JP4707570B2 - Method for producing fine graphite particles - Google Patents

Description

  The present invention relates to a method for producing fine graphite particles.

  In recent years, with the miniaturization or high performance of electronic devices, there is an increasing demand for higher energy density of batteries. In particular, lithium ion secondary batteries are attracting attention because they are capable of higher voltages than other secondary batteries and can increase energy density. A lithium ion secondary battery has a negative electrode, a positive electrode, and a non-aqueous electrolyte as main components. Lithium ions generated from the non-aqueous electrolyte move between the negative electrode and the positive electrode during the discharge process and the charge process to form a secondary battery. Usually, a carbon material is used for the negative electrode material of the lithium ion secondary battery. As such a carbon material, graphite (Patent Document 1) that is excellent in charge / discharge characteristics and exhibits high discharge capacity and potential flatness is particularly promising.

  The graphite (graphite particles) used as the negative electrode material includes bulk graphite particles such as natural graphite and artificial graphite, as well as bulk mesophase graphite obtained by heat treatment of mesophase pitch and mesophase spherules made from tar and pitch. Particles, mesophase small spherical graphite particles, mesophase graphite particles and mesophase graphite fibers obtained by heat-treating particulate or fibrous mesophase pitch after oxidation infusibilization, natural graphite and artificial graphite are coated with tar, pitch, etc. And composite graphite particles obtained by heat treatment.

  Among them, as composite graphite particles, natural graphite powder is granulated and formed into a substantially spherical shape with a binder, impregnated with a binder pitch, fired (Patent Document 2), discharge capacity, rapid charge / discharge characteristics and cycle. For the purpose of improving characteristics, graphite particles are granulated into a spherical shape, and then a carbon coating layer is formed on the surface of the graphite particles by chemical vapor deposition (Patent Document 3), graphitizable aggregate, binder, graphitization Examples thereof include those obtained by mixing, firing and pulverizing a catalyst (Patent Document 4).

  Since the conventional lithium ion secondary battery negative electrode material contains graphite having high crystallinity, the discharge capacity of the lithium ion secondary battery can be increased, and the graphite is aligned in one direction within the particles. Therefore, it has good rapid charge / discharge characteristics and cycle characteristics under specific use conditions, but there are also the following problems.

  For example, the granulated negative electrode material described in Patent Document 2 is obtained by impregnating a granulated natural graphite with a binder pitch and baking it, and the sintered product of the pitch is hard. It is difficult to increase the density. If the pitch impregnation amount is reduced so that the density of the negative electrode can be increased, the natural graphite has a weak binding force and the granulated structure cannot be maintained.

  The granulated negative electrode material described in Patent Document 3 is a material in which graphite is finely pulverized and bent, and then a crystalline carbon coating layer is formed by chemical vapor deposition, and the coating layer is thin and soft. The density of the negative electrode can be increased. However, as the density is increased, the laminated structure in which graphite is bent is changed to a structure arranged in one direction, and there is a problem that rapid charge / discharge characteristics and cycle characteristics are deteriorated.

  The composite graphite particles described in Patent Document 4 are relatively soft because the entire particles are graphitic, and the density of the negative electrode can be increased. However, as with the granulated negative electrode material described in Patent Document 3, the composite particles become crushed as the density increases, and the flat graphite in the composite particles is aligned in one direction, resulting in rapid charge. Discharge characteristics and cycle characteristics deteriorate.

Thus, although the conventional granulated negative electrode material exhibits relatively good battery characteristics when the density of the negative electrode is low, the density is particularly 1.7 g / cm ³ when the density of the negative electrode is increased. If it exceeds 1, graphite in the particles will be oriented, the diffusibility of lithium ions and the permeability of the electrolyte will decrease, and the rapid charge / discharge characteristics and cycle characteristics will drop sharply. In recent years, from the viewpoint of increasing the energy density of a lithium ion secondary battery, it has been desired to set the negative electrode density as high as possible. However, conventional negative electrode materials have a problem that the negative electrode density capable of maintaining the characteristics is low.

  As a method for obtaining excellent rapid charge / discharge characteristics and cycle characteristics, it is effective to reduce the particle diameter of the negative electrode material. As the particle size is smaller, the number of contact points between the negative electrode materials increases, the utilization factor of the negative electrode materials approaches 100%, and the reaction (lithium ion occlusion and release) area between the electrolyte and the negative electrode material increases, resulting in rapid charge and discharge. Improved characteristics. In addition, even when the negative electrode material expands and contracts with repeated charge and discharge, the contact between the negative electrode materials is easily maintained. However, in general, the negative electrode density is less likely to increase as the particle size is reduced. Accordingly, a soft negative electrode material having a small particle size is required.

  As a non-granulated negative electrode material, a graphitized material of mesophase microspheres (also referred to as mesocarbon microbeads) is known as a graphite material having a random crystal structure in the particles. Mesophase spherules are spherical polymers with optical anisotropy produced in heavy oils and pitches when coal or petroleum heavy oils and pitches are heat-treated. By keeping the degree low, the particle diameter can be adjusted small. However, reducing the particle size results in a decrease in productivity, resulting in an industrially high cost problem and low crystallinity after graphitization. When pulverizing mesophase spherules with a large particle size to reduce the particle size, the crushing surface generated by pulverization causes a side reaction of the electrolyte (including the solvent) when used as a negative electrode material, and the initial charge is reduced. Problems such as a reduction in discharge efficiency may occur. In addition, in both cases where the degree of polymerization is suppressed and the particle size is reduced or pulverized, the particles are hard and difficult to compress to a high negative electrode density.

Japanese Examined Patent Publication No. 62-23433 JP 2004-31038 A JP 2002-367611 A Japanese Patent Laid-Open No. 10-188959

  The present invention has been made in view of the above situation, and an object of the present invention is to provide a method for producing a new fine graphite particle having a small particle diameter, particularly for a lithium ion secondary battery at a high negative electrode density. An object of the present invention is to provide a method for producing fine graphite particles suitable as a negative electrode material.

The present invention
A metal and / or metal compound having at least one of a property of reacting with carbon and a property of dissolving carbon is attached to a carbon material that forms an optically isotropic crystal structure at least partially after graphitization. An adhering process,
A carbon material in which the metal and / or the metal compound is attached, after the metal evaporation and / or the metal compound is decomposed, and the metal element contained in the metal compound is heated at a temperature higher than the temperature at which evaporation, the While graphitizing the carbon material, a graphitization step of forming a protuberance on the surface of the graphitic material,
A protuberance falling to obtain a fine graphite particles by dropping from graphitic material該隆Okoshibutsu to impart mechanical energy mechanochemical treatment graphitic material having該隆Okoshibutsu,
A method for producing fine graphite particles, comprising:
In the production method of the present invention, it is preferable that, in the protruding product dropping step, the protruding product is dropped from the graphite material and the crushing surface is worn to obtain fine graphite particles.

  The present invention also provides
  A metal and / or metal compound having at least one of a property of reacting with carbon and a property of dissolving carbon is attached to a carbon material that forms an optically isotropic crystal structure at least partially after graphitization. An adhering process,
  The carbon material to which the metal and / or the metal compound is attached is heated at a temperature equal to or higher than the temperature at which the metal element contained in the metal compound evaporates after the metal evaporates and / or the metal compound decomposes, While graphitizing the carbon material, a graphitization step of forming a protuberance on the surface of the graphitic material,
  Protruding material dropping step of applying mechanical energy to the graphite material having the protruding material to drop the protruding material from the graphite material to obtain fine graphite particles;
A method for producing fine graphite particles, characterized by comprising:
  In the Raman spectrum of the fine graphite particles using an argon laser beam having a wavelength of 514.5 nm, 1570 to 1630 cm. ^-1 The intensity of the peak existing in the region _G 1350-1370cm ^-1 The intensity of the peak existing in the region _P I when _P / I _G The method is preferably a method for producing fine graphite particles, wherein the ratio is less than 0.2.

