WO2015146899A1 - Negative electrode carbon material for lithium secondary cell, negative electrode for lithium cell, and lithium secondary cell - Google Patents

Negative electrode carbon material for lithium secondary cell, negative electrode for lithium cell, and lithium secondary cell Download PDF

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WO2015146899A1
WO2015146899A1 PCT/JP2015/058706 JP2015058706W WO2015146899A1 WO 2015146899 A1 WO2015146899 A1 WO 2015146899A1 JP 2015058706 W JP2015058706 W JP 2015058706W WO 2015146899 A1 WO2015146899 A1 WO 2015146899A1
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carbon material
negative electrode
lithium secondary
secondary battery
lithium
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PCT/JP2015/058706
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French (fr)
Japanese (ja)
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騫 程
田村　宜之
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日本電気株式会社
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Priority to JP2016510329A priority Critical patent/JP6575509B2/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a negative electrode carbon material for a lithium secondary battery, a negative electrode for a lithium secondary battery, and a lithium secondary battery.
  • Lithium secondary batteries have been widely put into practical use as batteries for small electronic devices such as notebook computers and mobile phones because of their advantages such as high energy density, low self-discharge and excellent long-term reliability. In recent years, advanced functions of electronic devices and use in electric vehicles have progressed, and development of lithium secondary batteries with higher performance has been demanded.
  • carbon materials are generally used as negative electrode active materials for lithium secondary batteries, and various carbon materials have been proposed for improving battery performance.
  • Carbon materials include high crystalline carbon such as natural graphite and artificial graphite, low crystalline carbon such as graphitizable carbon (soft carbon) and non-graphitizable carbon (hard carbon), and amorphous carbon (amorphous). Carbon) is known. It is known that graphite, which is highly crystalline carbon, is excellent in reactivity with Li ions and has a capacity close to the theoretical capacity value. On the other hand, highly crystalline carbon easily reacts with propylene carbonate (PC), which is frequently used as a solvent for the electrolytic solution, thereby causing deterioration in charge rate characteristics due to deterioration of the electrolytic solution.
  • PC propylene carbonate
  • Low crystalline carbon and amorphous carbon have a theoretical capacity value that is higher than the theoretical capacity value of graphite, but the reactivity with Li ions is low and long-time charging is required. Lower. On the other hand, the reactivity with PC is low, and the deterioration of the electrolytic solution is small. Therefore, a composite carbon material combining graphite and amorphous carbon (including low crystalline carbon) has been proposed.
  • Patent Document 1 discloses a negative electrode active material in which amorphous carbon is adhered to the surface of graphite particles.
  • the graphite particles are oxidized to generate oxygen-containing functional groups on the surface of the graphite particles, and the surface of the graphite particles is roughened. It is disclosed.
  • Patent Document 1 discloses a method in which air oxidation is performed at a temperature of 200 ° C. to 700 ° C., and heat treatment is performed at 300 ° C. to 700 ° C. after alkali is attached to the surface of the graphite particles.
  • the negative electrode made of a carbon material has a reduced input characteristic and life when the amount of reaction with Li ions increases.
  • the tendency of graphite is remarkable, and the capacity at a high rate is small.
  • low crystalline carbon materials such as soft carbon and hard carbon have higher input characteristics than graphite, but their initial capacity is smaller than that of graphite. Therefore, there is a demand for a negative electrode material that has a large amount of reaction with Li ions, has better input characteristics and cycle life, and is inexpensive.
  • An object of the present invention is to solve the above-described problems, that is, a negative electrode carbon material from which a lithium secondary battery with improved charge rate characteristics as an index of input characteristics and cycle life can be obtained, and the same are used.
  • the object is to provide a negative electrode for a lithium secondary battery and a lithium secondary battery.
  • low crystalline carbon such as pitch coke is used instead of graphite, and a material in which pores are formed on the surface by heat treatment in an oxidizing atmosphere is used as the negative electrode material.
  • a negative electrode carbon material for a lithium secondary battery comprising a low crystalline carbon material having pores formed on the surface thereof, wherein the pore size is in the range of 20 nm to 1 ⁇ m.
  • a negative electrode carbon material for a secondary battery is provided.
  • the negative electrode for lithium secondary batteries containing said negative electrode carbon material is provided.
  • a lithium secondary battery including the negative electrode is provided.
  • the embodiment of the present invention it is possible to provide a negative electrode carbon material from which a lithium secondary battery with improved charge rate characteristics can be obtained, and a negative electrode for a lithium secondary battery and a lithium secondary battery using the same.
  • a negative electrode carbon material for a lithium secondary battery according to an embodiment of the present invention is made of a low crystalline carbon material, a carbon material called so-called soft carbon or hard carbon, and has a predetermined pore on the surface, thereby reducing the normal low-carbon material.
  • the holes include those formed in a groove shape.
  • This low crystalline carbon material having pores includes a crystalline graphite-like structure (a graphene laminated structure, hereinafter referred to as a graphene layer), and at least a plurality of pores are formed in the graphene layer on the surface side.
  • holes are formed in a plurality of graphene layers from the surface to the inside. These vacancies can pass lithium ions (Li ions) and function as a Li ion path (Li path) into the graphene layer.
  • Li path Li ion path
  • the Li path into the graphene layer of Li ions is almost limited to the path from the edge surface side of the graphene layer, and further to the back of the graphene layer (the center in the plane direction of the graphene layer) As the distance is long, and the amount of reaction with lithium increases, the charge rate characteristics deteriorate.
  • the graphene layer plane (basal surface) has holes that function as the Li path, so the Li path increases, and The path to the back of the graphene layer is shortened. As a result, the charge rate characteristics of the lithium secondary battery can be improved.
  • Such vacancies are preferably also formed in the graphene layer plane inside the surface-side graphene layer, and more preferably at least from the surface layer toward the inside. Holes can be formed in all graphene layers constituting the low crystalline carbon material. In addition, holes can be formed so as to penetrate a plurality of graphene layers. By forming such vacancies, a Li path reaching the inside in the stacking direction of the graphene layer (direction perpendicular to the graphene layer plane) is formed, and the charge rate characteristics can be further improved.
  • the pores in the plane of the graphene layer inside can be observed with an electron microscope such as TEM or SEM by cutting the low crystalline carbon material by various methods to obtain a cross section.
  • the opening size of these vacancies is not particularly limited as long as lithium ions can pass therethrough and the characteristics of the carbon material are not greatly deteriorated by vacancy formation, but it is preferably 20 nm or more, preferably 50 nm or more. More preferably, it is more preferably 100 nm or more. Further, from the viewpoint of not deteriorating the characteristics of the carbon material, the opening size is preferably 1 ⁇ m or less, more preferably 800 nm or less, and even more preferably 500 nm or less.
  • the “opening size” means the maximum length (maximum opening size) of the opening, and corresponds to the diameter of a circle having the smallest area that can accommodate the outline of the opening.
  • the opening size (minimum opening size) corresponding to the diameter of the circle with the largest area that can exist inside the outline of the hole opening is also preferably 20 nm or more, and more preferably 50 nm or more. More preferably, it is more preferably 100 nm or more.
  • the number density of holes having such an opening size is preferably in the range of 1 to 50 / ⁇ m 2 . It is preferable that pores having a number density in this range are formed at least in the surface layer. If the number density of vacancies is too low, a sufficient charge rate characteristic improvement effect cannot be obtained, and conversely, if the number density of vacancies is too high, the specific surface area becomes too large and side reactions during charge and discharge are likely to occur. Charge / discharge efficiency may decrease.
  • the number density of holes is selected from 10 1 ⁇ m ⁇ 1 ⁇ m areas on the surface of an electron microscope image of the surface of a low crystalline carbon material, and the number of holes having an opening size of 20 nm or more in each area is counted.
  • the vacancies are preferably formed over the entire surface of the carbon material, and more preferably uniformly distributed.
  • the interval between the plurality of holes is preferably in the range of 100 nm to 1 ⁇ m.
  • graphitizable carbon is preferable, and among them, petroleum pitch coke, coal pitch coke, mesophase pitch coke, etc. More preferably, pitch coke is used.
  • Pitch coke is obtained by charging soft pitch into a delayed coker and dry-distilling (carbonizing), and then calcining with a rotary kiln to form calcined pitch coke.
  • artificial graphite can be obtained by heat-treating these pitch cokes at 1500 ° C. or higher, particularly 2000 to 3300 ° C. In the present invention, pitch coke obtained at a lower cost than artificial graphite is used.
  • heat treatment is performed in an oxidizing atmosphere in the present invention.
  • the heat treatment in an oxidizing atmosphere is performed at a temperature lower than the ignition temperature of low crystalline carbon. If it ignites, temperature control becomes impossible by combustion of a carbon material, and it becomes difficult to form a desired hole.
  • the ignition temperature varies depending on the composition of the low crystalline carbon, the heat treatment temperature can usually be selected from the range of 350 to 800 ° C. under normal pressure.
  • the heat treatment time is in the range of about 30 minutes to 24 hours.
  • the oxidizing atmosphere include oxygen, carbon dioxide, and air. Also, the oxygen concentration and pressure can be adjusted as appropriate.
  • the opening size, number density, and distribution of pores can be controlled by heat treatment conditions such as heat treatment temperature, heat treatment time, and oxidizing atmosphere.
  • the vacancies thus formed on the surface of the carbon material are different from the voids inherent to the low crystalline carbon (voids between primary particles, defects, voids and cracks near the edges). Even when ordinary low crystalline carbon having voids is used for the negative electrode, the charge rate characteristics of the lithium secondary battery are low. Also, a treatment for roughening the surface of the low crystalline carbon (for example, a treatment of irradiating ultrasonic waves after immersing the low crystalline carbon in an alkaline solution) may be performed, and the low crystalline carbon after such treatment may be used for the negative electrode. The charge rate characteristics of lithium secondary batteries are low.
  • the chemical activation and gas activation methods used in the production of activated carbon expand the voids created by carbonization, open closed pores, and add more pores in the voids. Even if such normal activation treatment is performed on low crystalline carbon, it is difficult to obtain a lithium secondary battery having desired charge rate characteristics.
  • the highly crystalline graphene layer is preferentially oxidized, and the amorphous structure portion serves as a protective layer for protecting the graphene layer.
  • pores isolated from each other are formed on the surface of the carbon material. When graphite is oxidized, it does not become such a hole isolated from each other but forms a continuous groove (channel), which is clearly different.
  • lithium since it is possible to form vacancies in the surface layer without significantly degrading the structure of the low crystalline carbon, lithium does not significantly impair the battery characteristics due to the inherent characteristics of the low crystalline carbon.
  • the charge rate characteristics of the secondary battery can be improved.
  • the low crystalline carbon material after the vacancy formation according to the present embodiment example can have a structure and physical properties corresponding to the low crystalline carbon of the raw material.
  • the plane distance d 002 of the (002) plane of the low crystalline carbon material according to the present embodiment is preferably 0.350 nm or less, and more preferably 0.347 nm or less.
  • the surface spacing d 002 is greater than the typical graphite is usually, 0.340 nm or more.
  • This interplanar distance d 002 can be obtained by an X-ray diffraction method (X-Ray Diffraction: XRD).
  • the graphene layer contained in the low crystalline carbon material is much smaller in size than graphite.
  • the size of the graphene layer is represented by an average network size (the number of hexagonal meshes) based on a benzene ring obtained by the Diamond method.
  • the low crystalline carbon material according to the present embodiment is smaller than the raw low crystalline carbon material. Is also characterized in that the average mesh size increases. In the present invention, the average mesh size is preferably 60 or more.
  • a particulate material can be used from the viewpoint of filling efficiency, mixing property, moldability, and the like.
  • the particle shape include a spherical shape, an elliptical spherical shape, and a scale shape (flakes).
  • a general spheroidizing treatment may be performed.
  • the average particle size of the low crystalline carbon material according to the present embodiment is preferably 1 ⁇ m or more, more preferably 2 ⁇ m or more, and further preferably 5 ⁇ m or more from the viewpoint of suppressing side reactions during charging and discharging to suppress a decrease in charging and discharging efficiency.
  • it is preferably 40 ⁇ m or less, more preferably 35 ⁇ m or less, and even more preferably 30 ⁇ m or less from the viewpoints of input / output characteristics and electrode production (smoothness of the electrode surface).
  • the average particle diameter means the particle diameter (median diameter: D 50 ) at an integrated value of 50% in the particle size distribution (volume basis) by the laser diffraction scattering method.
  • the BET specific surface area (based on measurement at 77 K by the nitrogen adsorption method) of the low crystalline carbon material according to the present embodiment example is 10 m 2 / from the point of suppressing side reactions at the time of charge and discharge and suppressing a decrease in charge and discharge efficiency. Less than g is preferable, and 5 m 2 / g or less is more preferable. On the other hand, from the viewpoint of obtaining sufficient input / output characteristics, the BET specific surface area is preferably 0.5 m 2 / g or more, and more preferably 1 m 2 / g or more.
