JP2002050346A - Negative electrode for lithium secondary cell, its manufacturing method and lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a lithium secondary cell which is suited for a lithium secondary cell of high capacity, a manufacturing method for a negative electrode of high capacity for a lithium secondary cell which is suited for a lithium secondary cell having a good boosting charge and discharge characteristics and a cycle characteristics, and a lithium secondary cell which has a high capacity and good boosting charge and discharge characteristics and cycle characteristics. SOLUTION: The negative electrode for the lithium secondary cell made by integrating a collector and a mixture of graphite particles and an organic binder has a mixture density of the graphite particles and the organic binder after being pressurized and integrated from 1.5 to 1.9 g/cm3. As the manufacturing method of the negative electrode for the lithium secondary cell, a graphitized catalyst is added by 1 to 50 weight % to a graphitizable aggregate or graphite and a graphitizable binder, which is then mixed, calcined, and fractured into graphite particles, to which is added and mixed an organic binder and a solvent, and the mixture is applied on the collector, which is pressurized and integrated after the solvent is dried. The lithium secondary cell has the negative electrode for the lithium secondary cell or a negative electrode of a lithium secondary cell which is manufactured with the above manufacturing method, and the positive electrode placed face to face through a separator, and an electrolyte solution filled around them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to 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 devices, electric vehicles, power storage, and the like, a negative electrode for a lithium secondary battery for obtaining the same, and production thereof About the law.

[0002]

2. Description of the Related Art Conventional negative electrodes for lithium secondary batteries include, for example, natural graphite particles, artificial graphite particles obtained by graphitizing coke,
Examples include organic polymer materials, artificial graphite particles obtained by graphitizing pitch and the like, graphite particles obtained by pulverizing these, spherical particles obtained by graphitizing mesocarbon microbeads, and the like.
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. Sho 62-23433
As described in Japanese Patent Application Laid-Open Publication No. H10-107, the problem of internal short circuit due to lithium dendrite is solved by using graphite for the negative electrode, and the cycle characteristics are improved.

However, natural graphite in which graphite crystals are developed and artificial graphite particles in which coke is graphitized have a weaker bonding force between the layers in the c-axis direction than in the plane direction of the crystals. As a result, the bond between the graphite layers is broken, and so-called scale-like 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 to a current collector, the scale-like graphite particles are oriented in the plane direction of the current collector, and as a result, In addition to the problem of destruction of the inside of the electrode due to the distortion in the c-axis direction caused by the repeated insertion and extraction of lithium into and from the graphite crystal, the cycle characteristics are degraded,
When the negative electrode density is 1.5 g / cm ³ or more, it becomes difficult to insert and release lithium into the negative electrode graphite, and there is a problem that rapid charge / discharge characteristics and discharge capacity are rapidly reduced. The lithium secondary battery can be expected to increase the energy density per volume by increasing the negative electrode density. Therefore, in order to improve the energy density per volume of the lithium secondary battery, there is a demand for a negative electrode that has a small decrease in discharge capacity when the negative electrode density is increased.

[0004]

An object of the present invention is to provide a negative electrode for a lithium secondary battery suitable for a high capacity lithium secondary battery. The invention according to claims 2 and 3 provides a negative electrode for a lithium secondary battery which is suitable for a lithium secondary battery having high capacity and excellent in rapid charge / discharge characteristics and cycle characteristics. The invention described in claim 4 provides a method for producing a negative electrode for a lithium secondary battery which is suitable for a lithium secondary battery having a high capacity and excellent in rapid charge / discharge characteristics and cycle characteristics. The invention according to claim 5 provides a lithium secondary battery having high capacity and excellent in rapid charge / discharge characteristics and cycle characteristics.

[0005]

SUMMARY OF THE INVENTION The present invention provides a negative electrode for a lithium secondary battery obtained by integrating a mixture of graphite particles and an organic binder with a current collector. And the density of the mixture of the organic binder is 1.5 to 1.9 g /
The present invention relates to a negative electrode for a lithium secondary battery having a size of cm ³ . The present invention also relates to a negative electrode for a lithium secondary battery, wherein the graphite particles are graphite particles in which a plurality of flat particles are aggregated or combined such that the orientation planes are non-parallel. The present invention also relates to the negative electrode for a lithium secondary battery according to claim 1 or 2, wherein the graphite particles have an aspect ratio of 5 or less.

