JPH10158005A - Graphite particle, its production, graphite paste using the same, negative electrode of lithium secondary cell and lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide graphite particles having excellent rapid charge and discharge characteristics and cycle characteristics which are suitable for a lithium secondary cell, to provide graphite particles showing small irreversible capacity for a first cycle and excellent cycle characteristics which are suitable for a lithium secondary cell, and to provide a producing method of graphite particles and a graphite paste and a lithium secondary cell using the particles. SOLUTION: The graphite particles are produced by aggregating or bonding plural planer particles having orientation planes nonparallel to each other, <=5 aspect ratio and <=8m<2> /g specific surface area. The graphite particles are produced by mixing a graphite or an aggregate which can be graphitized, with a binder which can be graphitized with addition of a graphite catalyst by 1 to 50wt.%, and calcining and pulverizing. An org. binder and solvent are mixed to the obtd. graphite particles to obtain a graphite paste. The lithium secondary cell is produced by applying the graphite paste on an electric collector to form a body of a negative electrode for a lithium secondary cell, disposing the obtd. electrode to face a positive electrode through a separator, and injecting an electrolytic liquid around the electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventional graphite particles include, for example, natural graphite particles,
Examples include 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 shown in JP-B-62-23433,
By using graphite for the negative electrode, the problem of internal short circuit due to lithium dendrite is eliminated, and the cycle characteristics are improved.

[0003] However, natural graphite particles in which graphite crystals are developed and artificial graphite particles obtained by graphitizing coke are:
Since the bonding force between the layers of the crystal in the c-axis direction is weaker than the bonding in the plane direction of the crystal, the bonding between the graphite layers is broken by pulverization,
So-called graphite particles having a large aspect ratio are obtained. Since the scale-like graphite particles have a large aspect ratio, when the electrode is produced by kneading with a binder and applying the mixture to the current collector, the scale-like graphite particles are oriented in the plane direction of the current collector,
As a result, distortion in the c-axis direction caused by repeated occlusion and release of lithium into and from graphite crystals causes not only the problem of destruction of the inside of the electrode and the deterioration of cycle characteristics, but also the deterioration of rapid charge and discharge characteristics. It is in. further,
Scale-like graphite particles having a large aspect ratio not only have a large irreversible capacity in the first cycle of a lithium secondary battery obtained in some cases because of a large specific surface area, but also have poor adhesion with a current collector, and many There is a problem that requires a binder. If the adhesion to the current collector is poor, there is a problem that the current collecting effect is reduced and the discharge capacity, rapid charge / discharge characteristics, cycle characteristics, and the like are reduced. Therefore, graphite particles capable of improving the rapid charge / discharge characteristics and the cycle characteristics of the lithium secondary battery because the rapid charge / discharge characteristics and the cycle characteristics or the irreversible capacity in the first cycle are small, and the cycle characteristics or the irreversible capacity in the first cycle are small. Is required.

[0004]

The first to fifth aspects of the present invention provide graphite particles suitable for a lithium secondary battery having excellent rapid charge / discharge characteristics and cycle characteristics.
The invention according to claims 6 and 7 provides graphite particles suitable for lithium secondary batteries having a small irreversible capacity in the first cycle and excellent cycle characteristics. The inventions according to claims 8 and 9 provide graphite particles suitable for lithium batteries having a small irreversible capacity in the first cycle and excellent in rapid charge / discharge characteristics and cycle characteristics.

According to the tenth aspect of the present invention, the rapid charge / discharge characteristics and the cycle characteristics are excellent or the irreversible capacity in the first cycle is small, and the cycle characteristics are excellent or the irreversible capacity in the first cycle is small. Another object of the present invention is to provide a method for producing graphite particles suitable for a lithium secondary battery having excellent cycle characteristics. The invention according to claim 11 is excellent in rapid charge / discharge characteristics and cycle characteristics or has small irreversible capacity in the first cycle, excellent cycle characteristics or small irreversible capacity in the first cycle, and has rapid charge / discharge characteristics and cycle characteristics. It is intended to provide a graphite paste suitable for a lithium secondary battery excellent in excellentness.