  • the low crystalline carbon material according to this embodiment preferably has a discharge capacity of 240 mAh / g or more in charge / discharge at a lithium potential of 0 to 2 V, and a charge / discharge efficiency of 75% or more.
  • charging / discharging efficiency means the value shown in at least initial charging / discharging at room temperature.
  • the low crystalline carbon material according to the present embodiment has a feature that the discharge capacity is increased by the formation of a lithium path as compared with the raw low crystalline carbon material.
  • the low crystalline carbon material according to the present embodiment may form a metal that can be alloyed with Li or its oxide on the surface and in the pores.
  • This metal or metal oxide can react with lithium and is electrochemically active in charging / discharging of a lithium secondary battery.
  • a metal or metal oxide at least one metal selected from the group consisting of Si, Ge, Sn, Pb, Al, Ga, In, and Mg, or an oxide thereof can be used.
  • Such a metal or metal oxide is preferably formed around the pores formed in the low crystalline carbon material.
  • the reaction capacity can be increased by forming such a metal or metal oxide.
  • the metal or metal oxide since the metal or metal oxide is formed around the vacancies, the metal or metal oxide can be strongly bonded to the graphene layer around the vacancies compared to other sites, and there are Li reaction sites that are excellent in reversibility.
  • the reaction volume can be increased.
  • Examples of such a metal or metal oxide forming method include CVD, sputtering, electrolytic plating, electroless plating, and hydrothermal synthesis.
  • the content of metal or metal oxide in the negative electrode carbon material according to the present embodiment is preferably 0.1 to 30% by mass with respect to the low crystalline carbon material. If the content is too small, sufficient content effects cannot be obtained. If the content is too large, the volume or shrinkage of the metal or metal oxide during charge / discharge is large, and the low crystalline carbon material deteriorates. It becomes easy.
  • the low crystalline carbon material according to this embodiment can be coated with amorphous carbon.
  • the amorphous carbon can suppress the side reaction between the low crystalline carbon material and the electrolytic solution, the charge / discharge efficiency can be improved, and the reaction capacity can be increased.
  • the low crystalline carbon material in which the metal which can be alloyed with the above-mentioned lithium (Li), or its oxide was formed in the surface can also be coat
  • amorphous carbon does not mean only a material that is not completely crystalline, but means a material that has a lower degree of crystallinity (graphitization degree) than a raw material low-crystalline carbon material. . In general, it is a material with extremely low crystallinity called amorphous carbon. Further, it is a material that can be formed by the following method.
  • Examples of the method for coating amorphous carbon on the low crystalline carbon material include hydrothermal synthesis, CVD, and sputtering.
  • the amorphous carbon coating by the hydrothermal synthesis method can be performed, for example, as follows. First, powder of a low crystalline carbon material in which pores are formed is immersed in a carbon precursor solution and mixed. It is treated in a hydrothermal reactor at 180 ° C. for 3 hours, and then vacuum filtered to separate the powder. Next, the separated powder is heat-treated in an inert atmosphere. The powder agglomerates are then pulverized to the desired particle size. Also, amorphous carbon is coated on the low crystalline carbon material before forming vacancies, and then heat-treated in an oxidizing atmosphere to form continuous vacancies in amorphous carbon and low crystalline carbon. You can also.
  • the carbon precursor solution various sugar solutions can be used, and an aqueous sucrose solution is particularly preferable.
  • the sucrose concentration of this aqueous solution can be set to 0.1 to 6M, and the immersion time can be set to 1 minute to 24 hours.
  • the heat treatment can be performed at 400 to 1200 ° C. for 0.5 to 24 hours in an inert atmosphere such as nitrogen or argon.
  • a negative electrode carbon material for a lithium secondary battery obtained by heat-treating pitch coke at a temperature selected from the range of 350 to 800 ° C. in an oxidizing atmosphere
  • the (002) plane spacing d 002 is 0.340 or more and 0.350 nm or less
  • the intensity ratio of the D peak reflecting irregularity to the G peak reflecting the graphite structure in Raman spectroscopy (I D / I G
  • a negative electrode carbon material for a lithium secondary battery having a ratio of less than 0.8 and a mass fraction of the graphene laminated structure of 66% or more is provided. It is preferable to use calcined pitch coke as the pitch coke.
  • the mass fraction of the graphene stacked structure is preferably 70% or more.
  • the negative electrode carbon material of the present embodiment example preferably has various characteristics similar to those of the above-described embodiment example, and can be subjected to the same amorphous carbon coating treatment as that of the above-described embodiment example.
  • the initial capacity and the initial efficiency are not necessarily improved.
  • the Li path increases, and the graphene layer has As a result of the shorter path leading to the back, the charge rate characteristics of the lithium secondary battery can be advantageously improved.
  • the low crystalline carbon material described above can be applied to the negative electrode active material of a lithium ion secondary battery, and the lithium ion secondary battery having improved charge rate characteristics by using this low crystalline carbon material as the negative electrode active material. Can be provided.
  • a negative electrode for a lithium ion secondary battery can be prepared, for example, by forming a negative electrode active material layer including a negative electrode active material made of this low crystalline carbon material and a binder on a negative electrode current collector.
  • This negative electrode active material layer can be formed by a general slurry coating method.
  • a negative electrode can be obtained by preparing a slurry containing a negative electrode active material, a binder, and a solvent, applying the slurry onto a negative electrode current collector, drying, and pressing as necessary.
  • Examples of the method for applying the negative electrode slurry include a doctor blade method, a die coater method, and a dip coating method.
  • a negative electrode can be obtained by forming a thin film of aluminum, nickel, or an alloy thereof as a current collector by a method such as vapor deposition or sputtering.
  • the binder for the negative electrode is not particularly limited, but polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene.
  • NMP N-methyl-2-pyrrolidone
  • water carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, and polyvinyl alcohol can be used as a thickener.
  • the content of the binder for the negative electrode is preferably in the range of 0.1 to 30 parts by mass with respect to 100 parts by mass of the negative electrode active material, from the viewpoints of binding force and energy density that are in a trade-off relationship.
  • the range of 0.5 to 25 parts by mass is more preferable, and the range of 1 to 20 parts by mass is more preferable.
  • the negative electrode current collector is not particularly limited, but copper, nickel, stainless steel, molybdenum, tungsten, tantalum and an alloy containing two or more of these are preferable from the viewpoint of electrochemical stability.
  • Examples of the shape include foil, flat plate, and mesh.
  • the lithium ion secondary battery by embodiment of this invention contains the said negative electrode, a positive electrode, and electrolyte.
  • a positive electrode for example, a slurry containing a positive electrode active material, a binder, and a solvent (and a conductive auxiliary material if necessary) is prepared, applied to the positive electrode current collector, dried, and pressurized as necessary.
  • a positive electrode active material layer can be formed on the positive electrode current collector.
  • lithium complex oxide lithium iron phosphate, etc.
  • the lithium composite oxide include lithium manganate (LiMn 2 O 4 ); lithium cobaltate (LiCoO 2 ); lithium nickelate (LiNiO 2 ); and at least part of the manganese, cobalt, and nickel portions of these lithium compounds.
  • lithium composite oxides may be used individually by 1 type, and 2 or more types may be mixed and used for them.
  • the average particle diameter of the positive electrode active material for example, a positive electrode active material having an average particle diameter in the range of 0.1 to 50 ⁇ m can be used from the viewpoint of reactivity with the electrolytic solution, rate characteristics, and the like.
  • a positive electrode active material having a particle diameter in the range of 1 to 30 ⁇ m, more preferably an average particle diameter in the range of 5 to 25 ⁇ m can be used.
  • the average particle diameter means the particle diameter (median diameter: D 50 ) at an integrated value of 50% in the particle size distribution (volume basis) by the laser diffraction scattering method.
  • the binder for the positive electrode is not particularly limited, but the same binder as that for the negative electrode can be used. Among these, polyvinylidene fluoride is preferable from the viewpoint of versatility and low cost.
  • the content of the binder for the positive electrode is preferably in the range of 1 to 25 parts by mass with respect to 100 parts by mass of the positive electrode active material from the viewpoint of the binding force and energy density which are in a trade-off relationship. The range of 2 to 10 parts by mass is more preferable.
  • binders other than polyvinylidene fluoride (PVdF) vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer rubber, polytetrafluoroethylene, polypropylene, Examples include polyethylene, polyimide, and polyamideimide.
  • NMP N-methyl-2-pyrrolidone
  • the positive electrode current collector is not particularly limited, but from the viewpoint of electrochemical stability, for example, aluminum, titanium, tantalum, stainless steel (SUS), other valve metals, or alloys thereof are used. Can be used. Examples of the shape include foil, flat plate, and mesh. In particular, an aluminum foil can be suitably used.
  • a conductive auxiliary material may be added for the purpose of reducing the impedance.
  • the conductive auxiliary material include carbonaceous fine particles such as graphite, carbon black, and acetylene black.
  • a nonaqueous electrolytic solution in which a lithium salt is dissolved in one or two or more nonaqueous solvents can be used.
  • cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC); Dimethyl carbonate (DMC), Chain carbonates such as diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC); aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate; ⁇ -lactones such as ⁇ -butyrolactone Chain ethers such as 1,2-ethoxyethane (DEE) and ethoxymethoxyethane (EME); and cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofur
  • non-aqueous solvents include dimethyl sulfoxide, 1,3-dioxolane, dioxolane derivatives, void muamide, acetamide, dimethyl void muamide, acetonitrile, propionitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane , Sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone An aprotic organic solvent such as can also be used.
  • lithium salt dissolved in the nonaqueous solvent is not particularly limited, for example LiPF 6, LiAsF 6, LiAlCl 4 , LiClO 4, LiBF 4, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li (CF 3 SO 2 ) 2 , LiN (CF 3 SO 2 ) 2 , and lithium bisoxalatoborate are included.
  • These lithium salts can be used individually by 1 type or in combination of 2 or more types.
  • a polymer electrolyte may be used instead of the non-aqueous electrolyte solution.
  • a separator can be provided between the positive electrode and the negative electrode.
  • a porous film, a woven fabric, or a nonwoven fabric made of a polyolefin such as polypropylene or polyethylene, a fluororesin such as polyvinylidene fluoride, polyimide, or the like can be used.
  • Battery shapes include cylindrical, square, coin type, button type, and laminate type.
  • a laminate type it is preferable to use a laminate film as an exterior body that accommodates a positive electrode, a separator, a negative electrode, and an electrolyte.
  • the laminate film includes a resin base material, a metal foil layer, and a heat seal layer (sealant).
  • the resin base material include polyester and nylon
  • examples of the metal foil layer include aluminum, an aluminum alloy, and a titanium foil.
  • the material for the heat welding layer include thermoplastic polymer materials such as polyethylene, polypropylene, and polyethylene terephthalate.
  • the resin base material layer and the metal foil layer are not limited to one layer, and may be two or more layers. From the viewpoint of versatility and cost, an aluminum laminate film is preferable.
  • the positive electrode, the negative electrode, and the separator disposed between them are accommodated in an outer container made of a laminate film or the like, and an electrolyte is injected and sealed.
  • a structure in which an electrode group in which a plurality of electrode pairs are stacked can be accommodated.
  • Example 1 Pitch coke having an average particle size of 10 ⁇ m was heat-treated in air at 480 ° C. for 1 hour to obtain a carbon material having pores.
  • the SEM image of pitch coke before heat treatment is shown in FIG. 1 (a is 2000 times, b is 10,000 times), and the SEM image after heat treatment is shown in FIG. It can be seen that pores having a diameter of 20 nm to 1 ⁇ m are formed in the pitch coke after the heat treatment.
  • the XRD pattern of the carbon material before and after heat treatment is shown in FIG. In FIG. 3, the air-oxidized pitch coke is shown with the baseline raised.
  • Table 1 shows the average mesh size. As shown in Table 1, it can be seen that the surface spacing, the average number of layers, and the weight fraction are hardly changed by the heat treatment, but the average mesh size is increased. This is probably because very small graphene disappeared by heat treatment and the average mesh size increased.
  • Example 2 A carbon material having pores was obtained in the same manner as in Example 1 except that the heat treatment temperature was 600 ° C.
  • Example 2 A heat treatment was performed in the same manner as in Example 1 except that the atmosphere in Example 1 was changed to nitrogen and the heat treatment temperature was set to 800 ° C.
  • the potential of the working electrode with respect to the counter electrode was charged to 0 V (Li was inserted into the working electrode), and discharged to 1.5 V (Li was desorbed from the working electrode).
  • the current value at the time of charging / discharging was set to 1C as a current value for flowing the discharge capacity of the working electrode in one hour.
  • the first cycle charge / discharge is 0.1C constant current charge-0.025C constant current charge-0.1C discharge
  • the second cycle charge / discharge is 0.1C constant current charge-0.1C discharge.
  • the fourth cycle was 10 C constant current charge-0.1 C discharge.
