WO2010146832A1 - 非水電解質二次電池用負極の製造方法、負極、およびそれを用いた非水電解質二次電池 - Google Patents
非水電解質二次電池用負極の製造方法、負極、およびそれを用いた非水電解質二次電池 Download PDFInfo
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- WO2010146832A1 WO2010146832A1 PCT/JP2010/003963 JP2010003963W WO2010146832A1 WO 2010146832 A1 WO2010146832 A1 WO 2010146832A1 JP 2010003963 W JP2010003963 W JP 2010003963W WO 2010146832 A1 WO2010146832 A1 WO 2010146832A1
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- negative electrode
- graphite particles
- mixture layer
- secondary battery
- electrolyte secondary
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Classifications
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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
-
- 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
-
- 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
- H01M4/139—Processes of manufacture
- H01M4/1393—Processes of manufacture of 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
- H01M4/623—Binders being polymers fluorinated polymers
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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
- H01M4/64—Carriers or collectors
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- H01M4/661—Metal or alloys, e.g. alloy coatings
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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
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
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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
- H01M4/04—Processes of manufacture in general
- H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
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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 non-aqueous electrolyte secondary battery, and more particularly to a method for producing a negative electrode containing graphite particles as a negative electrode active material.
- a negative electrode of a nonaqueous electrolyte secondary battery represented by a lithium ion secondary battery generally contains graphite particles as a negative electrode active material.
- This negative electrode is produced as follows.
- the negative electrode slurry is prepared by mixing graphite particles, a binder, and a conductive agent added as necessary in the presence of a predetermined dispersion medium. After apply
- Patent Document 1 proposes to use graphite particles having an average circularity of 0.93 or more for the purpose of improving cycle characteristics. According to this proposal, the adhesive strength between the negative electrode mixture layer and the negative electrode core material can be increased.
- an object of the present invention is to provide a method for producing a negative electrode capable of suppressing the deformation of graphite particles during compression of the negative electrode precursor in order to solve the above-described conventional problems.
- Another object of the present invention is to provide a high-capacity non-aqueous electrolyte secondary battery excellent in charge / discharge cycle characteristics by using the negative electrode obtained by the above-described production method.
- the negative electrode for a non-aqueous electrolyte secondary battery comprises: (1) applying a negative electrode slurry containing graphite particles and a binder to a negative electrode core material, and drying to form a negative electrode mixture layer; And (2) compressing the negative electrode precursor while heating at a temperature at which the binder is softened to obtain a negative electrode,
- the compressed negative electrode mixture layer of the negative electrode contains 1.5 g or more of the graphite particles per 1 cm 3 of the negative electrode mixture layer, and the average circularity of the graphite particles is determined by the negative electrode
- the temperature for heating the negative electrode precursor and the force for compressing the negative electrode precursor are controlled so as to maintain 70% or more of the average circularity of the graphite particles of the precursor.
- the present invention also relates to a negative electrode core material, and a negative electrode for a non-aqueous electrolyte secondary battery including a graphite particle and a binder, and including a negative electrode mixture layer compressed on the negative electrode core material.
- the negative electrode mixture layer contains 1.5 g or more of the graphite particles per 1 cm 3 of the negative electrode mixture layer, and the average circularity of the graphite particles holds 70% or more of that before compression.
- the present invention since the deformation of the graphite particles is suppressed during the compression of the negative electrode precursor, the deterioration of the charge / discharge cycle characteristics due to the deformation of the graphite particles is suppressed.
- the binder By heating the negative electrode precursor during compression of the negative electrode precursor, the binder can be softened and deformed, which makes it easier for the binder to enter between the graphite particles even at a low pressure (improves slipperiness).
- the binding property between the graphite particles is greatly improved.
- the method for producing a negative electrode for a non-aqueous electrolyte secondary battery comprises: (1) applying a negative electrode slurry containing graphite particles as a negative electrode active material and a binder to a negative electrode core; Forming an agent layer and obtaining a negative electrode precursor, and (2) compressing the negative electrode precursor while heating at a temperature at which the binder softens to obtain a negative electrode.
- the negative electrode mixture layer having a compressed negative electrode contains 1.5 g or more of graphite particles per 1 cm 3 of the negative electrode mixture layer, and the average circularity of the graphite particles is the graphite of the negative electrode precursor.
- the temperature for heating the negative electrode precursor and the force for compressing the negative electrode precursor are controlled so as to maintain 70% or more of the average circularity of the particles. That is, after the step (2), the weight of the graphite particles contained per 1 cm 3 of the negative electrode mixture layer is 1.5 g or more, and the step (2) for the average circularity of the graphite particles before the step (2)
- the temperature at which the negative electrode precursor is heated and the negative electrode precursor are compressed so that the reduction rate of the average circularity of the graphite particles after (the reduction rate of the average circularity of the graphite particles during compression) is 30% or less.
- the graphite particles are particles including a layered structure in which six carbon rings are linked, and examples thereof include particles such as natural graphite, artificial graphite, and graphitized mesophase carbon.
- the negative electrode precursor In the conventional method in which the negative electrode precursor is compressed only once without heating, it is necessary to compress the negative electrode mixture layer with a large linear pressure in order to ensure the binding property of the negative electrode mixture layer.
- the negative electrode mixture layer When the negative electrode mixture layer is compressed at a high density until the weight of the graphite particles contained in 1 cm 3 of the negative electrode mixture layer is about 1.5 g, the reduction rate of the average circularity of the graphite particles exceeds 30%. Graphite particles are greatly deformed. As a result, the internal stress of the graphite particles increases. Therefore, the particle shape changes greatly upon repeated expansion / contraction associated with charge / discharge, and the graphite particles easily fall off from the negative electrode core, resulting in a significant reduction in charge / discharge cycle characteristics.