Further, the present invention provides a graphitizable aggregate or graphite and a graphitizable catalyst containing 1 to 50% by weight of a graphitizable binder.
An organic binder and a solvent are added to the mixed, calcined, and ground graphite particles, and the mixture is applied. The mixture is applied to a current collector, and the solvent is dried. And a method for producing a negative electrode for a lithium secondary battery. Further, in the present invention, the negative electrode for a lithium secondary battery, or the negative electrode for a lithium secondary battery manufactured by the above manufacturing method, and a positive electrode are arranged to face each other with a separator interposed therebetween, and an electrolyte is injected around the negative electrode. To a rechargeable lithium secondary battery.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The negative electrode for a lithium secondary battery according to the present invention is obtained by integrating a current collector with a mixture of graphite particles and an organic binder. The mixture has a density of 1.5 to 1.9 g / cm ³ .
The density is preferably in the range of 1.55 to 1.85 g / cm ³ , more preferably 1.6 to 1.85 g / cm ³ , and still more preferably 1.6 to 1.8 g / cm ³ . By increasing the density of the mixture of the graphite particles and the binder constituting the negative electrode of the present invention, the energy density per volume of the lithium secondary battery obtained using this negative electrode can be increased. When the density of the mixture of the graphite particles and the organic binder exceeds 1.9 g / cm ³ , the rapid charging characteristic is deteriorated, and when the density is less than 1.5 g / cm ³ , the energy density per unit volume of the obtained lithium secondary battery is obtained. Becomes smaller.

The graphite particles used in the negative electrode for a lithium secondary battery according to the present invention may be any particles capable of setting the density within the above range. For example, natural graphite may be used. It is preferable to use graphite particles in which a plurality of particles are aggregated or bonded so that the 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.

[0009] In the graphite particles, the flat particles are aggregated or bonded.
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 a negative electrode, it is difficult for the graphite particles to be oriented on the current collector, and lithium is inserted into the negative electrode graphite.
Since the lithium secondary battery is easily released, the charge / 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 used in the present invention. In FIG.
(A) is a scanning electron micrograph of the outer surface of the graphite particles used in the present invention, and (b) is a scanning electron micrograph of the cross section of the graphite particles. In (a), it can be observed that a number of fine flake-like graphite particles are formed, and the orientation planes of these particles are combined in a non-parallel manner to form graphite particles.

[0011] 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 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 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 used in the present invention preferably have a specific surface area of 8 m ² / g or less, more preferably 5 m ² / g or less. 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 extremely preferred that it is ^{2 to 5} 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 the graphite in the X-ray wide angle diffraction of each graphite particle used in the present invention is 3.3.
It is preferably at most 8 °, more preferably at most 3.37 °, even more preferably at most 3.36 °. The crystallite size Lc (002) in the c-axis direction is 500
Å or more is preferable, and 1000 to 10000Å is more preferable. 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 tends to increase.

Although there is no particular limitation on the method for producing the negative electrode for a lithium secondary battery of the present invention, 1 to 50% by weight of a graphitizing catalyst is added to graphitizable aggregate or graphite and a graphitizable binder. First, graphite particles are obtained by calcination and then crushing, and then an organic binder and a solvent are added to the graphite particles and mixed. The mixture is applied to a current collector, dried, and the solvent is dried. After removal, it can be obtained by pressurizing and integrating to obtain the above density.

As the graphitizable aggregate, for example, coke powder, carbide of resin 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, examples of the graphitization catalyst include graphitization catalysts such as metals such as iron, nickel, titanium, silicon, and boron, and carbides and oxides thereof. 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 resins and thermoplastic resins 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.

According to the present invention, a plurality of flat particles can be aggregated or bonded so that their orientation planes are non-parallel, and the aspect ratio is 5 through the above-described steps.
The following graphite particles can be obtained, and the specific surface area is 8
Graphite particles of m ² / g or less can be obtained.

The obtained graphite particles are formed into a sheet or pellet shape by mixing a material containing an organic binder and a solvent. As an organic binder, for example,
Polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, high molecular compounds having 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 of the graphite particles and the organic binder is as follows:
The organic binder is 3-1 to 100 parts by weight of the graphite particles.
It is preferable to use 0 parts by weight. 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, but is preferably used in an amount of 30 to 70% by weight based on the mixture.

As the current collector, for example, a metal current collector such as a foil of nickel, copper or the like, 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 obtained in this way is arranged with the positive electrode facing the other with a separator interposed therebetween, and injected with an electrolytic solution, so that the negative electrode is rapidly charged as compared with a conventional lithium secondary battery using a carbon material for the negative electrode. A lithium secondary battery having excellent discharge characteristics and cycle characteristics and small irreversible capacity can be manufactured.

The material used for the positive electrode of the lithium secondary battery according to the present invention is not particularly limited.
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, and propylene carbonate are dissolved can be used.

