JP4811699B2 - Negative electrode for lithium secondary battery - Google Patents

Description

  The present invention relates to a novel graphite particle for a lithium secondary battery negative electrode. More particularly, the present invention relates to a graphite particle suitable for use in a negative electrode of a lithium secondary battery excellent in rapid charge / discharge characteristics, cycle characteristics and the like, which is suitable for use in portable equipment, electric vehicles, power storage and the like.

  Examples of conventional graphite particles include 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 pulverizing these. 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, as disclosed in Japanese Examined Patent Publication No. 62-23433, the use of graphite for the negative electrode eliminates the problem of internal short circuit due to lithium dendrite and improves the cycle characteristics.

However, natural graphite particles in which graphite crystals are developed and artificial graphite particles graphitized from coke have a weaker bonding force between crystals in the c-axis direction than in the crystal plane direction. Bonds between layers are broken and so-called scaly graphite particles having a large aspect ratio are obtained. Since the scaly graphite particles have a large aspect ratio, when the electrodes are produced by kneading with a binder and applying to the current collector, the scaly graphite particles are oriented in the surface direction of the current collector, and as a result Further, there is a problem that the internal characteristics of the electrode are broken by the strain in the c-axis direction generated by repeated insertion and extraction of lithium into and from the graphite crystal, and the cycle characteristics are deteriorated. Therefore, there is a demand for graphite particles that can improve the cycle characteristics of lithium secondary batteries.
Japanese Examined Patent Publication No. 62-23433

  The inventions described in claims 1, 2 and 5 provide graphite particles suitable for a lithium secondary battery having excellent cycle characteristics.

The invention according to claim 3 provides graphite particles suitable for a lithium secondary battery excellent in rapid charge / discharge characteristics and cycle characteristics.
The invention described in claim 4 provides graphite particles that 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 present invention relates to graphite particles in which the pore volume of pores having a size in the range of 10 ² to 10 ⁶ Å is 0.4 to 2.0 cc / g per graphite particle weight.
In the present invention, the pore volume of pores having a size in the range of 1 × 10 ² to 2 × 10 ⁴ Å is applied to graphite particles having a pore volume of 0.08 to 0.4 cc / g per graphite particle weight.
In addition, the present invention relates to the graphite particles obtained by collecting or combining a plurality of flat particles so that the orientation planes are non-parallel.
The present invention also relates to a graphite particle having an aspect ratio of 5 or less.
Moreover, this invention relates to the said graphite particle whose specific surface area is 8 m < ² > / g or less.

The present invention also relates to a graphite particle for a lithium secondary battery negative electrode, which is a graphite particle having a layered structure therein and in which the layers inside the particle are arranged without being aligned in a certain direction.
The present invention also relates to the above-described graphite particles for lithium secondary battery negative electrodes, wherein the pore volume of pores having a size in the range of 10 ² to 10 ⁶ Å is 0.4 to 2.0 cc / g per graphite particle weight. .
The present invention also relates to the graphite particle for a negative electrode of a lithium secondary battery, wherein the graphite particles have an aspect ratio of 5 or less.
Furthermore, this invention relates to the said graphite particle for lithium secondary battery negative electrodes whose specific surface area is 8 m < ² > / g or less.
Furthermore, the present invention provides the negative electrode for a lithium secondary battery in which the pore volume of pores having a size in the range of 1 × 10 ² to 2 × 10 ⁴ Å is 0.08 to 0.4 cc / g per graphite particle weight. It relates to graphite particles.

