JP2849562B2 - Lithium ion secondary battery and negative electrode material for the battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery having a large capacity and excellent charge / discharge cycle characteristics, and a negative electrode material for the battery.

[0002]

2. Description of the Related Art As electronic devices become smaller and lighter, batteries are required to have a higher energy density. From the viewpoint of resource saving, there is an urgent need to develop secondary batteries that can be repeatedly charged and discharged. To meet this demand, lithium ion secondary batteries having a high energy density, a small size, and excellent charge / discharge cycle characteristics have been proposed. Lithium ion secondary batteries have been developed to solve the problems of lithium metal secondary batteries having poor quick chargeability, short cycle life, poor safety, and the like. Lithium metal secondary batteries use metallic lithium for the negative electrode, while lithium ion secondary batteries solve the above problem by using a carbon material for the negative electrode.

That is, when charging is performed using a lithium compound as a positive electrode and carbon as a negative electrode, the carbon negative electrode is doped with lithium ions to form a so-called carbon-lithium interlayer compound. On the other hand, at the time of discharging, lithium ions are undoped from the interlayer, and the lithium ions are combined with the lithium compound of the positive electrode again to form a chargeable / dischargeable battery.

When graphite is used as a negative electrode material of a lithium ion secondary battery, a graphite-lithium ion intercalation compound is formed which is theoretically doped with one lithium atom to six carbon atoms. At this time, the electric capacity per carbon weight is 372 mA · h / g. However, the electric capacity of the graphite negative electrode material used in commercially available lithium ion secondary batteries is 120 to 160 mA ·
h / g, which is usually only about 40% of theory.

[0005] 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 when charging, lithium is converted to carbon and C ₆ Li
Not only to form a lithium intercalation compound, carbon partially _{C n Li (n <6)} - - in carbon indicated suggesting that forms a lithium intercalation compound.

[0006]

As a result of various studies on carbon materials suitable for the negative electrode material of a lithium ion secondary battery, the present inventors have found that carbon materials having a large lithium doping amount, a large discharge capacity, and a long cycle life are used. The material has a diameter of 0.1 ~
50 μm spherical carbon particles, and the crystal lattice constant C _{0 (002)} of the carbon crystal 002 plane of the carbon fine particles is 0.750.
0.820 nm, and the carbon fine particles are 30
Volume resistance when pressurized at 0 kgf / cm ² is 6.0 ×
10 ^{−3 to} 1.0 × 10 ¹¹ Ω · cm. Further, the carbon fine particles are 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 forming the 520 to 1150 ° C.
It has been found that carbon fine particles obtained by sintering are particularly preferable. That is, after forming a condensate having a methylene-type bond of an aromatic sulfonic acid or a salt thereof into a spherical shape, low-crystalline carbon fine particles having specific physical properties obtained by carbonizing at a low temperature are used as a negative electrode material of a lithium ion secondary battery. It has been found that, when used, a lithium ion secondary battery having a charge / discharge capacity exceeding the conventional theoretical value, a long cycle life, and capable of quick charge / discharge can be configured, and the present invention has been completed. The purpose is to improve the carbon material used as the negative electrode to provide a lithium ion having a charge / discharge amount exceeding the theoretical discharge capacity of the graphite-lithium secondary battery of 372 mA · h / g and having a long cycle life. An object of the present invention is to provide a secondary battery and a negative electrode material for the battery.

[0007]

In order to achieve the above object, the present invention provides a method of forming a condensate of an aromatic sulfonic acid or a salt thereof by a methylene-type bond, followed by heat treatment in a non-oxidizing atmosphere at 520 to 1150 ° C. The obtained carbon fine particles are spherical particles having a diameter of 0.1 to 50 μm, and the carbon fine particles of the carbon fine particles have a crystal lattice constant C _{0 (002)} of 0.750 to 0.820 nm. And a molded product of carbon fine particles having a volume resistance of 6.0 × 10 ^{−3 to} 1.0 × 10 ¹¹ Ω · cm when the carbon fine particles are pressed at 300 kgf / cm ^2. Provided is a negative electrode material for a lithium ion secondary battery, wherein the condensate is a methylene-type bonded condensate of naphthalenesulfonic acid or a salt thereof.

Further, the present invention is a lithium ion secondary battery incorporating the above negative electrode material.

