JP2006312578A - Graphite material and its manufacturing method, negative electrode material for lithium ion secondary cell, negative electrode for lithium ion secondary cell and lithium ion secondary cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a graphite material capable of obtaining a high discharging capacity and a high initial charging and discharging efficiency as a negative electrode material for a lithium ion secondary cell and further capable of obtaining excellent rapid charging and discharging characteristic and cycle characteristic, further to provide a manufacturing method of the graphite material, the negative electrode material for the lithium ion secondary cell containing the graphite material, a negative electrode for the lithium ion secondary cell containing the negative electrode material and the lithium ion secondary cell using the negative electrode. <P>SOLUTION: In the manufacturing method of the graphite material, the graphite material having bump of ≥1 μm height on the surface, a graphite precursor and a metallic compound are mixed in a liquid phase, then the mixture is heated at ≥1,500°C to graphitize. The negative electrode material for the lithium ion secondary cell contains the graphite material. The negative electrode contains the negative electrode material. The lithium ion secondary cell uses the negative electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a graphite material and a production method thereof, a negative electrode material for a lithium ion secondary battery containing the graphite material, a negative electrode including the negative electrode material, and a lithium ion secondary battery using the negative electrode.

  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.

  Furthermore, for the purpose of improving rapid charge / discharge characteristics and cycle characteristics, it has been studied to mix and combine a conductive additive with the graphite particles. For example, a composite carbon material composed of a graphite material composed of spherical particles and carbon fibers (Patent Document 2), a mesophase small spherical graphite particle mixed with 3 to 30% by mass of vapor grown carbon fiber (Patent Documents 3 and 4) ), Spherical graphite or scaly graphite containing fibrous graphite (Patent Document 5), and a metal catalyst dispersed on the surface of the carbon material to produce vapor-grown carbon fiber or carbon nanotube, and the carbon material Are used as negative electrode active materials as they are (Patent Document 6), and mesophase spherules and other mother particles are made by integrating mechanical particles of amorphous carbon by applying mechanical force (Patent Document 7).

  The negative electrode material for the conventional lithium ion secondary battery can improve the rapid charge / discharge characteristics and cycle characteristics as it is without greatly degrading the discharge capacity and initial charge / discharge efficiency of the lithium ion secondary battery, It also has the following problems.

  In the case of a negative electrode material described in Patent Documents 2 to 5, in which vapor-grown carbon fibers are mixed with graphite particles, or in which only fibrous graphite is mixed with spherical graphite or scaly graphite, graphitized vapor-grown carbon Since the discharge capacity and initial charge / discharge efficiency of the fiber itself are lower than that of the base mesophase graphite, there is a problem that the discharge capacity and the initial charge / discharge efficiency as the negative electrode material are lowered. In addition, there are few opportunities for vapor-grown carbon fibers to come into contact with the base mesophase graphite, and many of them do not contribute to improvement of conductivity. As a result, it cannot be said that the effect of improving rapid charge / discharge characteristics and cycle characteristics is at a sufficient level. Furthermore, the vapor grown carbon fiber is relatively expensive and requires a large amount of mixing of 3 to 20% by mass, which causes a problem of cost increase. In addition, when manufacturing a negative electrode, generally, a method of preparing a negative electrode mixture paste by mixing a negative electrode material, a solvent and a binder and applying this to a current collector is adopted. Since the mixing amount is large, there is a problem that the viscosity of the negative electrode mixture paste becomes unstable.

  In the case of the negative electrode material in which vapor-grown carbon fibers or carbon nanotubes are generated on the surface of the carbon material described in Patent Document 6, the metal material is doped with the graphite catalyst directly or together with the amorphous carbon precursor, By forming carbon nanotubes starting from the catalyst, the conductivity between the graphite materials is improved. However, the formed carbon nanotubes are grown from the catalytic metal existing on the surface of the graphite material substrate or the surface of the amorphous carbon film, so that they are easily detached or damaged from the graphite material, and charge / discharge The effect of improving efficiency and cycle characteristics may be reduced. In addition, since the catalyst metal remains in the obtained negative electrode material, the battery characteristics may be adversely affected. Further, the manufacturing process is complicated and the yield is low, and there is a problem of cost increase industrially.

  In the case of an integrated negative electrode material in which child particles made of amorphous carbon or the like are attached to mother particles such as mesophase small spheres described in Patent Document 7 by mechanochemical treatment, amorphous carbon having a small average particle diameter of 100 nm or less, etc. It is intended to increase the reactivity by increasing the specific surface area of the negative electrode material by increasing the specific surface area in contact with the electrolytic solution. However, even if the average particle diameter of the child particles that can adhere to the mother particles by mechanochemical treatment is 100 nm or less, the formed child particles of the composite particles are removed by the stirring force when preparing the negative electrode mixture paste. In this method, it is difficult to attach the child particles having an average particle diameter of more than 100 nm (= 0.1 μm). The effect on the discharge characteristics is small and unstable.

Patent Document 8 describes a method of producing graphite for negative electrode by impregnating a carbon raw material with a solution of a metal compound and subsequently performing carbonization and graphitization. This production method utilizes the graphitization-promoting action of the metal of the metal compound, and is characterized in that the graphitization of the portion having low crystallinity is promoted and the capacity is improved. However, simply increasing the graphitization degree of the graphite for negative electrode, the effect of increasing the conductivity and reactivity is not as good as the above-mentioned prior art, and the high-level rapid charge / discharge characteristics and cycle characteristics in recent years are not sufficient. The request cannot be satisfied.
Japanese Examined Patent Publication No. 62-23433 JP-A-4-237971 JP-A-6-111818 Japanese Patent Laid-Open No. 11-176442 JP-A-9-213372 JP 2001-196064 A JP-A-11-265716 JP 10-255770 A

  The present invention has been made in view of the above situation, and as a negative electrode material for a lithium ion secondary battery, high discharge capacity and high initial charge / discharge efficiency are obtained, and further excellent rapid charge / discharge characteristics and excellent Another object of the present invention is to provide a graphitic material that can be produced easily and inexpensively from an industrial point of view. Also provided are a method for producing the graphite material, a negative electrode material for a lithium ion secondary battery using the graphite material, a negative electrode containing the negative electrode material, and a lithium ion secondary battery using the negative electrode. Is the purpose.

  The present invention is a graphitic material characterized by having a bulge having a height of 1 μm or more on the surface.

  In such a graphite material of the present invention, the average value of the ratio (h / g) between the height h of the ridge and the base length g is preferably 0.1 to 15.

  Moreover, it is preferable that the average particle diameter of the said graphite material is 1-100 micrometers.

Further, it is preferable that the number of said raised is 2-20 / 100 [mu] m ^2.

  Moreover, it is preferable that the graphite material is a graphitized product of mesophase spherules.

In addition, the present invention provides a metal material having at least one of a property of reacting with carbon and a property of dissolving carbon in contact with a precursor of a graphite material in a non-solution state, thereby bringing the metal material into the precursor. It is a method for producing a graphite material, which is scattered in the body and heated at a temperature of 1500 ° C. or higher.
Here, “the property of reacting with carbon” is preferably a property of forming a carbide with carbon.
Further, “to make the metal material interspersed with the precursor” means “to disperse the metal material and attach it to the precursor”.

  In such a method for producing a graphite material of the present invention, the metal material is preferably in the form of powder.

  Moreover, it is preferable that after mixing the metal material and the precursor in a dispersion medium, the dispersion medium is removed, and the metal material is interspersed in the precursor.

  In addition, the metal material is preferably interspersed with the precursor by a PVD (Physical Vapor Deposition) method or a CVD (Chemical Vapor Deposition) method.

  The precursor preferably has an optically isotropic crystal structure on at least a part of its surface.

  The present invention also provides a metal material having at least one of a property of reacting with carbon and a property of dissolving carbon, and a carbon source that forms an optically isotropic crystal structure at least partially after graphitization. This is a method for producing a graphite material, in which a substance is mixed and the obtained mixture is attached to a precursor of a graphite material and heated at a temperature of 1500 ° C. or higher.

  In such a method for producing a graphite material of the present invention, the heating temperature is preferably 1500 to 3300 ° C.

  The precursor is preferably a mesophase microsphere.

  Moreover, this invention is a negative electrode material for lithium ion secondary batteries containing the graphite material in any one of said.

  Moreover, this invention is a negative electrode for lithium ion secondary batteries containing the said negative electrode material for lithium ion secondary batteries.

  Furthermore, this invention is a lithium ion secondary battery using the said negative electrode for lithium ion secondary batteries.

