JP4896381B2 - Carbon material for battery electrode, production method and use thereof - Google Patents

Description

  The present invention relates to an electrode material for a non-aqueous electrolyte secondary battery having a large charge / discharge capacity, excellent charge / discharge cycle characteristics and large current load characteristics, an electrode using the same, and a non-aqueous electrolyte secondary battery, in particular, lithium secondary battery. The present invention relates to a negative electrode material for a secondary battery, a negative electrode using the negative electrode material, and a lithium secondary battery.

  As portable devices become smaller and lighter and have higher performance, there is an increasing demand for higher capacity lithium ion secondary batteries having high energy density, that is, lithium ion secondary batteries. As a negative electrode material used for a lithium ion secondary battery, graphite fine powder which is a material capable of inserting lithium ions between layers is mainly used. Since graphite having higher crystallinity exhibits a higher discharge capacity, studies have been made on the use of a material with high crystallinity centered on natural graphite for the negative electrode material of a lithium ion secondary battery. The theoretical capacity of the discharge capacity when using a graphite material is 372 mAh / g, but in recent years, a material close to the theoretical capacity of 350 to 360 mAh / g in the practical range has been developed.

  However, as the crystallinity of graphite increases, the decrease in Coulomb efficiency (“first discharge capacity / charge capacity”) and the increase in irreversible capacity, which are thought to be due to the decomposition of the electrolyte, have been regarded as problems (J. Electrochem Soc., 117, 1970, 222-224; Non-Patent Document 1). In order to solve this problem, the surface of a highly crystalline carbon material is covered with amorphous carbon to suppress the decrease in Coulomb efficiency, the increase in irreversible capacity, and the decrease in cycle characteristics, which are thought to be due to the decomposition of the electrolyte. A negative electrode material using a carbon material with high crystallinity has been proposed (Patent No. 2643035; Patent Document 1, Patent No. 2976299; Patent Document 2). However, according to the technology of Japanese Patent No. 2643035 (Patent Document 1), an amorphous carbon layer is formed on the surface of a highly crystalline carbon material by a CVD method (vapor phase method), which leads to cost and mass production. There is a big problem in practical use in terms of performance. In addition, the so-called double-layered negative electrode material covered with an amorphous carbon layer still has the disadvantages of the amorphous carbon layer (low capacity, low coulomb efficiency, etc.). Patent No. 2976299 (Patent Document 2) and the like describe a promising technique from the viewpoint of cost and mass productivity using liquid phase carbonization in which the surface is coated with coal tar pitch or the like and subjected to heat treatment. The disadvantages of the amorphous carbon layer remain as well.

  Japanese Patent Application Laid-Open No. 2001-6662 (Patent Document 3) proposes a method in which a thermosetting resin material dissolved in an organic solvent and graphite powder are mixed and then thermoset and then fired. ing. However, in this method, since the thermosetting resin material does not sufficiently penetrate into the inside of the graphite powder, the thermosetting resin only adheres to the surface of the graphite powder and is a homogeneous composite of the thermosetting resin and graphite. Cannot be formed, and the demerits of the amorphous carbon layer are not sufficiently eliminated.

J. et al. Electrochem. Soc. 117, 1970, 222-224. Japanese Patent No. 2643035 Japanese Patent No. 2976299 JP 2001-6662 A

  The present invention eliminates the problems associated with using highly crystalline graphite and the problems associated with providing an amorphous carbon layer, and has a large discharge capacity, excellent coulomb efficiency, excellent cycle characteristics, and a small irreversible capacity. An object of the present invention is to provide an electrode material.

As a result of intensive studies to solve the above problems, the present inventors have uniformly impregnated and compounded an organic compound as a polymer raw material into carbonaceous particles, polymerized the organic compound, and then carbonized the compound.・ By firing, carbon powder having a substantially uniform structure from the surface of the particle to the central part can be obtained, and a battery using the carbon powder as an electrode material can be obtained when highly crystalline graphite particles are used. The inventors have found that the coulomb efficiency and cycle characteristics are excellent while maintaining a comparable high discharge capacity, and that the irreversible capacity is reduced, thereby completing the present invention.
That is, this invention relates to the carbon material for battery electrodes which consists of the following structures, its manufacturing method, and its use.

1. A battery comprising carbon powder having a homogeneous structure obtained by adhering and / or penetrating an organic compound as a polymer raw material to carbonaceous particles, polymerizing the organic compound, and then heat-treating at a temperature of 1800 to 3300 ° C. Carbon material for electrodes.
2. 2. The carbon material for battery electrodes according to 1 above, wherein the polymerization is performed at a temperature of 100 to 500 ° C.
3. 3. The organic compound according to 1 or 2 above, wherein the organic compound is a raw material of at least one polymer selected from the group consisting of phenol resin, polyvinyl alcohol resin, furan resin, cellulose resin, polystyrene resin, polyimide resin, and epoxy resin. Carbon material for battery electrodes.
4). 4. The carbon material for battery electrodes as described in 3 above, wherein the organic compound is a raw material for phenol resin.
5). 5. The carbon material for battery electrodes as described in 4 above, wherein a drying oil or a fatty acid thereof is added during the reaction of the raw material of the phenol resin.
6). 6. The carbon material for battery electrodes according to any one of 1 to 5 above, wherein a region of a graphite crystal structure and a region of an amorphous structure are dispersed from the surface to the central portion of the particles constituting the battery electrode carbon material.
7). Two or more spot-like diffraction patterns in a limited field diffraction pattern of a 5 μm square region arbitrarily selected from a bright field image of a transmission electron microscope having a cross-section obtained by cutting particles constituting a carbon material for a battery electrode into thin pieces. 7. The battery according to 6 above, wherein the ratio of the area of the graphite crystal structure having an amorphous structure area having a diffraction pattern that appears only in one spot derived from the (002) plane is 99 to 30: 1 to 70 in area ratio. Carbon material for electrodes.
8). 8. The battery electrode according to any one of 1 to 7 above, which is obtained by repeating a polymerization step after attaching and / or infiltrating an organic compound to carbonaceous particles a plurality of times and then heat-treating at a temperature of 1800 to 3300 ° C. Carbon material.
9. The carbon material for battery electrodes according to any one of 1 to 8, wherein the organic compound is used in an amount of 4 to 500 parts by mass with respect to 100 parts by mass of the carbonaceous particles.
10. 10. The carbon material for battery electrodes as described in 9 above, wherein 100 to 500 parts by mass of an organic compound is used with respect to 100 parts by mass of the carbonaceous particles.
11. 11. The carbon material for battery electrodes according to any one of 1 to 10 above, containing 10 to 5000 ppm of boron.
12 12. The carbon material for a battery electrode according to 11, wherein boron or a boron compound is added after the polymerization of the organic compound, and then heat treatment is performed at 1800 to 3300 ° C.
13. The carbon material for a battery electrode according to any one of 1 to 12, wherein the carbonaceous particles are natural graphite particles, particles composed of petroleum-based pitch coke, or particles composed of coal-based pitch coke.
14 14. The carbon material for battery electrodes as described in 13 above, wherein the carbonaceous particles have an average particle diameter of 10 to 40 μm and an average circularity of 0.85 to 0.99.
15. 15. The carbon material for battery electrodes according to any one of 1 to 14 above, comprising carbon fibers having a fiber diameter of 2 to 1000 nm.
16. 16. The carbon material for battery electrodes as described in 15 above, wherein at least a part of the carbon fibers adheres to the surface of the carbon powder.
17. The carbon material for battery electrodes according to 15 or 16 above, containing 0.01 to 20 parts by mass of carbon fiber with respect to 100 parts by mass of carbonaceous particles.
18. 18. The carbon material for a battery electrode according to any one of 15 to 17, wherein the carbon fiber is a vapor grown carbon fiber having an aspect ratio of 10 to 15000.
19. 19. The carbon material for battery electrodes as described in 18 above, wherein the vapor grown carbon fiber is a graphite-based carbon fiber heat-treated at 2000 ° C. or higher.
20. 20. The carbon material for battery electrodes as described in 18 or 19 above, wherein the vapor grown carbon fiber has a hollow structure inside.
21. 21. The carbon material for a battery electrode according to any one of 18 to 20, wherein the vapor grown carbon fiber includes a branched carbon fiber.
22. Battery electrode carbon material according to any one of the 18 to 21 average spacing d ₀₀₂ of the vapor-grown carbon fibers by X-ray diffraction (002) plane is not more than 0.344 nm.
23. The carbon material for battery electrodes according to any one of 1 to 22, wherein the carbon powder satisfies one or more of the following requirements (1) to (6):
(1) The average circularity measured by a flow type particle image analyzer is 0.85 to 0.99,
(2) C ₀ of (002) plane in X-ray diffraction measurement is 0.6703 to 0.6800 nm, La (crystallite size in the a-axis direction)> 100 nm, Lc (crystallite size in the c-axis direction)> 100 nm,
(3) A BET specific surface area of 0.2 to ⁵ m ² / g,
(4) True density is 2.21 to 2.23 g / cm ³ ,
(5) Laser Raman R value (peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 by laser Raman spectrum) is 0.01 to 0.9,
(6) The average particle diameter by laser diffraction method is 10 to 40 μm.
24. Treating the carbonaceous particles with an organic compound as a polymer raw material or a solution thereof to attach and / or infiltrate the organic compound into the carbonaceous particles, polymerizing the organic compound, and heat treating at a temperature of 1800 to 3300 ° C. The manufacturing method of the carbon material for battery electrodes containing the carbon powder which has a homogeneous structure characterized by including a process.
25. A process in which carbonaceous particles are treated with a mixture containing an organic compound as a polymer raw material and carbon fibers having a fiber diameter of 2 to 1000 nm or a solution thereof, and the carbonaceous particles are adhered and / or permeated to adhere the carbon fibers. A battery electrode comprising at least a part of carbon fibers attached to the surface of a carbon powder having a homogeneous structure, the method comprising polymerizing the organic compound and heat treating at a temperature of 1800 to 3300 ° C. Carbon material manufacturing method.
26. The electrode paste containing the carbon material for battery electrodes in any one of said 1 thru | or 23, and a binder.
27. The electrode which consists of a molded object of the electrode paste of said 26.
28. A battery comprising the electrode according to 27 as a constituent element.
29. A secondary battery including the electrode according to 27 as a constituent element.
30. A non-aqueous electrolyte and / or a non-aqueous polymer electrolyte is used, and the non-aqueous solvent used in the non-aqueous electrolyte and / or non-aqueous polymer electrolyte is ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, butylene. 30. The secondary battery as described in 29 above, comprising at least one selected from the group consisting of carbonate and vinylene carbonate.
31. 24. A fuel cell separator containing 5 to 95% by mass of the carbon material for battery electrodes according to any one of 1 to 23 above.
32. 32. A fuel cell using the fuel cell separator as described in 31 above.

