JP3305995B2 - Graphite particles for lithium secondary battery negative electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel graphite particle and a method for producing the same, a graphite paste using the graphite particle, a negative electrode for a lithium secondary battery, a method for producing the same, and a lithium secondary battery. More specifically, a lithium secondary battery excellent in rapid charge / discharge characteristics, cycle characteristics, etc., suitable for use in portable equipment, electric vehicles, power storage, etc., graphite particles for obtaining the same, a method for producing the same, and graphite particles The present invention relates to a graphite paste, a negative electrode for a lithium secondary battery, and a lithium secondary battery using the same.

[0002]

2. Description of the Related Art Conventional graphite particles include, for example, natural graphite particles, artificial graphite particles obtained by graphitizing coke, organic polymer materials, artificial graphite particles obtained by graphitizing pitch and the like, and graphite particles obtained by grinding these. is there. These graphite particles
It is used as a negative electrode for a lithium secondary battery by mixing an organic binder and an organic solvent to form a graphite paste, applying the graphite paste to the surface of a copper foil, and drying the solvent. For example, as shown in Japanese Patent Publication No. 23433/1987, the use of graphite for the negative electrode solves the problem of internal short circuit due to lithium dendrite, thereby improving cycle characteristics.

[0003] However, natural graphite particles in which graphite crystals are developed and artificial graphite particles obtained by graphitizing coke are:
Since the bonding force between the layers of the crystal in the c-axis direction is weaker than the bonding in the plane direction of the crystal, the bonding between the graphite layers is broken by pulverization,
So-called graphite particles having a large aspect ratio are obtained. Since the scale-like graphite particles have a large aspect ratio, when the electrode is produced by kneading with a binder and applying the mixture to the current collector, the scale-like graphite particles are oriented in the plane direction of the current collector,
As a result, there is a problem that the strain in the c-axis direction caused by the repeated insertion and extraction of lithium into and from the graphite crystal causes destruction of the inside of the electrode, and the cycle characteristics are degraded. Therefore, graphite particles capable of improving the cycle characteristics of a lithium secondary battery are required.

[0004]

SUMMARY OF THE INVENTION The first and fifth aspects of the present invention provide graphite particles suitable for a lithium secondary battery having excellent cycle characteristics. Claims 2, 3, and 6
The inventions described in (7) and (7) provide graphite particles suitable for a lithium secondary battery having excellent rapid charge / discharge characteristics and cycle characteristics. The inventions according to claims 4 and 8 provide graphite particles which are excellent in rapid charge / discharge characteristics and cycle characteristics, have a small irreversible capacity in the first cycle, and are suitable for lithium secondary batteries.

The invention of claim 9 provides a method for producing graphite particles which is excellent in rapid charge / discharge characteristics and cycle characteristics, has a small irreversible capacity in the first cycle, and is suitable for a lithium secondary battery. . The invention according to claim 10 is to provide a graphite paste which is excellent in rapid charge / discharge characteristics and cycle characteristics, has a small irreversible capacity in the first cycle, and is suitable for a lithium secondary battery. The invention according to claim 11 is to provide a negative electrode for a lithium secondary battery which is excellent in rapid charge / discharge characteristics and cycle characteristics, has a small irreversible capacity in the first cycle, and is suitable for a lithium secondary battery. The twelfth aspect of the present invention provides a lithium secondary battery having excellent rapid charge / discharge characteristics and cycle characteristics, and having a small irreversible capacity in the first cycle.

[0006]

SUMMARY OF THE INVENTION The present invention is 10 ² to 10 ⁶
The present invention relates to graphite particles having a pore volume of 0.4 to 2.0 cc / g per weight of the graphite particles. In the present invention, the pore volume of pores having a size in the range of 1 × 10 ² to 2 × 10 ⁴ ° is 0.08 to 0.4 per weight of graphite particles.
It relates to graphite particles of cc / g. Further, the present invention relates to the graphite particles obtained by assembling or bonding a plurality of flat particles so that the orientation planes are non-parallel. The present invention also relates to graphite particles having an aspect ratio of 5 or less. The present invention also relates to the graphite particles having a specific surface area of 8 m ² / g or less.