According to a twelfth aspect of the present invention, the rapid charge / discharge characteristics and the cycle characteristics are excellent, or the irreversible capacity in the first cycle is small, and the cycle characteristics are excellent or the irreversible capacity in the first cycle is small. And a negative electrode for a lithium secondary battery having excellent cycle characteristics. The invention according to claim 13 is excellent in rapid charge / discharge characteristics and cycle characteristics or has a small irreversible capacity in the first cycle, excellent cycle characteristics or small irreversible capacity in the first cycle, and has rapid charge / discharge characteristics and cycle characteristics It is intended to provide a lithium secondary battery having excellent characteristics.

[0007]

SUMMARY OF THE INVENTION The present invention relates to graphite 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 the graphite particles, wherein the graphite particles have an aspect ratio of 5 or less.
Further, the present invention relates to graphite particles, wherein the graphite particles are made of an aggregate of graphite particles. The present invention also relates to graphite particles having an aspect ratio of 5 or less. Further, the present invention relates to graphite particles, wherein the graphite particles have an aspect ratio of 1.2 to 5. Further, the present invention has a specific surface area of 8 m ² / g
It relates to the following graphite particles. The present invention also relates to the graphite particles having a specific surface area of ² to 5 m ² / g. The present invention also relates to graphite particles obtained by assembling or bonding a plurality of flat graphite particles so that the orientation planes thereof are non-parallel. Further, in the present invention, the graphite particles may have an aspect ratio of 5
It relates to the following graphite particles.

The present invention also provides a graphite characterized in that 1 to 50% by weight of a graphitizing catalyst is added to a graphitizable aggregate or a graphite and a graphitizable binder, mixed, calcined and then pulverized. The present invention relates to a method for producing particles. Further, the present invention relates to a graphite paste obtained by adding an organic binder and a solvent to any one of the above graphite particles or the graphite particles produced by the above method, and mixing them. The present invention also relates to a negative electrode for a lithium secondary battery obtained by applying the above graphite paste to a current collector and integrating the same. Furthermore, the present invention relates to a lithium secondary battery in which the above-described negative electrode for a lithium secondary battery and a positive electrode are arranged to face each other with a separator interposed therebetween, and an electrolyte is injected around the lithium secondary battery.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The graphite particles of the present invention are roughly classified into three types according to their characteristics. The first graphite particles of the present invention are obtained by assembling or bonding a plurality of flat particles so that their orientation planes are non-parallel. In the present invention, flat particles are particles having a shape having a major axis and a minor axis, and are not perfectly spherical. For example, a shape such as a scaly shape, a scaly shape, or a partial lump shape is included in this. In the graphite particles, the orientation plane of the plurality of flat particles is non-parallel, the flat surface having in the shape of each particle,
In other words, it refers to a state in which a plurality of flat particles assemble without aligning the respective orientation planes in a certain direction, with the plane closest to the plane being the orientation plane.

[0010] In the graphite particles, the flat particles are aggregated or bonded, and the bonding means that the particles are tar,
Through a carbonaceous material obtained by carbonizing a binder such as a pitch, it refers to a state in which the particles are chemically bonded.Assembling means that the particles are not chemically bonded to each other, but due to its shape and the like, A state in which the shape of the aggregate is maintained. From the standpoint of mechanical strength, it is preferable to combine them. In one graphite particle, the number of flat particles aggregated or bonded is preferably three or more. The size of each flat particle is preferably 1 to 100 μm in particle size, and is preferably 2/3 or less of the average particle size of the graphite particles in which these are aggregated or bonded.

When the graphite particles are used for a negative electrode, it is difficult for graphite crystals to be oriented on a current collector, and lithium is occluded in 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 of the present invention. In FIG. 1, (a) is a scanning electron micrograph of the outer surface of the graphite particles according to the present invention, and (b) is a scanning electron micrograph of a cross section of the graphite particles. In (a), 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.

