JP2003100291A - Negative electrode material of high performance lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the negative electrode material of a high performance lithium secondary battery, which enables the battery to show high performance and less discharge loss, and makes it possible to fill a large amount of negative electrode materials into the battery in a high bulk density and to perform rapid charging. SOLUTION: Graphite powder is mixed with more than one kind of fillers selected from mesophase pitch, raw coke, and calcined coke, and is further mixed with a binder pitch, then is kneaded to form a mixture. The mixture is molded under pressure, then is burnt, crushed and classified, and ultimately graphitized to obtain the negative electrode material of the high performance lithium secondary battery.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium secondary battery negative electrode material, and more specifically, it is obtained by mixing graphite powder with a filler material such as mesophase pitch and a binder pitch.
The present invention relates to a negative electrode material having a high capacity and a small capacity loss.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have been
It is widely used as a high-capacity secondary battery in portable devices such as mobile phones and personal computers, and it is expected that demand will increase further in the future.

In response to the trend toward miniaturization of such portable devices, there is an increasing demand for miniaturization and weight reduction of lithium secondary batteries.

For this reason, the performance and the performance of the parts and materials constituting the lithium secondary battery are becoming active, and in particular, the negative electrode material is becoming more important because it affects the performance of the battery.

Carbon-based materials are attracting attention as the negative electrode material. Carbon-based negative electrode materials are required to have a high discharge capacity, but in addition to this, it is important to reduce capacity loss, and in order to be able to fill a large amount of negative electrode material into a battery, Bulk density and rapid charging are also desired.

[0006] In response to such a demand for higher capacity, it has been proposed to use graphite powder such as artificial graphite or natural graphite as a negative electrode material.

However, although graphite powder is an excellent material in increasing the capacity, there are many problems such as large capacity loss and low bulk density.

Therefore, in order to meet the demand for higher performance of the lithium secondary battery as described above, it is desired to develop a more excellent negative electrode material.

[0009]

DISCLOSURE OF THE INVENTION In order to meet the above demand for higher performance of a lithium secondary battery negative electrode material, the present inventor has a high capacity, a small capacity loss, and a high bulk density in a battery. Provided is a high performance lithium secondary battery negative electrode material capable of being filled with a large amount of negative electrode material and capable of rapid charge and discharge.

[0010]

In order to solve the above problems, the present inventor proposes that the graphite powder is one or more fillers selected from mesophase pitch, green coke, and calcine coke. Lithium obtained by mixing with a material, kneading the mixture obtained by adding a binder pitch and kneading the mixture to obtain a molded body, followed by firing, pulverizing and classifying, and finally graphitizing. It is a secondary battery negative electrode material.

As mentioned above, the present inventors have found that graphite powder is an excellent material in that it has a high capacity, but in view of the problem in terms of capacity loss and the like, in addition to graphite powder, fillers such as mesophase pitch are used. It has been found that a negative electrode material having excellent properties can be obtained by using the material and the binder pitch.

That is, regarding the negative electrode material using graphite,
It was found that the specific surface area measured by the BET method tends to be large, and that there is a close relationship between this specific surface area and capacity loss.

Therefore, by preventing the increase of the specific surface area by specifying the mixing ratio of the graphite, the filler material and the binder pitch and the treatment temperature during the kneading and firing as described above,
The present invention has been completed to obtain a negative electrode material with reduced capacity loss without reducing the discharge capacity.

The constituent features of the present invention will be described in more detail below.

First, as the graphite powder, both artificial graphite and natural graphite can be used. However, the lattice constant of graphite measured by X-ray diffraction analysis is preferably Co (002) of 6.72Å or less. If it exceeds 6.72Å, the battery capacity of the negative electrode material decreases.

Next, a filler material is mixed with the above graphite powder. As the filler material, any one or more of mesophase pitch, raw coke and calcine coke is used.

The mixing ratio of the graphite powder and the filler material is 1/1.
9/1 is preferable. If it is less than 1/1, the battery capacity will decrease, and if it exceeds 9/1, the capacity loss will increase.

Binder pitch is further added to the above mixture of graphite powder and filler, and the mixture is kneaded. A normal low softening point pitch can be used for this binder pitch,
Coal-based pitch is preferred.

The ratio of binder pitch to the mixture of graphite powder and filler is preferably 100/20 to 100/60. If it is less than 100/20, the capacity loss increases, and if it exceeds 100/60, the battery capacity decreases.

