JPH09326254A - Negative electrode material for lithium ion secondary battery and manufacture therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a lithium ion secondary battery having large discharge capacity since charge capacity is large and initial discharge efficiency is high by forming a thermally decomposed carbon layer on a surface of a carbon particle by chemical evaporation processing, and using a negative electrode material having a prescribed characteristic. SOLUTION: A negative electrode material composed of a carbon particle and a thermally decomposed carbon layer formed by chemical evaporation processing by covering a surface of its carbon particle, is used as a negative electrode material to be used in a lithium ion secondary battery. In its negative electrode material, the specific surface area is set not more than 5m<2> /g, and a balanced adsorption moisture quantity is set not more than 0.3wt%. It is desirable that the carbon particle is formed by baking a condensate by methylene type bonding of aromatic sulfonic acid or its salt at 400 to 1100 deg.C, and an average particle diameter is 0.1 to 100μm, and a thickness of the thermally decomposed carbon layer is 0.1 to 2μm.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a negative electrode material for a lithium ion secondary battery, which has a large capacity and a high potential and is excellent in charge / discharge cycle characteristics.

[0002]

2. Description of the Related Art As electronic devices become smaller and lighter, higher energy density of batteries is required, and in terms of resource saving,
There is an urgent need to develop a secondary battery that can be repeatedly charged and discharged. In response to this demand, high energy density,
A lithium-ion secondary battery that is lightweight, compact, and has excellent charge / discharge cycle characteristics has been proposed. Lithium-ion secondary batteries have been developed to solve the problems of lithium metal secondary batteries, such as poor quick chargeability, short cycle life, and lack of safety due to dendrite formation. It is.

Conventionally, metallic lithium was used for the negative electrode in the lithium metal secondary battery, but in the lithium ion secondary battery, the above problem has been solved by using the carbon material for the negative electrode.

That is, when charging is performed using a lithium compound as a positive electrode and a carbon material or graphite material as a negative electrode, lithium ions are doped into the carbon material or graphite material at the negative electrode, so-called carbon-lithium intercalation compound or graphite-lithium intercalation compound. Is formed.

On the other hand, during discharge, lithium ions are dedoped from the layers, and the lithium ions are recombined with the lithium compound of the positive electrode. By repeating the above cycle, a chargeable / dischargeable battery is formed.

When graphite is used as the negative electrode material of a lithium ion secondary battery, a graphite-lithium ion intercalation compound, which is doped at a ratio of 6 carbon atoms to 1 lithium atom, is formed during charging. At this time, the theoretical discharge electric capacity per carbon weight is 372 mA · h / g.
However, the graphite negative electrode material used in commercially available lithium ion secondary batteries has an electric capacity of 250 to 30.
It is 0 mA · h / g, and only about 70 to 80% of the theoretical discharge amount is utilized.

Recently, it has been reported that when a non-graphitized carbon material is used for the negative electrode, the charge / discharge capacity of the lithium ion secondary battery exceeds the theoretical value of 372 mA · h / g.
This means that during charging, lithium is not only a carbon-lithium intercalation compound represented by carbon and C ₆ Li, but also partially C
_This suggests that a carbon-lithium intercalation compound represented by _n Li (n <6) may be formed, or lithium may be metallically contained in the void of carbon. However, as described above, most of carbon materials having a large charge capacity of 600 to 700 mA · h / g have low initial discharge efficiency, so that the discharge capacity is not only 400 to 450 mA · h / g. Since such a battery has a low discharge potential, the energy density of the lithium ion secondary battery is currently low.

[0008]

As a result of research on the cause of the irreversible capacity of the lithium ion secondary battery, the present inventors have found that the cause of the irreversible capacity is mainly on the surface of the carbon material constituting the negative electrode. It was found to be due to the electrolysis of the solvent. It is considered that the electrolysis of the solvent occurs by using the carbon material forming the negative electrode as a catalyst, and by making the negative electrode material into a structure inert to the electrolysis of the solvent,
We thought that the expression of irreversible capacity could be suppressed. For that purpose, it is desirable to make the specific surface area of the negative electrode carbon material as small as possible.

Generally, the specific surface area decreases as the particle size increases, and the irreversible capacity also decreases, but the charging capacity decreases as the particle size increases, and the discharge capacity of the lithium ion secondary battery decreases. In order to increase the charge capacity and simultaneously increase the charge / discharge density, it is preferable to reduce the particle size of the carbon material. The present inventors have solved this contradictory requirement by surface-treating carbon particles by a chemical vapor deposition method.

That is, fine carbon particles having a large charge capacity are used as the raw material carbon particles, and the surface of the carbon particles is subjected to a treatment by a chemical vapor deposition method to completely coat the surface of the carbon particles with pyrolytic carbon. Electrolysis of the solvent on the surface of carbon particles during charging is suppressed, and a large amount of charge and high initial discharge efficiency are exhibited, and as a result, carbon particles subjected to chemical vapor deposition can have a large reversible discharge capacity. Heading out, the present invention has been completed.

