JP5133543B2 - Method for producing mesocarbon microsphere graphitized material - Google Patents

Description

  The present invention relates to a mesocarbon microsphere graphitized product and a method for producing the same, a negative electrode material for a lithium ion secondary battery, the negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery comprising the mesocarbon microsphere graphitized product.

  In recent years, with the miniaturization or high performance of electronic devices, there is an increasing demand for increasing the energy density of batteries. In particular, lithium ion secondary batteries are attracting attention because they can achieve higher voltages than other secondary batteries, and thus achieve high energy density. A lithium ion secondary battery includes a negative electrode, a positive electrode, and an electrolytic solution (nonaqueous electrolyte) as main components.

  The negative electrode is generally composed of a current collector made of copper foil and a negative electrode material (active material) bound by a binder. Usually, a carbon material is used for the negative electrode material. As such a carbon material, for example, as described in Patent Document 1, graphite having excellent charge / discharge characteristics and high discharge capacity and potential flatness is generally used.

  Lithium ion secondary batteries installed in recent portable electronic devices are required to have excellent rapid chargeability and rapid discharge characteristics, and the initial discharge capacity does not deteriorate even after repeated charge and discharge (cycle characteristics) ) Is required.

  As a typical example of a conventional graphite-based negative electrode material, Patent Document 2 discloses a graphite particle in which a plurality of flat particles are aggregated or bonded so that their orientation planes are non-parallel, and the particles have pores. Is disclosed. Patent Document 3 discloses graphitized mesocarbon spherules made of Brooks-Taylor single crystals in which graphite basal planes are arranged in layers in a direction perpendicular to the diameter direction.

  An external appearance photograph of a typical representative mesocarbon microsphere graphitized material is shown in FIG. 6, and a cross-sectional polarization micrograph is shown in FIG. It can be seen that conventional mesocarbon spherules are close to true spheres without cracks on the surface.

  These graphite-based negative electrode materials have a random orientation of the basal plane of graphite in the active material layer, which reduces the problem of orientation as natural graphite. Compared to natural graphite, the negative electrode material of Patent Document 2 Has improved quick chargeability, rapid discharge properties, and cycle characteristics. The negative electrode material of Patent Document 3 also has improved rapid discharge properties and cycle characteristics.

  However, in order to meet the demand for higher capacity in recent years, when the density of the active material layer is increased and the discharge capacity per volume is set higher, that is, after the negative electrode material is applied to the current collector, the pressure is increased. When densified by pressing, these conventional negative electrode materials have various problems.

In the negative electrode material described in Patent Document 2, when the density of the active material layer exceeds 1.7 g / cm ³ , the composite particles are crushed, and the flat primary graphite particles constituting the composite particles are like natural graphite. It will be oriented in one direction. For this reason, the ion diffusibility of lithium ions is reduced, causing rapid chargeability, rapid discharge, and cycle characteristics to be deteriorated. In addition, the surface of the active material layer is likely to be clogged, the electrolyte permeability is lowered, the battery productivity is lowered, and the electrolyte is depleted inside the active material layer, which is also a cause of the deterioration of cycle characteristics. It has become.

  The negative electrode material of Patent Document 3 is spherical graphite particles, and the orientation of the graphite basal surface can be relatively suppressed even when the density is increased. However, since the graphite particles are dense and hard, high pressure is required to increase the density, and problems such as deformation, extension, and breakage of the copper foil as the current collector arise. In addition, the reaction area with the electrolytic solution is small. Due to these effects, particularly quick chargeability is low. The decrease in chargeability causes the electrodeposition of lithium on the negative electrode surface during charging and causes a decrease in cycle characteristics.

Thus, a negative electrode material that maintains excellent rapid chargeability, rapid discharge performance, and cycle characteristics even at high density, is soft, and can be easily densified even at a low press pressure has been desired.
Japanese Examined Patent Publication No. 62-23433 JP 2002-83587 A JP 2000-323127 A

  The purpose of the present invention, when used as a negative electrode material for a lithium ion secondary battery, reaches a high density at a low pressing pressure, has a high discharge capacity per volume, and a high density while suppressing orientation, It is an object of the present invention to provide a new graphitized material that does not impair the permeability and retention of the electrolyte, a method for producing the same, and a negative electrode material using the graphitized material.

The mesocarbon microsphere graphitized product of the present invention is characterized in that a crack is provided on the graphitized surface. Since there is a crack, it is easy to be deformed starting from the crack, and it is easy to increase the density. Moreover, when it is set as a negative electrode, it becomes easy to osmose | permeate electrolyte solution not only between graphitized materials but in graphitized materials, and the reaction area of electrolyte solution and graphitized materials increases. Moreover, since the mesocarbon microsphere graphitized material of the present invention has higher crystallinity than the conventional product, it becomes softer and more easily densified than the conventional product. In addition, since the form of the mesocarbon microsphere graphitized material of the present invention basically maintains the same spherical shape as the conventional mesocarbon microsphere graphitized material, the orientation of the graphite basal surface is comparable even if the density is increased. It can be suppressed.
The gist of the present invention is as follows.

