WO2011002097A1 - リチウム二次電池の電極合剤用スラリー、該スラリーを用いた電極およびリチウム二次電池 - Google Patents
リチウム二次電池の電極合剤用スラリー、該スラリーを用いた電極およびリチウム二次電池 Download PDFInfo
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- 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
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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
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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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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- 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
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- 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
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- H—ELECTRICITY
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- 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
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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
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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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
- H01M4/139—Processes of manufacture
- H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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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
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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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
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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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 slurry for an electrode mixture of a lithium secondary battery that provides a flexible electrode, an electrode using the slurry, and a lithium secondary battery with improved battery characteristics.
- Lithium secondary batteries are widely used as power sources for various portable electric and electronic devices or as batteries for electric vehicles.
- a lithium secondary battery is equipped with a positive electrode, a negative electrode, a non-aqueous electrolyte, and usually a separator, and development and improvement of each member is actively performed.
- the positive electrode is usually prepared by, for example, dispersing a positive electrode active material in a binder, and if necessary, a conductive material together with an organic solvent to prepare a slurry for a positive electrode mixture. After applying to a positive electrode current collector, the solvent is removed by drying. It is produced by rolling.
- PVdF polyvinylidene fluoride
- a positive electrode mixture prepared by mixing lithium-containing oxide such as LiCoO 2 as a positive electrode active material and graphite as a conductive agent with PVdF is dispersed in N-methylpyrrolidone to form a slurry.
- a negative electrode mixture prepared by mixing a carbonaceous material as a negative electrode active material and PVdF is dispersed in N-methylpyrrolidone to form a slurry.
- the electrode sheet using PVdF as a binder is poor in flexibility, and the electrode sheet used in the production of the square battery is folded at 180 degrees, or the electrode sheet used in the production of the cylindrical battery is used in the process of rounding the electrode sheet small.
- the problem that the electrode mixture is peeled off from the sheet is likely to occur, and the production yield becomes difficult.
- Patent Document 2 discloses vinylidene fluoride (VdF) -hexafluoropropylene (HFP) for the purpose of imparting binding properties to the expansion and contraction of the positive electrode active material during charge and discharge in a non-aqueous electrolyte secondary battery.
- a material having rubber elasticity which is mainly composed of a fluorine-based binary copolymer such as a copolymer, a VdF-3 fluoroethylene chloride (CTFE) copolymer, is described as a binder.
- Patent Document 3 describes that a fluorine-based polymer copolymer mainly composed of VdF, tetrafluoroethylene (TFE) and HFP is used as a binder instead of PVdF.
- TFE tetrafluoroethylene
- HFP tetrafluoroethylene
- HFP tetrafluoroethylene
- HFP tetrafluoroethylene
- HFP tetrafluoroethylene
- HFP tetrafluoroethylene
- Patent Document 4 describes a binder that is soluble in a general-purpose solvent but hardly swells in an organic solvent of an electrolytic solution.
- the binder disclosed in Patent Document 4 includes VdF 50 to 80 mol% and TFE 20 to 50 mol% binary fluorine-containing copolymer, VdF 50 to 80 mol%, TFE 17 to 50 mol%, and other copolymerization monomers. It is a ternary fluorine-containing copolymer of less than 3 mol%, and VdF / TFE copolymer and VdF / TFE / HFP copolymer are described as VdF / TFE copolymer used in the examples. Yes.
- the content of resin such as polymethacrylate, polymethyl methacrylate, polyacrylonitrile, polyimide, polyamide, polyamideimide, polycarbonate, etc. in the binder is about 20% by volume. It is described that it may be included below.
- Patent Document 5 proposes to use a polyimide on the positive electrode side and an aromatic polyamide on the negative electrode side in addition to PVdF as a binder in order to improve the cycle characteristics at high temperature. .
- Patent Document 6 proposes a method of treating the surface of the current collector with an acrylic polymer in order to improve the adhesion between the current collector and the binder. Further, it is described that a mixture of 50 to 95% by weight of PVdF and a copolymer of VdF and another polymer (for example, TFE, HFP, CTFE, etc.) can be used.
- Patent Documents 7 and 8 Although various proposals have been made to improve the adhesion to the current collector as described above, many have sacrificed the flexibility of the electrodes. In order to improve the flexibility of the electrode, it has been proposed to contain fine rubber particles of acrylic rubber or styrene-butadiene rubber (Patent Documents 7 and 8).
- Japanese Unexamined Patent Publication No. 04-249859 Japanese Patent Laid-Open No. 04-095363 Japanese Patent Publication No. 08-004007 Japanese Patent Laid-Open No. 10-233217 Japanese Patent Laid-Open No. 11-031513 JP 09-199133 A JP 2003-331825 A JP 2006-185887 A
- Patent Documents 7 and 8 which improve the flexibility of the electrode, acrylic rubber and styrene butadiene rubber are blended, but the swelling of the electrode with respect to the electrolytic solution increases and the high-temperature characteristics and cycle characteristics deteriorate, and the oxidation resistance is low. Therefore, there is a problem that gas generation increases and cycle characteristics deteriorate.
- An object of the present invention is to improve the adhesiveness with a current collector and increase the flexibility of an electrode without impairing battery characteristics.
- the present invention relates to a slurry for an electrode mixture of a lithium secondary battery containing an electrode active material (A), a binder (B), and fluorine rubber particles (C).
- the present invention also provides an electrode for a lithium secondary battery obtained by applying the slurry for electrode mixture of the present invention to a current collector and drying, and further using the electrode of the present invention as a positive electrode and / or a negative electrode.
- the present invention also relates to a lithium secondary battery having a liquid.