Further, the present invention provides a graphitizable aggregate or graphite and a graphitizable catalyst containing 1 to 50% by weight of a graphite and a binder.
The present invention relates to a method for producing the above graphite particles, which comprises adding, mixing, calcining and pulverizing. Further, the present invention relates to a graphite paste obtained by adding an organic binder and a solvent to either the graphite particles or the graphite particles produced by the above-described method and mixing them. The present invention also relates to a negative electrode for a lithium secondary battery obtained by applying the graphite paste to a current collector and integrating the same. Furthermore, the present invention relates to a lithium secondary battery having the above-described negative electrode for a lithium secondary battery and a positive electrode.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The graphite particles of the present invention are characterized by their pore volume from two viewpoints. First, the pore volume of pores in the range of 10 ² to 10 ⁶ Å is 0.4 to 2.0 cc / g per weight of graphite particles. When the graphite particles are used as a negative electrode, the pores of the graphite particles absorb the expansion and contraction of the electrode due to charging and discharging, thereby suppressing the destruction of the inside of the electrode, thereby reducing the cycle characteristics of the resulting lithium secondary battery. Can be improved. Pore volume of the pores in the range of 10 ² to 10 ⁶ Å is 0.4
~ 1.5 cc / g, more preferably 0.6 cc / g.
More preferably, it is in the range of 1.2 to 1.2 cc / g. If the total pore volume is less than 0.4 cc / g, the cycle characteristics deteriorate,
If it exceeds 2.0 cc / g, a large amount of a binder is required to be used when integrating the graphite particles and the current collector, and there is a problem that the capacity of the lithium secondary battery to be produced is reduced. The pore volume can be determined by measuring the pore size distribution by the mercury intrusion method. The size of the pores can also be determined by measuring the pore size distribution by the mercury intrusion method.

Second, the pore volume of the pores in the range of 1 × 10 ² to 2 × 10 ^{4 、} is 0.08 to 0.08 per weight of graphite particles.
It is 0.4 cc / g. When the graphite particles are used as a negative electrode, the pores of the graphite particles absorb the expansion and contraction of the electrode due to charging and discharging, thereby suppressing the destruction of the inside of the electrode, thereby reducing the cycle characteristics of the resulting lithium secondary battery. Can be improved. 1 × 10 ^{2 to} 2 × 10 ⁴
The pore volume in the range of Å is more preferably 0.1 to 0.3 cc / g. The pore volume in this size range is 0.
If it is less than 08 cc / g, the cycle characteristics deteriorate. If it exceeds 0.4 cc / g, a large amount of binder is required to be used when integrating the graphite particles and the current collector. There is a problem of decline. The pore volume in this range can also be determined by measuring the pore size distribution by the mercury intrusion method.

[0010] The graphite particles of the present invention are preferably formed by assembling or bonding a plurality of flat particles so that their orientation planes are non-parallel. In the present invention, flat particles are particles having a shape having a major axis and a minor axis, and are not perfectly spherical. For example, a shape such as a scaly shape, a scaly shape, or a partial lump shape is included in this. In the graphite particles, the orientation plane of the plurality of flat particles is non-parallel, and the flat surface having the shape of each particle, in other words, the plane closest to the plane is the orientation surface, and the plurality of flat particles are This refers to a state in which the respective alignment planes are gathered without being aligned in a certain direction.

In the graphite particles, the flat particles are aggregated or bonded, and the bonding means that the particles are tar,
Through a carbonaceous material obtained by carbonizing a binder such as a pitch, it refers to a state in which the particles are chemically bonded.Assembling means that the particles are not chemically bonded to each other, but due to its shape and the like, A state in which the shape of the aggregate is maintained. From the standpoint of mechanical strength, it is preferable to combine them. In one graphite particle, the number of flat particles aggregated or bonded is preferably three or more. The size of each flat particle is preferably 1 to 100 μm in particle size, and is preferably 2/3 or less of the average particle size of the graphite particles in which these are aggregated or bonded.

