JP2003282049A - Manufacturing method of negative electrode material for lithium secondary battery and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a negative electrode material for a lithium secondary battery in which a charge/discharge efficiency in the initial period can be maintained or improved. <P>SOLUTION: The negative electrode material in which a mixture of a carbonaceous material of a difficult graphitization characteristic and graphite is fired and which is constituted of difficult graphitization graphite and the graphite is manufactured. The carbonaceous material (for example, a bitumen substance which may be cross-linked, a resin or the like) may be infusion or oxidation treated. The negative electrode material can be manufactured by firing the mixture at around 900 to 1,300°C. If the lithium secondary battery is constituted of this negative electrode material, the charge/discharge efficiency of the lithium secondary battery in the initial period can be maintained or improved. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a negative electrode material for a lithium secondary battery having high initial charge / discharge efficiency, and a lithium secondary battery provided with the negative electrode material obtained by this production method.

[0002]

2. Description of the Related Art In recent years, electronic devices, especially portable electronic devices (personal computers, MD players, CD players, DVD players, mobile phones, etc.) have been made smaller, thinner, and lighter.
As a driving power source or a backup power source for these electronic devices, a lithium secondary battery that can be charged with high energy density and that can be discharged with high efficiency has been rapidly developed, and has been put into practical use. ing.

A conventional lithium secondary battery uses a carbonaceous or graphitic material as a negative electrode active material, and occludes (deintercalates) or deintercalates (intercalates) lithium in the carbonaceous or graphitic material in an ionic state. Charging and discharging are repeated. For example, when graphite is used as the negative electrode active material, the theoretical charge / discharge capacity of the graphite intercalation compound (composition: LiC ₆ ) is 372 Ah / kg.
Is. However, the charge / discharge capacity of this negative electrode is 1 / the theoretical charge / discharge capacity (3862 Ah / kg) of lithium metal alone.
Not only does it become as low as about 10 or less, but also the graphite crystal structure deteriorates (e.g., the distance between graphite layers increases) with repeated charging / discharging (charging / discharging cycle), and the charging / discharging capacity decreases.

Japanese Unexamined Patent Publication (Kokai) No. 6-333564 discloses a secondary battery having a negative electrode composed of a mixture of non-graphitizable carbonaceous material (non-graphitizable carbonaceous material) and easily graphitizable carbonaceous material (graphite or graphitic material). Is disclosed. In this secondary battery, it is possible to increase the charge / discharge capacity as compared with the negative electrode composed of graphite alone, by absorbing lithium ions not only between the crystallites of graphite but also in difficult graphite. The cycle characteristics can be improved. However, in the secondary battery, since the difficult graphite and the graphite are mixed in the negative electrode, the decomposition reaction of the electrolytic solution (for example, propylene carbonate) may occur on the surface of the graphite, and the initial charge / discharge efficiency may decrease. .

[0005]

Therefore, an object of the present invention is to provide a method for producing a negative electrode material for a lithium secondary battery, which can maintain or improve not only charge and discharge capacity but also initial charge and discharge efficiency, and a method for producing the same. To provide a lithium secondary battery.

Another object of the present invention is to provide a method for producing a negative electrode material for a lithium secondary battery, which can maintain or improve the initial charge / discharge efficiency by a simple method.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a mixture of graphite with a carbon material capable of forming difficult graphite (low crystalline carbon) by firing. The present invention has been completed by discovering that, when calcined, it is possible to produce a negative electrode material for a lithium secondary battery with high initial charge / discharge efficiency, probably because the graphite of the carbon material generated by the thermal CVD reaction coats the graphite surface. .

That is, in the present invention, a mixture of a non-graphitizable carbon material and graphite is fired to produce a negative electrode material for a lithium secondary battery composed of the non-graphite and graphite.

The non-graphitizable carbon material may be a bituminous substance which may be crosslinked, a resin, etc., and may be infusibilized or oxidized. In the firing of the mixture, the firing temperature may be about 900 to 1300 ° C., and the ratio of the difficult graphite and the graphite is the former / the latter (weight ratio) = about 5/95 to 95/5. May be.

