JPH11171519A - Graphite powder, its production, negative electrode for lithium secondary battery and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain graphite powder suitable for a lithium secondary battery having high capacity, ensuring low irreversible capacity on the 1st cycle and excellent in rapid charge-discharge characteristics by comminuting a graphite compact having a specified bulk density. SOLUTION: A graphite compact having <=1.6 g/cm<3> , preferably 1.01.6 g/cm<3> , particularly preferably 1.2-1.45 g/cm<3> bulk density is comminuted to form the objective graphite powder. A method for producing the graphite compact is not particularly limited and the compact is produced, e.g. by mixing material containing a graphitizable aggregate or graphite and a graphitizable binder, compacting the mixture in a prescribed shape and heat-treating the resultant graphite precursor in a nonoxidizing atmosphere. A component which volatilizes in the temp. range of 400-3,200 deg.C, preferably a metal such as Si or B is preferably added at the time of mixing the materials. The graphite powder preferably has 10-50 μm average particle diameter, <=8 m<3> /g specific surface area and an aspect ratio of <=5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a graphite powder, a method for producing the same, a negative electrode for a lithium secondary battery, and a lithium secondary battery. More specifically, a lithium secondary battery with small irreversible capacity, excellent rapid charge / discharge characteristics, etc., and high capacity suitable for use in portable devices, electric vehicles, and electric power storage, and a lithium secondary battery for obtaining the same. The present invention relates to a negative electrode for a battery and the graphite powder for a negative electrode for a lithium secondary battery.

[0002]

2. Description of the Related Art Conventional graphite particles include, for example, natural graphite particles, artificial graphite particles obtained by graphitizing coke, artificial graphite particles obtained by graphitizing organic polymer materials and pitch, graphite particles obtained by pulverizing them, and high-density graphite. Examples include graphite particles obtained by pulverizing a molded body. These graphite particles are mixed with an organic binder and an organic solvent to form a graphite paste, the graphite paste is applied to the surface of a copper foil, and the solvent is dried to be used as a negative electrode for a lithium secondary battery. . For example, Japanese Patent Publication No. 622-2
As disclosed in Japanese Patent No. 3433, the use of graphite for the negative electrode solves the problem of internal short circuit due to lithium dendrite, and improves cycle characteristics.

However, graphite materials such as natural graphite in which graphite crystals are developed and artificial graphite obtained by graphitizing coke have a weaker bonding force between the layers of the crystals in the c-axis direction than in the plane direction of the crystals. Therefore, the bond between the graphite layers is broken by the pulverization, and so-called scale-like graphite particles having a large aspect ratio are obtained. Since the scale-like graphite has a large aspect ratio, it is kneaded with a binder and applied to a current collector to produce an electrode.When the electrode is produced, the scale-like graphite particles are oriented in the surface direction of the current collector, and as a result, the graphite crystal is formed. There is a problem that the expansion and contraction in the C-axis direction caused by the repetition of the insertion and extraction of lithium causes destruction of the inside of the electrode, thereby deteriorating the cycle characteristics. In addition, these graphites have a problem that the surface state of the graphite particles changes due to the impact due to the pulverization, resulting in an increase in the specific surface area and an increase in the irreversible capacity in the first cycle of the lithium secondary battery to be manufactured. Therefore, there is a need for a graphite powder that has a small irreversible capacity in the first cycle of a lithium secondary battery and can improve the cycle characteristics of high-capacity rapid charge / discharge characteristics.

[0004]

