JPH1145715A - Manufacture of nonaqueous electrolytic secondary battery and of its negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize higher reliability of a lithium secondary battery and heighten its energy density. SOLUTION: Following powder is used as a negative electrode material for this battery. Flake graphite particles, in which a spacing (d002) of latice planes (002) is 3.350 to 3.360 Å and crystallite size (Lc) in the C axis direction is at least 1000 Å or more, are chamfered into disk-shaped or tablet-shaped particles in a process for being pulverized further. By screening these, powder is obtained wherein the mean particle size is 10 to 30 μm, the mean thickness value of the thinnest part is 3 to 9 μm, and an X-ray diffraction peak intensity ratio of (110)/(004) according to the wide-angle X-ray diffraction method is regulated within a range not less than 0.015. By this, high energy density, a high-rate discharge performance, and improvement of reliability can be achieved when stored for a longtime under a high-temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a carbon material for a negative electrode of a lithium ion secondary battery.

[0002]

2. Description of the Related Art Conventionally, as a nonaqueous electrolyte secondary battery, with a view to increasing the energy density by a high voltage and a high capacity, lithium metal is used as a negative electrode active material, and an oxide or sulfide of a transition metal is used as a positive electrode active material. Secondary batteries using an organic electrolytic solution composed of an organic solvent solution of a lithium salt as a non-aqueous electrolyte, such as a chalcogen compound such as manganese dioxide, molybdenum disulfide, or titanium selenide, such as manganese dioxide or selenide, are being studied. .

[0003] However, this lithium secondary battery is
As the positive electrode active material, an interlayer compound having relatively excellent charge / discharge characteristics can be selected, but the charge / discharge characteristics of metallic lithium of the negative electrode are not necessarily excellent. Therefore, it is difficult to prolong the cycle life of repeated charge and discharge, and furthermore, there is a possibility that heat may be generated due to an internal short circuit, and there is a problem in safety. That is, metallic lithium as the negative electrode active material is eluted as lithium ions into the organic electrolyte by discharge. The eluted lithium ions deposit on the negative electrode surface as metallic lithium upon charging, but some do not deposit as smooth as the original, but deposit as active dendritic or mossy metal crystals. The active metal crystal decomposes the organic solvent in the electrolytic solution, and at the same time, the surface of the metal crystal itself is covered with a passivation film to be inactivated and hardly contribute to discharge.
As a result, the negative electrode capacity decreases as the charge / discharge cycle progresses. Therefore, it was necessary to make the negative electrode capacity significantly larger than that of the positive electrode during cell fabrication. The active dendritic lithium metal crystal may penetrate the separator and come into contact with the positive electrode to cause an internal short circuit. The cell may generate heat due to an internal short circuit.

Therefore, a so-called lithium ion secondary battery using a carbon material capable of reversibly repeating intercalation and deintercalation by charging and discharging as a negative electrode material has been proposed and actively researched and developed. Has already reached the stage of practical application. As long as the lithium ion secondary battery is not overcharged, no active dendritic lithium metal crystals are deposited on the surface of the negative electrode during charge / discharge, so that improvement in safety can be greatly expected. Further, since this battery has remarkably superior high-rate charge / discharge characteristics and cycle life as compared with a lithium secondary battery using metallic lithium as a negative electrode active material, the demand for this battery has been rapidly growing in recent years.

As a positive electrode active material of a 4 V class lithium ion secondary battery, LiCoO ₂ , Li
Composite oxides of lithium and a transition metal such as NiO ₂ , LiMnO ₂ , and LiMn ₂ O ₄ have been adopted or studied. As the electrolyte, a nonaqueous electrolyte such as an organic electrolyte or a polymer solid electrolyte is used as in the case of the lithium secondary battery.

When graphite is used as the negative electrode material, the theoretical value of the capacity per 1 g of carbon based on C ₆ Li, which is an intercalation compound generated by intercalation of lithium ions, is 372 mAh. Therefore, in various carbon materials, the one which approaches the theoretical value of the specific capacity and has a capacity value per unit volume, that is, a capacity density (mAh / cc) as high as possible as a negative electrode of a practical battery should be used. You should choose.

