JP4839180B2 - Carbon powder and manufacturing method thereof, negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

The present invention has high initial charge / discharge efficiency and excellent cycle characteristics, and in particular, a lithium ion secondary battery capable of rapid charging even when the electrode density is higher than 1.6 g / cm ^3. The present invention relates to a negative electrode for a lithium ion secondary battery for obtaining an ion secondary battery, a negative electrode material for a lithium ion secondary battery for obtaining the negative electrode, a carbon powder as a material for the negative electrode material, and a method for producing the same.

  In recent years, with the miniaturization or high performance of electronic devices, there is an increasing demand for higher energy density of batteries. Under such circumstances, lithium ion secondary batteries have attracted attention as batteries that have high energy density and can be increased in voltage. As a negative electrode material constituting the negative electrode of this lithium ion secondary battery, graphite that is excellent in charge / discharge characteristics and exhibits high discharge capacity and potential flatness has become the mainstream (for example, Patent Document 1). Examples of the graphite used as the negative electrode material include graphite particles such as natural graphite and artificial graphite, and mesophase-based graphite particles obtained by heat-treating mesophase pitch using tar and pitch as raw materials, for example, mesophase microspheres. It is done.

  A lithium ion secondary battery using graphite particles obtained by graphitizing mesophase spherules as a negative electrode material exhibits very good discharge characteristics, but the graphite particles have low press compressibility (not easily densified), In terms of improving the energy density per volume by increasing the density of the negative electrode, it is more disadvantageous than natural graphite or highly crystalline artificial graphite. On the other hand, natural graphite and highly crystalline artificial graphite have very high press-compressibility (easy to be densified), but their orientation is strong. Therefore, when trying to increase the density of electrodes and increase energy density, Since the charge / discharge characteristics are remarkably deteriorated and the cycle characteristics are also deteriorated, there is a great drawback that good battery characteristics are exhibited only in a range where the energy density is lower than that of graphite particles of mesophase spherules.

In order to compensate for the drawbacks of such graphite particles as a negative electrode material, when producing the negative electrode, foreign graphite particles are mixed and prepared to improve the above-mentioned drawbacks.
For example, by utilizing the fact that the gaps between mesophase spherules are difficult to compress, natural graphite or artificial graphite mixed with highly crystalline natural graphite or graphitized mesophase spherules, etc. are easily oriented during rolling in electrode manufacturing. A method has been proposed in which a negative electrode is prepared so that graphite and artificial graphite are not oriented, such as maintaining a void structure of the electrode and not deteriorating battery characteristics in a high density region (Patent Document 2). In order to prevent the orientation of artificial graphite, a method of mixing graphitized carbon fibers from mesophase pitch has been proposed (Patent Documents 3 and 4).

In recent years, the demand for an increase in the discharge capacity of lithium ion secondary batteries has increased, and if the electrode density is further increased in order to meet this demand, battery characteristics such as rapid charge / discharge characteristics tend to be reduced. There is a limit to the proposed prior art in promoting higher density. The reason is that if a hard component such as graphite particles of mesophase spherules and a soft component such as natural graphite particles are mixed, the soft component has a higher density and is easily oriented, depending on the mixed composition. It is presumed that the greater the orientation, the more the orientation between the graphite particles is promoted, the worse the permeability of the electrolyte solution between the graphite particles, and the hindrance to the entry and exit of lithium ions.
That is, as in Patent Document 2 or 3 and 4, carbon fibers from mesophase spherules and mesophase pitch are hard, so if this is the main material, it is difficult to increase the density of the negative electrode. On the other hand, if the amount of flake graphite such as natural graphite is increased, good battery characteristics are exhibited at relatively low density. However, when this density is increased, battery characteristics that are thought to be unevenly distributed in the electrode Degradation occurs.

In addition, lithium ion secondary batteries using graphite particles hydrophilized by mechanochemical treatment as a negative electrode material have a high discharge capacity and high initial charge / discharge efficiency, and the graphite material hydrophilized by mechanochemical treatment. A lithium ion secondary battery using a negative electrode material obtained by adding non-mechanochemically treated graphite particles to particles is known to further improve the rapid charging efficiency (Patent Document 5).
However, in this case as well, when the electrode density of the negative electrode was set to a high density exceeding 1.6 g / cm ³ , the discharge capacity was not increased, and the rapid charging efficiency was unsatisfactory.

Patent Document 1: Japanese Patent Publication No. 62-23433 Patent Document 2: Japanese Patent Application Laid-Open No. 6-163032 Patent Document 3: Japanese Patent Application Laid-Open No. 2001-135304 Patent Document 4: Japanese Patent Application Laid-Open No. 2002-33104 Patent Document 5: Japanese Patent Application Laid-Open No. 2002-33104 No. 2003-132889

Therefore, the present invention has high initial charge / discharge efficiency and excellent cycle characteristics, and in particular, a lithium ion secondary battery that can be rapidly charged even when the electrode density is higher than 1.6 g / cm ³ , Provided are a negative electrode for a lithium ion secondary battery for obtaining the lithium ion secondary battery, a negative electrode material for a lithium ion secondary battery for obtaining the negative electrode, a carbon powder as a material for the negative electrode material, and a method for producing the same. Is the purpose.

  The present invention solves the problems of the conventional negative electrode materials for graphite-based lithium ion secondary batteries as described above. As a result of intensive studies on carbon particles, the present inventor has good initial charge and discharge efficiency by using carbon particles whose dibutyl phthalate absorption amount is in the following range and satisfies the following formula (1). The present inventors have found that battery characteristics (rapid charge / discharge characteristics, cycle characteristics) in a high density region are dramatically improved, and have completed the present invention. The present invention is as follows.