The invention according to claims 1 and 2 provides a graphite powder suitable for a lithium secondary battery having a high capacity, a small irreversible capacity in the first cycle, and an excellent rapid charge / discharge characteristic. It provides a manufacturing method. The third aspect of the present invention provides a graphite powder suitable for a lithium secondary battery having a high capacity, a small irreversible capacity in the first cycle, and an excellent rapid charge / discharge characteristic. The fourth aspect of the present invention provides a negative electrode for a lithium secondary battery having a small irreversible capacity in the first cycle and excellent in rapid charge / discharge characteristics. The invention according to claim 5 provides a lithium secondary battery having a small irreversible capacity in the first cycle and excellent in rapid charge / discharge characteristics.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for producing graphite powder, which comprises a step of pulverizing a graphite compact having a bulk density of 1.6 g / cm ³ or less. Further, the present invention provides the graphite molded body having a bulk density of 1.6 g / cm ³ or less,
The present invention relates to a method for producing a graphite powder, which is obtained by graphitizing a graphite precursor containing at least one component that volatilizes in the range of 400 to 3200 ° C. The present invention also relates to a graphite powder having an average particle size of 10 to 50 μm, a specific surface area of 8 m ² / g or less, and an aspect ratio of 5 or less. The present invention also relates to a negative electrode for a lithium secondary battery containing the graphite powder or the graphite powder obtained by the production method.
Further, the present invention relates to a lithium secondary battery having the above-mentioned negative electrode and positive electrode.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The graphite powder of the present invention is characterized by including a step of pulverizing a graphite molded body having a bulk density of 1.6 g / cm ³ or less. The bulk density of the graphite molded body to be ground is 1.
The range of 0 to 1.6 g / cm ³ is preferable, and 1.2 to 1.5 g / c.
more preferably be in the range of m ^3, 1.2~1.45g /
A range of cm ³ is particularly preferred. If the bulk density of the graphite compact to be crushed exceeds 1.6 g / cm ³ , a large crushing force is required in the crushing, and the state of the surface of the produced graphite powder changes due to the crushing force, resulting in an increase in the specific surface area. However, the irreversible capacity of the manufactured lithium secondary battery is reduced. Further, the crystallinity of the surface of the graphite powder to be produced also decreases, and the discharge capacity of the obtained lithium secondary battery decreases.
On the other hand, if the density of the graphite molded body to be ground is less than 1.0 g / cm ³ , the handleability of the graphite molded body tends to decrease. In addition, the furnace filling weight during graphitization tends to decrease, and the graphitization treatment efficiency tends to deteriorate. The bulk density can be calculated from the measured values of the weight and volume of the graphite molded body.

There is no particular limitation on the method for producing a graphite molded body having a bulk density of 1.6 g / cm ³ or less. For example, it can be obtained by mixing a material containing a graphitizable aggregate or graphite and a graphitizable binder, and then heat-treating the graphite precursor formed into a predetermined shape in a non-oxidizing atmosphere.

[0008] The graphitizable aggregate is not particularly limited as long as it is a powder material that can be graphitized. For example, coke powder, carbide of resin and the like can be used. As the graphite, for example, natural graphite powder, artificial graphite powder and the like can be used, but there is no particular limitation as long as it is in powder form. The particle size of the graphitizable aggregate or graphite is preferably smaller than the particle size of the graphite powder produced in the present invention. Examples of the binder capable of being graphitized include tar, pitch, and organic materials such as thermosetting resins and thermoplastic resins. The amount of the binder is preferably 30 to 50% by weight based on the total amount of the graphitizable aggregate or graphite from the viewpoint of the density of the graphite molded body to be produced and the aspect ratio and the specific surface area of the graphite powder to be produced. The method of mixing the graphitizable aggregate or graphite with the graphitizable binder is not particularly limited, but it is preferable to mix at a temperature equal to or higher than the softening temperature of the binder, and the temperature varies depending on the type of the binder used. The range of -350 ° C is preferred.

The shape of the molded graphite precursor is not particularly limited, but is preferably, for example, a block, a cylinder, a lump, or the like, from the viewpoint of workability and packing efficiency in a furnace during graphitization. There is no particular limitation on the size of the molded body, but a molded body having a length of at least 5 mm is preferred. Here, in order to obtain the above bulk density, a method of including a component which is volatilized in a temperature range of 400 to 3200 ° C. in the graphite precursor, a method in which the pressing pressure at the time of press-molding the graphite precursor is reduced, and the bulk density is reduced There is a method of adjusting the temperature of the graphite precursor.
It is preferable to include a component that volatilizes in the above temperature range. In this method, the volatilization temperature of the contained components is 4
If the temperature is lower than 00 ° C., the bulk density of the graphite molded body tends to be high, and if it exceeds 3200 ° C., there is a problem that volatile components easily remain in the graphite molded body. Here, the volatilization temperature refers to a temperature at which the components volatilize at normal pressure due to sublimation, decomposition, melt gasification, and the like, causing weight loss. In general, a graphite precursor tends to shrink and become denser when carbonized at a firing temperature of 400 to 900 ° C. Therefore, as a volatile component, even after shrinkage during carbonization at 400 to 1000 ° C., it is preferable in terms of the density of a graphite molded body that easily remains, and the volatilization temperature is preferably in a range of 800 to 3000 ° C.,
The range of 1000-3000 degreeC is more preferable.