Among various carbon materials, among hard-graphitizable carbons commonly called hard carbons, materials exceeding the above-mentioned theoretical specific capacity (372 mAh / g) have been found and studied. However, the true specific gravity of the non-graphitizable amorphous carbon is small and bulky, so that it is substantially difficult to increase the capacity density of the negative electrode per unit volume. Moreover,
There are many problems that the negative electrode potential after charging is not so low as to approximate the metallic lithium potential, and the discharge potential is poor in flatness.

On the other hand, when natural graphite and artificial graphite powder having high crystallinity are used for the negative electrode, the potential after charging is close to the lithium metal potential, and the flatness of the discharging potential is excellent, so that a practical battery can be used. As the charge and discharge characteristics are improved,
Recently, graphite-based powders are becoming the mainstream of negative electrode materials.

Among them, if the average particle size of the graphite powder for a negative electrode of a lithium ion secondary battery is large, the charge / discharge characteristics at a high rate and the discharge characteristics at a low temperature tend to be inferior.

Therefore, if the average particle size of the powder is reduced,
Although the high-rate charge / discharge characteristics and the low-temperature discharge characteristics are improved, if the average particle size is too small, the specific surface area of the powder becomes too large. There is a problem that the irreversible capacity that cannot contribute to the discharge after the cycle increases. This phenomenon is a fatal drawback to the trend toward higher energy density, and when a battery is left at a high temperature exceeding 100 ° C., the solvent in the organic electrolyte is decomposed and self-discharge occurs only. However, there is a danger that a liquid leakage accident may occur due to an increase in the internal pressure of the cell, which causes a reduction in the reliability of the battery.

From the above, it is easily understood that an appropriate specific surface area and an average particle size are important for graphite powder for a negative electrode. An invention proposed from such a viewpoint is disclosed in, for example, JP-A-6-295725, in which the BET method has a specific surface area of 1 to 10 m ² / g, an average particle diameter of 10 to 30 μm, and a particle diameter of 10 to 30 μm. It is disclosed to use a graphite powder in which at least one of the content of a powder of 10 μm or less and the content of a powder of 30 μm or more in particle size is 10% or less. Further, in Japanese Patent Application Laid-Open No. 7-134988, mesocarbon microbeads produced by heat-treating petroleum pitch at a low temperature are graphitized, and the (002) plane spacing (d002) is 3.3 by wide-angle X-ray diffraction.
6 to 3.40 °, the specific surface area by the BET method is 0.7 to
It is disclosed to use a spheroidal graphite powder that is 5.0 m ² / g.

[0012]

The above-described invention is not only extremely effective in improving the high-rate charge / discharge characteristics and the discharge characteristics at low temperatures of a lithium ion secondary battery, but also can be said to be fatal. Was effective in reducing the irreversible capacity determined by However, storage stability and reliability due to standing at a high temperature were insufficient, and dissatisfaction remained in terms of specific capacity (mAh / g) and capacity density (mAh / cc) of the negative electrode.

An object of the present invention is to further improve the reliability and energy density of a lithium secondary battery.

[0014]