When the graphite particles are used for the negative electrode, the graphite particles are hardly oriented on the current collector, the wettability with the electrolytic solution is improved, and lithium is easily inserted into and released from the negative electrode graphite. The rapid charge and discharge characteristics and the cycle characteristics of the obtained lithium secondary battery can be improved. FIG. 1 shows a scanning electron micrograph of the particle structure of one example of the graphite particles. In FIG. 1, (a) is a scanning electron micrograph of the outer surface of the graphite particles according to the present invention, and (b) is a scanning electron micrograph of a cross section of the graphite particles. In (a),
A large number of fine flake-like graphite particles can be observed in which the orientation planes of these particles are non-parallel and combined to form graphite particles.

[0013] Graphite particles having an aspect ratio of 5 or less are preferable because the particles tend to be hardly oriented on the current collector and easily occlude and release lithium as described above. The aspect ratio is more preferably 1.2 to 5. If the aspect ratio is less than 1.2, the contact area between the particles tends to decrease, so that the conductivity tends to decrease. For the same reason, the lower limit of the more preferable range is 1.3 or more. Further, the upper limit of the more preferable range is 3 or less, and when the aspect ratio is larger than this, the rapid charge / discharge characteristics tend to be easily deteriorated. Therefore, a particularly preferable aspect ratio is 1.3 to 3.

The aspect ratio is defined as A / B where A is the length of the graphite particle in the major axis direction and B is the length of the graphite particle in the minor axis direction.
It is represented by The aspect ratio in the present invention is obtained by magnifying graphite particles with a microscope, arbitrarily selecting 100 graphite particles, measuring A / B, and taking the average value.
In addition, the structure of the graphite particles having an aspect ratio of 5 or less is preferably an aggregate or a combination of smaller graphite particles, and a plurality of the flat particles, the orientation plane of which is non-parallel. It is more preferable to use graphite particles that are aggregated or bonded to the same.

The graphite particles of the present invention have a specific surface area of 8
It is preferably at most m ² / g, more preferably at most 5 m ² / g. When the graphite particles are used for a negative electrode, the obtained lithium secondary battery can have improved rapid charge / discharge characteristics and cycle characteristics, and can have a reduced irreversible capacity in the first cycle. When the specific surface area exceeds 8 m ² / g, the irreversible capacity in the first cycle of the obtained lithium secondary battery tends to increase, the energy density is low, and many binders are used when producing a negative electrode. Tends to be needed. The specific surface area is more preferably 1.5 to ⁵ m ² / g, from the viewpoint that the obtained lithium secondary battery has more favorable rapid charge / discharge characteristics and cycle characteristics.
It is very preferred that it is ５5 m ² / g. The specific surface area can be measured by a known method such as a BET method (nitrogen gas adsorption method).

Further, the interlayer distance d (002) of crystals of the graphite particles used in the present invention in X-ray wide angle diffraction is 3.3.
8 ° or less is preferable, and the range of 3.37 to 3.35 ° is more preferable. Crystal interlayer distance d (002) is 3.38 °
If it exceeds, the discharge capacity tends to be small. The crystallite size Lc (002) in the c-axis direction is preferably 500 ° or more, and more preferably 1000 to 100000 °. When the interlayer distance d (002) of the crystal decreases or the crystallite size Lc (002) in the c-axis direction increases,
The discharge capacity tends to increase.

Although there is no particular limitation on the method for producing the graphite particles of the present invention, 1 to 50% by weight of a graphitization catalyst is added to a graphitizable aggregate or graphite and a graphitizable binder, mixed and calcined. It is preferable to obtain graphite particles first by post-grinding. Then, an organic binder and a solvent are added to the graphite particles and mixed, and the viscosity is adjusted. The mixture is applied to a current collector, dried, and the solvent is removed. To form a negative electrode for a lithium secondary battery.