The addition of components that evaporate in the temperature range of 400 to 3200 ° C. may be added before molding the graphite precursor, but in terms of uniform mixing, it can be graphitized with the aggregate or graphite. It is preferable to add these binders when mixing them and to mix them simultaneously. 400-3200 ° C
The graphite precursor containing a component that volatilizes in the temperature range of 1) is volatilized when performing a heat treatment for firing or graphitization in a non-oxidizing atmosphere to have a bulk density of 1.6 g / cm ^3.
The following low-density graphite molded body can be obtained. 400 ~
There are no particular restrictions on the types of components that evaporate in the temperature range of 3200 ° C., for example, thermoplastic resins such as polyvinyl alcohol (evaporation temperature of 400 to 700 ° C.) and resins obtained from plants such as rosin (evaporation temperature of 400 to 1000).
C), metals such as silicon, boron, iron, titanium and nickel, oxides and carbides thereof (volatilization temperature of 2200 to 3
200 ° C) can be used. Among these, the use of a metal, an oxide or a carbide thereof also functions as a graphitization catalyst, and is more preferable in view of the crystallinity of the graphite powder to be produced.

The firing of the graphite precursor is preferably carried out under conditions that are difficult to oxidize, and examples thereof include a method of firing in a nitrogen atmosphere, an argon atmosphere, and in a vacuum. The firing temperature is preferably 2000 ° C. or higher, more preferably 2500 ° C. or higher, even more preferably 2800 ° C. or higher. If the firing temperature is low, the development of graphite crystals is poor, and the discharge capacity tends to be low. On the other hand, when the temperature for graphitization is low, the added volatile component tends to remain in the graphite molded body, and the density of the graphite molded body tends to increase. Although there is no upper limit on the firing temperature, it is generally 3200 ° C. or lower. When the volatile components remain in the graphite compact to be produced, not only the specific surface area of the obtained graphite powder becomes large, but also the discharge capacity tends to decrease. Is preferably increased. The firing temperature may be increased stepwise, for example, once from 500 to 120.
After calcination at about 0 ° C., calcination can be further performed at 2,000 ° C. or more.

Thus, a graphite molded body having a bulk density of 1.6 g / cm ³ or less is obtained and then pulverized. The method of pulverization is not particularly limited, for example, impact milling such as jet mill, hammer mill, and pin mill has a specific surface area, irreversible capacity,
It is preferable in terms of discharge capacity. The average particle size of the pulverized graphite powder is preferably 10 to 50 μm. In the present invention, the average particle size can be measured by a laser diffraction particle size distribution meter.

According to the method described above, the obtained graphite powder can have a specific surface area of 8 m ² / g or less. The specific surface area is more preferably 6 m ² / g or less, further preferably 4 m ² / g or less. The specific surface area can be measured by a BET method using nitrogen gas adsorption. The obtained graphite powder preferably has an aspect ratio of 5 or less, more preferably 3 or less. If the aspect ratio is too large, the rapid charge / discharge characteristics tend to decrease. The aspect ratio is represented by A / B, where A is the length in the major axis direction of the graphite particles and B is the length in the minor axis direction. The aspect ratio of the present invention is obtained by magnifying graphite particles with a microscope, arbitrarily selecting 10 or more graphite particles, measuring A / B, and taking the average value.

The interlayer distance d (002) of the obtained graphite powder in X-ray wide-angle diffraction is preferably 3.40 ° or less, more preferably 3.38 ° or less, and more preferably 3.38 ° or less.
It is particularly preferable that the angle is 37 ° or less. The crystallite size Lc (002) in the c-axis direction is preferably at least 500 °, more preferably at least 1000 °. As the interlayer distance d (002) of the crystal decreases or the crystallite size Lc (002) in the c-axis direction increases, the discharge capacity increases.