(1) The first invention relates to the property of reacting with carbon and the property of dissolving carbon in one or more raw materials selected from coal-based and / or petroleum-based heavy oil, tars and pitches. A mesocarbon microsphere generating step of generating a mesocarbon microsphere by adding a metal material having at least one of the above properties and a thermosetting resin, and the mesocarbon microsphere generating step. A method for producing a mesocarbon small sphere graphitized product having a graphitization step of heating and graphitizing carbon small spheres, wherein the mesocarbon small sphere graphitized product has an outer circumference length ratio (L ) Having an average value of 1.2 or more, and having a cracked portion on the surface, a method for producing mesocarbon microsphere graphitized material.

(2) The second invention is the method for producing a mesocarbon microsphere graphitized product according to the first invention, wherein the metal material is attached to and / or included in the thermosetting resin .

(3) The third invention is, mesocarbon spherules according to the first or second invention features that the value of the average lattice spacing d ₀₀₂ of the mesocarbon spherules graphitized product is less than 0.3363nm Method for producing graphitized material.

(4) The fourth invention is the mesocarbon microsphere graphite according to any one of the first to third inventions , wherein the mesocarbon microsphere graphitized material is for a negative electrode of a lithium ion secondary battery. Method for producing chemicals .

The negative electrode for a lithium ion secondary battery using the mesocarbon microsphere graphitized material of the present invention as a negative electrode material does not cause deformation or breakage of the current collector even when the density of the active material layer is increased. Excellent electrolyte permeability. Since the electrolyte is likely to exist around the mesocarbon microsphere graphitized material, the diffusibility of Li ⁺ is improved. For this reason, the lithium ion secondary battery using the mesocarbon microsphere graphitized material of the present invention as a negative electrode material has a high discharge capacity per volume and good battery characteristics such as quick chargeability, rapid discharge performance, and cycle characteristics. .

Hereinafter, the present invention will be described more specifically.
A lithium ion secondary battery usually has an electrolyte solution (non-aqueous electrolyte), a negative electrode, and a positive electrode as main battery components, and these elements 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.

1. Mesocarbon small sphere graphitized material The mesocarbon small sphere graphitized material of the present invention is non-granulated, non-crushed graphite particles, and has a feature of having cracks on the surface. A schematic cross-sectional view of the mesocarbon microsphere graphitized product of the present invention is shown in FIG. FIG. 1 (a) shows a conventional mesocarbon microsphere graphitized product, and FIG. 1 (b) shows a mesocarbon microsphere graphitized product of the present invention.

  The mesocarbon small sphere graphitized material has a substantially spherical shape, but the mesocarbon small sphere graphitized material of the present invention has a spherical outer periphery and a cracked portion (dent) on the surface.

  The mesocarbon microsphere graphitized product of the present invention has a value of an outer peripheral length ratio (L) defined by the formula (1) of 1.2 or more.

Here, the outer peripheral length of the cross section of the mesocarbon microsphere graphitized material is obtained by observing the cross section of the particle at a magnification at which the shape of the particle (graphitized material) can be recognized and measuring the outer peripheral length. The average value of the outer peripheral length is an average value for arbitrary 50 or more particles.
Further, when the mesocarbon microsphere is assumed to be a true sphere, the outer peripheral length of the cross section is measured by measuring the particle diameter at which the cumulative frequency of particle size distribution is 50% by volume using a laser diffraction particle size distribution meter. The outer circumference is assumed to be a true sphere.

As will be described later, since a specific metal material is used during production, the mesocarbon microsphere graphitized product of the present invention has high crystallinity. Because of its high crystallinity, it is soft and contributes to increasing the density of the active material layer. As an index of crystallinity, average lattice spacing d ₀₀₂ of (002) plane in the X-ray wide angle diffraction of less than 0.3363 nm, it is preferable that particularly 0.3360nm or less.

Here, the average lattice spacing d ₀₀₂ of (002) plane in X-ray wide angle diffraction is a diffraction peak of (002) plane of graphite particles using CuKα ray as X-ray and using high purity silicon as a standard substance. Is calculated from the peak position. The calculation method follows the Japan Science and Technology Act (measurement method established by the 17th Committee of the Japan Society for the Promotion of Science). Specifically, “Carbon Fiber” [Sugirou Otani, 733-742 (March 1986) ), Measured by the method described in Modern Editorial Company].

  The average particle size of the mesocarbon microsphere graphitized product of the present invention is preferably 3 to 100 μm, particularly preferably 5 to 50 μm, in terms of volume average particle size. If it is 3 μm or more, the density of the active material layer can be increased, and the discharge capacity per volume is improved, and if it is 100 μm or less, quick chargeability and cycle characteristics are improved. 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.