1. Absorption of dibutyl phthalate 10 cm ^3/100 g or ^more, 30 cm 3/100 g or less and a carbon powder density ratio represented by the following formula (1) is characterized in that it is a 4 to 6.5.
Density ratio = (Density when pressure is 1 MPa) / (Tap density) (1)
2. After mechanochemical treatment of the graphite material and a carbon material having a density ratio and an average particle diameter smaller than the graphite material represented by the following formula (1), the carbon material is further applied to the graphite material using a binder. A method for producing a carbon powder, characterized by adhering.
Density ratio = (Density when pressure is 1 MPa) / (Tap density) (1)
3. 2. The method for producing carbon powder as described in 2 above, wherein the density ratio of the graphite material is 3 to 9, and the average particle diameter is 50 μm or less.
4). After mechanochemical treatment of 100 parts by mass of the graphite material and 1 to 50 parts by mass of the carbon material having a density ratio and an average particle diameter represented by the following formula (1) smaller than the graphite material, using a binder, absorption of dibutyl phthalate for causing the graphite material is deposited the carbon material is 10 cm ^3/100 g or ^more, or less 30 cm 3/100 g, and the density ratio shown by the following formula (1) is 4-6. 5. The method for producing the carbon powder according to 2 or 3, which is 5.
Density ratio = (Density when pressure is 1 MPa) / (Tap density) (1)

5). A negative electrode material for a lithium ion secondary battery, comprising the carbon powder of 1.
6). 5. The negative electrode for a lithium ion secondary battery, comprising the negative electrode material for a lithium ion secondary battery according to 5 above.
7). A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to 6 above.

  When the carbon powder of the present invention is used as a negative electrode material for a lithium ion secondary battery, the discharge capacity of the battery and the initial charge / discharge efficiency are high. Shows rapid charge / discharge characteristics. Therefore, the lithium ion secondary battery of the present invention satisfies the recent demand for higher energy density of the battery, and is effective in reducing the size and performance of the mounted device.

Hereinafter, the present invention will be specifically described.
[Carbon powder]
Carbon powder of this invention, the absorption amount of dibutyl phthalate (DBP) (hereinafter, simply referred to as DBP absorption) of 10 cm ^3/100 g or ^more, 30 cm 3/100 g or less and the density ratio of the following formula (1) To meet.
Density ratio = (Density when pressure is 1 MPa) / (Tap density) (1)

DBP absorption usually quantifies the structure of fine particles such as carbon black, and is considered to be a measure for knowing the amount of binder absorbed when producing a negative electrode for a lithium ion secondary battery. In this invention, it measured by the method based on B method (squeezing method) prescribed | regulated to JISK6217-4: 2001. Details will be described later.
Among the carbon powder, although an average particle size, such as furnace carbon black is small and a few tens of nm is DBP absorption 100 cm ^3/100 g or more, with a much larger average particle size than carbon black graphite particles, DBP absorption amount is very small, a typical natural graphite, artificial graphite is about 25 cm ^3/100 g, is usually less than 10 cm ^3/100 g is graphite particles, such as graphite product of mesocarbon spherules .

The density ratio defined by the formula (1) is an index for viewing the degree of strength for maintaining the shape and form of the carbon powder, that is, the compression resistance and hardness when the carbon powder is filled. Compared to the density when the carbon powder is lightly shaken and filled, that is, the so-called tap density, the index indicated by the ratio of the density when pressurized to 1 MPa and the tap density has an electrode density of 1.6 g / cm ^3. Appropriate display of compression resistance and hardness when filled to a high density such as super. That is, when the density ratio is 4 to 6.5, preferably 4.5 to 6.3, and more preferably 4.8 to 6.0, the amount of voids in the carbon powder that allows the electrolyte solution to enter and exit is ensured. The compression resistance when the electrode density exceeds 1.6 g / cm ³ is good, the carbon powder is not crushed, the voids are maintained, and the rapid charge / discharge efficiency of the lithium ion secondary battery can be significantly improved. it can. A method for measuring the density will be described later.
In addition, the density ratio of natural graphite and artificial graphite which are easily crushed is as large as 7 to 9, and the density ratio of spherulite graphite which is not easily crushed is as small as 1 to 3.

A negative electrode material for a lithium ion secondary battery (hereinafter, also simply referred to as a negative electrode material) is a paste-like negative electrode mixture in which graphite or a carbon material is usually added to a solution or dispersion of an aqueous or organic binder. To be prepared. The negative electrode mixture is applied to a current collector to produce a negative electrode, but it is advantageous from the viewpoint of the characteristics and productivity of the negative electrode mixture that the amount of medium required for forming a paste is smaller. The carbon powder of the present invention is similarly prepared as a negative electrode material.
By the way, a carbon powder having a large DBP absorption amount needs to use a large amount of a solvent and a binder in order to make it a flowable paste. If the amount is small, it is difficult to prepare a negative electrode mixture. It is. Therefore, from the viewpoint of ease of preparing a paste-like negative electrode mixture from carbon powder and the characteristics of the negative electrode mixture, carbon powder having a small DBP absorption amount is preferable. For example, graphitized mesocarbon spherulites are preferred. Is preferred over natural graphite. Specific DBP absorption 10 cm ^3/100 g or ^more, or less 30 cm 3/100 g, preferably 12~25cm ³ / 100g, more preferably 14~22cm ³ / 100g.

However, since the graphitized mesocarbon spherules are harder and larger than natural graphite, they are mixed and compressed to produce a high-density negative electrode having an electrode density of more than 1.6 g / cm ^3. The natural graphite is crushed and enters the voids formed by the mesocarbon microspheres, reducing the size and number of the voids, and the natural graphite is oriented in advance. Therefore, in the lithium ion secondary battery using this (hereinafter also referred to simply as a secondary battery), the gap for the electrolyte solution is reduced, and the opportunity and amount of lithium ion entry and exit are reduced. Decreases. When the electrode density is less than 1.6 g / cm ³ , there is almost no decrease in the voids, and rapid charge / discharge efficiency is improved by mixing the mesocarbon microsphere graphitized material with natural graphite.

  The carbon powder of the present invention has a powder property that is harder to press-compress than natural graphite, in addition to the easy absorbability of the binder and electrolyte, so press the electrode coated with the negative electrode mixture using this. It is difficult to compress even during molding (the density ratio is small), and it is possible to keep the gaps of the electrodes even when the density is increased as compared with a readily compressible carbon material such as natural graphite.