In order to solve the above-mentioned problems in the lithium ion secondary battery, the present invention relates to a lithium ion secondary battery having a high purity (fixed carbon content of 98% or more) and a high crystalline average particle diameter of 20 μm. Above and the average thickness is 15 μm
The above flaky or massive graphite particles are dispersed in a liquid or gas, and the liquid or gas is discharged in a helical shape from a nozzle by applying pressure, crushed and sieved, tapping density, wide-angle X-ray diffraction method (110) / (00
By controlling the X-ray diffraction peak intensity ratio and the particle shape in 4), the irreversible capacity observed in the initial cycle is reduced as much as possible, and the storage stability and reliability of the battery when left at high temperatures are improved. The present invention has ensured excellent high-rate discharge characteristics and low-temperature discharge characteristics, and has realized a nonaqueous electrolyte secondary battery having a high specific capacity.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The invention according to claim 1 of the present invention comprises a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode. The negative electrode intercalates and deintercalates lithium ions by charging and discharging. As a negative electrode material capable of reversibly repeating intercalation, a (002) plane spacing (d002) by a wide-angle X-ray diffraction method
In the process of further pulverizing the flaky or massive graphite particles when the crystallite size (Lc) in the C-axis direction is at least 1000 ° or more, and in the process of further pulverizing the scale-like or massive graphite particles, The particles having a mean particle size of 10 to 30 μm by sieving and an average thickness of the thinnest portion of 3 to 9 μm were determined by wide-angle X-ray diffraction (11
0) / (004) X-ray diffraction peak intensity ratio is 0.015
By using a non-aqueous electrolyte secondary battery using the powder restricted to the above range, various characteristics of the lithium secondary battery can be improved and high energy density can be achieved.

The inventions described in claims 2 to 6 are the same as in claim 1.
Regarding the graphite powder for a negative electrode described above, the specific surface area by the BET method is 2.0 to 8.0 m ² / g, and the tapping density is 0.6 to
By adjusting the content to 1.2 g / cc, in particular, by controlling the content of powder having a particle size of less than 5 μm and exceeding 50 μm, the above-mentioned object is surely achieved.

According to a seventh aspect of the present invention, in the nonaqueous electrolyte secondary battery according to the first aspect, a lithium-containing transition metal oxide (chemical formula LixMO ₂ ,
M is at least one transition metal selected from Co, Ni, Mn and Fe, x = 0 or more and 1.2 or less)
An object of the present invention is to provide a lithium ion secondary battery excellent in safety and high-rate charge / discharge characteristics. The positive electrode active material is, in particular, LixC
Preferred are oO ₂ , LixNiO ₂ , LixMn ₂ O _4, and those in which some of Co, Ni, and Mn are substituted with elements such as other transition metals.

According to the eighth aspect of the present invention, the (002) plane spacing (d002) of 3.350 or more is determined by the wide-angle X-ray diffraction method.
3.360 °, the size of the crystallite in the C-axis direction (L
c) is at least 1000 ° and the average particle size is 20 μm.
m or more and the average value of the thickness of the thinnest part is 15 μm or more. Disperse flake-like or massive graphite particles in a liquid or gas, apply pressure to the liquid or gas, and discharge it spirally from a nozzle. The present invention relates to a method for producing a negative electrode for a non-aqueous electrolyte secondary battery, characterized in that fine particles are sieved and then sieved to obtain disk-shaped or tablet-shaped particles, which are used to form a negative electrode. In carrying out the method of the present invention, any of a wet method and a dry method may be used, and the wet method of dispersing graphite particles in a liquid and pulverizing the particles to obtain disk-shaped or tablet-shaped graphite particles is performed in a liquid. Is preferably 5 to 30% by weight, more preferably 15 to 25% by weight. The nozzle diameter is 0.3-3m
m, more preferably 0.6 to 1.2 mm. Further, the discharge pressure is 100 to 1000 kg /
cm ² is preferable, and 400 to 700 kg / cm ² is more preferable.

Regarding a dry method in which graphite particles are dispersed in a gas and finely pulverized to obtain disk-shaped or tablet-shaped graphite particles, the graphite concentration in the gas is 10 to 60 kg / kg.
m ³ is preferred. Nozzle diameter is 3 to 35m
m, more preferably 15 to 25 mm. Further, the discharge pressure is 0.3 to 10 kg / cm ²
Is preferable, and 0.5 to 3 kg / cm ² is more preferable.

The solvent used in the wet method of the present invention includes:
Water, ethanol, methanol and the like are suitable. As the gas used in the dry method, air, nitrogen, argon and the like are suitable.

Under the above conditions, a liquid or a gas is ejected in a helical manner from a nozzle by applying pressure, and a vortex flow is generated in a crushing vessel to finely pulverize the disc or tablet-shaped graphite particles efficiently. Can be.