2. Regarding the negative electrode material for lithium ion secondary battery, the negative electrode material of the present invention contains the mesocarbon microsphere graphitized product of the present invention, and the mesocarbon microsphere graphitized product of the present invention may be used alone, It may be a mixture or composite with various known negative electrode materials such as carbon materials, graphite materials, and metal materials.

  For example, graphite particles such as natural graphite and artificial graphite, or graphitizable carbonaceous materials such as mesophase microspheres, mesophase fired bodies (bulk mesophase), mesophase fibers, etc. Carbonaceous materials such as carbonaceous materials, petroleum coke, needle coke, raw coke, green coke, pitch coke, etc. can be mixed with graphitic particles formed by graphitizing coke-based carbonaceous materials at 1500 ° C or higher, preferably 2800 ° C or higher. . Also, carbonaceous materials such as amorphous hard carbon, carbonaceous particles or graphite particles containing organic substances, metals, metal compounds, etc. may be mixed.

  Examples of the case of a composite include the graphitized material of the present invention, a carbonaceous material such as a heterogeneous graphitized material, amorphous hard carbon, an organic material, a metal that forms an alloy with lithium such as Si or Sn, or a compound of the metal And the like may be combined by forms such as coating, adhesion, embedding, and inclusion.

3. Method for producing mesocarbon microsphere graphitized material Mesocarbon microspheres are produced by heat-treating coal-based and petroleum-based heavy oils, tars and pitches at 300 to 500 ° C. In the production method of the present invention, one or more raw materials selected from the above-mentioned coal-based and / or petroleum-based heavy oils, tars and pitches are further added. A metal material having at least one of a property of reacting with carbon and a property of dissolving carbon and a thermosetting resin are added.

  The metal material having at least one of the property of reacting with carbon and the property of dissolving carbon decomposes and evaporates in the graphitization step described later, and is substantially contained in the finally obtained graphitized product. Those which do not remain in are preferred.

  Examples of metal species constituting the metal material 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, and Tc. , Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, Pt, and other transition metals, Al, Ge, and the like, and B, Si, and the like. These metal materials may be a single metal or a compound. Examples of the compound include hydroxide, oxide, nitride, chloride, sulfide and the like. Such metal materials may be used alone, in combination of two or more, or may be used as two or more alloys.

  These metal materials are preferably processed into fine particles in advance and encapsulated and / or attached to the thermosetting resin. In this case, the average particle size of the fine particles is preferably 5 μm or less, particularly preferably 1 μm or less. By enclosing and / or adhering the metal material to the thermosetting resin, the surface of the graphitized material of the mesocarbon spherule can be surely cracked. The blending amount of the metal material is preferably 5 to 80% by mass based on the total amount of the metal material and the thermosetting resin.

  The thermosetting resin is preferably one that does not cause thermal decomposition, deformation, and melting as much as possible at 300 to 500 ° C., which is the formation temperature of mesophase spherules, such as urea resin, malein resin, coumarone resin, xylene resin, and phenol resin. Illustrated. The average particle diameter of the thermosetting resin is smaller than the average particle diameter of the mesophase microsphere graphitized product finally obtained. The average particle diameter is preferably 15 μm or less, particularly 1 to 10 μm. When the average particle size is more than 15 μm, the discharge capacity per mass of the mesophase microsphere graphitized product may be lowered.

  It is preferable to add 0.5 to 20% by mass of a thermosetting resin to a raw material selected from coal-based and / or petroleum-based heavy oil, tars and pitches. When the addition amount is in the range of 0.5 to 20% by mass, the mesophase microsphere graphitized material is cracked, and excellent rapid chargeability, rapid discharge property, and cycle characteristics can be exhibited. The shape of the thermosetting resin is not particularly limited, but a spherical one is particularly preferable.

  A raw material selected from coal-based and / or petroleum-based heavy oil, tars, and pitches is blended with a predetermined amount of a thermosetting resin in which a metal material is attached and / or included, and is 300 to 500 ° C., preferably Heat treatment is performed at 380 to 480 ° C. for 10 to 120 minutes. When coal tar pitch is used as the raw material, the content and particle size of the mesocarbon microspheres to be produced can be controlled by adjusting the amount of free carbon in the coal tar pitch. The content of mesocarbon microspheres in the pitch matrix is preferably controlled to 10 to 50% by mass.

  To illustrate the separation method and heat treatment method of the produced mesocarbon spherules, first, the mesocarbon spherules produced in the pitch matrix are extracted with extracted oil, and the mesocarbon spherules are separated by a method such as filtration or centrifugation. dry. Examples of the extracted oil include benzene, toluene, quinoline, tar oil, and tar heavy oil. A small amount of residual charcoal may be left on the mesophase spherules by operating the extraction conditions.