  • initial discharge capacity discharge capacity at the first cycle
  • initial efficiency discharge capacity at the first cycle / charge capacity at the first cycle
  • 1C / 0.1C charge rate characteristics discharge capacity at the third cycle
  • Discharge capacity at 2nd cycle Discharge capacity at 2nd cycle
  • 10C / 0.1C charge rate characteristics discharge capacity at 4th cycle / discharge capacity at 2nd cycle
  • Comparative Example 3 Flakes of pitch coke (average maximum diameter of 15 ⁇ m) were used as the carbon material of Comparative Example 3.
  • a battery was prepared in the same manner as above except that the coating amount of the negative electrode was 100 g / m 2, and the initial discharge capacity, initial efficiency, and charge rate characteristics (1C / 0.1C, 4C / 0.1C, 6C / 0.1C 10C / 0.1C). The results are shown in Table 3.
  • flaky pitch coke also becomes a carbon material excellent in initial discharge capacity, initial efficiency, and charge rate characteristics by heat treatment in an oxidizing atmosphere.
  • Comparative Example 4 Flaked calcined pitch coke was used as the carbon material of Comparative Example 4. This pitch coke is obtained by heat-treating raw coal at 1000 to 1500 ° C. in a nitrogen atmosphere, and this carbon material has relatively higher crystallinity than ordinary pitch coke (corresponding to Comparative Examples 1 and 3). .
  • Comparative Example 5 The carbon material of Comparative Example 4 was heat-treated at 600 ° C. for 1.5 hours in an atmosphere of 100% N 2 to obtain the carbon material of Comparative Example 5.
  • a battery was prepared in the same manner as above except that the coating amount of the negative electrode was 50 g / m 2, and the initial discharge capacity and the initial efficiency were measured.
  • the results are shown in Table 4.
  • Each carbon material was measured by Raman spectroscopic analysis, and the intensity ratio (I D / I G ) of the D peak reflecting irregularity with respect to the G peak reflecting the graphite structure was obtained.
  • the interplanar interplanar spacing d 002 of each carbon material and the mass fraction Ps of the graphene laminated structure were determined from the XRD pattern. The results are summarized in Table 4.
  • FIG. 5 shows charge / discharge curves of batteries using the carbon materials of Example 4 and Comparative Example 4.
  • Example 4 From the results of Comparative Example 4 and Example 4, it can be seen that the air oxidation of high-capacity soft carbon reduces the initial capacity and initial efficiency, but greatly improves the rate characteristics. This is because the carbon material of Comparative Example 4 had a surplus capacity derived from pitch coke nanocavities, but it was considered that such nanocavities burned due to air oxidation and the capacity was reduced. Although the heat treatment itself shows an increase in the overall crystallinity as a decrease in the I D / IG ratio (Example 4 and Comparative Example 5), Example 4 in which the nanocavities are reduced by the oxidation treatment is a graphene stack. It also leads to an increase in the mass fraction of the structure.
  • Comparative Example 5 where heat treatment was similarly performed in a nitrogen atmosphere, the capacity was further reduced, which was due to an increase in the interplanar spacing d002 . In the air oxidation, the surface distance d002 does not increase. Further, as shown in FIG. 4, the rate characteristics of the comparative example 4 and the comparative example 5 are almost the same, and the rate characteristics are not improved even by simple heat treatment. Thus, the low crystalline carbon material can be made into a negative electrode active material having excellent rate characteristics by heat treatment in an oxidizing atmosphere.

Abstract

　In order to provide a negative electrode carbon material that yields a lithium secondary cell having improved charge rate characteristics, there is used a low-crystalline carbon material having pores formed in the surface thereof, particularly, a negative electrode carbon material for a lithium secondary cell comprising pitch coke, wherein the pores have an aperture of 20 nm-1 μm. The pores can be formed by heat-treating pitch coke in an oxidizing atmosphere.

Description

リチウム二次電池用負極炭素材料、リチウム電池用負極およびリチウム二次電池Negative electrode carbon material for lithium secondary battery, negative electrode for lithium battery and lithium secondary battery
　本発明は、リチウム二次電池用負極炭素材料、リチウム二次電池用負極およびリチウム二次電池に関するものである。 The present invention relates to a negative electrode carbon material for a lithium secondary battery, a negative electrode for a lithium secondary battery, and a lithium secondary battery.
　リチウム二次電池は、エネルギー密度が高く、自己放電が少なく長期信頼性に優れる等の利点により、ノート型パソコンや携帯電話などの小型電子機器用の電池として広く実用化されている。近年では電子機器の高機能化や電気自動車への利用が進み、より性能の高いリチウム二次電池の開発が求められている。 Lithium secondary batteries have been widely put into practical use as batteries for small electronic devices such as notebook computers and mobile phones because of their advantages such as high energy density, low self-discharge and excellent long-term reliability. In recent years, advanced functions of electronic devices and use in electric vehicles have progressed, and development of lithium secondary batteries with higher performance has been demanded.
　現在、リチウム二次電池の負極活物質としては、炭素材料が一般的であり、電池性能の向上のために種々な炭素材料が提案されている。 At present, carbon materials are generally used as negative electrode active materials for lithium secondary batteries, and various carbon materials have been proposed for improving battery performance.
　炭素材料としては、天然黒鉛、人造黒鉛などの高結晶性炭素、易黒鉛化性炭素（ソフトカーボン）や難黒鉛化性炭素（ハードカーボン）などの低結晶性炭素、及び非晶質炭素（アモルファスカーボン）が知られている。高結晶性炭素である黒鉛は、Ｌｉイオンとの反応性に優れ、理論容量値に近い容量が得られることが知られている。一方、高結晶性炭素は電解液の溶媒として多用されるプロピレンカーボネート（ＰＣ）と反応しやすいことで電解液の劣化による充電レート特性低下を引き起こす。低結晶性炭素及び非晶質炭素は、理論容量値こそ黒鉛の理論容量値よりも高いが、Ｌｉイオンとの反応性が低く、長時間の充電が必要となり、単位時間当たりの容量値は黒鉛より低い。一方、ＰＣとの反応性は低く、電解液の劣化は少ない。そこで、黒鉛と非晶質炭素（低結晶性炭素を含む）とを組み合わせた複合炭素材料が提案されている。 Carbon materials include high crystalline carbon such as natural graphite and artificial graphite, low crystalline carbon such as graphitizable carbon (soft carbon) and non-graphitizable carbon (hard carbon), and amorphous carbon (amorphous). Carbon) is known. It is known that graphite, which is highly crystalline carbon, is excellent in reactivity with Li ions and has a capacity close to the theoretical capacity value. On the other hand, highly crystalline carbon easily reacts with propylene carbonate (PC), which is frequently used as a solvent for the electrolytic solution, thereby causing deterioration in charge rate characteristics due to deterioration of the electrolytic solution. Low crystalline carbon and amorphous carbon have a theoretical capacity value that is higher than the theoretical capacity value of graphite, but the reactivity with Li ions is low and long-time charging is required. Lower. On the other hand, the reactivity with PC is low, and the deterioration of the electrolytic solution is small. Therefore, a composite carbon material combining graphite and amorphous carbon (including low crystalline carbon) has been proposed.
　例えば、特許文献１では、黒鉛粒子の表面に非晶質炭素を付着させた負極活物質が開示されている。同文献では、黒鉛粒子と非晶質炭素との密着性を改善するため、黒鉛粒子を酸化処理し、黒鉛粒子表面に酸素含有官能基を生成し、また、黒鉛粒子の表面を粗面化することが開示されている。例えば、特許文献１では、２００℃～７００℃の温度での空気酸化、黒鉛粒子表面にアルカリを付着させた後に３００℃～７００℃で熱処理する方法が開示されている。 For example, Patent Document 1 discloses a negative electrode active material in which amorphous carbon is adhered to the surface of graphite particles. In this document, in order to improve the adhesion between graphite particles and amorphous carbon, the graphite particles are oxidized to generate oxygen-containing functional groups on the surface of the graphite particles, and the surface of the graphite particles is roughened. It is disclosed. For example, Patent Document 1 discloses a method in which air oxidation is performed at a temperature of 200 ° C. to 700 ° C., and heat treatment is performed at 300 ° C. to 700 ° C. after alkali is attached to the surface of the graphite particles.
特開平１０－４０９１４号公報Japanese Patent Laid-Open No. 10-40914
　本発明者らの検討に依れば、黒鉛を空気酸化すると、初期容量が大きく低下するという問題があることが分かった。 According to the study by the present inventors, it has been found that there is a problem that the initial capacity is greatly reduced when graphite is oxidized with air.
　また、炭素材料からなる負極は、Ｌｉイオンとの反応量が多くなると入力特性と寿命が低下する。特に黒鉛はその傾向は顕著であり、高レートでの容量は少ない。一方、ソフトカーボン、ハードカーボン等の低結晶性炭素材料の入力特性は黒鉛より高くなるが、初期容量が黒鉛より小さい。そこで、Ｌｉイオンとの反応量が多く、入力特性とサイクル寿命がより良好で安価な負極材料が求められている。 Also, the negative electrode made of a carbon material has a reduced input characteristic and life when the amount of reaction with Li ions increases. In particular, the tendency of graphite is remarkable, and the capacity at a high rate is small. On the other hand, low crystalline carbon materials such as soft carbon and hard carbon have higher input characteristics than graphite, but their initial capacity is smaller than that of graphite. Therefore, there is a demand for a negative electrode material that has a large amount of reaction with Li ions, has better input characteristics and cycle life, and is inexpensive.
　本発明の目的は、上述した課題を解決することにあり、すなわち入力特性とサイクル寿命との指標となる充電レート特性が改善されたリチウム二次電池が得られる負極炭素材料、並びにこれを用いたリチウム二次電池用負極およびリチウム二次電池を提供することにある。 An object of the present invention is to solve the above-described problems, that is, a negative electrode carbon material from which a lithium secondary battery with improved charge rate characteristics as an index of input characteristics and cycle life can be obtained, and the same are used. The object is to provide a negative electrode for a lithium secondary battery and a lithium secondary battery.
　本発明では、黒鉛に代えてピッチコークス等の低結晶性炭素を用い、これに酸化雰囲気下に熱処理することで表面に空孔を形成したものを負極材料として用いる。 In the present invention, low crystalline carbon such as pitch coke is used instead of graphite, and a material in which pores are formed on the surface by heat treatment in an oxidizing atmosphere is used as the negative electrode material.
　すなわち、本発明の一態様によれば、表面に空孔が形成された低結晶性炭素材料からなるリチウム二次電池用負極炭素材料であって、空孔サイズが２０ｎｍ～１μｍの範囲であるリチウム二次電池用負極炭素材料が提供される。 That is, according to one aspect of the present invention, there is provided a negative electrode carbon material for a lithium secondary battery comprising a low crystalline carbon material having pores formed on the surface thereof, wherein the pore size is in the range of 20 nm to 1 μm. A negative electrode carbon material for a secondary battery is provided.
　本発明の他の態様によれば、上記の負極炭素材料を含むリチウム二次電池用負極が提供される。
　本発明の他の態様によれば、上記の負極を含むリチウム二次電池が提供される。 According to the other aspect of this invention, the negative electrode for lithium secondary batteries containing said negative electrode carbon material is provided.
According to another aspect of the present invention, a lithium secondary battery including the negative electrode is provided.
　本発明の実施形態によれば、充電レート特性が改善されたリチウム二次電池が得られる負極炭素材料、並びにこれを用いたリチウム二次電池用負極およびリチウム二次電池を提供することができる。 According to the embodiment of the present invention, it is possible to provide a negative electrode carbon material from which a lithium secondary battery with improved charge rate characteristics can be obtained, and a negative electrode for a lithium secondary battery and a lithium secondary battery using the same.
熱処理前のピッチコークスの表面状態を示すＳＥＭ像であり、ａは２０００倍、ｂは１万倍での倍率で測定したものである。It is a SEM image which shows the surface state of the pitch coke before heat processing, a is measured by the magnification of 2000 times, b is 10,000 times. 酸化雰囲気下で熱処理後のピッチコークスの表面状態を示すＳＥＭ像である。It is a SEM image which shows the surface state of the pitch coke after heat processing in an oxidizing atmosphere. 熱処理前後のピッチコークスのＸＲＤデータである。It is XRD data of pitch coke before and after heat treatment. 実施例４，比較例４，５の炭素材料を用いた二次電池のレート特性を示す図である。It is a figure which shows the rate characteristic of the secondary battery using the carbon material of Example 4, Comparative Examples 4 and 5. FIG. 実施例４と比較例４の炭素材料を用いた二次電池の充放電カーブである。It is a charging / discharging curve of the secondary battery using the carbon material of Example 4 and Comparative Example 4.
