JP3487155B2 - Carbon particles, negative electrode for lithium secondary battery and lithium secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to carbon particles, a negative electrode for a lithium secondary battery, and a lithium secondary battery. More specifically, the present invention relates to a lithium secondary battery having excellent cycle characteristics and high capacity, which is suitable for use in portable devices, electric vehicles, power storage, and the like, and a lithium secondary battery negative electrode and carbon particles for obtaining the same.

[0002]

BACKGROUND ART Conventional graphite particles are, for example, natural graphite particles,
There are artificial graphite particles obtained by graphitizing coke, artificial polymer particles obtained by graphitizing an organic polymer material or pitch, graphite particles obtained by crushing them, and graphite particles obtained by crushing a high-density graphite compact. 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 Examined Patent Publication Sho 62-2343
As disclosed in Japanese Patent Publication No. 3, the use of graphite for the negative electrode solves the problem of internal short circuit due to lithium dendrites and improves cycle characteristics.

However, in graphite materials such as natural graphite in which graphite crystals have been developed and artificial graphite obtained by graphitizing coke, the bonding force between the layers of the crystals in the c-axis direction is weaker than that in the planar direction of the crystals. Therefore, the pulverization breaks the bond between the graphite layers to form so-called graphite particles having a large aspect ratio. Since scaly graphite has a large aspect ratio, when it is kneaded with a binder and applied to a current collector to prepare an electrode, the scaly graphite particles are oriented in the plane direction of the current collector, resulting in graphite crystals. The expansion and contraction in the C-axis direction caused by the repeated storage and release of lithium causes the inside of the electrode to be destroyed, which not only causes a problem of deterioration of cycle characteristics, but also tends to deteriorate rapid charge and discharge characteristics. Therefore,
There is a demand for a graphite powder having a small irreversible capacity in the first cycle of a lithium secondary battery, a high capacity, and improved cycle characteristics.

[0004]

The invention described in claim 1 provides a carbon particle suitable for a lithium secondary battery having a high capacity and excellent cycle characteristics. In addition to the object of the invention described in claim 1, the invention described in claim 2 provides carbon particles suitable for a higher capacity lithium secondary battery. The invention according to claim 3 provides carbon particles suitable for a lithium secondary battery having a high capacity, a small irreversible capacity in the first cycle, and an excellent cycle characteristic. The invention according to claim 4 provides a carbon particle suitable for a lithium secondary battery, which has a high capacity, a small irreversible capacity in the first cycle, an excellent cycle characteristic, and an excellent rapid charge / discharge characteristic. . The invention according to claim 5 provides a negative electrode for a lithium secondary battery, which has a high capacity, a small irreversible capacity in the first cycle, an excellent cycle characteristic, and an excellent rapid charge / discharge characteristic. The invention according to claim 6 has a high capacity and a small irreversible capacity in the first cycle,
The present invention provides a lithium secondary battery having excellent cycle characteristics and rapid charge / discharge characteristics.

[0005]

According to the present invention, the aspect ratio is 5 or less, and the formula (I) is used.

[Equation 2] Relates to carbon particles having a compression degree of 25% or more. Further, in the present invention, the interlayer distance d (002) of the crystal is 3.
The present invention relates to the carbon particles which are graphite particles having a particle size of 4Å or less. The present invention also relates to the above carbon particles having a specific surface area of 8 m ² / g or less. The present invention also relates to the above-mentioned carbon particles obtained by assembling or bonding a plurality of flat particles so that their orientation planes are non-parallel. The present invention also relates to a negative electrode for a lithium secondary battery containing the carbon particle according to any one of the above. The present invention also relates to a lithium secondary battery comprising the above negative electrode and a positive electrode containing a lithium compound.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The carbon particles of the present invention are required to have an aspect ratio of 5 or less and a compressibility represented by the above formula (I) of 25% or more. The degree of compression in the present invention is
It is calculated by the above formula (I) from the measured values of the solid apparent specific gravity and the loose apparent specific gravity. The loose apparent specific gravity is measured by using a funnel to put a carbon particle sample into a 100-ml graduated cylinder of known mass until it freely falls from the mouth of the graduated cylinder to 100 ml, and measure the weight of the graduated cylinder. Using the sample weight obtained by subtraction, it is calculated by (sample weight) / (sample volume). Further, the solidified apparent specific gravity was measured by inserting a rubber stopper into the measuring cylinder after the measurement of the loose apparent specific gravity, dropping the sample from the height of 5 cm 50 times, and reading the volume of the compressed sample, (sample weight) / (50
It is calculated by the sample volume after one drop.