As the graphitizable aggregate, for example, coke powder, resin carbide and the like can be used, but there is no particular limitation as long as the material can be graphitized. Among them, coke powder such as needle coke which is easily graphitized is preferable.
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 the powder is in the form of powder. The particle size of the graphitizable aggregate or graphite is preferably smaller than the particle size of the graphite particles produced in the present invention.

Further, as the graphitization catalyst, for example, metals such as iron, nickel, titanium, silicon and boron, and their graphitization catalysts such as carbides and oxides can be used. Of these, carbides or oxides of silicon or boron are preferred. The amount of the graphitization catalyst to be added is preferably 1 to 50% by weight, more preferably 5 to 50% by weight based on the obtained graphite particles.
-40% by weight, more preferably 5-30% by weight
If the content is less than 1% by weight, the aspect ratio and the specific surface area of the graphite particles tend to be large, and the development of graphite crystals tends to be poor. On the other hand, if it exceeds 50% by weight, it is difficult to mix them uniformly. Workability tends to deteriorate.

As the binder, for example, organic materials such as thermosetting resin and thermoplastic resin are preferable in addition to tar and pitch. The binder is preferably added in an amount of 5 to 80% by weight, more preferably 10 to 80% by weight, and more preferably 15 to 80% by weight, based on the flat graphitizable aggregate or graphite. Is more preferable.
If the amount of the binder is too large or too small, the graphite particles to be produced tend to have an increased aspect ratio and specific surface area. The method of mixing the graphitizable aggregate or graphite and the binder is not particularly limited, and is performed using a kneader or the like, but it is preferable to mix at a temperature equal to or higher than the softening point of the binder. Specifically, when the binder is pitch, tar or the like, the temperature is preferably 50 to 300 ° C, and when the binder is a thermosetting resin, the temperature is preferably 20 to 100 ° C.

Next, the above mixture is fired and graphitized. The mixture may be formed into a predetermined shape before this treatment. Further, after the molding, it may be pulverized before graphitization, and after adjusting the particle size, graphitization may be performed. The firing is preferably performed under conditions in which the mixture is unlikely to be oxidized. Examples of the firing include a method of firing in a nitrogen atmosphere, an argon gas atmosphere, or a vacuum. The temperature for graphitization is preferably 2000 ° C. or higher, more preferably 2500 ° C. or higher, and further preferably 2800 ° C. to 3200 ° C. If the graphitization temperature is low, the development of graphite crystals is poor,
The discharge capacity tends to decrease and the added graphitization catalyst tends to remain in the produced graphite particles. If the graphitization catalyst remains in the graphite particles to be produced, the discharge capacity decreases. If the graphitization temperature is too high, the graphite may sublime.

Next, the obtained graphitized product is preferably pulverized. The method of pulverizing the graphitized material is not particularly limited,
For example, a known method such as a jet mill, a vibration mill, a pin mill, and a hammer mill can be used. The particle size after pulverization is preferably such that the average particle size is 1 to 100 μm,
More preferably, it is μm. If the average particle size is too large, the surface of the electrode to be produced tends to have irregularities. In the present invention, the average particle size can be measured by a laser diffraction particle size distribution meter.

Through the steps described above, the graphite particles of the present invention can be obtained. The obtained graphite particles are formed into a sheet-like or pellet-like shape by mixing a material containing an organic binder and a solvent. 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 content of the organic binder is preferably 3 to 20% by weight based on the mixture of the graphite powder and the organic binder. The solvent is not particularly limited, and N-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.
It is preferably used in an amount of up to 70% by weight.