　以下、本発明の実施形態例について詳細に説明する。
　本発明の実施形態例によるリチウム二次電池用負極炭素材料は、低結晶性炭素材料、いわゆるソフトカーボンやハードカーボンと呼ばれる炭素材料からなり、表面に所定の空孔を有することで、通常の低結晶性炭素材料に比べてリチウム二次電池の充電レート特性を改善することができる。ここで、空孔は、溝状に形成されるものも含む。この空孔を有する低結晶性炭素材料は、結晶質の黒鉛類似構造（グラフェンの積層構造、以下、グラフェン層という）を含み、少なくとも表面側のグラフェン層にも複数の空孔が形成されていることが好ましく、表面から内部にかけて複数のグラフェン層に空孔が形成されていることがより好ましい。これらの空孔は、リチウムイオン（Ｌｉイオン）を通過させることができ、グラフェン層間内へのＬｉイオンの経路（Ｌｉパス）として機能することができる。通常の炭素材料では、Ｌｉイオンのグラフェン層間内へのＬｉパスはグラフェン層のエッジ面側からの経路にほぼ限られ、また、グラフェン層間内の奥（グラフェン層平面方向の中央）に至るまでの距離が長く、そのため、リチウムとの反応量が多くなると、充電レート特性が低下していた。本実施形態例による低結晶性炭素材料においては、エッジ面側からのＬｉパスに加えて、グラフェン層平面（ベーサル面）にＬｉパスとして機能する空孔を有するため、Ｌｉパスが増加し、またグラフェン層内の奥に至る経路が短くなる。その結果、リチウム二次電池の充電レート特性を向上することができる。 Hereinafter, exemplary embodiments of the present invention will be described in detail.
A negative electrode carbon material for a lithium secondary battery according to an embodiment of the present invention is made of a low crystalline carbon material, a carbon material called so-called soft carbon or hard carbon, and has a predetermined pore on the surface, thereby reducing the normal low-carbon material. Compared with the crystalline carbon material, the charge rate characteristics of the lithium secondary battery can be improved. Here, the holes include those formed in a groove shape. This low crystalline carbon material having pores includes a crystalline graphite-like structure (a graphene laminated structure, hereinafter referred to as a graphene layer), and at least a plurality of pores are formed in the graphene layer on the surface side. It is preferable that holes are formed in a plurality of graphene layers from the surface to the inside. These vacancies can pass lithium ions (Li ions) and function as a Li ion path (Li path) into the graphene layer. In a normal carbon material, the Li path into the graphene layer of Li ions is almost limited to the path from the edge surface side of the graphene layer, and further to the back of the graphene layer (the center in the plane direction of the graphene layer) As the distance is long, and the amount of reaction with lithium increases, the charge rate characteristics deteriorate. In the low crystalline carbon material according to the present embodiment example, in addition to the Li path from the edge surface side, the graphene layer plane (basal surface) has holes that function as the Li path, so the Li path increases, and The path to the back of the graphene layer is shortened. As a result, the charge rate characteristics of the lithium secondary battery can be improved.
　このような空孔は、表面側グラフェン層の内側のグラフェン層平面にも形成されていることが好ましく、少なくとも表層から内側に向かって空孔が形成されていることがより好ましい。低結晶性炭素材料を構成する全てのグラフェン層に空孔を形成することができる。また、複数のグラフェン層を貫通するように空孔を形成することもできる。このような空孔が形成されることにより、グラフェン層の積層方向（グラフェン層平面に垂直方向）の内部へ至るＬｉ経路が形成され、充電レート特性をより向上することができる。内部のグラフェン層平面の空孔は、種々の方法で低結晶性炭素材料を切断して断面を出し、ＴＥＭ、ＳＥＭ等の電子顕微鏡で観測することができる。 Such vacancies are preferably also formed in the graphene layer plane inside the surface-side graphene layer, and more preferably at least from the surface layer toward the inside. Holes can be formed in all graphene layers constituting the low crystalline carbon material. In addition, holes can be formed so as to penetrate a plurality of graphene layers. By forming such vacancies, a Li path reaching the inside in the stacking direction of the graphene layer (direction perpendicular to the graphene layer plane) is formed, and the charge rate characteristics can be further improved. The pores in the plane of the graphene layer inside can be observed with an electron microscope such as TEM or SEM by cutting the low crystalline carbon material by various methods to obtain a cross section.
　これらの空孔の開口サイズは、リチウムイオンを通過させることができ、且つ空孔形成により炭素材料の特性を大きく劣化させない限り、特に制限はないが、２０ｎｍ以上であることが好ましく、５０ｎｍ以上がより好ましく、１００ｎｍ以上がさらに好ましい。また、炭素材料の特性を劣化させない点から、開口サイズは、１μｍ以下が好ましく、８００ｎｍ以下がより好ましく、５００ｎｍ以下がさらに好ましい。ここで、「開口サイズ」とは、開口の最大長さ（最大開口サイズ）を意味し、開口の輪郭を収容できる最小面積の円の直径に相当する。また、リチウムイオン通過の観点から、空孔開口の輪郭の内側に存在できる最大面積の円の直径に相当する開口サイズ（最小開口サイズ）も２０ｎｍ以上であることが好ましく、５０ｎｍ以上であることがより好ましく、１００ｎｍ以上がさらに好ましい。 The opening size of these vacancies is not particularly limited as long as lithium ions can pass therethrough and the characteristics of the carbon material are not greatly deteriorated by vacancy formation, but it is preferably 20 nm or more, preferably 50 nm or more. More preferably, it is more preferably 100 nm or more. Further, from the viewpoint of not deteriorating the characteristics of the carbon material, the opening size is preferably 1 μm or less, more preferably 800 nm or less, and even more preferably 500 nm or less. Here, the “opening size” means the maximum length (maximum opening size) of the opening, and corresponds to the diameter of a circle having the smallest area that can accommodate the outline of the opening. From the viewpoint of lithium ion passage, the opening size (minimum opening size) corresponding to the diameter of the circle with the largest area that can exist inside the outline of the hole opening is also preferably 20 nm or more, and more preferably 50 nm or more. More preferably, it is more preferably 100 nm or more.
　このような開口サイズを有する空孔の数密度は、１～５０個／μｍ２の範囲であることが好ましい。少なくとも表面層においてこの範囲の数密度の空孔が形成されていることが好ましい。空孔の数密度が低すぎると十分な充電レート特性向上効果が得られず、逆に空孔の数密度が高すぎると比表面積が大きくなりすぎて充放電時の副反応が生じやすくなり、充放電効率が低下する場合がある。この空孔の数密度は、低結晶性炭素材料表面の電子顕微鏡画像において、表面の１μｍ×１μｍの領域を任意に１０カ所選び、各領域内で開口サイズが２０ｎｍ以上の空孔の個数をカウントし、１０カ所における平均値（個数／μｍ２）として求めることができる。本実施形態によれば、表層から内部へ空孔の数密度がほとんど変わらない低結晶性炭素材料を形成することができる。また、表層から内部へ複数のグラフェン層を貫通する空孔を形成することができ、グラフェン層であれば３０層程度までに到達する空孔を形成することもできる。その際、表層から内側へ奥にいくほど、空孔の開口径は小さくなり、数密度も低下する傾向がある。 The number density of holes having such an opening size is preferably in the range of 1 to 50 / μm 2 . It is preferable that pores having a number density in this range are formed at least in the surface layer. If the number density of vacancies is too low, a sufficient charge rate characteristic improvement effect cannot be obtained, and conversely, if the number density of vacancies is too high, the specific surface area becomes too large and side reactions during charge and discharge are likely to occur. Charge / discharge efficiency may decrease. The number density of holes is selected from 10 1 μm × 1 μm areas on the surface of an electron microscope image of the surface of a low crystalline carbon material, and the number of holes having an opening size of 20 nm or more in each area is counted. And it can obtain | require as an average value (number / micrometer < 2 >) in ten places. According to this embodiment, it is possible to form a low crystalline carbon material in which the number density of vacancies hardly changes from the surface layer to the inside. In addition, vacancies penetrating the plurality of graphene layers from the surface layer to the inside can be formed, and vacancies reaching up to about 30 layers can be formed in the case of the graphene layer. At that time, as it goes inward from the surface layer, the opening diameter of the holes becomes smaller and the number density tends to decrease.
　また、空孔は炭素材料表面全面にわたって形成されていることが好ましく、均一に分布していることがより好ましい。複数の空孔の間隔（隣り合う空孔の開口間の最小距離、平均値）は、１００ｎｍ～１μｍの範囲にあることが好ましい。このように空孔が形成されていることにより、低結晶性炭素材料の特性による電池特性を損なうことなく、充電レート特性を向上することができる。この空孔間隔は、低結晶性炭素材料表面の電子顕微鏡画像において、表面の１μｍ×１μｍの領域を任意に１０カ所選び、各領域内で空孔の間隔を測定し、１０カ所における平均値として求めることができる。 Also, the vacancies are preferably formed over the entire surface of the carbon material, and more preferably uniformly distributed. The interval between the plurality of holes (minimum distance between openings of adjacent holes, average value) is preferably in the range of 100 nm to 1 μm. By forming the holes as described above, the charge rate characteristics can be improved without impairing the battery characteristics due to the characteristics of the low crystalline carbon material. As for the space between the holes, in the electron microscopic image of the surface of the low crystalline carbon material, arbitrarily select 10 regions of 1 μm × 1 μm on the surface, measure the space between the holes in each region, and calculate the average value at the 10 regions. Can be sought.
　本実施形態例による低結晶性炭素材料に用いられる原料の低結晶性炭素としては、易黒鉛化性炭素（ソフトカーボン）が好ましく、中でも、石油ピッチコークス、石炭ピッチコークス、メゾフェーズピッチコークスなどのピッチコークスを用いることがより好ましい。ピッチコークスは、軟ピッチをディレードコーカーに装入し、乾留（炭化）させたもので、更にロータリーキルンでか焼（かしょう）するとか焼ピッチコークス（calcined pitch coke）となる。さらにこれらピッチコークスを１５００℃以上、特に２０００～３３００℃で熱処理することで人造黒鉛が得られる。本発明では、人造黒鉛より安価に得られるピッチコークスを使用するものである。 As the low crystalline carbon of the raw material used for the low crystalline carbon material according to the present embodiment, graphitizable carbon (soft carbon) is preferable, and among them, petroleum pitch coke, coal pitch coke, mesophase pitch coke, etc. More preferably, pitch coke is used. Pitch coke is obtained by charging soft pitch into a delayed coker and dry-distilling (carbonizing), and then calcining with a rotary kiln to form calcined pitch coke. Further, artificial graphite can be obtained by heat-treating these pitch cokes at 1500 ° C. or higher, particularly 2000 to 3300 ° C. In the present invention, pitch coke obtained at a lower cost than artificial graphite is used.
　このような低結晶性炭素表面に空孔を形成するため、本発明では、酸化雰囲気で加熱処理する。なお、酸化雰囲気下での熱処理は、低結晶性炭素の発火温度未満の温度で行う。発火してしまうと、炭素材料の燃焼により温度制御ができなくなり、所望の空孔を形成することが困難となる。低結晶性炭素の組成により発火温度は種々異なるが、通常、熱処理温度は常圧下では３５０～８００℃の範囲から選択できる。また、熱処理時間は３０分から２４時間程度の範囲である。酸化雰囲気としては、酸素、二酸化炭素、空気などが挙げられる。又、酸素濃度や圧力を適宜調整することもできる。 In order to form vacancies on such a low crystalline carbon surface, heat treatment is performed in an oxidizing atmosphere in the present invention. Note that the heat treatment in an oxidizing atmosphere is performed at a temperature lower than the ignition temperature of low crystalline carbon. If it ignites, temperature control becomes impossible by combustion of a carbon material, and it becomes difficult to form a desired hole. Although the ignition temperature varies depending on the composition of the low crystalline carbon, the heat treatment temperature can usually be selected from the range of 350 to 800 ° C. under normal pressure. The heat treatment time is in the range of about 30 minutes to 24 hours. Examples of the oxidizing atmosphere include oxygen, carbon dioxide, and air. Also, the oxygen concentration and pressure can be adjusted as appropriate.
　空孔の開口サイズ、数密度、分布は、熱処理温度、熱処理時間、酸化雰囲気等の熱処理条件によって制御することができる。 The opening size, number density, and distribution of pores can be controlled by heat treatment conditions such as heat treatment temperature, heat treatment time, and oxidizing atmosphere.