By using the carbon particles of the present invention for the negative electrode, the cycle characteristics of the lithium secondary battery to be produced can be improved. The compressibility of the carbon particles of the present invention is 25
% Is required, 26% or more is preferable, 29% or more is more preferable, and 31% or more is further preferable. If the degree of compression of carbon particles is less than 25%, the cycle characteristics of the lithium secondary battery to be manufactured deteriorate. The upper limit of the degree of compression of carbon particles is not particularly limited, but is usually 50% or less.

The aspect ratio of the carbon particles of the present invention is required to be 5 or less, and more preferably 3 or less. When the aspect ratio exceeds 5, the cycle characteristics tend to deteriorate and the rapid charge / discharge characteristics also tend to deteriorate. In addition, the aspect ratio is such that the length in the major axis direction of the carbon particles is A,
When the length in the minor axis direction is B, it is represented by A / B. The aspect ratio in the present invention is obtained by enlarging carbon particles with a microscope, arbitrarily selecting 10 carbon particles, measuring A / B, and taking the average value thereof.

Further, the carbon particles used in the present invention are preferably graphite particles, and the crystal interlayer distance d (00
2) is preferably 3.4 Å or less, and 3.38 Å
It is more preferable if it is not more than 3.37, and it is more preferable if it is not more than 3.37. The interlayer distance d (002) of the crystal is 3.4Å
If it exceeds, the discharge capacity tends to be small. The d (002) of the carbon particles of the present invention was measured by wide-angle X method
It can be determined by line diffraction measurement. The crystallite size Lc (002) in the C-axis direction of the crystal is preferably 500 Å or more, more preferably 700 Å or more, and more preferably 10
More preferably, it is 00Å or more. The true specific gravity of the carbon particles of the present invention is preferably 2.1 g / cm ³ or more, and 2.
More preferably, it is 2 g / cm ³ or more. The true specific gravity of the carbon particles of the present invention can be determined by the butanol substitution method.
The carbon particles of the present invention preferably have high crystallinity in terms of discharge capacity, and when the crystallinity is low, Lc (002) and true specific gravity tend to be low.

[0010] carbon particles of the present invention preferably has a specific surface area of less 8m ² / g, more preferably not more than 5 m ² / g or less. When the specific surface area exceeds 8 m ² / g, the irreversible capacity of the obtained lithium secondary battery in the first cycle becomes large,
Energy density tends to be small. The specific surface area can be measured by a known method such as a nitrogen gas adsorption BET method.

The carbon particles of the present invention are preferably carbon particles having a structure in which a plurality of flat particles are aggregated or combined so that their orientation planes are non-parallel. In the present invention,
The flat particles are particles having a long axis and a short axis, and do not have a perfect spherical shape. Scale-like,
This includes scales, some lumps, and the like.
In the carbon particles, the orientation planes of the plurality of flat particles are non-parallel, and the flat surface having each particle shape, in other words, the plane that is the most flat is the orientation surface, and the plurality of flat particles are respectively Refers to a state in which the orientation planes of are assembled in a certain direction without being aligned.

In this carbon particle, the flat particles are aggregated or bonded, but the bonding means that the mutual particles are pitch,
Through a carbonaceous material obtained by carbonizing a binder such as a resin, it means a state in which they are chemically bonded, and aggregate particles are not chemically bonded to each other, but due to their shape, A state in which the shape of the aggregate is maintained. From the viewpoint of mechanical strength, those bonded are preferable. When such carbon particles are used for the negative electrode, the carbon particles on the current collector are less likely to be oriented, and the wettability with the electrolytic solution is improved, and lithium is easily absorbed and released in the negative electrode. It is possible to improve the rapid charge / discharge characteristics of the secondary battery.