As the current collector, for example, a metal current collector such as a foil of nickel or copper, or a mesh can be used. In addition, the integration can be performed by a molding method such as a roll, a press, or the like, and these may be combined and integrated. The negative electrode thus obtained is used as a negative electrode of a lithium secondary battery such as a lithium ion secondary battery or a lithium polymer secondary battery. For example, in a lithium ion secondary battery, a positive electrode is arranged to face a separator, and an electrolyte is injected. ADVANTAGE OF THE INVENTION According to this invention, compared with the lithium secondary battery which used the conventional carbon material for the negative electrode, the lithium secondary battery which is excellent in a quick charge / discharge characteristic and a cycle characteristic, and whose irreversible capacity is small can be manufactured.

There is no particular limitation on the material used for the positive electrode of the lithium secondary battery in the present invention.
₂ , LiCoO ₂ , LiMn ₂ O _4, etc. can be used alone or as a mixture. LiClO ₄ ,
LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃
For example, a so-called organic electrolytic solution in which a lithium salt such as ethylene carbonate, diethyl carbonate, dimethoxyethane, dimethyl carbonate, tetrahydrofuran, or a non-aqueous solvent such as propylene carbonate is dissolved or contained in a polymer solid electrolyte such as polyvinylidene fluoride is used. can do.

As the separator used when a liquid electrolyte is used, for example, a nonwoven fabric, cloth, microporous film or the like in which a polyolefin such as polyethylene or polypropylene as a main component can be used. FIG. 2 shows a partial cross-sectional front view of an example of the cylindrical lithium secondary battery. The cylindrical lithium secondary battery shown in FIG. 2 is formed by winding a positive electrode 1 processed into a thin plate and a negative electrode 2 processed in the same manner 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 to be sealed. Positive electrode 1
Is connected to the positive electrode lid 6 via the positive electrode tab 4, and the negative electrode 2 is connected to the battery bottom via the negative electrode tab 5. Positive electrode cover 6
Is fixed to the battery can 7 by a gasket 8.

[0028]

【Example】

Example 1 40 parts by weight of coke powder having an average particle diameter of 5 μm, 25 parts by weight of tar pitch, 5 parts by weight of silicon carbide having an average particle diameter of 48 μm, and 20 parts by weight of coal tar were mixed and stirred at 200 ° C. for 1 hour. Next, the powder was fired at 2800 ° C. in a nitrogen atmosphere and then pulverized to produce graphite particles having an average particle diameter of 30 μm. The obtained graphite particles were subjected to a pore size distribution measurement using a mercury intrusion method (using Shimadzu Pore Sizer 9320 type). As a result, the graphite particles had pores in the range of 10 ² to 10 ⁶ Å, and the total pore volume per graphite particle weight was determined. Was 0.6 cc / g. Also, 1
The pore volume in the range of × 10 ^{2 to} 2 × 10 ⁴ ０．２ was 0.20 cc / g per weight of graphite particles. In addition, 100 obtained graphite particles were arbitrarily selected and the average value of the aspect ratio was measured. As a result, the specific surface area of the graphite particles determined by the BET method was 1.5 m ² / g. The crystal interlayer distance d (002) by X-ray wide angle diffraction was 3.362 ° and the crystallite size Lc (002) was 1000 ° or more. Further, according to a scanning electron micrograph (SEM photograph) of the obtained graphite particles, the graphite particles had a structure in which flat particles were aggregated or bonded such that a plurality of orientation planes became non-parallel. .

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 graphite particle layer has a thickness of 90 μm and a density of 1.
It was 6 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. 3 is a schematic diagram of a lithium secondary battery,
As shown in FIG. 3, the evaluation of the sample electrode was performed by adding LiPF ₆ to the glass cell 9 as the electrolytic solution 10 using ethylene carbonate (E).
C) and dimethyl carbonate (DMC) (EC and DM
C is a solution prepared by dissolving a mixed solvent having a volume ratio of 1: 1) so as to have a concentration of 1 mol / liter.
The separator 12 and the counter electrode 13 were stacked and arranged, and the reference electrode 14 was suspended from above to produce a lithium secondary battery. Note that metallic lithium was used for the counter electrode 13 and the reference electrode 14, and a polyethylene microporous membrane was used for the separator 4. Using the obtained lithium secondary battery, between the sample electrode 11 and the counter electrode 13, with respect to the area of the sample electrode,
5 mV (V vs. Li / L) at a constant current of 0.5 mA / cm ²
i ⁺ ) and the test of discharging to 1 V (Vvs. Li ^/ Li ⁺ ) was repeated. Table 1 shows the charge capacity and the discharge capacity per unit weight of the graphite particles in the cycle and the discharge capacity per unit weight of the graphite particles in the 30th cycle.