　このように炭素材料表面に形成された空孔は、低結晶性炭素に固有の空隙（一次粒子間の空隙や、欠陥、エッジ近傍の空隙や割れ）とは異なる。空隙を有する通常の低結晶性炭素を負極に用いても、リチウム二次電池の充電レート特性は低い。また、低結晶性炭素の表面を荒らす処理（例えば低結晶性炭素をアルカリ溶液に浸漬した後に超音波を照射する処理）を行い、このような処理後の低結晶性炭素を負極に用いても、リチウム二次電池の充電レート特性は低い。また、活性炭の製造において行われる薬品賦活法やガス賦活法による賦活処理は、炭化処理によってできた空隙を拡大したり、閉孔部を開口したり、空隙内にさらに多くの細孔を付加したりするものであり、このような通常の賦活処理を低結晶性炭素に対して行っても、所望の充電レート特性を有するリチウム二次電池を得ることは困難である。特に、結晶性の高いグラフェン層が優先的に酸化され、非晶質構造部分はグラフェン層を保護する保護層の役割を果たす。これによって、互いに隔離された空孔が炭素材料表面に形成される。黒鉛を酸化した場合は、このような互いに隔離された空孔とはならず、連続した溝（チャネル）状となり、明らかに異なる。 The vacancies thus formed on the surface of the carbon material are different from the voids inherent to the low crystalline carbon (voids between primary particles, defects, voids and cracks near the edges). Even when ordinary low crystalline carbon having voids is used for the negative electrode, the charge rate characteristics of the lithium secondary battery are low. Also, a treatment for roughening the surface of the low crystalline carbon (for example, a treatment of irradiating ultrasonic waves after immersing the low crystalline carbon in an alkaline solution) may be performed, and the low crystalline carbon after such treatment may be used for the negative electrode. The charge rate characteristics of lithium secondary batteries are low. In addition, the chemical activation and gas activation methods used in the production of activated carbon expand the voids created by carbonization, open closed pores, and add more pores in the voids. Even if such normal activation treatment is performed on low crystalline carbon, it is difficult to obtain a lithium secondary battery having desired charge rate characteristics. In particular, the highly crystalline graphene layer is preferentially oxidized, and the amorphous structure portion serves as a protective layer for protecting the graphene layer. As a result, pores isolated from each other are formed on the surface of the carbon material. When graphite is oxidized, it does not become such a hole isolated from each other but forms a continuous groove (channel), which is clearly different.
　本実施形態例によれば低結晶性炭素の構造を著しく劣化させることなく、表面層に空孔を形成することができるため、低結晶性炭素本来の特性による電池特性を大きく損なうことなく、リチウム二次電池の充電レート特性を改善することができる。 According to the present embodiment example, since it is possible to form vacancies in the surface layer without significantly degrading the structure of the low crystalline carbon, lithium does not significantly impair the battery characteristics due to the inherent characteristics of the low crystalline carbon. The charge rate characteristics of the secondary battery can be improved.
　このように本実施形態例による空孔形成後の低結晶性炭素材料は、原料の低結晶性炭素に応じた構造や物性を有することができる。本実施形態による低結晶性炭素材料の（００２）面の面間隔ｄ００２は０．３５０ｎｍ以下であることが好ましく、０．３４７ｎｍ以下であることがより好ましい。なお、面間隔ｄ００２は、一般的な黒鉛よりも大きく、通常、０．３４０ｎｍ以上である。この面間隔ｄ００２はＸ線回折法（Ｘ－Ｒａｙ　Ｄｉｆｆｒａｃｔｉｏｎ：ＸＲＤ）により求めることができる。 Thus, the low crystalline carbon material after the vacancy formation according to the present embodiment example can have a structure and physical properties corresponding to the low crystalline carbon of the raw material. The plane distance d 002 of the (002) plane of the low crystalline carbon material according to the present embodiment is preferably 0.350 nm or less, and more preferably 0.347 nm or less. The surface spacing d 002 is greater than the typical graphite is usually, 0.340 nm or more. This interplanar distance d 002 can be obtained by an X-ray diffraction method (X-Ray Diffraction: XRD).
　また、低結晶性炭素材料に含まれるグラフェン層は、黒鉛に比してそのサイズははるかに小さい。グラフェン層のサイズは、Ｄｉａｍｏｎｄ法により得られるベンゼン環を基本とした平均網目サイズ（六角網目の個数）で表されるが、本実施形態による低結晶性炭素材料は原料の低結晶性炭素材料よりも平均網目サイズが増加するという特徴を有する。本発明では平均網目サイズが６０個以上であることが好ましい。 Also, the graphene layer contained in the low crystalline carbon material is much smaller in size than graphite. The size of the graphene layer is represented by an average network size (the number of hexagonal meshes) based on a benzene ring obtained by the Diamond method. The low crystalline carbon material according to the present embodiment is smaller than the raw low crystalline carbon material. Is also characterized in that the average mesh size increases. In the present invention, the average mesh size is preferably 60 or more.
　本実施形態例による低結晶性炭素材料は、充填効率や混合性、成形性等の点から、粒子状のものを用いることができる。粒子の形状としては、球状、楕円球状、鱗片状（フレーク状）が挙げられる。一般的な球状化処理を行ってもよい。 As the low crystalline carbon material according to this embodiment, a particulate material can be used from the viewpoint of filling efficiency, mixing property, moldability, and the like. Examples of the particle shape include a spherical shape, an elliptical spherical shape, and a scale shape (flakes). A general spheroidizing treatment may be performed.
　本実施形態例による低結晶性炭素材料の平均粒径は、充放電時の副反応を抑えて充放電効率の低下を抑える点から、１μｍ以上が好ましく、２μｍ以上がより好ましく、５μｍ以上がさらに好ましく、入出力特性の観点や電極作製上の観点（電極表面の平滑性等）から、４０μｍ以下が好ましく、３５μｍ以下がより好ましく、３０μｍ以下がさらに好ましい。ここで、平均粒径は、レーザー回折散乱法による粒度分布（体積基準）における積算値５０％での粒径（メジアン径：Ｄ５０）を意味する。 The average particle size of the low crystalline carbon material according to the present embodiment is preferably 1 μm or more, more preferably 2 μm or more, and further preferably 5 μm or more from the viewpoint of suppressing side reactions during charging and discharging to suppress a decrease in charging and discharging efficiency. Preferably, it is preferably 40 μm or less, more preferably 35 μm or less, and even more preferably 30 μm or less from the viewpoints of input / output characteristics and electrode production (smoothness of the electrode surface). Here, the average particle diameter means the particle diameter (median diameter: D 50 ) at an integrated value of 50% in the particle size distribution (volume basis) by the laser diffraction scattering method.
　本実施形態例による低結晶性炭素材料のＢＥＴ比表面積（窒素吸着法による７７Ｋでの測定に基づく）は、充放電時の副反応を抑えて充放電効率の低下を抑える点から、１０ｍ２／ｇ未満が好ましく、５ｍ２／ｇ以下がより好ましい。一方、十分な入出力特性を得る点から、ＢＥＴ比表面積は、０．５ｍ２／ｇ以上が好ましく、１ｍ２／ｇ以上がより好ましい。 The BET specific surface area (based on measurement at 77 K by the nitrogen adsorption method) of the low crystalline carbon material according to the present embodiment example is 10 m 2 / from the point of suppressing side reactions at the time of charge and discharge and suppressing a decrease in charge and discharge efficiency. Less than g is preferable, and 5 m 2 / g or less is more preferable. On the other hand, from the viewpoint of obtaining sufficient input / output characteristics, the BET specific surface area is preferably 0.5 m 2 / g or more, and more preferably 1 m 2 / g or more.
　本実施形態例による低結晶性炭素材料は、対リチウム電位が０～２Ｖにおける充放電において放電容量が２４０ｍＡｈ／ｇ以上であることが好ましく、また、充放電効率が７５％以上であることが好ましい。なお、充放電効率は、室温において少なくとも初期の充放電において示される値を意味する。本実施形態による低結晶性炭素材料は、原料の低結晶性炭素材料よりも、リチウムパスの形成により放電容量が増加するという特徴を有する。 The low crystalline carbon material according to this embodiment preferably has a discharge capacity of 240 mAh / g or more in charge / discharge at a lithium potential of 0 to 2 V, and a charge / discharge efficiency of 75% or more. . In addition, charging / discharging efficiency means the value shown in at least initial charging / discharging at room temperature. The low crystalline carbon material according to the present embodiment has a feature that the discharge capacity is increased by the formation of a lithium path as compared with the raw low crystalline carbon material.
　本実施形態例による低結晶性炭素材料は、その表面及び空孔内に、Ｌｉと合金化できる金属またはその酸化物を形成してもよい。この金属または金属酸化物は、リチウムと反応可能であり、リチウム二次電池の充放電において電気化学的に活性なものである。このような金属または金属酸化物としては、Ｓｉ、Ｇｅ、Ｓｎ、Ｐｂ、Ａｌ、Ｇａ、Ｉｎ及びＭｇからなる群から選ばれる少なくとも一種の金属またはその酸化物を用いることができる。 The low crystalline carbon material according to the present embodiment may form a metal that can be alloyed with Li or its oxide on the surface and in the pores. This metal or metal oxide can react with lithium and is electrochemically active in charging / discharging of a lithium secondary battery. As such a metal or metal oxide, at least one metal selected from the group consisting of Si, Ge, Sn, Pb, Al, Ga, In, and Mg, or an oxide thereof can be used.
　このような金属または金属酸化物は、低結晶性炭素材料に形成された空孔周辺に形成されることが好ましい。 Such a metal or metal oxide is preferably formed around the pores formed in the low crystalline carbon material.
　このような金属または金属酸化物を形成することにより、反応容量を増大することができる。特に、金属または金属酸化物が空孔周辺に形成されることにより、空孔周辺において、その他の部位と比べて金属または金属酸化物がグラフェン層と強く結合でき、可逆性に優れるＬｉ反応サイトが増加し、反応容量を向上させることができる。 The reaction capacity can be increased by forming such a metal or metal oxide. In particular, since the metal or metal oxide is formed around the vacancies, the metal or metal oxide can be strongly bonded to the graphene layer around the vacancies compared to other sites, and there are Li reaction sites that are excellent in reversibility. The reaction volume can be increased.
　このような金属または金属酸化物の形成手法としては、ＣＶＤ、スパッタ、電解めっき、無電解めっき、水熱合成法などが挙げられる。 Examples of such a metal or metal oxide forming method include CVD, sputtering, electrolytic plating, electroless plating, and hydrothermal synthesis.
　本実施形態例による負極炭素材料における金属または金属酸化物の含有量は、低結晶性炭素材料に対して０．１～３０質量％が好ましい。この含有量が少なすぎると十分な含有効果が得られず、この含有量が多すぎると、金属または金属酸化物の充放電時の体積膨張収縮の影響が大きく、低結晶性炭素材料が劣化しやすくなる。 The content of metal or metal oxide in the negative electrode carbon material according to the present embodiment is preferably 0.1 to 30% by mass with respect to the low crystalline carbon material. If the content is too small, sufficient content effects cannot be obtained. If the content is too large, the volume or shrinkage of the metal or metal oxide during charge / discharge is large, and the low crystalline carbon material deteriorates. It becomes easy.
　本実施形態例による低結晶性炭素材料は非晶質炭素で被覆することができる。これにより、非晶質炭素が低結晶性炭素材料と電解液との副反応を抑制でき、充放電効率が向上し、反応容量を増大することができる。また、前述のリチウム（Ｌｉ）と合金化できる金属またはその酸化物が表面に形成された低結晶性炭素材料を非晶質炭素で被覆することもできる。これにより、電解液との副反応を抑えながら、反応容量をさらに増大することができる。なお、ここでいう非晶質炭素とは、完全に結晶性のない材料のみを意味するものでは無く、原料の低結晶性炭素材料よりも結晶化度（黒鉛化度）の低い材料を意味する。一般的には、アモルファスカーボンと呼ばれる結晶化度の極めて低い材料である。又、下記のような方法で形成できる材料である。 The low crystalline carbon material according to this embodiment can be coated with amorphous carbon. Thereby, the amorphous carbon can suppress the side reaction between the low crystalline carbon material and the electrolytic solution, the charge / discharge efficiency can be improved, and the reaction capacity can be increased. Moreover, the low crystalline carbon material in which the metal which can be alloyed with the above-mentioned lithium (Li), or its oxide was formed in the surface can also be coat | covered with an amorphous carbon. As a result, the reaction capacity can be further increased while suppressing side reactions with the electrolytic solution. The term “amorphous carbon” as used herein does not mean only a material that is not completely crystalline, but means a material that has a lower degree of crystallinity (graphitization degree) than a raw material low-crystalline carbon material. . In general, it is a material with extremely low crystallinity called amorphous carbon. Further, it is a material that can be formed by the following method.
　低結晶性炭素材料への非晶質炭素の被覆方法としては、水熱合成法、ＣＶＤ、スパッタなどが挙げられる。 Examples of the method for coating amorphous carbon on the low crystalline carbon material include hydrothermal synthesis, CVD, and sputtering.
　水熱合成法による非晶質炭素の被覆は、例えば次のようにして行うことができる。まず、空孔が形成された低結晶性炭素材料の粉末を炭素前駆体溶液に浸漬し、混合する。水熱反応装置で１８０℃３時間処理して、その後、真空ろ過を行って粉末を分離する。次に、分離された粉末を不活性雰囲気下で熱処理する。次いで、得られた粉末の凝集体を粉砕して所望の粒径に揃える。また、空孔を形成する前の低結晶性炭素材料に非晶質炭素を被覆し、その後、酸化雰囲気で熱処理して、非晶質炭素と低結晶炭素とに連続する空孔を形成することもできる。 The amorphous carbon coating by the hydrothermal synthesis method can be performed, for example, as follows. First, powder of a low crystalline carbon material in which pores are formed is immersed in a carbon precursor solution and mixed. It is treated in a hydrothermal reactor at 180 ° C. for 3 hours, and then vacuum filtered to separate the powder. Next, the separated powder is heat-treated in an inert atmosphere. The powder agglomerates are then pulverized to the desired particle size. Also, amorphous carbon is coated on the low crystalline carbon material before forming vacancies, and then heat-treated in an oxidizing atmosphere to form continuous vacancies in amorphous carbon and low crystalline carbon. You can also.