The crystallinity of the carbon powder of the present invention is not particularly limited. However, the higher the crystallinity, the higher the energy density, and thus the higher the crystallinity. Preferably the lattice spacing _{d 002} is 0.340nm less in X-ray diffraction, more preferably not more than 0.337 nm. The lattice spacing d ₀₀₂ is obtained by measuring the diffraction peak of the (002) plane of the carbon powder using CuKα ray as the X-ray and using high-purity silicon as a standard substance, and calculating d ₀₀₂ from the peak position. calculate. The calculation method follows the Japan Science and Technology Act (measurement method defined by the 117th Committee of the Japan Society for the Promotion of Science). Specifically, “Carbon Fiber” (Suguro Otani, pages 733-742 (March 1986) ), Modern Editing Co.) and the like.
The R value in the laser Raman spectrum using an argon laser with a wavelength of 514.5 nm is ID for the peak intensity appearing near 1360 cm ^{−1 in} the D band, and IG for the peak intensity appearing near 1580 cm ^{−1 in} the G band. The ratio ID / IG is 0.3 or less, preferably 0.1 or less.

  The particle size distribution of the carbon powder of the present invention is not particularly limited, but a smaller average particle size is preferred, preferably 20 μm or less, more preferably 15 μm or less. However, if it is too fine, it becomes difficult to disperse when used as a negative electrode material, and there is a charge / discharge loss of the lithium ion secondary battery, which is preferably 1 μm or more, and more preferably 3 μm or more.

The carbon powder of the present invention is preferably a structure in which a graphite material and a material containing a carbon material or a carbon precursor are combined and integrated. Compounding means, for example, that a graphite material and a carbon material are mechanochemically treated, and a carbon material is firmly attached to the surface of the graphite material using a binder. More preferable carbon powder uses a graphite material having a high density ratio (also simply referred to as graphite material) and a carbon material having a low density ratio, such as mesophase graphite material or a precursor thereof (these are also simply referred to as carbon materials). However, they are combined without any bias.
In addition, a simple mixture of graphite material and mesophase spherules which are carbon materials does not clear the DBP absorption amount and density ratio of the present invention.

The graphite material has a larger density ratio and average particle size than the carbon material, but the density ratio is 3
To 9, preferably 4 to 8.9, more preferably 5 to 8.8, and the average particle size is preferably 50 μm or less, more preferably 1 to 20 μm.
Examples of the graphite material include highly crystalline artificial graphite or natural graphite obtained by heat-treating an easily graphitizable carbon material at a high temperature of 3000 ° C. or higher. These shapes are preferably scaly or scaly, or may be needles. A scale-like or scaly shape is particularly preferred because it easily satisfies the density ratio of the obtained carbon powder of 4 to 6.5.
The crystallinity of the graphite material as the main raw material is not particularly limited, but a higher crystallinity is preferable because higher energy density can be achieved. Preferably the lattice spacing _{d 002} is 0.340nm less in X-ray diffraction, more preferably not more than 0.337 nm.

The carbon material has a smaller density ratio and average particle size than the graphite material, but the density ratio is 1 to 5, preferably 1.3 to 4.5, more preferably 1.5 to 4. The particle diameter is preferably 10 μm or less, more preferably 3 μm or less, regardless of the particle shape.
Examples of the carbon material include mesophase spherules, fine powder obtained by pulverizing the mesophase, and those obtained by graphitizing the mesophase carbon fiber, fine powder obtained by pulverizing mesophase carbon fiber, and thermal carbon black. The average particle diameter of the carbon material is preferably smaller than the long diameter of the graphite material, and is preferably a massive material having a particle diameter about half the long diameter of the graphite material. The carbon precursor is a mesophase pitch powder, or a heat-treated, oxidized or crosslinked resin powder such as a phenol resin, a furan resin, a polyvinyl alcohol resin, or a cellulose resin, and the average particle diameter thereof is 10 μm or less. Preferably it is 3 micrometers or less.

  Examples of the combination of the graphite material and the carbon material include, for example, a combination of highly crystalline scaly natural graphite and finely pulverized mesophase graphite particles, or an average particle size among highly crystalline scaly artificial graphite and carbon black. A combination with thermal carbon black that has a large particle size and little secondary particles is preferable.

  The mixing ratio of the graphite material and the carbon material varies depending on the particle diameter, shape, etc., so it cannot be generally stated, but the ratio of the carbon material is more than the case where the carbon material adheres as a single layer on the entire surface of the graphite material. Less is preferable. If the particle size of the carbon material is small, the number of particles increases with the same mass. Therefore, the mass of the carbon material is usually 1 to 50 parts by mass with respect to 100 parts by mass of the graphite material. This is a preferred range.

[Manufacture of carbon materials]
The carbon powder of the present invention can be produced, for example, by the following method.
Graphite material with high press-compressibility (high density ratio) and large average particle diameter, and agglomerated fine graphite or carbon particles with a smaller density ratio and smaller average particle diameter, preferably carbon obtained by pulverizing mesophase spherules After a mechanochemical treatment is applied to the material with sufficient shearing force, the carbon material is adhered to the surface of the graphite material in a gas phase or a liquid phase via a binder, and the carbon material is fixed and combined. Furthermore, the carbon powder of this invention can be obtained by performing heat processing and carbonizing or graphitizing a carbon material.

  Mechanochemical treatment refers to a treatment in which a compressive force and a shear force are simultaneously applied to a graphite material and a carbon material. Although the shearing force and compressive force are usually larger than general stirring force, these mechanical stresses are preferably applied to the surfaces of the graphite material and the carbon material, and preferably do not destroy the skeleton of the graphite material and the carbon material. When the skeleton is destroyed, when used as a negative electrode material, the irreversible capacity tends to increase. In general, the shearing force and the compressive force are preferably such that the reduction rate of the average particle diameter of the graphite material and the carbon material by mechanochemical treatment is suppressed to 20% or less.

  As long as the mechanochemical treatment apparatus is an apparatus that can simultaneously apply a shearing force and a compressive force to a graphite material and a carbon material, the type and structure of the device are not particularly limited. For example, a kneader such as a pressure kneader, two rolls, a rotating ball mill, a high-speed impact dry compounding device such as a “hybridization system” (manufactured by Nara Machinery Co., Ltd.), a “mechanomicro system” (manufactured by Nara Machinery Co., Ltd.), A compression shear type dry powder compounding device such as “Mechano-Fusion System” (manufactured by Hosokawa Micron) can be used.

