WO2015152114A1 - 黒鉛系活物質材料、負極及びリチウムイオン二次電池 - Google Patents
黒鉛系活物質材料、負極及びリチウムイオン二次電池 Download PDFInfo
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- WO2015152114A1 WO2015152114A1 PCT/JP2015/059841 JP2015059841W WO2015152114A1 WO 2015152114 A1 WO2015152114 A1 WO 2015152114A1 JP 2015059841 W JP2015059841 W JP 2015059841W WO 2015152114 A1 WO2015152114 A1 WO 2015152114A1
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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
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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
- 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
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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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
- H01M4/362—Composites
- H01M4/364—Composites as mixtures
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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
- H01M4/362—Composites
- H01M4/366—Composites as layered products
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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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- 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 graphite-based active material, a negative electrode, and a lithium ion secondary battery.
- lithium ion secondary batteries Since lithium ion secondary batteries have high energy density and excellent charge / discharge cycle characteristics, they are widely used as power sources for small mobile devices such as mobile phones and laptop computers. In recent years, demand for large-capacity batteries that require a large capacity and a long life, such as electric vehicles, hybrid electric vehicles, and the power storage field, has increased due to increased consideration for environmental issues and energy conservation.
- a lithium ion secondary battery includes a negative electrode including a carbon material capable of occluding and releasing lithium ions as a negative electrode active material, a positive electrode including a lithium composite oxide capable of occluding and releasing lithium ions as a positive electrode active material, and a negative electrode and a positive electrode. And a non-aqueous electrolyte in which a lithium salt is dissolved in a non-aqueous solvent.
- amorphous carbon or graphite is used as the carbon material used as the negative electrode active material.
- graphite is used for applications requiring high energy density, and various graphite-based materials have been developed.
- Patent Document 1 discloses composite graphite particles having a core material made of graphite and a carbonaceous layer present on the surface as a negative electrode material for a lithium ion battery.
- This carbonaceous layer is obtained by attaching an organic compound to the core material and heat-treating at 500 ° C. or higher.
- the carbonaceous layer is 0.05 to 10 parts by mass with respect to 100 parts by mass of the core material, and the BET specific surface area is 0. 2 to 30 m 2 / g. It is described that this composite graphite particle has a high lithium ion acceptability, and by using this, it is possible to obtain a lithium ion battery having good cycle characteristics and input / output characteristics.
- Patent Document 2 discloses a negative electrode including a graphite particle in which coated graphite particles coated with amorphous carbon and uncoated graphite particles not coated with amorphous carbon are mixed in a nonaqueous electrolyte secondary battery. Is disclosed. The mass of the amorphous carbon in 100 parts by mass of the coated graphite particles is 0.1 to 10 parts by mass, and the specific surface area of the mixed graphite particles of the coated graphite particles and the uncoated graphite particles is 2 to 5 m 2 / g. It is described that. It is described that by using such mixed graphite particles, lithium precipitation during high-rate charging can be suppressed, and internal resistance of the negative electrode can be reduced to suppress cycle deterioration.
- Patent Document 3 discloses a mixed carbon material including a carbon material A and a carbon material B, and each of the carbon material A and the carbon material B adheres or covers a core material made of graphite powder and a part of the surface.
- a material composed of a surface carbon material (at least one of amorphous carbon and disordered carbon) is disclosed.
- the compressed density of carbon material A is 1.80 ⁇ 1.90 g / cm 3
- compressed density of carbon material B is 1.45 ⁇ 1.65g / cm 3
- the average particle size of the carbon material B is 7 ⁇ m or more and 14 ⁇ m or less, smaller than the average particle size of the carbon material A
- the specific surface area of the carbon material A is 4 m 2 / g or less, It is described that the specific surface area is 6 m 2 / g or less. It is described that a lithium ion secondary battery using such a mixed carbon material has a high capacity due to a high negative electrode density, yet achieves a high charge acceptability and a low irreversible capacity.
- Patent Document 4 when pressing is performed to improve the capacity of the negative electrode and the packing density of the negative electrode is increased, the vicinity of the negative electrode surface is excessively compressed, and the size of the voids near the surface becomes smaller than the inside. As a result, it is described that the non-aqueous electrolyte does not easily penetrate into the negative electrode, so that the amount of electrolyte held in the negative electrode is insufficient, and the charge / discharge cycle characteristics of the secondary battery are deteriorated.