　炭素前駆体溶液としては種々の糖溶液を用いることができ、特にスクロース水溶液が好ましい。この水溶液のスクロース濃度は０．１～６Ｍに設定でき、浸漬時間は１分～２４時間に設定できる。熱処理は、窒素やアルゴン等の不活性雰囲気下で、４００～１２００℃、０．５～２４時間行うことができる。 As the carbon precursor solution, various sugar solutions can be used, and an aqueous sucrose solution is particularly preferable. The sucrose concentration of this aqueous solution can be set to 0.1 to 6M, and the immersion time can be set to 1 minute to 24 hours. The heat treatment can be performed at 400 to 1200 ° C. for 0.5 to 24 hours in an inert atmosphere such as nitrogen or argon.
　また、本発明の別の実施形態例によれば、ピッチコークスを酸化雰囲気下、３５０～８００℃の範囲から選択される温度で熱処理して得られるリチウム二次電池用負極炭素材料であって、（００２）面の面間隔ｄ００２が０．３４０以上０．３５０ｎｍ以下、ラマン分光分析におけるグラファイト構造を反映したＧピークに対して不規則性を反映したＤピークの強度比（ＩＤ／ＩＧ比）が０．８未満、グラフェン積層構造の質量分率が６６％以上であるリチウム二次電池用負極炭素材料が提供される。
　ピッチコークスとしてはか焼ピッチコークスを使用することが好ましい。また、グラフェン積層構造の質量分率は７０％以上が好ましい。
　本実施形態例の負極炭素材料は、上記した実施形態例と同様の各種特性を有することが好ましく、上記した実施形態例と同様の非晶質炭素被覆処理等を行うことができる。
　本実施形態例では、か焼ピッチコークスを使用した場合には必ずしも初期容量や初期効率が向上するものではないが、上記の実施形態例と同様に、Ｌｉパスが増加し、またグラフェン層内の奥に至る経路が短くなる結果、リチウム二次電池の充電レート特性を有利に向上することができる。 According to another embodiment of the present invention, there is provided a negative electrode carbon material for a lithium secondary battery obtained by heat-treating pitch coke at a temperature selected from the range of 350 to 800 ° C. in an oxidizing atmosphere, The (002) plane spacing d 002 is 0.340 or more and 0.350 nm or less, and the intensity ratio of the D peak reflecting irregularity to the G peak reflecting the graphite structure in Raman spectroscopy (I D / I G A negative electrode carbon material for a lithium secondary battery having a ratio of less than 0.8 and a mass fraction of the graphene laminated structure of 66% or more is provided.
It is preferable to use calcined pitch coke as the pitch coke. Further, the mass fraction of the graphene stacked structure is preferably 70% or more.
The negative electrode carbon material of the present embodiment example preferably has various characteristics similar to those of the above-described embodiment example, and can be subjected to the same amorphous carbon coating treatment as that of the above-described embodiment example.
In the present embodiment example, when the calcined pitch coke is used, the initial capacity and the initial efficiency are not necessarily improved. However, as in the above embodiment example, the Li path increases, and the graphene layer has As a result of the shorter path leading to the back, the charge rate characteristics of the lithium secondary battery can be advantageously improved.
　以上に説明した低結晶性炭素材料は、リチウムイオン二次電池の負極活物質に適用でき、この低結晶性炭素材料を負極活物質として用いることにより充電レート特性が改善されたリチウムイオン二次電池を提供することができる。 The low crystalline carbon material described above can be applied to the negative electrode active material of a lithium ion secondary battery, and the lithium ion secondary battery having improved charge rate characteristics by using this low crystalline carbon material as the negative electrode active material. Can be provided.
　リチウムイオン二次電池用の負極は、例えば、負極集電体上に、この低結晶性炭素材料からなる負極活物質と結着剤を含む負極活物質層を形成することで作製することができる。この負極活物質層は、一般的なスラリー塗布法で形成することができる。具体的には、負極活物質、結着剤および溶媒を含むスラリーを調製し、これを負極集電体上に塗布し、乾燥し、必要に応じて加圧することで、負極を得ることができる。負極スラリーの塗布方法としては、ドクターブレード法、ダイコーター法、ディップコーティング法が挙げられる。予め負極活物質層を形成した後に、蒸着、スパッタ等の方法でアルミニウム、ニッケルまたはそれらの合金の薄膜を集電体として形成して、負極を得ることもできる。 A negative electrode for a lithium ion secondary battery can be prepared, for example, by forming a negative electrode active material layer including a negative electrode active material made of this low crystalline carbon material and a binder on a negative electrode current collector. . This negative electrode active material layer can be formed by a general slurry coating method. Specifically, a negative electrode can be obtained by preparing a slurry containing a negative electrode active material, a binder, and a solvent, applying the slurry onto a negative electrode current collector, drying, and pressing as necessary. . Examples of the method for applying the negative electrode slurry include a doctor blade method, a die coater method, and a dip coating method. After the negative electrode active material layer is formed in advance, a negative electrode can be obtained by forming a thin film of aluminum, nickel, or an alloy thereof as a current collector by a method such as vapor deposition or sputtering.
　負極用の結着剤としては、特に制限されるものではないが、ポリフッ化ビニリデン（ＰＶｄＦ）、ビニリデンフルオライド－ヘキサフルオロプロピレン共重合体、ビニリデンフルオライド－テトラフルオロエチレン共重合体、スチレン－ブタジエン共重合ゴム、ポリテトラフルオロエチレン、ポリプロピレン、ポリエチレン、ポリイミド、ポリアミドイミド、メチル（メタ）アクリレート、エチル（メタ）アクリレート、ブチル（メタ）アクリレート、（メタ）アクリロニトリル、イソプレンゴム、ブタジエンゴム、フッ素ゴムが挙げられる。スラリー溶媒としては、Ｎ－メチル－２－ピロリドン（ＮＭＰ）や水を用いることができる。水を溶媒として用いる場合、さらに増粘剤として、カルボキシメチルセルロース、メチルセルロース、ヒドロキシメチルセルロース、エチルセルロース、ポリビニルアルコールを用いることができる。 The binder for the negative electrode is not particularly limited, but polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene. Copolymer rubber, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamideimide, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, isoprene rubber, butadiene rubber, fluorine rubber Can be mentioned. As the slurry solvent, N-methyl-2-pyrrolidone (NMP) or water can be used. When water is used as a solvent, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, and polyvinyl alcohol can be used as a thickener.
　この負極用の結着剤の含有量は、トレードオフの関係にある結着力とエネルギー密度の観点から、負極活物質１００質量部に対して０．１～３０質量部の範囲にあることが好ましく、０．５～２５質量部の範囲がより好ましく、１～２０質量部の範囲がさらに好ましい。 The content of the binder for the negative electrode is preferably in the range of 0.1 to 30 parts by mass with respect to 100 parts by mass of the negative electrode active material, from the viewpoints of binding force and energy density that are in a trade-off relationship. The range of 0.5 to 25 parts by mass is more preferable, and the range of 1 to 20 parts by mass is more preferable.
　負極集電体としては、特に制限されるものではないが、電気化学的な安定性から、銅、ニッケル、ステンレス、モリブデン、タングステン、タンタルおよびこれらの２種以上を含む合金が好ましい。その形状としては、箔、平板状、メッシュ状が挙げられる。 The negative electrode current collector is not particularly limited, but copper, nickel, stainless steel, molybdenum, tungsten, tantalum and an alloy containing two or more of these are preferable from the viewpoint of electrochemical stability. Examples of the shape include foil, flat plate, and mesh.
　本発明の実施形態によるリチウムイオン二次電池は、上記負極と正極と電解質を含む。
　正極は、例えば、正極活物質、結着剤及び溶媒（さらに必要により導電補助材）を含むスラリーを調製し、これを正極集電体上に塗布し、乾燥し、必要に応じて加圧することにより、正極集電体上に正極活物質層を形成することにより作製できる。 The lithium ion secondary battery by embodiment of this invention contains the said negative electrode, a positive electrode, and electrolyte.
For the positive electrode, for example, a slurry containing a positive electrode active material, a binder, and a solvent (and a conductive auxiliary material if necessary) is prepared, applied to the positive electrode current collector, dried, and pressurized as necessary. Thus, a positive electrode active material layer can be formed on the positive electrode current collector.
　正極活物質としては、特に制限されるものではないが、例えば、リチウム複合酸化物やリン酸鉄リチウムなどを用いることができる。リチウム複合酸化物としては、マンガン酸リチウム（ＬｉＭｎ２Ｏ４）；コバルト酸リチウム（ＬｉＣｏＯ２）；ニッケル酸リチウム（ＬｉＮｉＯ２）；これらのリチウム化合物のマンガン、コバルト、ニッケルの部分の少なくとも一部をアルミニウム、マグネシウム、チタン、亜鉛など他の金属元素で置換したもの；マンガン酸リチウムのマンガンの一部を少なくともニッケルで置換したニッケル置換マンガン酸リチウム；ニッケル酸リチウムのニッケルの一部を少なくともコバルトで置換したコバルト置換ニッケル酸リチウム；ニッケル置換マンガン酸リチウムのマンガンの一部を他の金属（例えばアルミニウム、マグネシウム、チタン、亜鉛の少なくとも一種）で置換したもの；コバルト置換ニッケル酸リチウムのニッケルの一部を他の金属元素（例えばアルミニウム、マグネシウム、チタン、亜鉛の少なくとも一種）で置換したものが挙げられる。これらのリチウム複合酸化物は一種を単独で使用してもよいし、二種以上を混合して用いてもよい。正極活物質の平均粒径については、電解液との反応性やレート特性等の観点から、例えば平均粒径が０．１～５０μｍの範囲にある正極活物質を用いることができ、好ましくは平均粒径が１～３０μｍの範囲にある正極活物質、より好ましくは平均粒径が５～２５μｍの範囲にあるものを用いることができる。ここで、平均粒径は、レーザー回折散乱法による粒度分布（体積基準）における積算値５０％での粒径（メジアン径：Ｄ５０）を意味する。 Although it does not restrict | limit especially as a positive electrode active material, For example, lithium complex oxide, lithium iron phosphate, etc. can be used. Examples of the lithium composite oxide include lithium manganate (LiMn 2 O 4 ); lithium cobaltate (LiCoO 2 ); lithium nickelate (LiNiO 2 ); and at least part of the manganese, cobalt, and nickel portions of these lithium compounds. Replaced with other metal elements such as aluminum, magnesium, titanium, zinc; nickel-substituted lithium manganate in which part of manganese in lithium manganate is replaced with at least nickel; part of nickel in lithium nickelate is replaced with at least cobalt Cobalt-substituted lithium nickelate; a part of manganese of nickel-substituted lithium manganate substituted with another metal (for example, at least one of aluminum, magnesium, titanium, and zinc); one nickel of cobalt-substituted lithium nickelate Other metal elements (e.g. aluminum, magnesium, titanium, at least one zinc) include those substituted with. These lithium composite oxides may be used individually by 1 type, and 2 or more types may be mixed and used for them. With respect to the average particle diameter of the positive electrode active material, for example, a positive electrode active material having an average particle diameter in the range of 0.1 to 50 μm can be used from the viewpoint of reactivity with the electrolytic solution, rate characteristics, and the like. A positive electrode active material having a particle diameter in the range of 1 to 30 μm, more preferably an average particle diameter in the range of 5 to 25 μm can be used. Here, the average particle diameter means the particle diameter (median diameter: D 50 ) at an integrated value of 50% in the particle size distribution (volume basis) by the laser diffraction scattering method.
　正極用の結着剤としては、特に制限されるものではないが、負極用結着剤と同様のものを用いることができる。中でも、汎用性や低コストの観点から、ポリフッ化ビニリデンが好ましい。正極用の結着剤の含有量は、トレードオフの関係にある結着力とエネルギー密度の観点から、正極活物質１００質量部に対して１～２５質量部の範囲が好ましく、２～２０質量部の範囲がより好ましく、２～１０質量部の範囲がさらに好ましい。ポリフッ化ビニリデン（ＰＶｄＦ）以外の結着剤としては、ビニリデンフルオライド－ヘキサフルオロプロピレン共重合体、ビニリデンフルオライド－テトラフルオロエチレン共重合体、スチレン－ブタジエン共重合ゴム、ポリテトラフルオロエチレン、ポリプロピレン、ポリエチレン、ポリイミド、ポリアミドイミドが挙げられる。スラリー溶媒としては、Ｎ－メチル－２－ピロリドン（ＮＭＰ）を用いることができる。 The binder for the positive electrode is not particularly limited, but the same binder as that for the negative electrode can be used. Among these, polyvinylidene fluoride is preferable from the viewpoint of versatility and low cost. The content of the binder for the positive electrode is preferably in the range of 1 to 25 parts by mass with respect to 100 parts by mass of the positive electrode active material from the viewpoint of the binding force and energy density which are in a trade-off relationship. The range of 2 to 10 parts by mass is more preferable. As binders other than polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer rubber, polytetrafluoroethylene, polypropylene, Examples include polyethylene, polyimide, and polyamideimide. As the slurry solvent, N-methyl-2-pyrrolidone (NMP) can be used.