- the present invention it is possible to provide a homogeneous and stable slurry for an electrode mixture, and further excellent adhesion to a current collector formed using this slurry for an electrode mixture, and also having resistance to swelling to an electrolytic solution. It is possible to provide a lithium secondary battery excellent in battery characteristics by using a flexible electrode without damaging and further using this electrode mixture.
- the electrode mixture slurry of the lithium secondary battery of the present invention includes an electrode active material (A), a binder (B), and fluororubber particles (C).
- A electrode active material
- B binder
- C fluororubber particles
- Electrode active material In this invention, a positive electrode active material (A1) or a negative electrode active material (A2) may be sufficient.
- (A1) Cathode Active Material As the cathode active material (A1), the formula (A1): Li x M 1 y M 2 1-y O 2 (Wherein 0.4 ⁇ x ⁇ 1; 0.3 ⁇ y ⁇ 1; M 1 is at least one selected from the group consisting of Ni and Mn; M 2 is selected from the group consisting of Co, Al and Fe) A lithium-containing composite metal oxide represented by at least one).
- Formula (A1-1) LiNi x Co y Al z O 2 (Wherein 0.7 ⁇ x ⁇ 1; 0 ⁇ y ⁇ 0.3; 0 ⁇ z ⁇ 0.03; 0.9 ⁇ x + y + z ⁇ 1.1),
- lithium-containing composite metal oxide represented by the formula (A1-1) include, for example, LiNi 0.8 Co 0.2 O 2 , LiNi 0.7 Co 0.3 O 2 , LiNi 0.82 Co 0.15 Al 0.03 O 2 , LiNi 0.7 Co 0.2 Al Examples thereof include 0.1 O 2 and LiNi 0.85 Co 0.1 Al 0.5 O 2. Among them, LiNi 0.82 Co 0.15 Al 0.03 O 2 (NCA) is preferable.
- lithium-containing composite metal oxide represented by the formula (A1-2) include, for example, LiNi 0.5 Mn 0.5 O 2 , LiNi 0.75 Mn 0.25 O 2 , LiNi 0.25 Mn 0.75 O 2 , LiNi 1/3 Co 1 / 3 Mn 1/3 O 2 , LiNi 0.4 Co 0.2 Mn 0.4 O 2 , LiNi 0.3 Co 0.5 Mn 0.2 O 2, etc., among which LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM) preferable.
- NCM LiNi 1/3 Co 1/3 Mn 1/3 O 2
- lithium-containing composite metal oxide represented by the formula (A1-3) include Li 0.5 MnO 2 (spinel manganese), LiMnO 2 and the like.
- lithium-containing composite metal oxide represented by the formula (A1-4) include, for example, LiFe 1/3 Co 1/3 Mn 1/3 O 2 , Li 0.5 Fe 1/3 Co 1/3 Mn 1 / 3 O 2 , LiFe 0.4 Co 0.3 Mn 0.3 O 2 , Li 0.5 Fe 0.4 Co 0.3 Mn 0.3 O 2 and the like can be mentioned.
- LiCoO 2 , LiNiO 2 , LiMn 2 O 4 and the like can also be used.
- Negative electrode active material examples include known basic materials such as a basic material containing Si and / or Sn. Specifically, metal compounds capable of inserting lithium ions, such as metal oxides and metal nitrides, Si, SiCuAl, SiNiAg, and CoSn 2 can also be used. Examples of the metal oxide include metal oxides containing Si and Sn, and examples of the metal nitride include Li 2.6 Co 0.4 N.
- PVdF As PVdF, those conventionally used for electrodes of lithium secondary batteries can be used as they are. PVdF may be used alone or in combination with other binder components.
- the molecular weight of PVdF is preferably such that the number average molecular weight measured by GPC (gel permeation chromatography) is 10,000 to 500,000 in terms of polystyrene.
- the positive electrode active material has also been variously developed from the viewpoints of battery characteristics, safety, resource (rare metal) depletion, etc.
- a positive electrode active material in which Co, which is a rare metal, is reduced has appeared.
- these positive electrode materials containing Ni and Mn have high basicity, so that the slurry is easily gelled.
- an active material made of a basic material has appeared in addition to the carbon-based material that has been used conventionally.
- Lithium-containing composite oxides including these LiCoO 2 , LiNiO 2 , and LiMn 2 O 4 are basically basic, and the reason has not been confirmed, but they were coexisted with PVdF and many VdF-based copolymers.
- gelation may occur, and the stability of the slurry may be impaired.
- negative electrode when a basic material is used as the negative electrode active material, there is a similar tendency.
- VdF / TFE copolymer obtained by copolymerizing TFE with a specific amount of VdF is surprisingly stable against a basic electrode active material.
- the slurry for electrode mixture prepared by mixing was found to be homogeneous and stable.
- Such excellent base resistance is specifically seen in VdF / TFE copolymers not found in other VdF copolymers such as VdF / HFP copolymers and VdF / CTFE copolymers. Is a characteristic.
- the binder (B2) is preferably a fluorine-containing polymer represented by the composition formula (B2).
- VdF / TFE fluorine-containing copolymer is preferred from the viewpoint of good flexibility and alkali resistance.
- VdF / TFE binary fluorine-containing copolymer A polymer is preferable from the viewpoint of good flexibility and alkali resistance.
- n (TFE) is preferably from 0.10 to 0.40, particularly preferably from 0.15 to 0.40 because of good base resistance and flexibility.
- a polymer is preferable from the viewpoint of good flexibility and alkali resistance.