Hereinafter, the present invention will be described in detail.
In the present invention, after sufficiently adhering and / or penetrating an organic compound as a polymer raw material to the carbonaceous particles, the organic compound is polymerized, and this is carbonized and fired to obtain a surface portion from the central portion. A carbon powder having a substantially homogeneous structure is prepared.

[1] Carbonaceous particles The type of carbonaceous particles used as nuclei in the present invention is not particularly limited as long as lithium ions can be inserted and released. The lithium ion insertion / release amount is preferably as large as possible. From such a viewpoint, highly crystalline graphite such as natural graphite is preferable. As high crystalline graphite, C ₀ of (002) plane in X-ray diffraction measurement is 0.6703 to 0.6800 nm (average plane spacing d ₀₀₂ is 0.33515 to 0.3400 nm), La (crystallite size in a-axis direction)> 100 nm, a> 100 nm (crystallite size in the c-axis direction) Lc, laser Raman R value 0.01 to 0.9: those (R value 1360cm peak intensity ratio of ^-1 to the peak intensity of 1580 cm ^-1 by laser Raman spectrum) preferable.

  Further, as the carbonaceous particles, particles made of a graphitizable carbon material (soft carbon) that is graphitized by a heat treatment at 1800 to 3300 ° C. in the subsequent step can also be used. Specific examples include particles made of coke such as petroleum pitch coke and coal pitch coke.

  As the carbonaceous particles, those having any shape such as a lump shape, a scale shape, a sphere shape, and a fiber shape can be used, but those having a spherical shape and a lump shape are preferable. The carbonaceous particles as the core preferably have an average circularity of 0.85 to 0.99 as measured by a flow type particle image analyzer. When the average circularity is less than 0.85, the packing density at the time of forming the carbon powder when the electrode carbon material is used does not increase, and the discharge capacity per volume decreases. On the other hand, when the average circularity is larger than 0.99, the fine powder portion has a low circularity, and therefore the fine powder portion is hardly included, and the discharge capacity at the time of forming the electrode does not increase. Furthermore, it is preferable that the content ratio of particles having an average circularity of less than 0.90 is controlled in the range of 2 to 20% by number. The average circularity can be adjusted using, for example, a particle shape control device such as a mechano-fusion (surface fusion) process.

  The carbonaceous particles preferably have an average particle size of 10 to 40 μm as measured by a laser diffraction scattering method. More preferably, it is 10-30 micrometers. Moreover, the particle size distribution which does not substantially contain particles of 1 μm or less and / or 80 μm or more is good. This is because when the particle size is large, the particle size of the carbon powder when used as a carbon material for an electrode also increases, and when used as a secondary battery negative electrode material, fine particles are generated due to a charge / discharge reaction, resulting in a decrease in cycle characteristics. is there. On the other hand, when the particle size is small, the particles cannot efficiently participate in the electrochemical reaction with lithium ions, and the capacity and cycle characteristics are lowered.

  In order to adjust the particle size distribution, known pulverization methods and classification methods can be used. Specific examples of the pulverizer include a hammer mill, a jaw crusher, and a collision pulverizer. As a classification method, airflow classification or classification using a sieve is possible. Examples of the airflow classifying device include a turbo cryfire and a turboplex.

  The carbonaceous particles may have both a crystalline (graphite crystalline) carbon portion and an amorphous (amorphous) carbon portion in a bright field image in a transmission electron microscope. Transmission electron microscope technology has long been used for structural analysis of carbon materials. In particular, the carbon laminate structure can be directly observed by enlarging it to about 400,000 times or more by a high resolution technique capable of observing a crystal plane as a lattice image, particularly a hexagonal network as a 002 lattice image. Therefore, as an effective method for characterizing carbon, a crystalline carbon portion and an amorphous carbon portion can be analyzed by a transmission electron microscope.

  Specifically, limited-field electron diffraction (SAD) is performed on a region to be discriminated in the bright-field image, and discrimination is performed from the pattern. For details, see “Latest Carbon Materials Experimental Technology (Analysis and Analysis)”, Carbon Materials Society (Sipec Co., Ltd.), pages 18 to 26, pages 44 to 50, Michio Inagaki et al., “Introduction to Revised Carbon Materials”, It is described in pages 29 to 40 of the Carbon Materials Society.