As the separator, for example, a nonwoven fabric, cloth, microporous film, or a combination thereof, containing 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. The positive electrode 1 is connected to a positive electrode cover 6 via a positive electrode tab 4, and the negative electrode 2 is connected to a battery bottom via a negative electrode tab 5. The positive electrode lid 6 is fixed to the battery can 7 with a gasket 8.

[0026]

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 size of 8 μm, 20 parts by weight of tar pitch, 5 parts by weight of silicon carbide and 15 parts by weight of coal tar were mixed and stirred at 100 ° C. for 1 hour. Next, it was baked at 2800 ° C. in a nitrogen atmosphere and then pulverized to produce graphite particles having an average particle size of 25 μm. As a result of arbitrarily selecting 100 obtained graphite particles and measuring the average value of the aspect ratio, it was 1.5. The specific surface area of the obtained graphite particles by the BET method was 2.1 m ² / g, and the interlayer distance d (00) of the crystals of the graphite particles by X-ray wide-angle diffraction was found.
2) was 3.365 ° 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
Polyvinylidene fluoride (PVDF) dissolved in methyl-2-pyrrolidone was added at a solid content of 10% by weight and kneaded to obtain a graphite paste. This graphite paste has a thickness of 10 μm.
N-methyl-2-
The pyrrolidone was removed and the sample was compressed with a press at a pressure of 30 MPa to obtain a sample electrode having a mixture layer of graphite particles and PVDF having a thickness of 80 μm and a density of 1.55 g / cm ³ .

The obtained 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 view of a lithium secondary battery. The evaluation of the sample electrode is performed by using LiPF 4 as an electrolyte 10 in ethylene carbonate (EC) in a glass cell 9 as shown in FIG.
And a solution prepared by dissolving a mixture of dimethyl carbonate (DMC) (EC and DMC in a volume ratio of 1: 1) to a concentration of 1 mol / liter was added, and a sample electrode 11, a separator 12, and a counter electrode 13 were laminated. The lithium secondary battery was produced by suspending the reference electrode 14 from above. Metal lithium was used for the counter electrode 13 and the reference electrode 14, and a polyethylene microporous membrane was used for the separator 12. Using the obtained lithium secondary battery, graphite particles of the sample electrode and PVDF were placed between the sample electrode 11 and the counter electrode 13.
5 mV at a constant current of 0.2 mA / cm ^{2 with} respect to the area of the mixture of
(Vvs. Li / Li +) and 1V (Vvs. Li / L)
The test for discharging to i +) was repeated 50 cycles, but no decrease in discharge capacity was confirmed. In order to evaluate the rapid charge / discharge characteristics, the graphite was charged at a constant current of 0.3 mA / cm ² , and the discharge current was changed to 0.5, 2.0, 4.0 and 6.0 mA / cm ^2. Table 1 shows the discharge capacity with respect to the volume of the mixture of the particles and PVDF.

Example 2 A sample electrode was obtained through the same steps as in Example 1 except that the compression force of the press was set to 40 MPa. The thickness of the mixture of graphite particles and PVDF of the obtained sample electrode was 80 μm, and the density was 1.63 g / cm ³ . Next, a lithium secondary battery was manufactured through the same steps as in Example 1, and the same test as in Example 1 was performed, but no decrease in discharge capacity was confirmed. As a quick charge / discharge characteristic evaluation, the discharge capacity when charging at a constant current of 0.3 mA / cm ² and changing the discharge current to 0.5, 2.0, 4.0, and 6.0 mA / cm ^2. Are shown in Table 1.

Example 3 A sample electrode was obtained through the same steps as in Example 1 except that the compression force in the press was changed to 80 MPa. The thickness of the mixture of graphite particles and PVDF of the obtained sample electrode was 80 μm, and the density was 1.75 g / cm ³ . Next, a lithium secondary battery was manufactured through the same steps as in the example, and the same test as in example 1 was performed, but no decrease in discharge capacity was confirmed.
As a quick charge / discharge characteristic evaluation, the battery was charged at a constant current of 0.3 mA / cm ² and the discharge current was 0.5, 2.0, 4.0, and 6.
Table 1 shows the discharge capacity when the discharge capacity was changed to 0 mA / cm ² .

Example 4 Example 1 was repeated except that the compression force in the press was 100 MPa.
A sample electrode was obtained through the same steps as described above. The thickness of the mixture of graphite particles and PVDF of the obtained sample electrode was 80 μm, and the density was 1.85 g / cm ³ . Next, a lithium secondary battery was manufactured through the same steps as in Example 1, and the same test as in Example 1 was performed, but no decrease in discharge capacity was confirmed. As a quick charge / discharge characteristic evaluation, the discharge capacity when charging at a constant current of 0.3 mA / cm ² and changing the discharge current to 0.5, 2.0, 4.0, and 6.0 mA / cm ^2. Are shown in Table 1.