The graphite powder of the present invention is kneaded with an organic binder and a solvent for a negative electrode of a lithium secondary battery, and is formed into a sheet shape, a pellet shape or the like. As the organic binder, for example, polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, a polymer compound having a high ionic conductivity, and the like can be used. In the present invention, as the polymer compound having a large ionic conductivity, polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, and the like can be used. Among these, a polymer compound having a large ionic conductivity is preferable, and polyvinylidene fluoride is particularly preferable.

The mixing ratio between the graphite powder and the organic binder is as follows:
The organic binder is preferably used in an amount of 20 parts by weight or less, more preferably 3 to 10 parts by weight, based on 100 parts by weight of the graphite powder. There is no particular limitation on the solvent.
-Methyl 2-pyrrolidone, dimethylformamide, isopropanol and the like are used. The amount of the solvent is not particularly limited as long as it can be adjusted to a desired viscosity, but is preferably used in an amount of 30 to 70% by weight based on the mixture. The graphite powder is kneaded with an organic binder and a solvent, and after adjusting the viscosity, applied to a current collector, and integrated with the current collector to form a negative electrode. As the current collector, for example, a metal current collector such as a foil of nickel or copper, or a mesh can be used. The integration is
For example, it can be performed by a molding method such as a roll, a press, or the like, and may be integrated by combining them.

The negative electrode thus obtained is used as a negative electrode of a lithium ion secondary battery, a lithium polymer secondary battery or the like. For example, in a lithium ion secondary battery, a positive electrode is arranged to face a separator, and an electrolyte is injected. By using the negative electrode for a lithium secondary battery of the present invention, compared to a lithium secondary battery using a conventional carbon material for the negative electrode, the irreversible capacity is small, high capacity, rapid charge / discharge characteristics, and excellent in cycle characteristics. A lithium secondary battery can be manufactured.

The material used for the positive electrode of the lithium secondary battery in the present invention is not particularly limited.
NiO ₂ , LiCoO ₂ , LiMn ₂ O _{4 and the} like can be used alone or in combination. As the electrolyte, LiC
10 ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO
Lithium salts such as ₃ CF ₃ are, for example, ethylene carbonate,
A so-called organic electrolyte dissolved or contained in a non-aqueous solvent such as diethyl carbonate, dimethoxyethane, dimethyl carbonate, tetrahydrofuran, and propylene carbonate, or a solid polymer electrolyte such as polyvinylidene fluoride and polyaniline can be used. As a separator used when a liquid electrolyte is used, for example, a nonwoven fabric, a cloth, a microporous film, or a combination thereof, containing a polyolefin such as polyethylene or polypropylene as a main component can be used.

FIG. 1 is a partially sectional front view of an example of a cylindrical lithium ion secondary battery. The cylindrical lithium ion secondary battery shown in FIG.
And the negative electrode 2 processed in the same manner is wound by laminating the negative electrode 2 with a separator 3 such as a polyethylene microporous membrane interposed therebetween.
This is inserted into a battery can 7 made of metal or the like, and sealed. The positive electrode 1 is joined to the positive electrode lid 6 via the positive electrode tab 4,
The negative electrode 2 is joined to the battery bottom via the negative electrode tab 5. The positive electrode lid 6 is fixed to the battery can 7 with a gasket 8.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 50 parts by weight of coke powder having an average particle diameter of 10 μm, 15 parts by weight of a pitch, and silicon carbide (volatilization temperature 2500 to 300
(0 ° C.) and 10 parts by weight of coal tar were mixed and stirred at 200 ° C. for 1 hour. Next, the mixture was pulverized to an average particle size of 20 μm, and the pulverized product was put into a mold and press-formed to obtain a rectangular graphite precursor molded body having a size of 15 mm × 25 cm × 6 cm. This graphite precursor molded body was heat-treated at 1000 ° C. in a nitrogen atmosphere, and further heat-treated at 3000 ° C. in a nitrogen atmosphere to obtain a graphite molded body. The bulk density of the obtained graphite molded body was calculated from the measured values of the weight and volume of the graphite molded body. Furthermore, this graphite molded body is crushed,
It was graphite powder. The average particle size of the obtained graphite powder was determined by a laser diffraction particle size analyzer, and the specific surface area was determined by a BET five-point method using nitrogen gas adsorption. The aspect ratio was measured by enlarging the obtained graphite powder with an electron microscope, arbitrarily selecting ten pieces, and measuring the average value of the aspect ratio. Table 1 shows the density of the graphite compact before pulverization, the average particle size of the graphite powder, the specific surface area,
The measurement result of an aspect ratio is shown.