Therefore, the present invention improves the initial discharge efficiency of the lithium ion secondary battery by improving the carbon material,
An object of the present invention is to provide a negative electrode material for a lithium ion secondary battery, which has a large discharge capacity, a high energy density, and enables a long cycle life to be completed, and a method for producing the same. It is a thing.

[0012]

Means for Solving the Problems The present invention, which achieves the above object, provides a lithium ion secondary battery comprising carbon particles and a pyrolytic carbon layer formed by chemical vapor deposition to coat the surface of the carbon particles. A negative electrode material for lithium ion secondary batteries, characterized in that the negative electrode material has a specific surface area of 5 m ² / g or less and an equilibrium adsorbed water content of 0.3 wt% or less. The average particle size of the carbon particles is 0.1 to 100 μm, the thickness of the pyrolytic carbon layer is 0.1 to 2 μm, the carbon particles are non-graphitizable carbon, and the carbon particles Is a condensate of aromatic sulfonic acid or a salt thereof with a methylene type bond of 400 to 110.
It is obtained by firing at 0 ° C., has a 002 plane lattice constant C _{0 (00 2)} of 0.750 to 0.820 nm, and has a volume resistance of the carbon particles pressed at 300 kgf / cm ^2. It includes that it is 6.0 × 10 ^{−3 to} 1.0 × 10 ¹¹ Ω · cm.

Further, the present invention is characterized in that the surface of carbon particles is treated by a chemical vapor deposition method, and the pyrolytic carbon layer formed by the chemical vapor deposition treatment to coat the surface of the carbon particles. And a specific surface area of the negative electrode material is 5 m ² / g.
The method for producing a negative electrode material for a lithium ion secondary battery having an equilibrium adsorbed water content of 0.3 wt% or less, wherein the average particle diameter of the carbon particles is 0.1 to 100 μm, and the thickness of the pyrolytic carbon layer is Is 0.1 to 2 μm, the carbon particles are non-graphitizable carbon, and the chemical vapor deposition treatment is 800 to 11
It is carried out at 00 ° C., and the carbon particles form a condensate of aromatic sulfonic acid or a salt thereof by a methylene type bond in a range of 400 to 1100.
It is obtained by firing at 0 ° C., has a 002 plane lattice constant C _{0 (00 2)} of 0.750 to 0.820 nm, and has a volume resistance of 6 when the carbon particles are pressed at 300 kg / cm ^2. It includes that it is 0.0 × 10 ^{−3 to} 1.0 × 10 ¹¹ Ω · cm.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Raw material carbon particles used for producing a negative electrode material for a lithium ion secondary battery of the present invention are:
Either graphitizable carbon particles or non-graphitizable carbon particles can be used. These carbon particles can be obtained by carbonizing bituminous substances produced by thermal decomposition of coal or petroleum, and various synthetic resins.

The carbon particles are preferably non-graphitizable carbon having a 002 plane crystal lattice constant C _{0 (002)} of 0.750 to 0.820 nm. Particularly preferred are carbon particles obtained by molding a condensate of an aromatic sulfonic acid or a salt thereof by a methylene type bond into a spherical shape and then calcining at 550 to 1100 ° C.

The aromatic sulfonic acids or salts thereof used in the present invention include naphthalenesulfonic acid, anthracenesulfonic acid, phenanthrenesulfonic acid, methylnaphthalenesulfonic acid, dimethylnaphthalenesulfonic acid, creosote oil, anthracene oil, tar, and Examples include sulfonated mixtures of polycyclic aromatic compounds such as pitch, toluenesulfonic acid, phenolsulfonic acid and mixtures thereof, or salts thereof. These sulfonic acids can be produced by sulfonation of the corresponding aromatic compounds by a method known per se. Examples of the cation forming the aromatic sulfonate include Li ⁺ , Na ⁺ , K ⁺ , NH ^{4+ and the} like. An ammonium salt is preferable from the viewpoint of easy handling. Alkali metal salts such as lithium salts may ignite when exposed to the atmosphere after carbonization, so care must be taken when handling them.
It is suitable for producing carbon particles with low crystallinity, that is, having a large crystal lattice constant, and when the negative electrode material produced using this is used in a lithium ion secondary battery, it is effective in suppressing the generation of irreversible components. Is. The potassium salt is particularly preferred for this purpose.

Aromatic sulfonic acids or their condensates can be produced by a method known per se. That is, in general, aromatic sulfonic acids or salts thereof are condensed with formalin, paraformaldehyde, hexamethylenetetramine, or other aldehydes. Moreover, you may use the polymer of the aromatic sulfonic acid which has a methylene type bond obtained by superposing | polymerizing the aromatic sulfonic acid which has a vinyl group like polystyrene sulfonic acid. As the linking group for binding the aromatic sulfonic acids, a —CH ₂ — group is particularly preferable because of its easy production and ready availability. But,
_{- (CH 2) n -T X} - (CHR) m - ( However, T is a benzene ring or a naphthalene ring, R represents hydrogen, a lower alkyl group or a benzene ring, n, m, x and each are an integer of 0 or 1 A compound having a linking group represented by the formula) can also be used. These condensates may be a mixture of two or more condensates or a copolymer.

An example of a condensate of aromatic sulfonic acids or salts thereof used in the present invention is a formaldehyde condensate of ammonium β-naphthalene sulfonate.