- a copolymer of 0.60 ⁇ m ⁇ 0.90 and 0.09 ⁇ n ⁇ 0.45 and 0.01 ⁇ l ⁇ 0.04 is obtained.
- a copolymer satisfying 0.60 ⁇ m ⁇ 0.70, 0.30 ⁇ n ⁇ 0.40 and 0.02 ⁇ l ⁇ 0.04 is preferable.
- the molecular weight of the VdF / TFE copolymer preferably has a number average molecular weight of 10,000 to 500,000 in terms of polystyrene as measured by GPC (gel permeation chromatography). If it is less than 10,000, the molecular weight is too low to form a film, and if it exceeds 500,000, the thixotropy of the electrode mixture becomes very large and it tends to be difficult to apply to the electrode current collector. . In order to improve the cycle characteristics, it is preferable that the molecular weight is relatively high. From this point, for example, in the case of a terpolymer, 150,000 to 500,000 are preferable.
- the VdF / TFE copolymer used as the binder (B2) in the present invention can be polymerized by a known polymerization method, and among them, the radical copolymerization method is mainly preferred. That is, the polymerization method is not limited as long as it proceeds radically, but is initiated by, for example, an organic or inorganic radical polymerization initiator, heat, light, ionizing radiation, or the like.
- the polymerization mode solution polymerization, bulk polymerization, suspension polymerization, emulsion polymerization and the like can be used.
- This VdF / TFE copolymer (B2) has excellent base resistance and is not limited to nitrogen-containing organic solvents such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide, which are used as solvents for PVdF. It is also soluble in low-boiling general-purpose organic solvents that are commonly used, does not cause gelation even when mixed with an electrode active material, can impart flexibility to the electrode, and swells in non-aqueous electrolytes Is also small.
- nitrogen-containing organic solvents such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide
- VdF / TFE copolymer (B2) may be used alone or in combination with PVdF (B1) or other binder component (B3).
- the VdF / TFE copolymer (B2) When used in combination with PVdF (B1), the VdF / TFE copolymer (B2) is 20 to 80% by mass of the total amount of (B1) and (B2) to maintain flexibility and adherence. From the viewpoint of good properties.
- binder components examples include solvent-soluble thermoplastic resins, VdF / HFP copolymers, and VdF / CTFE copolymers. Among these, a solvent-soluble thermoplastic resin that functions to improve the adhesion to the current collector is preferable.
- the “solvent-soluble thermoplastic resin” is a thermoplastic resin that dissolves in an organic solvent at 25 ° C. at 5% by mass or more to form a uniform solution.
- a polyacrylic acid polymer A polymethacrylic acid polymer, polyimide, polyamide, polyamideimide and the like are preferable.
- polyacrylic acid polymers include polyacrylic acid, ammonium salts and sodium salts thereof; polyacrylic acid alkyl esters; polyacrylic acid amides; alkoxysilyl-modified polyacrylic acid esters.
- polymethacrylic acid polymer examples include polymethacrylic acid, ammonium salts and sodium salts thereof; polymethacrylic acid alkyl esters; polymethacrylic acid amides; alkoxysilyl-modified polymethacrylic acid esters.
- the binder (B3) When at least one selected from the group consisting of polyacrylic acid polymers, polymethacrylic acid polymers, polyimides, polyamides and polyamideimides is used as the binder (B3), the entire binder (B) From 5 to 50% by mass, it is preferable from the standpoint of maintaining flexibility and good adhesion.
- the fluororubber particles (C) have a role of imparting flexibility, particularly elongation, and properties such as rubber elasticity to the electrode mixture.
- fluoro rubber of the fluoro rubber particles (C) conventionally known fluoro rubber can be used.
- fluoro rubber non-perfluoro fluoro rubber and perfluoro fluoro rubber are preferable.
- Non-perfluorofluorororubbers include vinylidene fluoride (VdF) fluorine rubber, tetrafluoroethylene (TFE) / propylene fluorine rubber, tetrafluoroethylene (TFE) / propylene / vinylidene fluoride (VdF) fluorine rubber, ethylene / Hexafluoropropylene (HFP) fluorine rubber, Ethylene / Hexafluoropropylene (HFP) / Vinylidene fluoride (VdF) fluorine rubber, Ethylene / Hexafluoropropylene (HFP) / Tetrafluoroethylene (TFE) fluorine rubber, Fluoro Examples thereof include silicone-based fluororubber, fluorophosphazene-based fluororubber, and the like, which can be used alone or in any combination as long as the effects of the present invention are not impaired.
- VdF / HFP copolymer rubber VdF / HFP / TFE copolymer rubber, TFE / propylene copolymer rubber, TFE / HFP / propylene copolymer rubber, and TFE / PAVE copolymer rubber are suitable. is there.
- VdF rubbers (VdF / HFP copolymer rubber, VdF / HFP / TFE copolymer rubber, etc.) have repeating VdF repeating units derived from VdF repeating units and other comonomers. 20 mol% or more and 90 mol% or less of the total number of moles with the unit is preferable, and 40 mol% or more and 85 mol% or less is more preferable. A more preferred lower limit is 45 mol%, a particularly preferred lower limit is 50 mol%, and a more preferred upper limit is 80 mol%.
- the other monomer in the VdF rubber is not particularly limited as long as it is copolymerizable with VdF.
- TFE, HFP, PAVE, CTFE trifluoroethylene, trifluoropropylene, tetrafluoropropylene, penta Fluorine-containing monomers such as fluoropropylene, trifluorobutene, tetrafluoroisobutene, vinyl fluoride, iodine-containing fluorinated vinyl ether; fluorine-free monomers such as ethylene (Et), propylene (Pr), and alkyl vinyl ether These fluorine-containing monomers and non-fluorine-containing monomers can be used alone or in combination of two or more.