- the density is 1.0 to 1.3 g / cm 3 by applying a coating material containing a fibrous carbonaceous material and a graphite material to the current collector and then drying it.
- a negative electrode is produced by a method including a step of forming an active material-containing layer and a step of increasing the density of the active material-containing layer to 1.3 to 1.6 g / cm 3 by pressing. It is described that by preparing the negative electrode in this way, the size of the voids in the active material-containing layer of the negative electrode can be made uniform, so that the charge / discharge cycle life of the secondary battery can be improved.
- Patent Document 5 discloses a non-aqueous electrolyte secondary solution having a density distribution or a porosity distribution in the thickness direction of a sheet and made of a sheet-like carbonaceous molded body whose inside has a higher density or a lower porosity than the outer surface portion.
- a carbonaceous electrode plate for a battery is disclosed. Such a carbonaceous electrode plate has the function of allowing the electrolyte to penetrate into the electrode at the same time that the outer surface portion exhibits the performance as a negative electrode, and the inner layer plays a role of doping and dedoping more lithium. It is described that it is an excellent negative electrode as well as acting as a collector with high conductivity.
- the gap is small and the packing density is high near the surface of the electrode, it is difficult for the electrolyte to penetrate into the negative electrode, the amount of electrolyte held in the negative electrode is insufficient, and the cycle characteristics of the secondary battery may be degraded. Furthermore, the thickness of the electrode may increase (spring back) due to the residual stress after pressing, which may lead to a decrease in capacity of the negative electrode.
- An object of the present invention is to solve at least the above-described problems related to cycle characteristics, a graphite-based active material suitable for a lithium ion secondary battery, a negative electrode using the same, and lithium ion two having improved cycle characteristics.
- the next battery is to provide.
- the first composite particles composed of the first graphite core particles and the first non-graphitic carbon material covering the surface thereof, and the second graphite core particles and the surface thereof are covered.
- the mass ratio B (covering amount B) of the second non-graphitic carbon material in the second composite particles is 5% by mass or more, and the mass ratio of the first non-graphitic carbon material in the first composite particles Larger than A (covering amount A)
- a graphite-based active material in which the content ratio of the second composite particles to the total of the first composite particles and the second composite particles is 1% by mass or more.
- a negative electrode for a lithium ion secondary battery comprising the above graphite-based active material.
- a lithium ion secondary battery including a positive electrode capable of occluding and releasing lithium ions, the negative electrode, and a non-aqueous electrolyte.
- a graphite-based active material suitable for a lithium ion secondary battery with excellent cycle characteristics, a negative electrode using the same, and a lithium ion secondary battery with improved cycle characteristics are provided. Can do.
- the graphite-based active material according to the present embodiment includes first composite particles composed of first graphite core particles and a first non-graphite carbon material covering the surface, and second graphite core particles and a surface thereof. Second composite particles made of a second non-graphitic carbon material to be coated are included.
- the coating means that at least a part of the surface of the graphite core particle is covered with a non-graphitic carbon material.
- the surface of the graphite core particle Including all of the cases covered. It is preferable that 70% or more of the surface of the graphite core particle is covered, more preferably 80% or more is covered, and more preferably 90% or more is covered.
- the mass ratio (covering amount B) of the second non-graphite carbon material in the second composite particles is the first non-graphite carbon in the first composite particles. It is larger than the mass ratio of the material (covering amount A).
- the coating amount B is larger than the coating amount A, the second composite particles are harder than the first composite particles.
- the vicinity of the electrode surface is excessively compressed during pressing, the particles near the surface are deformed, and the size of the void tends to be smaller and the density is higher than the inside. .
- the press pressure is not sufficiently transmitted near the internal current collector, the voids are large and the density tends to be low.
- the first composite particles having a relatively low hardness are mixed with the second composite particles that are relatively hard, so that the press pressure is uniformly transmitted in the electrode thickness direction and the density is uniform. A secondary battery with excellent cycle characteristics can be obtained.
- first and second graphite core particles As the core material (first and second graphite core particles) of the first and second composite particles contained in the active material according to this embodiment, normal natural graphite or artificial graphite can be used.