The lithium ion secondary battery using the graphite material of the present invention as a negative electrode material has a high rapid charge rate and rapid discharge rate, excellent initial charge / discharge efficiency and cycle characteristics, and excellent discharge capacity. In addition, the manufacturing cost of the graphite material itself is low.
Therefore, the lithium ion secondary battery using the negative electrode material 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 described more specifically.
A lithium ion secondary battery usually has a non-aqueous electrolyte, a negative electrode, and a positive electrode as main battery components, and these components are enclosed in, for example, a battery can. The negative electrode and the positive electrode each act as a lithium ion carrier. The battery mechanism is such that lithium ions are occluded in the negative electrode during charging, and lithium ions are released from the negative electrode during discharging.

(Graphite material)
As shown in FIG. 1, the graphite material of the present invention has a ridge 3 on the surface 2 of the base material 1. The protuberance 3 is in a state of rising from the surface 2 of the base material 1 of the graphite material, and the protuberance 3 is integrally formed with the same material as the base material 1, and an interface and a boundary line are formed between the protuberance 3 and the base material 1. Is preferably absent. The ridge 3 is often a spherical body or a curved body having substantially no ridge line, such as a hemispherical shape or a spherical shape, and a cylindrical shape having a spherical head portion, but is not limited thereto. However, the shape of the bulge 3 is more preferable as the ratio of hemisphere or sphere is higher, and particularly as the ratio of sphere is higher. By adopting such a shape, when used as a negative electrode material for a lithium ion secondary battery, the number of contacts between the graphite materials increases, and the size of the formed space is moderate, and the electrolyte (hereinafter referred to as the electrolyte) Electrolyte solutions are also called electrolytes). Unlike the wavy continuous wrinkles 4 that usually occur during graphitization, the ridges 3 are preferably scattered individually on the surface of the base material 1 of the graphite material. The ridges 3 can be present on the wrinkles 4.
In addition, as can be seen from FIG. 1, the base material in the present invention refers to a bulge, wrinkle, and / or deposit (when a mesophase microsphere is manufactured, This is a portion where parts that can be regarded as foreign substances adhering to (such as soot) and fine powder fused during graphitization (derived from the same graphite precursor) are assumed and removed.

The height of the ridge is 1 μm or more as the height h from the base of each ridge to the highest point. By having a ridge of such a height, when used as a negative electrode material of a lithium ion secondary battery, the contact between graphite materials increases, and the size of the formed space is moderate, As will be described later, it is estimated that the effect of improving battery characteristics is increased. The height of the ridge is preferably 2 to 15 μm, more preferably 3 to 10 μm. Further, the average value of the ratio (h / g) of the height h from the base to the base length g of the bulge is 0.1 to 15, preferably 0.10 to 15, more preferably 0.8. When it is 2 to 5, and more preferably 0.5 to 3, the above-described effect is further increased, and the battery characteristics are further improved. The base length g of the bulge is a length in contact with the base material at the bottom of the bulge when the cross section of the bulge is observed. The base length g is preferably 1 to 10 μm. The height h of the bumps, the base length g, and h / g are average values of values obtained by measuring 100 bumps by cross-sectional observation using a scanning electron microscope. In particular, h / g is an average value of 100 h / g values obtained for each ridge.
In FIG. 4, the cross-sectional schematic diagram of the graphite material which has a protrusion is shown. In the figure, h and g are shown.

  The bumps are preferably scattered on the surface of the graphite material.

The number of the bulges of the graphite material is not particularly limited, but is preferably in a density range of 2 to 20 per 100 μm ^{2 of} the surface. The bumps are preferably scattered in such a density range without being unevenly distributed on the surface of the graphite material.

The magnitude | size of a base material is 1-100 micrometers in an average particle diameter, and 2-45 micrometers is more preferable. If the size of the matrix is in such a range, the ratio of the average particle diameter of the graphite material and the height of the ridges is a preferred range, battery characteristics when used as a negative electrode material for lithium ion secondary batteries, in particular, The effect of improving rapid charge / discharge characteristics and cycle characteristics is increased.
In addition, the average particle diameter here is the maximum major axis length of the particle and the length of the axis orthogonal to the particle length by cross-sectional observation with a scanning electron microscope, and this average value is defined as the particle diameter of the particle. This particle diameter is an average value measured for 100 particles.

The average particle diameter of the graphite material of the present invention is preferably 1 to 100 μm, particularly preferably 3 to 50 μm, in terms of volume average particle diameter. If it is less than 1 μm, the initial charge / discharge efficiency of a lithium ion secondary battery using the same may be reduced, and if it exceeds 100 μm, rapid charge / discharge characteristics and cycle characteristics may be deteriorated. The average particle diameter in terms of volume is a particle diameter at which the cumulative frequency of particle size distribution is 50% by volume by a laser diffraction particle size distribution meter.
Hereinafter, there is no notice in particular, and what is simply described as “average particle diameter” means the particle diameter when measured by such a method.
A preferable range of the ratio between the average particle diameter d of the graphite material and the height h of the bulge is h / d = 0.05 to 0.3. Within such a range, contact between the graphite materials and securing of the space to be formed can both be achieved, which is effective in improving battery characteristics.

  The shape of the graphite material of the present invention is not particularly limited, and may be any of granular, massive, spherical, ellipsoidal, plate-like, fibrous, film-like, scale-like, etc., but the aspect ratio is 3 or less It is preferable that it is 2 or less. It is particularly preferable that the shape is close to a sphere, that is, a sphere or a particle having an aspect ratio close to 1. When the aspect ratio is 3 or less, 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 graphite material does not align in one direction and the electrolyte easily penetrates into the inside. Here, the aspect ratio represents the ratio between the maximum long axis length of the graphite material and the length of the axis perpendicular thereto, and each of a plurality (50 or more) of graphite materials is observed by cross-sectional observation using a scanning electron microscope. It is the average value of the measured ratio.

  Specific examples of the graphite material of the present invention include mesophase microspheres, mesophase fired bodies (bulk mesophase), mesophase carbonaceous materials such as mesophase fibers, petroleum coke, needle coke, green coke, green coke, pitch coke, and the like. An example is a graphitized product (graphitized product) of a coke-based carbonaceous material. The graphitic material of the present invention is preferably a graphitized material of mesophase carbonaceous material such as mesophase spherules, mesophase fired bodies, and mesophase fibers, and particularly preferably a mesophase spherulitic graphitized material having an aspect ratio in the above range. Further, the graphitic material of the present invention may be a carbonaceous material other than the above graphitized material, a composite of metal, organic matter, or inorganic material, a laminate, a mixture, or a covering.

Graphitic material of the present invention, the X-ray wide angle diffraction (002) an average lattice spacing d ₀₀₂ of face 0.34nm or less, particularly 0.337nm or less, and further preferably not larger than 0.3365 nm. This means that the crystallinity is high, and when used as a negative electrode material of a lithium ion secondary battery, a high discharge capacity is obtained and a high conductivity is obtained. In the present invention, the ridge is integrated with the base material, and it is difficult to evaluate the crystallinity by separating from the base material. it is preferable surface spacing d ₀₀₂ is less 0.34 nm.
Here, the average lattice spacing d ₀₀₂ of (002) plane in X-ray wide angle diffraction is CuKα ray as X-ray, high purity silicon is used as a standard substance, and (002) plane of graphitic material particles is used. A diffraction 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].

It graphitic material of the present invention, compared with the graphite material having no bumps, large specific surface area, its value is preferably from 0.5 to 20 m ² / g, particularly 1 to 10 m ² / g Is preferred. If it exceeds 20 m ² / g, the viscosity adjustment of the negative electrode mixture paste may become unstable, or the binding force by the binder may be reduced. If it is less than 0.5 m ² / g, the number of ridges is small or the size of the ridges is insufficient, and the effect expected by the present invention may not be obtained. The specific surface area was determined by the BET method by adsorption of nitrogen gas.

  Since the bulge of the graphite material of the present invention is integrated with the base material, compared to composite particles in which fine particles are applied and embedded by mechanical force as in the prior art, or composite particles in which the fine particles are attached via an adhesive component, Even if mechanical force is applied from the outside, the bumps are difficult to fall off. Further, the bulge of the present invention is larger than that of the composite particles of the prior art, so that the number of contacts between the graphite materials can be increased, and a void through which the electrolyte permeates can be secured. Together, these characteristics are considered to contribute to the improvement of battery characteristics as a negative electrode for a lithium ion secondary battery, as will be described later.