Among them, an apparatus that applies a shearing force and a compressing force simultaneously using a rotational speed difference is preferable. Specifically, an apparatus ("a rotating rotor), an internal member (inner piece) having a rotational speed different from that of the drum, and a circulation mechanism (eg, a circulation blade) of graphite material and carbon material (" circulation blade "). Using a mechano-fusion system "), while applying centrifugal force to the graphite material and carbon material supplied between the rotating drum and the internal member, shear force and compressive force due to the speed difference from the rotating drum by the internal member It is preferable to carry out mechanochemical treatment by repeating the above simultaneously.
In addition, by passing graphite particles and fine graphite particles between a fixed drum (stator) and a rotating rotor rotating at high speed, the shear force and compressive force due to the speed difference between the fixed drum and rotating rotor can be reduced. Also preferred are devices that simultaneously apply particles ("hybridization system").

  The conditions of mechanochemical treatment differ depending on the equipment used, and cannot be generally stated. For example, in the case of the “mechanofusion system”, the peripheral speed difference between the rotating drum and the internal member is 5 to 50 m / sec. The distance is preferably 1 to 100 mm and the processing time is 3 to 90 min. In the case of the “hybridization system”, the peripheral speed difference between the stationary drum and the rotating rotor is preferably 10 to 100 m / sec, and the processing time is preferably 30 sec to 10 min.

Next, the graphite material and the carbon material are firmly adhered to the mechanochemically processed product using a binder to obtain a carbon powder. For example, a method in which 0.5 to 20 parts by mass of a binder is added to 100 parts by mass of a mechanochemically processed product, and if necessary, the binder is fluidized and adhered is employed. Since the graphite material and the carbon material may be combined and combined, the layer thickness of the binder layer cannot be specified unconditionally.
For the binder, it is preferable to use a graphitizable or non-graphitizable precursor. Specifically, petroleum pitch, coal pitch, pitch modified by oxidation, pitch generated by decomposing resin, and the like can be used.
Further, the same effect can be obtained by thermally decomposing an organic substance in a gas phase or a liquid phase and depositing a polymerization component of the decomposition product on a contact portion between particles. For example, benzene, methane, ethylene, aliphatic alcohol, etc. may be thermally decomposed in the gas phase and contacted with the mechanochemically treated product. Or after making resin which leaves a residual carbon component after thermal decomposition contact with a mechanochemical treatment product in a liquid phase, heat treatment (for example, heating at 600 to 1200 ° C. in a non-oxidizing atmosphere) is performed to decompose the resin. Also good. In this case, as the resin, a phenol resin, a furan resin, a polyvinyl alcohol resin, a cellulose resin, or the like is preferably used.
After complexing with the binder, uncomplexed materials and the like are removed, and the product coarse particles and fine particles are separated, and if necessary, carbon powder having an average particle diameter in a certain range can be obtained.

[Negative electrode]
The negative electrode of the present invention is produced using a negative electrode material containing carbon powder having a constant DBP absorption amount and a density ratio. Even if the carbon powder is used alone, a negative electrode having good battery characteristics in a high density region can be obtained. However, conductive materials, modifiers, additives and the like which are usually used may be mixed. These addition amounts cannot be generally specified because the optimum amount varies depending on the material to be added, but are 0.1 to 10% by mass with respect to 100% by mass of the carbon powder.
Other negative electrode active materials include artificial graphite, natural graphite, natural graphite or granulated granulated graphite, mesophase microsphere graphitized material, bulk mesophase graphite, mesophase pitch carbon fiber graphitized material, nano graphite fiber, etc. It can mix with this carbon powder in the range which does not impair the effect of invention.

The production of a negative electrode using a negative electrode material containing the carbon powder of the present invention is to obtain a negative electrode that is sufficiently chemically and electrochemically drawn out of the performance of the carbon powder and that is highly moldable to the carbon powder. The molding method is not particularly limited as long as it can be performed, and can be performed according to a normal molding method. For example, the carbon powder can be dry-mixed with resin powders such as polyethylene and polyvinyl alcohol, and hot press molded in a mold to produce a negative electrode. The layer thickness is 10 to 200 μm, preferably 20 to 200 μm.
In addition, since the negative electrode material containing the carbon powder of this invention has fixed press compressibility, there are few cracks of a carbon powder also at the time of a press, and when it uses for a negative electrode material, charging / discharging efficiency is high.

  Moreover, a negative electrode can be produced using a negative electrode mixture prepared by adding a binder to the carbon powder of the present invention. The negative electrode mixture is prepared, for example, by adjusting the carbon powder of the present invention and another carbon material to an appropriate particle size by classification or the like and mixing with a binder. By using the carbon powder of the present invention, not only an organic solvent-based binder that dissolves and / or disperses in an organic solvent, but also a water-soluble and / or water-dispersible aqueous binder can be used. A negative electrode that exhibits discharge characteristics can be obtained.

As the binder, those having chemical stability and electrochemical stability with respect to the electrolyte are preferable. For example, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene, polyvinyl alcohol, and carboxy. Methyl cellulose, styrene butadiene rubber or the like is used. These can also be used together. Among them, in order to achieve the object of the present invention and make the most of the effect, an aqueous binder such as carboxymethyl cellulose (water-soluble), polyvinyl alcohol (water-soluble), styrene butadiene rubber (water-dispersible) is used. Is particularly preferred.
In general, the binder is preferably used at a ratio of 0.5 to 20% by mass in the total amount of the negative electrode mixture.

  For example, the carbon powder of the present invention and a fluorine resin powder such as polyvinylidene fluoride and polytetrafluoroethylene are mixed with a solvent such as N-methylpyrrolidone and dimethylformamide to form a slurry. Among these, in consideration of the influence on the safety and environmental aspects in drying and removing the solvent, it is preferable to use an aqueous slurry obtained by dissolving or dispersing carboxymethyl cellulose, styrene butadiene rubber or the like using water as a solvent. The slurry is usually applied to one side or both sides of a current collector to form a negative electrode mixture layer.

In addition, if the negative electrode mixture is dispersed in a solvent and made into a paste, and then applied to the current collector and dried, a negative electrode mixture layer uniformly and firmly adhered to the current collector is formed. The solvent may be a conventional solvent used for preparing the slurry. The paste is prepared by mixing using a known stirrer, mixer, kneader, kneader, or the like. For example, the paste is prepared by stirring at about 300 to 3000 rpm with a wing-type homomixer.
The layer thickness when applying the negative electrode mixture obtained by mixing the negative electrode material and the binder according to the present invention to the current collector is 10 to 200 μm, preferably 20 to 200 μm.
When the negative electrode mixture layer is formed and then pressure bonding such as press working is performed, the adhesive strength between the negative electrode mixture layer and the current collector can be further increased.