The graphite particles of the present invention are characterized by their pores 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 graphite particle weight. When the graphite particles are used for the negative electrode, the pores of the graphite particles absorb the expansion and contraction of the electrode that accompanies charging and discharging, so that the destruction inside the electrode is suppressed, and the cycle characteristics of the resulting lithium secondary battery are improved. Can be improved. The pore volume of pores in the range of 10 ² to 10 ⁶よ り is more preferably in the range of 0.4 to 1.5 cc / g, and in the range of 0.6 to 1.2 cc / g. Further preferred. If the total pore volume is less than 0.4 cc / g, the cycle characteristics deteriorate, and if it exceeds 2.0 cc / g, a large amount of binder used when integrating the graphite particles and the current collector is required, There is a problem that the capacity of the lithium secondary battery to be produced decreases. The pore volume can be determined by measuring the pore size distribution by mercury porosimetry. The pore size can also be determined by measuring the pore size distribution by mercury porosimetry.

Second, the pore volume of pores in the range of 1 × 10 ² to 2 × 10 ⁴ Å is 0.08 to 0.4 cc / g per graphite particle weight. When the graphite particles are used for the negative electrode, the pores of the graphite particles absorb the expansion and contraction of the electrode that accompanies charging and discharging, so that the destruction inside the electrode is suppressed, and the cycle characteristics of the resulting lithium secondary battery are improved. Can be improved. The pore volume in the range of 1 × 10 ^{2 to} 2 × 10 ⁴ Å is more preferably 0.1 to 0.3 cc / g. If the pore volume in this size range is less than 0.08 cc / g, the cycle characteristics decrease. If it exceeds 0.4 cc / g, many binders are used when integrating graphite particles and the current collector. There is a problem that the capacity of the lithium secondary battery to be produced is reduced. The pore volume in this range can also be determined by measuring the pore size distribution by mercury porosimetry.

Moreover, the graphite particles of the present invention are preferably those in which a plurality of flat particles are aggregated or bonded so that the orientation planes are non-parallel.
In the present invention, flat particles are particles having a major axis and a minor axis, and are not completely spherical. This includes, for example, those having a shape such as a scale shape, a scale shape, and a partial lump shape.
In graphite particles, the orientation planes of a plurality of flat particles are non-parallel. The flat surfaces in the shape of each particle, in other words, the plane that is closest to the plane is the orientation plane, and the plurality of flat particles are A state in which the orientation planes are gathered together in a certain direction.

In this graphite particle, the flat particles are aggregated or bonded, but the bond is a state in which the particles are chemically bonded through carbonaceous carbonized binder such as tar and pitch. The term “aggregate” refers to a state in which the particles are not chemically bonded to each other, but the shape of the aggregate is maintained due to the shape and the like. From the viewpoint of mechanical strength, those bonded are preferable.
In one graphite particle, the number of flat particles aggregated or bonded is preferably 3 or more. The size of the individual flat particles is preferably 1 to 100 μm in particle size, and preferably 2/3 or less of the average particle size of the aggregated or bonded graphite particles.

When the graphite particles are used for the negative electrode, the graphite particles are less likely to be oriented on the current collector, the wettability with the electrolyte is improved, and lithium is easily occluded / released into the negative electrode graphite. The rapid charge / discharge characteristics and cycle characteristics of the secondary battery can be improved.
FIG. 1 shows a scanning electron micrograph of the particle structure of an 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 the cross section of the graphite particles. In (a), it can be observed that there are many fine scaly graphite particles that are bonded with the orientation planes of these particles non-parallel to form graphite particles.

Further, graphite particles having an aspect ratio of 5 or less are preferred because the particles tend not to be oriented on the current collector, and lithium can be easily inserted and extracted as described above.
The aspect ratio is more preferably 1.2-5. If the aspect ratio is less than 1.2, the contact area between particles tends to decrease, and 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 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 enlarging graphite particles with a microscope, arbitrarily selecting 100 graphite particles, measuring A / B, and taking the average value.
Further, 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 above-mentioned flat particles and the orientation planes are non-parallel. It is more preferable to use graphite particles aggregated or bonded to each other.