  The graphite material of the present invention can be included even if it mixes different types of graphite materials, carbonaceous materials such as amorphous hard carbon, organic substances, metals, metal compounds, etc., as long as the object of the present invention is not impaired. Alternatively, it may be coated or laminated. In addition, the graphite material of the present invention may be subjected to various chemical treatments in the liquid phase, gas phase, and solid phase, heat treatment, physical treatment, oxidation treatment, and the like.

  When the graphite material of the present invention is used as a negative electrode material, the mechanism by which rapid charge / discharge characteristics, cycle characteristics, and the like are improved is not clear, but is estimated as follows. That is, the bulge is integrated with the graphite material (base material), and when the negative electrode is formed, the bulge does not fall off, and the contact between the graphitic materials increases, so the resistance decreases, The conductivity is improved. By improving the conductivity, the utilization rate of the graphite material is increased, and the discharge capacity is increased. Since the ridge is the same quality as the base material having a high degree of graphitization, it is soft. Therefore, when filled, the bulk density increases, the discharge capacity per volume increases, and a high energy density is obtained. In addition, since the gap formed by the bulge that does not fall off is large, the electrolyte sufficiently permeates, the amount of electrolyte retained increases, the diffusibility of lithium ions improves, and the rapid discharge rate improves. Further, since there is a bulge, the specific surface area increases and the number of sites where lithium ions enter and exit also contributes to the improvement of the rapid discharge rate and the rapid charge rate. Further, since the binding force with the binder is increased, the contact between the graphite materials is maintained even by repeated charge and discharge, and the cycle characteristics are excellent.

(Manufacture of graphite materials)
The graphite material of the present invention can be produced by any method as long as it can produce a graphite material having a bulge on the surface. However, the graphite material obtained by embedding the fine particle portion corresponding to the ridge by applying mechanical energy to the graphite material (base material) or attaching it through an adhesive component is effective for the present invention. Excluded because it cannot be fully expressed. A typical production method of the present invention is shown below.

Step (1): The graphite precursor is preliminarily adjusted to a desired shape and size by pulverization, classification or the like.
Step (2): Disperse and attach a metal material (metal and / or metal compound) capable of forming carbon and carbide and / or dissolving carbon on the outer surface of the adjusted graphite precursor. .
Step (3): The graphite precursor obtained by attaching the metal material to the outer surface obtained in the step (2) is heated and graphitized at a temperature of 1500 ° C. or higher to obtain a graphite material.

Next, each step will be described in detail.
Step (1): The raw material of the graphite material of the present invention is not specified, but a graphite precursor that is easily graphitized when heat-treated at a temperature of 1500 ° C. or higher is preferable. As a graphite precursor, from a heat treatment product in which a petroleum-based or coal-based tar or pitch containing free carbon is heat-treated at a temperature of 350 to 450 ° C. in an inert gas atmosphere to generate mesophase microspheres, Examples include mesophase microspheres obtained by removing the matrix, mesophase fired bodies, mesophase carbonaceous materials such as mesophase fibers, and coke carbonaceous materials such as petroleum coke, needle coke, raw coke, green coke, and pitch coke. The Mesophase carbonaceous materials such as mesophase spherules, mesophase fired bodies, and mesophase fibers are preferred, and mesophase spherules are particularly preferred in order to obtain a graphite material having a preferred aspect ratio.
Moreover, it is preferable to use the raw material of the graphite material of the present invention that has been preheated in advance so as not to be melted by heat treatment at a temperature of 1500 ° C. or higher. The final temperature of the preliminary heat treatment is less than 1500 ° C, preferably less than 800 ° C. It is preferable to adjust the shape and size of the graphitized material after graphitization after preliminary heat treatment. For example, mesophase spherules having an average particle diameter of 1 to 100 μm are preheated at a temperature of 800 ° C. or lower. Thus, it is preferable to prepare agglomerated particles having a smaller average particle diameter as they are or by pulverization. The method of pulverization and classification is not particularly limited. Further, the preliminary heat treatment can be performed a plurality of times.
The graphite material of the present invention may be manufactured using a graphitized material (graphitized material) of a mesophase-based carbonaceous material or a coke-based carbon material, as described above, even if it is not a graphite precursor. You can also.

A graphite precursor which is a preferred form as a raw material for the graphite material will be described.
The graphite precursor preferably has an optically isotropic crystal structure (optical isotropic phase) on at least a part of its surface. The presence or absence of the optically isotropic phase can be determined by observing the cross section of the graphite precursor with a polarizing microscope.

When a graphite precursor having an optically isotropic phase is heated at a temperature of 1500 ° C. or higher, the portion of the optically isotropic phase forms a polycrystalline crystal structure.
Here, the polycrystalline crystal structure is defined as a crystal structure having a crystallite size of 10 to 100 nm. The size of the crystallite is defined as the length of the portion exposed on the surface when the cross section of the crystallite is observed with a transmission electron microscope. A more preferable size of the crystallite is 30 to 80 nm, and a more preferable size is 30 to 60 nm.

A specific example of a method for measuring the crystallite size will be described. First, the graphite precursor is placed in a graphite crucible and heated at 3000 ° C. for 6 hours in a non-oxidizing atmosphere to obtain a graphitized graphite precursor (graphitized product). Next, this graphitized material is supported by a resin and thinned by focused ion beam processing or the like. Then, five or more crystallites are randomly selected and observed with a transmission microscope, and the size of the crystallite defined above is measured.
Note that the size of the crystallites can also be measured by observing the surface of the graphite material obtained by the same method with a scanning electron microscope.

  In obtaining the graphite material of the present invention, all of the graphite precursor particles may be in an optically isotropic phase, but as a negative electrode material for a lithium ion secondary battery, a high discharge capacity is obtained. Then, it is preferable that the inside of the particle | grains of a graphite precursor consists of an optically anisotropic crystal structure (optically anisotropic phase), and the exterior (surface of this particle | grain) is an optically isotropic phase.

  In this case, the optically isotropic phase is preferably arranged in a thin film on part or all of the particle surface of the graphite precursor, and particularly covers 30% or more of the total area of the particle surface. Preferably it is. Furthermore, it is particularly preferable that the thin film optically isotropic phase is integrated with the optically anisotropic phase. Here, “integrated” means a so-called gradient composition state in which there is no gap at the boundary between the isotropic phase and the anisotropic phase, and the phase gradually changes.

  Further, the thickness of the thin film optically isotropic phase is 3 μm or less, preferably 1 μm or less, more preferably 0.5 μm or less. If the thickness of the optically isotropic phase is too thick, the discharge capacity may be reduced. The lower limit is preferably 0.01 μm. When the thickness is less than 0.01 μm, there is a tendency that the formation of ridges, which is a feature of the graphite material of the present invention, is insufficient.

  Such a graphite precursor can also be obtained by coating the surface of a graphite precursor with a carbon material having an optically isotropic phase, but the optically isotropic phase and the optically anisotropic phase Mesophase spherules integrated with are optimal as a graphite precursor.

  Further, a carbon source material exhibiting an optically isotropic phase may be attached to the surface of the graphite precursor. The carbon source material only needs to exhibit an optically isotropic phase at a temperature of 1500 ° C. or higher (for example, after graphitization). For example, resins such as phenol resin and furfuryl alcohol resin, oxygen-crosslinked petroleum pitch An optical isotropic pitch such as is exemplified. The graphite precursor to which the carbon source material is attached does not necessarily require an optically isotropic crystal structure.

  Step (2): Carbon and carbides contained in the graphite precursor can be formed and / or dissolved in the outer surface of the graphite precursor obtained in step (1). A metal material (metal and / or metal compound) is dispersed and adhered.

  Metals that can form and / or dissolve carbides with carbon contained in the graphite precursor include alkali metals such as Na and K, alkaline earth metals such as Mg and Ca, Ti , V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, Pt and other transition metals, Al, Ge, etc. Metals, semi-metals such as B and Si are exemplified.

Further, as a metal compound capable of forming and / or dissolving carbon and carbon contained in the graphite precursor, compounds of these metals, that is, hydroxides, oxides, nitrides , Chloride, sulfide and the like.
Such metals and metal compounds may be used alone or in combination of two or more. A metal and a metal compound may be mixed and used.

  Among these, at least one selected from the group consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, and these metal compounds is preferable. These metals and / or metal compounds are stable until they carbonize with the graphite precursor, and in the graphitization treatment in the step (3) described later, all of them are evaporated and carbon is easily dissolved. Because there is.