The present invention also includes a lithium secondary battery provided with the negative electrode material obtained by the above manufacturing method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a mixture of a non-graphitizable carbon material and graphite is fired to obtain a non-graphitizable carbon (low crystalline carbon).
A negative electrode material for a lithium secondary battery composed of and graphite is manufactured.

In the present invention, the difficult graphite (low crystalline carbon) means a carbonaceous material (low crystalline carbonaceous material) in which the graphite structure is not sufficiently developed, and its crystal structure is
For example, the surface spacing d (002) is 0.34 nm or more (for example, 0.34 to 0.5 nm, preferably 0.34 to
0.4 nm), the length in the c-axis direction (Lc) and the length in the a-axis direction (La) are 10 nm or less (for example, 1 to 10).
nm, preferably about 1 to 8 nm) in many cases.

The non-graphitizable carbon material (hereinafter sometimes simply referred to as a carbon material) is not particularly limited as long as it is a material which can be carbonized by firing to form the non-graphitizable material. (Carbon material that does not form graphite even by carbonization or graphitization) is used. The non-graphitizable carbon material may be used alone or in combination of two or more kinds.

Examples of the non-graphitizable carbon material include aromatic compounds (eg, phenolphthalein, 9,9 ').
-Dibenzylanthracene, p-terphenyl, Δ9,
Fused polycyclic hydrocarbons such as 9′-bifluorene and 1,3,6,8-tetraphenylpyrene; Δ10,10′-bianthrone, phenanthrenequinone, acenaphthenequinone, 9-xanthylideneanthrone, 9,9 '-Bixanthylene, 9-methylacenaphthoquinoxaline, condensed ring compounds in which a heterocyclic ring such as phthalazine is condensed with an aromatic hydrocarbon ring), sugars, resins (phenolic resin, furan resin, furfural resin, cellulosic resin, poly Examples thereof include vinylidene chloride, aramid resin, polyamide resin), and bituminous substances (isotropic pitch, isotropic tar, etc.).

The bituminous substance may be derived from petroleum or coal, and a substance from which light components have been removed beforehand may be used.

Preferred non-graphitizable carbon materials are bituminous substances (eg isotropic pitch, isotropic tar), phenol resins, aramid resins, polyamide resins and the like.

The carbon material (for example, the bituminous material) may be crosslinked. The cross-linking (or condensation) reaction is usually performed in the presence of a cross-linking agent, and as the cross-linking agent, xylene halide (such as xylene chloride such as p-chloromethyltoluene) and xylene dihalide (1,4-bis ( Aromatic halides such as xylene dichloride such as chloromethyl) benzene; Aromatic alcohols such as xylenol (2,4-dimethylphenol), xylene glycol (bis (hydroxymethyl) benzene, dimethyl-p-xylene glycol, etc.) Aromatic compounds such as terephthalic acid halides (terephthalic acid chloride, etc.), isophthalic acid halides (isophthalic acid dichloride, etc.), phthalic acid halides (phthalic acid dichloride, etc.), naphthalenedicarboxylic acid halides (2,6-naphthalenedicarboxylic acid chloride, etc.) acid Ride: benzaldehyde, hydroxybenzaldehyde (p-hydroxybenzaldehyde, 2,5-dihydroxybenzaldehyde, etc.), alkoxybenzaldehyde (p-methoxybenzaldehyde, etc.), benzaldehyde dimethyl acetal, terephthalaldehyde, isophthalaldehyde, salicylaldehyde, and other aromatic aldehydes It can be illustrated. Preferred crosslinking agents are bifunctional crosslinking agents (eg, xylene dihalide, xylene diol, terephthalic acid halide, etc.).
The crosslinking agents may be used alone or in combination of two or more.

The ratio of the carbon material (for example, the above-mentioned bituminous substance) and the crosslinking agent is, for example, the former / the latter (weight ratio) = 9.
9.99 / 0.01 to 60/40, preferably 99/1
It is about 70/30.