[0009]

The carbon material used as a negative electrode material of a lithium ion secondary battery having a large charge / discharge capacity is desired to have extremely low crystallinity. In order to perform quick charging, it is desirable that the negative electrode material be formed of a carbon material having a high packing density and a path through which the electrolytic solvent permeates. The carbon material for a negative electrode used in the present invention is a carbon material having a high packing density and extremely low crystallinity because it is substantially spherical carbon fine particles. As a result, when this carbon material is molded and used for an electrode, doping and undoping of a large amount of lithium ions are performed smoothly, and a large charge / discharge capacity and short-time charging become possible.

Hereinafter, the present invention will be described in detail.

In the present invention, as described above, the carbon fine particles to be molded into an electrode are produced by forming a condensate of an aromatic sulfonic acid or a salt thereof by a methylene type bond into a sphere and then heat-treating the sphere. You.

Examples of the aromatic sulfonic acid used in the present invention include sulfonating a mixture of polycyclic aromatic compounds such as naphthalenesulfonic acid, anthracenesulfonic acid, phenanthrenesulfonic acid, creosote oil, anthracene oil, tar and pitch. And toluene sulfonic acid, phenol sulfonic acid and mixtures thereof. These sulfonic acids can be obtained by sulfonating the corresponding aromatic compounds according to a method known per se. Further, salts of these aromatic sulfonic acids can also be used. Li ⁺ , Na ⁺ , K ⁺ ,
NH ₄ ^{+ and the} like. Ammonium salts are preferred for ease of handling. Alkali metal salts such as lithium salts ignite when exposed to the atmosphere after carbonization by heat treatment, so care must be taken.However, lithium ions are suitable for obtaining fine carbon particles with low crystallinity, that is, large crystal lattice constants. It is effective in suppressing irreversible components of the battery. From the viewpoint of such effects as low crystallinity, potassium salts are particularly effective among salts.

In the present invention, methylene condensates of these aromatic sulfonic acids or salts thereof are used.

The condensate of an aromatic sulfonic acid or a salt thereof can be produced by a method known per se.
It is common to condense using acetaldehyde, paraformaldehyde, hexamethylenetetramine or other aldehyde derivatives. Further, a polymer of an aromatic sulfonic acid having a methylene type bond obtained by polymerizing an aromatic sulfonic acid having a vinyl group like polystyrene sulfonic acid may be used. As a linking group for bonding aromatic sulfonic acids, a --CH ₂ -group is particularly preferred from the viewpoint of its production and availability.
_{- (CH 2) n-Tx-} (CHR) m- ( wherein, T is a benzene ring, or a naphthalene ring, R represents hydrogen, a lower alkyl group or a benzene ring, n, m, x are each an integer of 0 or 1 A compound having a linking group represented by the following formula: can also be used. These condensates can also be used in the form of a mixture or copolymer of two or more condensates.

A preferred example of the condensate of aromatic sulfonic acids or salts thereof used in the present invention is naphthalene-β
-Shows an example of a formaldehyde condensate of ammonium sulfonate. The condensate is a mixture consisting of a monomer to a condensate of about 200-mers, and has an average molecular weight of 2000 to 2000.
It is about 50,000. It is a solid at room temperature, hardly soluble in non-polar solvents such as benzene, but soluble in polar organic solvents such as acetone and acetonitrile at a low concentration and easily soluble in aqueous solvents. The viscosity at 60 ° C. of a 60% by weight aqueous solution is 10 to 2000 pois.
e, but by adjusting the degree of condensation of the same condensate, the concentration of the solution, etc. to adjust to an appropriate viscosity, columnar, spherical, plate-like, flake-like, film-like, fibrous, honeycomb-like, etc. It can be molded into any shape. As a molding aid, a water-soluble polymer compound such as polyvinyl alcohol, polyethylene oxide, and polyacrylic acid can be used. The aromatic sulfonic acids used in the present invention or polystyrene sulfonic acid, which is a kind of condensate of a salt thereof, and the like can be used as the water-soluble polymer.

In the present invention, the above condensate is molded into a spherical shape to obtain microspheres. The method for forming the microspheres is not particularly limited. For example, after dissolving a condensate of an aromatic sulfonic acid or a salt thereof in a solvent, particularly water, which is preferable, a spray drying method and an antisolvent are added. It can be formed into microspheres by a known method such as a precipitation method. Among them, the spray-drying method has the advantages that the particle diameter can be reduced, the obtained sphere is close to a true sphere, and the production apparatus is simple.Therefore, the condensation of the aromatic sulfonic acids or salts thereof of the present invention is performed. This is suitable as a method for molding an object into microspheres.