  The separated mesocarbon spherules are pre-fired directly or at 350 to 1300 ° C., and then heat-treated at 1500 to 3300 ° C. in a non-oxidizing atmosphere to graphitize. As the graphitization method, a known high-temperature furnace such as an Acheson furnace can be used.

  In graphitization, it is preferable to set the temperature so that the metal material is substantially removed by evaporation or decomposition. In addition to being unable to graphitize at temperatures below 1500 ° C., the metal material may remain and the discharge capacity may be insufficient when used as a negative electrode. When the temperature exceeds 3300 ° C., some of the graphite particles may sublime, which is not preferable because the yield decreases. Although the time required for graphitization cannot be generally stated, it is about 1 to 50 hours.

  The reason why the cracked mesophase microsphere graphitized product of the present invention can be obtained by the above-described manufacturing method is not clear, but a process in which a mixture of a thermosetting resin and a metal material is disposed inside the mesophase microsphere and heat-treated. Is expected to be involved in the generation of gases derived from volatiles and decomposition products generated from thermosetting resins, evaporation of metals constituting metal materials, or decomposition products of reaction products of metals and carbon . In addition, the metal material acts as a graphitization catalyst for mesophase spherules and / or thermosetting resins, improves the crystallinity of mesophase spherules and / or thermosetting resins, and contributes to the development of soft and high discharge capacity. It is thought that there is.

4). About the negative electrode for lithium ion secondary batteries Although the production of the negative electrode of a lithium ion secondary battery can be carried out according to a normal method of forming a negative electrode, it is possible to obtain a chemically and electrochemically stable negative electrode. The method is not limited at all.

  Moreover, the negative electrode mixture which added the binder to the said negative electrode material can be used at the time of preparation of a negative electrode. As the binder, those having chemical stability and electrochemical stability with respect to the electrolyte are preferably used. For example, fluorine-based resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene, polyvinyl alcohol, and styrene Butadiene rubber, carboxymethyl cellulose and the like are used. Moreover, these can also be used together. In general, the binder is preferably used in an amount of about 1 to 20% by mass in the total amount of the negative electrode mixture.

  As a specific example of the preparation of the negative electrode, a negative electrode mixture is prepared by mixing the particles of the negative electrode material with a binder, and this negative electrode mixture is usually applied to one or both sides of a current collector to form a negative electrode mixture. The method of forming an agent layer is mentioned.

  A normal solvent for preparing a negative electrode can be used for preparing the negative electrode. When the negative electrode mixture is dispersed in a solvent and made into a paste, and then applied to the current collector and dried, the negative electrode mixture layer is uniformly and firmly adhered to the current collector.

  More specifically, for example, the negative electrode material particles and a fluorine-based resin powder such as polyvinylidene fluoride or a water-dispersible binder such as styrene butadiene rubber, or a water-soluble binder such as carboxymethyl cellulose are used. A paste is prepared by mixing with pyrrolidone, dimethylformaldehyde or a solvent such as water or alcohol to form a slurry, and then kneading with a kneader. If this 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 can be obtained. The film thickness of the negative electrode mixture layer is 10 to 200 μm, preferably 30 to 100 μm.

  Alternatively, the negative electrode material particles can be dry-mixed with resin powders such as polyethylene and polyvinyl alcohol as a binder, and hot-press molded in a mold to produce a negative electrode. However, dry mixing requires a large amount of binder to obtain sufficient negative electrode strength, and if the binder is excessive, the discharge capacity and rapid charge / discharge characteristics of the lithium ion secondary battery may be reduced. .

  When the negative electrode mixture layer is formed and then pressure bonding such as pressurization is performed, the adhesive strength between the negative electrode mixture layer and the current collector can be further increased.

  The shape of the current collector used for the negative electrode is not particularly limited, but is preferably a foil shape or a net shape such as a mesh or expanded metal. Moreover, as a material of the said electrical power collector, copper, stainless steel, nickel, etc. are preferable. Moreover, it is preferable that the thickness of an electrical power collector shall be about 5-20 micrometers in the case of foil shape.

5. About lithium ion secondary battery Moreover, this invention is also a lithium ion secondary battery formed using the said negative electrode for lithium ion secondary batteries.
The lithium ion secondary battery of the present invention is not particularly limited except that the negative electrode is used, and other battery components are in accordance with elements of a general lithium ion secondary battery.

5.1 Cathode Material As the cathode material (positive electrode active material) used in the lithium ion secondary battery of the present invention, a lithium compound is used, but a material capable of occluding / desorbing a sufficient amount of lithium is selected. It is preferable. For example, lithium-containing transition metal oxide, transition metal chalcogenide, vanadium oxide, other lithium-containing compounds, general formula M _x Mo ₆ S _8-Y (where X is 0 ≦ X ≦ 4, Y is 0 ≦ Y) A numerical value in the range of ≦ 1, and M represents at least one kind of transition metal) can be used. Examples of the vanadium _oxide, or the like can be used those represented by _{V 2 O 5, V 6 O} 13, V 2 O 4, V 3 O 8.