  The method for producing micrographitic particles of the present invention further comprises separating the micrographitic particles from the mixture of the micrographitic particles and the graphite material obtained in the protruding product dropping step to obtain the micrographitic particles. It is preferable to have a separation step to obtain.

  In the method for producing fine graphite particles of the present invention, the metal and the metal compound are preferably powders.

  In the method for producing fine graphite particles of the present invention, the temperature at which the metal is evaporated and / or the metal element is evaporated is preferably 1500 to 3300 ° C.

  In the method for producing fine graphite particles of the present invention, the fine graphite particles are preferably a material for a negative electrode of a lithium ion secondary battery.

  The lithium ion secondary battery using the fine graphite particles of the present invention as a negative electrode material has excellent discharge capacity, initial charge / discharge efficiency, and rapid charge / discharge characteristics (rapid charge rate and rapid discharge rate) even at a high negative electrode density. And has cycle characteristics. For this reason, the lithium ion secondary battery satisfies the recent demand for higher energy density of the battery, and is effective in reducing the size and performance of the mounted device. Moreover, the micrographitic particles of the present invention can be produced by a simple method and the production cost is low.

Hereinafter, the present invention will be described more specifically.
(Micrographite particles)
The fine graphite particles obtained by the production method of the present invention (hereinafter also simply referred to as the fine graphite particles of the present invention) are highly crystalline and exhibit optical anisotropy. Since the crystallinity is high, it is soft and the negative electrode density can be increased. As an index of crystallinity, it is preferable that an average lattice spacing d ₀₀₂ of (002) plane in X-ray wide angle diffraction is 0.3365 nm or less, particularly 0.3360 nm or less. When d ₀₀₂ exceeds 0.3360 nm, a high discharge capacity may not be obtained, and in order to increase the negative electrode density to exceed 1.7 g / cm ³ , a high pressing pressure is required. Problems such as breakage of a copper foil as a current collector may occur. More preferably, it is 0.3358 nm or less.
Here, the average lattice spacing d ₀₀₂ of the (002) plane in the X-ray wide angle diffraction is the diffraction of the (002) plane of the graphite particles using CuKα ray as the X-ray and using high-purity silicon as a standard material. A peak is measured and calculated from the position of the peak. The calculation method follows the Japan Science and Technology Act (measurement method defined by the 17th Committee of the Japan Society for the Promotion of Science). Specifically, “Carbon Fiber” [Sugirou Otani, pages 733-742 (March 1986) ), Modern Editorial Company].

The shape of the fine graphite particles of the present invention is preferably spherical or pseudo-spherical as shown in FIG. The pseudo-spherical shape refers to an ellipsoidal shape, a polyhedral shape, a lump shape, and the like. The standard for the pseudo sphere is when the average aspect ratio is 1.0 to 1.5. When the aspect ratio is within this range, the rapid charge / discharge characteristics and cycle characteristics of a lithium ion secondary battery using the aspect ratio are improved. This is because when the negative electrode is formed, the fine graphite particles are not arranged in one direction and the electrolyte easily penetrates into the inside. Here, the average aspect ratio represents the ratio between the maximum major axis length of the graphite particles and the length of the axis perpendicular thereto, and a plurality (50 or more) of the graphite particles are observed by an appearance observation with a scanning electron microscope. It is an average value of the ratios measured for the graphite particles.
The fine graphite particles of the present invention may have pores or pores on the surface or inside thereof.

  The average particle size of the fine graphite particles of the present invention is preferably 1 to 20 μm. When the thickness is less than 1 μm, in the lithium ion secondary battery using the same, side reactions with the electrolyte increase, and the initial charge / discharge efficiency may decrease. If it exceeds 20 μm, rapid charge / discharge characteristics and cycle characteristics will not be improved. A particularly preferable average particle diameter is 3 to 10 μm. The average particle diameter is a particle diameter at which the cumulative frequency of particle size distribution measured by a laser diffraction particle size distribution meter is 50% by volume.

It is preferable that the fine graphite particles of the present invention have a small proportion of crushing surfaces generated in the protruding product dropping step. The proportion of the crushed surface in the outer surface area of the fine graphite particles is 30% or less, preferably 15% or less. Here, the ratio of the crushing surface is the ratio of the length of the outer periphery of the fractured portion caused by crushing the particle cross section with respect to the outer peripheral length of the particle cross section.
In general, the edge surface of the graphite crystal is exposed on the crushed surface of the graphite particles. The edge surface exposure rate is preferably 30% or less, particularly preferably 15% or less. Here, the exposure rate is a ratio of the outer peripheral lengths of the edge surface and the basal surface to the outer peripheral length of the particle cross section. The exposed state of the edge surface and the basal surface can be confirmed by observing the cross section of the particle with a scanning electron microscope or a transmission electron microscope. The edge surface refers to the end of the hexagonal carbon surface of carbon forming graphite, and the basal surface refers to the surface orthogonal to the edge surface.

As an indicator of exposure of the edge surface, it is also possible to use a I _{P /} I _G ratio in the Raman spectrum. It is preferable that the ratio is less than 0.2, particularly 0.15 or less because the exposure is small. Here, the I _P / I _G ratio is the intensity of a peak existing in the region of 1570 to 1630 cm ⁻¹ in a Raman spectrum using an argon laser beam having a wavelength of 514.5 nm, I _G , 1350 to 1370 cm ^−1. I _P / _IG ratio when the intensity of the peak existing in the region is I _P. When the exposure amount of the edge surface of the graphite crystal increases, the _IP / _IG ratio increases. exposure of the basal surface is increased when the _I P / _{I G} ratio decreases.

(Method for producing fine graphite particles)
A method for producing the fine graphite particles of the present invention will be described below.
Adhesion step: a metal having at least one of a property of reacting with carbon and a property of dissolving carbon in a carbon material that forms an optically isotropic crystal structure at least partially after graphitization and / or It is a step of attaching a metal compound.
Graphitization step: After the attached metal evaporates or the metal compound decomposes, the carbon material is heated to a temperature equal to or higher than the temperature at which the contained metal element evaporates, and the metal evaporates or the metal compound. This is a step of forming spherical or pseudo-spherical ridges on the surface of the graphitized material (graphitic material) by removing metal elements by decomposition / evaporation.
-Protrusion fall-off process: It is a process which gives mechanical energy to the graphitized material (graphite material) which has a protuberance, and makes this protuberance fall off from a graphitized material (graphitic material) base material.
-Separation process: A process of separating and removing the ridges (micrographitic particles) that have fallen off from the graphitized base material.

Next, each material and each process will be described in detail.
(Carbon material)
The carbon material (hereinafter, also simply referred to as carbon material) used in the production of the micrographitic particles of the present invention is a carbon material that forms an optically isotropic crystal structure at least partially after graphitization. A carbon material that forms an optically isotropic crystal structure at least partially after graphitization refers to an optically isotropic crystal structure (optical isotropic) when a cross section of the graphitized material is observed with a polarizing microscope. A carbon material having a relatively low crystallinity. As will be described later, if there is no portion that forms an optically isotropic crystal structure, the bulge does not occur.
The carbon material can be used in any shape such as a plate shape, a granular shape, a fiber shape, and a lump shape, but a granular shape is particularly preferable. What is the average particle size? In the case of a granular shape, it is 5 to 100 μm, preferably 10 to 50 μm. If the thickness is less than 5 μm, it is difficult to separate and collect the raised ridges, and if it exceeds 100 μm, it is difficult to drop the ridges.

  Even if a carbon material exhibiting optical isotropy is used alone as the carbon material, the surface of the carbon material having an optically anisotropic crystal structure (optically anisotropic phase) is optically isotropic. You may use what attached the carbon material which has a crystal structure (optically isotropic phase). The latter optically isotropic carbon material is preferably attached in the form of a thin film, and the film thickness is 3 μm or less, preferably 1 μm or less, more preferably 0.5 μm or less. If the film thickness is too large, the average particle diameter of the finally obtained fine graphite particles tends to be excessive. Moreover, it is preferable that the lower limit of this film thickness is 0.01 micrometer. If it is less than 0.01 μm, the average particle diameter of the finally obtained fine graphite particles tends to be too small.