In the step (2), such a metal material is scattered on the outer surface of the precursor of the graphite material. In that case, the metal material is brought into contact with the precursor in a non-solution state. When the metal material is brought into contact with the precursor in a solution state, the metal material spreads in the form of a film on the precursor and is not scattered, and no bulge is generated, or even if it occurs, there is only a small bulge. It is. A typical example of the non-solution state is a solid phase state and / or a gas phase state of the metal compound. Further, the metal compound can be melted and scattered in the precursor in a liquid phase state.
In short, the non-solution state is defined in order to exclude contact with the precursor using only the solution of the metal material. For example, even if a part of the metal compound is dissolved in the solvent, it corresponds to the non-solution state of the present invention as long as the insoluble part is used. The case of using a suspension in which an insoluble material of a metal compound is precipitated by a chemical operation after adjusting a saturated solution of the metal compound corresponds to the non-solution state of the present invention. Further, when a suspension obtained by adding a metal compound to a saturated solution of a metal compound is used, the suspended portion corresponds to a non-solution state and falls within the technical scope of the present invention.

  In addition, the “outer surface” referred to here does not include the surface of the void inside the particle when the graphite precursor is porous, and the outer surface of the particle, that is, the plurality of graphite precursors are in contact with each other. Means a surface that can.

The size of the deposited metal material is preferably 5 μm or less, more preferably 0.01 to 5 μm, and still more preferably 0.01 to 1 μm. If it exceeds 5 μm, the ridges that are characteristic of the graphite material of the present invention may be excessive, and may exceed the range of the preferred base length, the ridges may fall off, or ridges may not be generated. On the other hand, when the thickness is less than 0.01 μm, the ridge is not generated or is too small, and the effect of the present invention may not be obtained.
Here, the size of the deposited metal material is the measurement of the major axis length of each of 50 or more metal materials using a scanning electron microscope for the metal material in contact with the graphite precursor. It is the average of the values.

Further, the amount of metal in the metal adhesion amount or the metal compound adhesion amount is 0.1 to 30% by mass, preferably 0.5 to 15% by mass with respect to the graphite precursor in terms of metal amount. 1-10 mass% is further more preferable. If it is less than 0.1% by mass, the effects of the present invention may not be sufficiently obtained. On the other hand, if it exceeds 30% by mass, the effect of the present invention tends to be saturated, and further, a large amount of metal material evaporates inside the heating furnace used for heating in the step (3) described later, It may cause operational problems such as deposition of metal material at low temperature parts.
The adhesion amount of the metal material (metal and / or metal material) can be measured by a method such as ICP emission spectroscopic analysis.

As a specific example of a method for dispersing and attaching such a metal material to the outer surface of the graphite precursor,
(A) a method of removing the dispersion medium after mixing the graphite precursor and the metal material in the dispersion medium;
(B) A method of mixing the graphite precursor and the powdered metal material,
(C) After mixing the graphite precursor, the carbon source material (having an optically isotropic crystal structure at least partially after graphitization) and the metal material in a dispersion medium, the dispersion medium How to remove,
(D) a method of adhering a melt of the carbon source material (at least partially having an optically isotropic crystal structure after graphitization) in which the metal material is dispersed to the outer surface of the graphite precursor;
(E) a method of attaching the metal material to the outer surface of the graphite precursor by a PVD (Physical Vapor Deposition) method or a CVD (Chemical Vapor Deposition) method;
Is preferred.

  In the method (a), it is preferable that the dispersion medium does not dissolve at least the metal material or has low solubility even when dissolved. In the method of the present invention, the metal material is preferably dispersed. Further, a dispersion medium in which not only the metal material but also the precursor is not dissolved is more preferable. As an example of such a dispersion medium, an aqueous dispersion medium such as water, alcohol, and ketone is preferable, and water is particularly preferable. The reason is that the influence on the environment at the time of drying and removal is smaller than that of an organic solvent-based dispersion medium, which is advantageous in terms of safety and cost.

  The average particle diameter of the metal material (metal and / or metal compound) put into such a dispersion medium is preferably 5 μm or less, and more preferably 1 μm or less. If the average particle diameter is more than 5 μm, the number of bulges of the resulting graphite material tends to be reduced, and it tends to be difficult to control to a hemispherical or spherical shape.

In the method (a), first, the graphite precursor and the metal material are mixed in a dispersion medium. The order in which the graphite precursor and the metal material are introduced into a dispersion medium is not limited. First, the powder of such a metal material may be dispersed in a dispersion medium, and then a graphite precursor may be added thereto.
The dispersion medium in which the metal material is dispersed is preferably colloidal. Here, the metal material is not colloidal but dissolved in the dispersion medium (for example, Japanese Patent Laid-Open No. 10-255770), and after the mixing and separation operations described later, the metal material is formed into a film on the outer surface of the graphite precursor. When formed, the bulge is not generated or is too small, and the graphite particles of the present invention may not be obtained.

In such a dispersion medium, the graphite precursor and the metal material are mixed.
The mixing is preferably performed using a stirrer until the graphite precursor and the metal material are uniformly dispersed. During mixing, it is preferable to remove bubbles by applying a pressure reducing operation or ultrasonic treatment to promote contact between the metal material and the graphite precursor.

After mixing, the dispersion medium is removed.
There is no restriction | limiting in this method, Methods, such as a heating and pressure reduction, can be employ | adopted suitably. For example, a method of heating the dispersion medium containing the metal material and the graphite precursor to a temperature of less than 1500 ° C. can be mentioned. Moreover, you may perform this isolation | separation operation in the temperature rising process in the case of heating at the temperature of 1500 degreeC or more in a process (3).

  In the method (b), the graphite precursor and the metal material in powder form are mixed. Here, the metal material preferably has an average particle size of 0.01 to 5 μm, and more preferably 0.01 to 1 μm. If it exceeds 5 μm, the ridges that are characteristic of the graphite material of the present invention may be excessive, and may exceed the range of the preferred base length, the ridges may fall off, or ridges may not be generated. On the other hand, when the thickness is less than 0.01 μm, the bulge is not generated or is too small, and the effect of the present invention may not be obtained.

  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 graphite precursor while being uniformly dispersed so as not to generate agglomerates of the powdered metal material. Can be made.

  Further, the graphite precursor and the metal material may be pulverized and mixed together.

In the method (c), in the method (a), the carbon source material that forms the crystal structure of the optically isotropic phase is dispersed or dissolved when adjusting the dispersion medium of the metal material. It is.
Examples of the carbon source material exhibiting an optically isotropic phase include resins such as phenol resins as described above, and the resins are in a state of a precursor before the polymerization reaction or the crosslinking reaction proceeds. Also good.

  In the method (d), a powder of a metal material having an average particle diameter of 0.01 μm or more and 5 μm or less is mixed with a melt of a carbon source material that forms a crystal structure of an optically isotropic phase, and this molten mixture is mixed. It is attached to the graphite precursor. Various kneaders such as a pressure kneader and a two-roll can be used for mixing the metal material powder and the carbon source substance and mixing the mixture and the graphite precursor. Mixing of the metal powder to the melt and adhesion to the graphite precursor may be performed sequentially or simultaneously.

  In the method (e), the metal material is attached to the outer surface of the graphite precursor by a PVD method or a CVD method. Preferred examples of such methods include PVD methods such as vacuum deposition, sputtering, ion plating, molecular beam epitaxy, atmospheric pressure CVD, reduced pressure CVD, plasma CVD, MO (Magneto-Optic) ) CVD methods such as CVD and photo-CVD.

  Of these, the 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 this 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 strike the target metal. A typical example is a method in which the metal is coated on a graphite precursor placed on the anode side.
A metal compound may be used in place of the metal, an alloy may be formed on the outer surface of the graphite precursor using a plurality of types of metals simultaneously, or the target may be mixed with the metal and the metal compound. It may be used. 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.

  In this case, mechanically agitating the graphite precursor, applying vibrations such as ultrasonic waves, or moving gas to move the graphite precursor and disperse the metal on the outer surface of the graphite precursor It is preferable to make it adhere.

  In the present invention, the method of dispersing and attaching the metal material to the outer surface of the graphite precursor is not limited to the above (a) to (e). For example, the metal material is attached to the outside of the graphite precursor. A method of fusing to the surface may be used.

  After the metal material is attached to the outer surface of the graphite precursor, various chemical treatments such as carbon material coating, gas treatment and oxidation treatment, and physical treatment such as application of mechanical energy are performed. May be.