In the present invention, the method for producing the carbon particles having the above characteristics is not particularly limited. For example, a graphitizable aggregate or graphite, a graphitizable binder and a graphitization catalyst are mixed and then formed into a predetermined shape. Graphite particles obtained by heat-treating the molded graphite precursor in a non-oxidizing atmosphere are preferable. Further, the heat treatment may be carried out after mixing a graphitizable aggregate or graphite and a graphitizable binder, if necessary, and then pulverizing.

As the aggregate which can be graphitized, coke powder, resin carbide and the like can be used, but there is no particular limitation as long as it is a powder material which can be graphitized. As the graphite, for example, natural graphite powder, artificial graphite powder or 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. As a binder, other than tar, pitch, etc.
Examples of organic materials include thermosetting resins and thermoplastic resins.

The graphitizing catalyst is not particularly limited, and metals such as silicon, boron, iron, titanium and nickel, and oxides and carbides thereof can be used, but the average particle size is 50 μm.
It is preferably a powdery compound of silicon, boron or iron of m or less. The addition amount of the graphitization catalyst is preferably 0.5 to 50% by weight, more preferably 1 to 40% by weight, and further preferably 3 to 30% based on the total amount of the material.
It is set in the range of% by weight. If it is less than 0.5% by weight, the discharge capacity of the obtained lithium secondary battery tends to decrease, and if it exceeds 50% by weight, the cycle characteristics tend to deteriorate.

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 softening temperature of the binder or higher, and the temperature varies depending on the type of binder used. But 80-35
The range of 0 ° C is preferred. The shape of the graphite precursor to be molded is
Although not particularly limited, for example, a block shape, a cylindrical shape, a lump shape, etc. are preferable in terms of workability and packing efficiency during graphitization.

The graphite precursor is preferably fired under the condition that the graphite molded body is difficult to oxidize, and examples thereof include a method of firing in a nitrogen atmosphere, an argon atmosphere, and a vacuum, but there is no particular limitation. . The firing temperature is 2000
C. or higher is preferable, 2500 ° C. or higher is more preferable, and 2800 ° C. or higher is further preferable. If the firing temperature is low, the graphite crystals are poorly developed and the discharge capacity tends to be low. Further, the temperature of the firing may be raised stepwise, for example, it is possible to perform the calcination once at about 500 to 1200 ° C. and then the firing at 2000 ° C. or more. It should be noted that calcination may be carried out before calcination and after adjusting the particle size.

The method for pulverizing the obtained graphite compact is not particularly limited, but for example, impact pulverization such as jet mill, hammer mill, pin mill, etc. may be used for specific surface area, irreversible capacity,
It is preferable in terms of discharge capacity. The average particle size of the crushed carbon particles is preferably 10 to 50 μm. However, crush it before firing,
If the particle size is adjusted, it may not be crushed. In the present invention, the average particle size can be measured with a laser diffraction particle size distribution meter.

The carbon particles of the present invention are used for the negative electrode of a lithium secondary battery. In this case, it is usually kneaded with an organic binder and a solvent to form a paste, which 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, or the like can be used.

Polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile and the like can be used as the high molecular compound having a high ionic conductivity. The mixing ratio of the carbon particles and the organic binder is preferably 3 to 20 parts by weight of the organic binder with respect to 100 parts by weight of the carbon particles.

The solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone, dimethylformamide and isopropanol. The amount of solvent is also not particularly limited,
The carbon particles are kneaded with an organic binder and a solvent to adjust the viscosity, and then coated on a current collector and integrated with the current collector to form a negative electrode. As the current collector, a metal current collector such as a foil of nickel or copper or a mesh can be used. The integration can be performed by a molding method such as roll and press, or these may be combined and integrated.

