JPH08298116A - Electrode material for secondary battery - Google Patents

Abstract

PURPOSE: To provide an electrode material for a secondary battery (particularly a negative electrode material for a lithium secondary battery) having an excellent charge/discharge capacity and charge/discharge efficiency. In more detail, to provide an electrode material for a secondary battery using very inexpensive specific artificial graphite powder capable of being manufactured in an industrially advantageous process and having a very excellent degree of graphitization. CONSTITUTION: A caking additive A1 which is the can residue obtained when the decompression distillation residue oil generated in a crude oil refining process is partially thermally decomposed by overheated steam is used as a raw material, and the caking additive A1 is coked at the cokable temperature to obtain a coked object A2. The coked object A2 is graphitized at the graphitizable temperature to obtain artificial graphite A3. The powder of the artificial graphite A3 is used as the electrode material for a secondary battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery electrode material using a specific carbon material, and more particularly to a negative electrode material for a lithium secondary battery.

[0002]

2. Description of the Related Art Conventionally, coke made from coal, petroleum, etc., natural graphite, artificial graphite, etc. have been used as carbon materials used for electrode materials of secondary batteries (chargeable / dischargeable batteries). ing.

When a carbon material is used as a negative electrode material for a lithium secondary battery, a material close to a perfect crystal of graphite is considered to be advantageous in terms of charge / discharge capacity and charge / discharge efficiency. Also,
When assembling the battery, it is necessary to apply the carbon material to the copper plate of the negative electrode and the like, so it is necessary to crush the carbon material to an appropriate particle size.

A lithium secondary battery using natural graphite is described, for example, in JP-A-6-290781. In the invention of this publication, natural graphite heat-treated at a temperature of 1800 ° C. or higher is used as a negative electrode material capable of inserting and extracting lithium ions.

Regarding artificial graphite, a typical product thereof is an artificial graphite electrode. A typical method for producing artificial graphite is as follows (for example, "Shin Carbon Industry", published by Modern Editing Co., Ltd., 2nd edition: October 27, 1982, pages 27-40). reference). (1) Mixing (kneading) First, a binder (bonding material) such as pitch is added to a filler (aggregate) such as petroleum coke and mixed under heating. The amount of binder added to 100 parts of filler is
It is usually 25 to 50 parts. The mixing temperature is, for example, 14
It is 0 to 170 ° C. (2) Molding (forming) Next, the above-mentioned mixed material is molded into a predetermined shape. Molding includes extrusion molding and molding molding. (3) Baking (baking) The above molded product is embedded in a packing material such as coke powder or silica sand to prevent deformation and oxidation during heat treatment.
The binder is carbonized by heating at 00 to 1300 ° C. (4) Impregnation (Implantation), Re-baking (Re-baking) Since 30 to 40% of the binder is volatilized in the above baking step to generate pores in the material, the pores (and originally existing in the filler) The open porosity) is filled with an impregnating agent such as molten pitch and refired to reduce the porosity. The impregnation / rebaking step may be omitted and the process may directly proceed to the next graphitization step. (5) Graphitization (Graftification) The fired product is heated to around 3000 ° C to be heat-treated. As a result, the minute graphite crystals that are irregularly arranged grow sufficiently and are oriented in an orderly manner. In this graphitization step, it takes 2 to 4 days for heating by energization and 1 to 2 weeks for cooling. By processing this, it becomes a graphite product.

Artificial graphite is also important as an electrode material for a secondary battery, but powdery artificial graphite is too expensive if it is manufactured according to the above method for that purpose. It is usual to crush and use nonstandard products at the time of manufacture.

[0007]

The method for producing high-purity powdery graphite from natural graphite has problems of securing a raw material source and of variations in the quality of raw materials, and in addition to hydrofluoric acid for removing ash. It has the disadvantage of requiring a step of cleaning with various dangerous chemicals.

In addition, when a crushed product of natural graphite is used as a negative electrode material of a lithium secondary battery, charge and discharge capacity after the second time, charge and discharge efficiency (percentage of the discharged electricity amount with respect to the first charged electricity amount), etc. There is still room for improvement in terms of basic battery characteristics. Further, since the flaky one is used as the natural graphite, it takes time to knead with the electrolytic solution or the binder, the adhesion to the copper plate of the negative electrode is not always sufficient, the amount of the electrolytic solution used becomes large, etc. The problem to be solved remains.