The second graphite particles of the present invention have an aspect ratio of 5 or less. These graphite particles have a tendency that the particles are hardly oriented on the current collector, and easily occlude and release lithium as described above. The aspect ratio is preferably from 1.2 to 5. If the aspect ratio is less than 1.2,
When the contact area between the particles decreases, the conductivity tends to decrease. For the same reason, a more preferable range is 1.3.
That is all. On the other hand, the upper limit of the aspect ratio of the graphite particles is more preferably 3 or less. When the aspect ratio is larger than this, the rapid charge / discharge characteristics tend to deteriorate. Therefore, a particularly preferable aspect ratio is 1.3 to 3. In addition, the aspect ratio, when the length in the major axis direction of the graphite particles is A, and 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 magnifying graphite particles with a microscope, arbitrarily selecting 100 graphite particles, measuring A / B, and taking the average value.

The first graphite particles preferably have an aspect ratio of 5 or less, and have an aspect ratio of 1.2 or less.
To 5, more preferably 1.3 to 3. Further, it is preferable that the second graphite particles are an aggregate or a combination of smaller graphite particles.

The third graphite particles of the present invention have a specific surface area of 8
m ² / g or less. The specific surface area is preferably 5 m ² / g
It is as follows. 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. The specific surface area is 8m ² / g
If it exceeds, the irreversible capacity in the first cycle of the obtained lithium secondary battery becomes large, the energy density becomes small, and more binders are required when producing the negative electrode. The specific surface area is preferably from 1.5 to 5 m ² / g, and more preferably from 2 to 5 from the viewpoint that the obtained lithium secondary battery has better charge / discharge characteristics and cycle characteristics.
More preferably, m ² / g. The measurement of the specific surface area is B
A known method such as the ET method (nitrogen gas adsorption method) can be used. The third graphite particles are preferably graphite particles in which a plurality of flat particles, such as the first graphite particles, are aggregated or bonded so that the orientation planes thereof are non-parallel. As for graphite particles, those having an aspect ratio of 5 or less are preferable, those having an aspect ratio of 1.2 to 5 are more preferable, and those having an aspect ratio of 1.3 to 3 are still more preferable.

Further, the interlayer distance d (002) of crystals of each graphite particle used in the present invention in X-ray wide angle diffraction is 3.3.
It is preferably 8 ° or less, more preferably 3.37 ° or less. The crystallite size Lc (002) in the c-axis direction is preferably 500 ° or more, more preferably 1000 ° or more. When the interlayer distance d (002) of the crystal is small or the crystallite size Lc (002) in the c-axis direction is large, the discharge capacity tends to be large, which is preferable.

There is no particular limitation on the method for producing each of the above graphite particles of the present invention. However, 1 to 50% by weight of a graphitizing catalyst is added to a graphitizable aggregate or graphite and a graphitizable binder, and mixed. It can be obtained by crushing after firing.
Thereby, pores are generated after the graphitization catalyst escapes,
Provides good properties of the graphite particles of the present invention. The above graphite particles can also be adjusted by appropriately selecting the mixing method of the graphite or the aggregate and the binder, adjusting the mixing ratio such as the amount of the binder, and the pulverizing conditions after firing.

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

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

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

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

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

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 graphite paste of the present invention comprises the graphite particles,
It is produced by mixing a material containing an organic binder and a solvent. As the organic binder, for example, polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, a polymer compound having a high ionic conductivity, and the like can be used. In the present invention, as the polymer compound having a large ionic conductivity, polyvinylidene fluoride, polyethylene oxide,
Polyepichlorohydrin, polyphosphazene, polyacrylonitrile and the like can be used. Among these, a polymer compound having a large ionic conductivity is preferable, and polyvinylidene fluoride is particularly preferable.

The 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 graphite paste.

The negative electrode for a lithium ion battery of the present invention is characterized by using each of the above graphite particles. This negative electrode for a lithium ion battery can be obtained by molding the graphite paste into a sheet shape, a pellet shape, or the like. As the current collector, for example, a metal current collector such as a foil of nickel or copper, or a mesh can be used. In addition, the integration can be performed by a molding method such as a roll, a press, or the like, and these may be combined and integrated. The negative electrode 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.