The crosslinking (or condensation) reaction may be carried out in the presence of a catalyst. An acid catalyst can be usually used as the catalyst. As the acid catalyst, for example, a conventional acid such as Lewis acid and Bronsted acid can be used, and as the Lewis acid, ZnCl ₂ , BF ₃ , AlCl ₃ , SnCl ₄ , T
Examples of the Bronsted acid include iCl _{4 and the} like.
Examples thereof include organic acids such as p-toluenesulfonic acid, trifluoromethanesulfonic acid and xylenesulfonic acid, and mineral acids such as hydrochloric acid, sulfuric acid and nitric acid. A preferred acid catalyst is Bronsted acid, such as p-toluenesulfonic acid. You may use these catalysts individually or in combination of 2 or more types. The amount of the catalyst used is not particularly limited, and is about 0.001 to 1 molar equivalent, preferably 0.05 to 0.5 molar equivalent, relative to 1 mole of the crosslinking agent. The crosslinking reaction may be carried out under an active atmosphere (air, oxygen etc.) or an inert atmosphere (nitrogen, helium, argon etc.) or under heating. The heating temperature is, for example, 50 to 400 ° C., preferably 80 to 35.
It is about 0 ° C.

The carbon material may be infusibilized (or oxidized). The infusibilizing treatment is particularly useful for improving the coverage of the non-graphite on the graphite, that is, for improving the initial charge / discharge efficiency. A known method can be used as the infusibilizing treatment. For example, it can be carried out by heating the carbon material, which has been pulverized (eg, pulverized by a ball mill, hammer mill, etc.) as necessary, in the presence of an oxidizing gas (eg, air, oxygen, ozone, etc.). . The infusibilizing treatment temperature is, for example, 120 to 40.
The temperature is 0 ° C, preferably 150 to 330 ° C, and more preferably 170 to 320 ° C.

The carbon material may be crushed by a crusher (ball mill, hammer mill, etc.).
The average particle size of the carbon material is not particularly limited, for example,
It may be 1 to 50 μm, preferably 1 to 30 μm, and more preferably about 1 to 20 μm.

As the graphite used in the present invention, artificial graphite and natural graphite, including graphitized mesophase spherules, can be used. These graphites can be used alone or in combination of two or more. The crystal structure of graphite is not particularly limited as long as it can transfer and receive lithium ions.
(002) is about 0.3354 to 0.34 nm, preferably about 0.3354 to 0.337 nm. The length Lc in the c-axis direction is 30 to 200 nm, preferably 50 to 1
It is about 50 nm. The length La in the a-axis direction is 50 to 3
It is about 00 nm, preferably about 70 to 200 nm. The raw material graphite may have a crystal structure of graphite in advance, or may be formed by firing. Usually, as the graphite, a material having a graphite structure is often used.

The form of graphite is not particularly limited, and an amorphous shape,
It may be flat (or flat), flaky, powdery, or the like. The average particle size of graphite is not particularly limited, and may be, for example, 0.
It can be selected from a wide range of about 1 to 100 μm, and usually 1
-40 μm, preferably 2-30 μm (for example, 5-2
It may be about 0 μm.

The specific surface area of graphite is, for example, 0.5 to 10
m ² / g, preferably about 0.5 to ⁵ m ² / g, and the bulk density is, for example, about 0.1 to 1.5 g / mL, preferably about 0.5 to 1.5 g / mL.

The ratio of the carbon material and the graphite is, for example, the former / the latter (weight ratio) = 5 /, in consideration of the carbonization rate by firing.
95-95 / 5, preferably 10 / 90-90 / 10,
More preferably, it can be selected from the range of about 20/80 to 80/20.

The carbon material and the graphite can be mixed using a conventional mixer. When the carbon material is crushed by the crusher, the carbon material and the graphite are mixed in this crusher. May be. If necessary, the mixture may be mixed while crushing the carbon material and graphite. Further, in the mixing step, if necessary, a solvent (for example, water, alcohols, hydrocarbons, esters, ketones, ethers, etc.) may be used and uniformly mixed.