- a graphite material having a (002) plane distance d 002 of preferably in the range of 0.3354 to 0.340 nm, more preferably in the range of 0.3354 to 0.338 nm by X-ray diffraction can be used.
- natural graphite (d 002 0.3354) is preferable from the viewpoint of cost and the like.
- the first and second graphite core particles may be made of different materials, or may be made of the same material.
- the shape of the first and second graphite core particles is not particularly limited.
- a spherical shape, a lump shape, or a scale-like shape can be used, and the spherical graphite can be preferably used.
- the first and second graphite core particles may have different shapes or the same shape.
- the average particle size of the first and second core particles can be appropriately selected according to the desired average particle size of the first and second composite particles, respectively.
- the average particle size is preferably in the range of 2 to 40 ⁇ m, more preferably in the range of 5 to 30 ⁇ m, and more preferably in the range of 10 to 20 ⁇ m from the viewpoint of charge / discharge efficiency, input / output characteristics, and the like. It is particularly preferred.
- the average particle diameter means a particle diameter (median system: D 50 ) at an integrated value of 50% in a particle size distribution (volume basis) by a laser diffraction scattering method.
- the particle size distribution D 50 / D 5 for example, the first and second core particles in the range of 1.2 to 5 can be used, and as the particle size distribution D 50 / D 5 , for example, in the range of 2 to 4 First and second core particles can be used.
- D 5 denotes a particle diameter at an integrated value 5% in the particle size distribution by laser diffraction scattering method (by volume).
- the BET specific surface areas of the first and second core particles are, for example, 0.3 to 10 m 2 / g from the viewpoint of charge / discharge efficiency and input / output characteristics, respectively. Is preferably in the range of 0.5 to 10 m 2 / g, and more preferably in the range of 0.5 to 7 m 2 / g.
- Coating material first and second non-graphite carbon materials
- the hardness of the obtained composite particles can be increased according to the coating amount.
- side reactions between the active material and the electrolytic solution can be suppressed, charging / discharging efficiency can be improved, and reaction capacity can be increased.
- Non-graphitic carbon materials are carbon materials that do not have the three-dimensional crystal regularity of graphite, and include turbulent structure carbon materials and amorphous carbon materials, such as glassy carbon and heat treatment temperature. A carbon material that has not been crystallized because it is low is also included. Among these non-graphitic carbon materials, amorphous carbon materials having relatively high hardness are preferable.
- the first and second non-graphitic carbon materials may be different materials or the same material.
- the method of coating the core material with the non-graphite carbon material can be performed according to a normal method.
- a method of attaching an organic material to the surface of the core material and performing a heat treatment a chemical vapor deposition method (CVD method), a sputtering method (for example, an ion beam sputtering method), a vacuum evaporation method, a plasma method, an ion plating method, etc.
- a membrane method can be used.
- the method of attaching the organic substance to the surface of the core material includes a method of dry mixing the organic substance and the core material, and a method of removing the solvent by mixing the organic material solution and the core material. It is done.
- pitches such as petroleum pitch and coal pitch, phenol resin, polyvinyl alcohol resin, furan resin, polystyrene resin, polyimide resin, epoxy resin, cellulose, sucrose, and other resins can be used.
- Carbonization by heat treatment is performed in a non-oxidizing atmosphere such as an argon gas atmosphere or a nitrogen gas atmosphere, for example, at a temperature of 400 to 2000 ° C., preferably 800 to 1200 ° C., for example, 0.5 to 12 hours, preferably 0.5.
- the heat treatment time can be from 6 hours to 6 hours.
- the coating amount A (mass ratio of the non-graphitic carbon material in the first composite particles) is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and further preferably 0.5% by mass or more. . If the coating amount A is too small, the electrolytic solution is likely to be decomposed at the active end of the graphite, and gas may be generated or the cycle life may be reduced.
- the coating amount A is less than the coating amount B, preferably less than 5% by mass, more preferably 4% by mass or less, and further preferably 3% by mass or less. If the coating amount A is too large, the initial capacity of a battery using this active material may be reduced, the irreversible capacity at the beginning of the cycle may be increased, or the compression density of the electrode may be difficult to increase.
- the coating amount B (mass ratio of the non-graphitic carbon material in the second composite particles) is more than the coating amount A, preferably 5% by mass or more, more preferably 7% by mass or more, and more than 10% by mass. More preferably, 20 mass% or more is especially preferable, and it can be set to 30 mass% or more. If the coating amount B is too small, the desired cycle characteristics improving effect may be reduced.