The condensate of the aromatic sulfonic acids or their salts molded into microspheres is then carbonized by heat treatment to form carbon fine particles. The heat treatment atmosphere is not particularly limited as long as it is a non-oxidizing atmosphere, but usually a nitrogen atmosphere is used, and in addition to ammonia, sulfur dioxide gas, steam generated from the thermal decomposition of a condensate of an aromatic sulfonic acid or a salt thereof, and carbonization. Lower hydrocarbons, hydrogen sulfide,
It is preferable to perform the heat treatment while passing an inert gas for purging a gas such as hydrogen.

The heat treatment temperature is preferably from 520 to 1150 ° C. A more preferred heat treatment temperature is 600 ° C.
To 1100 ° C, especially 675 to 1000 ° C.
The heat treatment time can be 1 minute to 120 minutes. When the heat treatment temperature is lower than 520 ° C., the carbonization of the aromatic sulfonic acid condensate or a salt thereof is insufficient, and the ratio (efficiency) of the discharge capacity to the charge capacity decreases, so that the electric capacity of the lithium ion secondary battery decreases. In addition, the volume resistivity becomes 1.0 × 10 ¹¹ Ω · cm or more, the conductivity of the obtained carbon fine particles becomes insufficient, and the internal resistance of the battery becomes large, so that it is not used as a negative electrode material. The heat treatment temperature is 11
If the temperature exceeds 50 ° C., the doping amount of lithium ions becomes insufficient, and a sufficient charge amount cannot be obtained.

The particle size (diameter) of the fine carbon particles used in the negative electrode material of the lithium ion secondary battery of the present invention thus obtained is preferably 0.1 to 50 μm. 0.1
When the number of particles having a particle diameter of less than μm increases, the bulk density of the carbon fine particles decreases, so that the carbon material filling amount per volume of the negative electrode cannot be increased. Also, when the number of particles exceeding 50 μm increases,
Similarly, not only the amount of carbon material per volume of the negative electrode cannot be increased, but also the charging rate decreases. Most preferably it has an average diameter between 5 μm and 20 μm, and
Carbon fine particles having a particle size distribution that is substantially normally distributed in a particle size range of 1 μm to 50 μm. As a method for controlling the particle size of the fine particles within this range, a method of controlling the particle size of the microspheres at the time of molding, a method of fractionating the heat-treated carbon fine particles by wind separation or the like can be adopted.

The shape of the carbon fine particles used in the present invention is preferably spherical. On the other hand, a method in which a condensate of an aromatic sulfonic acid or a salt thereof is carbonized by heat treatment and then pulverized into fine particles is considered.However, a carbide of a condensate of an aromatic sulfonic acid or a salt thereof is a low-temperature carbide. However, it is hard carbon unique to amorphous carbon, and it is extremely difficult to finely pulverize it to a micro size, and it is not possible to obtain spherical carbon fine particles.

In the present invention, the reason why the carbon fine particles are made as close as possible to a true sphere is that when the carbon fine particles are pressure-molded using a binder to produce a negative electrode material, the closest packing is performed as much as possible. This is because the carbon material filling amount per volume can be increased. As a result, the charge / discharge amount of the battery can be increased, and the penetration path of the electrolytic solvent can be ensured, so that rapid charge / discharge can be performed. The carbon fine particles used in the present invention are low-crystalline carbon fine particles. The crystal lattice constant C _{0 (002)} of the 002 plane of the carbon fine particles is 0.750 to 0.820 nm.
More preferably, it is 0.78 to 0.81 nm. When the crystal lattice constant C _{0 (002)} is less than 0.750 nm, the doping amount of lithium ions is insufficient, and a sufficient charge amount cannot be obtained. When the crystal lattice constant C _{0 (002)} exceeds 0.820 nm, the doping amount of lithium ions is insufficient, and not only a sufficient charge amount cannot be obtained, but also the ratio (efficiency) of the discharge amount to the charge amount is low. In other words, the so-called irreversible component increases, so that the electric capacity of the lithium ion secondary battery decreases. At the same time, since the volume resistance is large and the internal resistance of the negative electrode material is large, it is not used as an electrode material.