The graphite particles of 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 the negative electrode, the rapid charge / discharge characteristics and cycle characteristics of the obtained lithium secondary battery can be improved, and the irreversible capacity in the first cycle can be reduced. When the specific surface area exceeds 8 m ² / g, the irreversible capacity of the first cycle of the obtained lithium secondary battery tends to be large, the energy density is small, and many binders are used when producing a negative electrode. Tend to be needed. The specific surface area is more preferably 1.5 to ⁵ m ² / g, more preferably ^{2 to 5} m ² / g, from the viewpoint that the rapid charge / discharge characteristics, cycle characteristics, and the like of the obtained lithium secondary battery are further improved. Is very preferred. The specific surface area can be measured by a known method such as the BET method (nitrogen gas adsorption method).

  Further, the crystal interlayer distance d (002) in the X-ray wide-angle diffraction of each graphite particle used in the present invention is preferably 3.38 mm or less, and more preferably in the range of 3.37 to 3.35 mm. When the crystal interlayer distance d (002) exceeds 3.38 mm, the discharge capacity tends to decrease. The crystallite size Lc (002) in the c-axis direction is preferably 500 Å or more, and more preferably 1000 to 100,000 Å. When the crystal interlayer distance d (002) decreases or the crystallite size Lc (002) in the c-axis direction increases, the discharge capacity tends to increase.

The method for producing graphite particles of the present invention is not particularly limited, but 1 to 50% by weight of a graphitization catalyst is added to a graphitizable aggregate or graphite and a graphitizable binder, mixed, burned and then pulverized. It is preferable to obtain graphite particles first.
Next, an organic binder and a solvent are added to the graphite particles and mixed to adjust the viscosity. Then, the mixture is applied to a current collector, dried to remove the solvent, and then pressurized to be integrated. Thus, a negative electrode for a lithium secondary battery can be obtained.

Examples of the aggregate that can be graphitized include coke powder and resin carbide, but there is no particular limitation as long as it is a powder material that can be graphitized. Among these, coke powder that is easily graphitized such as needle coke is preferable.
Moreover, as graphite, natural graphite powder, artificial graphite powder, etc. can be used, for example, but there is no particular limitation as long as it is powdery. 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, a graphitization catalyst such as a metal such as iron, nickel, titanium, silicon, or boron, or a carbide or oxide thereof can be used. Of these, silicon or boron carbides or oxides are preferred.
The addition amount of these graphitization catalysts is preferably 1 to 50% by weight, more preferably 5 to 40% by weight, and further preferably 5 to 30% by weight with respect to the obtained graphite particles. If the amount is less than wt%, the aspect ratio and specific surface area of the graphite particles tend to increase and the development of graphite crystals tends to deteriorate. On the other hand, if it exceeds 50 wt%, it is difficult to mix uniformly and workability tends to deteriorate. is there.

As the binder, for example, an organic material such as a thermosetting resin and a thermoplastic resin is preferable in addition to tar and pitch. The blending amount of the binder is preferably 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. More preferably. If the amount of the binder is too large or too small, the aspect ratio and specific surface area of the produced graphite particles tend to be large.
The method for 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, 50 to 300 ° C is preferable, and when the binder is a thermosetting resin, 20 to 100 ° C is preferable.

Next, the above mixture is fired and graphitized. In addition, you may shape | mold the said mixture in a predetermined shape before this process. Furthermore, after forming and pulverizing before graphitization to adjust the particle size, graphitization may be performed. Firing is preferably performed under conditions where the mixture is not easily oxidized, and examples thereof include a method of baking in a nitrogen atmosphere, an argon gas atmosphere, and in a vacuum. The graphitization temperature is preferably 2000 ° C. or higher, more preferably 2500 ° C. or higher, and further preferably 2800 ° C. to 3200 ° C.
When the graphitization temperature is low, the development of graphite crystals tends to be poor, the discharge capacity tends to be low, and the added graphitization catalyst tends to remain in the graphite particles produced. When 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, it is preferable to grind the obtained graphitized material. The method for pulverizing the graphitized material is not particularly limited, and known methods such as a jet mill, a vibration mill, a pin mill, a hammer mill and the like can be used. As for the particle size after pulverization, the average particle size is preferably 1 to 100 μm, and more preferably 10 to 50 μm. If the average particle size becomes too large, the surface of the electrode to be produced tends to be uneven. In the present invention, the average particle diameter can be measured with a laser diffraction particle size distribution meter.