Step (3): As a graphitization method, a method of heating at a temperature of 1500 ° C. or more and 3300 ° C. or less using a known high-temperature furnace such as an Acheson furnace can be adopted. As a result, the metal material does not evaporate or sublime and remain in the obtained graphite material. The heating temperature is preferably 2500 ° C. or higher and 3300 ° C. or lower, more preferably 2800 ° C. to 3300 ° C. If it is less than 1500 degreeC, it cannot graphitize and a metal material remains, and when it is used for a negative electrode, discharge capacity is insufficient. If it exceeds 3300 ° C., the graphite material may partially sublime, which is not preferable because the yield decreases. 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.
The obtained graphite material is crushed and pulverized as necessary, and the particle size is adjusted by classification and used as a negative electrode material.

  By the above method, the graphite material of the present invention can be obtained by interspersing the metal material with the precursor of the graphite material and heating. Although this mechanism is not clear, a bump that is integrated with the base material in the process of graphitizing (ie, heating to 1500 ° C. or higher) the precursor in which the granular or spherical metal material is scattered on the outer surface Is considered to be generated. The metal material seems to evaporate and dissipate in this heating process, and does not substantially remain in the final product, the graphite material of the present invention. The mechanism is further estimated below. The metal compound reacts with the precursor carbon to form a metal carbide at a stage prior to the graphitization treatment at a relatively low temperature. At that time, the metal compound is supplied with carbon from the precursor, and the metal carbide bumps are once generated. However, when the graphitization temperature rises to the vicinity of the boiling point of the metal forming the metal carbide, transpiration of the metal starts from carbon and metal in a chemical equilibrium state with the metal carbide. Thereafter, as the temperature rises, the chemical equilibrium proceeds favorably for the reverse reaction. Eventually, all of the metal evaporates, and the same graphitized bump as the base material remains. In the graphitization treatment, the temperature is raised to about 3000 ° C. For example, when the metal forming the metal compound is iron, it is estimated that the transpiration of iron starts near 2800 ° C. Accordingly, in the base material of the present invention, the remaining portion after the graphitization treatment of the precursor of the graphite material used in the step (1) usually occupies the majority.

  Accordingly, it is considered that the metal or metal compound is preferably dispersed and adhered to the outer surface of the graphite precursor. Further, it is considered preferable to use a metal or a metal compound that can form a carbide.

(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.
The lithium ion secondary battery of the present invention is not particularly limited except that it contains the graphite material of the present invention as a negative electrode material, 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 method that can sufficiently bring out the battery characteristics of the graphite material of the present invention, and can provide a chemically and electrochemically stable negative electrode with high moldability. The graphite material of the present invention and the 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 obtained negative electrode mixture paste is used as a paste. Generally, after applying to the current collector, the solvent is removed, and solidification and / or shaping is performed by pressing or the like. That is, first, the graphite material of the present invention is 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.

  More specifically, a slurry obtained by mixing the graphite material 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 fluororesin powder such as polyvinylidene fluoride with a solvent such as isopropyl alcohol, N-methylpyrrolidone, dimethylformamide, etc., using a known stirrer, mixer, kneader, kneader, etc. A negative electrode mixture paste is prepared by stirring and mixing. 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 graphite material 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 used in the present invention, 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, 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, dimethyl Sulfoxide, 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 of the present invention, 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 of the present invention, a gel electrolyte can also be used.

  A lithium ion secondary battery using a polymer electrolyte is generally referred to as a polymer battery, and includes a negative electrode using the graphite material 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.

  Furthermore, the structure of the lithium ion secondary battery of 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. Can do. 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. 2 was produced and 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 graphite precursor and the graphite material were measured by the following methods.
The aspect ratio of the graphite precursor and the graphite material is an average value measured for 100 pieces with a magnification by which the shape can be confirmed by observation with a scanning electron microscope.
The average particle diameter in terms of volume of the graphite precursor and the graphite material is a particle diameter at which the cumulative frequency of the particle size distribution measured by a laser diffraction particle size distribution meter is 50% by volume.
The lattice spacing d ₀₀₂ of the graphite material was determined by the X-ray diffraction method described above.
The specific surface area of the graphite material was determined by the BET method using nitrogen gas adsorption.
The height h and the base length g and the height h and the base length g of the graphite material are measured by a magnification capable of confirming the shape by cross-sectional observation with a scanning electron microscope. The average value of the ratio h / g of h to the base length g was determined. The average value of h / g was the average value of 100 h / g values obtained for each ridge.
The “magnification that can be confirmed” here is usually about 3000 times. The base referred to in the present application is a virtual flat section in which the corresponding ridge contacts the base material, and the base length (g) is the longest virtual straight line connecting two points on the outer periphery of the virtual flat section. is there. Further, the height (h) of the bulge is the highest vertical height from the base (the virtual plane section).

  The number of bumps of the graphite material was obtained by measuring the number of bumps existing in a 10 μm square field in 10 fields of view by observation with a scanning electron microscope, and obtaining an average value.

[Example 1]
(Preparation of graphite precursor)
Mesophase microspheres (manufactured by JFE Chemical Co., Ltd., average particle size 25 μm) obtained by heat treatment of coal tar pitch were fired at 600 ° C. for 3 hours in a nitrogen atmosphere to prepare a spherical graphite precursor. The aspect ratio was 1.2.
The graphite precursor prepared by such a method is defined as a graphite precursor (1).

  In addition, as a result of observing this graphite precursor (1) with a polarizing microscope, it had a thin film-like optical isotropic phase on the surface, and the inside had an optically anisotropic phase. Further, the graphite precursor was heated at 3000 ° C. for 6 hours in a non-oxidizing atmosphere as it was, and the surface crystal structure of the graphite precursor graphitized (graphitized product) was analyzed.

  In the analysis, this was supported by a resin, and a thin film having a thickness of about 0.1 μm was formed using a focused ion beam processing apparatus (FB2000, manufactured by Hitachi, Ltd.). Next, an electron beam is irradiated to 10 places in the region (1 μm × 1 μm) near the surface of the graphitized material using a transmission electron microscope (HF2000, manufactured by Hitachi, Ltd. and JEM2010F, manufactured by JEOL Ltd.). (Pressurized voltage is 150 to 200 kV, electron beam diameter is several tens of nm), electron diffraction was performed, and crystallinity and crystallite size were measured. As a result, polycrystalline properties were recognized in 8 out of 10 locations, and it was proved to have a polycrystalline crystalline structure. The crystallite size was 60 nm (average value rounded to the nearest 10 nm).

  In addition, the size of the crystallite is obtained by observing a cross section of the crystallite with a transmission electron microscope and measuring the length of the portion exposed on the surface.

(Preparation of graphite material)
To 100 parts by mass of ferric chloride aqueous solution (acidic) corresponding to a concentration of 5% by mass in terms of iron, 100 parts by mass of the graphite precursor (1) is added, and sodium hydroxide aqueous solution is added until pH 7 Neutralized. In the obtained neutral dispersion, the precursor (1) was dispersed in a suspension of iron hydroxide: [FeO (OH)]. Subsequently, the mixture was heated to 100 ° C. to remove water, and then vacuum-dried at 150 ° C. for 5 hours to completely remove water.

  The graphite precursor having iron hydroxide scattered on the surface thus obtained is also referred to as “iron hydroxide-spotted graphite precursor” below.

  After drying, the appearance of the iron hydroxide interspersed graphite precursor was observed with a scanning electron microscope. As a result, granular and acicular iron hydroxides were scattered and adhered. Moreover, when the maximum length was measured about 50 iron compounds adhering to the surface of this iron hydroxide interspersed graphite precursor, it was 0.5 micrometer in average value.

Moreover, the iron hydroxide interspersed graphite precursor was heated at 3000 ° C. for 6 hours in a non-oxidizing atmosphere to obtain a graphite material (referred to as graphite material (1)). This graphite material had an average particle diameter of 24 μm, and had a structure having 6 hemispherical or spherical ridges / 100 μm ^{2 on} the surface of the granular graphite material ([FIG. 1]). The height h of the ridge was 3.5 μm, the base length g was 3.0 μm, and h / g was 1.2. The aspect ratio of the graphite material was 1.2, the specific surface area was 3.1 m ² / g, and the lattice spacing d ₀₀₂ was 0.3356 nm. Table 1 shows the characteristics of the graphite precursor, the graphite material, the protuberance, and the like.

In addition, although the contained element was analyzed about the obtained graphite material (1) using the ICP emission-spectral-spectroscopy apparatus, iron was not detected. Further, when the contained compound was identified by X-ray diffraction analysis of the iron hydroxide interspersed graphite precursor heated at 1490 ° C. for 4 hours in a non-oxidizing atmosphere, Fe ₃ C was detected. From this, it was confirmed that iron carbide was generated in the process of heating and graphitizing the graphite precursor (1) to which the iron compound was adhered.