When crushing a nonstandard product in the production of an artificial graphite electrode into powdery artificial graphite, since the main product is an artificial graphite electrode and it is used as little as possible, a certain amount of It is difficult to secure powdered artificial graphite stably, and the price fluctuates greatly.

Therefore, it is conceivable to produce powdery artificial graphite from petroleum coke or the like, but the method is considerably high in cost, and the graphitization degree of the powdery artificial graphite obtained by the method is satisfactory. However, there is a problem in that it is significantly inferior to high quality natural graphite.

The inventors of the present invention have long been keenly studying the effective use of a binder as a bottom of a can when a vacuum distillation residue oil generated in a crude oil refining step is partially pyrolyzed by superheated steam. Since this binder has undergone a melting process once, the selective orientation of the aromatic condensed ring (layer surface) has been developed to some extent, and it may be a graphitizable carbon material. I had the idea.

The present invention is directed to an electrode material of a secondary battery (particularly, a negative electrode material for a lithium secondary battery) which has an excellent charge / discharge capacity and charge / discharge efficiency in such a background, and more specifically, it is extremely inexpensive. It is an object of the present invention to provide an electrode material for a secondary battery using a specific artificial graphite powder having an excellent graphitization degree even though it can be produced using raw materials and industrially advantageous steps. is there.

[0013]

The electrode material of the secondary battery of the present invention is a binder that is a residue of a can when the vacuum distillation residue oil generated in the crude oil refining step is partially pyrolyzed by superheated steam ( A1) as a raw material, the binder (A1) is coked at a coking temperature to form a coke product (A2), and the coking product (A2) is graphitized at a graphitizable temperature. The obtained artificial graphite (A3) powder is used as an electrode material of a secondary battery.

The present invention will be described in detail below.

In the present invention, as a raw material, a binder (A1), which is a bottom of a can when the vacuum distillation residue oil generated in the crude oil refining step is partially pyrolyzed by superheated steam, is used.
This binder (A1) is a by-product of the crude oil refining process, but since there is practically no use other than the binder for coke for iron making, it was something that was conventionally difficult to treat. It is available at a very low price. The product of partial thermal decomposition of the vacuum distillation residue oil with superheated steam is about 5% of cracked gas, about 65% of cracked oil (light oil, heavy oil), and about 30% of binders in the bottoms. %.

In the present invention, the above binder (A
The coke product (A2) is formed by coking 1) at a coking temperature, and the coke product (A2) is graphitized at a graphitizing temperature to produce artificial graphite (A3).
The coking is a step for achieving complete coking because the volatile content in the raw material binder (A1) is large. In order to obtain high quality artificial graphite (A3), the obtained coke product (A2) is usually ground under a 3 mm sieve, especially around 100 mesh, before being subjected to graphitization. Grinding, for example,
It is carried out by appropriately combining crushing methods using a crusher such as a jaw crusher, a roll crusher and a Henschel mixer. Then, by performing the graphitization step, ash and sulfur contained in the coke product (A2) fly away, and high-purity artificial graphite (A3) is obtained.

In the coking and graphitization described above, it is not necessary to mix the binder and the additive as in the conventional case (that is, the compounding may be simple), and therefore the complicated mixing process and the addition of the additives are required. Not only can the kneading steps be omitted, but the control and energy for those steps are also unnecessary, which is a great industrial advantage.

The above coking is carried out in an inert gas atmosphere at a temperature of 500 to 1200 ° C. (preferably 600 to 110).
0 ° C). When the temperature is lower than 500 ° C, the degree of coking is insufficient, and when the temperature is higher than 1200 ° C, a special furnace is required for coking, resulting in high cost. Graphitization is
The temperature is 2300 to 3000 ° C. (preferably 2500 to 3000 ° C., particularly preferably 2600) under an inert gas atmosphere.
~ 2900 ° C). If it is less than 2300 ° C, the degree of graphitization is insufficient, and if it exceeds 3000 ° C, the cost is high in terms of equipment and required power.