Example 2 50 parts by weight of coke powder having an average particle diameter of 20 μm, 20 parts by weight of pitch, 7 parts by weight of silicon carbide having an average particle diameter of 48 μm, and 10 parts by weight of coal tar were mixed and stirred at 200 ° C. for 1 hour. did. Next, the powder was fired at 2800 ° C. in a nitrogen atmosphere and then pulverized to obtain graphite particles having an average particle diameter of 30 μm.
The obtained graphite particles were subjected to a pore size distribution measurement using a mercury intrusion method (using Shimadzu Pore Sizer 9320).
0 ^2-10 have pores in the range of ⁶ Å, the total pore volume per graphite particle weight was 1.5 cc / g. Also, 1 × 10 ²
The pore volume in the range of ２2 × 10 ⁴ ０．１ was 0.13 cc / g per graphite particle weight. Further, the obtained graphite particles were
The average value of the aspect ratio was 2.3 as determined by arbitrarily selecting zero particles. The specific surface area of the graphite particles determined by the BET method was 3.6 m ² / g. The interlayer distance d (002) was 3.361 ° and the crystallite size Lc (002) was 1000 ° or more.
Further, the obtained graphite particles had a structure in which flat particles were aggregated or bonded so that a plurality of orientation planes became non-parallel. Hereinafter, a lithium secondary battery was manufactured through the same steps as in Example 1, and the same test as in Example 1 was performed. Table 1 shows the charge capacity and the discharge capacity per unit weight of the graphite particles in the first cycle and the discharge capacity per unit weight of the graphite particles in the 30th cycle.

Comparative Example 1 Mesocarbon microbeads (KMFC, manufactured by Kawasaki Steel Corporation) were fired at 2800 ° C. in a nitrogen atmosphere to obtain graphite particles having an average particle size of 25 μm. The obtained graphite particles are measured for pore size distribution by mercury intrusion method (Shimadzu Pore Sizer 9).
As a result, the fine particles had pores in the range of 10 ² to 10 ⁶ °, and the total pore volume per graphite particle weight was 0.3%.
It was 5 cc / g. Further, the pore volume in the range of 1 × 10 ^{2 to} 2 × 10 ⁴ ０．０ was 0.06 cc / g per weight of graphite particles. In addition, arbitrarily select 100 obtained graphite particles,
As a result of measuring the average value of the aspect ratio, it was 1, and the specific surface area of the graphite particles by the BET method was 1.4 m ² / g.
The interlayer distance d (00) of the crystal by X-ray wide angle diffraction of graphite particles
2) is 3.378 ° and the crystallite size Lc (002)
Was 500 °. Hereinafter, a lithium secondary battery was manufactured through the same steps as in Example 1, and the same test as in Example 1 was performed. Table 1 shows the charge capacity and the discharge capacity per unit weight of the graphite particles in the first cycle and the discharge capacity per unit weight of the graphite particles in the 30th cycle.