Specific examples of the carbon material exhibiting optical isotropy are resins such as phenol resin and furfuryl alcohol resin, and optical isotropic pitches such as oxygen-crosslinked petroleum pitch. A coke or natural graphite plate or particle coated with the resin or the optically isotropic pitch is preferably used. Among these, mesophase microspheres that originally have an optically isotropic phase on the outer surface and are internally composed of an optically anisotropic phase are optimal without any coating treatment. When mesophase spherules are used, the formation of ridges (micrographitic particles), which will be described later, and graphitization of mesophase spherules can be realized at the same time. If a thing is dropped, a mixture of both can be easily obtained.
The mesophase spherules include petroleum-based or coal-based tar pitches containing 0.01 to 2% by mass, preferably 0.3 to 0.9% by mass of free carbon, at 350 to 1000 ° C., preferably 400 to It can be obtained by heat treatment at 600 ° C., more preferably at 400 to 450 ° C. Examples of the pitch include coal tar, tar light oil, tar middle oil, tar heavy oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, oxygen-crosslinked petroleum pitch, heavy oil and the like, and coal tar pitch is preferable.

(Metal material)
The metal or metal compound attached to the carbon material is a metal or metal compound (hereinafter also referred to as a metal material) having a property of reacting with carbon and / or a property of dissolving carbon. That is, it is a metal material that is stable until the carbon material is graphitized, and that the entire amount is evaporated or decomposed in the graphitization step and does not remain in the graphitized material of the carbon material. The shape of the metal material can be any shape such as powder, plate, granule, fiber, lump, and sphere. In the case of sphere and granule, Since the contact area with a base material becomes small, it is particularly preferable because the raised matter is easily dropped. Moreover, since the area of a crushing surface becomes small, when it uses for the negative electrode material of a lithium ion secondary battery, an irreversible capacity | capacitance becomes small.

Specific examples of the metal material include alkali metals such as K, alkaline earth metals such as Mg and Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Ta, W, Re, and Pt. Transition metals and compounds of these metals. These may be used alone or in combination of two or more. Moreover, you may use as 2 or more types of alloys. Preference is given to transition metals of Fe, Co, Ni, Pt and compounds of the transition metals.
Metal compounds include halides such as chloride, bromide, oxychloride, inorganic acid salts such as sulfate and nitrate, organic acid salts such as acetate and oxalate, oxides, hydroxides, nitrides, Examples thereof include sulfides. Preference is given to chlorides, oxides and hydroxides in terms of stability and cost. Particularly preferred metal compounds are iron oxide, iron chloride, cobalt oxide, nickel oxide and the like.
The metal material is preferably granular or powdery, and the average particle diameter is preferably 5 μm or less, more preferably 0.01 to 5 μm, and even more preferably 0.01 to 1 μm. . When it exceeds 5 μm, the average particle diameter of the fine graphite particles tends to be excessive, and when it is less than 0.01 μm, the average particle diameter of the fine graphite particles tends to be excessive.

(Adhesion process)
The method for attaching the metal material to the carbon material may be any method as long as the metal material can be attached to the carbon material. For example, powder, granular metal material and carbon material are mixed, embedded, and supported in a dry process, metal material solution or dispersion is contacted with carbon material, medium is removed, metal material is carbon material The method of vapor deposition is mentioned. The adhesion force does not need to be particularly strong, and it is sufficient that the metal material is in contact with the carbon material. As described later, the adhesion force may be removed by applying mechanical energy after graphitization.
The attachment form of the metal material is not particularly limited and may be any of a film form, a granular form, an indeterminate form, etc., but the form in which the metal material particles are scattered and attached to the outer surface of the carbon material. preferable. Due to the interspersed points, it is easy to form a raised product in the graphitization process, and the size variation of the raised product is reduced. Here, the outer surface does not include the surface of the voids inside the pores of the carbon material when the carbon material is porous.

  The mixing amount of the metal material, and hence the adhesion amount, is 0.1 to 30% by mass, preferably 0.5 to 15% by mass, and more preferably 1 to 10% by mass with respect to 100% by mass of the carbon material. If it is less than 0.1% by mass, the amount of fine graphite particles produced is small and the production efficiency is low. If it exceeds 30% by mass, the amount of the metal material that evaporates or decomposes in the graphitization process is large, and it may cause operational problems such as metal material being deposited at a low temperature in the graphitization furnace. is there. Note that the adhesion amount of the metal material can be measured by a method such as ICP emission spectroscopic analysis.

Specific examples of the method for dispersing and attaching the metal material to the outer surface of the carbon material will be described below.
In the dry deposition method, a carbon material and a metal material are mixed in powder form. The mixing is preferably performed using various known mixers such as a mechanical type (stirring type), a rotary type, and a wind type. According to such a method, the powdered metal material is dispersed and adhered so as to be scattered on the outer surface of the carbon material while being uniformly dispersed so as not to form an aggregate of the powdered metal material. Can do. Further, the carbon material and the metal material may be pulverized and mixed together.

  In the wet deposition method, first, a carbon material and a metal material are mixed in a dispersion medium. In this case, it is preferable to use a colloidal dispersion in which a metal material is dispersed. The mixing is preferably performed using a stirrer until the carbon material and the metal material are uniformly dispersed. During mixing, it is preferable to apply a pressure reduction operation or ultrasonic treatment to remove bubbles to promote contact between the carbon material and the metal material. After mixing, the dispersion medium is removed, but the method is not limited, and methods such as heating and decompression can be appropriately employed. The dispersion medium is more preferably a dispersion medium that does not dissolve not only the metal material but also the carbon material, and is preferably an aqueous dispersion medium such as water, alcohol, or ketone. Among these, water is particularly preferable because it has less influence on the environment during drying and removal than the organic solvent-based dispersion medium, and is advantageous in terms of safety and cost.

In the vapor deposition method, a metal material is attached to the outer surface of a carbon material by a PVD method or a CVD method. Specifically, PVD methods such as vacuum deposition, sputtering, ion plating, molecular beam epitaxy, atmospheric pressure CVD, reduced pressure CVD, plasma CVD, MO (Magneto-Optic) CVD, optical Although CVD methods, such as CVD method, are mentioned, Sputtering method is preferable. Examples of the sputtering method include a direct current spaccling method, a magnetron sputtering method, a high frequency sputtering method, a reactive spackling method, a bias sputtering method, and an ion beam sputtering method.
In the sputtering method, a metal target is set on the cathode side, and generally a glow discharge is generated between the electrodes in an inert gas atmosphere of about 1 to 10 ⁻² Pa to ionize the inert gas and knock out the target metal. As a typical example, a method of coating the metal on a carbon material placed on the anode side can be given. A metal compound may be used in place of the metal, an alloy may be formed on the outer surface of the carbon material using a plurality of types of metals simultaneously, or a metal and a metal compound may be mixed and used as a target Also good. Furthermore, sputtering may be performed twice or more using two or more types of targets, and a plurality of metals and / or metal compounds may be attached in order. A reactive gas may be used instead of the inert gas.

(Graphitization process)
The mixture of the carbon material and the metal material is graphitized by heating to a temperature equal to or higher than the temperature at which the metal contained in the metal material evaporates or the metal compound decomposes and evaporates. Graphitization is performed by a general method of heating and graphitizing using, for example, a high temperature furnace such as an Acheson furnace. As a result, the metal in the metal material evaporates or the metal compound evaporates and evaporates to substantially remove the entire amount, so that substantially no metal element remains in the generated graphitized material. Simultaneously with the removal of the metal element, spherical or pseudo-spherical ridges are formed in a dispersed state as shown in FIG. 1 almost uniformly on the entire surface of the graphitized material. The metal element does not substantially remain in the graphitized protuberance (micrographitic particles).