- the coating layer B is preferably 50% by mass or less, or preferably less than 50% by mass, more preferably 45% by mass or less, and further preferably 40% by mass or less. If the coating amount B is too large, the initial capacity of a battery using this active material may be reduced, the irreversible capacity at the beginning of the cycle may be increased, or the compression density of the electrode may be difficult to increase.
- the coating amounts A and B can be determined by thermogravimetric analysis. More specifically, using a thermogravimetric analyzer, the first and second composite particles are each heated to about 900 ° C. at a predetermined temperature increase rate, and the weight change due to combustion accompanying the temperature increase is measured. It can be calculated by analyzing the obtained weight loss curve (the horizontal axis is temperature and the vertical axis is weight change). There is a weight reduction due to combustion of the coating material (non-graphitic carbon material such as amorphous carbon) on the low temperature side, and there is a weight reduction due to combustion of the core material on the high temperature side.
- the coating material non-graphitic carbon material such as amorphous carbon
- the coating amount can be calculated from the integrated value of the low temperature side peak and the integrated value of the high temperature side peak of the differential curve (temperature is on the horizontal axis and weight loss rate (% / K) is on the vertical axis) obtained from this weight loss curve.
- the average particle size of the graphite-based active material containing the first and second composite particles is preferably in the range of 2 to 40 ⁇ m from the viewpoint of charge / discharge efficiency, input / output characteristics, etc., and in the range of 5 to 30 ⁇ m. More preferably.
- 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 average particle size of the second composite particles is preferably sufficiently large with respect to the average particle size of the first composite particles from the viewpoint of improving cycle characteristics, and is about the same or larger than the same. It is preferable that If the average particle size of the second composite particles having a relatively high hardness is too small with respect to the average particle size of the first composite particles having a relatively low hardness, the function of transmitting the press pressure at the time of electrode preparation is sufficiently exerted. This may make it difficult to reduce the effect of improving cycle characteristics. From such a viewpoint, the average particle diameter of the first composite particles is preferably in the range of 2 to 38 ⁇ m, and more preferably in the range of 5 to 28 ⁇ m. The average particle size of the second composite particles is preferably in the range of 5 to 40 ⁇ m, and more preferably in the range of 8 to 30 ⁇ m.
- the BET specific surface area of the negative electrode active material containing the first and second composite particles is 0.3 to 10 m 2 / from the viewpoint of charge / discharge efficiency and input / output characteristics. It is preferably within the range of g, more preferably within the range of 0.5 to 10 m 2 / g, and even more preferably within the range of 0.5 to 7.0 m 2 / g.
- the BET specific surface area of the first composite particles is preferably in the range of 3.4 m 2 / g or more and 7.0 m 2 / g or less, and the BET specific surface area of the second composite particles is 0.9 m 2. / G or more and less than 3.4 m 2 / g.
- the BET specific surface area of the first composite particles is preferably in the range of 2.0 m 2 / g or more and 7.0 m 2 / g or less
- the BET specific surface area of the second composite particles is 0.9 m 2. / G or more and less than 2.0 m ⁇ 2 > / g.
- the first and second composite particles preferably satisfy the following conditions.
- Second is linear pressure B required the compressed density for the 1.5 g / cm 3 of the composite particles, a linear pressure A necessary compression density of the first composite particles to the 1.5 g / cm 3 Be bigger.
- the first composite particles have a linear pressure A required to have a compression density of 1.5 g / cm 3 in a range of 10 kgf / cm (98 N / cm) or more and less than 50 kgf / cm (490 N / cm). It is preferable that it exists in.
- the second composite particles have a linear pressure B required to make the compression density 1.5 g / cm 3 in a range of 50 kgf / cm (490 N / cm) to 180 kgf / cm (1765 N / cm). It is preferable that it exists in.
- the linear pressure B is more preferably 100 kgf / cm (490 N / cm) or more, and more preferably 170 kgf / cm (1667 N / cm) or less.
- Such a linear pressure value is related to the hardness of the first and second composite particles, and particles having a higher linear pressure value tend to have higher hardness.
- the linear pressure is a value obtained by dividing the load applied to the electrode surface by the roll press machine by the electrode width.