In both the wet method and the dry method of the present invention, pulverization does not proceed sufficiently in a high concentration range other than the above-mentioned concentration limit range, and it is difficult to obtain disk-shaped or tablet-like graphite particles, and lacks productivity in a low concentration range. .

In areas other than the above-mentioned nozzle diameter range, the crushing efficiency is reduced in a region having a large nozzle diameter, resulting in poor productivity. In a region having a small nozzle diameter, crushing proceeds excessively, making it difficult to obtain disk-shaped or tablet-shaped graphite particles.

Further, in regions other than the above-mentioned discharge pressure range, pulverization does not proceed in a region where the discharge pressure is small, and thus the productivity is lacking. In a region where the discharge pressure is large, pulverization proceeds too much, making it difficult to obtain disk-shaped or tablet-shaped graphite particles.

The present invention does not particularly limit the electrolyte, and may be any of an electrolytic solution, a polymer electrolyte, and a combination thereof. However, the present invention relates to a battery using the 4V-class positive electrode according to claim 7 and the negative electrode of the present invention. As a solvent for the electrolytic solution used, one or more cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate having excellent oxidation resistance and low-temperature properties, and one or more cyclic carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are used. It is preferable to use a mixed solvent of the above as a main component. Further, if necessary, other solvents such as aliphatic carboxylic acid esters and ethers can be mixed. As for the mixing ratio, the cyclic carbonate is preferably in the range of 5 to 50%, particularly 15 to 40%, and the chain carbonate in the range of 10 to 90%, particularly preferably 20 to 80% of the whole solvent.

When a material having a relatively low potential such as a 3 V class is used for the positive electrode, a solvent other than the above solvents can be used.

As the solute of these solvents, lithium salts are used. Commonly known lithium salts include LiCl
O ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , Li
SbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ ,
LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAs
F ₆ and LiN (CF ₃ SO ₂ ) ₂ .

There are no restrictions on the selection of other components necessary for the battery configuration other than those described above.

[0029]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Basic Experimental Example) FIG. 1 is a sectional view of a coin-shaped cell for measuring a reversible capacity and an irreversible capacity of a carbon material for a negative electrode of a lithium ion secondary battery. In FIG. 1, a grid 3 made of stainless steel expanded metal is spot-welded to the inner bottom surface of a stainless steel cell case 1 in advance, and the grid 3 and carbon powder for a negative electrode of a lithium ion secondary battery are mainly used. The resulting mixture is integrally fixed as a carbon electrode 5 by an in-can molding method. The mixture of the carbon electrode 5 is a mixture of the test carbon powder and the acrylic binder in a weight ratio of 100: 5. A gasket 7 made of polypropylene is fitted around the periphery of the lid 2 made of stainless steel, and metallic lithium 4 is pressed on the inner surface of the lid 2. After pouring and impregnating the carbon electrode 5 with a non-aqueous electrolyte, the lid 2 with the gasket 7 is coupled to the cell case 1 via the separator 6 made of a microporous polyethylene membrane, and the upper edge opening of the cell case 1 is opened. Is curled inward and sealed. As the non-aqueous electrolyte, lithium hexafluorophosphate was added to a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1.
An organic electrolyte dissolved at a concentration of mol / l was used. A cell was prepared using 29 kinds of test carbon powders for the carbon electrode 5, and the carbon electrode 5 was used as a positive electrode and the metal lithium electrode 4 was used as a negative electrode at a constant current of 0.3 mA / cm ² at 20 ° C. To charge and discharge. After intercalating lithium into carbon until the cell voltage becomes 0 V, the capacity obtained by deintercalating lithium from carbon until the cell voltage becomes 1.0 V is defined as the reversible capacity. The value obtained by dividing the reversible capacity from the amount of electricity required for intercalation was defined as the irreversible capacity. The charge / discharge end voltage values of these test cells substantially correspond to the charge end voltage 4.20 V and the discharge end voltage 2.75 V of the negative electrode carbon / cathode LiCoO ₂ -based practical battery.