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

[0028]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 (1) Preparation of Graphite Particles 70 parts by weight of coke powder having an average particle diameter of 10 μm, 20 parts by weight of tar pitch, 10 parts by weight of iron oxide and 20 parts by weight of coal tar were mixed and stirred at 100 ° C. for 1 hour. . Then, after firing at 2800 ° C. in a nitrogen atmosphere, pulverization is performed,
Graphite particles having an average particle size of 20 μm were obtained. According to a scanning electron micrograph (SEM photograph) of the obtained graphite particles, the graphite particles had a structure in which a large number of flat particles were aggregated or bonded so that the orientation planes were non-parallel. As a result of arbitrarily selecting 100 obtained graphite particles and measuring the average value of the aspect ratio, it was 1.8. The interlayer distance d (00) of the obtained graphite particles by X-ray wide angle diffraction
2) is 3.360 ° and the crystallite size Lc (002)
It was 1000 mm or more. Further, the specific surface area by the BET method was 3.5 m ² / g.

(2) Production of Lithium Secondary Battery A lithium secondary battery having the shape shown in FIG. 2 was produced as follows. 88% by weight of LiCoO ₂ as a positive electrode active material, 7% by weight of flaky natural graphite having an average particle diameter of 1 μm as a conductive agent, and polyvinylidene fluoride (PV) as a binder
DF) was added at 5% by weight, and N-methyl-2-pyrrolidone (50% by weight of the paste, the same proportion was added in the following examples) was added thereto and mixed to prepare a paste of the positive electrode mixture. Similarly, the graphite powder 9 obtained in (1) was used as a negative electrode active material.
0% by weight and 10% by weight of PVDF as a binder were added thereto, and N-methyl-2-pyrrolidone (5% of the paste) was added thereto.
0% by weight, and the same ratio was added in the following examples) to obtain a paste of the negative electrode mixture.

Next, paste the paste of the positive electrode mixture to a thickness of 25 μm.
On both sides of aluminum foil
Vacuum dried for hours. After vacuum drying, the electrode was pressure-formed by a roller press to a thickness of 190 μm. The positive electrode mixture application amount per unit area is 49 mg / cm ² and the width is 40
The positive electrode 1 was prepared by cutting out a piece having a length of 285 mm in mm. However, the positive electrode mixture was not applied to the 10 mm long portions of both ends of the positive electrode 1 and the aluminum foil was exposed,
The positive electrode tab 4 is press-bonded to one side by ultrasonic bonding.

On the other hand, the paste of the negative electrode mixture has a thickness of 10 μm.
m, and then vacuum dried at 120 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed by a roller press to a thickness of 175 μm. The applied amount of the negative electrode mixture per unit area was 20 mg / cm ² , and the negative electrode 2 was produced by cutting out a size having a width of 40 mm and a length of 290 mm. As in the case of the positive electrode 1, the negative electrode 2 was not coated with the negative electrode mixture at the both ends of the negative electrode 2 and the copper foil was exposed, and the negative electrode tab 5 was pressure-bonded to one of the two parts by ultrasonic bonding.

The separator 3 has a thickness of 25 μm and a width of 4 μm.
A 4 mm polyethylene microporous membrane was used. Next, as shown in FIG. 2, the positive electrode 1, the separator 3, the negative electrode 2, and the separator 3 were superimposed in this order, and were wound to form an electrode group.
This was inserted into an AA size battery can 7, the negative electrode tab 5 was welded to the bottom of the can, and a throttle portion for caulking the positive electrode lid 6 was provided. Thereafter, an electrolyte solution (not shown) in which lithium hexafluorophosphate is dissolved at 1 mol / liter in a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1 is injected into the battery can 7, and then the positive electrode tab is formed. After welding 4 to the positive electrode cover 6, the positive electrode cover 6 was caulked to obtain a lithium secondary battery. Using the obtained lithium secondary battery, a charge / discharge current of 300 m
A, charge end voltage 4.15V and discharge end voltage 2.8
Charge and discharge were repeated at V. Also, charge / discharge current is 300mA
, And rapid charging and discharging were also performed.
The results are shown in FIGS.