  The shape of the current collector used for the negative electrode is not particularly limited, but a foil or a net-like material such as a mesh or an extended metal is used. Examples of the current collector include copper, stainless steel, and nickel. In the case of a foil, the thickness of the current collector is preferably 5 to 20 μm.

  The reason why a lithium ion secondary battery including a negative electrode using the carbon powder of the present invention as a negative electrode material exhibits excellent charge / discharge characteristics is that when preparing a negative electrode mixture using the carbon powder, a binder or the like. As a result of the binder being thinly dispersed on the surface of the carbon powder, it surely penetrates into the secured voids and firmly bonds the carbon powders with the anchor effect. It is considered that the strong adhesion between the carbon powder and the current collector is maintained through the adhesive and does not hinder the conductivity, ion conductivity, electrolyte permeability, and the like. Furthermore, in the negative electrode, it is presumed that the electrolyte solution is taken into the gap and held around the carbon powder.

[Positive electrode]
As the positive electrode active material, it is preferable to select a material capable of doping / dedoping a sufficient amount of lithium. Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal chalcogenides, vanadium oxides (V ₂ O ₅ , V ₆ O ₁₃ , V ₂ O ₄ , V ₃ O _{8 and the} like) and lithium compounds thereof, general formulas M _x Mo ₆ S _8-y (where X is a number in a range of 0 ≦ X ≦ 4, Y is a number in a range of 0 ≦ Y ≦ 1, and M represents a metal such as a transition metal). A compound, activated carbon, activated carbon fiber, etc. can be used.

The lithium-containing transition metal oxide is a composite oxide of lithium and a transition metal, and may be a solid solution of lithium and two or more transition metals. Specifically, the lithium-containing transition metal oxide is LiM (1) _1-p M (2) _p O ₂ (wherein P is a number in the range of 0 ≦ P ≦ 1, M (1), M (2) comprises at least one transition metal element.) Or LiM (1) _2-Q M (2) _Q O ₄ (wherein Q is a number in the range of 0 ≦ Q ≦ 1, M (1) , M (2) is composed of at least one transition metal element).
In the above, examples of the transition metal element represented by M include Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, and Sn, and preferably Co, Ni, Fe, Mn, and Ti. , Cr, V, and Al.

Examples of the lithium-containing transition metal oxide, more _{specifically, LiCoO 2, Li p Ni Q} M 1-Q O 2 (M is said transition metal elements excluding Ni, preferably Co, Fe, Mn, Ti, Lithium composite oxide, LiNiO ₂ , LiMnO ₂ , LiMn represented by (at least-selected from Cr, V, Al, 0.05 ≦ p ≦ 1.10, 0.5 ≦ q ≦ 1.0) ₂ O ₄ or the like.

The lithium-containing transition metal oxide as described above includes, for example, lithium, transition metal oxides or salts as starting materials, these starting materials are mixed according to a desired composition, and are heated at 600 to 1000 ° C. in an oxygen atmosphere. It can be obtained by firing at a temperature. The starting material is not limited to oxides or salts but may be hydroxides.
In the present invention, the positive electrode active material may be used alone or in combination of two or more. For example, an alkali carbonate such as lithium carbonate can be added to the positive electrode material.

  In order to form a positive electrode with such a positive electrode material, for example, a positive electrode mixture comprising a positive electrode material, a binder, and a conductive agent for imparting conductivity to the electrode is applied to both surfaces of the current collector. Form a layer. As the binder, any of those exemplified for the negative electrode can be used. As the conductive agent, for example, a carbon material, graphite or carbon black is used.

The shape of the current collector is not particularly limited, and a box shape or a mesh shape such as a mesh or an extended metal is used. Examples of the current collector substrate include aluminum, stainless steel, and nickel. The thickness is preferably 10 to 40 μm.
Also in the case of the positive electrode, like the negative electrode, the positive electrode mixture is dispersed in a solvent to form a paste, and the paste-like positive electrode mixture is applied to a current collector and dried to form a positive electrode mixture layer. Alternatively, after the positive electrode mixture layer is formed, pressure bonding such as press pressing may be further performed. As a result, the positive electrode mixture layer is uniformly and firmly bonded to the current collector.

[Electrolytes]
As the electrolyte used for the present invention can be used an electrolyte salt used in the conventional non-aqueous electrolyte solution, for _{example, LiPF 6, LiBF 4, LiAsF} 6, LiClO 4, LiB (C 6 H 5) 4, LiCi, LiBr, LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ CH ₂ OSO ₂ ) ₂ , LiN (CF ₃ CF ₂ OSO _{2) 2, LiN (HCF 2} CF 2 CH 2 OSO 2) 2, LiN [(CF 3) 2 CHOSO 2] 2, LiB [C 6 H 3 (CF 3) 2] 4, LiAlCl 4, LiSiF such ₆ A lithium salt or the like can be used. In particular, LiPF ₆ and LiBF ₄ are preferably used from the viewpoint of oxidation stability.
The electrolyte salt concentration in the electrolytic solution is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 3.0 mol / l.

  The nonaqueous electrolyte may be a liquid nonaqueous electrolyte or a polymer electrolyte such as a solid electrolyte or a gel electrolyte. In the former case, the non-aqueous electrolyte battery is configured as a so-called lithium ion secondary battery, and in the latter case, the non-aqueous electrolyte battery is configured as a polymer electrolyte battery such as a polymer solid electrolyte battery or a polymer gel electrolyte battery. The

  Dimethyl carbonate, diethyl carbonate, 1,1 mono or 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, γ-ptyrolactone, 1,3-dioxolane, 4-methyl-1,3 -Dioxolane, anisole, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, chloronitrile, propionitrile, trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene , Aprotic such as benzoyl chloride, benzoyl bromide, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, dimethyl sulfite Machine solvent can be used.

When the non-aqueous electrolyte is a polymer electrolyte such as a polymer solid electrolyte or a polymer gel electrolyte, it contains a matrix polymer gelled with a plasticizer (non-aqueous electrolyte). Is an ether-based resin such as polyethylene oxide or its cross-linked product, a fluorine-based resin such as polymethacrylate-based, polyacrylate-based, polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer, or a mixture thereof. Can be used.
Among these, from the viewpoint of oxidation-reduction stability, it is desirable to use a fluorine-based resin such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer.