The condensate is a mixture of a condensate from a monomer to about 200-mer, and its average molecular weight is 2000.
It is about 50,000. This substance is a solid at room temperature and hardly dissolves in a non-polar solvent such as benzene, but dissolves in a polar organic solvent such as acetone or acetonitrile at a low concentration, and is easily dissolved in an aqueous solvent. The viscosity of this 60% by weight aqueous solution at 60 ° C. is 10 to 2000 pois.
Although it is about e, columnar, spherical, plate-like, flaky, film-like, fibrous, honeycomb-like etc. can be freely adjusted by changing the degree of condensation of the condensate and the concentration of the solution to adjust to an appropriate viscosity. It can be molded into various shapes. Further, as a molding aid, a water-soluble polymer compound such as polyvinyl alcohol, polyethylene oxide or polyacrylic acid can be used. Further, the formaldehyde condensate of ammonium β-naphthalene sulfonate may be dried and then crushed to adjust the viscosity to an appropriate value. The aromatic sulfonic acids used in the present invention or polystyrene sulfonic acids, which are a kind of condensate of their salts, can be used as the water-soluble polymer. The shape of the carbon particles is not specified, and various shapes such as spherical shape, flaky shape, and fibrous shape can be adopted, and spherical shape with a minute particle size is particularly preferable. When it is not necessary to specify the shape of the carbon particles, the carbon particles can be obtained by crushing a condensate of sulfonic acids or their salts as described below. That is, a method of crushing and condensing a condensate of aromatic sulfonic acids or salts thereof that is a raw material of carbon particles, aromatic sulfonic acids, or condensate of a salt thereof is crushed after heat treatment at 400 to 500 ° C., Further, a method of carbonizing, a method of crushing an aromatic sulfonic acid, or a condensate of a salt thereof at 700 to 1100 ° C. and then crushing is preferable.

The method of forming the condensate of aromatic sulfonic acids or salts thereof into microspheres is not particularly limited, but for example, the condensate of aromatic sulfonic acids or salts thereof is preferably a solvent, especially water. , And then can be formed into microspheres by a known method such as a spray drying method or a precipitation method in which an antisolvent is added. Among them, the spray drying method has the advantage that the particle size can be reduced, the obtained sphere is a true sphere, and further the production apparatus is simple. Therefore, the aromatic sulfonic acids of the present invention, or a salt thereof is used. It is suitable as a method for molding the condensate into microspheres.

There is a method of carbonizing a condensate of an aromatic sulfonic acid or a salt thereof and then pulverizing this to obtain fine carbon particles. The carbonized product of a condensate of an aromatic sulfonic acid or a salt thereof is low temperature. Although it is a carbide, it is hard carbon unique to amorphous carbon. Therefore, it is extremely difficult to grind this to a micron size, and it is not possible to obtain carbon particles having a spherical shape.

In the present invention, when the carbon particles are made spherical, the purpose thereof is to make the negative electrode material produced by pressure molding with a binder to form a negative electrode, and the negative electrode material is packed closest to the negative electrode material, and The carbon filling amount can be increased, and as a result, it is useful for increasing the charge / discharge capacity of the battery, and it is also possible to secure the permeation route of the electrolytic solvent, and it is expected that rapid charging / discharging can be performed. Especially.

Aromatic sulfonic acids molded into microspheres,
Alternatively, the condensate of those salts is then carbonized into carbon particles. Alternatively, the aromatic sulfonic acid or a condensate of a salt thereof is carbonized and then crushed to obtain carbon particles. The carbonizing atmosphere is not particularly limited as long as it is a non-oxidizing atmosphere, but a nitrogen atmosphere is usually preferable. When carbonizing a condensate of aromatic sulfonic acids or salts thereof, ammonia generated with thermal decomposition, sulfurous acid gas, steam, lower hydrocarbons generated with further carbonization, hydrogen sulfide, gases such as hydrogen, Purge with inert gas.

Aromatic sulfonic acids, or condensates of their salts, can be graphitized at 2800 ° C.
The crystal lattice constant C _{0 (002)} of the plane is 0.680 nm to 0.7
It is about 00 nm, and aromatic sulfonic acids or salts thereof can be said to be so-called non-graphitizable carbon. In addition, β which is a kind of condensate of aromatic sulfonic acids or their salts
Methylene-bonded condensate of naphthalene sulfonic acid 70
The crystal lattice constant C _{0 (002)} of the 002 surface of the 0 ° C.-treated product is 0.7.
It is 86 nm, and the crystal lattice constant C _{0 (002)} of the 002 plane of the 1000 ° C.-treated product is also equal to 0.786 nm, and therefore crystallization hardly progresses even by the heat treatment at 700 to 1000 ° C. It is understood that sulfonic acids, or condensates of their salts, are non-graphitizable.

