., Ltd. “PR-50731”) and 100 parts of hexamethylenetetramine, the temperature was raised to 400 ° C. at 100 ° C./hour, and 3 times at 400 ° C. After maintaining the time, the mixture was cooled to room temperature to obtain a carbon precursor, and then pulverized until the average particle size became about 20 μm to obtain a powdery carbon precursor.
The obtained powdery carbon precursor was heated at 100 ° C./hour in an atmosphere of hydrogen: nitrogen = 0.1: 99.9 (volume ratio), reached 1100 ° C., and maintained for 3 hours. To obtain a carbon material.
(Evaluation of carbon materials)

Evaluation of battery characteristics (1) Preparation of positive electrode Lithium cobaltate (LiCoO ₂ ) was used as a positive electrode active material, and acetylene black and polyvinylidene fluoride (PVDF) were blended at a ratio of 5%, respectively, and further diluted. An appropriate amount of N-methyl-2-pyrrolidone as a solvent was added and mixed to prepare a slurry-like positive electrode mixture.
This positive electrode slurry-like mixture was applied to both sides of a 25 μm aluminum foil, and then vacuum dried at 110 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed by a roll press. This was cut into a size of 40 mm in width and 280 mm in length to produce a positive electrode. Aluminum foil was exposed at the 10 mm both ends of the positive electrode, and a positive electrode tab was pressure-bonded to one side.

(2) Production of Negative Electrode The carbon material obtained above was used and blended in a proportion of 10% polyvinylidene fluoride and 3% acetylene black as a binder, and N-methyl-2 as a diluent solvent. -An appropriate amount of pyrrolidone was added and mixed to prepare a slurry-like negative electrode mixture.
This negative electrode slurry mixture was applied to both sides of a 10 μm copper foil, and then vacuum dried at 110 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed by a roll press. This was cut into a size of 40 mm in width and 290 mm in length to produce a negative electrode. The copper foil was exposed at the 10 mm both ends of the negative electrode, and a negative electrode tab was pressure-bonded to this one.

(3) Production of secondary battery The positive electrode, the separator (polypropylene porous film: width 45 mm, thickness 25 μm), the negative electrode, the separator, the positive electrode, and so on are wound in a spiral shape so that the negative electrode is on the outside. Thus, an electrode was produced. The produced electrode was inserted into an AA type battery can, and the negative electrode tab was welded to the bottom of the can. Further, an electrolytic solution prepared by dissolving lithium perchlorate at a concentration of 1 [mol / liter] in a mixed solution of ethylene carbonate and diethylene carbonate (volume ratio is 1: 1) is prepared. Then, the positive electrode tab was welded to the positive electrode cover, and the positive electrode cover was attached to produce a secondary battery.

(4) Evaluation Regarding the charging capacity, constant current charging is performed with the current density at the time of charging being 25 mA / g. When the potential reaches 0 V, constant voltage charging is performed at 0 V, and the current density is 1.25 mA / g. The amount of electricity charged up to is the charge capacity.
On the other hand, with respect to the discharge capacity, constant current discharge was performed with a current density at the time of discharge of 25 mA / g, and constant voltage discharge was performed at 2.5 V from the time when the potential reached 2.5 V, and the current density was 1.25 mA. The amount of electricity discharged up to / g was taken as the discharge capacity.
Each of the first cycle charge capacities is referred to as an initial charge capacity, a discharge capacity is referred to as an initial discharge capacity, and a ratio between the two (initial discharge capacity / initial charge capacity) is defined as initial charge / discharge efficiency.
The above evaluation results are shown in Table 1.

  From the results in Table 1, since Examples 1 to 4 all had an appropriate amount of hydrogen gas in the heat treatment atmosphere, when used as a negative electrode material for a lithium ion secondary battery, they were more highly charged than Comparative Examples 1 and 2. A secondary battery having discharge efficiency and high charge / discharge capacity could be obtained.

  When the carbon material obtained in the present invention is used as a negative electrode material for a lithium ion secondary battery, a lithium ion secondary battery having excellent charge / discharge characteristics can be obtained.

Claims (6)

A method for producing a carbon material obtained by heat-treating a phenol resin composition, wherein the heat treatment atmosphere contains 1 to 5% by volume of hydrogen gas. The method for producing a carbon material according to claim 1, wherein the amount of hydrogen gas relative to the phenol resin composition is 1 to 5% by volume. The method for producing a carbon material according to claim 1 or 2, wherein the heat treatment temperature is 900 to 1400 ° C. A carbon material obtained by the method for producing a carbon material according to claim 1. A negative electrode material for a secondary battery comprising the carbon material according to claim 4. A secondary battery comprising the negative electrode material for a secondary battery according to claim 5.