By passing through the process shown above, the graphite particle of this invention can be obtained.
The obtained graphite particles are formed into a sheet shape, a pellet shape or the like by mixing an organic binder and a material containing a solvent.
As the organic binder, for example, polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, a high molecular compound having high ionic conductivity, and the like can be used.
In the present invention, polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile and the like can be used as the polymer compound having a high ionic conductivity.
Among these, a polymer compound having a high 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.
There is no restriction | limiting in particular as a solvent, N-methyl 2-pyrrolidone, a dimethylformamide, isopropanol etc. are used.
There is no restriction | limiting in particular in the quantity of a solvent, Although it should just be able to adjust to a desired viscosity, It is preferable to use 30 to 70 weight% with respect to a mixture.

As the current collector, for example, a metal current collector such as a foil or mesh of nickel, copper or the like can be used.
The integration can be performed by a molding method such as a roll or a press, or these may be combined and integrated.
The negative electrode thus obtained is used as a negative electrode for lithium secondary batteries such as lithium ion secondary batteries and lithium polymer secondary batteries. For example, in a lithium ion secondary battery, a positive electrode is disposed opposite to a separator, and an electrolytic solution is injected. According to the present invention, it is possible to produce a lithium secondary battery that is excellent in rapid charge / discharge characteristics and cycle characteristics and has a small irreversible capacity as compared with a lithium secondary battery that uses a conventional carbon material as a negative electrode.

There is no particular limitation on the material used for a cathode of a lithium secondary battery of the present invention may be used alone or as a mixture of _{LiNiO 2, LiCoO 2, LiMn 2} O 4 or the like.
As the electrolyte, lithium salts such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ are used in non-aqueous solvents such as ethylene carbonate, diethyl carbonate, dimethoxyethane, dimethyl carbonate, tetrahydrofuran, propylene carbonate, A so-called organic electrolytic solution dissolved or contained in a polymer solid electrolyte such as polyvinylidene fluoride can be used.

As a separator used when using a liquid electrolytic solution, for example, a nonwoven fabric, a cloth, a microporous film, or a combination thereof, which is mainly composed of a polyolefin such as polyethylene or polypropylene, can be used.
FIG. 2 shows a partial cross-sectional front view of an example of a cylindrical lithium secondary battery. The cylindrical lithium secondary battery shown in FIG. 2 is formed by winding a thin plate-like positive electrode 1 and a similarly processed negative electrode 2 with a separator 3 such as a polyethylene microporous membrane overlaid. This is inserted into a battery can 7 made of metal or the like and sealed. The positive electrode 1 is bonded to the positive electrode lid 6 via the positive electrode tab 4, and the negative electrode 2 is bonded to the battery bottom via the negative electrode tab 5. The positive electrode lid 6 is fixed to the battery can 7 with a gasket 8.

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. Subsequently, it was fired at 2800 ° C. in a nitrogen atmosphere and then pulverized to produce graphite particles having an average particle size of 30 μm. The obtained graphite particles were measured for pore size distribution by mercury porosimetry (using Shimadzu pore sizer 9320 type). As a result, the pores were in the range of 10 ² to 10 ⁶ 、, and the total pore volume per graphite particle weight Was 0.6 cc / g. The pore volume in the range of 1 × 10 ^{2 to} 2 × 10 ⁴ １０ was 0.20 cc / g per graphite particle weight. In addition, 100 graphite particles obtained were arbitrarily selected and the average value of the aspect ratio was measured. As a result, the specific surface area of the graphite particles by the BET method per 1.5 was 1.5 m ² / g. The inter-layer distance d (002) of the crystal by X-ray wide-angle diffraction was 3.362 mm, and the crystallite size Lc (002) was 1000 mm or more. Furthermore, according to the scanning electron microscope (SEM photograph) of the obtained graphite particles, the graphite particles had a structure in which flat particles were assembled or bonded so that a plurality of orientation planes were non-parallel.