It is desirable that the carbon particles, which are the carbonized product of the condensation product of the aromatic sulfonic acids or their salts, used in the negative electrode material for a lithium ion secondary battery of the present invention be a low temperature carbonized product. The heat treatment temperature is preferably 550 to 1100 ° C, particularly preferably 600 to less than 800 ° C. The processing time for processing at this temperature is preferably 1 to 120 minutes. However, since the carbon particles are inevitably subjected to heat treatment in the subsequent chemical vapor deposition treatment, there is practically no problem even if the heat treatment temperature of the carbon particles is lower than the chemical vapor deposition treatment temperature. For this reason, the actual heat treatment temperature required for carbonization is such that ammonia, sulfurous acid gas, and steam are generated during the thermal decomposition of the condensation product of aromatic sulfonic acids or their salts, and the shape of the carbon particles does not change thereafter. 400
~ 550 ° C is practically sufficient. In summary, the heat treatment temperature of 400 to 1100 ° C. is preferable as a whole.

The carbon particles obtained by the above method and the like are of low crystallinity, and the crystal lattice constant C _{0 (002)} of the 002 plane is preferably 0.750 to 0.820 nm. When the crystal lattice constant C _{0 (002)} is less than 0.750 nm, the lithium ion doping amount is insufficient and a sufficient charge capacity cannot be obtained.

When the crystal lattice constant C _{0 (002)} exceeds 0.820 nm, the doping amount of lithium ions becomes insufficient,
Not only a sufficient charge amount cannot be obtained, but also the ratio (efficiency) of the discharge capacity to the charge capacity becomes low and so-called irreversible components increase, so that the electric capacity of the lithium ion secondary battery decreases. Furthermore, the volume resistance increases and the internal resistance of the negative electrode increases accordingly, which is unsuitable as an electrode material.

The volume resistance of the carbon particles is 30
Volume resistance when pressurized at 0 kgf / cm ² is 6.0 ×
It is preferably 10 ^{−3 to} 1.0 × 10 ¹¹ Ω · cm. When the volume resistance is less than 6.0 × 10 ⁻³ Ω · cm, the lithium ion doping amount is insufficient, and a sufficient charge capacity cannot be obtained. When the volume resistance exceeds 1.0 × 10 ¹¹ Ω · cm, the doping amount of lithium ions is insufficient and a sufficient charge amount cannot be obtained, and the ratio (efficiency) of the discharge capacity to the charge capacity becomes low. The so-called irreversible component increases, and the electric capacity of the lithium ion secondary battery decreases. Furthermore, when the volume resistance increases, the internal resistance of the negative electrode increases, which is unsuitable as an electrode material.

Japanese Unexamined Patent Publication (Kokai) No. 1332031/1994 describes that a carbon material obtained by carbonizing a methylene bond-type condensate of aromatic sulfonic acid is suitable for a negative electrode material of a lithium ion secondary battery. . However, JP-A-6-1320
The carbonization temperature of the salt of the aromatic sulfonic acid condensate described in 31 is 800 to 1800 ° C, which is higher than the heat treatment temperature (carbonization temperature) 550 to 1100 ° C adopted in the present invention. The difference is that carbonization is performed. Further, by pulverizing after carbonization, the method disclosed in JP-A-6-13
The crystal lattice constant C _{0 (002)} of the 002 plane of the carbon material used in 2031 is 0.68 to 0.72 nm.
This has a crystal lattice constant C _{0 (002)} of 002 plane of the carbon particles of 0.750 to 0.8.
Small compared to 20 nm. That is, JP-A-6-1320
The carbon material used in No. 31 is a carbon material having high crystallinity, which is obviously different from the carbon particles used in the present invention, particularly the carbon particles starting from the aromatic sulfonic acid condensate.

The carbon particles are then subjected to chemical vapor deposition on their surfaces.

The average particle size of the carbon particles used in the chemical vapor deposition treatment is preferably 0.1 to 100 μm. When the number of particles having an average particle size of less than 0.1 μm increases, the bulk density of the carbon particles decreases, and in this case, the filling amount of the carbon material per volume of the manufactured negative electrode cannot be increased. Further, if the number of particles having an average particle size of more than 100 μm increases, the charging amount of the carbon material per volume of the negative electrode cannot be increased and the charging speed further decreases, as in the above case. The most preferable one has an average particle size of 5 to 20 μm, and 0.1 to 1
The carbon particles have a particle size distribution that is almost normally distributed in the particle size range of 00 μm.

In the present invention, the carbon particles are subjected to a chemical vapor deposition treatment to form a pyrolytic carbon layer on the surface of the carbon particles, thereby coating the surface of the carbon particles. By this operation, the carbon particles are reformed into a carbon material having a small specific surface area and become the negative electrode material of the present invention.

Japanese Unexamined Patent Publication No. 7-230803 discloses a method of chemically refining non-graphitizable carbon to modify it into a carbon material suitable for a negative electrode material for a lithium ion secondary battery.
According to this, the carbon material subjected to the chemical vapor deposition treatment is one in which the adsorption amount of the organic solvent is reduced as much as possible while maintaining the porous characteristics having a large specific surface area. Therefore, the chemical vapor deposition treatment method of the present invention is a method for producing molecular sieve carbon itself, and therefore the chemical vapor deposition temperature is 700 ° C. or lower. As a result, carbon generated by thermal decomposition is deposited at the pore inlet portion of the obtained carbon material, and the pore inlet portion is narrowed so that the solvent cannot penetrate.