The lithium-containing transition metal oxide is a composite oxide of lithium and a transition metal, and may be a solid solution of lithium and two or more transition metals. The composite oxide may be used alone or in combination of two or more. 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 _1-Y M ² _Y O ₄ (where Y is a numerical value in the range of 0 ≦ Y ≦ 1, and M ¹ and M ² are at least one transition metal element) It is. In the formula, transition metals represented by M ¹ and M ² are Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn, and the like. Preferably, Co, Mn, Cr, Ti, V, Fe, Al and the like are used. Specific 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.

  Further, the lithium-containing transition metal oxide is, for example, lithium, transition metal oxide, salts and the like as a starting material, these starting materials are mixed according to the composition of the desired metal oxide, and 600 ~ It can be obtained by firing at a temperature of 1000 ° C. The starting materials are not limited to oxides and salts, and may be hydroxides.

  In the lithium ion secondary battery of the present invention, the positive electrode active material may be used alone or in combination of two or more of the above lithium compounds. Further, an alkali carbonate such as lithium carbonate can be added to the positive electrode.

  The positive electrode is formed by, for example, applying a positive electrode mixture composed of the lithium compound, a binder, and a conductive agent for imparting conductivity to the positive electrode on one or both sides of the current collector to form a positive electrode mixture layer. Produced. As the binder, the same one as that used for producing the negative electrode can be used. As the conductive agent, a carbon material such as graphite or carbon black is used.

  Similarly to the negative electrode, the positive electrode mixture may be formed in a paste by dispersing the positive electrode mixture in a solvent, and the paste-like positive electrode mixture may be applied to a current collector and dried to form a positive electrode mixture layer. After forming the agent layer, 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.

  The shape of the current collector is not particularly limited, but is preferably a foil shape or a mesh shape such as a mesh or expanded metal. Moreover, as a material of the said electrical power collector, aluminum, stainless steel, nickel, etc. are preferable. The thickness of the current collector is preferably about 10 to 40 μm in the case of a foil shape.

5.2 Nonaqueous Electrolyte The nonaqueous electrolyte used in the lithium ion secondary battery of the present invention is an electrolyte salt used in a normal nonaqueous electrolytic solution. LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ), 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 Lithium salts such as [{C ₆ H ₃ (CF ₃ ) ₂ }] ₄ , LiAlCl ₄ , LiSiF ₆ can be used. From the viewpoint of oxidation stability, LiPF ₆ and LiBF ₄ are particularly preferable.
The electrolyte salt concentration in the electrolytic solution is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 3.0 mol / l.

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

  As a solvent for preparing the nonaqueous electrolyte solution, carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, 1,1- or 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, ethers such as anisole and diethyl ether, thioethers such as sulfolane and methylsulfolane, acetonitrile, chloronitrile, propionitrile, etc. Nitrile, trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene, benzoyl chloride, Benzoyl, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, aprotic organic solvents such as dimethyl sulfite may be used.

  When the non-aqueous electrolyte is a polymer electrolyte such as a polymer solid electrolyte or a polymer gel electrolyte, it is preferable to use a polymer gelled with a plasticizer (non-aqueous electrolyte) as a matrix. Examples of the polymer constituting the matrix include ether-based polymer compounds such as polyethylene oxide and cross-linked products thereof, polymethacrylate-based polymer compounds, polyacrylate-based polymer compounds, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene. It is particularly preferable to use a fluorine-based polymer compound such as a copolymer.

  A plasticizer is blended in the polymer solid electrolyte or polymer gel electrolyte, and the electrolyte salt or non-aqueous solvent can be used as the plasticizer. In the case of a polymer gel electrolyte, the electrolyte salt concentration in the non-aqueous electrolyte solution that is a plasticizer is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 2.0 mol / l.

  The method for producing the polymer solid electrolyte is not particularly limited. For example, a method in which a polymer compound constituting a matrix, a lithium salt, and a nonaqueous solvent (plasticizer) are mixed and heated to melt the polymer compound, organic After dissolving a polymer compound, a lithium salt, and a non-aqueous solvent (plasticizer) in a solvent, a method of evaporating an organic solvent for mixing, a polymerizable monomer, a lithium salt, and a non-aqueous solvent (plasticizer) are mixed, Examples include a method of obtaining a polymer by irradiating the mixture with ultraviolet rays, an electron beam, a molecular beam or the like to polymerize a polymerizable monomer.

  Here, the ratio of the non-aqueous solvent (plasticizer) in the solid electrolyte is preferably 10 to 90% by mass, and more preferably 30 to 80% by mass. If it is less than 10% by mass, the electrical conductivity will be low, and if it exceeds 90% by mass, the mechanical strength will be weak and film formation will be difficult.