　正極集電体としては、特に制限されるものではないが、電気化学的な安定性の観点から、例えば、アルミニウム、チタン、タンタル、ステンレス鋼（ＳＵＳ）、その他のバルブメタル、又はそれらの合金を用いることができる。その形状としては、箔、平板状、メッシュ状が挙げられる。特にアルミニウム箔を好適に用いることができる。 The positive electrode current collector is not particularly limited, but from the viewpoint of electrochemical stability, for example, aluminum, titanium, tantalum, stainless steel (SUS), other valve metals, or alloys thereof are used. Can be used. Examples of the shape include foil, flat plate, and mesh. In particular, an aluminum foil can be suitably used.
　正極の作製に際して、インピーダンスを低下させる目的で、導電補助材を添加してもよい。導電補助材としては、グラファイト、カーボンブラック、アセチレンブラック等の炭素質微粒子が挙げられる。 In the production of the positive electrode, a conductive auxiliary material may be added for the purpose of reducing the impedance. Examples of the conductive auxiliary material include carbonaceous fine particles such as graphite, carbon black, and acetylene black.
　電解質としては、１種又は２種以上の非水溶媒に、リチウム塩を溶解させた非水系電解液を用いることができる。非水溶媒としては、特に制限されるものではないが、例えばエチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、ビニレンカーボネート（ＶＣ）などの環状カーボネート；ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）、ジプロピルカーボネート（ＤＰＣ）などの鎖状カーボネート；ギ酸メチル、酢酸メチル、プロピオン酸エチルなどの脂肪族カルボン酸エステル；γ－ブチロラクトンなどのγ－ラクトン；１，２－エトキシエタン（ＤＥＥ）、エトキシメトキシエタン（ＥＭＥ）などの鎖状エーテル；テトラヒドロフラン、２－メチルテトラヒドロフランなどの環状エーテルが挙げられる。その他、非水溶媒として、ジメチルスルホキシド、１，３－ジオキソラン、ジオキソラン誘導体、空孔ムアミド、アセトアミド、ジメチル空孔ムアミド、アセトニトリル、プロピオニトリル、ニトロメタン、エチルモノグライム、リン酸トリエステル、トリメトキシメタン、スルホラン、メチルスルホラン、１，３－ジメチル－２－イミダゾリジノン、３－メチル－２－オキサゾリジノン、プロピレンカーボネート誘導体、テトラヒドロフラン誘導体、エチルエーテル、１，３－プロパンサルトン、アニソール、Ｎ－メチルピロリドンなどの非プロトン性有機溶媒を用いることもできる。 As the electrolyte, a nonaqueous electrolytic solution in which a lithium salt is dissolved in one or two or more nonaqueous solvents can be used. Although it does not restrict | limit especially as a nonaqueous solvent, For example, cyclic carbonates, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC); Dimethyl carbonate (DMC), Chain carbonates such as diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC); aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate; γ-lactones such as γ-butyrolactone Chain ethers such as 1,2-ethoxyethane (DEE) and ethoxymethoxyethane (EME); and cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran. Other non-aqueous solvents include dimethyl sulfoxide, 1,3-dioxolane, dioxolane derivatives, void muamide, acetamide, dimethyl void muamide, acetonitrile, propionitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane , Sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone An aprotic organic solvent such as can also be used.
　非水溶媒に溶解させるリチウム塩としては、特に制限されるものではないが、例えばＬｉＰＦ６、ＬｉＡｓＦ６、ＬｉＡｌＣｌ４、ＬｉＣｌＯ４、ＬｉＢＦ４、ＬｉＳｂＦ６、ＬｉＣＦ３ＳＯ３、ＬｉＣＦ３ＣＯ２、Ｌｉ（ＣＦ３ＳＯ２）２、ＬｉＮ（ＣＦ３ＳＯ２）２、リチウムビスオキサラトボレートが挙げられる。これらのリチウム塩は、一種を単独で、または二種以上を組み合わせて使用することができる。また、非水系電解液の代わりにポリマー電解質を用いてもよい。 Examples of the lithium salt dissolved in the nonaqueous solvent, is not particularly limited, for example LiPF 6, LiAsF 6, LiAlCl 4 , LiClO 4, LiBF 4, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li (CF 3 SO 2 ) 2 , LiN (CF 3 SO 2 ) 2 , and lithium bisoxalatoborate are included. These lithium salts can be used individually by 1 type or in combination of 2 or more types. Further, a polymer electrolyte may be used instead of the non-aqueous electrolyte solution.
　正極と負極との間にはセパレータを設けることができる。このセパレータとしては、ポリプロピレン、ポリエチレン等のポリオレフィン、ポリフッ化ビニリデン等のフッ素樹脂、ポリイミド等からなる多孔性フィルムや織布、不織布を用いることができる。 A separator can be provided between the positive electrode and the negative electrode. As this separator, a porous film, a woven fabric, or a nonwoven fabric made of a polyolefin such as polypropylene or polyethylene, a fluororesin such as polyvinylidene fluoride, polyimide, or the like can be used.
　電池形状としては、円筒形、角形、コイン型、ボタン型、ラミネート型が挙げられる。ラミネート型の場合、正極、セパレータ、負極および電解質を収容する外装体としてラミネートフィルムを用いることが好ましい。このラミネートフィルムは、樹脂基材と、金属箔層、熱融着層（シーラント）を含む。この樹脂基材としては、ポリエステルやナイロンが挙げられ、この金属箔層としては、アルミニウム、アルミニウム合金、チタン箔が挙げられる。熱溶着層の材質としては、ポリエチレン、ポリプロピレン、ポリエチレンテレフタレート等の熱可塑性高分子材料が挙げられる。また、樹脂基材層や金属箔層はそれぞれ１層に限定されるものではなく２層以上であってもよい。汎用性やコストの観点から、アルミニウムラミネートフィルムが好ましい。 Battery shapes include cylindrical, square, coin type, button type, and laminate type. In the case of a laminate type, it is preferable to use a laminate film as an exterior body that accommodates a positive electrode, a separator, a negative electrode, and an electrolyte. The laminate film includes a resin base material, a metal foil layer, and a heat seal layer (sealant). Examples of the resin base material include polyester and nylon, and examples of the metal foil layer include aluminum, an aluminum alloy, and a titanium foil. Examples of the material for the heat welding layer include thermoplastic polymer materials such as polyethylene, polypropylene, and polyethylene terephthalate. Moreover, the resin base material layer and the metal foil layer are not limited to one layer, and may be two or more layers. From the viewpoint of versatility and cost, an aluminum laminate film is preferable.
　正極と負極とこれらの間に配置されたセパレータは、ラミネートフィルム等からなる外装容器に収容され、電解液が注入され、封止される。複数の電極対が積層された電極群が収容された構造とすることもできる。 The positive electrode, the negative electrode, and the separator disposed between them are accommodated in an outer container made of a laminate film or the like, and an electrolyte is injected and sealed. A structure in which an electrode group in which a plurality of electrode pairs are stacked can be accommodated.
　以下に実施例を挙げて本発明をさらに説明する。
　（実施例１）
　平均粒径１０μｍのピッチコークスを空気中で４８０℃、１時間熱処理し、空孔のある炭素材料を得た。熱処理前のピッチコークスのＳＥＭ像を図１（ａは２０００倍、ｂは１万倍）に、熱処理後のＳＥＭ像を図２に示す。熱処理後のピッチコークスには、直径２０ｎｍ～１μｍの空孔が形成されていることがわかる。また熱処理前後の炭素材料のＸＲＤパターンを図３に示す。なお、図３において、空気酸化ピッチコークスについてはベースラインを引き上げて表示している。このＸＲＤパターンから得られたグラフェン間の面間隔ｄ００２、グラフェンの平均積層数ｎ、グラフェンの積層構造を形成する炭素原子の重量分率Ｐｓ、およびＤｉａｍｏｎｄ法により得られるベンゼン環を基本としたグラフェンの平均網目サイズを表１に示す。表１に示すように、熱処理によって面間隔、平均積層数、重量分率はほとんど変わらないが、平均網目サイズは増加していることがわかる。これは、非常に小さなグラフェンが熱処理により消失し、平均網目サイズが増加したものと考えられる。 The following examples further illustrate the present invention.
Example 1
Pitch coke having an average particle size of 10 μm was heat-treated in air at 480 ° C. for 1 hour to obtain a carbon material having pores. The SEM image of pitch coke before heat treatment is shown in FIG. 1 (a is 2000 times, b is 10,000 times), and the SEM image after heat treatment is shown in FIG. It can be seen that pores having a diameter of 20 nm to 1 μm are formed in the pitch coke after the heat treatment. Moreover, the XRD pattern of the carbon material before and after heat treatment is shown in FIG. In FIG. 3, the air-oxidized pitch coke is shown with the baseline raised. Interplanar spacing d 002 obtained from this XRD pattern, average number n of graphene stacks, weight fraction Ps of carbon atoms forming the graphene stack structure, and graphene based on a benzene ring obtained by the Diamond method Table 1 shows the average mesh size. As shown in Table 1, it can be seen that the surface spacing, the average number of layers, and the weight fraction are hardly changed by the heat treatment, but the average mesh size is increased. This is probably because very small graphene disappeared by heat treatment and the average mesh size increased.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　（実施例２）
　熱処理温度を６００℃にした以外は実施例１と同様にして、空孔のある炭素材料を得た。 (Example 2)
A carbon material having pores was obtained in the same manner as in Example 1 except that the heat treatment temperature was 600 ° C.
　（比較例１）
　実施例１で用いたものと同じピッチコークスで、熱処理しないものを用いた。 (Comparative Example 1)
The same pitch coke as that used in Example 1 and not heat-treated was used.
　（比較例２）
　実施例１で雰囲気を窒素とし、熱処理温度を８００℃にした以外は実施例１と同様に熱処理したものを用いた。 (Comparative Example 2)
A heat treatment was performed in the same manner as in Example 1 except that the atmosphere in Example 1 was changed to nitrogen and the heat treatment temperature was set to 800 ° C.
　これらの炭素材料と導電剤と結着剤（ＰＶｄＦ）を、黒鉛材：導電剤：結着剤＝９２：１：７の質量比率で混合し、ＮＭＰに分散させてスラリーを作製した。このスラリーを銅箔上に塗布し、乾燥、圧延した後、２２×２５ｍｍに切り出して電極を得た。この電極を作用極とし、セパレータを挟んで対極のＬｉ箔と組み合わせて積層体を得た。この積層体と電解液（１ＭのＬｉＰＦ６を含むＥＣとＤＥＣの混合溶液、容量比ＥＣ／ＤＥＣ＝１／１）をアルミラミネート容器内に封入し、電池を作製した。 These carbon materials, a conductive agent, and a binder (PVdF) were mixed at a mass ratio of graphite material: conductive agent: binder = 92: 1: 7 and dispersed in NMP to prepare a slurry. The slurry was applied on a copper foil, dried and rolled, and then cut into 22 × 25 mm to obtain an electrode. This electrode was used as a working electrode, and a laminate was obtained by combining with a counter electrode Li foil across a separator. This laminate and an electrolytic solution (a mixed solution of EC and DEC containing 1 M LiPF 6 and a volume ratio EC / DEC = 1/1) were sealed in an aluminum laminate container to produce a battery.
　所定の電流値で、対極に対する作用極の電位が０Ｖまで充電（作用極にＬｉを挿入）し、１．５Ｖまで放電（作用極からＬｉを脱離）した。この充放電時の電流値は、作用極の放電容量を１時間で流す電流値を１Ｃとした。１サイクル目の充放電は０．１Ｃ定電流充電－０．０２５Ｃ定電流充電－０．１Ｃ放電とし、２サイクル目の充放電は０．１Ｃ定電流充電－０．１Ｃ放電とし、３サイクル目は１Ｃ定電流充電－０．１Ｃ放電とし、４サイクル目は１０Ｃ定電流充電－０．１Ｃ放電とした。 At a predetermined current value, the potential of the working electrode with respect to the counter electrode was charged to 0 V (Li was inserted into the working electrode), and discharged to 1.5 V (Li was desorbed from the working electrode). The current value at the time of charging / discharging was set to 1C as a current value for flowing the discharge capacity of the working electrode in one hour. The first cycle charge / discharge is 0.1C constant current charge-0.025C constant current charge-0.1C discharge, and the second cycle charge / discharge is 0.1C constant current charge-0.1C discharge. Was 1 C constant current charge-0.1 C discharge, and the fourth cycle was 10 C constant current charge-0.1 C discharge.