According to the research conducted by the present inventors, in order to modify a carbon material into a carbon material suitable for a negative electrode material for a lithium ion secondary battery, a pyrolytic carbon to be deposited at a pore inlet portion of the carbon material. The amount of is not sufficient if the pore inlet is narrowed to the extent that the solvent cannot penetrate into the pores, and the surface of carbon particles is completely covered with a pyrolytic carbon layer and cannot be measured by the gas adsorption method. It was found that the carbon material must have a small specific surface area and that the amount of water adsorbed must be extremely small. In order to produce such a carbon material, the chemical vapor deposition treatment temperature needs to be a high temperature which is considered unsuitable as a method for producing molecular sieve carbon. That is, the chemical vapor deposition treatment can be performed at a temperature not required to narrow the pore inlet, but at a high temperature at which the pore inlet distributed on the entire surface of the carbon particles can be completely covered with the pyrolytic carbon layer. is necessary.

Further, in order to completely cover the entire surface of the carbon particles with the pyrolytic carbon layer, a method of previously coating the surface of the carbon particles with a pyrolytic hydrocarbon compound and thermally decomposing this to deposit carbon Is insufficient. That is, it was found that it is necessary to introduce an organic substance in a gas state into a chemical vapor deposition treatment system to perform uniform chemical vapor deposition treatment.

The surface area of the carbon material whose surface is completely covered with the pyrolytic carbon layer is substantially the same as the geometrically calculated outer surface area, and the amount of adsorbed water is small.

The specific surface area of the carbon particles subjected to the chemical vapor deposition treatment, that is, the negative electrode material of the present invention is 5 m ² / g or less, preferably 1
m ² / g or less. If the specific surface area exceeds 5 m ² / g, the initial discharge efficiency will be low even if chemical vapor deposition is performed.

The thickness of the pyrolytic carbon layer is preferably 0.1 to 2 μm, particularly preferably 0.5 to 1 μm.

The chemical vapor deposition treatment temperature is preferably 800 to 1100 ° C. When the treatment temperature is lower than 800 ° C., the deposition rate of the pyrolytic carbon layer during the chemical vapor deposition treatment is low, and the chemical vapor deposition treatment time becomes excessively long. For example, when benzene is used as a pyrolytic carbon source, the temperature at which chemical vapor deposition starts is 774 ° C.
It is. On the other hand, when the chemical vapor deposition treatment temperature exceeds 1100 ° C., the charge / discharge capacity decreases, and a high capacity negative electrode material for a lithium ion secondary battery cannot be obtained.

Organic substances used as a pyrolytic carbon source for chemical vapor deposition include benzene, toluene, xylene,
Styrene, ethylbenzene, diphenylmethane, diphenyl, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, etc., or a mixture thereof, gas light oil obtained in the tar distillation step, creosote oil, anthracene oil, Naphtha cracked tar oil and the like are preferable. Also, ethylene, propylene, isopropylene,
Butadiene and the like are also used as a carbon source for the chemical vapor deposition process.

The negative electrode material produced by the above chemical vapor deposition treatment has a small specific surface area and thus a small amount of equilibrium adsorbed water.
The value is 0.3 wt% or less. When the equilibrium adsorbed water content exceeds 0.3 wt%, the initial discharge efficiency becomes small. When the equilibrium adsorbed water content is 0.3 wt% or less, the initial discharge efficiency rapidly increases, especially when the equilibrium adsorbed water content is 0.2 w.
When it is t% or less, the initial discharge efficiency is 90% or more.

In the present invention, the carbon particles produced as described above and having a pyrolytic carbon layer formed on the surface thereof by the chemical vapor deposition treatment are used as a negative electrode material for a lithium ion secondary battery.

A method for preparing a negative electrode for a lithium ion secondary battery using the above-mentioned negative electrode material is not particularly limited, but for example, a binder and a solvent are added to the negative electrode material and sufficiently kneaded, and then a current collector such as a metal mesh is formed. It can be pressure bonded to form a negative electrode. As the binder, for example, various pitches,
Known materials such as polytetrafluoroethylene can be used. Among them, polyvinylidene fluoride (PVDF), ethylene propylene diene polymer (E
PDP) is preferred.

The positive electrode material is not particularly limited, but LiCo
Lithium-containing oxides such as O ₂ , LiNiO ₂ and LiMn ₂ O ₄ are preferred. The powdered positive electrode material can be produced by adding a conductive material, a solvent, and the like, if necessary, in addition to the binder, kneading the mixture sufficiently, and then molding the resultant with a current collector.

The separator is also not particularly limited,
Known materials can be appropriately used.

As the non-aqueous solvent used as the electrolytic solvent,
Known aprotic low-dielectric constant solvents that dissolve lithium salts are preferred. For example, ethylene carbonate, propylene carbonate, diethylene carbonate, acetonitrile, propionitrile, tetrahydrofuran, γ-butyrolactone, 2-methyltetrahydrofuran,
Solvents such as 3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, sulfolane, methylsulfolane, nitromethane, N, N-dimethylformamide, dimethylsulfoxide, etc. are used alone. , Or a mixture of two or more solvents.