Even if a condensate of an aromatic sulfonic acid or a salt thereof is graphitized at 2800 ° C., the crystal lattice constant C _{0 (002)} of the 002 plane of the graphitized product is 0.680 nm to 0.70.
It is about 00 nm. Therefore, the carbides of the condensates of aromatic sulfonic acids or their salts can be said to be so-called non-graphitizable carbon. Further, the crystal lattice constant C _{0 (002)} of the 002 plane of a 700 ° C. treated product of a methylene-bonded condensate of naphthalene-β-sulfonic acid, which is one of condensates of aromatic sulfonic acids or salts thereof, is 0. .786 nm and 1000 ° C.
The crystal lattice constant C _{0 (002)} of the 002 plane of the processed material is also set to 0.
Equal to 786, crystallization hardly progresses even with a heat treatment from 700 ° C. to 1000 ° C. This also indicates that the condensates of aromatic sulfonic acids or their salts are hardly graphitizable.

Further, the volume resistance of the carbon fine particles may be 6.0 × 10 ^{−3 to} 1.0 × 10 ¹¹ Ω · cm when the carbon fine particles are pressurized at 300 kgf / cm ^2. preferable. If the volume resistance is less than 6.0 × 10 ⁻³ Ω · cm, the doping amount of lithium ions is insufficient, and a sufficient charge amount cannot be obtained. Volume resistance is 1.0 × 10 ¹¹ Ω
-If it exceeds cm, the doping amount of lithium ion is insufficient and not only a sufficient charge amount cannot be obtained, but also the ratio (efficiency) of the discharge amount to the charge amount decreases, and the so-called irreversible component increases, so that the lithium ion increases. The electric capacity of the secondary battery decreases. At the same time, the volume resistance is large and the internal resistance of the negative electrode is large, so that it is not used as an electrode material.

Note that the carbon fine particles are 52% as described above.
Heat-treated at 0 to 1150 ° C.
No. 1320301 describes that a carbon material obtained by carbonizing a methylene bond type condensate of an aromatic sulfonic acid is suitable for a negative electrode material of a lithium ion secondary battery. However, the carbonization temperature of the salt of the aromatic sulfonic acid condensate described in JP-A-6-13231 is 800 to 1800 ° C., and carbonization is performed at a higher temperature than the carbonization temperature of 550 ° C. to 1100 ° C. used in the present invention. ing. Further, by pulverizing after carbonization, the crystal lattice constant C _{0 (002)} of the carbon crystal 002 plane of the carbon material used in JP-A-6-132031 is set to 0.1.
68 to 0.72 nm, and 0.750 to 0.820 of the crystal lattice constant C _{0 (002)} of the carbon fine particles used in the present invention.
As compared with nm, the crystal lattice constant C _{0 (002)} of the carbon material used in JP-A-6-132131 is small. That is, the carbon material used in JP-A-6-132031 is carbon having high crystallinity, and is different from the carbon fine particles used in the present invention.

A method for preparing a negative electrode material of a lithium ion secondary battery using the above-mentioned carbon fine particles can use a known technique, and is not particularly limited. For example, after a binder and a solvent are added to the carbon fine particles and sufficiently kneaded, A negative electrode material made of a molded body of carbon fine particles can be manufactured by pressure bonding to a current collector such as a metal mesh and evaporating the solvent. As the binder, known materials, for example, various pitches, polytetrafluoroethylene and the like are used, and among them, polyvinylidene fluoride is most suitable.

The mixing ratio (weight) of the carbon fine particles to the binder is preferably 100: 1 to 100: 10. In addition, the pressing pressure is 500 to 20,000 kgf / cm ²
Is preferred. As the solvent, one that dissolves the binder is appropriately selected.

Next, a description will be given of a lithium ion secondary battery formed using the negative electrode material, the positive electrode, and the electrolytic solution manufactured as described above. It is a publicly known thing except for.

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

The separator is not particularly limited, and a known material can be used.

As the organic solvent used in the present invention, a known aprotic solvent having a low dielectric constant that dissolves a lithium salt is used. For example, ethylene carbonate, propylene carbonate, diethylene carbonate, acetonitrile, propionitrile, tetrahydrofuran, γ-butyrolactone, 2-methyltetrahydrofuran, 1,3-
Dioxolan, 4-methyl-1,3-dioxolan,
Solvents such as 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, sulfolane, methylsulfolane, nitromethane, N, N-dimethylformamide and dimethylsulfoxide may be used alone or as a mixture of two or more. it can.