  The crystalline region refers to, for example, those showing characteristics of diffraction patterns of graphitized carbon treated at 2800 ° C. (in the limited field diffraction pattern, showing two or more spot-like diffraction patterns), amorphous The region refers to, for example, a characteristic of a diffraction pattern obtained by processing 1200 to 2800 ° C. of non-graphitizable carbon, that is, a region showing a diffraction pattern that appears only in one spot derived from the (002) plane in a limited field diffraction pattern.

  In this case, the carbonaceous particles preferably have a ratio of the crystalline carbon portion to the amorphous carbon portion in the range of 95 to 50: 5 to 50 in a bright field image in a transmission electron microscope. More preferably, it is the range of 90-50: 10-50. When the ratio of the crystalline carbon portion to the amorphous carbon portion of the carbonaceous particles is smaller than 50:50, a high discharge capacity cannot be obtained as a negative electrode material. On the other hand, if the ratio of the crystalline carbon part to the amorphous carbon part is larger than 95: 5, the coulomb efficiency and cycle characteristics are deteriorated unless the surface is completely covered with the carbon layer because there are many crystalline carbon parts. If the surface is completely covered, a so-called double layering problem occurs, and the capacity decreases.

[2] Organic Compound The organic compound used in the present invention is a raw material for the polymer. By using the polymer raw material, it is possible to uniformly infiltrate the inside of the carbonaceous particles as the core. When the polymer itself is used, the molecular weight and viscosity are high, so it cannot be uniformly penetrated into the carbonaceous particles compared to the case of using the polymer raw material, and as a result, good characteristics as an electrode material Cannot be obtained.

  The polymer obtained by polymerizing the organic compound is preferably one having adhesion to carbonaceous particles and / or fibrous carbon. An adhesive polymer is a covalent bond, van der Waals force, hydrogen bond, etc. by interposing between the two bodies in order to keep the carbonaceous particles and fibrous carbon in contact with each other. Both objects are integrated, including physical adhesion such as chemical bonding and anchor effect. In the processing such as mixing, stirring, solvent removal, and heat treatment, any material can be used as long as it exhibits resistance to forces such as compression, bending, peeling, impact, pulling, and tearing to such an extent that peeling does not occur. For example, the polymer is preferably at least one selected from the group consisting of phenol resin, polyvinyl alcohol resin, furan resin, cellulose resin, polystyrene resin, polyimide resin, and epoxy resin. Preferable are phenol resin and polyvinyl alcohol resin, and particularly preferable is phenol resin.

  The phenol resin becomes a dense carbonaceous material by firing. This is presumed to be because the unsaturated bond portion of the phenol resin raw material undergoes a chemical reaction to become a phenol resin, which further eases decomposition and prevents foaming in the heat treatment (or calcination) process.

  As the phenol resin, a novolak-type or resol-type phenol resin and a modified phenol resin obtained by partially modifying them can be used.

Examples of the raw material organic compound for preparing such a phenol resin include phenols, aldehydes, necessary catalysts, and crosslinking agents.
Phenols mean phenol and phenol derivatives, and examples thereof include phenol, cresol, xylenol, alkylphenol having a C20 or lower alkyl group, and tetrafunctional compounds such as bisphenol A. As aldehydes, formaldehyde, especially formalin is most suitable from the viewpoint of availability, economy, etc., but a form such as paraformaldehyde can also be used. As the reaction catalyst, a basic substance that generates a —NCH ₂ bond between a phenol and a benzene nucleus, such as hexamethylenediamine, can be used.

  Among the phenol resins, a so-called modified phenol resin in which a drying oil or a fatty acid thereof is mixed is preferable. By mixing the drying oil or its fatty acid, foaming in the firing process is further suppressed, and a denser carbonaceous layer can be obtained.

  As a phenol resin mixed with drying oil or its fatty acid, phenol and drying oil are first added in the presence of a strong acid catalyst, then a basic catalyst is added to make the system basic, and formalin is added. Or a product obtained by reacting phenols with formalin and then adding a drying oil or a fatty acid thereof.

Dry oil is a vegetable oil that has the property of solidifying and drying in a relatively short time when left in the air as a thin film, such as commonly known tung oil, linseed oil, dehydrated castor oil, soybean oil, cashew nut oil, etc. May be its fatty acid.
As for the ratio of the drying oil or its fatty acid to the phenol resin, for example, 5 to 50 parts by mass of the drying oil or its fatty acid is suitable for 100 parts by mass of the condensate of phenol and formalin. When the amount is more than 50 parts by mass, the adhesion to the carbonaceous particles and the fibrous carbon serving as nuclei is lowered.

[3] Adhesion and / or penetration and polymerization of organic compound The adhesion and / or penetration of the organic compound to the carbonaceous particles can be performed by dispersing and stirring the carbonaceous particles in the organic compound or a solution thereof. .
In order to uniformly penetrate into the carbonaceous particles, it is preferable to use an organic compound as a low viscosity solution. The solvent used in the solution is not particularly limited as long as the polymer raw material is dissolved and / or dispersed, and examples thereof include water, acetone, ethanol, acetonitrile, ethyl acetate and the like.

  In the case of using a solvent (for example, water) having poor affinity with the graphite powder, the graphite powder can be used after being subjected to a pretreatment such as surface oxidation. As the surface oxidation method, a known method such as air oxidation, treatment with nitric acid, potassium dichromate aqueous solution treatment, or the like can be used.

  In order to sufficiently penetrate the organic compound or a solution thereof into the voids inside the carbonaceous particles, vacuuming can be performed once to dozen times before or during stirring. By evacuating, the air remaining in the fine voids of the carbonaceous particles can be extracted. However, since the organic compound may be volatilized by evacuation, the evacuation is performed after mixing the carbonaceous particles and the solvent, and after returning to normal pressure, the organic compound can be added and mixed. The lower the degree of vacuum, the better, but about 13 kPa to 0.13 kPa (about 100 Torr to 1 Torr) is preferable.

  The atmosphere at the time of adhesion and / or infiltration may be any of atmospheric pressure, pressure, and reduced pressure. However, since the affinity between the carbonaceous particles and the organic compound is improved, there is a method of attaching under reduced pressure. preferable.

  As for the usage-amount of the organic compound as a polymer raw material, 4-500 mass parts is preferable with respect to 100 mass parts of carbonaceous particles, More preferably, it is 100-500 mass parts. If the amount of the organic compound used is too small, sufficient performance cannot be obtained.

  After the treatment, the organic compound is polymerized. The polymerization conditions are not particularly limited as long as the polymerization reaction proceeds. Usually, the polymerization is performed by heating. The heating temperature also varies depending on the polymer raw material to be used, and cannot be generally defined, but can be performed in the range of 100 to 500 ° C, for example.

  In the present invention, the step of polymerizing after attaching and / or infiltrating the organic compound to the carbonaceous particles can be repeated a plurality of times. Thereby, an insufficient adhesion and / or penetration portion can be reduced as much as possible.

Next, the case where a phenol resin raw material is used as the organic compound to adhere and / or permeate the carbonaceous particles will be specifically described.
First, phenols, aldehydes, a reaction catalyst and carbonaceous particles are added to a reaction vessel and stirred. At this time, it is preferable that at least a stirrable amount of water is present as a solvent. The blending ratio of phenols and aldehydes is preferably set within a range of aldehydes 1 to 3.5 with respect to phenols 1 in terms of molar ratio. Further, the carbonaceous particles are preferably set within a range of 5 to 3000 parts by mass with respect to 100 parts by mass of phenols.
Prior to and / or during agitation, evacuation can be performed from one to a dozen times as described above. However, since a lot of phenols and aldehydes volatilize when evacuated, the carbonaceous particles can be mixed with water and then evacuated. After returning to normal pressure, the phenols and aldehydes can be added and mixed. .