5.3 Separator In the lithium ion secondary battery of the present invention, a separator can also be used.
Although the material of a separator is not specifically limited, For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. can be used. As a material for the separator, a microporous membrane made of synthetic resin is suitable. Among them, a polyolefin microporous membrane is suitable in terms of thickness, membrane strength, and membrane resistance. Specifically, polyethylene and polypropylene microporous membranes, or microporous membranes composed of these are suitable.

5.4 Lithium Ion Secondary Battery The lithium ion secondary battery of the present invention is composed of the negative electrode, the positive electrode, and the nonaqueous electrolyte containing the graphite material in the above-described configuration, for example, in order of the negative electrode, the nonaqueous electrolyte, and the positive electrode. It is configured by stacking and housing in a battery exterior material. Further, a non-aqueous electrolyte may be disposed outside the negative electrode and the positive electrode.

  In addition, the structure of the lithium ion secondary battery of the present invention is not particularly limited, and the shape and form thereof are not particularly limited, and are cylindrical, depending on the application, mounted equipment, required charge / discharge capacity, and the like. , Square shape, coin shape, button shape, and the like. In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to use a battery equipped with means for detecting an increase in the internal pressure of the battery and shutting off the current when an abnormality such as overcharging occurs.

In the case where the lithium ion secondary battery is a polymer solid electrolyte battery or a polymer gel electrolyte battery, a structure in which the lithium ion secondary battery is enclosed in a laminate film may be used.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. 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.

[Invention Example 1]
1 (a) Preparation of mixture of thermosetting resin and metal material 100 parts by mass of spherical phenol resin with an average particle size of 7 μm (shown in SEM photograph of the phenol resin used in FIG. 3), nickel with an average particle size of 0.2 μm 100 parts by mass of ultrafine powder was mixed, and both were integrated by a ball mill to prepare a composite in which nickel ultrafine powder was embedded on the surface of the phenol resin.

1 (b) Preparation of mesocarbon microspheres 90 parts by mass of coal tar pitch containing 1% by mass of free carbon was mixed with 10 parts by mass of the composite of the above metal material and thermosetting resin, and 450 in an inert atmosphere. Heat treatment was carried out at 30 ° C. for 30 minutes to produce 30% by mass of mesocarbon microspheres in the pitch matrix. Thereafter, the pitch matrix was dissolved and extracted from the coal tar pitch using tar oil, and the mesocarbon spherules were separated by filtration and dried at 120 ° C. in a nitrogen atmosphere. This was heat-treated at 600 ° C. for 3 hours in a nitrogen atmosphere to prepare a fired product of mesocarbon microspheres.

1 (c) Preparation of mesocarbon microsphere graphitized product The obtained mesocarbon microsphere calcined product was filled in a graphite crucible and graphitized at 3150 ° C. for 5 hours in a non-oxidizing atmosphere. Spherical graphitized material was prepared.
When the obtained mesocarbon microsphere graphitized product was analyzed, the average particle size was 22 μm, and the average lattice spacing d ₀₀₂ of the (002) plane in X-ray wide angle diffraction was 0.3358 nm.

When observed with a scanning electron microscope, as shown in the appearance photograph in FIG. 4, it was confirmed that the appearance had a true spherical shape but had cracks.
Furthermore, as shown in FIG. 5, when the cross section is observed with a polarizing microscope, it is clear that there are cracks. About 50 pieces, the outer peripheral length was measured, and the outer peripheral length ratio (L) was obtained. L) was 1.6.

1 (d) Preparation of Negative Electrode Mixture Paste 98 parts by mass of the mesocarbon microsphere graphitized material, 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 mix the negative electrode mixture paste. Was prepared.

1 (e) Production of Working Electrode The negative electrode mixture paste was applied on a copper foil having a thickness of 16 μm with a uniform thickness, and further, water in a dispersion medium was evaporated at 90 ° C. in a vacuum and dried. Next, the negative electrode mixture applied on the copper foil is pressed with a hand press at a pressure of 20 kN / cm ² (200 MPa), and then punched into a circular shape with a diameter of 15.5 mm. A working electrode 12 comprising a negative electrode mixture layer (thickness 60 μm) in close contact with was prepared. The density of the active material layer reached 1.80 g / cm ³ . The density was measured as follows.

The average thickness was measured using a micrometer whose contact portion was a mirror surface having a diameter of 5 mm at the end portion and the central portion of the working electrode, and the thickness of the copper foil was reduced to determine the thickness of the negative electrode mixture. Next, the mass of the negative electrode mixture was determined by subtracting the mass of the copper foil of the same size from the mass of the working electrode.
The density was calculated from equation (2).

1 (f) Production of counter electrode Lithium metal foil was pressed against a nickel net, punched into a circular shape with a diameter of 15.5 mm, and a current collector made of nickel net, and a lithium metal foil (thickness 0) adhered to the current collector 0.5 mm) was prepared.