Example 2 70 parts by weight of coke powder having an average particle size of 10 μm, 10 parts by weight of tar pitch, 2 parts by weight of iron oxide and 2 parts of coal tar
0 parts by weight were mixed and stirred at 100 ° C. for 1 hour. Then, after firing at 2800 ° C. in a nitrogen atmosphere, pulverization is performed,
Graphite particles having an average particle size of 20 μm were obtained. As a result of observing the graphite particles obtained with an electron microscope, a large number of flat particles,
It was confirmed that the graphite particles were formed by assembling or bonding such that the orientation planes are non-parallel. As a result of arbitrarily selecting 100 obtained graphite particles and measuring the average value of the aspect ratio, it was 4.8. Further, the interlayer distance d (002) of the obtained graphite particles by X-ray wide-angle diffraction is 3.
363 ° and the crystallite size Lc (002) are 1000
It was more than Å. Further, the specific surface area by the BET method is 4.
It was 3 m ² / g. Using the obtained graphite particles, a lithium secondary battery was manufactured through the same steps as in Example 1, and a battery characteristic test similar to that of Example 1 was performed. The results are shown in FIGS.

Comparative Example 1 Coke powder having an average particle size of 20 μm was placed in a nitrogen atmosphere.
It was fired at 800 ° C. to obtain graphite particles having an average particle size of 20 μm. The obtained graphite particles have an average aspect ratio of 6,
The specific surface area is 11 m ² / g, the crystal interlayer distance d (002) is 3.365 °, and the crystallite size Lc (002) is 80.
It was scaly graphite of 0 °. The obtained scaly graphite was prepared in Example 1.
A lithium secondary battery was manufactured through the same steps as described above, and a battery characteristic test similar to that of Example 1 was performed. The results are shown in FIGS.

The results of comparative tests on the insertion and extraction of lithium of the lithium secondary batteries obtained in Examples 1 and 2 of the present invention and Comparative Example 1 are shown below. FIG. 3 is a graph showing the relationship between the discharge capacity of the battery and the number of charge / discharge cycles when the charge / discharge of the lithium secondary battery is repeatedly performed. In FIG. 3, 9 is the discharge capacity of the lithium secondary battery obtained in Example 1, 10 is the discharge capacity of the lithium secondary battery obtained in Example 2, and 11 is the discharge capacity of the lithium secondary battery obtained in Comparative Example 1. Is shown.

In FIG. 3, the maximum discharge capacity of the lithium secondary battery obtained in Example 1 was 750 mAh, and the rate of decrease in the discharge capacity relative to the maximum capacity at the 500th cycle was 8%. The maximum discharge capacity of the lithium secondary battery obtained in Example 2 was 720 mAh, and the rate of decrease in the discharge capacity with respect to the maximum capacity at the 500th cycle was 12%.
Met. The maximum discharge capacity of the lithium secondary battery obtained in the comparative example was 650 mAh, and the rate of decrease in the discharge capacity relative to the maximum capacity at the 500th cycle was 31%.

FIG. 4 shows the relationship between the charge / discharge current and the discharge capacity when rapid charge / discharge is performed. 12 indicates the discharge capacity of the lithium secondary battery obtained in Example 1, 13 indicates the discharge capacity of the lithium secondary battery obtained in Example 2, and 14 indicates the discharge capacity of the lithium secondary battery obtained in Comparative Example 1. Charge / discharge current 900
In mA, the discharge capacity of the lithium secondary battery obtained in Example 1 was 630 mAh and the discharge capacity of the lithium secondary battery obtained in Example 2 was 520 mAh, whereas the discharge capacity of the lithium secondary battery obtained in Comparative Example 1 was 520 mAh. The discharge capacity of the battery was 350 mAh. The capacity reduction rate with respect to the discharge capacity at a charge / discharge current of 300 mAh was 16% for the lithium secondary battery obtained in Example 1.
%, The lithium secondary battery obtained in Example 2 was 28%, and the lithium secondary battery obtained in Comparative Example 1 was 46%. From the test results of Examples 1 and 2 and Comparative Example 1, it was confirmed that the lithium secondary batteries according to Examples of the present invention had high capacity, excellent charge / discharge cycle characteristics, and rapid charge / discharge characteristics. .