The polymer raw material is sufficiently adhered and infiltrated into the carbonaceous particles by the stirring treatment, and then polymerized. Polymerization can be performed by heat-treating to conditions equivalent to general phenol resin production conditions, for example, 100 to 500 ° C.
When mixing phenols, aldehydes, catalysts, carbonaceous particles and water, the reaction system has a viscosity of about mayonnaise at the beginning of the reaction, but gradually the phenols containing carbonaceous particles and aldehydes The condensation reaction product begins to separate from the water in the reaction system. After the reaction has progressed to the desired level, stirring is stopped and cooling produces black particles as a precipitate. This can be used after washing and filtration.

  The amount of resin precipitation can be increased by increasing the concentration of phenols and aldehydes in the reaction system, and can be decreased by decreasing the concentration. Therefore, the control can be performed by adjusting the amount of water, and by adjusting phenols and aldehydes. In addition to being adjusted before the reaction, these can also be adjusted by dropping into the system during the reaction.

[4] Carbon fiber The carbon material for battery electrodes of the present invention may contain carbon fiber. In that case, it is particularly preferable that at least a part of the carbon fibers adhere to the surface of the carbon powder constituting the carbon material for battery electrodes.
As the carbon fiber, a so-called vapor grown carbon fiber manufactured by a vapor phase growth method is preferable because it has high conductivity, a small fiber diameter, and a large aspect ratio. Further, among vapor grown carbon fibers, higher conductivity is preferable, and high crystallinity is desirable. In addition, when the carbon material of the present invention is used as a negative electrode material for a lithium ion battery or the like, it is necessary to quickly pass a current through the entire negative electrode. It is preferable that the fiber is branched (branched). If it is a branched fiber, it will become easy to electrically join between carbon particles with a fiber, and electroconductivity will improve.

The vapor grown carbon fiber can be produced, for example, by blowing an organic compound gasified with iron serving as a catalyst in a high temperature atmosphere.
Vapor grown carbon fiber can be used as it is, for example, heat treated at 800-1500 ° C., eg, graphitized at 2000-3000 ° C., but heat treated at about 1500 ° C. Is more preferred.

Further, as a preferable form of vapor grown carbon fiber, there is a branched fiber, but the branched portion may include a portion having a hollow structure in which the entire fiber including the portion is in communication with each other. Therefore, the carbon layer which comprises the cylindrical part of a fiber is continuing. A hollow structure is a structure in which a carbon layer is wound in a cylindrical shape, and includes a structure that is not a complete cylinder, a structure that has a partial cut portion, and a structure in which two stacked carbon layers are bonded to one layer. . Further, the cross section of the cylinder is not limited to a perfect circle, but includes an ellipse or a polygon. Note that the interplanar spacing d ₀₀₂ of the carbon layer is not limited for the crystallinity of the carbon layer. Incidentally, it is preferable that the average interplanar spacing d ₀₀₂ by the X-ray diffraction method is 0.344 nm or less, preferably 0.339 nm or less, more preferably 0.338 nm or less, and the thickness Lc in the C-axis direction of the crystal is 40 nm or less. Is.

  The vapor grown carbon fiber is a carbon fiber having a fiber outer diameter of 2 to 1000 nm and an aspect ratio of 10 to 15000, preferably a fiber outer diameter of 10 to 500 nm, a fiber length of 1 to 100 μm (aspect ratio of 2 to 2000), or a fiber. The outer diameter is 2 to 50 nm and the fiber length is 0.5 to 50 μm (aspect ratio 10 to 25000).

  Vapor-grown carbon fiber can be further heat-treated at a temperature of 2000 ° C. or higher after its production to further increase the crystallinity and increase the conductivity. Also in this case, it is effective to add boron or the like having a function of promoting the degree of graphitization before the heat treatment.

  The content of the vapor grown carbon fiber is preferably in the range of 0.01 to 20% by mass of the carbon material for electrodes, preferably 0.1 to 15% by mass, and more preferably 0.5 to 10% by mass. When the content exceeds 20% by mass, the electric capacity decreases, and when the content is less than 0.01% by mass, the value of internal resistance at a low temperature (for example, −35 ° C.) increases.

  Vapor-grown carbon fibers often have irregularities and disturbances on the fiber surface, but their adhesion to the carbonaceous particles that form the core improves, and as a negative electrode active material and a conductive auxiliary agent even after repeated charge and discharge The vapor grown carbon fiber which also serves as a role can be kept in a close contact state without dissociating, the electron conductivity can be maintained, and the cycle characteristics can be improved.

  In addition, when vapor grown carbon fiber contains a lot of branched fibers, the carbon fibers can straddle between the active materials and can be uniformly dispersed in a network form on the surface, increasing the strength of the negative electrode and making contact between particles Can be maintained well, a network can be efficiently formed, and high electronic conductivity and thermal conductivity can be obtained.

In addition, since the vapor grown carbon fiber enters between the particles, the liquid retaining property of the electrolytic solution is increased, and lithium ions are smoothly doped and undoped even in a low temperature environment.
The method for attaching the carbon fiber to the carbon powder constituting the carbon material for battery electrodes of the present invention is not particularly limited. For example, the fiber is used in the step of attaching and / or infiltrating the organic compound or the solution thereof to the carbonaceous particles serving as the nucleus. By adding a carbon fiber having a diameter of 2 to 1000 nm and adhering the carbon fiber to the carbonaceous particle via an organic compound, the carbon fiber having a fiber diameter of 2 to 1000 nm can be adhered onto the particle. Moreover, after making an organic compound adhere to a carbonaceous particle, the particle | grains containing the mixture containing a carbon fiber are mixed, and carbon fiber can also be made to adhere by carrying out a stirring process.

  Although the stirring method is not particularly limited, for example, apparatuses such as a ribbon mixer, a screw type kneader, a spartan luzer, a redige mixer, a planetary mixer, and a universal mixer can be used.

  The temperature and time during the stirring treatment are not particularly limited and are appropriately selected according to the components and viscosity of the particles and the organic compound, but are usually in the range of about 0 ° C to 150 ° C, preferably about 20 ° C to 100 ° C. To do.

[5] Heat treatment conditions It is necessary to improve the crystallinity of the carbon material in order to increase the charge / discharge capacity by inserting lithium ions or the like. Since the crystallinity of carbon generally improves with the highest thermal history, it is preferable that the heat treatment temperature be higher in order to improve battery performance.
In this invention, after polymerizing an organic compound, it heat-processes at 1800-3300 degreeC, and is carbonized and baked. The heat treatment temperature is preferably 2500 ° C. or higher, more preferably 2800 ° C. or higher, and particularly preferably 3000 ° C. or higher.

By adding boron or a boron compound before the heat treatment, graphitization by the heat treatment can be promoted. Examples of the boron compound include boron carbide (B ₄ C), boron oxide (B ₂ O ₃ ), elemental boron, boric acid (H ₃ BO ₃ ), borate, and the like.

  The temperature increase rate for the heat treatment does not particularly affect the performance within the range of the maximum temperature increase rate and the minimum temperature increase rate in a known apparatus. However, since it is a powder, there is almost no problem of cracking as in the case of a molded material or the like. Therefore, it is preferable that the rate of temperature rise is high from the viewpoint of cost. The arrival time from the normal temperature to the maximum temperature is preferably 12 hours or less, more preferably 6 hours or less, and particularly preferably 2 hours or less.

  As a heat treatment apparatus for firing, a known apparatus such as an Atchison furnace or a direct current heating furnace can be used. These devices are also advantageous in terms of cost. However, since the presence of nitrogen gas may decrease the resistance of the powder or the strength of the carbonaceous material may decrease due to oxidation by oxygen, the furnace atmosphere can be preferably maintained in an inert gas such as argon or helium. A furnace having such a structure is preferred. For example, a batch furnace in which the container itself can be evacuated and replaced with gas, a batch furnace in which a furnace atmosphere can be controlled with a tubular furnace, or a continuous furnace.