1 (g) Production of Electrolytic Solution and Separator LiPF ₆ was dissolved at a concentration of 1 mol / l in a mixed solvent of ethylene carbonate 33 vol% -methylethyl carbonate 67 vol% to prepare a nonaqueous electrolytic solution. The obtained nonaqueous electrolytic solution was impregnated into a polypropylene porous body (thickness 20 μm) to produce a separator impregnated with the electrolytic solution.

1 (h) Production of Evaluation Battery A button type secondary battery shown in FIG. 2 was produced as an evaluation battery.
The exterior cup 1 and the exterior can 3 were sealed by interposing an insulating gasket 6 at the peripheral portion thereof and caulking both peripheral portions. Inside, in order from the inner surface of the outer can 3, a current collector 7 a made of nickel net, a cylindrical counter electrode (positive electrode) 4 made of lithium foil, a separator 5 impregnated with an electrolyte, and a disk-like made of a negative electrode mixture A battery system in which a working electrode (negative electrode) 2 and a current collector 7b made of copper foil are laminated.

  In the evaluation battery, the separator 5 impregnated with the electrolytic solution was stacked between the working electrode 2 in close contact with the current collector 7b and the counter electrode 4 in close contact with the current collector 7a, and then the working electrode 2 was attached to the exterior cup. 1, the counter electrode 4 is accommodated in the outer can 3, the outer cup 1 and the outer can 3 are combined, and an insulating gasket 6 is interposed between the outer peripheral portion of the outer cup 1 and the outer can 3. The part was crimped and sealed.

The evaluation battery is a battery composed of a working electrode 2 containing graphite particles that can be used as a negative electrode active material in a real battery and a counter electrode 4 made of a lithium metal foil.
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 discharge capacity per mass, discharge capacity per volume, rapid charge rate, rapid discharge rate, and cycle characteristics. . The evaluation results are shown in Table 1.

1 (i) Evaluation of discharge capacity per mass and discharge capacity per volume After constant-current charging at 0.9 mA until the circuit voltage reaches 0 mV, switching to constant-voltage charging is continued until the current value reaches 20 μA. It was. The charge capacity per mass was determined from the energization amount 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 per mass was determined from the amount of electricity supplied during this period. This was the first cycle.

  The discharge capacity per volume was calculated from equation (3).

  The reason why 0.98 is multiplied by the expression (3) is because it contains a binder (2% by mass) that does not contribute to the battery capacity.

1 (j) Rapid charge rate and rapid discharge rate evaluation circuit Until the circuit voltage reaches 0 mV, the current value is set to 3.6 mA, which is four times the first cycle, and then the constant current charge is performed. The battery was fully charged until the value reached 20 μA. Then, it rested for 120 minutes. Next, the current value was set to 14.4 mA, 16 times the first cycle, and constant current discharge was performed until the circuit voltage reached 1.5V. From the obtained constant current charging capacity, the rapid charging rate was determined by the equation (4). Moreover, the rapid discharge rate was calculated by the formula (5) from the obtained discharge capacity.

Evaluation of 1 (k) cycle characteristics An evaluation battery different from the evaluation battery evaluated for the discharge capacity per mass, the rapid charge rate, and the rapid discharge rate was prepared 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 per mass using Equation (6).

  As shown in Table 1, the evaluation battery obtained using the negative electrode material of Inventive Example 1 as the working electrode can increase the density of the active material layer and has a high discharge capacity per mass. For this reason, the discharge capacity per volume can be improved significantly. Even at the high density, the rapid charge rate, rapid discharge rate, and cycle characteristics maintain excellent values.

[Comparative Example 1]
In Example 1 of the present invention, mesocarbon microsphere graphitized material was prepared in the same manner as Example 1 except that the thermosetting resin and the metal material were not blended.

Finally mesocarbon spherules graphitized product obtained had an average particle diameter of 23 .mu.m, the average lattice spacing d ₀₀₂ of (002) plane in the X-ray wide angle diffraction was 0.3363 nm. When observed with a scanning electron microscope, it was almost spherical, and as a result of observing the cross section with a polarizing microscope, there was no crack, and the average value of the actual contour length with respect to the spherical outer circumference was 1.0.

Using this graphitized product, a working electrode and an evaluation battery were produced under the same method and conditions as in Invention Example 1, and a charge / discharge test was performed. The evaluation results of the battery characteristics are shown in Table 1.
The packing density reached only 1.65 g / cm ³ .

  As shown in Table 1, when mesocarbon microsphere graphitized material of the prior art is used as the negative electrode material for the working electrode, the density cannot be increased and the discharge capacity per volume is insufficient. Become. In addition, the rapid charging rate is insufficient.