  Needless to say, the temperature at which the metal evaporates or the metal compound evaporates varies depending on the metal species, but in many cases, it is generally 1500 to 3300 ° C, preferably 2500 to 3300 ° C, more preferably 2800 to 3300 ° C. It is. Below 1500 ° C., the carbon material is not graphitized, the metal material remains, and the reaction between the metal material and the optically isotropic carbon does not occur or dissolve, so that the formation of ridges is insufficient. Even if the bumps are formed, the discharge capacity of the lithium ion secondary battery is insufficient when the carbon material is used as the negative electrode material. If it exceeds 3300 ° C., part of the formed ridges (micrographitic particles) may sublime from the base material of the graphitized material, which is not preferable because the yield of the micrographitic material is lowered. The graphitization is preferably performed in a non-oxidizing atmosphere. Although the time required for graphitization cannot be generally stated, it is about 1 to 20 hours.

Unlike the wavy continuous wrinkles that normally occur during graphitization, the ridges are preferably scattered individually on the surface of the base material of the graphitized material. Raised objects can be present on the fence.
The number of raised objects is not particularly limited, but is preferably in a density range of 2 to 20 per 100 μm ^{2 on the} surface of the base material. It is preferable that the raised objects are scattered in the density range without being unevenly distributed on the surface of the base material. The height of the protuberance is preferably 2 to 15 μm, more preferably 3 to 10 μm.
Since the raised material is integrated with the base material of the graphitized material, it is necessary to apply mechanical energy from the outside to detach the raised material.
In addition, the base material as used in the field of this invention means the graphitized material after the protruding matter formed in the graphitization process of the carbon material to which the metal material adhered fell off as shown in FIG. 2 (a).

The mechanism of ridge formation is not clear, but is presumed as follows.
In the previous stage of graphitization, where the temperature is relatively low, the molten metal material reacts with the carbon of the carbon material exhibiting optical isotropy to produce a metal carbide. Alternatively, the metal material dissolves carbon that exhibits the optical isotropy of the carbon material to generate a solid solution. At this time, the metal material is supplied with carbon from the carbon material, and a bump of the metal carbide is once generated. However, when the graphitization temperature rises to near the boiling point of the metal forming the metal carbide, evaporation of the metal starts from carbon and metal in a chemical equilibrium state with the metal carbide. Thereafter, as the temperature rises, all of the metal eventually evaporates, and the same graphitized raised matter as the base material remains. In graphitization, the temperature is raised to about 3000 ° C. For example, when the metal material is iron, it is estimated that the evaporation of iron starts near 2800 ° C. Therefore, the base material of the graphitized material usually occupies most of the remaining part after graphitization of the carbon material used in the adhesion process. Therefore, the metal or metal compound is preferably dispersed and attached to the outer surface of the carbon material.

Before the graphitization, the metal material is melted and has a spherical shape due to surface tension. Since the metallic material reacts with or dissolves carbon having optical isotropy to form a raised product, the raised product is considered to have a spherical shape.
A feature of the present invention is that a carbon material that exhibits optical isotropy is used as a raw material, but by the action of a metal material, a protuberance exhibiting optical anisotropy is formed after graphitization. The purpose is to obtain fine graphite particles having a small optical anisotropy.

(Protrusion removal process)
Mechanical energy is imparted to the graphitized material having the protuberance, and the protuberance is dropped. The raised bulges are fine graphite particles. Giving mechanical energy means a state in which various stresses such as shearing, compression, collision, vibration, and rolling are applied. For example, shear compression processors (mechanochemical processing machines) such as hybridization systems (manufactured by Nara Machinery Co., Ltd.), mechanomicros (manufactured by Nara Machinery Co., Ltd.), mechanofusion systems (manufactured by Hosokawa Micron), and nobilta (manufactured by Hosokawa Micron) The process to be used is mentioned. It is preferable to adjust the mechanical energy to such a strength that the raised material falls off and the graphitized material as a base material is not crushed. The mechanochemical treatment using the hybridization system, mechanomicros, mechanofusion system, etc. can efficiently remove the raised material, and can suppress the pulverization of the graphitized material as a base material. This is particularly preferable because the crushing surface of the fine graphite particles can be worn and spheroidized. In the case where the graphitized material having the raised material is plate-like, the raised material can be removed by using a brush or a cloth.

(Separation process)
The fallen raised matter is separated from the base material and collected as fine graphite particles as necessary. The separation is performed using a known particle separation apparatus, for example, a dry classifier such as an air classifier or an air classifier, a wet classifier, a sieve, or the like.

(Lithium ion secondary battery)
A lithium ion secondary battery usually has a negative electrode, a positive electrode, and a non-aqueous electrolyte as main battery components. Each of the positive electrode and the negative electrode is composed of a lithium ion carrier, and during charging, lithium ions are occluded in the negative electrode and discharged. It depends on the battery mechanism that is detached from the negative electrode.
When the fine graphite particles of the present invention are used as the negative electrode material, there is no particular limitation, and other battery components conform to the elements of a general lithium ion secondary battery.
Hereinafter, the negative electrode, the positive electrode, the electrolyte, and the like will be described.

(Negative electrode)
The production of a negative electrode for a lithium ion secondary battery is a molding that can sufficiently draw out the battery characteristics of the micrographitic particles of the present invention and has a high moldability and can provide a chemically and electrochemically stable negative electrode. Any method may be used, but the fine graphite particles of the present invention and a binder are mixed in a solvent and / or a dispersion medium (hereinafter also simply referred to as a solvent) to form a paste, and the resulting negative electrode mixture In general, the paste is applied to the current collector, and then the solvent is removed, followed by solidification and / or shaping by a press or the like. That is, first, the fine graphite particles of the present invention are adjusted to a desired particle size by classification or the like, and a composition obtained by mixing with a binder is dispersed in a solvent to prepare a negative electrode mixture in the form of a paste.

  The fine graphite particles of the present invention are subjected to various chemical treatments in the liquid phase, gas phase, and solid phase, heat treatment, physical treatment, oxidation treatment, etc., as long as the characteristics of the fine graphite particles of the present invention are not impaired. May be. The fine graphite particles of the present invention can be used by mixing with a negative electrode active material such as graphitized mesophase spherules. The mass mixing ratio is fine graphite particles: graphitized mesophase spherules = 5 to 70:95 to 30. When the amount is less than 5% by mass, the effect of improving rapid charge / discharge characteristics and cycle characteristics is small. If it exceeds 70% by mass, the advantages derived from the graphitized mesophase spheroids, that is, particularly excellent initial charge / discharge efficiency, excellent stability of the negative electrode mixture paste, and paintability may not be obtained.

  More specifically, a slurry obtained by mixing the fine graphite particles of the present invention and a binder such as carboxymethyl cellulose and styrene-butadiene rubber in a solvent such as water or alcohol, or polytetrafluoroethylene A slurry obtained by mixing a fluorine resin powder such as polyvinylidene fluoride with a solvent such as isopropyl alcohol, N-methylpyrrolidone, dimethylformamide, etc., using a known stirrer, mixer, kneader, kneader, etc. The mixture is stirred and mixed to prepare a negative electrode mixture paste. When the paste is applied to one or both sides of the current collector and dried, a negative electrode in which the negative electrode mixture layer is uniformly and firmly bonded is obtained. The film thickness of the negative electrode mixture layer is 10 to 200 μm, preferably 30 to 100 μm.

  The negative electrode mixture layer can also be produced by dry-mixing the fine graphite particles of the present invention and resin powders such as polyethylene and polyvinyl alcohol and hot pressing in a mold. However, dry mixing requires a large amount of binder to obtain sufficient strength of the negative electrode, and if the binder is excessive, the discharge capacity and rapid charge / discharge efficiency of the lithium ion secondary battery may be reduced. .