Next, 10% by weight of polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone was added to 90% by weight of the obtained graphite particles in a solid content and kneaded to prepare a graphite paste. This graphite paste was applied to a rolled copper foil having a thickness of 10 μm, further dried, and compression molded at a surface pressure of 490 MPa (0.5 ton / cm ² ) to obtain a sample electrode. The thickness of the graphite particle layer was 90 μm and the density was 1.6 g / cm ³ .
The prepared sample electrode was subjected to constant current charge / discharge by the 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. Evaluation of the sample electrode was performed in a glass cell 9 as shown in FIG. 3, LiPF ₆ as an electrolytic solution 10 with ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC and DMC is put in a mixed solvent of 1: 1) in a volume ratio so that a solution dissolved to a concentration of 1 mol / liter is placed, the sample electrode 11, the separator 12 and the counter electrode 13 are laminated and arranged, and the reference electrode 14 is further arranged. A lithium secondary battery was produced by hanging from the top. Note that metallic lithium was used for the counter electrode 13 and the reference electrode 14, and polyethylene micropores were used for the separator 4. Using the obtained lithium secondary battery, the sample electrode 11 and the counter electrode 13 were charged to 5 mV (Vvs. Li / Li ⁺ ) with a constant current of 0.5 mA / cm ^{2 with} respect to the area of the sample electrode. The test of discharging to 1 V (Vvs. Li ^/ Li ⁺ ) was repeated. Table 1 shows the charge capacity per unit weight of the graphite particles at the cycle, the discharge capacity, and the discharge capacity per unit weight of the graphite particles at 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. Subsequently, it was fired at 2800 ° C. in a nitrogen atmosphere and then pulverized to obtain graphite particles having an average particle size of 30 μm. The obtained graphite particles were measured for pore size distribution by mercury porosimetry (using Shimadzu pore sizer 9320 type). As a result, the pores were in the range of 10 ² to 10 ⁶ 、, and the total pore volume per graphite particle weight Was 1.5 cc / g. The pore volume in the range of 1 × 10 ^{2 to} 2 × 10 ⁴ １０ was 0.13 cc / g per graphite particle weight. Further, 100 graphite particles obtained were arbitrarily selected and the average value of the aspect ratio was measured. As a result, it was 2.3. The specific surface area of the graphite particles by the BET method was 3.6 m ² / g. The crystal interlayer distance d (002) by X-ray wide angle diffraction was 3.361３６, the crystallite size Lc (002) was 1000Å, and the crystallite size Lc (002) was 1000Å or more. Further, the obtained graphite particles had a structure in which flat particles were assembled or bonded so that the plurality of orientation planes were non-parallel.
A lithium secondary battery was produced through the same steps as in Example 1 and the same test as in Example 1 was performed. Table 1 shows the charge capacity per unit weight of the graphite particles in the first cycle, the discharge capacity, and the discharge capacity per unit weight of the graphite particles in the 30th cycle.

Comparative Example 1
Mesocarbon microbeads (manufactured by Kawasaki Steel Corporation, trade name KMFC) were fired at 2800 ° C. in a nitrogen atmosphere to obtain graphite particles having an average particle diameter of 25 μm. The obtained graphite particles were measured for pore size distribution by mercury porosimetry (using Shimadzu pore sizer 9320 type). As a result, the pores were in the range of 10 ² to 10 ⁶ 、, and the total pore volume per graphite particle weight Was 0.35 cc / g. The pore volume in the range of 1 × 10 ^{2 to} 2 × 10 ⁴ １０ was 0.06 cc / g per graphite particle weight. Further, 100 graphite particles obtained were arbitrarily selected and the average value of the aspect ratio was measured. As a result, the specific surface area of the graphite particles according to the BET method was 1.4 m ² / g. The crystal interlayer distance d (002) by line wide angle diffraction was 3.37 cm, and the crystallite size Lc (002) was 500 mm.
Thereafter, a lithium secondary battery was manufactured through the same process as in Example 1, and the same test as in Example 1 was performed. Table 1 shows the charge capacity per unit weight of the first cycle graphite particles, the discharge capacity, and the discharge capacity per unit weight of the 30th cycle graphite particles.