- the pressure applied to the negative electrode precursor during compression can be reduced and the binder is easily deformed. It becomes easy for the binder to enter between the graphite particles. For this reason, the binding property between the graphite particles is greatly improved, and the negative electrode mixture layer can be firmly integrated with the negative electrode core material. Therefore, a negative electrode mixture layer having a desired negative electrode thickness and graphite particle density and excellent binding property between graphite particles can be easily and reliably obtained in a single compression step.
- the weight of the graphite particles contained per 1 cm 3 of the negative electrode mixture layer is 1.5 g or more, the deformation of the graphite particles is suppressed, and the reduction rate of the average circularity of the graphite particles can be suppressed to 30% or less. it can.
- a high capacity and high energy density negative electrode in which the weight of graphite particles contained per 1 cm 3 of the negative electrode mixture layer is 1.5 g or more can be obtained without impairing charge / discharge cycle characteristics.
- an extremely high packing density of graphite particles is achieved, in which the weight of graphite particles contained in 1 cm 3 of the negative electrode mixture layer is 1.6 g or more, which could not be obtained by the conventional method. be able to.
- the reduction rate of the average circularity of the graphite particles during compression is preferably 20% or less. When the reduction rate of the average circularity of the graphite particles during compression is 20% or less, the charge / discharge cycle characteristics can be greatly improved.
- the weight of the graphite particles contained per 1 cm 3 of the negative electrode mixture layer is preferably 1.7 g or less. When the weight of the graphite particles contained per 1 cm 3 of the negative electrode mixture layer exceeds 1.7 g, Li acceptability of the negative electrode is lowered, so that Li may precipitate on the negative electrode surface during charging.
- the average circularity can be measured, for example, by image processing of the negative electrode cross section with a scanning electron microscope (SEM). At this time, the circularity of any 100 particles having an equivalent circle diameter that matches the average particle diameter is obtained, and the average value is obtained.
- the equivalent circle diameter is the diameter of a circle having the same area as the area of the two-dimensional projection image of the particles.
- the average particle size of the graphite particles after compression is preferably 10 to 30 ⁇ m. If the average particle size of the graphite particles exceeds 30 ⁇ m, the reactivity of the graphite particles with lithium during charging may be reduced. If the average particle size of the graphite particles is less than 10 ⁇ m, the specific surface area becomes too large, and the irreversible capacity may increase. More preferably, the average particle diameter of the graphite particles is 15 to 25 ⁇ m.
- an average particle diameter means the median diameter (D50) in the volume particle size distribution of a negative electrode active material.
- the volume particle size distribution of the negative electrode active material can be measured by a commercially available laser diffraction particle size distribution analyzer (for example, LA-920 manufactured by HORIBA Ltd.).
- the average circularity of the graphite particles after compression is preferably 0.5 or more. If the average circularity of the graphite particles after compression is less than 0.5, the orientation of the graphite particles generated by the compression increases, and the reactivity of the graphite particles with lithium may decrease. More preferably, the average circularity of the graphite particles after compression is 0.7 or more. In order to set the average circularity of the graphite particles after compression to 0.5 or more, the average circularity of the graphite particles before compression is 0.7 or more from the viewpoint of the degree of decrease in the average circularity of the graphite particles during compression. Is preferred.
- Step (2) is, for example, a step of pressing the negative electrode precursor using a hot plate or a step of passing the negative electrode precursor between a pair of heat rolls. By carrying out this step once, the negative electrode mixture layer and the negative electrode core material can be brought into close contact and integrated.
- the negative electrode obtained in the step (2) includes a negative electrode core material made of a metal foil and a negative electrode mixture layer formed on both surfaces of the negative electrode core material
- the total thickness of the negative electrode is, for example, 100 to 300 ⁇ m.
- the thickness per side of the negative electrode mixture layer is, for example, 46 to 146 ⁇ m, and preferably 60 to 80 ⁇ m.
- the compression ratio in step (2) (ratio of the thickness of the negative electrode mixture layer in the negative electrode after compression to the thickness of the negative electrode mixture layer in the negative electrode precursor before compression) Is preferably 50 to 70%.
- the force (linear pressure) for compressing the negative electrode precursor in the step (2) is preferably 1 ⁇ 10 2 to 3 ⁇ 10 2 kgf / cm.
- the linear pressure is 1 ⁇ 10 2 kgf / cm or more, excellent binding properties can be obtained between the graphite particles and between the negative electrode mixture layer and the negative electrode core material even after one compression.
- the linear pressure is 3 ⁇ 10 2 kgf / cm or less, the deformation of the graphite particles is significantly suppressed.
- the linear pressure is more preferably 1 ⁇ 10 2 to 2 ⁇ 10 2 kgf / cm.
- the temperature at which the negative electrode precursor is heated in the step (2) is preferably a temperature at which the elastic modulus of the binder is 30% or less of the elastic modulus at 25 ° C. of the binder.
- the binder preferably has an elastic modulus at 25 ° C. of 0.5 ⁇ 10 3 to 3 ⁇ 10 3 MPa.
- the elastic modulus of styrene butadiene rubber (SBR) at 25 ° C. is 1.7 ⁇ 10 3 MPa.
- the elastic modulus is an index indicating the difficulty of deformation. When the elastic modulus decreases, the elastic modulus is easily deformed.
- the heating temperature in the step (2) is such that the elastic modulus of the binder is 0.05% or more of the elastic modulus of the binder at 25 ° C. Is more preferable.