Example 3 50 parts by weight of coke powder having an average particle diameter of 10 μm, 20 parts by weight of tar pitch, 10 parts by weight of silicon carbide and 20 parts by weight of coal tar were mixed and stirred at 100 ° C. for 1 hour.
Next, the powder was fired at 2800 ° C. in a nitrogen atmosphere and then pulverized to produce graphite particles having an average particle diameter of 20 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 2.9 m ² / g, and the interlayer distance d of the crystals by X-ray wide-angle diffraction of the graphite particles.
(002) is 3.360 ° and the crystallite size Lc (0
02) was 1000 ° or more. Further, according to a scanning electron microscope photograph (SEM photograph) of the obtained graphite particles,
The graphite particles had a structure in which flat particles were aggregated or bonded so 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.
Rolled copper foil, and further dried, surface pressure 490MPa
(0.5 ton / cm ² ) to obtain a sample electrode by compression molding. The thickness of the graphite particle layer is 75 μm and the density is 1.5 g / cm
^{It was set to 3} .

The prepared sample electrode was charged and discharged at a constant current by a three-terminal method, and evaluated as a negative electrode for a lithium secondary battery. FIG. 5 is a schematic diagram of the lithium secondary battery.
The evaluation of the sample electrode was performed using a glass cell 15 as shown in FIG.
In addition, LiPF ₄ is used as an electrolytic solution 16 in ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC
And DMC are mixed at a volume ratio of 1: 1) in a mixed solvent having a concentration of 1 mol / liter, and a sample electrode (negative electrode) 17, a separator 18 and a counter electrode (positive electrode) 19 are stacked and arranged. Then, the reference electrode 20 was suspended from above to produce a lithium secondary battery. In addition, metallic lithium was used for the counter electrode 19 and the reference electrode 20, and the separator 1 was used.
8 used a polyethylene microporous membrane. Using the obtained lithium secondary battery, 5 mV at a constant current of 0.3 mA / cm ² between the sample electrode 17 and the counter electrode 19 with respect to the area of the sample electrode.
(Vvs. Li ^/ Li ⁺ ) and 1 V (Vvs.
The test for discharging to Li / Li ⁺ ) was repeated. Table 1 shows the charge capacity per unit weight of the graphite particles, the discharge capacity per unit weight of the graphite particles, the irreversible capacity and 50 in the first cycle.
It shows the discharge capacity per unit weight of graphite particles in the cycle. As a quick charge / discharge characteristic evaluation, the battery was charged at a constant current of 0.3 mA / cm ² and discharged when the discharge current was changed to 0.3, 2.0, 4.0 and 6.0 mA / cm ^2. Table 2 shows the capacities.

Example 4 50 parts by weight of coke powder having an average particle diameter of 10 μm, 10 parts by weight of tar pitch, 5 parts by weight of silicon carbide and 10 parts by weight of coal tar were mixed and stirred at 100 ° C. for 1 hour. Then, after firing at 2800 ° C. in a nitrogen atmosphere, pulverization is performed,
Graphite particles having an average particle size of 20 μm were prepared. As a result of arbitrarily selecting 100 obtained graphite particles and measuring the average value of the aspect ratio, it was 4.5. The specific surface area of the obtained graphite particles by the BET method was 4.9 m ² / g,
The interlayer distance d (00) of the crystal by X-ray wide angle diffraction of graphite particles
2) is 3.362 ° and the crystallite size Lc (002)
Was 1000 ° or more. Further, the obtained graphite particles had a structure in which flat particles were aggregated or bonded so that a plurality of orientation planes became non-parallel.