- PAVE perfluoro (methyl vinyl ether) and perfluoro (propyl vinyl ether) are preferable, and perfluoro (methyl vinyl ether) is particularly preferable.
- VdF rubber examples include VdF / HFP copolymer, VdF / HFP / TFE copolymer, VdF / CTFE copolymer, VdF / CTFE / TFE copolymer, VdF / PAVE copolymer, VdF / TFE copolymer, PAVE copolymer, VdF / HFP / PAVE copolymer, VdF / HFP / TFE / PAVE copolymer, VdF / TFE / Pr copolymer, or VdF / Et / HFP copolymer are preferred, and other More preferably, the monomer has TFE, HFP, and / or PAVE, in particular, VdF / HFP copolymer, VdF / HFP / TFE copolymer, VdF / PAVE copolymer, VdF. / TFE / PAVE copolymer, VdF / HFP /
- the VdF / HFP copolymer preferably has a VdF / HFP composition of (45 to 85) / (55 to 15) (mol%), more preferably (50 to 80) / (50 to 20). (Mol%), more preferably (60 to 80) / (40 to 20) (mol%).
- the VdF / HFP / TFE copolymer preferably has a VdF / HFP / TFE composition of (30 to 80) / (10 to 35) / (4 to 35) (mol%).
- the VdF / PAVE copolymer preferably has a VdF / PAVE composition of (65 to 90) / (35 to 10) (mol%).
- the VdF / TFE / PAVE copolymer preferably has a VdF / TFE / PAVE composition of (40-80) / (3-40) / (15-35) (mol%).
- VdF / HFP / TFE / PAVE copolymerization the composition of VdF / HFP / TFE / PAVE is (40 to 90) / (0 to 25) / (0 to 40) / (3 to 35) (mol%). (40 to 80) / (3 to 25) / (3 to 40) / (3 to 25) (mol%) is more preferable.
- the TFE / propylene-based fluororubber is a fluorine-containing copolymer comprising TFE 45 to 70 mol% and propylene 55 to 30 mol%.
- a specific third component for example, PAVE may be contained in an amount of 0 to 40 mol%.
- perfluoro fluorine rubber examples include those made of TFE / PAVE.
- the composition of TFE / PAVE is preferably (50 to 90) / (50 to 10) (mol%), more preferably (50 to 80) / (50 to 20) (mol%). More preferred is (55 to 75) / (45 to 25) (mol%).
- PAVE examples include perfluoro (methyl vinyl ether), perfluoro (propyl vinyl ether), and the like, and these can be used alone or in any combination.
- the fluororubber preferably has a number average molecular weight of 1,000 to 1,200,000, more preferably 5,000 to 900,000.
- the non-perfluorofluorororubber and perfluorofluorororubber described above can be produced by conventional methods such as emulsion polymerization, suspension polymerization, and solution polymerization.
- a fluororubber having a narrow molecular weight distribution can be produced according to a polymerization method using an iodine compound known as iodine (bromine) transfer polymerization.
- fluororubber containing VdF / HFP copolymer rubber, VdF / HFP / TFE copolymer rubber or TFE / propylene copolymer rubber as a unit is preferable.
- the fluororubber particles may be uncrosslinked rubber (raw rubber) particles or crosslinked rubber particles, but crosslinked rubber particles are preferred from the viewpoint of good solvent resistance (swelling resistance).
- the cross-linking of the fluororubber may be performed according to a known standard method.
- the particle diameter of the fluororubber particles (C) is about 0.1 to 2.0 ⁇ m, more preferably about 0.15 to 1.5 ⁇ m, particularly about 0.2 to 1.0 ⁇ m in terms of average primary particle diameter. It is preferable from the viewpoint that both the dispersibility of the film and the improvement of the strength of the film can be achieved.
- the blending amount of the fluororubber particles (C) is 0.1% by mass or more, preferably 0.5% by mass or more, particularly preferably 1% by mass of the total amount of the binder (B) and the fluororubber particles (C). That's it. If the amount is too small, the effect of improving the flexibility of the electrode mixture, particularly the elongation, tends to be small.
- the upper limit is preferably 50% by mass, and more preferably 30% by mass. If the amount is too large, dispersibility in the binder (B) tends to be poor, and swelling at high temperatures tends to increase. A particularly preferred upper limit is 20% by mass.
- the electrode mixture slurry of the present invention is obtained by mixing and dispersing an electrode active material (A), a binder (B), rubber particles (C), and an electrode material such as a conductive material described later in a solvent (D). It is obtained with.
- the solvent (D) may be an organic solvent (D1) or an aqueous solvent (D2), but an organic solvent (D1) is preferred from the viewpoint of slurry stability and coating properties.
- Examples of the organic solvent (D1) include nitrogen-containing organic solvents such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide, and ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; ethyl acetate, butyl acetate, and the like.
- Examples include ester solvents; ether solvents such as tetrahydrofuran and dioxane; and low-boiling general-purpose organic solvents such as mixed solvents thereof.
- N-methylpyrrolidone is particularly preferred because of its excellent slurry stability and coating properties.
- the water content of the organic solvent (D1) is important. That is, when the water content is 100 ppm or less, further 40 ppm or less, particularly 35 ppm or less, the basic expression due to the basic electrode active material is small, and gelation can be suppressed.
- Water is a representative example of the aqueous solvent (D2), and can be employed when safety and cost are emphasized.
- a conductive material As another electrode material, for example, a conductive material is exemplified.