- the heating temperature in the step (2) is a temperature at which the elastic modulus of the binder is less than 0.05% of the elastic modulus at 25 ° C. of the binder, the negative electrode capacity may decrease. This is presumably because the portion of the negative electrode mixture layer in which the entire surface of the graphite particles is densely covered with the binder increases, and the lithium acceptability of the graphite particles decreases.
- the temperature at which the elastic modulus of the binder is 30% or less of the elastic modulus at 25 ° C. of the binder is, for example, 50 to 100 ° C.
- the heating temperature in the step (2) is preferably 50 to 100 ° C.
- the binder that has an elastic modulus at 50 to 100 ° C. of 30% or less of an elastic modulus at 25 ° C. include SBR.
- the content of the binder in the negative electrode mixture layer is preferably 0.5 to 3 parts by weight per 100 parts by weight of the graphite particles. More preferably, the content of the binder in the negative electrode mixture layer is 0.5 to 2 parts by weight per 100 parts by weight of the graphite particles.
- the binder for example, a material that can be used in a non-aqueous electrolyte secondary battery, and a material whose elastic modulus satisfies the above conditions, that is, an elastic modulus at 25 ° C. of 0.5 ⁇ 10 3 to 3 ⁇
- a material having a viscosity of 10 3 MPa and an elastic modulus at 50 to 100 ° C. being 0.05 to 30% of the elastic modulus at 25 ° C. is used.
- binder examples include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin) , Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer ( CTFE), vinylidene fluoride - hexafluor
- the negative electrode mixture layer may further contain an optional component such as a conductive agent, but the amount of the optional component in the entire negative electrode mixture is desirably 3% by weight or less.
- the negative electrode mixture layer can contain 0.5 to 2 parts by weight, preferably 0.5 to 1 part by weight of a conductive agent per 100 parts by weight of graphite particles.
- the conductive agent carbon black, carbon nanofiber, and the like are preferable.
- the negative electrode core material for example, metal foil such as copper foil and copper alloy foil is used. Of these, copper foil (which may contain 1% or less of trace components other than copper) is preferable, and electrolytic copper foil is particularly preferable. From the viewpoint of the strength of the negative electrode core material and the high energy density of the battery, the thickness of the metal foil is preferably 5 to 15 ⁇ m.
- the nonaqueous electrolyte secondary battery of the present invention includes a negative electrode obtained by the above production method, a positive electrode capable of electrochemically inserting and extracting Li, a separator interposed between the negative electrode and the positive electrode, a nonaqueous electrolyte, It comprises.
- the present invention can be applied to non-aqueous electrolyte secondary batteries having various shapes such as a cylindrical shape, a flat shape, a coin shape, and a square shape, and the shape of the battery is not particularly limited.
- the strain stress of the graphite particles generated when the negative electrode mixture layer is compressed is gradually eliminated, and the average circularity of the graphite particles reduced by the compression increases.
- the strain stress is small, and the degree to which the average circularity of the graphite particles increases with repeated charge / discharge is small. Therefore, the shape change of the graphite particles is small. Therefore, the graphite particles in the negative electrode mixture layer are prevented from dropping from the negative electrode core material due to excessive increase in the average circularity of the graphite particles with repeated charge / discharge, and good charge / discharge cycle characteristics are obtained. .
- the increase rate of the average circularity of the graphite particles at 100 cycles relative to the average circularity of the graphite particles at the initial time (for example, at one cycle) (hereinafter, the average at 100 cycles)
- the circularity increase rate is preferably 20% or less. That is, the average circularity of the graphite particles at 100 cycles is preferably 120% or less of the average circularity of the initial graphite particles.
- the increase rate of the average circularity at 100 cycles is expressed by the following formula.
- Increase rate (%) of average circularity at 100 cycles (average circularity of graphite particles at 100 cycles ⁇ average circularity of initial graphite particles) / average circularity of initial graphite particles ⁇ 100
- dropping of the graphite particles from the negative electrode core material accompanying the charge / discharge cycle is suppressed, and the ratio of the discharge capacity at the 100th cycle to the initial capacity (for example, the discharge capacity at the first cycle) (hereinafter, the capacity at the 100th cycle).
- the maintenance ratio is 95% or more, and excellent cycle characteristics are obtained.
- the strain stress of the graphite particles generated during compression of the negative electrode mixture layer is gradually eliminated, and the average circularity of the graphite particles reduced by compression increases, thereby increasing the negative electrode The thickness of the mixture layer increases.
- the strain stress is small, and the degree of increase in the thickness of the negative electrode mixture layer with charge / discharge repetition is small. Therefore, the average circularity of the graphite particles excessively increases with repeated charging and discharging, so that the thickness of the negative electrode mixture layer increases excessively, and the graphite particles in the negative electrode mixture layer may fall off the negative electrode core material.
- the rate of increase in the thickness of the negative electrode mixture layer at 100 cycles relative to the thickness of the negative electrode mixture layer at 1 cycle Is preferably 5% or less. That is, the thickness of the negative electrode mixture layer at 100 cycles is preferably 105% or less of the thickness of the negative electrode mixture layer at one cycle.
- the rate of increase in thickness at 100 cycles is represented by the following formula.
- Thickness increase rate at 100 cycles (%) (thickness of negative electrode mixture layer at 100 cycles ⁇ 1 thickness of negative electrode mixture layer at cycle) / thickness of negative electrode mixture layer at one cycle ⁇ 100 In this case, falling off of the graphite particles from the negative electrode core material accompanying the charge / discharge cycle is suppressed, the capacity retention rate at 100 cycles is 95% or more, and excellent cycle characteristics are obtained.
- a positive electrode will not be specifically limited if it can be used as a positive electrode of a nonaqueous electrolyte secondary battery.
- the positive electrode for example, after applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent such as carbon black, and a binder such as polyvinylidene fluoride to a positive electrode core material such as an aluminum foil, is dried, Obtained by compression.