The lithium salt used as the electrolyte is L
iClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , Li
B (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ SO ₃ L
i, CF ₃ SO ₃ Li and the like are preferable, and these salts are used alone,
Alternatively, they may be used in combination.

Each physical property value was measured by the following methods.

Crystal lattice constant C ₍₀₀₂₎ : Cu-Kα rays were monochromaticized by a monochromator using an X-ray diffractometer RINT1400 manufactured by Rigaku Denki KK, tube voltage 40 KV, tube current 2
The measurement was performed under the conditions of 00 mA, scanning speed 1.0 °, divergence slit 1/2 °, scattering slit 1/2 °, and light receiving slit 0.15 mm.

Average particle size and particle size distribution: SALD 1100 manufactured by Shimadzu Corporation was used and measured with water as a dispersion medium.

Volume resistance: A steel tube having an inner diameter of 1 cm and an inner surface lined with vinyl chloride was filled with the sample, and the sample was pressed with a steel piston at 300 kgf / cm ² , and the resistance value r in the pressing direction and the sample thickness d were measured. The volume resistance R = r × (0.
5) Calculated from the formula of ² × 3.14 / d.

Specific surface area: Determined by the BET method from the adsorption amount of carbon dioxide gas at the acetone-dry ice temperature using a gas adsorption tester Sorptograph ADS-1B manufactured by Shimadzu Corporation.

Equilibrium adsorbed water content: Tabai Espec Co., Ltd.
Using a small-sized environmental tester, the sample was adsorbed with water at a temperature of 20 ° C. and a humidity of 95%, and the weight of the sample reached a equilibrium value.

[0054]

The present invention will be described below in detail with reference to examples.

Example 1 To 1280 g of naphthalene having a purity of 95% by weight, 1050 g of sulfuric acid having a concentration of 98% by weight was added,
After sulfonation at 160 ° C. for 2 hours, unreacted naphthalene and reaction product water were distilled out of the system under reduced pressure. Then, add 857 g of formalin with a concentration of 35% by weight at 105 ° C for 5
The reaction was carried out for a time to obtain a methylene-bonded condensate of β-naphthalenesulfonic acid. Further, the condensate was neutralized with ammonia water, and then No. 5 It filtered with the filter paper and the filtrate was obtained. The number average molecular weight of the obtained methylene-bonded condensate of β-naphthalenesulfonic acid was 4,300. Water was added to this filtrate to prepare an aqueous solution in which the concentration of the methylene-bonded condensate of β-naphthalenesulfonic acid ammonium salt was 13.3% by weight.

This aqueous solution was granulated with a spray dryer and dried. The spherical particles of the methylene-bonded condensate of β-naphthalenesulfonic acid thus obtained were heated in a nitrogen stream at a heating rate of 20 ° C / min,
It was kept at 550 ° C. for 1 hour for carbonization. The obtained carbon particles have a crystal lattice constant C _{0 (002)} of 0.810 nm, a minimum particle diameter of 0.2 μm, a maximum particle diameter of 44 μm, and an average particle diameter (5
0% volume average diameter) is 8.45 μm, volume resistance is 1.05
× 10 ¹⁰ Ω · cm.

The carbon particles were heated to 25 using an ebullated bed reactor.
Nitrogen gas saturated with benzene at ℃ was sent to the carbon particles heated to 1000 ℃, the chemical vapor deposition treatment was performed at that temperature for 60 minutes. The average particle size (50% volume average particle size) of the negative electrode material of the present invention obtained by this treatment was 9.34 μm, the specific surface area was 1.2 m ² / g, and the average water adsorption amount was 0.15 wt%. It was

In order to study the performance of the negative electrode material for a lithium ion secondary battery thus prepared, a non-aqueous solvent battery having the negative electrode material as a positive electrode and metallic lithium as a negative electrode was prepared and a charge / discharge test was conducted. Lithium ion doping (intercalation) and dedoping (disintercalation) capacity of the positive electrode made of the present negative electrode material were measured.

The details will be described below.

A positive electrode composed of the present negative electrode material was prepared by the following method. That is, to 40 parts by weight of the present negative electrode material, 1 part by weight of ethylene propylene dimonomer as a binder and a small amount of dimethylformamide were added and mixed well to form a paste, and 2 t was added to a circular stainless mesh (2.5 cm ² ).
It was pressure-molded at on / cm ² . Then, it was vacuum dried at 200 ° C. for 2 hours to prepare an electrode, which was used as a positive electrode. A battery was constructed by using this positive electrode and metallic lithium as a negative electrode, and the negative electrode material was subjected to an evaluation test using the battery. The electrolytic solvent was a mixed solvent of propylene carbonate and dimethyl carbonate (volume ratio 1: 2), LiPF ₆ was used as the electrolyte, and the concentration was adjusted to 1.0 mol / l.

A porous polypropylene non-woven fabric is used as a separator, and a glass fiber filter paper is impregnated with an electrolytic solution.
A coin cell was created under an argon atmosphere. A charge / discharge test was carried out with the current density at the time of charging / discharging being 1.0 mA / cm ² .