By firing the mixture (homogeneous mixture) thus obtained, it is possible to obtain a fired product in which the surface of graphite is coated with non-graphite. Probably, when this fired product is used, the charge and discharge capacity and A negative electrode material having high initial charge / discharge efficiency can be obtained. The firing may be performed by firing the mixture (or pulverized product). The firing temperature can be selected at least in the range that allows carbonization, and is, for example, 700 to 3300 ° C, preferably 800 to 2000 ° C, more preferably 900 to 1
500 ° C. (eg 900-1300 ° C., especially 100
0 to 1200 ° C.). The firing time is, for example, 1
It is about 10 hours, preferably about 1 to 5 hours, more preferably about 1 to 3 hours. Firing can be usually performed in an inert atmosphere (eg, nitrogen, helium, argon, etc.), in a vacuum, or the like.

In the calcined product, the ratio of difficult graphite to graphite is, for example, former / latter (weight ratio) = 5/95 to 95 /
5, preferably 20/80 to 90/10, more preferably 30/70 to 80/20 (for example, 40/60 to 7).
It may be about 0/30). If the ratio of the difficult graphite is too small, the coverage of the difficult graphite on the graphite may not be sufficient, and the initial charge / discharge efficiency may be reduced.

The calcined product (carbon material) can usually be used in the form of powder. The average particle size of the powdery carbonaceous material (carbonaceous negative electrode material) may be usually 1 to 40 μm, preferably about 1 to 30 μm. The aspect ratio (ratio of major axis to minor axis of particles) of the powdery carbon material (carbonaceous negative electrode material) is 1 to 1.
It is 0, preferably about 1 to 6 (for example, 1 to 3).
The specific surface area of the powdery carbonaceous material is, for example, 0.1 to 5
m ² / g, preferably from 0.5~4.5m ² / g, more preferably 0.8~4m ² / g approximately.

The reason why the initial charge / discharge efficiency (or capacity) is increased by using the thus obtained fired product as the negative electrode material is considered as follows. When a negative electrode material containing graphite is used, a decomposition reaction of an electrolytic solution (for example, propylene carbonate) usually occurs on the surface of graphite, and the initial charge / discharge efficiency (or capacity) is often lowered. In the negative electrode material of the present invention, it is because the difficult graphite (low crystalline carbon) carbonized by the thermal CVD reaction coats the surface of the graphite, or the negative electrode material obtained by simply mixing the difficult graphite and the graphite. In comparison, since the specific surface area for the electrolytic solution can be reduced, the decomposition reaction of the electrolytic solution can be suppressed, and the initial charge / discharge efficiency can be maintained or improved without lowering. In addition, since the decomposition reaction of the electrolytic solution and the side reaction caused by the electrolytic solution can be suppressed, the safety is improved.

The carbonaceous negative electrode material obtained by the method of the present invention is
It can be used as a constituent material of a negative electrode for a lithium secondary battery by a conventional method. For example, a method of molding a mixture containing a negative electrode material, a binder, etc .; a method of applying a paste containing a negative electrode material, an organic solvent, a binder, etc., onto a negative electrode current collector using a coating means (such as a doctor blade). It can be a shaped negative electrode for a lithium secondary battery. In forming the negative electrode, it may be combined with a terminal if necessary.

The negative electrode current collector is not particularly limited, and a known current collector, for example, a conductor such as copper can be used. As the organic solvent, a solvent capable of dissolving or dispersing a binder is usually used, and examples thereof include organic solvents such as N-methylpyrrolidone and N, N-dimethylformamide. The amount of the organic solvent used is not particularly limited as long as it is in a paste form, and is, for example, usually about 60 to 150 parts by weight, preferably about 60 to 100 parts by weight, relative to 100 parts by weight of the negative electrode material.