- a positive electrode active material a lithium-containing transition metal oxide is preferable.
- lithium-containing transition metal compounds include LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiMnO 2 , LiNi 1-y Co y O 2 (0 ⁇ y ⁇ 1), LiNi 1-yz Co y Mn and z O 2 (0 ⁇ y + z ⁇ 1).
- a liquid electrolyte comprising a non-aqueous solvent and a lithium salt dissolved therein is preferable.
- a non-aqueous solvent a mixed solvent of cyclic carbonates such as ethylene carbonate and propylene carbonate and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is generally used. Further, ⁇ -butyrolactone, dimethoxyethane and the like are also used.
- lithium salts include inorganic lithium fluorides and lithium imide compounds. Examples of the inorganic lithium fluoride include LiPF 6 and LiBF 4 , and examples of the lithium imide compound include LiN (CF 3 SO 2 ) 2 .
- a microporous film made of polyethylene, polypropylene or the like is generally used as the separator.
- the thickness of the separator is, for example, 10 to 30 ⁇ m.
- Example 1 Production of negative electrode 3 kg of artificial graphite (manufactured by Mitsubishi Chemical Corporation, average particle diameter 20 ⁇ m, average circularity 0.72) as negative electrode active material, and BM-400B (styrene butadiene rubber) manufactured by Nippon Zeon Co., Ltd. 75 g of an aqueous dispersion containing 40% by weight of (SBR), 30 g of carboxymethyl cellulose (CMC), and an appropriate amount of water were stirred with a double-arm kneader to prepare a negative electrode slurry. This negative electrode slurry was applied to both surfaces of a negative electrode core material made of a copper foil having a thickness of 10 ⁇ m, and then dried to form a negative electrode mixture layer. In this way, a negative electrode precursor was obtained.
- SBR aqueous dispersion containing 40% by weight of
- CMC carboxymethyl cellulose
- the negative electrode precursor was passed between a pair of heat rollers and compressed.
- the number of times of compression was one. More specifically, the negative electrode precursor was compressed at a linear pressure of 1.5 ⁇ 10 2 kgf / cm while being heated to 80 ° C. with a heat roller. At this time, the thickness of the negative electrode mixture layer (one side) decreased from 120 ⁇ m to 67 ⁇ m. In this way, a negative electrode having a total thickness of 144 ⁇ m was obtained.
- the negative electrode was cut into a 45 mm wide strip.
- Table 1 shows the elastic modulus at each temperature of SBR, which is a binder, and the ratio of the elastic modulus at each temperature to the elastic modulus at 25 ° C.
- the elastic modulus here refers to a storage elastic modulus.
- nonaqueous electrolyte LiPF LiPF at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 1: 1: 1. 6 was dissolved to prepare a non-aqueous electrolyte.
- the non-aqueous electrolyte contained 3% by weight of vinylene carbonate.
- Battery assembly A square lithium ion secondary battery as shown in FIG. 1 was produced.
- a group of electrodes having a substantially elliptical cross section wound around a separator (A089 (trade name) manufactured by Celgard Co., Ltd.) made of a polyethylene microporous film having a thickness of 20 ⁇ m interposed between the negative electrode and the positive electrode 1 was configured.
- the electrode group 1 was accommodated in a square battery can 2 made of aluminum.
- the battery can 2 has a bottom part and a side wall, the top part is opened, and the shape thereof is substantially rectangular. Thereafter, an insulator 7 for preventing a short circuit between the battery can 2 and the positive electrode lead 3 or the negative electrode lead 4 was disposed on the upper part of the electrode group 1.
- a rectangular sealing plate 5 having a negative electrode terminal 6 surrounded by an insulating gasket 8 and a safety valve 10 was disposed in the opening of the battery can 2.
- the negative electrode lead 4 was connected to the negative electrode terminal 6.
- the positive electrode lead 3 was connected to the lower surface of the sealing plate 5.
- the end of the opening of the battery can 2 and the sealing plate 5 were welded with a laser to seal the opening of the battery can 2. Thereafter, 2.5 g of nonaqueous electrolyte was injected into the battery can 2 from the injection hole of the sealing plate 5.
- liquid injection hole was closed with a plug 9 by welding to complete a prismatic lithium ion secondary battery having a height of 50 mm, a width of 34 mm, a thickness of about 5.4 mm, and a design capacity of 850 mAh.
- step (2) the negative electrode precursor was compressed at a linear pressure of 4 ⁇ 10 2 kgf / cm without heating so that the total thickness (density of graphite particles) was the same as that of the negative electrode of Example 1, A negative electrode was produced in the same manner as in Example 1. Using this negative electrode, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.
- step (2) a negative electrode was produced in the same manner as in Example 1, except that the negative electrode precursor was compressed without heating. At this time, the total thickness of the negative electrode was 159 ⁇ m. Using this negative electrode, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.
- the average particle size of the above graphite particles was obtained as an average value of the particle sizes of 100 arbitrary graphite particles extracted from the negative electrode mixture layer by SEM image processing.
- the graphite particles having a particle size of 1 ⁇ m or less were excluded.
- the negative electrode of Comparative Examples 1 and 2 Compared to a battery using the battery, excellent charge / discharge cycle characteristics were obtained.
- Comparative Example 1 since the negative electrode precursor is not heated during compression, the linear pressure during compression is higher than that in Example 1 when compressed to have the same negative electrode thickness (density of graphite particles) as in Example 1. became. As a result, the deformation of the graphite particles increased, the reduction rate of the average circularity of the graphite particles during compression increased, and the charge / discharge cycle characteristics deteriorated.