Deposition and / or penetration carbon layer of the present invention, in the laser Raman spectrum showing a state of the carbon surface layer, the peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 is preferably the crystalline 0.4 It is a rich carbon layer. When the peak intensity ratio is 0.4 or more, the crystallinity of the carbon layer is not sufficient, and the discharge capacity and the Coulomb efficiency of the battery electrode carbon material of the present invention are lowered, which is not preferable.
However, when graphitization is performed by adding boron, the peak intensity ratio is about 0.7 to 0.9, but the discharge capacity and the Coulomb efficiency are maintained well.

[6] Carbon material for battery electrodes The carbon material for battery electrodes of the present invention obtained by the above method contains carbon powder having the following physical properties.

A graphite crystal structure region and an amorphous structure region are dispersed from the surface to the center of the carbon powder, and in particular, a bright field image in a transmission electron microscope having a cross-section obtained by cutting the carbon powder into thin pieces is arbitrarily selected 5 μm. The ratio of the graphite crystal structure area having two or more spot-like diffraction patterns to the amorphous structure area having a diffraction pattern that appears only in one spot derived from the (002) plane is The area ratio is preferably 99 to 30: 1 to 70.
When the area ratio is smaller than 30:70, a high discharge capacity as a negative electrode material cannot be obtained. On the other hand, when the area ratio is larger than 99: 1, the coulombic efficiency and the irreversible capacity increase, which are the same disadvantages as when the graphite crystal is used.

The average circularity measured by the flow type particle image analyzer (refer to the section of Examples described later for the calculation method) is preferably 0.85 to 0.99.
When the average circularity is less than 0.85, the packing density at the time of forming the electrode does not increase, so the discharge capacity per volume decreases. On the other hand, when the average circularity is larger than 0.99, the fine powder portion has a low circularity, and therefore the fine powder portion is hardly included, and the discharge capacity at the time of forming the electrode does not increase. Furthermore, it is preferable that the content ratio of particles having a circularity of less than 0.90 is controlled in the range of 2 to 20% by number.

It is preferable that the average particle diameter by a laser diffraction scattering method is 10-40 micrometers. More preferably, it is 10-30 micrometers.
When the average particle size is large, when used as a secondary battery negative electrode material, fine particles are formed by a charge / discharge reaction, and cycle characteristics deteriorate. In addition, when particles having a particle size of 80 μm or more are mixed, irregularities are increased on the electrode surface, which may cause damage to the separator used in the battery.
If the average particle size is small, the particles cannot efficiently participate in the electrochemical reaction with lithium ions, and the capacity and cycle characteristics deteriorate. Further, when the particle size is reduced, the aspect ratio is increased and the specific surface area is likely to be increased. When producing an electrode for a battery, a method is generally employed in which a negative electrode material is made into a paste with a binder and applied, but if the negative electrode material contains small particles having a particle size of 1 μm or less, the viscosity of the paste increases. Applicability also deteriorates.
Accordingly, those substantially free of particles of 1 μm or less and particles of 80 μm or more are preferable.

Further, C ₀ of the (002) plane in X-ray diffraction measurement is 0.6703 to 0.6800 nm (average plane spacing d ₀₀₂ is 0.33515 to 0.3400 nm), La (crystallite size in the a-axis direction)> 100 nm, Lc (c The crystallite size in the axial direction) is preferably> 100 nm. The BET specific surface area is preferably 0.2 to ⁵ m ² / g, more preferably 3 m ² / g or less. When the specific surface area increases, the surface activity of the particles increases, and when used as an electrode material for a lithium ion battery, the Coulomb efficiency decreases due to decomposition of the electrolyte or the like. The true density is preferably 2.21 to 2.23 g / cm ³ . Laser Raman R value (peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 by laser Raman spectrum) is preferably from 0.01 to 0.9, more preferably 0.1 to 0.8.

[7] Secondary Battery The carbon material for battery electrodes of the present invention can be suitably used as a negative electrode material for lithium ion secondary batteries. The lithium ion secondary battery using the carbon material for battery electrodes of the present invention can be produced by a known method.

  The electrode can be produced by diluting a binder (binder) with a solvent as usual, kneading it with the electrode material (negative electrode material) of the present invention to form a paste, and applying the paste to a current collector (base material).

As the binder, known polymers such as fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene, and rubber-based materials such as SBR (styrene butadiene rubber) can be used. As the solvent, a known solvent suitable for each binder, for example, a fluorine-based polymer such as toluene and N-methylpyrrolidone, and a SBR that is known in water can be used.
When the negative electrode material is 100 parts by mass, the amount of the binder used is suitably 0.5 to 20 parts by mass, and particularly preferably about 1 to 10 parts by mass.

  For kneading the carbon material for battery electrodes and the binder of the present invention, known devices such as a ribbon mixer, a screw kneader, a Spartan rewinder, a redige mixer, a planetary mixer, and a universal mixer can be used.

  Application to the current collector after kneading can be carried out by a known method. For example, a method of forming by a roll press or the like after applying with a doctor blade or a bar coater can be mentioned.

  As the current collector, known materials such as copper, aluminum, stainless steel, nickel, and alloys thereof can be used.

  Although a well-known thing can be used for a separator, the microporous film with a thickness of 5-50 micrometers made from polyethylene or a polypropylene is especially preferable.

  As the electrolyte and electrolyte in the lithium ion battery of the present invention, known organic electrolytes, inorganic solid electrolytes, and polymer solid electrolytes can be used. Preferably, an organic electrolyte is preferable from the viewpoint of electrical conductivity.

  Examples of organic electrolytes include diethyl ether, dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, and ethylene glycol phenyl ether. Ether; formamide, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, N-methylacetamide, N, N-dimethylacetamide, N-ethylacetamide, N, N-diethyl Acetamide, N, N-dimethylpropionamide, hexamethylphosphorylamide Amides such as: Sulfur-containing compounds such as dimethyl sulfoxide and sulfolane; Dialkyl ketones such as methyl ethyl ketone and methyl isobutyl ketone; ethylene oxide, propylene oxide, tetrahydrofuran, 2-methoxytetrahydrofuran, 1,2-dimethoxyethane, 1,3-dioxolane, etc. Cyclic ethers; carbonates such as ethylene carbonate and propylene carbonate; γ-butyrolactone; N-methylpyrrolidone; solutions of organic solvents such as acetonitrile and nitromethane are preferred. Furthermore, preferably esters such as ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, vinylene carbonate, γ-butyrolactone, ethers such as dioxolane, diethyl ether, diethoxyethane, dimethyl sulfoxide, acetonitrile, tetrahydrofuran, etc. Particularly preferred are carbonate-based non-aqueous solvents such as ethylene carbonate and propylene carbonate. These solvents can be used alone or in admixture of two or more.

Lithium salts are used as solutes (electrolytes) for these solvents. Commonly known lithium salts include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiN (CF ₃ SO ₂ ) _2, LiN (C ₂ F ₅ SO ₂ ) ₂ etc.

  Examples of the polymer solid electrolyte include a polyethylene oxide derivative and a polymer containing the derivative, a polypropylene oxide derivative and a polymer containing the derivative, a phosphate ester polymer, a polycarbonate derivative and a polymer containing the derivative.