Comparative Example 1 A sample electrode was obtained through the same steps as in Example 1 except that the compression force in the press was changed to 20 MPa. The thickness of the mixture of graphite particles and PVDF of the obtained sample electrode was 80 μm, and the density was 1.45 g / cm ³ . Next, a lithium secondary battery was manufactured through the same steps as in Example 1, and the same test as in Example 1 was performed, but no decrease in discharge capacity was confirmed. As a quick charge / discharge characteristic evaluation, the discharge capacity when charging at a constant current of 0.3 mA / cm ² and changing the discharge current to 0.5, 2.0, 4.0, and 6.0 mA / cm ^2. Are shown in Table 1.

Comparative Example 2 Example 1 except that the compression force in the press was 140 MPa.
A sample electrode was obtained through the same steps as described above. The thickness of the mixture of graphite particles and PVDF of the obtained sample electrode was 80 μm, and the density was 1.93 g / cm ³ . Next, a lithium secondary battery was manufactured through the same steps as in Example 16, and the same test as in Example 16 was performed. As a result, the discharge capacity was reduced by 15.7%.
As a quick charge / discharge characteristic evaluation, the battery was charged at a constant current of 0.3 mA / cm ² and the discharge current was 0.5, 2.0, 4.0, and 6.
Table 1 shows the discharge capacity when the discharge capacity was changed to 0 mA / cm ² .

[0034]

[Table 1]

As shown in Table 1, it is shown that the lithium secondary battery using the negative electrode for a lithium secondary battery of the present invention has a high discharge capacity and excellent rapid discharge characteristics.

[0036]

The negative electrode for a lithium secondary battery according to the first aspect is suitable for a high capacity lithium secondary battery. Claim 2
The negative electrode for a lithium secondary battery described in (3) and (3) is suitable for a lithium secondary battery having high capacity and excellent in rapid charge / discharge characteristics and cycle characteristics. According to the manufacturing method of the fourth aspect, a negative electrode for a lithium secondary battery that is suitable for a lithium secondary battery having high capacity and excellent in rapid charge / discharge characteristics and cycle characteristics can be obtained. The lithium secondary battery according to the fifth aspect has a high capacity and is excellent in rapid charge / discharge characteristics and cycle characteristics.

[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

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Jun Fujita 3-3-1 Ayukawacho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Chemical Co., Ltd. Yamazaki Plant (72) Inventor Kazuo Yamada 3-chome Ayukawacho, Hitachi City, Ibaraki Prefecture No. 1 F-term in Hitachi Chemical Co., Ltd. Yamazaki Plant (reference) 4G046 EA06 EC02 EC06 5H029 AJ02 AJ05 AK03 AL07 AM02 AM03 AM04 AM07 CJ06 CJ08 DJ07 DJ08 DJ16 EJ01 EJ12 HJ05 HJ07 HJ08 5H050 AA02 AA07 DA07 CB08 GA10 HA05 HA07 HA08

Claims (8)

[Claims] 1. A negative electrode for a lithium secondary battery obtained by integrating a current collector with a mixture of graphite particles and an organic binder, wherein the graphite particles have an aspect ratio of 1.2 to 5; A negative electrode for a lithium secondary battery, wherein the density of the mixture of the graphite particles and the organic binder after integration is 1.5 to 1.9 g / cm ³ . 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the graphite particles have an aspect ratio of 1.3 to 3. 3. A graphite particle having a specific surface area of 1.5 to ⁵ m ² /
3. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode is g. 4. The negative electrode for a lithium secondary battery according to claim 1, wherein the graphite particles have an average particle size of 1 to 100 μm. 5. A graphite particle used for producing a negative electrode for a lithium secondary battery, wherein the graphite particle is a mixture of a mixture of graphite particles and an organic binder and a current collector. For use in producing a negative electrode for a lithium secondary battery having a density of 1.5 to 1.9 g / cm ³ , and for an anode of a lithium secondary battery having an aspect ratio of 1.2 to 5. Graphite particles. 6. The graphite particles for a negative electrode of a lithium secondary battery according to claim 5, wherein the graphite particles have an aspect ratio of 1.3 to 3. 7. The graphite particles having a specific surface area of 1.5 to ⁵ m ² /
7. The graphite particles for a negative electrode of a lithium secondary battery according to claim 5, which are g. 8. The graphite particles for a negative electrode of a lithium secondary battery according to claim 5, wherein the average particle size of the graphite particles is 1 to 100 μm.