- This electrode width corresponds to the electrode width (coating width) in the roll width direction at the electrode installation position during pressing.
- Compressive density can be derived according to the following for an electrode punched into a predetermined size after pressing.
- an electrode means what applied the slurry containing 1st or 2nd composite particle on collectors, such as foil, and dried and formed the electrode application layer.
- the “linear pressure necessary to make the compression density 1.5 g / cm 3 ” is a roll press with various loads, the compression density of the electrode after each press is measured, and the compression density is “ The linear pressure can be determined from the load when it becomes “1.5 g / cm 3 ”.
- the content ratio of the second composite particles to the total of the first composite particles and the second composite particles is preferably 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more. If the content ratio of the second composite particles is too small, the effect of improving cycle characteristics may be reduced.
- the content ratio of the second composite particles to the total of the first composite particles and the second composite particles is preferably 30% by mass or less, more preferably 25% by mass or less, and further preferably 20% by mass or less. It can be set to less than 10% by mass and can be set to 8% by mass or less. If the content ratio of the second composite particles is too large (that is, the content ratio of the first composite particles is too small), the initial capacity of the battery using this active material is reduced or the irreversible capacity at the beginning of the cycle is increased. Or it may be difficult to increase the compression density of the electrode.
- the graphite-based active material according to the present embodiment can be manufactured by mixing the first and second composite particles described above by a known mixing method. If necessary, the graphite-based active material may be mixed with other active material as long as the desired effect is not impaired.
- the content of the first and second composite particles with respect to the entire graphite-based active material is preferably 90% by mass or more, and more preferably 95% by mass or more.
- the graphite-based active material according to the present embodiment can be composed of only the first and second composite particles.
- a negative electrode for a lithium ion secondary battery according to an embodiment of the present invention can be obtained, for example, by forming a negative electrode active material layer containing the above graphite-based active material 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 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, formamide, acetamide, dimethylformamide, acetonitrile, propionitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, sulfolane, methyl Non-protons such as sulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone An organic solvent 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. Moreover, a polymer component may be included as a non-aqueous electrolyte.
- 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.
- FIG. 1 shows a cross-sectional view of an example (laminate type) lithium ion secondary battery according to the present embodiment.
- the lithium ion secondary battery according to the present embodiment includes a positive electrode current collector 3 made of a metal such as an aluminum foil, and a positive electrode active material layer 1 containing a positive electrode active material provided thereon.
- a negative electrode current collector 4 made of a metal such as copper foil and a negative electrode active material layer 2 containing a negative electrode active material provided thereon.
- the positive electrode and the negative electrode are laminated via a separator 5 made of a nonwoven fabric or a polypropylene microporous film so that the positive electrode active material layer 1 and the negative electrode active material layer 2 face each other.
- This electrode pair is accommodated in a container formed of exterior bodies 6 and 7 such as an aluminum laminate film.
- a positive electrode tab 9 is connected to the positive electrode current collector 3, and a negative electrode tab 8 is connected to the negative electrode current collector 4, and these tabs are drawn out of the container.
- An electrolytic solution is injected into the container and sealed. It can also be set as the structure where the electrode group by which the several electrode pair was laminated
- Example 1 Natural graphite and an organic substance were mixed at a predetermined mass ratio and fired according to a normal method to prepare composite graphite particles A and B in which the graphite particles were coated with amorphous carbon.
- the amount of amorphous carbon in the obtained composite graphite particles A was 3% by mass, and the amount of amorphous carbon in the obtained composite graphite particles B was 40% by mass.
- D 5 of the composite graphite particles A is 13.3,
- D 50 is 18.4Myuemu, a specific surface area of 2.5 m 2 / g.
- D 5 of the composite graphite particle B is 9.4 .mu.m
- D 50 is 12.4, a specific surface area of 1.0 m 2 / g.
- This slurry was applied to one side of a 10 ⁇ m thick copper foil, and the coating film was dried. Then, it roll-pressed so that the density of a coating film (negative electrode coating film) might be 1.4 g / cm ⁇ 3 >, and the 33x45 mm negative electrode sheet was obtained.
- a slurry was prepared by dispersing in methyl-2-pyrrolidone. This slurry was applied to both surfaces of an aluminum foil, and the coating film was dried. Then, it roll-pressed so that the density of a coating film (positive electrode coating film) might be 3.0 g / cm ⁇ 3 >, and the positive electrode sheet of 30x40 mm was obtained.