The positive electrode material in the lithium ion battery is a lithium-containing transition metal oxide. Preferably, an oxide mainly containing at least one transition metal element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo and W and lithium, wherein the molar ratio of lithium to the transition metal Is a compound of 0.3 to 2.2. More preferably, it is an oxide mainly containing at least one transition metal element selected from V, Cr, Mn, Fe, Co and Ni, and a molar ratio of lithium to transition metal of 0.3 to 2.2. A compound. In addition, Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, or the like may be contained in a range of less than 30 mole percent with respect to the transition metal present mainly. Among the above positive electrode active materials, the general formula Li _x MO ₂ (M is at least one of Co, Ni, Fe, and Mn, x = 0 to 1.2), or Li _y N ₂ O ₄ (N is at least Mn). It is preferable to use at least one material having a spinel structure represented by y = 0 to 2).

Further, as the cathode active _{material, Li y M a D 1-} a O 2 (M is Co, Ni, Fe, at least one of Mn, D is Co, Ni, Fe, Mn, Al, Zn, Cu, Mo , Ag, W, Ga, In, Sn, Pb, Sb, Sr, B, P, at least one type other than M, y = 0 to 1.2, a = 0.5 to 1.), or Li _z (N _b E _1-b ) ₂ O ₄ (N is Mn, E is Co, Ni, Fe, Mn, Al, Zn, Cu, Mo, Ag, W, Ga, In, Sn, Pb, Sb, Sr, It is particularly preferable to use at least one of materials having a spinel structure represented by at least one of B and P and b = 1 to 0.2z = 0 to 2).

_{Specifically, Li x CoO 2, Li x} NiO 2, Li x MnO 2, Li x Co a Ni 1-a O 2, Li x Co b V 1-b O z, Li x Co b Fe 1-b _{O 2, Li x Mn 2 O} 4, Li x Mn c Co 2-c O 4, Li x Mn c Ni 2-c O 4, Li x Mn c V 2-c O 4, Li x Mn c Fe 2- _c O ₄ (where x = 0.02 to 1.2, a = 0.1 to 0.9, b = 0.8 to 0.98, c = 1.6 to 1.96, z = 2.01 to 2.3). The most preferred lithium-containing transition metal _{oxides, Li x CoO 2, Li x} NiO 2, Li x MnO 2, Li x Co a Ni 1-a O 2, Li x Mn 2 O 4, Li x Co b V 1 _-b O _z (x = 0.02 to 1.2, a = 0.1 to 0.9, b = 0.9 to 0.98, z = 2.01 to 2.3). In addition, the value of x is a value before the start of charging / discharging, and increases / decreases by charging / discharging.

The average particle size of the positive electrode active material is not particularly limited, but is preferably 0.1 to 50 μm. The volume of particles of 0.5 to 30 μm is preferably 95% or more. More preferably, the volume occupied by a particle group having a particle size of 3 μm or less is 18% or less of the total volume, and the volume occupied by a particle group of 15 μm or more and 25 μm or less is 18% or less of the total volume. Although the specific surface area is not particularly limited, but is preferably 0.01 to 50 m ² / g by the BET method, particularly preferably 0.2m ² / g~1m ² / g. The pH of the supernatant when 5 g of the positive electrode active material is dissolved in 100 ml of distilled water is preferably 7 or more and 12 or less.

  There are no restrictions on the selection of members necessary for battery configuration other than those described above.

  The carbon material for battery electrodes of the present invention can be used as a separator for fuel cells in addition to the above-described negative electrode material for lithium ion secondary batteries. In that case, what is necessary is just to produce a separator so that 5-95 mass% of carbon materials of this invention may be included.

The present invention will be described in more detail below with typical examples. Note that these are merely illustrative examples, and the present invention is not limited thereto.
The physical properties used in the following examples were measured by the following methods.

[1] Average circularity:
The average circularity of the carbon material was measured as follows using a flow particle image analyzer FPIA-2100 (manufactured by Sysmex Corporation).
The sample for measurement was purified by removing fine dust through a 106 μm filter. A sample dispersion for measurement was prepared by adding 0.1 g of the sample to 20 ml of ion-exchanged water and uniformly dispersing 0.1 to 0.5% by mass of an anionic / nonionic surfactant. Dispersion was performed by using an ultrasonic cleaner UT-105S (manufactured by Sharp Manufacturing System) for 5 minutes.
The outline of the measurement principle and the like is described in “Powder and Industry”, VOL. 32, No. 2, 2000, Japanese Patent Laid-Open No. 8-136439, etc., and is specifically as follows.
When the dispersion liquid of the measurement sample passes through the flow path of a flat and transparent flow cell (thickness: about 200 μm), strobe light is irradiated at 1/30 second intervals and imaged with a CCD camera. A certain number of the still images were taken and analyzed, and calculated according to the following formula.
The equivalent circle diameter is the diameter of a true circle having the same projected area as the circumference of the actually imaged particle, and the circumference of the circle obtained from this equivalent circle diameter is divided by the circumference of the actually imaged particle. Value. For example, it is 1 for a perfect circle, and the value becomes smaller as the shape becomes more complicated. The average circularity is an average value of circularity of each measured particle.

[2] Average particle size:
It measured using the laser diffraction scattering type particle size distribution measuring apparatus Microtrac HRA (made by Nikkiso Co., Ltd.).

[3] Specific surface area:
Using a specific surface area measuring device NOVA-1200 (manufactured by Yuasa Ionics Co., Ltd.), the measurement was performed by the BET method which is a general method for measuring the specific surface area.

[4] Battery evaluation method:
(1) Paste creation:
Add 0.1 part by mass of KF polymer L1320 (N-methylpyrrolidone (NMP) solution containing 12% by mass of polyvinylidene fluoride (PVDF)) to 1 part by mass of the negative electrode material, and knead with a planetary mixer. The main agent stock solution was used.

(2) Electrode production:
NMP was added to the main agent stock solution to adjust the viscosity, and then applied onto a high purity copper foil to a thickness of 250 μm using a doctor blade. This was vacuum-dried at 120 ° C. for 1 hour and punched out to 18 mmφ. Further, the punched electrode is sandwiched between super steel press plates, and the press pressure is about 1 × 10 ^{2 to} 3 × 10 ² N / mm ² (1 × 10 ^{3 to} 3 × 10 ³ kg / cm ² ) with respect to the electrode. It pressed so that it might become. Then, it dried at 120 degreeC and 12 hours with the vacuum dryer, and was set as the electrode for evaluation.

(3) Battery creation:
A triode cell was produced as follows. The following operation was carried out in a dry argon atmosphere with a dew point of -80 ° C or lower.
In a cell with polypropylene screw-in lid (inner diameter of about 18 mm), the carbon electrode with copper foil (positive electrode) and the metal lithium foil (negative electrode) prepared in (2) above were separated by separator (polypropylene microporous film (Selga -2400)). Further, metallic lithium for reference was laminated in the same manner. An electrolytic solution was added thereto to obtain a test cell.

(4) Electrolyte:
In a mixed product of 8 parts by mass of EC (ethylene carbonate) and 12 parts by mass of DEC (diethyl carbonate), 1 mol / liter of LiPF ₆ was dissolved as an electrolyte.

(5) Charge / discharge cycle test:
A constant current low voltage charge / discharge test was conducted at a current density of 0.2 mA / cm ² (equivalent to 0.1 C).
Charging (insertion of lithium into carbon) was performed by CC (constant current) at 0.2 mA / cm ² from the rest potential to 0.002V. Next, it was switched to CV (constant voltage: constant voltage) charging at 0.002 V and stopped when the current value decreased to 25.4 μA.
Discharge (release from carbon) was performed by CC discharge at 0.2 mA / cm ² (equivalent to 0.1 C) and cut off at a voltage of 1.5V.