After the negative electrode mixture layer is formed, the adhesive strength between the negative electrode mixture layer and the current collector can be further increased by press bonding such as pressurization.
The shape of the current collector used for the negative electrode is not particularly limited, but is preferably a foil, a mesh, a net-like material such as expanded metal, or the like. The material for the current collector is preferably copper, stainless steel, nickel or the like. The thickness of the current collector is preferably 5 to 20 μm in the case of a foil.

(Positive electrode)
The positive electrode is formed, for example, by applying a positive electrode mixture comprising a positive electrode material, a binder and a conductive agent to the surface of the current collector. It is preferable to select a positive electrode material (positive electrode active material) that can occlude / release a sufficient amount of lithium. A composite chalcogenide of lithium and transition metal, in particular, a composite oxide of lithium and transition metal (lithium-containing) (Also referred to as transition metal oxide) is preferred. The composite oxide may be a solid solution of lithium and two or more transition metals.
Specifically, the lithium-containing transition metal oxide is LiM ¹ _1-X M ² _X O ₂ (where X is a numerical value in the range of 0 ≦ X ≦ 1, and M ¹ and M ² are at least one kind of transition. A metal element) or LiM ¹ _2-Y M ² _Y O ₄ (where Y is a numerical value in the range of 0 ≦ Y ≦ 2 and M ¹ and M ² are at least one transition metal element) It is. Transition metal elements represented by M are Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn, and the like. Preferred examples include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _0.9 Co _0.1 O ₂ , LiNi _0.5 Co _0.5 O ₂ and the like.

The lithium-containing transition metal oxide is obtained by, for example, using lithium, transition metal oxides, hydroxides, salts, and the like as starting materials, mixing these starting materials, and firing at a temperature of 600 to 1000 ° C. in an oxygen atmosphere. Obtainable.
The positive electrode active material may be used alone or in combination of two or more. For example, a carbon salt such as lithium carbonate can be added to the positive electrode. Moreover, when forming a positive electrode, conventionally well-known various additives, such as a electrically conductive agent, can be used suitably.

The positive electrode is manufactured by applying a positive electrode mixture made of a positive electrode material, a binder, and a conductive agent for imparting conductivity to the positive electrode on both surfaces of the current collector to form a positive electrode mixture layer. As the binder, the same one as that used for producing the negative electrode can be used. As the conductive agent, known ones such as graphitized materials are used.
The shape of the current collector is not particularly limited, and a foil or mesh or net-like material such as expanded metal is used. The material of the current collector is aluminum, stainless steel, nickel or the like. The thickness is preferably 10 to 40 μm.

  Similarly to the negative electrode, the positive electrode mixture may be dispersed in a solvent to form a paste, and the paste-like positive electrode mixture may be applied to a current collector and dried to form a positive electrode mixture layer. After the 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, an organic electrolyte composed of a solvent and an electrolyte salt, a polymer electrolyte composed of a polymer compound and an electrolyte salt, and the like are used. Examples of the electrolyte salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, 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 ₆ and other lithium salts can be used. In particular, LiPF ₆ and LiBF ₄ are preferable from the viewpoint of oxidation stability.
The electrolyte salt concentration in the organic electrolyte is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 3.0 mol / l.

  Examples of organic electrolyte solvents include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,1- or 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran. , Γ-butyrolactone, 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, trimethylorthoformate, nitrobenzene, benzoyl chloride, benzoyl bromide, tetrahydrothiophene, dimethylsulfate Kishido, 3-methyl-2-oxazolidone, ethylene glycol, may be used an aprotic organic solvent such as dimethyl sulfite.

When a non-aqueous electrolyte is used as a polymer electrolyte, it includes a matrix polymer compound gelled with a plasticizer (non-aqueous solvent). Examples of the matrix polymer compound include ethers such as polyethylene oxide and cross-linked products thereof. Resin, polymethacrylate resin, polyacrylate resin, fluorine resin such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer can be used alone or in combination. Among these, from the viewpoint of oxidation-reduction stability, it is preferable to use a fluorine-based resin such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer.
10-90 mass% is preferable and, as for the ratio of the solvent in a polymer electrolyte, 30-80 mass% is more preferable. Within this range, the electrical conductivity is high, the mechanical strength is strong, and a film is easily formed.

  The production of the polymer electrolyte is not particularly limited, and examples thereof include a method in which a polymer compound constituting a matrix, a lithium salt, and a nonaqueous solvent (plasticizer) are mixed and heated to melt and dissolve. Also, after dissolving the polymer compound, lithium salt, and non-aqueous solvent in the mixing organic solvent, the method of evaporating the mixing organic solvent, mixing the polymerizable monomer, lithium salt and non-aqueous solvent, ultraviolet rays, Examples thereof include a method of polymerizing a polymerizable monomer by irradiation with an electron beam or a molecular beam to obtain a polymer.

In the lithium ion secondary battery, a separator can also be used.
Although a separator is not specifically limited, For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are mentioned. A synthetic resin microporous membrane is preferred, and among them, a polyolefin microporous membrane is preferred in terms of thickness, membrane strength, and membrane resistance. Specifically, it is a microporous membrane made of polyethylene and polypropylene, or a microporous membrane that combines these.
In the lithium ion secondary battery, it is also possible to use a gel electrolyte.

  A lithium ion secondary battery using a polymer electrolyte is generally called a polymer battery, and is composed of a negative electrode using the fine graphite particles of the present invention, a positive electrode, and a polymer electrolyte. For example, the negative electrode, the polymer electrolyte, and the positive electrode are laminated in this order, and are housed in a battery outer packaging material. In addition to this, a polymer electrolyte may be further arranged outside the negative electrode and the positive electrode.

  Further, the structure of the lithium ion secondary battery 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. In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to include means for detecting an increase in the internal pressure of the battery and shutting off the current when an abnormality such as overcharge occurs. In the case of a polymer battery using a polymer electrolyte, a structure enclosed in a laminate film can also be used.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. Further, in the following examples and comparative examples, a button-type secondary battery for evaluation having a configuration as shown in FIG. 3 was produced and battery characteristics were evaluated. The battery can be produced according to a known method based on the object of the present invention.

In the following examples and comparative examples, the physical properties of the carbon material and the fine graphite particles were measured by the following methods.
The aspect ratio of the carbon material and the fine graphite particles is a ratio of the average value of the long side length and the short side length orthogonal to the long side length measured with a magnification capable of confirming the shape by observation with a scanning electron microscope. .
The volume-converted average particle size of the carbon material and the fine graphite particles is a particle size at which the cumulative frequency of the particle size distribution measured by a laser diffraction particle size distribution meter is 50% by volume.
Raman spectrum ratio I _{P /} I _G of the fine graphite particles was determined by the method and conditions described above.
The lattice spacing d ₀₀₂ of the fine graphite particles was determined by the X-ray diffraction method described above.
The exposure rate of the edge surface of the crushed surface of the fine graphite particles was determined by the method described above.

Example 1
(Preparation of carbon material)
The coal tar pitch was heat-treated at 450 ° C. in a nitrogen atmosphere to generate mesophase spherules. Thereafter, the pitch matrix was extracted from the coal tar pitch using tar oil, and the mesophase spherules were further separated from the tar oil and dried to obtain spherical mesophase spherules (average particle size 25 μm). The small spheres were heat-treated at 600 ° C. for 3 hours under a nitrogen atmosphere to prepare spherical fired products. As a result of observing the cross section of the fired product with a polarizing microscope, a thin-film optically isotropic phase (thickness of about 0.5 μm) is formed on the surface of the fired product, and the inside of the fired product is an optically anisotropic phase. Was showing.