[Comparative Example 2]
Using the mesocarbon microsphere graphitized material produced in Comparative Example 1, a working electrode and an evaluation battery were produced in the same manner and under the same conditions as in Invention Example 1, but the negative electrode mixture coated on the copper foil was hand-held. During the pressing, the pressing pressure was increased until the same packing density (1.80 g / cm ³ ) as Example 1 was reached.

As a result, the packing density reached 1.80 g / cm ³ by applying a pressure of 35 kN / cm ² (350 MPa), but wrinkles were formed on the copper foil. The obtained working electrode was subjected to the same charge / discharge test as Example 1 of the present invention. The evaluation results of the battery characteristics are shown in Table 1.

  As shown in Table 1, when the mesocarbon microsphere graphitized material of the prior art is used as the negative electrode material for the working electrode and the press pressure is increased to increase the packing density, the deformation of the copper foil as the current collector is changed. In addition, the rapid discharge rate and cycle characteristics are greatly reduced.

[Invention Examples 2 to 5]
A mesocarbon microsphere graphitized product was prepared in the same manner as in Invention Example 1 except that the amount of the thermosetting resin and the kind and amount of the metal material were changed.
Using this graphitized product, a working electrode and an evaluation battery were produced under the same method and conditions as in Example 1, and a charge / discharge test was performed. The evaluation results of the battery characteristics are shown in Table 1.

  As shown in Table 1, when the negative electrode material made of the mesocarbon microsphere graphitized material of the present invention was used for the working electrode, the discharge capacity per volume was high, and the rapid charge rate, rapid discharge rate, and cycle characteristics were also high. A good lithium ion secondary battery can be obtained.

[Comparative Example 3]
As the negative electrode material, scaly natural graphite having an average particle diameter of 10 μm was used. Average lattice spacing d ₀₀₂ of the X-ray wide angle diffraction (002) plane was 0.3357Nm.
Using this natural graphite, a working electrode and an evaluation battery were produced under the same method and conditions as in Example 1, and a charge / discharge test was conducted. The evaluation results of the battery characteristics are shown in Table 1.

The packing density reached 1.80 g / cm ³ when pressed at 13 kN / cm ² (130 MPa). A working electrode was prepared at a packing density of 1.80 g / cm ³ . As shown in Table 1, when natural graphite as a negative electrode material is used for the working electrode, the discharge capacity per volume is high, but the rapid charge rate, rapid discharge rate, and cycle characteristics are extremely low. It becomes.

  The mesocarbon microsphere graphitized product of the present invention can be used as a negative electrode material for a lithium ion secondary battery that contributes effectively to downsizing and high performance of the mounted equipment. Further, since the graphitized product has conductivity, it can be mixed with a resin or the like as a conductive material.

It is a schematic cross section of a mesocarbon microsphere graphitized material. (A) is a conventional product, and (b) is a product of the present invention. It is a schematic cross section which shows the structure of the button type evaluation battery for using for a charging / discharging test. It is a SEM photograph which shows the external appearance of the spherical phenol resin used by the example of this invention. It is a SEM photograph which shows the external appearance of the mesocarbon microsphere graphitized material of this invention. It is a polarization microscope photograph of the section of mesocarbon microsphere graphitized material of the present invention. It is a SEM photograph which shows the external appearance of the conventional mesocarbon microsphere graphitized material. It is a polarizing microscope photograph of the cross section of the conventional mesocarbon microsphere graphitized material.

Explanation of symbols

1 exterior cup 2 working electrode (negative electrode)
3 Exterior can 4 Counter electrode (positive electrode)
5 Separator 6 Insulating gasket 7a, 7b Current collector

Claims (4)

Metal having at least one of the property of reacting with carbon and the property of dissolving carbon in one or more raw materials selected from coal-based and / or petroleum-based heavy oil, tars and pitches A material and a thermosetting resin are added and heated to produce mesocarbon spherules, and the mesocarbon spherules obtained in the mesocarbon spherule production step are heated to produce graphite. A mesocarbon small sphere graphitized product having a graphitization step to be converted, wherein the mesocarbon small sphere graphitized product has an average outer peripheral length ratio (L) defined by the formula (1) of 1.2 or more. And a method for producing a mesocarbon microsphere graphitized material having a crack portion on the surface .
(Equation 1)
Peripheral length ratio (L) = (peripheral length of cross section of mesocarbon microsphere graphitized material) / (mesocarbon
Perimeter length of cross section assuming small sphere as true sphere) (1) The method for producing a mesocarbon microsphere graphitized product according to claim 1 , wherein the metal material is attached to and / or included in the thermosetting resin. Method for producing mesocarbon spherules graphitized product according to claim 1 or 2, characterized in that the value of the average lattice spacing d ₀₀₂ of the mesocarbon spherules graphitized product is less than 0.3363 nm. The method for producing a mesocarbon microsphere graphitized product according to any one of claims 1 to 3, wherein the mesocarbon microsphere graphitized product is used for a negative electrode of a lithium ion secondary battery.