Example 1:
As the core carbonaceous particles, the average particle diameter by laser diffraction scattering method is 20 μm, the average circularity is 0.88, and the ratio of the area of the crystalline carbon portion to the amorphous carbon portion is 80 in the bright field image in the transmission electron microscope. : 20 powder was used.
500 parts by mass of this granulated product, 398 parts by mass of phenol, 466 parts by mass of 37% formalin, 38 parts by mass of hexamethylenetetramine as a reaction catalyst, and 385 parts by mass of water were added to a reaction vessel. This was stirred at 60 rpm for 20 minutes. Next, while stirring, the container was evacuated to 0.4 kPa (3 Torr) and held for 5 minutes, and the operation of returning to atmospheric pressure was repeated three times to impregnate the liquid into the granulated product. Further, the mixture was heated and maintained at 150 ° C. while stirring was continued. The contents initially had a mayonnaise-like fluidity, but gradually, a reaction product of phenol and formaldehyde containing graphite and a water-based layer began to separate, and after about 15 minutes from graphite and phenolic resin. As a result, the black granular material was dispersed in the reaction vessel. After that, after further stirring for 60 minutes at 150 ° C., the contents of the reaction vessel were cooled to 30 ° C. and stirring was stopped. The black granular material obtained by filtering the contents of the container is washed with water, further filtered, and dried using a fluidized bed dryer at a hot air temperature of 55 ° C. for 5 hours, whereby graphite / phenolic resin granular material is obtained. Obtained.
Next, this graphite phenol resin granular material was pulverized with a Henschel mixer at 1800 rpm for 5 minutes. This was put into a heating furnace, the inside of the furnace was replaced with a vacuum to make it under an argon atmosphere, and then the temperature was raised while flowing argon gas. It was kept at 2900 ° C. for 10 minutes and then cooled. After cooling to room temperature, the obtained heat-treated product was sieved with a sieve having a mesh size of 63 μm, and the lower sieve was used as a negative electrode material sample.

  A transmission electron micrograph (× 25000) of this material is shown in FIG. In the limited-field diffraction pattern of a square region having an arbitrarily selected side of 5 μm in FIG. 1, a region having two or more spot-like diffraction patterns (FIG. 2 (B)), one derived from the (002) plane The ratio of the area where only the spots appear (FIG. 2A) was 85:15 in area ratio.

Peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 by laser Raman spectrum of the surface of the material (laser Raman R value) was 1580 cm ^-1 peak intensity / 1360 cm ^-1 peak intensity = 0.05. The average particle size was 25 μm, the specific surface area was 1.1 m ² / g, C ₀ was 0.6716 nm, and the average circularity was 0.934. The results are shown in Table 1.
The battery was evaluated using this material, and the capacity at the first cycle of the charge / discharge cycle test, the coulomb efficiency, and the capacity at the 50th cycle were measured. The results are shown in Table 2.

Example 2:
As the carbonaceous particles serving as the core, particles obtained by granulating scaly graphite having an average particle size of 5 μm with a Redige mixer, and adjusting the average particle size by laser diffraction scattering method to 20 μm and the average circularity to 0.88 Except that it was used, the same operation as in Example 1 was performed, and the physical properties of the obtained carbon material were measured and the battery using the same was evaluated. The results are shown in Tables 1 and 2.

Example 3:
To the same carbonaceous particles as used in Example 1, 5.0 parts by mass of water was added to an ethanol solution of phenol resin monomer (BRS-727; manufactured by Showa Polymer Co., Ltd.) (5.5 parts by mass in terms of resin solid content). The solution which was stirred and sufficiently dissolved was added so that the solid content of the phenol resin was 10% by mass with respect to the carbonaceous powder, and kneaded for 30 minutes with a planetary mixer. This mixture was dried in a vacuum dryer at 150 ° C. for 2 hours. This was put into a heating furnace, the inside of the furnace was replaced with a vacuum to make it under an argon atmosphere, and then the temperature was raised while flowing argon gas. It was kept at 2900 ° C. for 10 minutes and then cooled. After cooling to room temperature, the obtained heat-treated product was sieved with a sieve having a mesh size of 63 μm, and the lower sieve was used as a negative electrode material sample.
Peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 by laser Raman spectrum of the carbon layer on the surface of the material was 1580 cm ^-1 peak intensity / 1360 cm ^-1 peak intensity = 0.15. Other physical properties are shown in Table 1. Table 2 shows the results of battery evaluation using the same.

Example 4:
The same procedure as in Example 1 except that 5% by mass of vapor grown carbon fiber (fiber diameter 150 nm, aspect ratio 100) graphitized at 2800 ° C. was added to the reaction vessel before the start of the reaction of Example 1 and stirred and mixed. Then, the physical properties of the obtained carbon material were measured and the battery using the carbon material was evaluated. The results are shown in Tables 1 and 2.

Example 5:
The same operation as in Example 1 was performed except that 0.01% by mass of B ₄ C (Denka) was added to the graphite phenol resin granules of Example 1 and pulverized at 1800 rpm for 5 minutes with a Henschel mixer. Measurement of physical properties of the obtained carbon material and evaluation of a battery using the carbon material were performed. The results are shown in Tables 1 and 2.

Comparative Example 1:
As the core carbonaceous particles, the average particle diameter by laser diffraction scattering method is 23 μm, the average circularity is 0.83, and the area of the crystalline carbon part and the amorphous carbon part in the bright-field image in the transmission electron microscope. A carbon material was obtained in the same manner as in Example 1 except that a natural graphitized product having a ratio of 997: 3 was used. The physical property values are shown in Table 1.
The obtained carbon material is a bright-field image in a transmission electron microscope having a square area of 5 μm on one side. The area ratio of the crystalline carbon part to the amorphous carbon part is 80:20 near the surface, and near the center. 995: 5.
Using this carbon material, the battery was evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 2:
The carbonaceous powder used in Example 1 was used without a surface carbon layer. A transmission electron micrograph (× 25000) of this material is shown in FIG.
With respect to this carbon material, the physical properties were measured and the battery was evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

Comparative Example 3:
Carbon powder was produced in the same manner as in Example 1 except that the final heat treatment temperature was 1000 ° C. FIG. 4 shows a transmission electron micrograph (× 25000) of the cross section. In the limited field diffraction pattern of a square region having a side of 5 μm arbitrarily selected in FIG. 4, the ratio of the region having two or more spot-like diffraction patterns and the region where only one spot derived from the (002) plane appears is In the vicinity of the surface, the area ratio was 25:75, and in the vicinity of the center, the area ratio was 70:30.
The obtained carbon material was measured for physical properties and evaluated for the battery in the same manner as in Example 1. The results are shown in Tables 1 and 2.

  According to the present invention, by forming a carbon material having both a crystalline carbon part and an amorphous carbon part in a bright-field image in a transmission electron microscope, the discharge capacity is large as a negative electrode material for a lithium ion secondary battery. In addition, a useful carbon material having excellent coulomb efficiency and cycle characteristics and a small irreversible capacity can be obtained. Moreover, the method for producing a carbon material of the present invention is excellent in economic efficiency and mass productivity, the covering material used is easy to handle, and the safety is improved.

2 is a transmission electron micrograph of the carbon powder obtained in Example 1. FIG. A photograph (A) of a limited field diffraction pattern of one spot derived from the (002) plane indicating an amorphous structure region, and two or more spot-shaped limited fields indicating a graphite crystal structure region It is a photograph (B) of a diffraction pattern. 4 is a transmission electron micrograph of the carbon powder obtained in Comparative Example 2. 4 is a transmission electron micrograph of the carbon powder obtained in Comparative Example 3.