Although the process of obtaining the artificial graphite (A3) is simple in this way, the obtained powdery artificial graphite (A3) is obtained.
Is of very high quality and the theoretical interlayer distance d of natural graphite
(002) = 3.354 very close to angstrom 3.360 ± 0.00
6 angstroms can be obtained on an industrial scale. Further, the crystallite size Lc (002), which is a characteristic of graphite, is as large as about 1000 angstroms, and the degree of graphitization is high.

The powdered artificial graphite (A
3) is ground to a predetermined particle size, usually 1 to 100 μm, preferably 2 to 50 μm, more preferably 3 to 30 μm. The crushing method at this time is optimally a jet mill method without frictional crushing, but other crushing methods such as a disc mill method can also be adopted.

In the present invention, the artificial graphite (A3) powder obtained above is used as an electrode material for secondary batteries, particularly as a negative electrode material for lithium secondary batteries. In addition to the negative electrode material for lithium secondary batteries, it can also be used as an electrode material for polymer film batteries (paper batteries) and the like.

As the positive electrode material in the lithium secondary battery, modified MnO ₂ , LiCoO ₂ , LiNiO ₂ , LiNi _1-y Co _y O ₂ ,
_{LiMnO 2, LiMn 2 O 4,} LiFeO 2 and the like are used. As the electrolytic solution, an organic solvent such as ethylene carbonate, or a mixed solvent of the organic solvent and a low boiling point solvent such as dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxymethane, or ethoxymethoxyethane. In addition, a solution in which an electrolyte solute such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ is dissolved is used.

[0023]

The charging / discharging reaction of the lithium secondary battery is represented by the following formula 1, and lithium ions move back and forth between the positive electrode and the negative electrode. This reaction is stable when C has a crystal structure of graphite close to a perfect crystal, and a stable improvement in charge / discharge capacity and charge / discharge efficiency is expected.

[0024]

(Equation 1)

Generally, regarding the required performance of the negative electrode material for the lithium secondary battery, the charge / discharge capacity after the second time is 200 mAh /
It is considered to be good if it is g or more, but the above binder (A
The electrode material of the secondary battery of the present invention composed of the artificial graphite (A3) derived from 1) has a charge / discharge capacity after the second time of 280 mAh / g or more, and further 290 mAh / g or more as in Examples described later. , 300 mAh / g or more.

In the present invention, such excellent action and effect are obtained because the binder (A1) used as a raw material has undergone a step of once melting, so that the aromatic condensed ring (layer surface) is selectively oriented. It is thought that this is because the graphitized carbon material that has been considerably developed is obtained, and the obtained artificial graphite powder (A3) is of high quality having a graphitization degree close to that of an ideal graphite crystal.

In addition, the electrode material of the secondary battery of the present invention composed of the above-mentioned artificial graphite (A3) has better compatibility with the electrolytic solution and the binder as compared with that composed of scale-like natural graphite, and is suitable for the copper plate of the negative electrode. Since it has good adhesion, it is advantageous in terms of handling and also has an advantage that the amount of electrolyte used can be about 2/3.

In the present invention, the extremely inexpensive specific binder (A1) is used as a raw material as described above, and a plain and powdery artificial graphite is added without adding any binder or additive. Since (A3) is obtained, the process is simplified and the raw material cost and the manufacturing cost are significantly reduced.

[0029]

EXAMPLES The present invention will be further described with reference to examples.

<Test Method> The test graphite and about 4% by weight of polytetrafluoroethylene (PTFE) were kneaded and then applied to a stainless mesh. This was vacuum-dried at 150 ° C. for 12 hours and used as a test electrode. In the test, a bipolar cell was used in which a metal lithium sheet was pressure-bonded to a stainless steel plate as a counter electrode. Assemble in a dry box adjusted to a water content of 20 ppm or less, and
M-LiClO ₄ / (EC + DME (1: 1)), that is, LiClO ₄ dissolved at a 1M ratio in a mixed solvent of ethylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 1 is used. I was there.

<Preparation of Negative Electrode Material and Charge / Discharge Performance> Example 1 (Preparation of Raw Material) The residue of vacuum distillation generated in the crude oil refining step was partially pyrolyzed by superheated steam, and the bottoms of the bottom after further vacuum distillation were carried out. The binder (A1) was used as a raw material.
This binder is currently manufactured and sold by Fuji Oil Co., Ltd. under the trade name of “ASP”, “Yurika” or “Yurika ASP”.