Scaly natural graphite (average particle diameter of about 50 μm, average thickness of the thinnest part of about 25 μm) or lump natural graphite (average particle diameter of about 50 μm) obtained by pulverization by a conventional method.
μm, the average thickness of the thinnest part is about 30 μm) and the flaky artificial graphite particles (average particle diameter: about 50 μm, the average thickness of the thinnest part: about 30 μm) of the present invention shown in Table 2 or Table 3. Graphite powder whose average particle size is regulated by sieving after pulverizing under the conditions (Sample Nos. 12 to 29)
Is used as a test carbon powder for a negative electrode, and the physical properties of the powder and the above-mentioned reversible capacity and irreversible capacity are summarized in Tables 2 and 3. As a comparative sample, flaky or massive natural graphite and artificial graphite particles obtained by pulverizing by a conventional method were finely pulverized by a conventional impact pulverizer such as a ball mill, a jet mill, a hammer mill, and a pin mill ( Sample Nos. 1 to 9) and spherical mesocarbon microbeads (MCMB, Sample No. 10) obtained by graphitizing mesocarbon microbeads disclosed in JP-A-7-134988 and petroleum pitch coke powder (Sample N).
o. 11) is used as a test carbon powder for a negative electrode, and the physical properties and irreversible capacity and reversible capacity of the powder are shown in Table 1.

The tapping density of the test carbon powder was measured with a powder tester (apparatus name) manufactured by Hosokawa Micron Co., Ltd. The average particle size is LA-910 manufactured by HORIBA, Ltd. (device name)
Was used to irradiate a laser beam to analyze the diffraction phenomenon (scattering) of light. The specific surface area is ASAP20 manufactured by Shimadzu Corporation
The measurement was performed by BET multipoint method using No. 10 (apparatus name).
The average value of the thickness of the carbon powder was obtained from an SEM image of a surface obtained by pressing each test graphite powder using a metal mold and then cutting the molded body parallel to the pressing direction. That is, 100 or more values in the thickness direction of the thinnest portion of the carbon powder were measured, and the average value was obtained.

The X-ray peak intensity ratio of (110) / (004) is determined by pressing a carbon powder using a metal mold to obtain a density of about 1.7 g.
/ Cc pellet, the peak intensity of the (110) and (004) planes obtained by wide-angle X-ray diffraction measurement is measured at five points, and the peak intensity ratio of (110) / (004) is calculated.
The average was determined.

The diffraction lines of the (004) plane and the (110) plane are the diffraction lines on the plane of the six-membered carbon network of the graphite crystal and on the plane perpendicular thereto. In the case where the scale-like shape is large, the graphite particles are selectively oriented in the direction parallel to the pressing surface at the time of pellet production, as compared with the case where the disk-shaped or tablet-shaped graphite particles are large. Therefore, when the ratio of the scale-like particles is larger than that of the disk-like or tablet-like graphite particles, (110) /
The X-ray peak intensity ratio of (004) becomes small.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

From the results of Tables 1, 2, and 3, Lc was 1000 °
Spheroidal graphite powder of the comparative sample less than (sample No. 10)
And the coke powder (Sample No. 11) had a relatively small irreversible capacity, but both had a small reversible capacity, which greatly affected the energy density, of less than 300 mAh / g.
On the other hand, the raw materials were sample Nos. Of natural graphite and artificial graphite powder. The reversible capacities of 1 to 9 and 12 to 29 were all at least 350 mAh / g, which was close to the theoretical value of the specific capacity (372 mAh / g). Among these, sample No. The irreversible capacity of the graphite powders of Nos. 12 to 29 was 17 to 30 mAh / g, and the other graphite powders (Sample Nos.
It is noted that it is at the same level or lower than that of 1-9).

As a prerequisite for the present invention, the plane spacing (d002) of the (002) plane by wide-angle X-ray diffraction is 3.350-.
3.360 °, the size of the crystallite in the C-axis direction (L
It is understood that a high level of reversible capacity can be obtained by using natural graphite or artificial graphite having a high crystallinity and purity in which c) is at least 1000 ° as the negative electrode material of the lithium ion secondary battery.