Thereafter, a lithium secondary battery was manufactured through the same steps as in Example 3, and the same test as in Example 3 was performed. Table 1 shows the charge capacity per unit weight of the graphite particles in the first cycle, the discharge capacity per unit weight of the graphite particles, the irreversible capacity, and the discharge capacity per unit weight of the graphite particles in the 50th cycle. As a quick charge / discharge characteristic evaluation, 0.3 mA / cm ²
And a discharge current of 0.3, 2.0, 4.0
Table 2 shows the discharge capacity when the discharge capacity was changed to 6.0 mA / cm ² .

Example 5 A mixture of 50 parts by weight of coke powder having an average particle diameter of 10 μm, 5 parts by weight of tar pitch and 5 parts by weight of coal tar was mixed.
Stirred at 00 ° C. for 1 hour. Then, in a nitrogen atmosphere, 28
After firing at 00 ° C., the powder was pulverized to produce graphite particles having an average particle diameter of 20 μm. As a result of arbitrarily selecting 100 obtained graphite particles and measuring the average value of the aspect ratio, it was 5. The specific surface area of the obtained graphite particles by the BET method was 6.3 m ² / g, the interlayer distance d (002) of the graphite particles by X-ray wide-angle diffraction was 3.368 °, and the crystallite size Lc (002) was 700 °. Further, the obtained graphite particles had a structure in which a plurality of flat particles were aggregated or bonded so that the orientation planes were non-parallel.

Thereafter, a lithium secondary battery was manufactured through the same steps as in Example 3, and the same test as in Example 3 was performed. Table 1 shows the charge capacity per unit weight of the graphite particles in the first cycle, the discharge capacity per unit weight of the graphite particles, the irreversible capacity, and the discharge capacity per unit weight of the graphite particles in the 50th cycle. As a quick charge / discharge characteristic evaluation, 0.3 mA / cm ²
And a discharge current of 0.3, 2.0, 4.0
Table 2 shows the discharge capacity when the discharge capacity was changed to 6.0 mA / cm ² .

Comparative Example 2 Coke powder having an average particle size of 22 μm was mixed with nitrogen in a nitrogen atmosphere.
By firing at 800 ° C., graphite particles having an average particle size of 20 μm were obtained. The obtained graphite particles have an average aspect ratio of 7, a specific surface area of 8.5 m ² / g by BET method, an interlayer distance d (002) of 3.368 ° by X-ray wide-angle diffraction, and a crystallite size of Lc (002) was a scale-like graphite of 800 °.

A lithium secondary battery was manufactured through the same steps as in Example 3, and the same test as in Example 3 was performed. Table 1 shows the charge capacity per unit weight of the graphite particles in the first cycle, the discharge capacity per unit weight of the graphite particles, the irreversible capacity, and the discharge capacity per unit weight of the graphite particles in the 50th cycle. As a quick charge / discharge characteristic evaluation, 0.3 mA / cm ²
And a discharge current of 0.3, 2.0, 4.0
Table 2 shows the discharge capacity when the discharge capacity was changed to 6.0 mA / cm ² .

[0047] ☆

[Table 1]

☆

[Table 2]

As shown in Tables 1 and 2, the lithium secondary batteries obtained in Examples of the present invention have a large discharge capacity, a small irreversible capacity in the first cycle, and low cycle characteristics and rapid discharge characteristics. It is clear that it is excellent.

[0050]

The graphite particles according to the first to fifth aspects are graphite particles suitable for a lithium secondary battery having excellent rapid charge / discharge characteristics and cycle characteristics. The graphite particles according to claims 6 and 7 have a small irreversible capacity in the first cycle and are suitable for lithium secondary batteries having excellent cycle characteristics. The graphite particles according to claims 8 and 9 have excellent rapid charge / discharge characteristics and cycle characteristics or a small irreversible capacity in the first cycle, and excellent cycle characteristics or small irreversible capacities in the first cycle. Graphite particles suitable for lithium secondary batteries having excellent cycle characteristics.

The graphite particles obtained by the method according to claim 10 are excellent in rapid charge / discharge characteristics and cycle characteristics or small in irreversible capacity in the first cycle, excellent in cycle characteristics or small in irreversible capacity in the first cycle, Graphite particles suitable for lithium secondary batteries having excellent rapid charge / discharge characteristics and cycle characteristics. The graphite paste according to claim 11, which is excellent in rapid charge / discharge characteristics and cycle characteristics or has a small irreversible capacity in the first cycle, has excellent cycle characteristics or has a small irreversible capacity in the first cycle, and has rapid charge / discharge characteristics and cycle characteristics. It is a graphite paste suitable for a lithium secondary battery having excellent heat resistance.