- the conductive material include carbon blacks such as acetylene black and ketjen black, and carbon materials such as graphite.
- the electrode active material (A), the fluororubber particles (C), and the conductive material (E) are dissolved in a solution obtained by dissolving the binder (B) in the solvent (D).
- a method of dispersing and mixing these is generally used.
- the powders of the binder (B), the fluororubber particles (C), the electrode active material (A), and the conductive material (E) are first mixed together, and then the solvent (D) is added to prepare a slurry. May be.
- the amount of electrode active material (A) is as follows: solid content (electrode active material (A), binder (B), fluororubber particles (C), conductive material (E). Etc.) is 70 to 98% by mass, preferably 90 to 97% by mass.
- the blending ratio of the binder (B) is 0.1 to 20% by mass, preferably 1 to 10% by mass in the solid content regardless of whether it is a positive electrode or a negative electrode.
- the blending amount of the fluororubber particles (C) is 0.1 to 20% by mass, preferably 0.5 to 10% by mass in the solid content.
- the blending amount of the conductive material (E) is 1 to 20% by mass, preferably 2 to 10% by mass in the solid content.
- the solid content concentration of the slurry is preferably 40 to 70% by mass from the viewpoint of good workability, coating property, and slurry stability.
- the slurry for electrode mixture of the present invention is a stable and homogeneous fluid that does not gel, and can be applied to a current collector, dried, rolled, and cut into a predetermined size to produce an electrode. Conventional methods and conditions can be adopted as the method and conditions for producing the positive electrode and the negative electrode.
- Examples of the current collector on which the electrode mixture slurry is applied include aluminum foil, etched aluminum foil, and aluminum foil coated with a conductive paste.
- the electrode of the present invention does not cause cracking or peeling of the electrode mixture layer even if it is processed into a spiral type or a folded type electrode by blending the fluororubber particles (C) that give flexibility.
- the battery since the battery hardly swells with respect to the non-aqueous electrolyte, the battery characteristics are not greatly deteriorated even if the charge and discharge are repeated.
- the present invention also relates to a lithium secondary battery in which the electrode of the present invention is used as a positive electrode and / or a negative electrode and provided with a non-aqueous electrolyte.
- the negative electrode may include an electrode of the present invention containing a negative electrode active material made of a basic material such as an alloy, or a negative electrode using a known carbon material as a negative electrode active material. It may be.
- a negative electrode using a carbon material is prepared using a negative electrode active material and a negative electrode binder by a known material and method, and is applied or adhered to a negative electrode current collector such as a copper foil. Can be produced.
- a carbonaceous material that can be doped / undoped with lithium or the like is used.
- a conductive polymer such as polyacene or polypyrrole, coke, polymer charcoal, carbon fiber, or the like per unit volume.
- a conductive polymer such as polyacene or polypyrrole, coke, polymer charcoal, carbon fiber, or the like per unit volume.
- pyrolytic carbons such as polyacene or polypyrrole, coke, polymer charcoal, carbon fiber, or the like per unit volume.
- cokes petroleum coke, pitch coke, coal coke, etc.
- carbon black acetylene black, etc.
- glassy carbon organic polymer material fired bodies
- organic polymer materials Preferred are those fired in an inert gas stream or in vacuum at a temperature of 500 ° C. or higher.
- non-aqueous electrolyte a solution obtained by dissolving a known electrolyte salt in a known electrolyte salt dissolving organic solvent can be used.
- the organic solvent for dissolving the electrolyte is not particularly limited, but propylene carbonate, ethylene carbonate, butylene carbonate, ⁇ -butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate
- Known hydrocarbon solvents such as fluorinated solvents such as fluoroethylene carbonate, fluoroether, and fluorinated carbonate can be used.
- electrolyte salt examples include LiClO 4 , LiAsF 6 , LiBF 4 , LiPF 6 , LiN (SO 2 CF 3 ) 2 , and LiN (SO 2 C 2 F 5 ) 2.
- LiPF 6 , LiBF 4 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 or combinations thereof are preferred.
- the concentration of the electrolyte salt is required to be 0.8 mol / liter or more, and further 1.0 mol / liter or more. Although the upper limit depends on the organic solvent for dissolving the electrolyte salt, it is usually 1.5 mol / liter.
- the lithium secondary battery of the present invention can be produced by enclosing these members in a battery case and sealing them.
- a separator may be interposed between the positive electrode and the negative electrode.
- Example 1 (Preparation of slurry for positive electrode mixture) The ratio of each of the electrode materials shown in Table 1 is the positive electrode active material (A1): binder (B1) + (B2): fluoro rubber particles (C): conductive material (E) in a mass ratio of 92: 4. 1: Weighed to be 1: 3.
- NMP N-methylpyrrolidone
- a predetermined amount of the positive electrode active material (A1) and fluororubber particles are added to the NMP solution of the binder.
- C) and conductive material (E) were added and mixed thoroughly with a stirrer. While stirring, NMP was sequentially added so that the solid content concentration was 50% by mass to prepare a slurry for positive electrode mixture.
- the prepared slurry for positive electrode mixture was filtered through a Ni mesh (200 mesh) sieve to uniformize the particle size of the solid content. Subsequently, the positive electrode mixture slurry after filtration was vacuum defoamed. After the defoaming of the positive electrode mixture slurry is completed, the positive electrode mixture slurry is applied to an Al foil having a thickness of 22 ⁇ m, which is a current collector plate, by an applicator (amount that the dry mass of the positive electrode coating film is 18 mg / cm 2 ). ) After the application, NMP was completely volatilized while drying at 100 to 120 ° C. using a blast dryer or a hot plate to produce a strip-shaped positive electrode.