(Preparation of fine graphite particles)
To 92 parts by mass of the fired product, 8 parts by mass of nickel powder (average particle size 0.21 μm) was added and mixed using a Henschel mixer (Mitsui Mining Co., Ltd.). The mixture was surrounded by coke breeze and heat-treated at 3150 ° C. for 5 hours in a non-oxidizing atmosphere to graphitize the fired product. The obtained graphitized material was a graphitized material of mesophase spherules having fine ridges on the outer surface, and the average particle size was 26 μm (FIG. 1).
The graphitized product was put into a mechano-fusion system (manufactured by Hosokawa Micron Corporation) and operated at a rotor peripheral speed of 20 m / s for 30 minutes to drop off the raised matter. When the particle size distribution of the product was measured, two particle size peaks were confirmed at 8 μm and 25 μm. Subsequently, it was separated into fine powder (fine graphite particles) and coarse powder (graphite base material) with an air classifier. Fine powder [average particle diameter 8 μm, FIG. 2 (b)] was 18 parts by mass, and coarse powder [average particle diameter 25 μm, FIG. 2 (a)] was 82 parts by mass.

The fine powder, average lattice spacing _{d 002} of (002) plane in the X-ray wide angle diffraction 0.3356nm, _I P / _{I G} in the Raman spectrum using argon laser beam having a wavelength of 514.5nm is 0.13 met It was. When the fine powder was observed with a scanning electron microscope, it was almost spherical. When the average aspect ratio of the 50 fine powders was calculated from the particle appearance, it was 1.2. Moreover, when the particle | grain cross section was observed with the polarization microscope, all the areas were optically anisotropic phases. Furthermore, as a result of observing the cross section of the five measured at random with a transmission electron microscope and observing the crystal structure of the outer surface of the fine powder, almost the entire periphery was covered with the basal surface of graphite. The exposed area was about 5%.

(Negative electrode mixture)
98 parts by mass of the fine graphite particles, 1 part by mass of the binder carboxymethyl cellulose and 1 part by mass of styrene-butadiene rubber were put in water and stirred to prepare a negative electrode mixture paste.

(Production of working electrode)
The negative electrode mixture paste was applied to a copper foil with a uniform thickness, and further dried by evaporating the water of the dispersion medium at 90 ° C. in vacuum. Next, the negative electrode mixture applied on the copper foil is pressed by a roller press, and further punched into a circular shape having a diameter of 15.5 mm, thereby adhering to the current collector made of copper foil (thickness 16 μm). A working electrode 12 composed of an agent layer (thickness 60 μm, density 1.72 g / cm ³ ) was produced.
The electrode density was measured as follows. The average thickness was measured using a micrometer whose contact portion was a mirror surface having a diameter of 5 mm, and the thickness of the negative electrode mixture was determined by reducing the thickness of the copper foil. Next, the mass of the negative electrode mixture was determined by subtracting the mass of the copper foil of the same size from the mass of the working electrode. The electrode density was calculated from the following formula (1).
Electrode density (g / cm ³ ) = mass of negative electrode mixture layer / (thickness of negative electrode mixture layer × electrode area) (1)

(Production of counter electrode)
Lithium metal foil is 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 (thickness 0.5 μm) in close contact with the current collector did.

(Electrolyte / Separator)
LiPF ₆ was dissolved at a concentration of 1 mol / dm ^{3 in} a mixed solvent of ethylene carbonate 33 vol% -methyl ethyl carbonate 67 vol% to prepare a non-aqueous electrolyte. The obtained non-aqueous electrolyte was impregnated into a polypropylene porous body (thickness 20 μm) to produce a separator impregnated with the electrolyte.

(Production of evaluation battery)
A button-type secondary battery shown in FIG. 3 was produced as an evaluation battery.
The separator 5 impregnated with an electrolyte 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. Thereafter, the exterior cup 1 and the exterior can 3 were combined so that the collector 7 b side of the working electrode was accommodated in the exterior cup 1 and the collector 7 a side of the counter electrode was accommodated in the exterior can 3. In that case, the insulating gasket 6 was interposed in the peripheral part of the exterior cup 1 and the exterior can 3, and both peripheral parts were crimped and sealed.

The evaluation battery produced as described above was subjected to a charge / discharge test as shown below at a temperature of 25 ° C. to evaluate the discharge capacity, initial charge / discharge efficiency, rapid charge rate, rapid discharge rate, and cycle characteristics. The evaluation results are shown in Table 2.
(Discharge capacity, initial charge / discharge efficiency)
After 0.9 mA constant current charging was performed until the circuit voltage reached 0 mV, switching to constant voltage charging was continued until the current value reached 20 μA. The charging capacity was determined from the amount of electricity applied during that time. Then, it rested for 120 minutes. Next, constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 1.5 V, and the discharge capacity was obtained from the energization amount during this period. This was the first cycle. The initial charge / discharge efficiency was calculated from the following equation (2).
Initial charge / discharge efficiency (%) = (first cycle discharge capacity / first cycle charge capacity)
× 100 (2)
In this test, the process of occluding lithium ions in the graphite material was charged, and the process of detaching from the negative electrode material was discharge.

(Rapid charge rate)
Subsequently, high-speed charging was performed in the second cycle.
Constant current charging was performed until the circuit voltage reached 0 mV, the current value was set to 3.6 mA, which is four times the first cycle, the charging capacity was obtained, and the rapid charging rate was calculated from the following equation (3).
Rapid charge rate = (constant current charge capacity in the third cycle / in the first cycle
Discharge capacity) x 100 (3)

(Rapid discharge rate)
Following the constant current charging in the second cycle, high-speed discharge was performed in the third cycle. After switching to constant voltage charging in the same way as in the first cycle and fully charging, constant current discharge was performed until the circuit voltage reached 1.5 V, with the current value being 14.4 mA, 16 times that of the first cycle. From the obtained discharge capacity, the rapid discharge rate was calculated by the following equation (4).
Rapid discharge rate = (discharge capacity in the second cycle / discharge capacity in the first cycle
) × 100 (4)
Note that the performance of the rapid charge rate and the rapid discharge rate may be collectively referred to as rapid charge / discharge characteristics.

(Cycle characteristics)
An evaluation battery different from the evaluation battery that evaluated the discharge capacity, initial charge / discharge efficiency, rapid charge rate, and rapid discharge rate was produced and evaluated as follows.
After 4.0 mA constant current charging was performed until the circuit voltage reached 0 mV, switching to constant voltage charging was continued until the current value reached 20 μA, and then rested for 120 minutes. Next, constant current discharge was performed at a current value of 4.0 mA until the circuit voltage reached 1.5V. The charge / discharge was repeated 20 times, and the cycle characteristics were calculated from the obtained discharge capacity using the following equation (5).
Cycle characteristics = (discharge capacity in the 20th cycle / discharge in the first cycle)
Capacity) x 100 (5)

  As shown in Table 2, the evaluation battery obtained using the negative electrode material of Example 1 as the working electrode exhibits a high discharge capacity and a high initial charge / discharge efficiency at a high negative electrode density. Furthermore, it exhibits excellent rapid charge / discharge characteristics and excellent cycle characteristics.

(Comparative Example 1)
In Example 1, except that the carbon material is graphitized as it is without mixing nickel powder in the carbon material, Example 1 is repeated with the same method and conditions as in Example 1, and a small mesophase with no raised matter is obtained. A spherical graphitized product was obtained. The average particle diameter of the graphitized product was 25 μm, d ₀₀₂ was 0.3360 nm, and I _P / I _G was 0.12. The graphitized material was almost spherical and had an average aspect ratio of 1.1.
Using the graphitized product, a working electrode and an evaluation battery were produced under the same method and conditions as in Example 1, and a charge / discharge test was performed. The evaluation results of the battery characteristics are shown in Table 2.
As is apparent from Table 2, when the graphitized mesophase spherule is used alone as the negative electrode material for the working electrode, the discharge capacity, rapid charge / discharge characteristics, and cycle characteristics are low.