(Examples and Comparative Examples) A cylindrical cell was prepared using the carbon powder for a negative electrode (Sample Nos. 1 to 29) for which the reversible capacity and the irreversible capacity were determined in Basic Experimental Example 1, and a high-temperature cell at a low temperature was prepared. The rate-discharge characteristics and the liquid leakage when left in a charged state at a high temperature were measured.

FIG. 2 is a sectional view of a cylindrical cell having a spiral electrode group configuration. In FIG. 2, one strip-shaped positive electrode 10 and one strip-shaped negative electrode 11 are separated by a separator 1 made of a microporous polyethylene film.
The electrode group is formed by spirally winding through the electrodes 2. The positive electrode 10 is composed of LiCoO ₂ , a composite oxide of lithium and cobalt as active material, carbon black as conductive material, and polytetrafluoroethylene (PTFE) as binder at a weight ratio of 1%.
A paste mixed at a ratio of 00: 3: 10 is applied to both sides of an aluminum foil as a current collector, dried, roll-pressed, and cut into a predetermined size. In addition, P of the binder
The TFE used was a dispersion solution. Positive electrode 1
The positive electrode lead piece 13 is spot-welded to the aluminum foil of No. 0. The negative electrode 11 is obtained by applying a paste obtained by adding an acrylic binder solution to a test carbon powder on both sides of a copper foil serving as a current collector, drying the roll, and cutting it into a predetermined size. A negative electrode lead piece 14 is spot-welded to the copper foil of the negative electrode 11. After attaching the bottom insulating plate 15 to the lower surface of the wound electrode group and housing it in the cell case 16 made of nickel-plated steel plate, the negative electrode lead piece 14 is spot-welded to the inner bottom surface of the cell case 16. Thereafter, the upper insulating plate 17 is placed on the electrode group, and is then grooved at a predetermined position of the opening of the cell case 16, and a predetermined amount of an organic electrolyte is injected and impregnated. As the organic electrolyte, the same organic electrolyte as used in the basic experimental example was used.

Thereafter, the positive electrode lead piece 13 is spot-welded to the inner bottom surface of the sealing plate 19 with the gasket 18 fitted on the periphery. The cell is completed when the sealing plate 19 is fitted into the opening of the cell case 16 via the gasket 18 and the upper edge of the cell case 16 is curled inward and sealed.

The discharge capacity of each cell was regulated by the capacity of the negative electrode, and the weight of the carbon powder for the negative electrode of each cell was the same regardless of the type. The amounts of other component materials used and the production method were exactly the same so that the carbon powder for the negative electrode could be compared.

Cell a using 29 kinds of carbon powder for negative electrode
After charging all the cells at a constant current of 100 mA (１００ C) at 20 ° C. until the terminal voltage of each cell becomes 4.2 V for each of the 5 cells A to R and A to R, 100 mA (1 /
5C) The battery was discharged at a constant current up to 2.75 V to obtain a 1 / 5C discharge capacity. After that, after charging in the same manner, 500 mA
(1C) The battery was discharged at a constant current to 2.75 V to determine a 1C discharge capacity. Next, after charging at 20 ° C., the battery was allowed to stand at −20 ° C. for 24 hours, and the 1C discharge capacity was determined at the same −20 ° C. Each cell was allowed to stand still at 20 ° C, and after the cell temperature was returned to 20 ° C, the battery was charged in the same manner, and then left at 100 ° C for 1 day. Was observed for all cells.

The above-mentioned battery performance (average value of 5 cells) is summarized in Table 4 in comparison with the physical property values of the test carbon powder.

[0046]

[Table 4]

From Table 4, it can be seen that Sample No. having a small reversible capacity shown in Table 1 was obtained. Although the 1/5 C and 1 C discharge capacities at 20 ° C. of Samples 10 and 11 were low, Sample Nos. Those of the graphite powders 1 to 9 are relatively large. However, the reason why the high-rate discharge capacity (−20 ° C., 1 C) at a low temperature showed 415 mAh or more was that in Sample No. 1, 2, 6, 7, 8, 10
And cells a, b, f,
g, h, j and AR only. Further, no leakage was observed after standing at a high temperature. 4
And cells d, j, k and AR with carbon powders of 10-29. From these results, it was found that Sample No. of the present invention was excellent over all battery performances. 12-2
9 were cells A to R using graphite powder.