(Preparation of negative electrode mixture paste)
98 parts by mass of the graphite material (1), 1 part by mass of carboxymethyl cellulose as a binder, 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) was produced.

(Production of counter electrode)
Press the lithium metal foil against the nickel net and punch it into a circular shape with a diameter of 15.5 mm to produce a current collector made of nickel net and a counter electrode consisting of a lithium metal foil (thickness 0.5 μm) in close contact with the current collector did.

(Electrolyte / Separator)
Ethylene carbonate 33 vol% - methyl ethyl carbonate 67Vol% of the mixed solvent, dissolved at a concentration of a 1 mol / dm ³ of LiPF6, was prepared a non-aqueous electrolyte solution. 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. 2 was produced as an evaluation battery.
The working electrode 12 in close contact with the current collector 17b and the counter electrode 14 in close contact with the current collector 17a were stacked with a separator 15 impregnated with electrolyte interposed therebetween. Thereafter, the exterior cup 11 and the exterior can 13 were combined so that the working electrode current collector 17 b side was accommodated in the exterior cup 11 and the counter electrode current collector 17 a side was accommodated in the exterior can 13. In that case, the insulating gasket 16 was interposed in the peripheral part of the exterior cup 11 and the exterior can 13, 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 formula (I).
Initial charge / discharge efficiency (%) = (first cycle discharge capacity / first cycle charge capacity)
× 100 (I)
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.
The current value was set to 3.6 mA, which is four times the first cycle, constant current charging was performed until the circuit voltage reached 0 mV, the charge capacity was obtained, and the rapid charge rate was calculated from the following formula (II).
Rapid charge rate = (constant current charge capacity in the second cycle / in the first cycle
Discharge capacity) x 100 (II)

(Rapid discharge rate)
Following the constant current charging in the second cycle, high-speed discharge was performed in the second cycle. After switching to constant voltage charging in the same manner 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 formula (III).
Rapid discharge rate = (discharge capacity in the second cycle / discharge capacity in the first cycle
) × 100 (III)
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 formula (IV).
Cycle characteristics = (discharge capacity in the 20th cycle / discharge in the first cycle)
Capacity) x 100 (IV)

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

(Comparative Example 1)
In Example 1, without using a metal material, only the graphite precursor (1) was directly heated to a temperature of 3000 ° C. to graphitize to prepare a graphite material (10). The obtained graphite material (10) had an average particle size of 24 μm and was a spherical particle having no bulge. The aspect ratio of the particles was 1.2, the specific surface area was 0.5 m ² / g, and the lattice spacing d ₀₀₂ was 0.3358 nm. Table 1 shows the characteristics of the graphite precursor and the graphite material.
Using the graphite material (10), 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 shown in Table 2, in the case of the graphite material (10) having no bulge on the surface, although the initial charge / discharge efficiency is high, high rapid charge / discharge characteristics and cycle characteristics cannot be obtained. Moreover, since there are few contacts between graphitized materials, the discharge capacity which graphitized materials originally have is not fully expressed, but the discharge capacity is falling.

(Example 2)
In Example 1, the method for preparing the graphite precursor was changed. The mesophase spherules were previously pulverized to obtain massive particles having an average particle size of 15 μm. This was calcined at 600 ° C. for 3 hours in a nitrogen atmosphere to obtain a massive graphite precursor. The aspect ratio of this was 1.5.
Let the graphite precursor obtained by such a method be a graphite precursor (2).
Using the graphite precursor (2), a graphite material (2) was prepared by the same method and conditions as in Example 1. The obtained graphite material (2) had an average particle diameter of 14 μm, and had a structure having 7 hemispherical or spherical bulges / 100 μm ^{2 on} the surface of the massive graphite material (2). The height h of the ridge was 2.8 μm, the base length g was 2.3 μm, and h / g was 1.2. The aspect ratio of the graphite material was 1.5, the specific surface area was 4.5 m ² / g, and the lattice spacing d ₀₀₂ was 0.3356 nm. Table 1 shows the characteristics of the graphite precursor, the graphite material, the protuberance, and the like.
Using the graphite material (2), 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 shown in Table 2, the evaluation battery obtained by using the graphite material (2) of Example 2 as the negative electrode material for the working electrode has a high discharge capacity and a high initial charge / discharge efficiency. Furthermore, it exhibits excellent rapid charge / discharge efficiency and cycle characteristics.

(Comparative Example 2)
In Example 2, without using a metal material, only the graphite precursor (2) was directly heated to a temperature of 3000 ° C. to graphitize to prepare a graphite material (20). The obtained graphite material (20) had an average particle diameter of 14 μm and was a massive particle having no bulge. The aspect ratio of the particles was 1.5, the specific surface area was 0.9 m ² / g, and the lattice spacing d ₀₀₂ was 0.3358 nm. Table 1 shows the characteristics of the graphite precursor and the graphite material.
Using the graphite material (20), a working electrode and an evaluation battery were produced under the same method and conditions as in Example 2, and a charge / discharge test was performed. The evaluation results of the battery characteristics are shown in Table 2.
As shown in Table 2, in the case of the graphite material (20) having no bulge on the surface, high rapid charge / discharge characteristics and cycle characteristics cannot be obtained. Moreover, the discharge capacity is also reduced.

(Example 3)
In Example 1, the method for preparing the graphite precursor was changed. The coal tar pitch was directly baked at 600 ° C. for 3 hours in a nitrogen atmosphere to obtain a bulk mesophase. This was pulverized to prepare a massive or scale-like graphite precursor having an average particle diameter of 25 μm.

  Next, 100 g of this graphite precursor and 5 g of a phenol resin (residual rate after graphitization of 40% by mass) are immersed in a mixture of 100 g of ethylene glycol and 0.5 g of hexamethylenetetramine, and the mixture is stirred under reduced pressure ( 1.3 Pa) at 150 ° C., ethylene glycol as a medium was removed, and a graphite precursor coated with a resin was obtained. This resin-coated graphite precursor (3) was heat-treated in air at 270 ° C. for 5 hours to cure the resin. The aspect ratio of the resin-coated graphite precursor (3) thus obtained was 2.8.

  As a result of observing this resin-coated graphite precursor (3) with a polarizing condylar microscope, it has a thin film-like optical isotropic phase on the surface, and the inside has an optically anisotropic phase. Was. Further, the resin-coated graphite precursor (3) was heated in a non-oxidizing atmosphere at 3000 ° C. for 6 hours to graphitize the resin-coated graphite precursor (3), and the surface crystal structure was changed. analyzed. In the same manner as in Example 1, electron diffraction was performed at 10 locations near the surface of the graphitized material, and crystallinity and crystallite size were measured. As a result, it was found that polycrystalline properties were observed at seven locations and a polycrystalline crystal structure was obtained. The crystallite size was 30 nm when the average value was rounded to the nearest 10 nm.

Using this resin-coated graphite precursor (3), a graphite material (3) was prepared in the same manner as in Example 1, and a working electrode and an evaluation battery were prepared by the same method and conditions. Then, a charge / discharge test was conducted. The evaluation results of the battery characteristics are shown in Table 2.
As shown in Table 2, the evaluation battery obtained using the graphite material (3) of Example 3 as the negative electrode material for the working electrode has a high discharge capacity and a high initial charge / discharge efficiency. Furthermore, it exhibits excellent rapid charge / discharge characteristics and cycle characteristics.

(Comparative Example 3)
In Example 3, without using a metal material, only the resin-coated graphite precursor (3) was directly heated to a temperature of 3000 ° C. to graphitize to prepare a graphite material (30). The obtained graphite material (30) had an average particle size of 24 μm, and was a lump or scale-like particle having no bulge. The aspect ratio of the particles was 2.4, the specific surface area was 0.7 m ² / g, and the lattice spacing d ₀₀₂ was 0.3357 nm. Table 1 shows the characteristics of the graphite precursor and the graphite material.
Using the graphite material (30), a working electrode and an evaluation battery were produced under the same method and conditions as in Example 3, and a charge / discharge test was performed. The evaluation results of the battery characteristics are shown in Table 2.
As shown in Table 2, in the case of the graphite material (30) having no bulge on the surface, high initial charge / discharge efficiency, rapid charge / discharge characteristics, and cycle characteristics cannot be obtained. Moreover, the discharge capacity is also reduced.

Example 4
(Adjustment of graphite precursor)
The graphite precursor (1) prepared by the same method as in Example 1 was used.