The lithium salt used as the electrolyte includes L
iClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ ,
LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ S
There are O ₃ Li, CF ₃ SO ₃ Li and the like. These salts can be used alone or in combination of two or more.

The physical properties described in this specification were measured by the following methods.

Crystal lattice constant C _{0 (002)} : Using a Rigaku X-ray diffractometer RINT1400, monochromatic Cu-Kα rays with a monochromator, a tube voltage of 40 KV and a tube current of 200
mA, scanning speed 1.0 °, divergence slit 1/2 °, scattering slit 1/2 °, light receiving slit 0.15 mm.

Average particle size and particle size distribution: S manufactured by Shimadzu Corporation
The measurement was performed using ALD-1100 with water as a dispersion medium.

Volume resistance: A sample was filled into a steel pipe having an inner surface lined with vinyl chloride and having an inner diameter of 1 cm, and the sample was pressed at 300 kgf / cm ² with a copper piston. The resistance value in the pressing direction: r and the sample thickness: d Measured, volume resistance: R = r ×
(0.5) ² × 3.14 ° d.

[0036]

The present invention will be described more specifically with reference to the following examples. Example 1 1,050 g of 98 wt% sulfuric acid was added to 1280 g of 95 wt% pure naphthalene, sulfonated at 160 ° C. for 2 hours, and unreacted naphthalene and reaction water were distilled out under reduced pressure. Then 857g of 35% by weight formalin
Was added and reacted at 105 ° C. for 5 hours to obtain a methylene-bonded condensate of naphthalene-β-sulfonic acid. Further, the condensate was neutralized with aqueous ammonia, and the product was manufactured by Toyo Filter Paper No. The mixture was filtered through a filter paper to give a filtrate. The obtained methylene-bonded condensate of naphthalene-β-sulfonic acid has a number average molecular weight of 430.
It was 0. Water was added to the filtrate to prepare an aqueous solution having a concentration of 13.3% by weight of a methylene-bound condensate of ammonium naphthalene-β-sulfonate. This aqueous solution was simultaneously granulated and dried with a spray dryer. Subsequently, naphthalene-β-sulfonate methylene-bonded condensate spherical fine particles were prepared in a nitrogen stream at 550 ° C. to 1100 ° C. in Table 1.
At a predetermined temperature as shown in Table 1. The rate of temperature rise from room temperature to the predetermined temperature was 2 ° C./min, and the holding time at the predetermined temperature was 1 hour. Crystal lattice constant C of the obtained carbon fine particles
_{0 (002)} , minimum particle size, maximum particle size, average particle size (50
% Volume average diameter) and the volume resistance are shown in Table 1.

In order to examine the performance of the carbon fine particles as a negative electrode material of a lithium ion secondary battery, a nonaqueous solvent battery was prepared using a molded body of carbon fine particles as a positive electrode and metallic lithium as a negative electrode, and a charge / discharge test was performed. The doping (intercalation) and dedoping (disintercalation) capacities of lithium ions on the positive electrode (graphite electrode) were measured.

The preparation of a positive electrode using carbon fine particles was carried out by the following method. That is, 1 part by weight of polyethylene propylene dimonomer and a small amount of dimethylformamide were added as a binder to 40 parts by weight of carbon fine particles, mixed well to form a paste, and applied to a circular stainless mesh (2.5 cm ² ) at 1 tonf / cm ² . After pressing, it was prepared by vacuum drying at 200 ° C. for 2 hours. A battery was constructed using the carbon electrode as a positive electrode and lithium metal as a negative electrode, and an evaluation test of these carbon fine particles was performed. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte in a solvent in which propylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 2 was used, and the concentration was 1.0 mol / l. In addition, a porous polypropylene nonwoven fabric was used as the separator. The electrolytic solution was impregnated into glass fiber filter paper to form a coin cell under an argon atmosphere.
A charge / discharge test was performed with the current density during charge and discharge set to 1.0 mA / cm ² .

Table 1 shows the initial discharge amount (the value obtained when the voltage was cut at 1.5 V and 3.0 V, respectively) and the efficiency (discharge amount / charge amount × 100%) after the third cycle. In addition,
All the samples were tested for 60 cycles, but no decrease in the discharge amount was recognized by the 60th cycle.