Sample No. The physical property values of the graphite powders of Nos. 12 to 29 were significantly different from those of the other graphite powders (Sample Nos. 1 to 9), except that the tapping density was 0.21 to 0.46 g / cc and 0.60 to 1 g / cc. .15 g / cc, and the ratio of the (110) / (004) X-ray diffraction peak intensity by the wide-angle X-ray diffraction method is 0.015 or more. These are no. The average particle size of graphite powder of 12 to 29 is 10.3
２９29.5 μm, and the specific surface area according to the BET method is 2.1 to 7.4 m ² / g, which means that the specific surface area is not too large for the average particle size. Sample N
o. The average thickness of the graphite powder of 12 to 29 is 3.1 to 8.
9 μm, 1.1 of other graphite powders (Sample Nos. 1 to 9)
A point larger than ２．５2.5 μm, that is, the graphite powder according to the present invention is obtained by dispersing flaky or massive graphite particles having high crystallinity and purity in a liquid or gas, and applying pressure to the liquid or gas. Spiral discharge from the nozzle to create a spiral shape and create a spiral shape in the process of pulverization to obtain disc-shaped or tablet-shaped particles, which are then sieved to the desired particle size, resulting in a high tapping density and a wide angle. (110) / (004) by X-ray diffraction method
Have a large X-ray diffraction peak intensity ratio. Therefore, the graphite powder has a desired average particle size distribution by appropriately pulverizing and sieving, thereby improving high-rate charge / discharge performance and high-rate discharge performance at low temperature. Moreover, even when finely pulverized, the powder thickness is large,
Among the flaky particles, those that are nearly spherical are collected, so that the specific surface area does not increase without difficulty, it is difficult to decompose the organic solvent in the electrolyte even at high temperatures, and it is difficult to raise the internal pressure of the cell It is considered that the liquid leakage accident could be completely eliminated.

Conventionally, carbon for the negative electrode of a lithium ion secondary battery, particularly graphite powder, has been controlled only by the average particle size and the specific surface area, but it will be understood that the importance of regulating by tapping density is important. In addition, as a result of many experiments other than the above,
The average particle size of the graphite powder according to the present invention is 10 to 30 μm,
It is found that the average value of the thickness of the thinnest portion is 3 to 9 μm, and the range of the (110) / (004) X-ray diffraction peak intensity ratio of 0.015 or more by the wide-angle X-ray diffraction method is appropriate. doing. It has also been confirmed that the specific surface area by the BET method in that case is 2.0 to 8.0 m ² / g, and the range of regulation of the tapping density is 0.6 to 1.2 g / cc. Further, the content of powder that is too fine to reduce reliability when left at high temperature with a particle size of less than 5 μm should be 15% or less, and the content of powder that exceeds 50 μm that inhibits high-rate discharge performance should be 30% or less. It has also been confirmed what to do.

[0050]

As described above, by using the graphite powder for a negative electrode according to the present invention, the theoretical value of the specific capacity (372 mA) is obtained.
h / g) of 351 to 360 mAh /
g (94.4-96.8%), and the irreversible capacity is 17
It is extremely small at 30 mAh / g, which contributes to the improvement of energy density. Furthermore, not only high rate charge / discharge and low temperature high rate discharge performance are excellent, but also there is an effect that a highly reliable lithium secondary battery can be provided without liquid leakage accident even when left at high temperature.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a coin-shaped cell for measuring a reversible capacity and an irreversible capacity to examine the effect of the present invention.

FIG. 2 is a cross-sectional view of a cylindrical cell having a spiral electrode group configuration according to an embodiment of the present invention.