- Each component for preparing the positive electrode mixture slurry was as follows.
- Positive electrode active material (A1) (A1-1): LiNi 0.82 Co 0.15 Al 0.03 O 2 (manufactured by Toda Kogyo Co., Ltd.)
- A1-2 LiNi 1/3 Co 1/3 Mn 1/3 O 2 (manufactured by Nippon Chemical Industry Co., Ltd.)
- Binder (B1) (B1-1): PVdF (KF1120 manufactured by Kureha Chemical Co., Ltd.)
- Fluoro rubber particles (C) (C-1): Cross-linked VdF / HFP (78/22 mol% ratio) copolymer rubber. (Average primary particle size 0.3 ⁇ m) (C-2): Cross-linked TFE / VdF / HFP (30/48/22 mol% ratio) copolymer rubber.
- C-3 Rubber particles having a core of acrylic rubber and a shell of polymethyl methacrylate (cross-linked) (EXL2313 manufactured by Rohm and Haas Japan Co., Ltd., average primary particle size 0.6 ⁇ m)
- C-4 Rubber particles having a styrene-butadiene rubber core and a polymethyl methacrylate shell (cross-linked) (BTA772 manufactured by Rohm and Haas Japan Co., Ltd.) 8 ⁇ m)
- Example 2 A positive electrode was produced in the same manner as in Example 1 except that (C-1) and (C-5) were used in the amounts shown in Table 2 as the fluororubber particles (C), and the density and crack presence were examined. The results are shown in Table 2.
- Fluorine rubber particles (C-5): Cross-linked TFE / propylene (50/50 mol% ratio) copolymer rubber. (Average primary particle size 0.3 ⁇ m)
- Example 3 A positive electrode was prepared in the same manner as in Example 1 except that the resin shown in Table 3 was used as the binder (B3) in the ratio shown in Table 3, and the density and the presence or absence of cracks were examined. The results are shown in Table 3.
- Example 4 Using the positive electrode shown in Table 4, a lithium secondary battery (laminated cell) was produced by the following method. For these lithium secondary batteries, rate characteristics and cycle characteristics were examined as follows.
- the strip-shaped positive electrode was cut to 40 mm ⁇ 72 mm (with a positive electrode terminal of 10 mm ⁇ 10 mm), the strip-shaped negative electrode was cut to 42 mm ⁇ 74 mm (with a negative electrode terminal of 10 mm ⁇ 10 mm), and a lead body was welded to each terminal. Further, a microporous polyethylene film having a thickness of 20 ⁇ m was cut into a size of 78 mm ⁇ 46 mm to form a separator, and a positive electrode and a negative electrode were set so as to sandwich the separator, and these were put in an aluminum laminate packaging material.
- Rate characteristic (%) 5C discharge capacity (mAh) /0.2C discharge capacity (mAh) ⁇ 100
- Capacity retention rate (%) 100 cycle discharge capacity (mAh) / 1 cycle discharge capacity (mAh) ⁇ 100
- Example 5 Disperse Si (negative electrode active material; manufactured by Fuji Silysia Chemical Co., Ltd.), acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) and the mixture shown in Table 5 at a mass ratio of 45:45:10.
- a slurry for negative electrode mixture was prepared by dispersing and mixing in N-methylpyrrolidone (water content: 30 ppm) with a mixer. This slurry was uniformly applied onto a negative electrode current collector (copper foil having a thickness of 10 ⁇ m) and dried to form a negative electrode mixture layer, then compression-molded with a roll press machine, cut, and then dried. The lead body was welded to produce a strip-shaped negative electrode.
- the positive electrode was produced in the same manner as in Example 1 except that A1-2 (LiNi 1/3 Co 1/3 Mn 1/3 O 2 ) was used as the positive electrode active material.
- a lithium secondary battery (laminate cell) was produced in the same manner as in Example 4, and the cycle characteristics were measured in the same manner as in Example 4. The results are shown in Table 5.
- Example 6 A positive electrode was prepared in the same manner as in Example 1 except that a mixture slurry having the components shown in Table 6 was used, and the density, the presence or absence of cracks, and the swelling ratio into the electrolyte were examined. The results are shown in Table 6.
- Positive electrode active material (A1) (A1-3): Li 2 Mn 2 O 4 (A1-4): LiNi 0.8 Mn 0.2 O 2 (A1-5): LiFe 1/3 Co 1/3 Mn 1/3 O 2
- Fluoro rubber particles (C) (C-1): Cross-linked VdF / HFP (78/22 mol% ratio) copolymer rubber. (Average primary particle size 0.3 ⁇ m)
- Example 7 In Example 4, the mixture No. A lithium secondary battery (laminate cell) is similarly used except that NMP having a water content of 100 ppm, 500 ppm NMP and 1000 ppm NMP, and water are used as NMP to prepare the slurry 1-1. Fabricated and examined for rate characteristics and cycle characteristics. The results are shown in Table 7.
- Example 8 A negative electrode was produced in the same manner as in Example 5 except that SiO 2 or Sn was used as the negative electrode active material instead of Si.
- the positive electrode was produced in the same manner as in Example 1 except that A1-2 (LiNi 1/3 Co 1/3 Mn 1/3 O 2 ) was used as the positive electrode active material.
- a lithium secondary battery (laminate cell) was produced in the same manner as in Example 4, and the cycle characteristics were measured in the same manner as in Example 4. The results are shown in Table 8.