(Preparation of graphite material)
100 parts by mass of this graphite precursor (1) and 3 parts by mass of nickel fine powder (average particle size 0.2 μm, spherical) were mixed using a Henschel mixer (Mitsui Mining Co., Ltd.). A graphite precursor (1) dispersed and adhered to the surface was obtained. Here, the stirring rotation speed of the Henschel mixer was set to 700 rpm, and mixing was performed for 30 minutes.
The thus obtained graphite precursor (1) to which nickel was adhered was heated at 3000 ° C. for 6 hours in a non-oxidizing atmosphere to obtain a graphite material (4). The obtained graphite material (4) had an average particle size of 24 μm, and had a structure having 4 hemispherical or spherical protrusions / 100 μm ^{2 on} the surface of the spherical graphite material (4). The height h of the ridge was 3.2 μm, the base length g was 3.3 μm, and h / g was 0.97. Graphite material (4) had an aspect ratio of 1.2, a specific surface area of 1.8 m ² / g, and a lattice spacing d ₀₀₂ of 0.3356 nm.
Table 1 shows the characteristics of the graphite precursor, the graphite material, and the bumps.

In addition, although the contained element was analyzed about the obtained graphite material (4) using the ICP emission-spectral-spectroscopy apparatus, nickel was not detected. In addition, when the graphite precursor (1) to which nickel was attached was heated at 1000 ° C. for 2 hours in a non-oxidizing atmosphere and the contained compound was identified by X-ray diffraction analysis, Ni ₃ C was detected. It was. Thus, it was confirmed that nickel carbide was generated in the process of graphitization by heating the graphite precursor (1) with nickel attached thereto at a temperature of 1500 ° C. or higher.

Using the graphite material (4) thus obtained, 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 shown in Table 2, the evaluation battery obtained by using the graphite material (4) of Example 4 as the negative electrode material for the working electrode has a high discharge capacity and a high charge / discharge efficiency. Furthermore, it exhibits excellent rapid charge / discharge characteristics and cycle characteristics.

(Example 5)
(Adjustment of graphite precursor)
The graphite precursor (1) prepared by the same method as in Example 1 was used.

(Preparation of graphite material)
This graphite precursor (1) is placed on the anode side stage of a DC bipolar sputtering apparatus, a 99.999% pure single crystal cobalt target is placed on the cathode side, pressure 0.5 Pa, voltage 600 V, current 0 Sputtering was performed for 3 hours under the condition of 5A.
An ultrasonic vibrator was attached to the stage on the anode side, and sputtering was performed while applying vibration to the graphite precursor (1). About the graphite precursor (1) to which the obtained cobalt adhered, cobalt was quantitatively analyzed with an ICP emission spectroscopic analyzer, and it was confirmed that it contained 7% by mass.

When the adhesion state of cobalt was observed with a scanning electron microscope, it was observed that cobalt was dispersed and adhered in a granular form. The maximum length of 50 granular cobalt adhering to the surface of the graphite precursor (1) to which cobalt adhered was measured, and the average value was 0.3 μm.
The obtained graphite precursor (1) to which cobalt was adhered was heated at 3000 ° C. for 6 hours in a non-oxidizing atmosphere to obtain a graphite material (5). The obtained graphite material (5) had an average particle diameter of 24 μm, and had a structure having 5 hemispherical or spherical protrusions / 100 μm ^{2 on} the surface of the spherical graphite material (5). The height h of the ridge was 1.8 μm, the base length g was 2.8 μm, and h / g was 0.64. The aspect ratio of the graphite material (5) was 1.2, the specific surface area was 2.5 m ² / g, and the lattice spacing d ₀₀₂ was 0.3356 nm.
Table 1 shows the characteristics of the graphite precursor, the graphite material, and the bumps.

In addition, although the contained element was analyzed about the obtained graphite material (5) using the ICP emission-spectral-analysis apparatus, cobalt was not detected. Further, when the cobalt-attached graphite precursor was heated at 1000 ° C. for 2 hours in a non-oxidizing atmosphere and the contained compound was identified by X-ray diffraction analysis, Co ₂ C was detected. From this, it was confirmed that cobalt carbide was formed in the process of depositing cobalt and heating it to a temperature of 1500 ° C. or higher for graphitization.

Using the graphite material (5) thus obtained, 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 shown in Table 2, the evaluation battery obtained using the graphite material (5) of Example 5 as the negative electrode material for the working electrode has a high discharge capacity and high charge / discharge efficiency. Furthermore, it exhibits excellent rapid charge / discharge characteristics and cycle characteristics.

(Comparative Example 4)
It was obtained by mixing 97 parts by mass of the spherical graphite material (10) obtained in Comparative Example 1 with 3 parts by mass of Ketjen Black [manufactured by Lion Corporation, EC600JD, average particle size 0.03 μm]. The raw material 23 was put into a mechanochemical processing apparatus [manufactured by Nara Machinery Co., Ltd., “hybridization system”] schematically shown in FIG. The apparatus includes a fixed drum 21, a rotating rotor 22, a raw material circulation mechanism 24 and a discharge mechanism 25, a blade 26, a stator 27, and a jacket 28. The raw material 23 is placed between the fixed drum 21 and the rotor 22. The mechanical force such as a compressive force, a shear force, and a friction force due to the difference in speed between the fixed drum 21 and the rotor 22 can be supplied to the raw material 23. A mechanical action was repeatedly imparted to the graphite material (10) and ketjen black by treating the rotary rotor 22 at a peripheral speed of 40 m / sec under a treatment time of 6 min. The graphite material (10) having ketjen black adhered to the surface by such a method is defined as a graphite material (40).
The obtained graphite material (40) had an average particle size of 24 μm, and had a structure in which fine carbonaceous particles derived from Ketjen Black had a deposit embedded in the surface of the graphite material (40). The number of deposits was 100/100 μm ² or more, and the height and base length of the deposits could not be measured because the deposit height was 0.1 μm or less. The graphite material (40) had an aspect ratio of 1.2, a specific surface area of 21.5 m ² / g, and a lattice spacing d ₀₀₂ of 0.3360 nm. Table 1 shows the characteristics of the graphite material (10), the graphite material (40), the deposits, and the like.

Using the graphite material (40), 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 shown in Table 2, there is no ridge integrated on the surface of the graphitic material (40), and when the fine carbonaceous particles are embedded to form deposits, high rapid charge / discharge efficiency and cycle Characteristics are not obtained. Moreover, since the specific surface area is excessively large, the initial charge / discharge efficiency is lowered. In addition, when the surface of the working electrode was observed with a scanning electron microscope, it was observed that a part of the fine carbonaceous particles dropped off and locally aggregated on the surface of the graphite material (40). Presumed to have fallen off during the electrode fabrication process.

(Comparative Example 5)
(Adjustment of graphite precursor)
The graphite precursor (1) prepared by the same method as in Example 1 was used.

(Preparation of graphite material)
100 parts by mass of the graphite precursor (1) was added to 100 parts by mass of an ethanol solution of iron nitrate corresponding to a concentration of 5% by mass in terms of iron, and the mixture was mixed and stirred in the liquid phase. The pressure was reduced from normal pressure to 50 Torr (= 1.3 Pa) to degas, and the solution was infiltrated into the graphite precursor (1). Subsequently, it was dried at 80 ° C. for 24 hours to completely remove ethanol. Thus, a graphite precursor (1) to which iron nitrate was adhered was obtained.

  When the appearance of the graphite precursor (1) to which the iron nitrate was adhered was observed with a scanning electron microscope, the iron compound was adhered to the surface of the graphite precursor (1) in a film form.

Next, the graphite precursor (1) to which iron nitrate was adhered was heated at 3000 ° C. for 6 hours in a non-oxidizing atmosphere to obtain a graphite material (50). The average particle diameter of the obtained graphite material (50) was 24 μm, and very fine bumps were observed on the surface of the granular graphite material (50). 2 ridges / 100 μm ^{2 were} observed, the height h was 0.4 μm, the base length g was 0.6 μm, and h / g was 0.67. The aspect ratio of the graphite material (50) was 1.2, the specific surface area was 1.0 m ² / g, and the lattice spacing d ₀₀₂ was 0.3357 nm. Table 1 shows the characteristics of the graphite precursor, the graphite material, and the bumps.