[Explanation of symbols]

 1: Cell case 2: Lid 3: Grid 4: Metal lithium electrode 5: Carbon electrode 6: Separator 7: Gasket 10: Positive electrode 11: Negative electrode 12: Separator 13: Positive electrode lead piece 14: Negative electrode lead piece 15: Bottom insulating plate 16 : Cell case 17: Upper insulating plate 18: Gasket 19: Sealing plate

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Toyoji Sugimoto 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Kunio Tsuruta 1006 Odaka Kadoma Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Shuji Ito 1006 Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Hajime Nishino 1006 Odaka, Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Kojiro Ishikawa Shiga, Inventor 5-1 Kuribayashi-cho, Otsu-shi, Nippon Graphite Industry Seta Plant Co., Ltd. (72) Inventor Hisanori Sugimoto 5-1 Kuribayashi-cho, Otsu-shi, Shiga Prefecture Nippon Graphite Industry Co., Ltd. Seta Plant Co., Ltd. (72) Inventor Kaoru Tsukamoto Otsu, Shiga Prefecture 5-1 Kuribayashi-cho, Nippon Graphite Industry Seta Factory Co., Ltd.

Claims (8)

[Claims] 1. A negative electrode material comprising a positive electrode, a negative electrode, and a separator disposed therebetween, wherein the negative electrode is a negative electrode material capable of reversibly repeating intercalation and deintercalation of lithium ions by charging and discharging. The (002) plane spacing (d002) is 3.350 to 3.360 ° by wide-angle X-ray diffraction, and the crystallite size (Lc) in the C-axis direction is at least 1000 °.
In the process of further pulverizing the flaky or massive graphite particles as described above, they are cut into disk-like or tablet-like particles, and the average particle diameter is 10 to 30 μm by sieving and the average of the thickness of the thinnest part Value is 3-9 μm and wide angle X
A non-aqueous electrolyte secondary battery using a powder whose X-ray diffraction peak intensity ratio of (110) / (004) determined by the X-ray diffraction method is 0.015 or more. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the graphite powder for the negative electrode has a specific surface area of 2.0 to 8.0 m ² / g by a BET method. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the powder having a particle size of less than 5 μm in the graphite powder for the negative electrode is 15% or less. 4. The graphite powder for a negative electrode has a particle size of 50 μm.
The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the content of the powder exceeding 30% is not more than 30%. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the powder having a particle size of less than 5 μm and a particle size having a particle size of more than 50 μm is 15% or less and 30% or less, respectively. 6. The negative electrode graphite powder has a tapping density of 0.5.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the amount is 6 to 1.2 g / cc. 7. A positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the positive electrode is a lithium-containing transition metal oxide (chemical formula: LixMO ₂ , where M is Co, Ni, M
n, at least one transition metal selected from Fe, x = 0 or more and 1.2 or less) as an active material, and the negative electrode reversibly intercalates and deintercalates lithium ions by charging and discharging. As a negative electrode material that can be repeated, by wide-angle X-ray diffraction method (002)
In the process of further pulverizing the flaky or massive graphite particles having a plane spacing (d002) of 3.350 to 3.360 ° and a crystallite size (Lc) of at least 1000 ° in the C-axis direction, Squaring into disk-shaped or tablet-shaped particles, and sieving has an average particle size of 10 to 30.
μm and the average value of the thickness of the thinnest part is 3 to 9 μm, and X of (110) / (004) is determined by the wide-angle X-ray diffraction method.
A non-aqueous electrolyte secondary battery using a powder whose line diffraction peak intensity ratio is regulated to 0.015 or more. 8. A plane distance (d002) of a (002) plane measured by a wide-angle X-ray diffraction method is 3.350 to 3.360 °,
The crystallite size (Lc) in the C-axis direction is at least 100
Disperse scaly or massive graphite particles having an average particle diameter of 20 μm or more at 0 ° or more and an average thickness of the thinnest part of 15 μm or more in a liquid or gas, and apply pressure to the liquid or gas. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, comprising discharging spirally from a nozzle, finely pulverizing and sieving to obtain disk-shaped or tablet-shaped particles, and forming the negative electrode using the particles.