Next, 90% by weight of the obtained graphite particles was added with N
Polyvinylidene fluoride (PVDF) dissolved in -methyl-2-pyrrolidone was added at a solid content of 10% by weight and kneaded to prepare a graphite paste. This graphite paste has a thickness of 1
0 μm rolled copper foil, and further dried to a contact pressure of 49 μm.
It was compression molded at a pressure of 0 MPa (0.5 ton / cm ² ) to obtain a sample electrode. The thickness of the graphite particle layer is 90 μm and the density is 1.5
g / cm ³ . The prepared sample electrode was charged and discharged at a constant current by a three-terminal method, and evaluated as a negative electrode for a lithium secondary battery.

FIG. 2 is a schematic view of the prepared lithium secondary battery. The evaluation of the sample electrode was performed by using LiPF ₆ as an electrolyte 10 in ethylene carbonate (EC) and dimethyl carbonate (E) as shown in FIG. DMC) (E
A solution prepared by dissolving C and DMC in a mixed solvent having a volume ratio of 1: 1) so as to have a concentration of 1 mol / liter is added, and the sample electrode 11, the separator 12, and the counter electrode 13 are stacked and arranged. 14 was suspended from above to produce a lithium secondary battery. The counter electrode 13 and the reference electrode 14
, Metal lithium was used, and a polyethylene microporous membrane was used for the separator 4. Using the obtained lithium secondary battery, 5 mV (Vvs. Li) between the sample electrode 11 and the counter electrode 13 at a constant current of 0.2 mA / cm ^{2 with} respect to the area of the sample electrode.
/ Li ⁺⁾ to charge, the test was repeated for discharging to 1V (Vvs.Li/Li ^+). The charge / discharge was repeated while replacing the counter electrode metal lithium with a new one every 30 cycles. Table 1 shows the discharge capacity at the first cycle, the irreversible capacity, and the discharge capacity at the 100th cycle.

Example 2 50 parts by weight of coke powder having an average particle size of 10 μm, 15 parts by weight of pitch, 5 parts by weight of silicon carbide, and 1 part of coal tar
0 parts by weight were mixed and stirred at 200 ° C. for 1 hour to produce a graphite molded body and graphite powder in the same manner as in Example 1. Table 1 shows the measurement results of the density of the graphite compact before pulverization, the average particle size of the graphite powder, the specific surface area, and the aspect ratio. A charge / discharge test was performed in the same manner as in Example 1. Table 1 shows the discharge capacity at the first cycle, the irreversible capacity, and the discharge capacity at the 100th cycle.

Example 3 50 parts by weight of coke powder having an average particle diameter of 10 μm, 15 parts by weight of pitch, 2 parts by weight of silicon carbide, and 1 part of coal tar
0 parts by weight were mixed and stirred at 200 ° C. for 1 hour to produce a graphite molded body and graphite powder in the same manner as in Example 1. Table 1 shows the measurement results of the density of the graphite compact before pulverization, the average particle size of the graphite powder, the specific surface area, and the aspect ratio. A charge / discharge test was performed in the same manner as in Example 1. Table 1 shows the discharge capacity at the first cycle, the irreversible capacity, and the discharge capacity at the 100th cycle.

Example 4 50 parts by weight of coke powder having an average particle diameter of 10 μm, 15 parts by weight of pitch, 1 part by weight of silicon carbide, and 1 part by weight of coal tar
0 parts by weight were mixed and stirred at 200 ° C. for 1 hour to produce a graphite molded body and graphite powder in the same manner as in Example 1. Table 1 shows the measurement results of the density of the graphite compact before pulverization, the average particle size of the graphite powder, the specific surface area, and the aspect ratio. A charge / discharge test was performed in the same manner as in Example 1. Table 1 shows the discharge capacity at the first cycle, the irreversible capacity, and the discharge capacity at the 100th cycle.