[0040]

[Table 1] (Example 2) 1050 g of 98 wt% sulfuric acid was added to 1420 g of an absorbing oil containing 91 wt% of methylnaphthalene as a main component.
In addition, sulfonation was performed at 145 ° C. for 2 hours, and unreacted oil and reaction water were distilled out under reduced pressure. Followed by 35% by weight
857 g of formalin was added and reacted at 105 ° C. for 4 hours.
A condensate of methylene bond type of methyl-naphthalene-based-β-sulfonic acid was obtained. Further, 90% of the condensate was neutralized with aqueous ammonia and 10% with potassium hydroxide, and then N
o. The mixture was filtered through a filter paper to give a filtrate. The number average molecular weight of the obtained methylene-bonded condensate of methylnaphthalene-based-β-sulfonic acid was 5,700. Water is added to the filtrate, and the concentration of a methylene-bonded condensate of a methyl naphthalene-based ammonium salt of β-sulfonic acid and a potassium salt is 12.
A 5% by weight aqueous solution was prepared. This aqueous solution was simultaneously granulated and dried with a spray dryer. Subsequently, the spherical fine particles of a condensate of a methylene-bonded type of methylnaphthalene-mainly-β-sulfonic acid were carbonized by heat treatment at 900 ° C. in a nitrogen stream. The rate of temperature rise from room temperature to the predetermined temperature was 2 ° C./min, and the holding time at the predetermined temperature was 1 hour. The crystal lattice constant C _{0 (002)} of the obtained carbon fine particles is 0.805 nm, the minimum particle size is 0.1 μm, the maximum particle size is 44 μm, and the average particle size is (5 μm).
0% volume average diameter) is 9.03 μm, and the volume resistance is 5.42.
× 10 ^-2 Ω · cm.

In order to examine the performance of the carbon fine particles as a negative electrode material for a lithium ion secondary battery, a nonaqueous solvent battery was prepared by using the molded carbon fine particles as a positive electrode and metallic lithium as a negative electrode in the same manner as in Example 1. To perform a charge / discharge test,
The doping (intercalation) and dedoping (disintercalation) capacities of lithium ions on the positive electrode (graphite electrode) were measured.

The initial discharge amount is 525 mA with 1.5 V cut.
H / g, 625 mA at 3.0 V h / g, efficiency after 9th cycle (discharge amount / charge amount × 100%) is 98.9
%Met. Further, no decrease in the discharge amount was recognized by the 60th cycle. Comparative Example 1 Spherical fine particles of a methylene-bonded condensate of naphthalene-β-sulfonic acid ammonium salt obtained in Example 1 were obtained at 500 ° C. or 12 ° C. in the same manner as in Example 1.
Heat treatment was performed at 00 ° C. to obtain carbon fine particles. In order to examine the performance of the carbon fine particles as a negative electrode material for a lithium ion secondary battery, a nonaqueous solvent battery was prepared by charging a molded body of carbon fine particles as a positive electrode and metallic lithium as a negative electrode in the same manner as in Example 1. A discharge test was performed to measure the doping (intercalation) and undoping (disintercalation) capacities of lithium ions on the positive electrode (graphite electrode).
Table 2 shows the physical properties of the carbon fine particles and the results of the charge / discharge test.

[0043]

[Table 2] (Comparative Example 2) When preparing spherical fine particles from the methylene-bonded condensate of naphthalene-β-sulfonate ammonium salt obtained in Example 1, methylene-bonded condensation of naphthalene-β-sulfonate ammonium salt After adjusting the concentration of the aqueous solution to 28.0% by weight to prepare spherical fine particles,
In a nitrogen stream, the temperature was raised to 700 ° C. at a rate of 2 ° C./min, and heat treatment was performed for 1 hour at the same temperature to obtain fine carbon particles. Crystal lattice constant C of the obtained carbon fine particles
_{0 (002)} is 0.786 nm, minimum particle diameter 2.6 μm, maximum particle diameter 100 μm, average particle diameter (50% volume average diameter)
Is 32.98 μm and volume resistance is 2.99 × 10Ω · cm
Met.

In order to examine the performance of the carbon fine particles as a negative electrode material for a lithium ion secondary battery, a nonaqueous solvent battery was prepared in the same manner as in Example 1 using a molded carbon fine particle as a positive electrode and metallic lithium as a negative electrode. To perform a charge / discharge test,
The doping (intercalation) and dedoping (disintercalation) capacities of lithium ions on the positive electrode (graphite electrode) were measured.