- Example 2 A negative electrode was produced in the same manner as in Example 1 except that the linear pressure was 2.0 ⁇ 10 2 kgf / cm and the heating temperature was changed to the values shown in Table 3 in the step (2). Using this negative electrode, a battery was produced in the same manner as in Example 1. The negative electrode and the battery were evaluated by the above method. The evaluation results are shown in Table 3.
- the density of the graphite particles in the negative electrode mixture layer was 1.5 g / cm 3 or more, and the reduction rate of the average particle circularity of the graphite particles during compression was 20% or less.
- the heating temperature in the step (2) was 50 to 100 ° C.
- a negative electrode having a high density of graphite particles in the negative electrode mixture layer was obtained, and excellent charge / discharge cycle characteristics were obtained.
- Example 3 A negative electrode was produced in the same manner as in Example 1, except that the heating temperature in the step (2) was 80 ° C. and the linear pressure was changed to the values shown in Table 4. Using this negative electrode, a battery was produced in the same manner as in Example 1. The negative electrode and the battery were evaluated by the above method. The evaluation results are shown in Table 4.
- the density of the graphite particles in the negative electrode mixture layer was 1.5 g / cm 3 or more, and the reduction rate of the average circularity of the graphite particles during compression was 30% or less.
- the linear pressure in the step (2) is 1.0 ⁇ 10 2 to 3.0 ⁇ 10 2 kgf / cm, a negative electrode having a high density of graphite particles in the negative electrode mixture layer is obtained and excellent. The charge / discharge cycle characteristics were obtained.
- the negative electrode of the present invention is suitably used for a non-aqueous electrolyte secondary battery such as a square type. Since the nonaqueous electrolyte secondary battery of the present invention has excellent initial characteristics and charge / discharge cycle characteristics, it is suitably used as a power source for electronic equipment such as information equipment.
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Abstract
Description
この負極は、以下のように作製される。黒鉛粒子、結着剤、および必要に応じて加える導電剤を、所定の分散媒の存在下で混合して、負極スラリーを調製する。この負極スラリーを、銅箔などからなる負極芯材に塗布した後、乾燥して負極合剤層を形成し、負極前駆体を得る。その後、負極前駆体をロールで圧縮することにより、負極合剤層の密度を高めるとともに、負極合剤層を負極芯材に密着させる。大判の負極芯材と一体化された負極合剤層は、複数の負極分の材料を含む原板であるため、これを、所定形状に裁断する。このようにして、個々の電池用の負極を得る。
そこで、特許文献1では、サイクル特性を改善する目的で、平均円形度が0.93以上の黒鉛粒子を用いることを提案している。この提案によると、負極合剤層と負極芯材との接着強度を高めることができる。