COMPARATIVE EXAMPLE 1 50 parts by weight of coke powder having an average particle size of 10 μm, 15 parts by weight of pitch, and 10 parts by weight of coal tar were mixed.
Stirred at 0 ° C. for 1 hour. Next, this mixture was pulverized to an average particle size of 20 μm, and the pulverized product was put into a mold and formed into a rectangular parallelepiped by a cold isostatic press (CIP press). Next, after heat-treating this compact at 1000 ° C. in a nitrogen atmosphere, pitch impregnation was performed, and this operation was repeated twice to obtain a graphite precursor. This graphite precursor was heat-treated at 1000 ° C. in a nitrogen atmosphere, and further heat-treated at 3000 ° C. in a nitrogen atmosphere.
A high-density graphite compact was obtained. Further, the graphite compact was pulverized to obtain graphite powder. Table 1 shows the measurement results of the density of the graphite compact before pulverization, the average particle size of the graphite powder, the specific surface area, and the aspect ratio. A charge / discharge test was performed in the same manner as in Example 1. Table 1 shows the discharge capacity at the first cycle, the irreversible capacity, and the discharge capacity at the 100th cycle.

Comparative Example 2 A mixture of 50 parts by weight of natural graphite powder having an average particle size of 15 μm, 15 parts by weight of pitch, and 20 parts by weight of coal tar was mixed.
A graphite molded body and graphite powder were produced in the same manner as in Example 1 except that the mixture was stirred at 1 ° C. for 1 hour. Table 1 shows the measurement results of the density of the graphite compact before pulverization, the average particle size of the graphite powder, the specific surface area, and the aspect ratio. A charge / discharge test was performed in the same manner as in Example 1. Table 1 shows the discharge capacity at the first cycle, the irreversible capacity, and the discharge capacity at the 100th cycle.

[0028]

[Table 1]

As shown in Table 1, the graphite powder according to the present invention has a small specific surface area and an aspect ratio, a small irreversible capacity in the first cycle, and excellent cycle characteristics as a negative electrode for a lithium secondary battery. It has been shown to be suitable.

[0030]

According to the production method according to claims 1 and 2,
A graphite powder suitable for a lithium secondary battery having high capacity, small irreversible capacity in the first cycle, and excellent in rapid charge / discharge characteristics can be obtained. The graphite powder according to claim 3 is suitable for a lithium secondary battery having a high capacity, a small irreversible capacity in the first cycle, and excellent in rapid charge / discharge characteristics. Claim 4
The described negative electrode for a lithium secondary battery has a small irreversible capacity in the first cycle and is excellent in rapid charge / discharge characteristics. The lithium secondary battery according to claim 5 has a small irreversible capacity in the first cycle and is excellent in rapid charge / discharge characteristics.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional front view of a cylindrical lithium secondary battery.

FIG. 2 is a schematic view of a lithium secondary battery used for measurement of charge / discharge characteristics and irreversible capacity in Examples of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode tab 5 Negative electrode tab 6 Positive electrode cover 7 Battery can 8 Gasket 9 Glass cell 10 Electrolyte 11 Sample electrode (negative electrode) 12 Separator 13 Counter electrode (positive electrode) 14 Reference electrode

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 10/40 H01M 10/40 Z (72) Inventor Jun Fujita 3-3-1 Ayukawacho, Hitachi City, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. (72) Inventor Kazuo Yamada 3-1-1 Ayukawacho, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Yamazaki Plant

Claims (5)

[Claims] 1. A method for producing graphite powder, comprising a step of pulverizing a graphite compact having a bulk density of 1.6 g / cm ³ or less. 2. A graphite molded product having a bulk density of 1.6 g / cm ³ or less, which is obtained by graphitizing a graphite precursor containing at least one component that volatilizes in the range of 400 to 3200 ° C. A method for producing the graphite powder according to claim 1. 3. A graphite powder having an average particle size of 10 to 50 μm, a specific surface area of 8 m ² / g or less and an aspect ratio of 5 or less. 4. A negative electrode for a lithium secondary battery comprising the graphite powder obtained by the method according to claim 1 or 2 or the graphite powder according to claim 3. 5. A lithium secondary battery comprising the negative electrode according to claim 4 and a positive electrode.