The negative electrode thus obtained is used in the lithium secondary battery of the present invention together with the positive electrode containing a lithium compound. A lithium secondary battery can be obtained, for example, by arranging a positive electrode and a negative electrode so as to face each other via a separator and injecting an electrolytic solution, which is a lithium secondary battery using a conventional carbon material for the negative electrode. Compared to batteries,
High capacity and excellent cycle characteristics and rapid charge / discharge characteristics.

The positive electrode of the lithium secondary battery in the present invention contains a lithium compound, but its material is not particularly limited,
For example, LiNiO ₂ , LiCoO ₂ , LiMn ₂ O ₄ or the like can be used alone or in combination. The lithium secondary battery in the present invention usually contains an electrolyte solution containing a lithium compound, in addition to the positive electrode and the negative electrode. As the electrolytic solution, Li
ClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiS
A so-called organic electrolyte in which a lithium salt such as O ₃ CF ₃ is dissolved in a non-aqueous solvent such as ethylene carbonate, diethyl carbonate, dimethoxyethane, dimethyl carbonate, tetrahydrofuran, propylene carbonate, or a solid or gel so-called polymer electrolyte is used. Can be used. As the separator, for example, a nonwoven fabric containing polyolefin such as polyethylene or polypropylene as a main component, a cloth, a microporous film, or a combination thereof can be used. If the lithium secondary battery to be manufactured has a structure in which the positive electrode and the negative electrode do not come into direct contact with each other, it is not necessary to use a separator.

Incidentally, FIG. 1 shows a partial sectional front view of an example of a cylindrical lithium ion secondary battery. The cylindrical lithium ion secondary battery shown in FIG. 1 has a positive electrode 1 processed into a thin plate shape.
And the negative electrode 2 processed in the same manner is wound with the negative electrode 2 superposed through a separator 3 such as a polyethylene microporous membrane,
This is inserted into a battery can 7 made of metal or the like and hermetically 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 bottom of the battery via the negative electrode tab 5. The positive electrode lid 6 is fixed to a battery can (positive electrode can) 7 with a gasket 8.

[0025]

EXAMPLES Examples of the present invention will be described below. Example 1 50 parts by weight of needle coke powder having an average particle size of 10 μm, 15 parts by weight of pitch, and iron oxide 15 having an average particle size of 1 μm
200 parts by weight by mixing 10 parts by weight of coal tar
It was stirred for 1 hour. This mixture is then treated with an average particle size of 25
The crushed product was crushed into μm, and the crushed product was put into a mold and press-molded to obtain a rectangular parallelepiped 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 to obtain a graphite compact. Further, this graphite compact was crushed to obtain graphite particles. Table 1 shows the measurement results of the loose apparent specific gravity, the solidified apparent specific gravity, the compression degree, the average particle size, the specific surface area, and the aspect ratio of the obtained graphite particles.

Next, a lithium secondary battery was produced using the obtained graphite particles. The lithium secondary battery of the present invention shown in FIG. 1 was prepared as follows. 88% by weight of LiCoO ₂ was used as a positive electrode active material, 7% by weight of scaly natural graphite having an average particle diameter of 1 μm was added as a conductive agent, and 5% by weight of polyvinylidene fluoride (PVDF) was added as a binder. -Methyl-2-pyrrolidone was added and mixed to prepare a slurry of the positive electrode mixture. Similarly, the graphite particles prepared by the above method as the negative electrode active material and PV as the binder were used.
10% by weight of DF was added, and N-methyl-2-pyrrolidone was added thereto and mixed to prepare a slurry of the negative electrode mixture. The positive electrode mixture was applied on both sides of an aluminum foil having a thickness of 25 μm, and then vacuum dried at 120 ° C. for 1 hour. After vacuum drying, the electrode was pressure-molded by a roller press to have a thickness of 190 μm. The amount of mixture applied per unit area is 5
It was 7 mg / cm ² and was cut into a size of width 40 mm and length 285 mm to prepare a positive electrode. However, the length of both ends of the positive electrode is 10 mm
The positive electrode mixture is not applied to the portion of (1) and the aluminum foil is exposed, and the positive electrode tab is pressure-bonded to this one by ultrasonic bonding.