The negative electrode for a lithium secondary battery according to claim 12 is excellent in rapid charge / discharge characteristics and cycle characteristics or has a small irreversible capacity in the first cycle, excellent cycle characteristics or a small irreversible capacity in the first cycle, It is a negative electrode for a lithium secondary battery suitable for a lithium secondary battery having excellent rapid charge / discharge characteristics and cycle characteristics. The lithium secondary battery according to claim 13 is excellent in rapid charge / discharge characteristics and cycle characteristics or has a small irreversible capacity in the first cycle,
The lithium secondary battery has excellent cycle characteristics or a small irreversible capacity in the first cycle, and has excellent rapid charge / discharge characteristics and cycle characteristics.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph showing the particle structure of graphite particles according to the present invention, wherein (a) is a photograph of the outer surface of the particles,
(B) is a photograph of a cross section of a particle.

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

FIG. 3 is a graph showing a relationship between a discharge capacity and the number of charge / discharge cycles.

FIG. 4 is a graph showing a relationship between a discharge capacity and a charge / discharge current.

FIG. 5 is a schematic diagram of a lithium secondary battery used in Examples 3, 4, 5 and Comparative Example 2 for measuring charge / discharge characteristics and irreversible capacity.

[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 Discharge capacity of the lithium secondary battery obtained in Example 1 10 Discharge capacity of the lithium secondary battery obtained in Example 2 11 Comparison Discharge capacity of lithium secondary battery obtained in Example 1 12 Discharge capacity of lithium secondary battery obtained in Example 1 13 Discharge capacity of lithium secondary battery obtained in Example 2 14 Lithium secondary obtained in Comparative Example 1 Battery discharge capacity 15 Glass cell 16 Electrolyte 17 Sample electrode (negative electrode) 18 Separator 19 Counter electrode (positive electrode) 20 Reference electrode

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 4/62 H01M 10/40 Z 10/40 C04B 35/52 A (72) Inventor Kazuo Yamada 3-chome Ayukawacho, Hitachi City, Ibaraki Prefecture No.3-1 Hitachi Chemical Co., Ltd. Yamazaki Plant

Claims (13)

[Claims] 1. Graphite particles obtained by assembling or bonding a plurality of flat particles so that their orientation planes are non-parallel. 2. The graphite particles according to claim 1, wherein the graphite particles have an aspect ratio of 5 or less. 3. Graphite particles having an aspect ratio of 5 or less. 4. The graphite particles according to claim 3, having an aspect ratio of 1.2 to 5. 5. The graphite particles according to claim 3, comprising an aggregate of graphite particles. 6. Graphite particles having a specific surface area of 8 m ² / g or less. 7. The graphite particles according to claim 6, having a specific surface area of ² to 5 m ² / g. 8. The graphite particles according to claim 6, wherein the graphite particles are formed by assembling or binding a plurality of flat particles so that their orientation planes are non-parallel. 9. The graphite particles according to claim 6, wherein the aspect ratio of the graphite particles is 5 or less. 10. A graphitizable aggregate or graphite and a graphitizable binder, wherein 1 to 50% by weight of a graphitizing catalyst is added, mixed, calcined and pulverized.
10. The method for producing graphite particles according to any one of 9 above. 11. A graphite paste obtained by adding and mixing an organic binder and a solvent to the graphite particles according to claim 1 or the graphite particles produced by the method according to claim 10. 12. A negative electrode for a lithium secondary battery obtained by applying and integrating the graphite paste according to claim 11 on a current collector. 13. A lithium secondary battery according to claim 12, wherein the negative electrode and the positive electrode for a lithium secondary battery according to claim 12 are arranged to face each other with a separator interposed therebetween, and an electrolyte is injected around the lithium secondary battery.