(Coke and Graphitization) The binder described above.
After carbonizing (coking) by heating (A1) in a nitrogen gas atmosphere at a temperature of 800 ° C. for 2 hours,
The obtained coke product (A2) was sequentially pulverized using a jaw crusher, a roll crusher, and a Henschel mixer to obtain a particle size of about 100 mesh.

Then, this pulverized product was put into a graphite crucible and heated in an Atchison furnace to 2800 ° C. at a rate of about 30 ° C./hr in a nitrogen gas atmosphere and left for about 2 hours, and then slowly over a long period of time. It is graphitized by allowing it to cool,
Made with artificial graphite (A3).

(Ash content, volatile content, total sulfur content) Raw material binder (A
The industrial analysis values of 1), coke compound (A2) and artificial graphite (A3) were as follows. The analysis of ash content is based on JIS K 8812.
4. Volatile content analysis is based on JIS K 8812 5. Raw material Binder (A1) Ash: 0.20%, Volatile: 38.4% Coke (A2) Ash: 0.48%, Volatile: 2.48% Artificial graphite (A3) Ash: 0.01%, Volatile: 0.01% or less

Further, raw material binder (A1), coke product (A2)
And elemental analysis values of artificial graphite (A3), total sulfur content (JI
SK 8813 5.3) had a raw material binder (A1): 5.50% coke (A2): 5.04% artificial graphite (A3): 0.001% or less. Of the elemental analysis values of the raw binder (A1), carbon, hydrogen, nitrogen, and oxygen were 85.5%, 5.7%, and
It was 1.7% and 1.4%.

From these results, artificial graphite, which is a graphitized product,
Ash content and sulfur content were sufficiently removed from (A3), which shows that the artificial graphite (A3) has high purity and high function.

(D Value and Crystallite Size of Artificial Graphite (A3)) The degree of graphitization of the artificial graphite (A3) obtained above was measured by an X-ray diffractometer (tube voltage: 40 kV, tube current: 40 mA,
When the scan speed was 0.250 ° / min), the peaks of (002) plane and (110) plane, which are characteristic of graphite, were strongly observed. The d value and crystallite size of this artificial graphite (A3) were d (002) 3.358 angstrom Lc (002) 1020 angstrom La (110) 7098 angstrom, and it was found that graphitization was highly developed.
The theoretical interlayer distance d (002) of natural graphite is 3.354 angstroms.

(Performance as a Secondary Battery) The artificial graphite (A3) obtained above was used in a counter-type jet mill manufactured by Alpine for 1
It was ground to 0 μm. Charge and discharge current 0.5 m
A charge and discharge test was conducted under the conditions of A (0.17 mA / cm ² ), charge and discharge voltage 0.02 to 0.5 V, and the first charge and discharge efficiency was 82%, 2
The charge / discharge capacity after the first time was 320 mAh / g, and the charge / discharge efficiency after that was 99.8% or more. In addition, when this artificial graphite (A3) was used, it was easy to form a slurry with the electrolytic solution, and the binding property with the metal plate was good.

When this crushed graphite was used, it was more compatible with the electrolytic solution and the binder and had better adhesion to the copper plate of the negative electrode, as compared with the case where scaly natural graphite of Comparative Example 1 described later was used. It was advantageous in terms of handling.
The amount of electrolyte used was about 2/3.

Example 2 The artificial graphite (A3) obtained in Example 1 was pulverized to 10 μm with a Hosokawa Micron Micron Jet Mill. Charge and discharge current 0.5 mA (0.17 mA / cm ² ), charge and discharge voltage
When the charge and discharge test was conducted under the condition of 0.02 to 0.5 V, the first charge and discharge efficiency was 81%, and the second and subsequent charge and discharge capacities were 315.
It was mAh / g, and the charge / discharge efficiency after that remained at 99.8% or higher. In addition, when this artificial graphite (A3) was used, it was easy to form a slurry with the electrolytic solution, and the binding property with the metal plate was good.

Example 3 The artificial graphite (A3) obtained in Example 1 was used in a disc mill at 10 μm.
crushed to m. Charge and discharge current 0.5 mA
(0.17 mA / cm ² ), the charge and discharge voltage was 0.02 to 0.5 V. When the charge and discharge test was conducted, the charge and discharge efficiency at the first time was 78%, and the charge and discharge capacity after the second time was 295 mAh / g. Charge / discharge efficiency remained above 99.8%. In addition, this artificial graphite
When (A3) was used, it was easy to form a slurry with the electrolytic solution, and the binding property with the metal plate was good.