　充放電特性として、初期放電容量（１サイクル目の放電容量）、初期効率（１サイクル目の放電容量／１サイクル目の充電容量）、１Ｃ／０．１Ｃ充電レート特性（３サイクル目の放電容量／２サイクル目の放電容量）、１０Ｃ／０．１Ｃ充電レート特性（４サイクル目の放電容量／２サイクル目の放電容量）を求めた。結果を表２に示す。なお合わせて得られた炭素材料の酸化状態Ｏ／Ｃ比をＣＨＮ法で測定した結果を示す。 As charge / discharge characteristics, initial discharge capacity (discharge capacity at the first cycle), initial efficiency (discharge capacity at the first cycle / charge capacity at the first cycle), 1C / 0.1C charge rate characteristics (discharge capacity at the third cycle) / Discharge capacity at 2nd cycle), 10C / 0.1C charge rate characteristics (discharge capacity at 4th cycle / discharge capacity at 2nd cycle) were determined. The results are shown in Table 2. In addition, the result of having measured the oxidation state O / C ratio of the carbon material obtained by combining by the CHN method is shown.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表２から、ピッチコークスを空気中で熱処理した実施例１、２は、未熱処理の比較例１および窒素中で熱処理した比較例２に比べ、初期放電容量、初期効率、充電レート特性に優れることがわかった。 From Table 2, Examples 1 and 2 in which pitch coke was heat-treated in the air were superior in initial discharge capacity, initial efficiency, and charge rate characteristics compared to Comparative Example 1 that had not been heat-treated and Comparative Example 2 that had been heat-treated in nitrogen. I understood.
　比較例３
　フレーク状のピッチコークス（平均最大径１５μｍ）を、比較例３の炭素材料とした。 Comparative Example 3
Flakes of pitch coke (average maximum diameter of 15 μm) were used as the carbon material of Comparative Example 3.
　実施例３
　比較例３の炭素材料を、Ｏ２：Ｎ２＝１：４（容量比）の雰囲気中５００℃で１時間の熱処理を実施し、実施例３の炭素材料とした。 Example 3
The carbon material of Comparative Example 3 was heat-treated at 500 ° C. for 1 hour in an atmosphere of O 2 : N 2 = 1: 4 (capacity ratio) to obtain the carbon material of Example 3.
　負極の塗布量を１００ｇ／ｍ２とした以外は上記と同様に電池を作製し、初期放電容量、初期効率、充電レート特性（１Ｃ／０．１Ｃ、４Ｃ／０．１Ｃ、６Ｃ／０．１Ｃ、１０Ｃ／０．１Ｃ）を測定した。結果を表３に示す。 A battery was prepared in the same manner as above except that the coating amount of the negative electrode was 100 g / m 2, and the initial discharge capacity, initial efficiency, and charge rate characteristics (1C / 0.1C, 4C / 0.1C, 6C / 0.1C 10C / 0.1C). The results are shown in Table 3.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　フレーク状のピッチコークスについても、酸化雰囲気中で熱処理することで、初期放電容量、初期効率、充電レート特性に優れた炭素材料となることがわかった。 It was also found that flaky pitch coke also becomes a carbon material excellent in initial discharge capacity, initial efficiency, and charge rate characteristics by heat treatment in an oxidizing atmosphere.
　比較例４
　フレーク状のか焼ピッチコークスを比較例４の炭素材料とした。このピッチコークスは原料炭を窒素雰囲気下で１０００～１５００℃で熱処理したもので、この炭素材料は通常のピッチコークス（比較例１及び３相当）よりも相対的に高い結晶性を有している。 Comparative Example 4
Flaked calcined pitch coke was used as the carbon material of Comparative Example 4. This pitch coke is obtained by heat-treating raw coal at 1000 to 1500 ° C. in a nitrogen atmosphere, and this carbon material has relatively higher crystallinity than ordinary pitch coke (corresponding to Comparative Examples 1 and 3). .
　実施例４
　比較例４の炭素材料を、Ｏ２：Ｎ２＝１：４（容量比）の雰囲気中６００℃で１．５時間の熱処理を実施し、実施例４の炭素材料とした。 Example 4
The carbon material of Comparative Example 4 was heat-treated at 600 ° C. for 1.5 hours in an atmosphere of O 2 : N 2 = 1: 4 (capacity ratio) to obtain the carbon material of Example 4.
　比較例５
　比較例４の炭素材料を、１００％Ｎ２の雰囲気中６００℃で１．５時間の熱処理を実施し、比較例５の炭素材料とした。 Comparative Example 5
The carbon material of Comparative Example 4 was heat-treated at 600 ° C. for 1.5 hours in an atmosphere of 100% N 2 to obtain the carbon material of Comparative Example 5.
　負極の塗布量を５０ｇ／ｍ２とした以外は上記と同様に電池を作製し、初期放電容量、初期効率を測定した。結果を表４に示す。また、各炭素材料をラマン分光分析により測定し、グラファイト構造を反映したＧピークに対して不規則性を反映したＤピークの強度比（ＩＤ／ＩＧ）を求めた。さらに、ＸＲＤパターンから各炭素材料のグラフェン間の面間隔ｄ００２及びグラフェン積層構造の質量分率Ｐｓを求めた。結果を表４にまとめて示す。 A battery was prepared in the same manner as above except that the coating amount of the negative electrode was 50 g / m 2, and the initial discharge capacity and the initial efficiency were measured. The results are shown in Table 4. Each carbon material was measured by Raman spectroscopic analysis, and the intensity ratio (I D / I G ) of the D peak reflecting irregularity with respect to the G peak reflecting the graphite structure was obtained. Furthermore, the interplanar interplanar spacing d 002 of each carbon material and the mass fraction Ps of the graphene laminated structure were determined from the XRD pattern. The results are summarized in Table 4.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　また、各実施例の炭素材料を用いて得られた電池のレート特性（各炭素材料の充電レートに対する容量維持率）を図４に示す。図５に実施例４と比較例４の炭素材料を用いた電池の充放電カーブを示す。 Moreover, the rate characteristics (capacity maintenance rate with respect to the charge rate of each carbon material) of the battery obtained using the carbon material of each example are shown in FIG. FIG. 5 shows charge / discharge curves of batteries using the carbon materials of Example 4 and Comparative Example 4.
　比較例４と実施例４の結果から、高容量のソフトカーボンの空気酸化は初期容量、初期効率を低下させるものの、レート特性を大いに改善していることが分かる。これは、比較例４の炭素材料ではピッチコークスのナノ空洞に由来する余剰容量を有していたが、空気酸化によりこのようなナノ空洞が燃焼し容量の低下となったと考えられる。加熱処理自体はＩＤ／ＩＧ比の減少として全体的な結晶性の増加を示しているが（実施例４及び比較例５）、酸化処理によりナノ空洞の減少した実施例４は、グラフェン積層構造の質量分率の上昇をももたらしている。窒素雰囲気下で同じように加熱処理を行った比較例５では、容量がさらに減少しているが、これは、グラフェン間の面間隔ｄ００２の増加による。空気酸化では面間隔ｄ００２は増加していない。また、図４に示したように、レート特性は比較例４と比較例５は殆ど変わらず、単に加熱処理してもレート特性は改善されない。このように、酸化雰囲気下での加熱処理により低結晶性炭素材料をレート特性に優れた負極活物質とすることができる。 From the results of Comparative Example 4 and Example 4, it can be seen that the air oxidation of high-capacity soft carbon reduces the initial capacity and initial efficiency, but greatly improves the rate characteristics. This is because the carbon material of Comparative Example 4 had a surplus capacity derived from pitch coke nanocavities, but it was considered that such nanocavities burned due to air oxidation and the capacity was reduced. Although the heat treatment itself shows an increase in the overall crystallinity as a decrease in the I D / IG ratio (Example 4 and Comparative Example 5), Example 4 in which the nanocavities are reduced by the oxidation treatment is a graphene stack. It also leads to an increase in the mass fraction of the structure. In Comparative Example 5 where heat treatment was similarly performed in a nitrogen atmosphere, the capacity was further reduced, which was due to an increase in the interplanar spacing d002 . In the air oxidation, the surface distance d002 does not increase. Further, as shown in FIG. 4, the rate characteristics of the comparative example 4 and the comparative example 5 are almost the same, and the rate characteristics are not improved even by simple heat treatment. Thus, the low crystalline carbon material can be made into a negative electrode active material having excellent rate characteristics by heat treatment in an oxidizing atmosphere.
　以上、実施例を参照して本願発明を説明したが、本願発明は上記実施例に限定されものではない。本願発明の構成や詳細には、本願発明のスコープ内で当業者が理解し得る様々な変更をすることができる。
　この出願は、２０１４年３月２６日に出願された日本出願特願２０１４－６３２８６を基礎とする優先権を主張し、その開示の全てをここに取り込む。 While the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.
This application claims priority based on Japanese Patent Application No. 2014-63286 filed on Mar. 26, 2014, the entire disclosure of which is incorporated herein.

Claims (12)

  1. 　表面に空孔が形成された低結晶性炭素材料からなるリチウム二次電池用負極炭素材料であって、前記空孔の開口サイズが２０ｎｍ以上１μｍ以下であるリチウム二次電池用負極炭素材料。 A negative electrode carbon material for a lithium secondary battery, which is made of a low crystalline carbon material having pores formed on the surface, wherein the opening size of the pores is 20 nm to 1 μm.
  2. 　前記空孔の数密度は、１～５０個／μｍ２の範囲にある、請求項１に記載のリチウム二次電池用負極炭素材料。 The negative electrode carbon material for a lithium secondary battery according to claim 1, wherein the number density of the holes is in the range of 1 to 50 / μm 2 .
  3. 　Ｄｉａｍｏｎｄ法で測定した平均網面サイズが６０個以上である、請求項１に記載のリチウム二次電池用負極炭素材料。 The negative electrode carbon material for a lithium secondary battery according to claim 1, wherein the average network surface size measured by the Diamond method is 60 or more.
  4. 　前記低結晶性炭素材料は、易黒鉛化性炭素である請求項１に記載のリチウム二次電池用負極炭素材料。 2. The negative electrode carbon material for a lithium secondary battery according to claim 1, wherein the low crystalline carbon material is graphitizable carbon.
  5. 　前記易黒鉛化性炭素は、ピッチコークスである、請求項４に記載のリチウム二次電池用負極炭素材料。 The negative graphitic carbon material for a lithium secondary battery according to claim 4, wherein the graphitizable carbon is pitch coke.
  6. 　前記リチウム二次電池用負極炭素材料は、ピッチコークスを酸化雰囲気下で熱処理して形成された、請求項５に記載のリチウム二次電池用負極炭素材料。 The negative electrode carbon material for a lithium secondary battery according to claim 5, wherein the negative electrode carbon material for a lithium secondary battery is formed by heat-treating pitch coke in an oxidizing atmosphere.
  7. 　前記低結晶性炭素材料の表面にリチウムと合金化できる金属またはその酸化物が形成された、請求項１に記載のリチウム二次電池用負極炭素材料。 The negative electrode carbon material for a lithium secondary battery according to claim 1, wherein a metal that can be alloyed with lithium or an oxide thereof is formed on the surface of the low crystalline carbon material.
  8. 　前記低結晶性炭素材料が非晶質炭素で被覆されている、請求項１乃至７のいずれか１項に記載のリチウム二次電池用負極炭素材料。 The negative electrode carbon material for a lithium secondary battery according to any one of claims 1 to 7, wherein the low crystalline carbon material is coated with amorphous carbon.
  9. 　ピッチコークスを酸化雰囲気下、３５０～８００℃の範囲から選択される温度で熱処理して得られるリチウム二次電池用負極炭素材料であって、（００２）面の面間隔ｄ００２が０．３４０以上０．３５０ｎｍ以下、ラマン分光分析におけるグラファイト構造を反映したＧピークに対して不規則性を反映したＤピークの強度比（ＩＤ／ＩＧ比）が０．８未満、グラフェン積層構造の質量分率が６６％以上であるリチウム二次電池用負極炭素材料。 A negative electrode carbon material for a lithium secondary battery obtained by heat-treating pitch coke in an oxidizing atmosphere at a temperature selected from a range of 350 to 800 ° C., and a (002) plane spacing d 002 is 0.340 or more. 0.350nm below, the intensity ratio of D peak reflecting the irregularities with respect to G peaks, reflecting a graphite structure in the Raman spectroscopic analysis (I D / I G ratio) is less than 0.8, the mass fraction of the graphene layered structure A negative electrode carbon material for a lithium secondary battery having a rate of 66% or more.
  10. 　前記ピッチコークスとしてか焼ピッチコークスを使用する請求項９に記載のリチウム二次電池用負極炭素材料。 The negative electrode carbon material for a lithium secondary battery according to claim 9, wherein calcined pitch coke is used as the pitch coke.
  11. 　請求項１乃至１０のいずれか１項に記載のリチウム二次電池用負極炭素材料を含むリチウム二次電池用負極。 A negative electrode for a lithium secondary battery, comprising the negative electrode carbon material for a lithium secondary battery according to any one of claims 1 to 10.
  12. 　請求項１１に記載の負極を含むリチウム二次電池。 A lithium secondary battery comprising the negative electrode according to claim 11.
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