As the electrolyte salt and non-aqueous solvent constituting the plasticizer contained in these polymer solid electrolyte and polymer gel electrolyte, any of those described above can be used. In the case of a polymer gel electrolyte, the electrolyte salt concentration in the non-aqueous electrolyte solution that is a plasticizer is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 2.0 mol / l.
The method for producing such a polymer electrolyte is not particularly limited. For example, a method of mixing a polymer that forms a matrix, a lithium salt, and a solvent, and heating and melting the polymer, a polymer, a lithium salt, and a suitable organic solvent After dissolving the solvent, the method of evaporating the organic solvent, and the polymerizable monomer, lithium salt, and solvent that are the raw materials for the polymer electrolyte are mixed, and the mixture is polymerized by irradiation with ultraviolet rays, electron beams, or molecular beams. Examples thereof include a method for producing a molecular electrolyte.
Moreover, it is preferable that the mixing ratio of the solvent in the solid electrolyte is 10 to 90% by mass because the electrical conductivity is high and the mechanical strength is high and the film is easily formed, and more preferably 30 to 80% by mass. .

[Lithium ion secondary battery]
In general, a lithium ion secondary battery includes a negative electrode, a positive electrode, and a nonaqueous electrolyte as main battery components, and the positive electrode and the negative electrode are each made of a lithium ion carrier, and lithium ions are input and output in the charge / discharge process between layers. Then, a battery mechanism in which lithium ions are doped into the negative electrode during charging and dedope from the negative electrode during discharging is established.
The lithium ion secondary battery of the present invention is not particularly limited except for the negative electrode material, and other battery components conform to the elements of a general lithium ion secondary battery.

  The separator used in the lithium ion secondary battery of the present invention is not particularly limited, and examples thereof include woven cloth, non-woven cloth, and a synthetic resin microporous film. In particular, a synthetic resin microporous membrane is preferably used. Among these, a polyolefin microporous membrane is preferable in terms of thickness, membrane strength, and membrane resistance. Specifically, it is a microporous film made of polyethylene and polypropylene, or a microporous film in which these are combined.

In the lithium ion secondary battery of the present invention, a gel electrolyte can also be used. The gel electrolyte secondary battery is configured by laminating a negative electrode, a positive electrode, and a gel electrolyte in the order of, for example, a negative electrode, a gel electrolyte, and a positive electrode, and housing the battery in a battery exterior material. Further, a gel electrolyte may be disposed outside the negative electrode and the positive electrode.

The structure of the lithium ion secondary battery according to the present invention is arbitrary, and the shape and form thereof are not particularly limited, and can be arbitrarily selected from a cylindrical shape, a square shape, a coin shape, a button shape, and the like. it can.
In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to include a means for detecting an increase in the internal pressure of the battery and shutting off the current when there is an abnormality such as overcharging. A structure encapsulated in an aluminum laminate film or the like can also be used.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited to these examples. Further, in the following examples and comparative examples, carbon powder was evaluated by producing a button type battery for evaluation having a structure as shown in FIG. The actual battery can be manufactured according to a known method based on the concept of the present invention.

The physical properties of the carbon powder particles were measured as follows.
[Average particle size]
The average particle diameter D50 was a particle diameter at which the cumulative frequency of particle size distribution was 50% by volume using a laser diffraction particle size distribution analyzer (manufactured by Seishin Enterprise Co., Ltd., LMS-30).
[Lattice spacing]
As described above, the lattice spacing d ₀₀₂ is X-rays using CuKα rays as X-rays and high-purity silicon as a standard material in an X-ray diffractometer (manufactured by Rigaku Corporation, “Rotorflex” RU-300). Obtained by the diffraction method.
[R value by Raman spectroscopy]
The R value is analyzed using a laser Raman spectrometer (NR-1800, manufactured by JASCO Corporation), the excitation light is 514.5 nm argon ion laser, the irradiation area is 50 μmφ, and appears near 1360 cm ^{−1 of} the D band. The ratio is ID / IG, where ID is the peak intensity and IG is the peak intensity appearing near 1580 cm ^{−1 of} the G band.
[Specific surface area]
The specific surface area is a BET specific surface area by nitrogen gas adsorption measured using “Monosorb” MS20 (manufactured by Yuasa Ionics).

[DBP absorption]
According to JIS K6217-4: 2001, method for measuring DBP absorption amount-B method (sparing method). That is, 1 g of a sample is placed on a smooth glass plate (300 mm × 300 mm), and if a powder is granular, it is crushed using a predetermined spatula. Furthermore, DBP is dropped little by little using a burette, mixed with the sample, water is added while kneading with a spatula, and the amount of DBP consumed when the mixture becomes uniform is determined. This operation should be completed in 10-15 minutes.

[Tap density]
Predetermined when a sample is placed in a metal cup and tapped 20 times at an amplitude of 3 cm and a tap speed of 1 / sec using an automatic tap device (type PT-D, manufactured by Hosokawa MicroMeditec Laboratory) The mass (g) of the sample occupying the volume (1 cm ³ ) is measured, and the tap density is calculated.
[Press compressibility and density ratio]
A metal cylinder (diameter 10 mm) is inserted into a phenol resin cylinder (height 50 mm, outer diameter 30 mm, inner diameter 10 mm), and a predetermined amount of sample is placed on the end of the cylinder. Next, another metal cylinder (diameter 10 mm) is inserted into the cylinder from another direction, and pressure is gradually applied to the sample with a hand press to compress it to 1 MPa in 5 minutes. At this time, the distance (the distance before and after compression) where the upper cylinder sinks is measured. The density at the time of compression is determined from the distance, the amount of sample, and the volume of the phenol resin tube, and the density ratio of the sample is determined from this and the tap density by the formula (1).

Example 1
[Production of carbon powder]
95 parts by mass of natural graphite (manufactured by SEC, SNO-10, average particle diameter 10 μm, density ratio 8.01), and spherulite graphite powder (manufactured by JFE Chemical, average particle diameter 3 μm, density ratio 1.7) 5 mass The part was subjected to mechanochemical treatment using a mechanochemical treatment apparatus (“Hybridization System” manufactured by Nara Machinery Co., Ltd.) under the conditions of a peripheral speed of the rotating rotor of 40 m / sec and a treatment time of 5 minutes or less. A mixture in which spherulite graphite powder and natural graphite were well dispersed was obtained. Next, the mechanochemically treated product is put in a pressure vessel, heated to 500 ° C. in an inert gas atmosphere, benzene is circulated in a gas phase, CVD treatment is performed for 30 minutes, and spherulite graphite powder adheres to natural graphite. As a result, a composite carbon powder was obtained. Table 1 shows the DBP absorption and press compressibility (density ratio) of the carbon powder.