(Example 2)
In Example 1, the raised material is dropped from the base material of the graphitized material, and then the mixture of the fine powder and the coarse powder is left as it is without separating the fine powder and the coarse powder by an air classifier, and the negative electrode mixture paste. A negative electrode material was obtained according to the method and conditions of Example 1 except that it was used in Using the negative electrode material, an evaluation battery was produced under the same method and conditions as in Example 1, and a charge / discharge test was performed. The evaluation results of the battery characteristics are shown in Table 2.
As is apparent from Table 2, when a negative electrode material obtained by using a combination of fine graphite particles and a graphitized base material is used for the working electrode, the negative electrode obtained by independently specifying the base material of the graphitized material Compared with the case of using a material, the initial charge / discharge efficiency is improved.

(Example 3)
(Preparation of carbon material)
Coke particles (average particle size 15 μm) 90 parts by mass, phenol resin (residual carbon ratio 40% by mass) 25 parts by mass, and ethanol 30 parts by mass were put into a biaxial kneader and kneaded at room temperature for 1 hour. The ethanol was removed by kneading in vacuum at 150 ° C. for 30 minutes. The kneaded product was primarily fired at 300 ° C. in a non-oxidizing atmosphere, and then secondary fired at 1300 ° C. The fired product was crushed with a hammer mill to obtain massive coke particles coated with carbonaceous material.
When the cross section of the coke particles was observed with a polarizing microscope, an optically isotropic phase was formed with a thickness of about 1 μm on the surface of the particles, and the inside of the particles showed an optically anisotropic phase.

(Preparation of fine graphite particles)
10 parts by mass of iron oxide powder (average particle size 0.30 μm) was added to 90 parts by mass of the carbon-coated coke particles, and mixed using a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.). The mixture was surrounded by coke breeze and heat-treated at 3150 ° C. for 5 hours in a non-oxidizing atmosphere to graphitize the fired product. The obtained graphitized material was a graphitized material of coated coke particles having fine protrusions on the outer surface, and the average particle size was 17 μm. It is considered that iron oxide is reduced to iron during graphitization, and then becomes iron carbide to form a protuberance. Thereafter, the iron element of the iron carbide evaporates.
The graphitized product was put into a mechano-fusion system (manufactured by Hosokawa Micron Corporation) and operated at a rotor peripheral speed of 20 m / s for 30 minutes to drop off the raised matter. When the particle size distribution of the product was measured, two particle size peaks were confirmed at 5 μm and 15 μm. Subsequently, it was separated into fine powder (fine graphite particles) and coarse powder (graphite base material) with an air classifier. The fine powder (average particle diameter 5 μm) was 25 parts by mass, and the coarse powder (average particle diameter 15 μm) was 75 parts by mass.

The fine powder, average lattice spacing _{d 002} of (002) plane in the X-ray wide angle diffraction 0.3358nm, _I P / _{I G} in the Raman spectrum using argon laser beam having a wavelength of 514.5nm is 0.14 met It was. When the fine powder was observed with a scanning electron microscope, it was almost spherical. The average aspect ratio calculated from the appearance of the 50 fine powders was 1.2. Further, when the cross section was observed with a polarizing microscope, the entire region was an optically anisotropic phase. Furthermore, as a result of observing the cross section of the five measured at random with a transmission electron microscope and observing the crystal structure of the outer surface of the fine powder, almost the entire periphery was covered with the basal surface of graphite. The exposed area was about 7%.

Using the graphitized product, a working electrode and an evaluation battery were produced under the same method and conditions as in Example 1, and a charge / discharge test was performed. The evaluation results of the battery characteristics are shown in Table 2.
As is apparent from Table 2, when the negative electrode material is made of fine graphite particles for the working electrode, the discharge capacity, initial charge / discharge efficiency, rapid charge / discharge characteristics and cycle characteristics are excellent even at a high negative electrode density. ing.

Example 4
(Preparation of fine graphite particles)
After adding 100 parts by mass of the calcined mesophase spherules of Example 1 to 100 parts by mass of ferric chloride aqueous solution (acidic) corresponding to a concentration of 5% by mass in terms of iron, an aqueous sodium hydroxide solution was added. Neutralized to pH 7. As a result, a dispersion liquid in which the mesophase microsphere fired product was dispersed in a suspension of iron hydroxide FeO (OH) was obtained. The dispersion was heated to 100 ° C. to remove water, and further vacuum-dried at 150 ° C. for 5 hours to completely remove water to obtain a mesophase spheroid fired product in which iron hydroxide was scattered on the surface. .
When the appearance of the obtained fired product was observed with a scanning electron microscope, granular and needle-like iron hydroxides were scattered. Moreover, about the 50 iron hydroxide scattered, the average value of the result of having measured each major-axis length using the scanning electron microscope was 0.5 micrometer.

Next, the mesophase small sphere fired product was surrounded by coke breeze and heat treated at 3150 ° C. for 5 hours in a non-oxidizing atmosphere to graphitize the fired product. The obtained graphitized product was a graphitized product of coated coke particles having fine protrusions on the outer surface, and the average particle size was 27 μm. In addition, it is thought that iron hydroxide is reduced to iron during graphitization, and then becomes iron carbide to form a raised product. Thereafter, the iron element of the iron carbide evaporates.
Using the same method and conditions as in Example 1, the protuberances were dropped and separated, and the separated fine powder was used as the negative electrode material, and an evaluation battery was produced under the same method and conditions as in Example 1, and a charge / discharge test was performed. The results of the battery characteristics are shown in Table 2.
As is apparent from Table 2, when the negative electrode material is made of fine graphite particles obtained by attaching iron hydroxide to the working electrode in a wet manner, the discharge capacity, initial charge / discharge efficiency, and rapidity are increased even at a high negative electrode density. Excellent charge / discharge characteristics and cycle characteristics.

(Example 5)
The mesophase microsphere fired product of Example 1 was placed on the anode side stage of a DC bipolar sputtering apparatus, a 99.999 mass% pure single crystal cobalt target was placed on the cathode side, and an ultrasonic wave was placed on the anode side stage. Sputtered for 3 hours under conditions of pressure of 0.5 Pa, voltage of 600 V, and current of 0.5 A while attaching a vibrator and applying vibration to the mesophase small sphere fired product, and mesophase small sphere fired product in which cobalt is scattered on the surface. Got. About the obtained baked product, cobalt was quantitatively analyzed with an ICP emission spectroscopic analyzer, and it was confirmed that 7 mass% was contained.
In addition, observation with a scanning electron microscope confirmed the situation where granular cobalt was scattered. Each maximum length of 50 interspersed cobalt was measured, and the average value was 0.3 μm.

Next, the mesophase small sphere fired product was surrounded by coke breeze and heat treated at 3150 ° C. for 5 hours in a non-oxidizing atmosphere to graphitize the fired product. The obtained graphitized material was a mesophase spheroidized graphitized material having minute protrusions on the outer surface, and the average particle size was 25 μm.
Using the same method and conditions as in Example 1, the raised matter was dropped. Thereafter, the negative electrode material was subjected to the same method and conditions as in Example 1 except that the mixture of fine powder and coarse powder was used as it was for the negative electrode mixture paste without separating fine powder and coarse powder with an air classifier. Then, an evaluation battery was prepared and a charge / discharge test was performed. The results of the battery characteristics are shown in Table 2.
As is apparent from Table 2, when the negative electrode material is made of fine graphite particles obtained by adhering cobalt to the working electrode by sputtering, the discharge capacity, initial charge / discharge efficiency, and rapid charge are increased even at a high negative electrode density. Excellent discharge and cycle characteristics.