- the negative electrode sheet was overlapped on both sides of the positive electrode sheet so that the positive electrode coating film and the negative electrode coating film face each other through a separator made of a microporous polyethylene film having a thickness of 25 ⁇ m. After the lead electrode for the positive electrode and the lead electrode for the negative electrode were provided, the laminate was wrapped with a laminate film, and an electrolyte solution was injected and sealed.
- lithium carbonate (LiPF 6 ) was dissolved to a concentration of 1.0 mol / L in a mixture of ethylene carbonate and diethyl carbonate at a volume ratio of 3: 7 was used.
- a negative electrode sheet was prepared in the same manner as above except that the composite graphite particles A were used alone, and the linear pressure A (linear pressure required to make the compression density 1.5 g / cm 3 ) was measured. / Cm 2 (294 N / cm).
- a negative electrode sheet was prepared in the same manner as described above except that the composite graphite particles B were used alone, and the linear pressure B (linear pressure required to make the compression density 1.5 g / cm 3 ) was measured. / Cm 2 (1667 N / cm).
- Example 1 A lithium ion secondary battery was produced in the same manner as in Example 1 except that only the composite graphite particles A were used as the negative electrode active material.
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Abstract
Description
第2の複合粒子に占める第2の非黒鉛系炭素材料の質量比率B(被覆量B)が、5質量%以上で且つ第1の複合粒子に占める第1の非黒鉛系炭素材料の質量比率A(被覆量A)より大きく、
第1の複合粒子と第2の複合粒子の合計に対する第2の複合粒子の含有比率が1質量%以上である、黒鉛系活物質材料が提供される。
本実施形態による活物質材料に含まれる第1及び第2の複合粒子の核材(第1及び第2の黒鉛コア粒子)としては、通常の天然黒鉛や人造黒鉛を用いることができる。X線回折法による(002)面の面間隔d002が好ましくは0.3354~0.340nmの範囲、より好ましくは0.3354~0.338nmの範囲にある黒鉛材料を用いることができる。これらの中でも、コスト等の観点から天然黒鉛(d002=0.3354)が好ましい。第1及び第2の黒鉛コア粒子は、互いに異なる材料からなるものであってもよいし、同じ材料からなるものであってもよい。
上述の核材(黒鉛コア粒子)の表面を非黒鉛系炭素材料で被覆することにより、その被覆量に従って、得られた複合粒子の硬度を高くすることができる。また、活物質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。
被覆量A(第1の複合粒子に占める非黒鉛系炭素材料の質量比率)は、0.1質量%以上が好ましく、0.2質量%以上がより好ましく、0.5質量%以上がさらに好ましい。被覆量Aが少なすぎると、黒鉛の活性な端部で電解液が分解しやすくなりガスが発生したり、サイクル寿命が低下したりする虞がある。