[Preparation of negative electrode mixture paste]
The carbon powder is put into a planetary mixer and stirred in a dry state, and then 1% by mass of sodium carboxymethylcellulose and carboxy-modified styrene butadiene rubber latex emulsion (manufactured by JSR) 1 so as to be each mass% in solid content. Mass% and water were added and mixed, followed by stirring to prepare a water-based negative electrode mixture paste.

[Production of working electrode]
The negative electrode mixture paste was applied on the copper foil so as to have a uniform thickness, and further dried at 90 ° C. in a vacuum. Next, the negative electrode mixture layer was pressurized by a roller press and punched into a circular shape having a diameter of 15.5 mm to produce a working electrode having a negative electrode mixture layer in close contact with the current collector.

[Production of counter electrode]
The lithium metal foil was pressed against a nickel net and punched into a circular shape with a diameter of 15.5 mm to produce a current collector made of nickel net and a counter electrode made of lithium metal foil in close contact with the current collector.

[Electrolyte and separator]
LiPF ₆ was dissolved at a concentration of 1 mol / dm ^{3 in a} mixed solvent obtained by mixing 33 vol% ethylene carbonate and 67 vol% methyl ethyl carbonate to prepare a non-aqueous electrolyte. The obtained non-aqueous electrolyte solution was impregnated in a polypropylene porous body to produce a separator impregnated with the electrolyte solution.

[Production of evaluation battery]
A button-type evaluation battery shown in FIG. 1 was produced as an evaluation battery.
The exterior cup 1 and the exterior can 3 form a sealed structure that is caulked through an insulating gasket 6 at the peripheral edge thereof, and in order from the inner surface of the exterior can 3, the current collector 7 a made of nickel net and the lithium foil In this battery structure, a disk-shaped counter electrode 4, a separator 5 impregnated with an electrolyte solution, a disk-shaped working electrode 2 made of a negative electrode mixture, and a current collector 7 b made of copper foil are laminated.

In the evaluation battery, the separator 5 impregnated with the electrolytic solution was sandwiched between the working electrode 2 in close contact with the current collector 7b and the counter electrode 4 in close contact with the current collector 7a, and then the working electrode 2 was attached to the exterior cup 1. Inside, the counter electrode 4 was accommodated in the exterior can 3, the exterior cup 1 and the exterior can 3 were combined, and the peripheral edge of the exterior cup 1 and the exterior can 3 was caulked and sealed through an insulating gasket 6. .
The evaluation battery is a battery composed of a working electrode 2 containing carbon powder that can be used as a negative electrode active material and a counter electrode 4 made of a lithium metal foil.

The evaluation battery was subjected to the following charge / discharge test at 25 ° C., and the discharge capacity, initial charge / discharge efficiency, rapid charge efficiency, and cycle characteristics were measured. Table 1 shows the discharge capacity (mAh / g), initial charge / discharge efficiency (%), rapid charge efficiency (%), rapid discharge efficiency (%), and cycle characteristics (%) per gram of carbon powder. The electrode density (g / cm ³ ) is also shown in Table 1.

[Discharge capacity and initial charge / discharge efficiency]
Constant current charging is performed until the circuit voltage reaches 0 mV at a current value of 0.9 mA, switching to constant voltage charging is performed when the circuit voltage reaches 0 mV, and charging is continued until the current value reaches 20 μA, and then 120 min. I paused for a while.
Next, constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 1.5V. At this time, the charge capacity and the discharge capacity were obtained from the energization amount in the first cycle, and the initial charge / discharge efficiency was calculated from the following equation (2).
Initial charge / discharge efficiency (%) = (discharge capacity / charge capacity) × 100 (2)
In this test, the process of doping lithium ions into the carbon powder was charged, and the process of dedoping from the carbon powder was discharge.

[Quick charging efficiency]
Following the above, high-speed charging was performed in the second cycle. Constant current charging was performed until the circuit voltage reached 0 mV, with the current value being 5 times 4.5 mA, the charging capacity was obtained, and the rapid charging efficiency was calculated from the following equation (3).
Rapid charging efficiency (%) = (Constant current charging capacity in the second cycle /
Discharge capacity in the first cycle) × 100 (3)

[Rapid discharge efficiency]
Following the above, high-speed discharge was performed in the third cycle. The current bond was set to 15 times 13.5 mA, constant current discharge was performed until the circuit voltage reached 2.5 V, the discharge capacity was obtained, and the rapid discharge efficiency was calculated from the following equation (4).
Rapid discharge efficiency (%) = (discharge capacity in the third cycle /
Discharge capacity in the first cycle) × 100 (4)

[Cycle characteristics]
Using a different evaluation battery, constant current charging of 4.0 mA is performed until the circuit voltage reaches 0 mV, then switching to constant voltage charging is performed when the circuit voltage reaches 0 mV, and charging is performed until the current value reaches 20 μA. After continuing, it paused for 120 minutes. Next, constant current discharge was performed until the circuit voltage reached 1.5 V at a current value of 4.0 mA, and the discharge capacity was obtained from the energization amount during this period. This charge / discharge was repeated 20 times, and the cycle characteristics were calculated from the obtained discharge capacity according to the following equation (5).
Cycle characteristics (%) = (discharge capacity in the 20th cycle /
Discharge capacity in the first cycle) × 100 (5)

[Electrode density]
The density of the negative electrode mixture was determined from the area, thickness, and mass of the working electrode, and the thickness and mass of the current collector, and this was used as the electrode density.