On the other hand, the negative electrode mixture was applied to both sides of a copper foil having a thickness of 10 μm, and then vacuum dried at 120 ° C. for 1 hour. After vacuum drying, the electrode was pressure-molded by a roller press to have a thickness of 175 μm. The amount of the mixture applied per unit area was 24 mg / cm ² , and the negative electrode was prepared by cutting into a size of width 40 mm and length 290 mm. Similarly to the positive electrode, the negative electrode mixture was not applied to the portions of both ends of the negative electrode having a length of 10 mm, and the copper foil was exposed. A negative electrode tab was pressure-bonded to this one by ultrasonic bonding. As the separator, a polyethylene microporous membrane having a thickness of 25 μm and a width of 44 mm was used. Positive electrode, separator,
The negative electrode and the separator were superposed in this order and wound to form an electrode group. This was inserted into an AA size battery can, the negative electrode tab was welded to the bottom of the can, and a narrowed portion for crimping the positive electrode lid was provided. After injecting into a battery can an electrolyte solution in which 1 mol / liter of lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate having a volume ratio of 1: 1 and after welding a positive electrode tab to a positive electrode lid, A battery was manufactured by crimping the positive electrode lid. Using this battery, a charge / discharge current of 300 mA and a charge / discharge end voltage of 4.2 V and 2.8, respectively.
The charging and discharging was repeated as V. The discharge capacity at the second cycle and the discharge capacity retention rate at the 300th cycle are shown. The charge / discharge current was increased from 300 mA to 900 mA, and the discharge maintenance ratio was evaluated to evaluate the rapid charge / discharge property.

Example 2 50 parts by weight of needle coke powder having an average particle size of 10 μm, 20 parts by weight of pitch, 1 part by weight of silicon carbide having an average particle size of 0.6 μm, and 10 parts by weight of coal tar were mixed to obtain 2 parts.
The mixture was stirred at 00 ° C for 3 hours. Next, this mixture was crushed to an average particle size of 15 μm, and the crushed product was put into a mold and press-molded to obtain a rectangular parallelepiped graphite precursor. This graphite precursor was heat-treated at 900 ° C. in a nitrogen atmosphere, pulverized, and further heat-treated at 3000 ° C. in a nitrogen atmosphere to obtain a graphite powder.
Table 1 shows the measurement results of the loose apparent specific gravity, the solidified apparent specific gravity, the compression degree, the average particle size, the specific surface area, and the aspect ratio of the obtained graphite particles. Next, a lithium secondary battery was prepared from the obtained graphite particles by the same method as in Example 1, and the same test as in Example 1 was performed. The results are shown in Table 1.

Example 3 50 parts by weight of needle coke powder having an average particle size of 10 μm, 25 parts by weight of pitch, 1 part by weight of boric acid and 10 parts by weight of coal tar were mixed and stirred at 200 ° C. for 3 hours.
Next, this mixture was crushed to an average particle size of 15 μm, and the crushed product was put into a mold and press-molded to obtain a rectangular parallelepiped graphite precursor. This graphite precursor was heat-treated at 900 ° C. in a nitrogen atmosphere, pulverized, and further heated to 2700 in an argon atmosphere.
Heat treatment was performed at ° C to obtain graphite powder. Table 1 shows the measurement results of the loose apparent specific gravity, the solidified apparent specific gravity, the compression degree, the average particle size, the specific surface area, and the aspect ratio of the obtained graphite particles. Then
A lithium secondary battery was produced from the obtained graphite particles in the same manner as in Example 1, and the same test as in Example 1 was performed.
The results are shown in Table 1.