The kneading temperature of the above graphite powder, filler and binder pitch is preferably 200 to 400 ° C. If the temperature is lower than 200 ° C., it is difficult to uniformly mix the three materials, and the capacity loss increases. If the temperature exceeds 400 ° C., binder pitch coking occurs and the performance of the final product deteriorates, which is a problem.

Next, the mixture obtained by kneading the graphite powder, the filler material and the binder pitch as described above is pressure-molded to obtain a molded body.

After forming the molded body, in an inert gas atmosphere,
Alternatively, firing is performed in a reducing atmosphere, and the firing temperature at this time is set to a low temperature of 800 ° C. or lower. If it exceeds 800 ° C., the specific surface area of the negative electrode material increases and the capacity loss increases, which is not preferable.

After firing, the powder is pulverized and classified to have a uniform particle size to obtain a powder. The particle size is not particularly limited, but usually the average particle size is adjusted to 50 μm or less.

Finally, the negative electrode material of the lithium secondary battery of the present invention is obtained by graphitizing in an inert gas or reducing gas atmosphere.

[0025]

EFFECT OF THE INVENTION The lithium secondary battery negative electrode material of the present invention obtained as described above has a high capacity, and at the same time, it is possible to reduce capacity loss by preventing an increase in the specific surface area of the material. Further, since the bulk density is high and the shape is close to a sphere, the filling property is good, and it is possible to fill a larger amount of the negative electrode material in the battery. Furthermore, it has a quick charge property,
It is also easy to handle. INDUSTRIAL APPLICABILITY The negative electrode material for a lithium secondary battery of the present invention is an excellent high-performance material, and is useful as a part or material for portable equipment, which is expected to grow in demand in the future.

[0026]

[Examples and Comparative Examples]

Example 1 Commercially available natural graphite crushed to an average particle size of 15 μm (product name: CPB, manufactured by Chuetsu Graphite Industry Co., Ltd., Co
(002): 6.7Å) and an average particle size of 10μ as filler material
Commercially available calcine coke (manufactured by Nippon Steel Chemical Co., Ltd.) pulverized to m or less was mixed at a ratio of 70/30. To this mixture, a commercially available coal-based pitch was used as a binder pitch at 100/4.
The mixture was added at a rate of 0 and kneaded in a kneader at 300 ° C., and the obtained mixture was pressure-molded to obtain a molded body. Next, this compact was fired at a low temperature of 600 ° C. in a nitrogen gas atmosphere,
After pulverizing and classifying to an average particle size of 20 μm, it was finally graphitized in an Acheson type graphitizing furnace to obtain graphite powder for a negative electrode material of a lithium secondary battery.

Next, using the obtained graphite powder, a battery was prepared as follows and the battery characteristics were evaluated. Originally, graphite powder was used as the negative electrode, but since lithium metal was used as the counter electrode in the present invention, the characteristics of the battery were evaluated with the positive electrode. The electrode is manufactured by 100 parts by weight of graphite powder and polyvinylidene fluoride 8
After adding N-methyl-2-pyrrolidone to the weight to form a paste, it was applied on a copper foil using a doctor blade,
Dried. After drying, this was punched out in a circular shape so as to have an area of 1 cm ² , and further pressed at a pressure of 1 ton / cm ^{2 to} prepare an electrode. Lithium metal is used as the counter electrode and the reference electrode, and the electrolyte is 1M LiClO4 / EC: DEC
A tripolar beaker cell was assembled using (volume ratio 1: 1).

Charging was carried out at a current density of 0.5 mA / cm ² at a low current and then switched to constant voltage charging at 10 mV for 0.0
It ended at 1mA. The discharge is 0.5 mA / cm ²
The constant current discharge was performed up to 1.5 V at the current density of. The measurement temperature is 30 ° C. The measurement result shows that the discharge capacity is 370 mAh /
g, the capacity loss was 35 mAh / g.

[0029]

COMPARATIVE EXAMPLE 1 Except that the ratio of natural graphite / calcine coke in Example 1 was 30/70, Example 1 was used.
A graphite powder for a lithium secondary battery was obtained by the same treatment as described above.
As a result of measuring the battery characteristics in the same manner as in Example 1, the discharge capacity was 330 mAh / g and the capacity loss was 34 mAh / g.

[0030]

Comparative Example 2 A graphite powder for a lithium secondary battery was obtained in the same manner as in Example 1 except that the ratio of natural graphite / calcinous coke in Example 1 was changed to 95/5. As a result of measuring the battery characteristics in the same manner as in Example 1, the discharge capacity was 370 mAh / g and the capacity loss was 65 mAh / g.