Examples of the binder include fluorine-containing resins (polyvinylidene fluoride, polytetrafluoroethylene, etc.). The amount of the binder used (in the case of a dispersion, the amount calculated as solid content) is not particularly limited, and the lower limit is usually 3 parts by weight or more with respect to 100 parts by weight of the negative electrode material (calcined product). The amount is preferably about 5 parts by weight or more. The upper limit of the amount of the binder used is usually 20 parts by weight or less (for example, 15 parts by weight or less), and preferably about 10 parts by weight or less with respect to 100 parts by weight of the negative electrode material. More specifically, the amount of the binder used is, for example, 3 to 20 parts by weight, preferably 5 to 15 parts by weight (e.g., 5 to 5 parts by weight) based on 100 parts by weight of the negative electrode material (calcined product) in terms of solid content. 10 parts by weight). The method for preparing the paste is not particularly limited, and examples thereof include a method of mixing a mixed liquid (or dispersion liquid) of a binder and an organic solvent with a negative electrode material.

The negative electrode material obtained by the method of the present invention and a conductive material (or a carbonaceous material or a conductive carbon material) are used in combination,
You may manufacture a negative electrode. The use ratio of the conductive material (or carbonaceous material) is not particularly limited, but is usually 1 to 1 with respect to the total amount of the negative electrode material and the carbonaceous material obtained by the method of the present invention.
It is about 0% by weight, preferably about 1 to 5% by weight. By using a conductive material (carbonaceous material) together, the conductivity as an electrode can be improved. Examples of such a conductive material (carbonaceous material) include carbon black (eg, acetylene black, thermal black, furnace black). The conductive material (conductive carbon material) can be used alone or in combination of two or more kinds.
The conductive material (carbonaceous material) can be effectively used together with the negative electrode material by, for example, mixing a paste containing a negative electrode material and a solvent and applying the paste to the negative electrode current collector.

The amount of the paste applied to the negative electrode current collector is not particularly limited and is usually about 5 to 15 mg / cm ² , preferably about 7 to 13 mg / cm ² . The thickness of the film applied to the negative electrode current collector (the thickness of the paste) is, for example, 50 to 300 μm, preferably 80 to 200 μm.
m, and more preferably about 100 to 150 μm.
After the application, the negative electrode current collector may be subjected to a drying treatment (for example, vacuum drying).

By using the negative electrode for a lithium secondary battery composed of the negative electrode material of the present invention, the charge / discharge capacity is large,
A lithium secondary battery having improved initial charge / discharge efficiency can be manufactured. Specifically, the lithium secondary battery has a battery configuration such as the negative electrode (negative electrode containing the negative electrode material), a positive electrode capable of inserting and extracting lithium, an electrolytic solution, a separator, a current collector, a gasket, a sealing plate, a case, and the like. The element can be manufactured by a conventional method. FIG. 1 is a partial cross-sectional view showing an example of a lithium secondary battery.

The lithium secondary battery comprises a positive electrode 1 composed of a positive electrode active material, a negative electrode 3 containing the negative electrode material, and the positive electrode 1.
The separator 2 is provided between the negative electrode 3 and the negative electrode 3.
The separator 2 is impregnated with a non-aqueous solvent electrolyte. The positive electrode 1, the separator 2 and the negative electrode 3 are case 4
It is housed inside and the opening of the case 4 is sealed with a sealing plate 5. Further, a current collector 6 made of nickel mesh, metal wire mesh or the like is arranged between the case 4 and the negative electrode 1. Reference numeral 7 is an insulating packing.

The positive electrode is not particularly limited, and a known positive electrode can be used, and the positive electrode can be composed of, for example, a positive electrode current collector, a positive electrode active material, a conductive agent and the like. Examples of the positive electrode current collector include aluminum. As the positive electrode active material, TiS ₂ , MoS ₃ , NbSe ₃ , FeS, VS ₂ ,
Metal chalcogenide having a layered structure such as VSe ₂ ; C
oO ₂ , Cr ₃ O ₅ , TiO ₂ , CuO, V ₃ O ₆ , Mo
₃ O, V ₂ O ₅ (.P ₂ O ₅ ), Mn ₂ O (.Li ₂ O), L
Examples thereof include metal oxides such as iCoO ₂ , LiNiO ₂ and LiMn ₂ O ₄ ; and conjugated polymer substances having conductivity such as polyacetylene, polyaniline, polyparaphenylene, polythiophene and polypyrrole. A preferred positive electrode active material is a lithium composite oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ . The positive electrode active material may be used alone or in combination of two or more kinds. As a conductive agent
For example, conductive carbon black (such as acetylene black) can be exemplified.