Claims (36)

For lithium secondary batteries containing carbon powder having a homogeneous structure obtained by polymerizing the organic compound in a state where the organic compound as a polymer raw material has penetrated into the carbonaceous particles and then heat-treating at a temperature of 1800 to 3300 ° C. Negative electrode material.   The negative electrode material for a lithium secondary battery according to claim 1, wherein the polymerization is performed at a temperature of 100 to 500 ° C.   The organic compound is a raw material of at least one polymer selected from the group consisting of a phenol resin, a polyvinyl alcohol resin, a furan resin, a cellulose resin, a polystyrene resin, a polyimide resin, and an epoxy resin. Negative electrode material for lithium secondary battery.   The negative electrode material for a lithium secondary battery according to claim 3, wherein the organic compound is a raw material of a phenol resin.   The negative electrode material for a lithium secondary battery according to claim 4, wherein a drying oil or a fatty acid thereof is added during the reaction of the raw material of the phenol resin. The negative electrode for a lithium secondary battery according to any one of claims 1 to 5, wherein the negative electrode for a lithium secondary battery is obtained by heat-treating at a temperature of 1800 to 3300 ° C after repeating the process of polymerizing the carbonaceous particles in a state where the organic compound has permeated a plurality of times. material.   A negative electrode material for a lithium secondary battery obtained by uniformly impregnating and combining an organic compound as a polymer raw material in a carbonaceous particle, polymerizing the organic compound, and then carbonizing and firing the particle. A negative electrode material for a lithium secondary battery having a substantially uniform structure from the surface to the central portion.   The negative electrode material for a lithium secondary battery according to any one of claims 1 to 7, wherein the organic compound is used in an amount of 4 to 500 parts by mass with respect to 100 parts by mass of the carbonaceous particles.   The negative electrode material for a lithium secondary battery according to claim 8, wherein the organic compound is used in an amount of 100 to 500 parts by mass with respect to 100 parts by mass of the carbonaceous particles.   The negative electrode material for a lithium secondary battery according to any one of claims 1 to 9, containing 10 to 5000 ppm of boron.   The negative electrode material for a lithium secondary battery according to claim 10, wherein boron or a boron compound is added after polymerization of the organic compound, and then heat treatment is performed at 1800 to 3300 ° C.   The negative electrode material for a lithium secondary battery according to any one of claims 1 to 11, wherein the carbonaceous particles are natural graphite particles, particles made of petroleum pitch coke, or particles made of coal pitch pitch coke.   The negative electrode material for a lithium secondary battery according to claim 12, wherein the carbonaceous particles have an average particle diameter of 10 to 40 μm and an average circularity of 0.85 to 0.99.   The negative electrode material for lithium secondary batteries according to any one of claims 1 to 13, comprising carbon fibers having a fiber diameter of 2 to 1000 nm.   The negative electrode material for a lithium secondary battery according to claim 14, wherein at least a part of the carbon fibers adheres to the surface of the carbon powder.   The negative electrode material for a lithium secondary battery according to claim 14 or 15, comprising 0.01 to 20 parts by mass of carbon fiber with respect to 100 parts by mass of carbonaceous particles.   The negative electrode material for a lithium secondary battery according to any one of claims 14 to 16, wherein the carbon fiber is a vapor grown carbon fiber having an aspect ratio of 10 to 15000.   18. The negative electrode material for a lithium secondary battery according to claim 17, wherein the vapor grown carbon fiber is a graphite-based carbon fiber heat-treated at 2000 ° C. or higher.   The negative electrode material for a lithium secondary battery according to claim 17 or 18, wherein the vapor grown carbon fiber has a hollow structure therein.   The negative electrode material for a lithium secondary battery according to any one of claims 17 to 19, wherein the vapor grown carbon fiber includes a branched carbon fiber. An anode material for lithium secondary battery according to any one of claims 17 to 20 average spacing d ₀₀₂ of the vapor-grown carbon fibers by X-ray diffraction (002) plane is not more than 0.344 nm.   The negative electrode material for a lithium secondary battery according to any one of claims 1 to 21, wherein an average circularity measured by a flow type particle image analyzer of carbon powder is 0.85 to 0.99. 0.6703~0.6800nm is C ₀ of (002) plane in the X-ray diffraction measurement of carbon powder, La (a-axis direction of the crystallite size)> 100 nm, Lc (c-axis direction of the crystallite size)> 100 nm and is claimed Item 23. The negative electrode material for a lithium secondary battery according to any one of Items 1 to 22. The negative electrode material for a lithium secondary battery according to any one of claims 1 to 23, wherein the carbon powder has a BET specific surface area of 0.2 to ⁵ m ² / g. 25. The negative electrode material for a lithium secondary battery according to claim 1, wherein the true density of the carbon powder is 2.21 to 2.23 g / cm ³ . Laser Raman R value of the carbon powder (the peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 by laser Raman spectrum) negative electrode for a lithium secondary battery according to any one of claims 1 to 25 is 0.01 to 0.9 material.   27. The negative electrode material for a lithium secondary battery according to any one of claims 1 to 26, wherein an average particle diameter of the carbon powder determined by a laser diffraction method is 10 to 40 [mu] m.   A bright-field image in a transmission electron microscope having a cross-section obtained by cutting particles constituting a negative electrode material for a lithium secondary battery into thin pieces, and in a limited-field diffraction pattern of a 5 μm square region arbitrarily selected, Lithium secondary battery in which the ratio of the area of the graphite crystal structure having the diffraction pattern and the area of the amorphous structure having the diffraction pattern that appears only in one spot derived from the (002) plane is 99 to 30: 1 to 70 in area ratio A negative electrode material for a lithium secondary battery, wherein a region of a graphite crystal structure and a region of an amorphous structure are dispersed from the surface of a particle constituting the negative electrode material for a lithium secondary battery to a central portion.   A bright-field image in a transmission electron microscope having a cross-section obtained by cutting particles constituting a negative electrode material for a lithium secondary battery into thin pieces, and in a limited-field diffraction pattern of a 5 μm square region arbitrarily selected, A negative electrode material for a lithium secondary battery, wherein a ratio of a graphite crystal structure region having a diffraction pattern to an amorphous structure region having a diffraction pattern that appears only in one spot derived from the (002) plane is 85:15 in area ratio.   30. The negative electrode material for a lithium secondary battery according to claim 28 or 29, containing 10 to 5000 ppm of boron. Including a step of treating the carbonaceous particles with an organic compound as a polymer raw material or a solution thereof to infiltrate the organic compound into the carbonaceous particles, a step of polymerizing the organic compound, and a step of heat-treating at a temperature of 1800 to 3300 ° C. A method for producing a negative electrode material for a lithium secondary battery comprising carbon powder having a homogeneous structure, characterized in that Treating the carbonaceous particles with a mixture containing an organic compound as a polymer raw material and carbon fibers having a fiber diameter of 2 to 1000 nm or a solution thereof, allowing the organic compound to penetrate into the carbonaceous particles and bonding the carbon fibers; A negative electrode for a lithium secondary battery comprising at least a part of carbon fibers attached to the surface of a carbon powder having a homogeneous structure, characterized by comprising a step of polymerizing the carbon and a heat treatment at a temperature of 1800 to 3300 ° C. Material manufacturing method.   An electrode paste for a negative electrode for a lithium secondary battery comprising the negative electrode material for a lithium secondary battery according to any one of claims 1 to 30 and a binder.   A negative electrode for a lithium secondary battery, comprising the molded article of the electrode paste according to claim 33.   A lithium secondary battery comprising the electrode according to claim 34 as a constituent element.   A non-aqueous electrolyte and / or a non-aqueous polymer electrolyte is used, and the non-aqueous solvent used in the non-aqueous electrolyte and / or non-aqueous polymer electrolyte is ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, butylene. 36. The lithium secondary battery according to claim 35, comprising at least one selected from the group consisting of carbonate and vinylene carbonate.