被覆量B(第2の複合粒子に占める非黒鉛系炭素材料の質量比率)は、被覆量Aより多く、5質量%以上が好ましく、7質量%以上がより好ましく、10質量%より大きいことがさらに好ましく、20質量%以上が特に好ましく、30質量%以上に設定できる。被覆量Bが少なすぎると、所望のサイクル特性改善効果が小さくなる虞がある。
第1及び2の複合粒子を含む黒鉛系活物質材料の平均粒径は、充放電効率や入出力特性等の観点から、2~40μmの範囲内にあることが好ましく、5~30μmの範囲内にあることがより好ましい。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。
第1及び第2の複合粒子は、次の条件を満たすものが好ましい。
電極密度D=A/(電極の厚さ-集電体の厚さ)
このようにして得られたプレス後の電極密度Dが圧縮密度に相当する。
第1の複合粒子と第2の複合粒子の合計に対する第2の複合粒子の含有比率は、1質量%以上が好ましく、3質量%以上がより好ましく、5質量%以上がさらに好ましい。第2の複合粒子の含有比率が少なすぎると、サイクル特性の改善効果が小さくなる虞がある。
以上に説明した第1及び第2の複合粒子を公知の混合方法で混合することによって、本実施形態による黒鉛系活物質材料を製造することができる。この黒鉛系活物質材料には、必要に応じて、所望の効果を損なわない範囲で他の活物質材料を混合してもよい。黒鉛系活物質材料全体に対する第1及び第2の複合粒子の含有量は90質量%以上が好ましく、95質量%以上がより好ましい。本実施形態による黒鉛系活物質材料は第1及び第2の複合粒子のみで構成できる。
本発明の実施形態によるリチウムイオン二次電池用負極は、例えば、負極集電体上に、上記の黒鉛系活物質材料と結着剤を含む負極活物質層を形成することで得ることができる。
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。
天然黒鉛と有機物を所定の質量比率で混合し、通常の方法に従って焼成を行って、黒鉛粒子が非晶質炭素で被覆された複合黒鉛粒子A及びBをそれぞれ調製した。
負極活物質として複合黒鉛粒子Aのみを用いた以外は実施例1と同様にしてリチウムイオン二次電池を作製した。
2 負極活物質層
3 正極集電体
4 負極集電体
5 セパレータ
6 ラミネート外装体
7 ラミネート外装体
8 負極タブ
9 正極タブ
Claims (13)
- 第1の黒鉛コア粒子とその表面を被覆する第1の非黒鉛系炭素材料からなる第1の複合粒子、及び第2の黒鉛コア粒子とその表面を被覆する第2の非黒鉛系炭素材料からなる第2の複合粒子を含み、
第2の複合粒子に占める第2の非黒鉛系炭素材料の質量比率Bが、5質量%以上で且つ第1の複合粒子に占める第1の非黒鉛系炭素材料の質量比率Aより大きく、
第1の複合粒子と第2の複合粒子の合計に対する第2の複合粒子の含有比率が1質量%以上である、黒鉛系活物質材料。 - 第1の複合粒子と第2の複合粒子の合計に対する第2の複合粒子の含有比率が3質量%以上である、請求項1記載の黒鉛系活物質材料。
- 第1の複合粒子と第2の複合粒子の合計に対する第2の複合粒子の含有比率が30質量%以下である、請求項1又は2記載の黒鉛系活物質材料。
- 第2の複合粒子に占める第2の非黒鉛系炭素材料の質量比率Bが10質量%より大きい、請求項1から3のいずれか一項に記載の黒鉛系活物質材料。
- 第2の複合粒子に占める第2の非黒鉛系炭素材料の質量比率Bが50質量%未満である、請求項1から4のいずれか一項に記載の黒鉛系活物質材料。
- 第1の複合粒子に占める第1の非黒鉛系炭素材料の質量比率Aが、0.1質量%以上5質量%未満の範囲にある、請求項1から5のいずれか一項に記載の黒鉛系活物質材料。
- 第1の複合粒子に占める第1の非黒鉛系炭素材料の質量比率Aが、0.1質量%以上4質量%以下の範囲にある、請求項1から5のいずれか一項に記載の黒鉛系活物質材料。
- 第2の複合粒子の圧縮密度を1.5g/cm3にするのに必要な線圧Bが、第1の複合粒子の圧縮密度を1.5g/cm3にするのに必要な線圧Aより大きい、請求項1から7のいずれか一項に記載の黒鉛系活物質材料。
- 第1の複合粒子の圧縮密度を1.5g/cm3にするのに必要な線圧Aが、10kgf/cm(98N/cm)以上50kgf/cm(490N/cm)未満の範囲にあり、
第2の複合粒子の圧縮密度を1.5g/cm3にするのに必要な線圧Bが、50kgf/cm(490N/cm)以上180kgf/cm(1765N/cm)以下の範囲にある、請求項1から8のいずれか一項に記載の黒鉛系活物質材料。 - 第1の黒鉛コア粒子および第2の黒鉛コア粒子がそれぞれ天然黒鉛からなる、請求項1から9のいずれか一項に記載の黒鉛系活物質材料。
- 第1の非黒鉛系炭素材料および第2の非黒鉛系炭素材料がそれぞれ非晶質炭素からなる、請求項1から10のいずれか一項に記載の黒鉛系活物質材料。
- 請求項1から11のいずれか一項に記載の黒鉛系活物質材料を含む、リチウムイオン二次電池用負極。
- リチウムイオンを吸蔵放出できる正極と、請求項12に記載の負極と、非水電解液を含むリチウムイオン二次電池。
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