The electrolytic solution is not particularly limited, and a known one can be used. For example, a non-aqueous lithium secondary battery can be manufactured by using a solution prepared by dissolving an electrolyte in an organic solvent as the electrolytic solution. Examples of the electrolyte include LiPF ₆ , LiClO ₄ , LiBF ₄ ,
_{LiClF 4, LiAsF 6, LiSbF 6} , LiAl
Examples thereof include lithium salts that generate anions that are difficult to solvate, such as O ₄ , LiAlCl ₄ , LiCl, and LiI. Examples of the organic solvent include carbonates (propylene carbonate, ethylene carbonate, diethyl carbonate, etc.), lactones (γ-butyrolactone, etc.), chain ethers (1,2-dimethoxyethane, dimethyl ether, diethyl ether, etc.), cyclic Ethers (tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, etc.), sulfolanes (sulfolane, etc.), sulfoxides (dimethylsulfoxide, etc.), nitriles (acetonitrile, propionitrile, benzonitrile, etc.), amides (N, N-dimethylformamide, N,
Examples thereof include aprotic solvents such as N-dimethylacetamide) and polyoxyalkylene glycols (diethylene glycol). The organic solvent is
They may be used alone or as a mixed solvent of two or more kinds.

The electrolyte concentration is, for example, about 0.3 to 5 mol, preferably 0.5 to 3 mol, and more preferably about 0.8 to 1.5 mol of electrolyte relative to 1 L of the electrolytic solution.

The separator is not particularly limited and may be a known separator, for example, a polyolefin-based porous film such as a porous polypropylene nonwoven fabric or a porous polyethylene nonwoven fabric.

The lithium secondary battery may have any shape such as a cylindrical shape, a square shape, and a button shape. The lithium secondary battery of the present invention, as a distributed type, portable battery,
It can be used as a power source or auxiliary power source for electronic devices, electric devices, automobiles, power storage, etc.

[0043]

In the present invention, by firing a mixture of a carbon material capable of forming difficult graphite by carbonization and graphite,
It is possible to obtain a negative electrode material for a lithium secondary battery that can suppress the decomposition reaction of the electrolytic solution and maintain or improve the initial charge / discharge efficiency, probably because the graphite surface is coated with the difficult graphite. Further, the initial charge / discharge efficiency can be improved by a simple method of mixing and firing, as compared with a negative electrode material for a lithium secondary battery formed of graphite (or a carbon material containing graphite). Therefore, a lithium secondary battery having excellent initial charge / discharge efficiency can be provided.

[0044]

EXAMPLES The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to these examples.

EXAMPLE Pitch 5 with a softening point of 68.2 ° C. containing no quinoline insoluble matter
00 g, 30 g of dimethyl paraxylene glycol and 1 g of paratoluenesulfonic acid as an acid catalyst were charged into a reactor having a capacity of 1 liter, heated to 330 ° C., and then blown with air at a rate of 5 liter / min under normal pressure. Two
The carbon precursor (crosslinked pitch) was prepared by polycondensing (or crosslinking) the pitch for 40 minutes.

The carbon precursor was cooled to room temperature, the obtained solid was crushed by a ball mill, and the mixture was heated at a rate of 2 ° C./min for 30 minutes while supplying air at a rate of 5 liters / min.
The infusibilizing treatment was performed by raising the temperature to 0 ° C.

Then, the obtained infusible substance and graphite were mixed at a ratio of the former / the latter (weight ratio) = 1/1, and the temperature was raised to 1100 ° C. in a nitrogen stream in a heating furnace, and the temperature was raised to 2 By holding for a time, carbonaceous negative electrode material particles having an average particle size of 5.7 μm were obtained.

Polyvinylidene fluoride was added as a binder to the obtained carbonaceous negative electrode material, and N, N-dimethylformamide was mixed as a solvent to obtain a uniform slurry, and the slurry was thickened on a copper foil roll. 100 ~
A negative electrode was prepared by applying a coating of 140 μm and vacuum drying at 200 ° C. for 6 hours.