(Comparative Example 2)
(Preparation of carbon material)
The scale-like natural graphite (average particle diameter 10 μm) was circulated and circulated in the apparatus for 1 hour at an air pressure of 300 kPa using a counter jet mill (manufactured by Hosokawa Micron Corporation: model 200AFG) to obtain spherical granulated graphite. I _P / I _G in a Raman spectrum using an argon laser beam having an average particle diameter of 8 μm, a (002) plane average lattice spacing d ₀₀₂ of 0.3356 nm, and a wavelength of 514.5 nm in X-ray wide angle diffraction. Was 0.11.
When the granulated graphite was observed with a scanning electron microscope, it was almost spherical. The average aspect ratio calculated from the appearance of the 50 fine powders was 1.2. In addition, when a cross-section was observed with a scanning electron microscope, it was confirmed that a plurality of natural graphite aggregated concentrically. Using the granulated graphite, the working electrode and the same conditions as in Example 1 were used. An evaluation battery was prepared and a charge / discharge test was performed. The evaluation results of the battery characteristics are shown in Table 2.
As is apparent from Table 2, when the negative electrode material is made of granulated graphite as the working electrode, the discharge capacity is high, but the rapid charge / discharge characteristics and the cycle characteristics are remarkably low at a high negative electrode density.

(Comparative Example 3)
90 parts by mass of the granulated graphite obtained in Comparative Example 2 and 30 parts by mass of petroleum-based tar (residual carbon ratio 35%) were charged into a biaxial kneader and kneaded at 150 ° C. for 1 hour. The kneaded product was primarily fired at 700 ° C. in a nitrogen atmosphere, and then secondary fired at 1300 ° C. The fired product was crushed with a hammer mill to obtain granulated graphite coated with carbonaceous material. The average particle diameter of the coated granulated graphite is 10 μm, the average lattice spacing d ₀₀₂ of (002) plane in X-ray wide angle diffraction is 0.3361 nm, and I _P / in Raman spectrum using an argon laser beam having a wavelength of 514.5 nm. I _G was 0.33. When the coated granulated graphite was observed with a scanning electron microscope, a fired product of petroleum-based tar adhered to the surface of the granulated graphite, which was almost spherical in shape, in the form of a film. The average aspect ratio of the 50 coated granulated graphites calculated from the appearance was 1.3.
Using the coated granulated graphite, a working electrode and an evaluation battery were produced under the same method and conditions as in Example 1, and a charge / discharge test was performed. The evaluation results of the battery characteristics are shown in Table 2.
As can be seen from Table 2, when the working electrode is made of carbonized granulated graphite and used as a negative electrode material, the discharge capacity is insufficient, and at a high negative electrode density, rapid charge / discharge characteristics and cycle characteristics are not obtained. Low.

(Comparative Example 4)
Coltar pitch was calcined at 600 ° C. in a non-oxidizing atmosphere to obtain a calcined bulk mesophase, and the calcined product was pulverized with a jet mill to prepare calcined particles having an average particle diameter of 5 μm. The fired particles were graphitized by heat treatment at 3200 ° C. for 5 hours in a non-oxidizing atmosphere. The average particle diameter of the obtained graphitized material is 5 μm, the average lattice spacing d ₀₀₂ of (002) plane in X-ray wide angle diffraction is 0.3362 nm, and I _P / in Raman spectrum using an argon laser beam having a wavelength of 514.5 nm. The _IG was 0.25. When the graphitized product was observed with a scanning electron microscope, it was partly a lump including scales. About 50 pieces, the cross section was observed with a scanning electron microscope, and as a result of observing the crystal structure of the outer surface of the particles, the exposed area of the edge surface of graphite was about 40%.
Using the graphitized product, a working electrode and an evaluation battery were produced under the same method and conditions as in Example 1, and a charge / discharge test was performed. The evaluation results of the battery characteristics are shown in Table 2.
As is clear from Table 2, the working electrode has a large proportion of the fracture surface, I _P / _IG is 0.2 or more, and graphite particles having an average aspect ratio exceeding 2.0 are used as a negative electrode material. In some cases, the discharge capacity, initial charge / discharge efficiency, rapid charge / discharge characteristics, and cycle characteristics are all low.

(Reference Example 1)
Coarse powder that is a base material of the graphitized product obtained in Example 1 [average particle diameter 25 μm, almost spherical, d ₀₀₂ : 0.3356 nm, I _P / I _G : 0.15, edge face exposure rate 5%, Using only the average aspect ratio 1.1 and FIG. 2 (a)], a negative electrode material was produced under the same method and conditions as in Example 1, an evaluation battery was produced, and a charge / discharge test was performed. The results of the battery characteristics are shown in Table 2.
As is clear from Table 2, when coarse powder is used as the negative electrode material of the working electrode, the discharge capacity, initial charge / discharge efficiency, and rapid charge / discharge are higher at higher negative electrode densities than in Examples 1 to 5 using fine powder. Characteristics and cycle characteristics are inferior.

  The fine graphite particles of the present invention can be used as a negative electrode material for a lithium ion secondary battery that contributes effectively to downsizing and high performance of equipment to be mounted. In addition, taking advantage of this feature, it can also be used in various applications that require electrical conductivity and heat resistance, such as resin additive conductive materials, fuel cell separator conductive materials, and refractory graphite.

It is a scanning electron micrograph of an example of the graphitized material which has a protruding object obtained by the graphitization process of this invention. (A) is a scanning electron micrograph of an example of the base material of the graphitized material obtained in the raised product dropping step of the present invention. (B) is a scanning electron micrograph of an example of a raised product (micrographitic particles) obtained in the raised product dropping step of the present invention. It is a schematic cross section which shows the structure of the button type evaluation battery for using for a charging / discharging test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exterior cup 2 Working electrode 3 Exterior can 4 Counter electrode 5 Electrolyte solution impregnation separator 6 Insulation gasket 7a, 7b Current collector

Claims (7)

A metal and / or metal compound having at least one of a property of reacting with carbon and a property of dissolving carbon is attached to a carbon material that forms an optically isotropic crystal structure at least partially after graphitization. An adhering process,
A carbon material in which the metal and / or the metal compound is attached, after the metal evaporation and / or the metal compound is decomposed, and the metal element contained in the metal compound is heated at a temperature higher than the temperature at which evaporation, the While graphitizing the carbon material, a graphitization step of forming a protuberance on the surface of the graphitic material,
A protuberance falling to obtain a fine graphite particles by dropping from graphitic material該隆Okoshibutsu to impart mechanical energy mechanochemical treatment graphitic material having該隆Okoshibutsu,
A method for producing fine graphite particles, comprising: 2. The method for producing fine graphite particles according to claim 1, wherein in the step of removing the raised matter, the raised matter is removed from the graphite material, and the crushing surface is worn to obtain fine graphite particles. A metal and / or metal compound having at least one of a property of reacting with carbon and a property of dissolving carbon is attached to a carbon material that forms an optically isotropic crystal structure at least partially after graphitization. An adhering process,
A carbon material in which the metal and / or the metal compound is attached, after the metal evaporation and / or the metal compound is decomposed, and the metal element contained in the metal compound is heated at a temperature higher than the temperature at which evaporation, the While graphitizing the carbon material, a graphitization step of forming a protuberance on the surface of the graphitic material,
A protuberance falling to obtain a fine graphite particles by dropping from graphitic material該隆Okoshibutsu to impart mechanical energy to the graphitic material having該隆Okoshibutsu,
A method for producing fine graphite particles, characterized by comprising :
Wherein the fine graphite particles, in the Raman spectrum using argon laser beam having a wavelength of 514.5 nm, peak present the intensity of a peak present in the region of 1570~1630cm ^-1 _I G, in the region of 1350 ^-1 method for producing fine graphite particles I _{P /} I _G ratio is equal to or less than 0.2 at the time of the strength of the the I _P. The method further comprises a separation step of separating the fine graphite particles from the mixture of the fine graphite particles and the graphite material obtained in the protruding product dropping step to obtain the fine graphite particles. The manufacturing method of the fine graphite particle in any one of 1-3. Method for producing fine graphite particles according to any one of claims 1-4, wherein the metal and the metal compound is a powder. The method for producing fine graphite particles according to any one of claims 1 to 5 , wherein the temperature at which the metal is evaporated and / or the metal element is evaporated is 1500 to 3300 ° C. The method for producing fine graphite particles according to any one of claims 1 to 6 , wherein the fine graphite particles are a material for a negative electrode of a lithium ion secondary battery.

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