しかし、圧縮時のロールの線圧を大きくすると、特許文献1の平均円形度の大きな黒鉛粒子を用いても、圧縮時に黒鉛粒子が大きく変形して、平均円形度が大幅に減少するため、内部応力(歪み)の大きい、扁平形状の黒鉛粒子となる。このような黒鉛粒子を含む負極を備える電池を充放電すると、黒鉛粒子は、膨張および収縮による形状変化だけでなく、大きな内部応力(歪み)を解消するために大きな形状変化を生じる。このため、黒鉛粒子は負極芯材から脱落し易くなり、充放電サイクル特性が低下する。
前記工程(2)において、前記負極の圧縮された前記負極合剤層が、前記黒鉛粒子を当該負極合剤層1cm3あたり1.5g以上含み、かつ前記黒鉛粒子の平均円形度が、前記負極前駆体の黒鉛粒子の平均円形度の70%以上を保持するように、前記負極前駆体を加熱する温度および前記負極前駆体を圧縮する力を制御することを特徴とする。
前記負極合剤層は、前記黒鉛粒子を当該負極合剤層1cm3あたり1.5g以上含み、かつ前記黒鉛粒子の平均円形度は、圧縮前のそれの70%以上を保持していることを特徴とする。
負極前駆体の圧縮時において負極前駆体を加熱することにより、結着剤を軟化させ変形させることができるため、低い圧力でも黒鉛粒子間に結着剤が入り込み易くなり(すべり性が改善し)、黒鉛粒子間の結着性が大幅に向上する。
本発明の負極を用いることにより、優れた充放電サイクル特性を有し、信頼性の高い非水電解質二次電池が得られる。
本発明の新規な特徴を添付の請求の範囲に記述するが、本発明は、構成および内容の両方に関し、本発明の他の目的および特徴と併せ、図面を照合した以下の詳細な説明によりさらによく理解されるであろう。
ここでいう黒鉛粒子とは、六炭素環が連なった層状の構造を含む粒子であり、例えば、天然黒鉛、人造黒鉛、黒鉛化メソフェーズカーボンなどの粒子が挙げられる。
圧縮時の黒鉛粒子の平均円形度の減少率は20%以下が好ましい。圧縮時の黒鉛粒子の平均円形度の減少率が20%以下であると、充放電サイクル特性を大幅に向上させることができる。負極合剤層1cm3あたりに含まれる黒鉛粒子の重量は1.7g以下であるのが好ましい。負極合剤層1cm3あたりに含まれる黒鉛粒子の重量が1.7gを超えると、負極のLi受け入れ性が低下するので、充電時に負極表面でLiが析出する場合がある。
円形度=(粒子の二次元投影像と同じ面積を有する円の周囲長)/(粒子の二次元投影像の実際の周囲長)
圧縮時の黒鉛粒子の平均円形度の減少率は、下記式により求められる。
圧縮時の黒鉛粒子の平均円形度の減少率(%)=(圧縮前の黒鉛粒子の平均円形度-圧縮後の黒鉛粒子の平均円形度)/(圧縮前の黒鉛粒子の平均円形度)×100
なお、平均粒径とは、負極活物質の体積粒度分布におけるメディアン径(D50)を意味する。負極活物質の体積粒度分布は、市販のレーザー回折式粒度分布測定装置(例えば、HORIBA(株)製のLA-920)により測定することができる。
圧縮後の黒鉛粒子の平均円形度を0.5以上とするためには、圧縮時の黒鉛粒子の平均円形度の減少度合いの観点から、圧縮前の黒鉛粒子の平均円形度は0.7以上が好ましい。
工程(2)で得られる負極が、金属箔からなる負極芯材、および負極芯材の両面に形成された負極合剤層からなる場合、その負極の総厚みは、例えば、100~300μmである。負極合剤層の片面あたりの厚みは、例えば、46~146μmであり、好ましくは60~80μmである。
負極芯材の両面に負極合剤層を設ける場合、工程(2)における圧縮率(圧縮前の負極前駆体における負極合剤層の厚みに対する圧縮後の負極における負極合剤層の厚みの割合)は、50~70%であるのが好ましい。
より優れた充放電サイクル特性を得るためには、より好ましくは、線圧は1×102~2×102kgf/cmである。
弾性率は、変形し難さを表す指標であり、弾性率が低下すると、変形し易くなる。負極前駆体を上記温度に加熱しながら圧縮すると、結着剤が軟化して変形し易くなり、黒鉛粒子間に結着剤が入り込み易くなり、黒鉛粒子間の結着性が大幅に向上する。
負極合剤層中に結着剤を均一に存在させるためには、工程(2)の加熱温度は、結着剤の弾性率が当該結着剤の25℃における弾性率の0.05%以上となる温度がより好ましい。工程(2)の加熱温度が、結着剤の弾性率が当該結着剤の25℃における弾性率の0.05%未満となる温度であると、負極容量が低下する場合がある。これは、負極合剤層中において黒鉛粒子の表面全体が結着剤で密に覆われる部分が多くなり、黒鉛粒子のリチウム受け入れ性が低下するためと考えられる。
工程(2)の圧縮時において、加熱温度が50~100℃、および線圧が1×102~3×102kgf/cmである場合、圧縮時の黒鉛粒子の平均円形度の減少率は、10%程度まで小さくすることが可能である。
また、結着剤としては、例えば、ポリエチレン、ポリプロピレン、ポリテトラフルオロエチレン(PTFE)、ポリフッ化ビニリデン(PVDF)、スチレンブタジエンゴム(SBR)、テトラフルオロエチレン-ヘキサフルオロプロピレン共重合体(FEP)、テトラフルオロエチレン-パーフルオロアルキルビニルエーテル共重合体(PFA)、フッ化ビニリデン-ヘキサフルオロプロピレン共重合体、フッ化ビニリデン-クロロトリフルオロエチレン共重合体、エチレン-テトラフルオロエチレン共重合体(ETFE樹脂)、ポリクロロトリフルオロエチレン(PCTFE)、フッ化ビニリデン-ペンタフルオロプロピレン共重合体、プロピレン-テトラフルオロエチレン共重合体、エチレン-クロロトリフルオロエチレン共重合体(ECTFE)、フッ化ビニリデン-ヘキサフルオロプロピレン-テトラフルオロエチレン共重合体、フッ化ビニリデン-パーフルオロメチルビニルエーテル-テトラフルオロエチレン共重合体、エチレン-アクリル酸共重合体もしくはその(Na+)イオン架橋体、エチレン-メタクリル酸共重合体もしくはその(Na+)イオン架橋体、エチレン-アクリル酸メチル共重合体もしくはその(Na+)イオン架橋体、エチレン-メタクリル酸メチル共重合体もしくはその(Na+)イオン架橋体、またはこれらの誘導体が挙げられる。これらを単独または2種以上を組み合わせて用いてもよい。これらのなかでも、SBRが好ましい。