Using this graphite material (50), 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 conducted. The evaluation results of the battery characteristics are shown in Table 2.
As shown in Table 2, the graphite material of Comparative Example 5 in which the metal compound was mixed as a solution with the graphite precursor and the resulting graphite material had a bulge that did not reach the specified size on the surface thereof was used as the negative electrode material. As for the evaluation battery used for the working electrode, high rapid charge / discharge characteristics and cycle characteristics cannot be obtained.
Comparative Example 5 corresponds to the method described in Patent Document 8.

(Comparative Example 6)
(Adjustment of graphite precursor)
The following mesophase-containing pitch obtained by polycondensation of naphthalene in the presence of an HF / BF ₃ catalyst was pulverized to an average particle size of 30 μm.
[Mesophase-containing pitch]
TI (toluene insoluble content): 73% by mass
QI (quinoline insoluble content): 44% by mass
Softening point (Mettler method): 255 ° C
When the cross section of the obtained mesophase pitch was observed with a polarizing microscope, the entire region was an optically anisotropic phase. This mesophase pitch is defined as a graphite precursor (60).

With respect to the graphite material (60) obtained by heating the graphite precursor (60) as it is at 3000 ° C. for 6 hours in a non-oxidizing atmosphere, the crystal structure of the surface was subjected to electron diffraction analysis. In the same manner as in Example 1, electron diffraction was performed at 10 locations near the surface of the graphite material (60) to measure crystallinity and crystallite size.
As a result, in any case, no polycrystal was observed, and the crystal was oriented. The crystallite size was 150 nm when the average value was rounded to the nearest 10 nm.

(Preparation of graphite material)
100 parts by mass of this graphite precursor (60) and 10 parts by mass of iron oxide (average particle size 0.3 μm, granular) were mixed using a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.). A graphite precursor dispersed and adhered to the surface was obtained. Here, the stirring rotation speed of the Henschel mixer was set to 700 rpm, and mixing was performed for 30 minutes.
The iron oxide-attached graphite precursor thus obtained was heat-treated at 450 ° C. for 6 hours in a nitrogen atmosphere. Since the iron oxide-attached graphite precursor was slightly fused by the heat treatment, it was pulverized again and the particle size was adjusted to an average particle size of 30 μm. The aspect ratio of the iron oxide-attached graphite precursor after the particle size adjustment was 3.5. Subsequently, it heated at 3000 degreeC under non-oxidizing atmosphere for 6 hours, and obtained the graphite material (60). The obtained graphite material (60) had an average particle size of 29 μm, and no bumps were formed on the surface of the massive graphite material (60). The graphite material (60) had an aspect ratio of 3.5, a specific surface area of 0.9 m ² / g, and a lattice spacing d ₀₀₂ of 0.3358 nm.
Table 1 shows the characteristics of the graphite precursor and the graphite material.

Using the graphite material (60) thus obtained, 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 shown in Table 2, when there is no bulge on the surface of the graphite material, high rapid charge / discharge characteristics and cycle characteristics cannot be obtained.
Comparative example 6 corresponds to the technique described in JP-A-2001-107057.

(Comparative Example 7)
(Preparation of graphite material)
8 parts by mass of a phenol resin (residual rate after graphitization 50% by mass) is dissolved in 100 parts by mass of ethanol, and then 96 parts by mass of scaly natural graphite (average particle size 10 μm, aspect ratio 4.7) is added to obtain a liquid. The mixture was stirred in the phase (this scaly natural graphite is referred to as natural graphite (70)). The pressure was reduced from normal pressure to 1.3 Pa to degas, and the dispersion was infiltrated into natural graphite. Next, after removing ethanol at 150 ° C., the resin was cured and carbonized by heat treatment at 500 ° C. for 7 hours in a nitrogen atmosphere. Since it was slightly fused by the heat treatment, it was pulverized again and the average particle size was adjusted to 12 μm. The aspect ratio after adjusting the particle size was 4.3.
In addition, as a result of observing this resin-coated natural graphite (70) with a polarizing microscope, the surface had a thin film-like optical isotropic phase, and the inside had an optically anisotropic phase.
This resin-coated natural graphite (70) was heated at 3000 ° C. for 6 hours in a non-oxidizing atmosphere to obtain a graphite material (70). In the same manner as in Example 1, electron diffraction was performed at 10 locations near the surface of the obtained graphite material (70), and the crystallinity was measured for the crystallite size.
As a result, it was found that polycrystalline properties were observed at eight locations, and a polycrystalline crystal structure was obtained. The crystallite size was 40 nm when the average value was rounded to the nearest 10 nm.
Table 1 shows the characteristics of the graphite material (70). Furthermore, using the graphite material (70) thus obtained, 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 shown in Table 2, the evaluation battery using the working electrode as a negative electrode material obtained by coating graphite with a resin and not having a bulge that has been graphitized has high rapid charge / discharge characteristics and cycle characteristics. I can't.

(Example 6)
(Preparation of graphite material)
In Comparative Example 7, 8 parts by mass of a phenol resin (residual rate after graphitization of 50% by mass) was dissolved in 100 parts by mass of ethanol, and then 96 parts by mass of natural graphite (70) was added. A graphite material (6) is obtained in the same manner as in Comparative Example 7 except that 6 parts by mass of fine powder (Fe ₂ O ₃ , average particle size 0.3 μm, granular) is mixed, mixed and stirred in the liquid phase. It was.
Table 1 shows the characteristics of the graphite material (6). Further, using the graphite material (6) thus obtained, 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 shown in Table 2, the evaluation battery obtained using the graphite material (6) of Example 6 as the negative electrode material for the working electrode has a high discharge capacity and a high charge / discharge efficiency. Furthermore, it exhibits excellent rapid charge / discharge characteristics and cycle characteristics.

  The graphite material of the present invention can be used as a negative electrode material of a lithium ion secondary battery that contributes effectively to downsizing and high performance of the 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 graphite material of this invention. It is a schematic cross section which shows the structure of the button type evaluation battery for using for a charging / discharging test. It is a schematic diagram of the mechanochemical processing apparatus used in the comparative example. It is a schematic diagram of the cross section of the graphite material which has a protrusion.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base material of graphite material 2 Surface of graphite material 3 Ridge of graphite material 4 Wrinkle of graphite material 11 Exterior cup 12 Working electrode 13 Exterior can 14 Counter electrode 15 Electrolyte solution impregnation separator 16 Insulating gasket 17a, 17b Current collector 21 Fixed drum 22 Rotating rotor 23 Raw material 24 Raw material circulation mechanism 25 Raw material discharge mechanism 26 Blade 27 Stator 28 Jacket h Height of protrusion g Base length

Claims (16)

  A graphite material characterized by having a bulge having a height of 1 μm or more on the surface.   2. The graphite material according to claim 1, wherein an average value of a ratio (h / g) between the height h of the ridge and the base length g is 0.1 to 15. 3.   The graphite material according to claim 1 or 2, wherein an average particle diameter of the graphite material is 1 to 100 µm. Graphitic material according to claim 1, wherein the number of said raised are 2-20 / 100 [mu] m ^2.   The graphite material according to any one of claims 1 to 4, wherein the graphite material is a graphitized product of mesophase spherules.   A metal material having at least one of a property of reacting with carbon and a property of dissolving carbon is brought into contact with a precursor of a graphite material in a non-solution state to interspers the metal material with the precursor; A method for producing a graphite material, which is heated at a temperature of 1500 ° C. or higher.   The method for producing a graphite material according to claim 6, wherein the metal material is in a powder form.   The method for producing a graphite material according to claim 6 or 7, wherein after mixing the metal material and the precursor in a dispersion medium, the dispersion medium is removed, and the metal material is scattered in the precursor. .   The method for producing a graphite material according to claim 6, wherein the metal material is scattered in the precursor by a PVD method or a CVD method.   The method for producing a graphite material according to any one of claims 6 to 9, wherein the precursor has an optically isotropic crystal structure on at least a part of a surface thereof.   A metal material having at least one of a property of reacting with carbon and a property of dissolving carbon, and a carbon source material that forms an optically isotropic crystal structure at least partially after graphitization; A method for producing a graphite material, wherein the obtained mixture is attached to a precursor of a graphite material and heated at a temperature of 1500 ° C. or higher.   The said heating temperature is 1500-3300 degreeC, The manufacturing method of the graphite material in any one of Claims 6-11.   The method for producing a graphite material according to any one of claims 6 to 12, wherein the precursor is a mesophase microsphere.   The negative electrode material for lithium ion secondary batteries containing the graphite material in any one of Claims 1-5.   The negative electrode for lithium ion secondary batteries containing the negative electrode material for lithium ion secondary batteries of Claim 14.   The lithium ion secondary battery using the negative electrode for lithium ion secondary batteries of Claim 15.

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