[0031]

COMPARATIVE EXAMPLE 3 The ratio of binder pitch to the mixture of natural graphite and calcine coke in Example 1 was 10%.
A graphite powder for a lithium secondary battery was obtained in the same manner as in Example 1 except that the amount was 0/10. As a result of measuring the battery characteristics in the same manner as in Example 1, the discharge capacity was 365 mAh / g,
The capacity loss was 70 mAh / g.

[0032]

Comparative Example 4 The ratio of the binder pitch to the mixture of natural graphite and calcine coke in Example 1 was 10%.
A graphite powder for a lithium secondary battery was obtained by the same procedure as in Example 1 except that the ratio was 0/80. As a result of measuring the battery characteristics in the same manner as in Example 1, the discharge capacity was 345 mAh.
/ G, the capacity loss was 41 mAh / g.

[0033]

Comparative Example 5 The kneading temperature in Example 1 was set to 150 ° C.
A graphite powder for a lithium secondary battery was obtained by the same procedure as in Example 1 except that the above was adopted. As a result of measuring the battery characteristics in the same manner as in Example 1, the discharge capacity was 368 mAh / g and the capacity loss was 72 mAh / g.

[0034]

Comparative Example 6 The firing temperature in Example 1 was set to 1000 ° C.
Graphite powder for a lithium secondary battery was obtained in the same manner as in Example 1 except that the above was adopted. As a result of measuring the battery characteristics in the same manner as in Example 1, the discharge capacity was 365 mAh / g and the capacity loss was 61 mAh / g.

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Claims (11)

[Claims] 1. A graphite powder containing mesophase pitch and green
Mixture and one or more filler materials selected from casks and calcine coke, and further mixed with a binder pitch to obtain a mixture, which is pressure-molded into a molded body, which is then calcined, pulverized and classified. And finally obtained by graphitization, a lithium secondary battery negative electrode material. 2. The graphite powder and filler according to claim 1.
A negative electrode material for a lithium secondary battery, wherein the mixing ratio of the materials is 1/1 to 9/1. 3. The graphite powder and filler according to claim 1.
A negative electrode material for a lithium secondary battery, wherein the ratio of the binder pitch added to the mixture in which the materials are mixed is 100/20 to 100/60. 4. The negative electrode material for a lithium secondary battery according to claim 1, wherein the temperature when the binder pitch is added and kneading is 200 to 400 ° C. 5. The firing temperature according to claim 1,
Lithium secondary battery negative electrode material at ℃ or below. 6. The graphite powder and filler according to claim 1.
The mixing ratio of the materials is 1/1 to 9/1, and the ratio of the binder pitch added to the mixture of the graphite powder and the filler material is 10
0/20 to 100/60, a negative electrode material for a lithium secondary battery in which a binder pitch was added and kneaded at a temperature of 200 to 400 ° C. 7. The graphite powder and filler according to claim 1.
The mixing ratio of the materials is 1/1 to 9/1, and the ratio of the binder pitch added to the mixture of the graphite powder and the filler material is 10
A lithium secondary battery negative electrode material having a firing temperature of 0/20 to 100/60 and a firing temperature of 800 ° C. or lower. 8. The graphite powder and filler according to claim 1.
The mixing ratio of the materials is 1/1 to 9/1, the temperature when the binder pitch is added and kneading is 200 to 400 ° C., and the firing temperature is 8
A negative electrode material for a lithium secondary battery at a temperature of 00 ° C or less. 9. The graphite powder and filler according to claim 1.
The ratio of the binder pitch added to the mixture in which the materials are mixed is 100/20 to 100/60, the temperature when the binder pitch is added and kneaded is 200 to 400 ° C., and the firing temperature is 8
A negative electrode material for a lithium secondary battery at a temperature of 00 ° C or less. 10. The graphite powder-filler mixture ratio according to claim 1, wherein the mixing ratio is 1/1 to 9/1.
The ratio of the binder pitch added to the mixture in which the materials are mixed is 100/20 to 100/60, the temperature at which the binder pitch is added and kneaded is 200 to 400 ° C., and the firing temperature is 8
A negative electrode material for a lithium secondary battery at a temperature of 00 ° C or less. 11. A lithium secondary battery using the negative electrode material for a lithium secondary battery according to claim 1.