Comparative Example 2 50 parts by weight of coke powder having an average particle size of 5 μm, pitch 1
0 parts by weight, 30 parts by weight of iron oxide having an average particle size of 65 μm, and 20 parts by weight of coal tar were mixed and stirred at 200 ° C. for 1 hour. Next, the powder was fired at 2800 ° C. in a nitrogen atmosphere and then pulverized to obtain graphite particles having an average particle size of 15 μm. The resulting pore size distribution measurement of graphite particles by mercury porosimetry (Shimadzu Poasaiza 9320 form used) the result of 10 ² -
It had pores in the range of 10 ⁶ %, and the total pore volume per graphite particle weight was 2.1 cc / g. Also, 1 × 10 ² to 2
The pore volume in the range of × 10 ⁴ ０．４ was 0.42 cc / g per graphite particle weight. The obtained graphite particles were
The average value of the aspect ratio was 2.8, and the specific surface area of the graphite particles by the BET method was 8.3 m ² / g. The interlayer distance d (002) was 3.365 ° and the crystallite size Lc (002) was 1000 ° or more. Hereinafter, a lithium secondary battery was manufactured through the same steps as in Example 1, and the same test as in Example 1 was performed. Table 1 shows the charge capacity and the discharge capacity per unit weight of the graphite particles in the first cycle and the discharge capacity per unit weight of the graphite particles in the 30th cycle.

[0033]

[Table 1]

As shown in Table 1, it is clear that the lithium secondary battery obtained by using the graphite particles of the present invention has high capacity and excellent cycle characteristics.

[0035]

The graphite particles according to the first and fifth aspects are suitable for a lithium secondary battery having excellent cycle characteristics. The graphite particles according to the second, third, sixth and seventh aspects are suitable for a lithium secondary battery having excellent rapid charge / discharge characteristics and cycle characteristics. The graphite particles according to claims 4 and 8 are excellent in rapid charge / discharge characteristics and cycle characteristics, and have a small irreversible capacity in the first cycle, and are suitable for lithium secondary batteries.

According to the method for producing graphite particles of the ninth aspect, the graphite particles are excellent in rapid charge / discharge characteristics and cycle characteristics, and have a small irreversible capacity in the first cycle, and are suitable for lithium secondary batteries. The graphite paste according to claim 10,
It is excellent in rapid charge / discharge characteristics and cycle characteristics, and has a small irreversible capacity in the first cycle, and is suitable for a lithium secondary battery. The negative electrode for a lithium secondary battery according to the eleventh aspect has excellent rapid charge / discharge characteristics and cycle characteristics, has a small irreversible capacity in the first cycle, and is suitable for a lithium secondary battery. The lithium secondary battery according to the twelfth aspect has excellent rapid charge / discharge characteristics and cycle characteristics, and has a small irreversible capacity in the first cycle.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph of graphite particles used in the present invention, wherein (a) is a photograph of the outer surface of the particles and (b) is a photograph of a cross section of the particles.

FIG. 2 is a partial cross-sectional front view of a cylindrical lithium secondary battery.

FIG. 3 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

Continuation of the front page (72) Inventor Kazuo Yamada 3-1-1, Ayukawa-cho, Hitachi-shi, Ibaraki Pref. Hitachi Chemical Co., Ltd. Yamazaki Plant (56) References JP-A-10-158005 (JP, A) JP Hei 8-31422 (JP, A) WO 97/42671 (WO, A1) WO 95/28011 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 C01B 31/04 101 H01M 4/02 H01M 4/04 H01M 10/40

Claims (6)

(57) [Claims] 1. The pore volume of pores having a size in the range of 10 ² to 10 ⁶ ° is 0.4 to 2.0 cc / weight per graphite particle weight.
g of graphite particles for a negative electrode of a lithium secondary battery. 2. The graphite particles for a negative electrode of a lithium secondary battery according to claim 1, wherein the graphite particles have an aspect ratio of 5 or less. 3. The graphite particles for a negative electrode of a lithium secondary battery according to claim 1, having a specific surface area of 8 m ² / g or less. 4. The pore volume of pores having a size in the range of 1 × 10 ² to 2 × 10 ^{4 、} is 0.08 to 0.08 per weight of graphite particles.
0.4 cc / g of graphite particles for a negative electrode of a lithium secondary battery. 5. The graphite particles for a negative electrode of a lithium secondary battery according to claim 4, wherein the graphite particles have an aspect ratio of 5 or less. 6. The graphite particles for a negative electrode of a lithium secondary battery according to claim 4, having a specific surface area of 8 m ² / g or less.