Comparative Example 1 Graphite particles produced by the same method as in Example 1 were pulverized with a jet mill to produce graphite particles. Loose apparent specific gravity, solidified apparent specific gravity, compressibility, average particle size of the obtained graphite particles,
Table 1 shows the measurement results of the specific surface area and the aspect ratio. Next, a lithium secondary battery was prepared from the obtained graphite particles by the same method as in Example 1, and the same test as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 2 Graphite particles were produced by crushing natural flake graphite originating from China with a jet mill. Loose apparent specific gravity, solidified apparent specific gravity, compressibility, average particle size, specific surface area of the obtained graphite particles,
Table 1 shows the measurement results of the aspect ratio. Next, a lithium secondary battery was prepared from the obtained graphite particles by the same method as in Example 1, and the same test as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 3 A lithium secondary battery was prepared in the same manner as in Example 1 except that graphite SFG-44 manufactured by Lonza Co. was used as the graphite particles, and the same test as in Example 1 was carried out. The results are shown in Table 1.
Shown in. Table 1 shows the measurement results of the loose apparent specific gravity, the solidified apparent specific gravity, the compression degree, the average particle size, the specific surface area, and the aspect ratio of the obtained graphite particles. Next, a lithium secondary battery was prepared from the obtained graphite particles by the same method as in Example 1, and the same test as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 4 Mesophase microbeads having an average particle diameter of 12 μm were fired at 900 ° C. in a nitrogen atmosphere, and then heat-treated at 2800 ° C. in a nitrogen atmosphere to obtain graphite particles. Table 1 shows the measurement results of the loose apparent specific gravity, the solidified apparent specific gravity, the compression degree, the average particle size, the specific surface area, and the aspect ratio of the obtained graphite particles.
Then, the obtained graphite particles were treated in the same manner as in Example 1,
A lithium secondary battery was produced and the same test as in Example 1 was performed. The results are shown in Table 1.

[0034]

[Table 1]

As shown in Table 1, it was shown that the graphite particles of the present invention have a high capacity and are suitable as a negative electrode for a lithium secondary battery having excellent cycle characteristics.

[0036]

The carbon particles according to claim 1 have a high capacity,
It is suitable for a lithium secondary battery having excellent cycle characteristics. The carbon particles according to claim 2 have a higher capacity in addition to the effect of the graphite particles according to claim 1. The carbon particles according to claim 3 have a high capacity, excellent cycle characteristics, and a small irreversible capacity in the first cycle, and are suitable for a lithium secondary battery. The carbon particles according to claim 4 have a high capacity, excellent cycle characteristics, and rapid charge / discharge characteristics, and are suitable for a lithium secondary battery. The negative electrode for a lithium secondary battery according to claim 5 has a high capacity, excellent cycle characteristics, and excellent rapid charge / discharge characteristics. The lithium secondary battery according to claim 6 has a high capacity, excellent cycle characteristics, and further excellent rapid charge / discharge characteristics.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a lithium secondary battery of the present invention.

[Explanation of symbols]

1 positive electrode 2 Negative electrode 3 separator 4 Positive tab 5 Negative electrode tab 6 Positive lid 7 battery cans 8 gasket

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Fujita 3-3-1 Ayukawa-cho, Hitachi City, Ibaraki Prefecture In the Yamazaki Factory of Nitatsu Kasei Co., Ltd. (72) Kazuo Yamada Inventor, 3-chome Ayukawa-cho, Hitachi City, Ibaraki Prefecture No. 3 No. 1 Yamashita Plant, Nititsu Kasei Co., Ltd. (56) Reference JP-A-9-231974 (JP, A) JP-A-10-330107 (JP, A) JP-A-11-139816 (JP, A) ) International publication 95/028011 (WO, A1) International publication 97/042671 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C01B 31/04 101 H01M 4/02 H01M 4/58 H01M 10/40

Claims (5)

(57) [Claims] 1. An aspect ratio of 5 or less and a value represented by the formula (I): A carbon particle having a compression degree of 25% to 50% and an interlayer distance d (002) of graphite crystals of 3.4 Å or less. 2. The carbon particles according to claim 1, which have a specific surface area of 8 m ² / g or less. 3. The carbon particles according to claim 1 or 2, wherein a plurality of flat particles are aggregated or combined so that the orientation planes are non-parallel. 4. A negative electrode for a lithium secondary battery, containing the carbon particles according to claim 1. 5. A lithium secondary battery comprising the negative electrode according to claim 4 and a positive electrode containing a lithium compound.