Then, together with the negative electrode obtained above, a positive electrode using LiCoO ₂ as a positive electrode active material, ethylene carbonate and diethyl carbonate as an electrolytic solution,
1 mol / L of lithium perchlorate (LiClO ₄ ) in a solvent mixed with the former / latter (volume ratio) = 1/1.
A lithium secondary battery having a structure shown in FIG. 1 was produced by using a solution dissolved at a ratio of and a polypropylene non-woven cloth as a separator. In FIG. 1, the lithium secondary battery includes a positive electrode 1, a separator 2, a negative electrode 3, a case 4,
It is composed of a sealing plate 5, a current collector 6, and an insulating packing 7.

The characteristics of the obtained carbonaceous negative electrode material as a negative electrode material for lithium secondary batteries were measured. Measurement is 1mA / c
It was carried out under a constant current charge / discharge of ² m ² , and the discharge capacity was 2.
The capacity was determined until the voltage dropped to 0V.

Comparative Example A negative electrode was prepared by using a mixture of a carbonaceous (non-graphite) material obtained by firing without mixing graphite and graphite in a ratio of former / latter (weight ratio) = 1/3. A lithium secondary battery was prepared in the same manner as in the example except that the body was prepared, and the characteristics of the lithium secondary battery were measured.

Table 1 shows the characteristics of the negative electrode materials obtained in Examples and Comparative Examples.

[0053]

[Table 1]

As can be seen from Table 1, in Example 1 in which graphite was mixed with the carbon precursor and fired, the specific surface area of the negative electrode material with respect to the electrolytic solution can be reduced, and the initial charge / discharge efficiency of the lithium secondary battery can be reduced. Has improved.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing an example of a lithium secondary battery.

[Explanation of symbols] 1 ... Positive electrode 2 ... Separator 3 ... Negative electrode 4 ... Case 5 ... Seal plate 6 ... Current collector 7 ... Insulating packing

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Natarajan Chinna Samii             4-1-2 Hirano-cho, Chuo-ku, Osaka City, Osaka             Gas Co., Ltd. F-term (reference) 4G146 AA01 AA02 AB01 AC16B                       AC20B AD23 AD25 BA02                       BA22 BC02 BC33B                 5H029 AJ03 AJ07 AK02 AK03 AK05                       AK16 AK18 AL07 AM03 AM04                       AM05 AM07 CJ02 CJ08 CJ14                       CJ24 DJ08 DJ16 DJ17 DJ18                       EJ04 HJ02 HJ14                 5H050 AA08 AA13 BA17 CA02 CA07                       CA11 CA20 CA29 CB08 DA03                       DA09 EA08 FA17 FA18 FA19                       FA20 GA02 GA10 GA15 GA24                       HA02 HA14

Claims (7)

[Claims] 1. A method for producing a negative electrode material for a lithium secondary battery, which is composed of non-graphitizable carbon and graphite by firing a mixture of a non-graphitizable carbon material and graphite. 2. The method according to claim 1, wherein the non-graphitizable carbon material is at least one selected from a bituminous substance which may be crosslinked and a resin. 3. The method according to claim 1, wherein the non-graphitizable carbon material is a bituminous substance that has been infusibilized or oxidized. 4. The manufacturing method according to claim 1, wherein the firing temperature is 900 to 1300 ° C. 5. The method according to claim 1, wherein the ratio (weight ratio) of the refractory graphite and the graphite is the former / the latter = 5/95 to 95/5. 6. A negative electrode material for a lithium secondary battery composed of non-graphite and graphite is produced by firing a mixture of an infusibilized or oxidized bituminous substance and graphite at 1000 to 1200 ° C. In the method, the ratio of the refractory graphite to the graphite is the former / the latter (weight ratio) = 30/70 to 95 /
The manufacturing method according to claim 1, wherein the manufacturing method is 5. 7. A lithium secondary battery comprising the negative electrode material obtained by the method according to claim 1.