負極芯材としては、例えば、銅箔および銅合金箔のような金属箔が用いられる。なかでも銅箔(銅以外の微量成分を1%以下含んでもよい。)が好ましく、特に電解銅箔が好ましい。負極芯材の強度および電池の高エネルギー密度化の観点から、金属箔の厚みは、5~15μmが好ましい。
上記非水電解質二次電池の充放電サイクル試験における、初期(例えば1サイクル時)の黒鉛粒子の平均円形度に対する100サイクル時の黒鉛粒子の平均円形度の増加率(以下、100サイクル時の平均円形度の増加率)は20%以下であるのが好ましい。すなわち、100サイクル時の黒鉛粒子の平均円形度は、初期の黒鉛粒子の平均円形度の120%以下であるのが好ましい。
100サイクル時の平均円形度の増加率は、下記式により表される。
100サイクル時の平均円形度の増加率(%)=(100サイクル時の黒鉛粒子の平均円形度-初期の黒鉛粒子の平均円形度)/初期の黒鉛粒子の平均円形度×100
この場合、充放電サイクルに伴う黒鉛粒子の負極芯材からの脱落が抑制され、初期容量(例えば、1サイクル目の放電容量)に対する100サイクル目の放電容量の割合(以下、100サイクル時の容量維持率)が95%以上となり、優れたサイクル特性が得られる。
上記非水電解質二次電池の充放電サイクル試験における、1サイクル時の負極合剤層の厚みに対する100サイクル時の負極合剤層の厚みの増加率(以下、100サイクル時の厚みの増加率)は5%以下であるのが好ましい。すなわち、100サイクル時の負極合剤層の厚みは、1サイクル時の負極合剤層の厚みの105%以下であるのが好ましい。
100サイクル時の厚みの増加率は、下記式により表される。
100サイクル時の厚みの増加率(%)=(100サイクル時の負極合剤層の厚み-1サイクル時の負極合剤層の厚み)/1サイクル時の負極合剤層の厚み×100
この場合、充放電サイクルに伴う黒鉛粒子の負極芯材からの脱落が抑制され、100サイクル時の容量維持率が95%以上となり、優れたサイクル特性が得られる。
具体例として、電池容量が850mAhの場合の充放電サイクル試験条件を以下に示す。
定電流充電:充電電流値850mA、充電終止電圧4.2V
定電圧充電:充電電圧値4.2V、充電終止電流100mA
定電流放電:放電電流値850mA、放電終止電圧3V
休止時間:10min
《実施例1》
(1)負極の作製
負極活物質である人造黒鉛3kg(三菱化学(株)製、平均粒子径20μm、平均円形度0.72)と、日本ゼオン(株)製のBM-400B(スチレンブタジエンゴム(SBR)を40重量%含む水性分散液)75gと、カルボキシメチルセルロース(CMC)30gと、適量の水とを、双腕式練合機で攪拌し、負極スラリーを調製した。この負極スラリーを厚み10μmの銅箔からなる負極芯材の両面に塗布した後、乾燥して負極合剤層を形成した。このようにして、負極前駆体を得た。
結着剤であるSBRの各温度における弾性率、および25℃の弾性率に対する各温度での弾性率の割合を表1に示す。ここでいう弾性率とは、貯蔵弾性率を指す。
正極活物質であるコバルト酸リチウム3kgと、(株)クレハ製のPVDF#7208(PVDFを8重量%含むN-メチル-2-ピロリドン(以下、NMPと略記)溶液)0.6kgと、アセチレンブラック90gと、適量のNMPとを、双腕式練合機で攪拌し、正極スラリーを調製した。この正極スラリーを厚み15μmのアルミニウム箔からなる正極芯材の両面に塗布した後、乾燥して、正極合剤層を形成した。この正極合剤層を圧縮して、総厚みが152μmの正極を得た。正極を43mm幅の帯状に裁断した。
エチレンカーボネート(EC)と、ジメチルカーボネート(DMC)と、エチルメチルカーボネート(EMC)との体積比1:1:1の混合溶媒に、1モル/リットルの濃度でLiPF6を溶解させて非水電解質を調製した。非水電解質には3重量%のビニレンカーボネートを含ませた。
図1に示すような角型リチウムイオン二次電池を作製した。
負極と正極と、これらの間に介在させた厚み20μmのポリエチレン製の微多孔質フィルムからなるセパレータ(セルガード(株)製のA089(商品名))を捲回し、断面が略楕円形の電極群1を構成した。電極群1はアルミニウム製の角型の電池缶2に収容した。電池缶2は、底部と、側壁とを有し、上部は開口しており、その形状は略矩形である。その後、電池缶2と正極リード3または負極リード4との短絡を防ぐための絶縁体7を、電極群1の上部に配置した。次に、絶縁ガスケット8で囲まれた負極端子6と安全弁10とを有する矩形の封口板5を、電池缶2の開口に配置した。負極リード4は、負極端子6と接続した。正極リード3は、封口板5の下面と接続した。電池缶2の開口の端部と封口板5とをレーザーで溶接し、電池缶2の開口を封口した。その後、封口板5の注液孔から2.5gの非水電解質を電池缶2に注入した。最後に、注液孔を封栓9で溶接により塞ぎ、高さ50mm、幅34mm、厚み約5.4mm、および設計容量850mAhの角型リチウムイオン二次電池を完成させた。
工程(2)において、実施例1の負極と、総厚み(黒鉛粒子の密度)が同じになるように、負極前駆体を加熱せずに線圧4×102kgf/cmで圧縮した以外、実施例1と同様の方法により負極を作製した。この負極を用いて、実施例1と同様の方法により、非水電解質二次電池を作製した。
工程(2)において、負極前駆体を加熱せずに圧縮した以外、実施例1と同様の方法により負極を作製した。このとき、負極の総厚みは159μmであった。この負極を用いて、実施例1と同様の方法により、非水電解質二次電池を作製した。
[負極の評価]
(1)負極合剤層1cm3あたりに含まれる黒鉛粒子の重量(以下、黒鉛粒子の密度)の測定
負極合剤層の寸法(縦、横、および厚み)および黒鉛粒子の重量より、下記式を用いて活物質密度を求めた。
黒鉛粒子の密度(g/cm3)=黒鉛粒子の重量(g)/負極合剤層の体積(cm3)
負極合剤層の断面を走査型電子顕微鏡(SEM)で観察して、負極合剤層中の黒鉛粒子の平均円形度を求めた。
具体的には、SEMの画像処理により、平均粒径と一致する円相当径を有する任意の100個の黒鉛粒子を抽出し、それらの円形度を求め、その平均値を求めた。円相当径とは、粒子の二次元投影像の面積と同じ面積を有する円の直径である。
円形度は、下記式より求めた。