(Example 2)
Natural graphite (SEC Co., SNO-10, average particle size 10 [mu] m, density ratio 8.01) 95 parts by mass, and thermal carbon black powder (average particle diameter 0.3 [mu] m, DBP absorption 30 cm ^3/100 g, a density ratio of 2 ) 5 parts by mass were mixed and subjected to mechanochemical treatment in the same manner as in Example 1. Next, the mechanochemically treated product is put into a planetary mixer, a solution consisting of 3 parts by mass of carboxymethyl cellulose and 100 parts by mass of distilled water is added, kneaded at 30 rpm for 1 hr, and kneaded with carbon black attached to natural graphite. I got a thing. Then, while continuing kneading | mixing of this kneaded material at 20 rpm, it heated up at 60 degreeC, the water | moisture content was evaporated, and also this kneaded material was dried under vacuum. The kneaded product was calcined at 700 ° C. in nitrogen gas to decompose carboxymethyl cellulose to obtain carbon powder. Table 1 shows the DBP absorption and density ratio of the obtained carbon powder.
From this carbon powder, a negative electrode mixture paste, a negative electrode, and an evaluation battery were produced in the same manner and under the same conditions as in Example 1, and the charge / discharge characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)
Natural graphite (SEC Co., SNO-10, average particle size 10 [mu] m, density ratio 8.01) 95 parts by mass, and thermal carbon black powder (average particle diameter 0.3 [mu] m, DBP absorption 38cm ^3/100 g, a density ratio of 2 ) 5 parts by mass were mixed and subjected to mechanochemical treatment in the same manner as in Example 1. Next, the mechanochemically treated product is put into a planetary mixer, 3 parts by mass of a liquid phenol resin and 100 parts by mass of ethanol are added, kneaded at 30 rpm for 1 hr, and a kneaded product in which carbon black adheres to natural graphite. Got. Then, while continuing kneading | mixing of this kneaded material at 20 rpm, it heated up at 60 degreeC, ethanol was evaporated, and also this kneaded material was dried under vacuum. The kneaded product was baked in nitrogen gas at 700 ° C. to decompose the phenol resin to obtain a carbon powder. Table 1 shows the DBP absorption and density ratio of the obtained carbon powder.
From this carbon powder, a negative electrode mixture paste, a negative electrode, and an evaluation battery were produced in the same manner and under the same conditions as in Example 1, and the charge / discharge characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
The amount of DBP absorption of natural graphite of Example 1 (manufactured by SEC, SNO-10, average particle diameter 10 μm, density ratio 8.01) itself was measured, and the results are shown in Table 1.
From the natural graphite, a negative electrode mixture paste, a negative electrode, and an evaluation battery were produced in the same manner and under the same conditions as in Example 1, and the charge / discharge characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)
The DBP absorption and density ratio of natural graphite (manufactured by SEC, SNO-5, average particle size 5 μm, density ratio 8.74) itself were measured, and the results are shown in Table 1.
From the natural graphite, a negative electrode mixture paste, a negative electrode, and an evaluation battery were produced in the same manner and under the same conditions as in Example 1, and the charge / discharge characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 3)
95 parts by mass of natural graphite (manufactured by SEC, SNO-5, average particle size 5 μm, density ratio 8.74) and spherulite graphite (manufactured by JFE Chemical Co., Ltd., average particle size 13 μm, density ratio 1.6, specific surface area 0) .9 m ² / g) 5 parts by mass were mixed. A negative electrode mixture, a paste, a negative electrode, and an evaluation battery were prepared from the mixture in the same manner and conditions as in Example 1 except that no mechanochemical treatment was performed, and charge / discharge and characteristics were evaluated in the same manner as in Example 1. . The DBP absorption amount and density ratio of the obtained mixture were measured, and the results are shown in Table 1.

(Comparative Example 4)
95 parts by mass of natural graphite (manufactured by SEC, SNO-10, average particle size 10 μm, density ratio 8.01) and spherulite graphite powder (manufactured by JFE Chemical Co., Ltd., average particle size 13 μm, density ratio 1.6, specific surface area) 0.9 m ² / g) Using 5 parts by mass, the mechanochemical treatment was performed under the same method and conditions as in Example 1.
With respect to the mechanochemically treated product, a negative electrode mixture, a paste, a negative electrode and an evaluation battery were prepared in the same manner and conditions as in Example 1 except that the CVD treatment was not performed. Evaluated. The DBP absorption amount and density ratio of the mechanochemically processed product were measured, and the results are shown in Table 1.

  In any of the secondary batteries using the carbon powders of Comparative Examples 1 to 4 as the negative electrode material, rapid charging efficiency and deterioration of cycle characteristics are recognized at a high electrode density. On the other hand, the secondary batteries using the carbon powders of Examples 1 to 3 as the negative electrode material have improved rapid charge efficiency, rapid discharge efficiency, and cycle characteristics at a high electrode density.

It is sectional drawing of the evaluation battery for evaluating the charging / discharging characteristic of carbon powder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exterior cup 2 Working electrode 3 Exterior can 4 Counter electrode 5 Separator 6 Insulating gasket 7a, 7b Current collector

Claims (7)

Absorption of dibutyl phthalate 10 cm ^3/100 g or ^more, 30 cm 3/100 g or less and a carbon powder density ratio represented by the following formula (1) is characterized in that it is a 4 to 6.5.
Density ratio = (Density when pressure is 1 MPa) / (Tap density) (1) After mechanochemical treatment of the graphite material and a carbon material having a density ratio and an average particle diameter smaller than the graphite material represented by the following formula (1), the carbon material is further applied to the graphite material using a binder. A method for producing a carbon powder, characterized by adhering.
Density ratio = (Density when pressure is 1 MPa) / (Tap density) (1)   The method for producing carbon powder according to claim 2, wherein the density ratio of the graphite material is 3 to 9, and the average particle diameter is 50 µm or less. After mechanochemical treatment of 100 parts by mass of the graphite material and 1 to 50 parts by mass of the carbon material having a density ratio and an average particle diameter represented by the following formula (1) smaller than the graphite material, using a binder, absorption of dibutyl phthalate for causing the graphite material is deposited the carbon material is 10 cm ^3/100 g or ^more, or less 30 cm 3/100 g, and the density ratio shown by the following formula (1) is 4-6. The method for producing carbon powder according to claim 2 or 3, wherein the carbon powder is 5.
Density ratio = (Density when pressure is 1 MPa) / (Tap density) (1)   A negative electrode material for a lithium ion secondary battery, comprising the carbon powder according to claim 1.   A negative electrode for a lithium ion secondary battery comprising the negative electrode material for a lithium ion secondary battery according to claim 5.   A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 6.

Images