Abstract
Description
本発明においては、正極活物質(A1)でも負極活物質(A2)でもよい。
正極活物質(A1)としては、式(A1):
LixM1 yM2 1-yO2
(式中、0.4≦x≦1;0.3≦y≦1;M1はNiおよびMnよりなる群から選ばれる少なくとも1種;M2はCo、AlおよびFeよりなる群から選ばれる少なくとも1種)で示されるリチウム含有複合金属酸化物である。
式(A1-1):
LiNixCoyAlzO2
(式中、0.7≦x≦1;0≦y≦0.3;0≦z≦0.03;0.9≦x+y+z≦1.1)、
式(A1-2):
LiNixCoyMnzO2
(式中、0.3≦x≦0.6;0≦y≦0.4;0.3≦z≦0.6;0.9≦x+y+z≦1.1)、
式(A1-3):
LixMnzO2
(式中、0.4≦x≦0.6;0.9≦z≦1)、または
式(A1-4):
LiFexCoyMnzO2
(式中、0.3≦x≦0.6;0.1≦y≦0.4;0.3≦z≦0.6;0.9≦x+y+z≦1.1)
で示されるリチウム含有複合金属酸化物が好ましい。
負極活物質(A2)としては、公知の塩基性材料、たとえばSiおよび/またはSnを含有する塩基性を呈する材料が例示できる。具体的には、リチウムイオンを挿入可能な金属化合物、たとえば金属酸化物や金属窒化物、Si、SiCuAl、SiNiAg、CoSn2なども使用できる。金属酸化物としてはSiやSnを含む金属酸化物が、金属窒化物としてはLi2.6Co0.4Nなどがあげられる。
本発明で使用する結着剤(B)としては、ポリフッ化ビニリデン(B1)、および/または組成式(B2):
(VDF)m(TFE)n(HFP)l
(式中、VDFはフッ化ビニリデン由来の構造単位;TFEはテトラフルオロエチレン由来の構造単位;HFPはヘキサフルオロプロピレン由来の構造単位;0.45≦m<1;0<n≦0.5;0≦l≦0.1。ただし、m+n+l=1)で示されるVdF/TFE系含フッ素重合体(B2)を含むものが好ましい。
PVdFとしては従来からリチウム二次電池の電極に使用されているものがそのまま使用できる。PVdFは単独で使用しても、他の結着剤成分と併用してもよい。
上記のように、正極活物質についても、電池特性や安全性、資源(希少金属)枯渇などの観点から種々開発が進められ、最近ではNiやMnを含み希少金属であるCoを少なくした正極活物質が出現している。しかし、これらNiやMnを含有する正極材料では塩基性が高いためスラリーがゲル化しやすくなる。また、負極活物質についても、従来から使用されている炭素系材料に加えて、塩基性の材料からなる活物質が出現している。
他の結着剤成分としては、溶剤可溶型熱可塑性樹脂、VdF/HFP系共重合体やVdF/CTFE系共重合体などが例示できる。なかでも、集電体との接着性を向上させる働きをする溶剤可溶型熱可塑性樹脂が好ましい。
本発明において、フッ素ゴム粒子(C)は電極合剤に柔軟性、特に伸びを与え、さらにゴム弾性などの性質を付与する役割をもっている。
CF2=CF-Rf 1 (1)
(式中、Rf 1は-CF3または-ORf 2(Rf 2は炭素数1~5のパーフルオロアルキル基))で表されるパーフルオロエチレン性不飽和化合物よりなる群から選ばれる少なくとも1種の単量体に由来する構造単位を含むことが、ゴム弾性体としての性質をもつ粒子が得られる点から好ましい。
本発明において、本発明の効果を損なわない範囲で、必要に応じて、他の電極材料を配合することができる。
(正極合剤用スラリーの調製)
目的とする表1に示す各電極材料の割合を正極活物質(A1):結着剤(B1)+(B2):フッ素ゴム粒子(C):導電材(E)が質量比で92:4:1:3となるように秤量した。結着剤(B)を濃度が10質量%になるようにN-メチルピロリドン(NMP)に溶解させたのち、この結着剤のNMP溶液に所定量の正極活物質(A1)とフッ素ゴム粒子(C)と導電材(E)を加え、攪拌機で充分に混合した。撹拌しながら固形分濃度が50質量%になるようにNMPを逐次追加し、正極合剤用スラリーを調製した。
調製した上記正極合剤用スラリーをNiメッシュ(200メッシュ)の篩を通してろ過して固形分の粒径を均一化した。つづいて、ろ過後の正極合剤用スラリーに真空脱泡処理を施した。正極合剤用スラリーの脱泡が完了した後、集電板である厚さ22μmのAl箔上に正極合剤用スラリーをアプリケーターにより塗布(正極塗膜の乾燥質量が18mg/cm2となる量)を行った。塗布後、送風乾燥機またはホットプレートを用いて100~120℃で乾燥しながらNMPを完全に揮発させ、帯状の正極を作製した。
(A1-1):LiNi0.82Co0.15Al0.03O2(戸田工業(株)製)
(A1-2):LiNi1/3Co1/3Mn1/3O2(日本化学工業(株)製)
(B1-1):PVdF(呉羽化学(株)製のKF1120)
結着剤(B2)
(B2-1):VdF/TFE共重合体(VdF/TFE=80/20モル%比)
(B2-2):VdF/TFE/HFP共重合体(VdF/TFE/HFP=65/32.5/2.5モル%比)
(C-1):架橋VdF/HFP(78/22モル%比)共重合体ゴム。平均1次粒子径0.3μm)
(C-2):架橋TFE/VdF/HFP(30/48/22モル%比)共重合体ゴム。平均1次粒子径0.2μm)