Comparative Example 2
50 parts by weight of coke powder having an average particle diameter of 5 μm, 10 parts by weight of pitch, 30 parts by weight of iron oxide having an average particle diameter of 65 μm and 20 parts by weight of coal tar were mixed and stirred at 200 ° C. for 1 hour. Subsequently, it was fired in a nitrogen atmosphere at 2800 ° C. and then pulverized to obtain graphite particles having an average particle diameter of 15 μm. The obtained graphite particles were measured for pore size distribution by mercury porosimetry (using Shimadzu pore sizer 9320 type). As a result, the pores were in the range of 10 ² to 10 ⁶ 、, and the total pore volume per graphite particle weight Was 2.1 cc / g. The pore volume in the range of 1 × 10 ^{2 to} 2 × 10 ⁴ １０ was 0.42 cc / g per graphite particle weight. Further, 100 graphite particles obtained were arbitrarily selected and the average value of the aspect ratio was measured. As a result, the specific surface area of the graphite particles by the BET method was 8.3 m ² / g. The X-ray wide angle diffraction revealed that the crystal interlayer distance d (002) was 3.365Å and the crystallite size Lc (002) was 1000Å or more.
Thereafter, through the same steps as in Example 1, a lithium secondary battery was produced, and the same test as in Example 1 was performed. Table 1 shows the charge capacity per unit weight of the first cycle graphite particles, the discharge capacity, and the discharge capacity per unit weight of the 30th cycle graphite particles.

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

  The graphite particles according to claims 1, 2, and 5 are suitable for a lithium secondary battery having excellent cycle characteristics.

The graphite particles according to claim 3 are suitable for a lithium secondary battery excellent in rapid charge / discharge characteristics and cycle characteristics.
The graphite particles according to claim 4 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.

It is a scanning electron micrograph of the graphite particle used for this invention, (a) is a photograph of the outer surface of particle | grains, (b) is a photograph of the cross section of particle | grains. It is a partial cross section front view of a cylindrical lithium secondary battery. In the Example of this invention, it is the schematic of the lithium secondary battery used for the measurement of a charging / discharging characteristic and an irreversible capacity | capacitance.

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 Electrolytic solution 11 Sample electrode (negative electrode)
12 Separator 13 Counter electrode (positive electrode)
14 Reference pole

Claims (4)

c-axis direction crystallite size Lc (002) is 1000 to 100000Å, and graphite particles having a large number of scaly graphite crystal layered structures therein, and a size in the range of 10 ² to 10 ^{6 6} the pore volume of the pores is a graphite particle weight per 0.4~2.0cc / g, the layer-like structure of the scale-like graphite crystals inside the graphite particles are arranged without being aligned in a predetermined direction Graphite particles for lithium secondary battery negative electrode. The graphite particles for a lithium secondary battery negative electrode according to claim 1, wherein the graphite particles have an aspect ratio of 5 or less. Specific surface area is 8m ² The graphite particles for a lithium secondary battery negative electrode according to claim 1 or 2, wherein the graphite particle is / g or less. 1 × 10 ² ~ 2x10 ^Four The graphite for negative electrodes of lithium secondary batteries according to any one of claims 1 to 3, wherein the pore volume of pores having a size in the range of soot is 0.08 to 0.4 cc / g per graphite particle weight. particle.

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