The initial charge capacity was 622 mA · h / g. The discharge was cut at 1.5 V and a cycle test was performed. The discharge capacity at the first cycle is 574 mA · h / g, and the initial discharge efficiency (discharge capacity / charge capacity × 100%)
Was 92.3%. The discharge capacity at the 500th cycle was 554 mA · h / g, and almost no decrease in discharge capacity was observed.

(Example 2) Tar produced by Mitsui Mining Co., Ltd. was distilled, and the distillation residue having a boiling point of 360 ° C. or higher had an average particle size of 20 μm.
It was ground to the following. Put the crushed product in a boiling bed reactor, 3
After heat-treating for 30 minutes in an air stream of 40 ° C to infusibilize the crushed product, the atmosphere gas was changed to nitrogen gas,
The temperature was raised to 1,000 ° C. at a heating rate of ° C./min to form carbon particles. Then, the carbon particles are added to the reactor in the same amount of 1000 times.
With the temperature kept at 0 ° C, the gas oil fraction of 120 to 180 ° C obtained by the previous distillation was introduced into a reactor in a nitrogen atmosphere to carry out chemical vapor deposition treatment.

The carbon particles before chemical vapor deposition had an average particle diameter of 5.6 μm, a specific surface area of 8.7 m ² / g and an equilibrium adsorbed water content of 4.3% by weight.

The carbon particles obtained by subjecting the above-mentioned carbon particles to chemical vapor deposition, that is, the negative electrode material according to the present invention has an average particle size of 6.17.
μm, the specific surface area was 2.8 m ² / g, and the equilibrium adsorbed water content was 0.11% by weight.

In order to examine the performance of the carbon particles (negative electrode material) subjected to the chemical vapor deposition as a negative electrode material for a lithium ion secondary battery, a non-aqueous solvent battery using this negative electrode material as a positive electrode and metallic lithium as a negative electrode was prepared. Create and do charge and discharge test,
Lithium ion doping (intercalation) and dedoping (disintercalation) capacity of the positive electrode made of the present negative electrode material were measured.

The initial charge capacity was 552 mA · h / g. The discharge was cut at 1.5 V and a cycle test was performed. The discharge capacity at the first cycle was 550 mA · h / g.
And the initial discharge efficiency (discharge capacity / charge capacity × 100
%) Was 91.0%. The discharge capacity at the 500th cycle was 502 mA · h / g, and almost no decrease in discharge capacity was observed.

(Study Examples 1 to 7) 1420 g of absorbing oil gives 98
1050 g of weight% sulfuric acid was added, the mixture was heated at 145 ° C. for 2 hours to sulfonate the absorbing oil, and then the unreacted oil and the reaction product water were distilled off under reduced pressure. Subsequently, 857 g of 35% by weight formalin was added and reacted at 105 ° C. for 4 hours to obtain a methylene-bonded condensate of β-sulfonic acid mainly composed of methylnaphthalene.

Furthermore, after 90% by weight of the obtained condensate was neutralized with aqueous ammonia and 10% by weight with potassium hydroxide, the filter paper No. No. manufactured by Toyo Roshi Kaisha, Ltd. was used. Filtration at 5 gave a filtrate. The number average molecular weight of the obtained methylene-bonded condensate of methylnaphthalene-based β-sulfonic acid was 5,700.

Water was added to the filtrate to prepare an aqueous solution having a concentration of 12.5% by weight of a methylene-bonded condensate of a methylnaphthalene-based ammonium salt of β-sulfonic acid and a potassium salt.

This aqueous solution was granulated with a spray dryer and dried. The methylene-bonded condensate spherical particles of β-sulfonic acid mainly composed of methylnaphthalene thus obtained were heated in a nitrogen stream at a temperature rising rate of 2 ° C./minute and held at 900 ° C. for 1 hour to be carbonized. . The obtained carbon particles have a crystal lattice constant C _{0 (002)} of 0.805 nm, a minimum particle diameter of 0.1 μm, a maximum particle diameter of 44 μm, an average particle diameter (50% volume average diameter) of 9.03 μm, and a volume resistance. was 5.42 × 10 ^{over 2 Ω} · cm.

Using a continuous boiling bed reactor, the above carbon particles, gas light oil and nitrogen gas were introduced from the bottom of the reactor. The chemical vapor deposition treatment was performed by heating at a reaction temperature of 1000 ° C. and variously changing the reaction time. Table 1 shows the physical properties of the negative electrode material obtained by this treatment and the results of charge and discharge tests.

The charging / discharging test method was the same as that described in Example 1. That is, a non-aqueous solvent battery having a negative electrode material as a positive electrode and metallic lithium as a negative electrode was prepared, and a charge / discharge test of this battery was conducted.

[0074]

[Table 1] (Comparative Example 1) The spherical particles of the methylene-bonded condensate of the β-naphthalene sulfonic acid ammonium salt obtained in Example 1 were put into a horizontal quartz reaction tube, and the particles were heated in a nitrogen gas atmosphere at 95
The heat treatment was performed by keeping at 0 ° C. for 60 minutes. The carbon particles obtained by this heat treatment had an average particle diameter (50% volume average diameter) of 31.2 μm, a specific surface area of 12.7 m ² / g, and an equilibrium adsorbed water content of 12.9% by weight.