円形度=(粒子の二次元投影像と同じ面積を有する円の周囲長)/(粒子の二次元投影像の実際の周囲長)
下記式より圧縮時の黒鉛粒子の平均円形度の減少率を求めた。
圧縮時の黒鉛粒子の平均円形度の減少率(%)=(圧縮前の黒鉛粒子の平均円形度-圧縮後の黒鉛粒子の平均円形度)/圧縮前の黒鉛粒子の平均円形度×100
黒鉛粒子の圧縮前後の負極合剤層の厚みを測定し、下記式により圧縮率を求めた。
圧縮率(%)=圧縮後の負極合剤層の厚み/圧縮前の負極合剤層の厚み×100
(1)充放電サイクル特性の評価
20℃環境下で、下記条件で充放電し、初期容量を求めた。その後、20℃環境下で、下記条件で、充放電を100サイクル繰り返し、100サイクル目の放電容量を求めた。下記式により、100サイクル時の容量維持率を求めた。
100サイクル時の容量維持率(%)=100サイクル目の放電容量/1サイクル目の放電容量×100
定電流充電:充電電流値850mA、充電終止電圧4.2V
定電圧充電:充電電圧値4.2V、充電終止電流100mA
定電流放電:放電電流値850mA、放電終止電圧3V
休止時間:10min
下記式より、100サイクル時の黒鉛粒子の平均円形度の増加率を求めた。
100サイクル時の黒鉛粒子の平均円形度の増加率=(100サイクル時の黒鉛粒子の平均円形度-1サイクル時の黒鉛粒子の平均円形度)/1サイクル時の黒鉛粒子の平均円形度×100
下記式より、100サイクル時の負極合剤層の厚み増加率を求めた。
100サイクル時の負極合剤層の厚みの増加率=(100サイクル時の負極合剤層の厚み-1サイクル時の負極合剤層の厚み)/1サイクル時の負極合剤層の厚み×100
評価結果を表2に示す。
比較例1では、圧縮時に負極前駆体を加熱しないため、実施例1と同じ負極厚み(黒鉛粒子の密度)となるように圧縮すると、圧縮時の線圧は、実施例1よりも高い値となった。その結果、黒鉛粒子の変形が大きくなり、圧縮時の黒鉛粒子の平均円形度の減少率が大きくなり、充放電サイクル特性が低下した。
比較例2では、圧縮時に負極前駆体を加熱しないため、実施例1と同じ線圧で圧縮すると、黒鉛粒子間に結着剤が十分に入り込まず、実施例1と比べて、負極合剤層中の黒鉛粒子間の結着性が低下し、充放電サイクル特性が低下した。
工程(2)において線圧を2.0×102kgf/cmとし、加熱温度を表3に示す値に変えた以外、実施例1と同様の方法により負極を作製した。この負極を用いて、実施例1と同様の方法により電池を作製した。上記方法により負極および電池を評価した。評価結果を表3に示す。
工程(2)における加熱温度を80℃とし、線圧を表4に示す値に変えた以外、実施例1と同様の方法により負極を作製した。この負極を用いて実施例1と同様の方法により電池を作製した。上記方法により負極および電池を評価した。評価結果を表4に示す。
Claims (11)
- (1)負極芯材に、黒鉛粒子および結着剤を含む負極スラリーを塗布し、乾燥して負極合剤層を形成し、負極前駆体を得る工程と、
(2)前記負極前駆体を前記結着剤が軟化する温度で加熱しながら圧縮し、負極を得る工程と、を含み、
前記工程(2)において、前記負極の圧縮された前記負極合剤層が、前記黒鉛粒子を当該負極合剤層1cm3あたり1.5g以上含み、かつ前記黒鉛粒子の平均円形度が、前記負極前駆体の黒鉛粒子の平均円形度の70%以上を保持するように、前記負極前駆体を加熱する温度および前記負極前駆体を圧縮する力を制御することを特徴とする非水電解質二次電池用負極の製造方法。 - 前記負極前駆体を加熱する温度が、前記結着剤の弾性率が、当該結着剤の25℃における弾性率の30%以下となる温度である請求項1記載の非水電解質二次電池用負極の製造方法。
- 前記負極前駆体を加熱する温度が、50~100℃である請求項1記載の非水電解質二次電池用負極の製造方法。
- 前記負極前駆体を圧縮する力が、1×102~3×102kgf/cmである請求項1記載の非水電解質二次電池用負極の製造方法。
- 請求項1記載の製造方法により得られた非水電解質二次電池用負極。
- 負極芯材、ならびに黒鉛粒子および結着剤を含み、前記負極芯材上に圧縮された負極合剤層を含む非水電解質二次電池用負極であって、
前記負極合剤層は、前記黒鉛粒子を当該負極合剤層1cm3あたり1.5g以上含み、かつ前記黒鉛粒子の平均円形度は、圧縮前のそれの70%以上を保持していることを特徴とする非水電解質二次電池用負極。 - 前記負極合剤層は、前記黒鉛粒子を、当該負極合剤層1cm3あたり1.6g以上含み、かつ前記黒鉛粒子の平均円形度が0.7以上である請求項6記載の非水電解質二次電池用負極。
- 前記負極芯材が金属箔からなり、
前記負極合剤層が前記金属箔の両面に形成され、
前記負極合剤層の片面あたりの厚みが60~80μmである請求項6記載の非水電解質二次電池用負極。 - 請求項6記載の負極、正極活物質を含む正極、前記正極と負極との間に介在するセパレータ、および非水電解質を備える非水電解質二次電池。
- 充放電サイクル試験における、1サイクル時の前記黒鉛粒子の平均円形度に対する100サイクル時の前記黒鉛粒子の平均円形度の増加率は、20%以下である請求項9記載の非水電解質二次電池。
- 充放電サイクル試験における、1サイクル時の前記負極合剤層の厚みに対する100サイクル時の前記負極合剤層の厚みの増加率は、5%以下である請求項9記載の非水電解質二次電池。
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JP6004088B2 (ja) * | 2013-03-26 | 2016-10-05 | 日産自動車株式会社 | 非水電解質二次電池 |
KR20160037949A (ko) | 2013-07-24 | 2016-04-06 | 니폰 에이 엔 엘 가부시키가이샤 | 전극용 바인더, 전극용 조성물 및 전극 시트 |
JP2017091885A (ja) * | 2015-11-12 | 2017-05-25 | トヨタ自動車株式会社 | 非水電解液二次電池 |
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