Comparative Example 1 Flake graphite produced in China (particle size: 100 mesh, 90% or more, purity: 99% or more) was pulverized with a ball mill to 7 μm. This crushed graphite was charged and discharged at a current of 0.5 mA (0.17 mA / cm
² ) When a charge / discharge test was conducted under the condition of charge / discharge voltage of 0.02 to 0.5 V, the charge / discharge capacity after the second time was less than 200 mAh / g.

Comparative Example 2 Lonza graphite “KS-15” having a mean particle size of about 8 μm, which is a typical artificial graphite, was charged and discharged at a current of 0.5 mA (0.17 mA / c).
When a charge / discharge test was conducted under the conditions of m ² ), charge / discharge voltage of 0.02 to 0.5 V, the charge / discharge efficiency at the first time was 49%, and the charge / discharge capacity at the second time and thereafter was only 245 mAh / g.

Comparative Example 3 Coal tar pitch was heated to 300 to 450 ° C. to generate spherulites, which were purified by solvent extraction or centrifugation to obtain mesophase small spheres having an average particle size of about 20 μm at a temperature of 2800 ° C. Artificial graphite obtained by graphitizing with
A charge / discharge test was conducted under the conditions of 0.5 mA (0.17 mA / cm ² ) and charge / discharge voltage of 0.02 to 0.5 V. The first charge / discharge efficiency was 84.
%, The charge and discharge capacity after the second time was 275 mAh / g, and the charge and discharge efficiency was good, but the charge and discharge capacity was insufficient.

Comparative Example 4 Carbon black was heat treated in an Acheson furnace in the same manner as in Example 1, and the degree of graphitization was measured by X-ray diffraction. The measurement result shows that d (002) is 3.420 angstrom and Lc (00
2) was 61.7 angstroms and La (110) was 0.0 angstroms, and the degree of graphitization was extremely low.

[0046]

EFFECT OF THE INVENTION The electrode material of the secondary battery of the present invention comprising the artificial graphite (A3) derived from the above binder (A1) is used as the negative electrode material for a lithium secondary battery after the second and subsequent times. The charge / discharge capacity is extremely high and the charge / discharge efficiency after the second time is 100.
It changes to a value close to%.

In addition, the electrode material of the secondary battery of the present invention composed of the above-mentioned artificial graphite (A3) has a better compatibility with the electrolytic solution and the binder as compared with that composed of scale-like natural graphite, and is suitable for the copper plate of the negative electrode. Since it has good adhesion, it is advantageous in terms of handling and also has an advantage that the amount of electrolyte used can be about 2/3.

In addition, the artificial graphite used as the electrode material is made of a specific binder which has been difficult to treat because it has no other application than the binder for iron coke. Therefore, effective use of such a binder is achieved. In addition to using such an extremely cheap binder as a raw material, a simple powdery artificial graphite can be obtained without adding any binder or additive, so the manufacturing process is simplified and the conventional powder The cost can be drastically reduced as compared with the artificial graphite manufacturing method.

Therefore, the electrode material of the secondary battery of the present invention is highly practical in terms of performance, cost and effective utilization of resources.

Claims (4)

[Claims] 1. A coke (A1) is used as a raw material, and the coke (A1) is a coke as a raw material when the vacuum distillation residue oil generated in the crude oil refining step is partially pyrolyzed by superheated steam. A coke product (A2) is formed by coking at a temperature that can be converted into a coke product (A2), and the coke product (A2) is graphitized at a temperature at which it can be graphitized. A secondary battery electrode material used as an electrode material. 2. The artificial graphite (A3) has a d (002) of 3.360 ± 0.006.
The electrode material for a secondary battery according to claim 1, which is angstrom. 3. The electrode material for a secondary battery according to claim 1, which has a charge / discharge capacity of 280 mAh / g or more after the second time when the charge / discharge test is performed under the condition of a charge / discharge voltage of 0.02 to 0.5 V. 4. The electrode material for a secondary battery according to claim 1, which is a negative electrode material for a lithium secondary battery.