In order to study the performance of the carbon particles (not subjected to the chemical vapor deposition treatment) obtained by the above heat treatment as a negative electrode material for a lithium ion secondary battery, the heat treatment was carried out by the same method as in Example 1. The obtained carbon particles are used as a positive electrode,
A non-aqueous solvent battery having metallic lithium as a negative electrode was prepared and a charge / discharge test was conducted to measure lithium ion doping (intercalation) and dedoping (disintercalation) capacity of a positive electrode composed of carbon particles. .

The initial charge capacity was 687 mA · h / g. The discharge was cut at 1.5 V and a cycle test was performed. The discharge capacity at the first cycle was 460 mA · h / g.
And the initial discharge efficiency (discharge capacity / charge capacity × 100
%) Was 67.0%. The discharge capacity at the 500th cycle was 421 mA · h / g, and a considerable decrease in discharge capacity was observed.

(Comparative Example 2) Using the carbon particles before the chemical vapor deposition treatment with the gas oil fraction of Example 2, the performance of the carbon particles as a negative electrode material for a lithium ion secondary battery was examined. In the same manner as in Example 1, a non-aqueous solvent battery having the above-mentioned carbon particles as a positive electrode and metallic lithium as a negative electrode was prepared and a charge / discharge test was conducted to dope lithium ions (intercalation) to the positive electrode made of carbon particles. ) And the dedoping (disintercalation) capacity were measured.

The initial charge capacity was 624 mA · h / g. The discharge was cut at 1.5 V and a cycle test was performed. The discharge capacity at the first cycle was 299 mA · h / g.
And the initial discharge efficiency (discharge capacity / charge capacity × 100
%) Was 47.7%. The discharge capacity at the 500th cycle was 257 mA · h / g, and a considerable decrease in discharge capacity was observed.

[0079]

Since the negative electrode material for a lithium ion secondary battery of the present invention is constructed as described above, the lithium ion secondary battery manufactured using the same has a large charge capacity and an initial discharge efficiency of the conventional one. It has a large discharge capacity because it is larger than that of the battery.

 ──────────────────────────────────────────────────の Continued on the front page (72) Koji Sakata, Inventor Mitsui Mining Co., Ltd. 2-1-1 Nihonbashi Muromachi, Chuo-ku, Tokyo

Claims (11)

[Claims] 1. A negative electrode material for a lithium ion secondary battery, comprising a carbon particle and a pyrolytic carbon layer which covers the surface of the carbon particle and is formed by chemical vapor deposition, the specific surface area of the negative electrode material. Is 5 m ² / g or less, and the equilibrium adsorbed water content is 0.3 wt% or less, a negative electrode material for a lithium ion secondary battery. 2. The average particle diameter of carbon particles is 0.1 to 100 μm.
The negative electrode material according to claim 1, which is m. 3. The negative electrode material according to claim 1, wherein the pyrolytic carbon layer has a thickness of 0.1 to 2 μm. 4. The negative electrode material according to claim 1, wherein the carbon particles are non-graphitizable carbon. 5. Carbon particles are obtained by calcining a condensate of an aromatic sulfonic acid or a salt thereof with a methylene type bond at 400 to 1100 ° C., and its 002 plane lattice constant C _{0 (002)} is 0. 5. The volume resistance of the carbon particles as pressed under 300 kgf / cm ² at 0.750 to 0.820 nm is 6.0 × 10 ^{−3 to} 1.0 × 10 ¹¹ Ω · cm. The negative electrode material as described in 1. 6. Lithium comprising carbon particles, wherein the surface of the carbon particles is treated by a chemical vapor deposition method, and a lithium comprising a carbon particle and a pyrolytic carbon layer formed by the chemical vapor deposition treatment to coat the surface of the carbon particles. A method for producing a negative electrode material for a lithium ion secondary battery, which is a negative electrode material for an ion secondary battery, wherein the negative electrode material has a specific surface area of 5 m ² / g or less and an equilibrium adsorbed water content of 0.3 wt% or less. 7. The average particle diameter of carbon particles is 0.1 to 100 μm.
The method for producing a negative electrode material according to claim 6, wherein m is m. 8. The method for producing a negative electrode material according to claim 6, wherein the pyrolytic carbon layer has a thickness of 0.1 to 2 μm. 9. The method for producing a negative electrode material according to claim 6, wherein the carbon particles are non-graphitizable carbon. 10. The method for producing a negative electrode material according to claim 6, wherein the chemical vapor deposition treatment is performed at 800 to 1100 ° C. 11. A carbon particle is a condensate of an aromatic sulfonic acid or its salt formed by a methylene type bond at 400 to 1100 ° C.
The 002 plane lattice constant C _{0 (002)} is 0.750 to 0.820 nm, and the carbon particles are pressed at 300 kgf / cm ² and the volume resistance is 6.0. The method for producing a negative electrode material according to claim 6, wherein the negative electrode material has a density of × 10 ^{-3 to} 1.0 × 10 ¹¹ Ω · cm.