The initial discharge amount is 302 mA at 1.5 V cut.
H / g, 469 mA at 3.0 Vh / g, efficiency after 3rd cycle (discharge amount / charge amount × 100%) is 98.7
%Met. Further, no decrease in the discharge amount was recognized by the 60th cycle. (Comparative Example 3) After melting 1280 g of naphthalene having a purity of 95% by weight at 90 ° C, 377 g of paraformaldehyde was melted.
And 98% by weight of sulfuric acid (192 g) were added.
, And maintained at the same temperature for 3 hours to carry out formalin condensation of naphthalene. After cooling the reaction solution to 80 ° C, 10
The naphthalene condensate was extracted with 00 g of toluene, the extract was neutralized with an aqueous sodium hydroxide solution, washed with water, centrifuged, and solids formed by the washing water and the condensation reaction were separated and removed from the toluene phase. The toluene phase was distilled under vacuum to obtain a methylene-type condensate of naphthalene, that is, a naphthalene formaldehyde resin as a distillation residue. Since the resin is a viscous liquid resin at room temperature, the temperature was raised from 80 ° C. to 320 ° C. at 1 ° C./min while blowing air to be solidified by an oxidative crosslinking reaction. Oxidation introduced 9.4% by weight of oxygen into the naphthalene formaldehyde resin.
After the oxidized naphthalene formaldehyde resin was pulverized by a centrifugal pulverizer, the particles passing through a 325 mesh sieve were subjected to a heat treatment. That is, the naphthalene oxide formaldehyde resin was heated to 700 ° C. at a rate of 2 ° C./min in a nitrogen stream, and heat-treated at the same temperature for 1 hour to obtain carbon fine particles. Crystal lattice constant C _{0 (002) of the} obtained carbon fine particles
Is 0.740 nm, the minimum particle diameter is 0.1 μm, the maximum particle diameter is 44 μm, and the average particle diameter (50% volume average diameter) is 18.
23 μm and volume resistance was 5.67 Ω · cm.

In order to examine the performance of the carbon particles as a negative electrode material for a lithium ion secondary battery, a non-aqueous solvent battery was prepared in the same manner as in Example 1 using a molded body of carbon fine particles as a positive electrode and metallic lithium as a negative electrode. A charge / discharge test was performed to measure the doping (intercalation) and dedoping (disintercalation) capacities of lithium ions on the positive electrode (graphite electrode).

The initial discharge amount is 127 mA at 1.5 V cut.
H / g, 176 mA at 3.0 Vh / g, efficiency after 3rd cycle (discharge amount / charge amount × 100%) is 96.7
%Met. Further, the discharge amount gradually decreased from the fifth cycle.

[0048]

In the production of carbon fine particles used for the negative electrode material of the present invention, fine particles of a condensate of methylene type bonds of aromatic sulfonic acid or a salt thereof are molded before or at the same time as heat treatment, so that fine and spherical particles are formed. Fine particles can be easily manufactured. The carbon fine particles obtained by calcining the carbon particles are spherical, so that the packing density is high and the crystallinity is low, and the charge / discharge capacity and the charge / discharge capacity of the lithium ion secondary battery using the negative electrode material formed by the carbon fine particles are increased. The discharge rate is high.

Continuation of the front page (72) Inventor Koji Sakata 2-1-1 Nihombashi Muromachi, Chuo-ku, Tokyo Mitsui Mining Co., Ltd. (56) References JP-A-6-132031 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) H01M 4/58 H01M 4/02 H01M 10/40

Claims (3)

(57) [Claims] 1. A carbon fine particle obtained by molding a condensate of an aromatic sulfonic acid or a salt thereof by a methylene-type bond and heat-treating the resulting product in a non-oxidizing atmosphere at 520 to 1150 ° C. It is a sphere of 1 to 50 μm, and has a crystal lattice constant C _{0 (002)}
Is 0.750 to 0.820 nm, and the volume resistivity when the carbon particles are pressed at 300 kgf / cm ² is 6.0 × 10 ^{−3 to} 1.0 × 10 ¹¹ Ω · cm. A negative electrode material for a lithium ion secondary battery, comprising a molded product of: 2. The negative electrode material according to claim 1, wherein the condensate is a methylene type condensate of naphthalenesulfonic acid or a salt thereof. 3. A lithium ion secondary battery incorporating the negative electrode material according to claim 1 or 2.