(C-3):コアがアクリルゴムでシェルがポリメタクリル酸メチルであるゴム粒子(架橋済み)(ローム・アンド・ハース・ジャパン(株)製のEXL2313。平均1次粒子径0.6μm)
(C-4):コアがスチレン-ブタジエンゴムでシェルがポリメタクリル酸メチルであるゴム粒子(架橋済み)(ローム・アンド・ハース・ジャパン(株)社製のBTA772。平均1次粒子径0.8μm)
(D-1):N-メチルピロリドン(水分含有量30ppm)
作製した正極の密度をつぎの要領で測定した。結果を表1に示す。
正極をギャップが75μmのロールプレスに70℃で2回通し、さらにギャップを35μmに変更して2回通した後、正極の面積/膜厚/重量を測定して密度(g/cm3)を算出する。
作製した正極を縦3cm、横6cmに切り取った後、180°折り畳んだ後拡げて、正極の割れの有無を目視で確認した。結果を表1に示す。
LiPF6の1M濃度のエチレンカーボネート/エチルメチルカーボネート(3/7体積比)電解液に電極を浸漬し、90℃で24時間保持したのち膜厚変化を測定し、電極の膨潤率(%)[=(浸漬後の膜厚-浸漬前の膜厚)/浸漬前の膜厚×100)]を算出する。
フッ素ゴム粒子(C)として、(C-1)と(C-5)を表2に示す量用いたほかは実施例1と同様にして正極を作製し、密度および割れの有無を調べた。結果を表2に示す。
結着剤(B3)として表3に示す樹脂を表3に示す割合で使用したほかは実施例1と同様にして正極を作製し、密度および割れの有無を調べた。結果を表3に示す。
(B3-1):ポリメチルメタクリレート(PMMA)(Aldrich社製)
(B3-2):メチルメタクリレート(MMA)/メタクリル酸(MA)(MMA/MA=1:0.016モル比)(Aldrich社製)
(B3-3):ポリアミドイミド(PAI)(日立化成工業(株)製のHPC7200)
(B3-4):ポリイミド(PI)(日立化成工業(株)製のHCI-7000)
(B3-5):ポリアクリル酸(Aldrich社製)
表4に示す正極を使用してつぎの方法でリチウム二次電池(ラミネートセル)を作製した。これらのリチウム二次電池について、レート特性およびサイクル特性をつぎの要領で調べた。
人造黒鉛粉末(日立化成(株)製。商品名MAG-D)に、蒸留水で分散させたスチレン-ブタジエンゴムを固形分で6質量%となるように加え、ディスパーザーで混合してスラリー状としたものを負極集電体(厚さ10μmの銅箔)上に均一に塗布し、乾燥し、負極合剤層を形成し、その後、ローラプレス機により圧縮成形し、切断した後、乾燥し、リード体を溶接して、帯状の負極を作製した。
このラミネートセルを用い、0.5C・4.2Vで充電電流が1/10Cになるまで充電し0.2C相当の電流で3.0Vまで放電し、放電容量を求める。引き続き、0.5C、4.2Vで充電電流が1/10Cになるまで充電し、5C相当の電流で3.0Vになるまで放電し、放電容量を求める。この5Cでの放電容量と、上記の0.2Cでの放電容量との比から、レート特性を評価する。レート特性はつぎの計算式で求められた値をレート特性として記載する。
レート特性(%)=5C放電容量(mAh)/0.2C放電容量(mAh)×100
充放電電流をCで表示した場合、72mAを1Cとして以下の充放電測定条件で測定を行う。
充放電条件
充電:0.5C、4.2Vにて充電電流が1/10Cになるまでを保持(CC・CV充電)
放電:1C、2.5Vcut(CC放電)。
容量維持率(%)=100サイクル放電容量(mAh)/1サイクル放電容量(mAh)×100
Si(負極活物質。富士シリシア化学(株)製)とアセチレンブラック(電気化学工業(株)製のデンカブラック)と表5に示す合剤とを質量比で45:45:10の割合でディスパーザーにてN-メチルピロリドン(水分含有量30ppm)に分散混合して負極合剤用スラリーを調製した。このスラリーを負極集電体(厚さ10μmの銅箔)上に均一に塗布し、乾燥し、負極合剤層を形成し、その後、ロールプレス機により圧縮成形し、切断した後、乾燥し、リード体を溶接して、帯状の負極を作製した。
実施例1において、表6に示す成分の合剤スラリーを用いたほかは同様にし正極を作製し、密度、割れの有無および電解液への膨潤率を調べた。結果を表6に示す。
(A1-3):Li2Mn2O4
(A1-4):LiNi0.8Mn0.2O2
(A1-5):LiFe1/3Co1/3Mn1/3O2
(B2-3):TFE/VdF共重合体(TFE/VdF=33/67モル%比)
(B2-4):TFE/VdF共重合体(TFE/VdF=38/62モル%比)
(B2-5):TFE/VdF共重合体(TFE/VdF=8/92モル%比)
(C-1):架橋VdF/HFP(78/22モル%比)共重合体ゴム。平均1次粒子径0.3μm)
実施例4において、合剤No.1-1のスラリーを調製する際に使用するNMPとして、水分含有量が100ppmのNMP、500ppmのNMPおよび1000ppmのNMP、ならびに水を用いたほかは同様にしてリチウム二次電池(ラミネートセル)を作製し、レート特性およびサイクル特性を調べた。結果を表7に示す。
実施例5において、負極活物質としてSiに代えてSiO2またはSnを用いたほかは同様にして負極を作製した。
Claims (17)
- 電極活物質(A)と結着剤(B)とフッ素ゴム粒子(C)を含むリチウム二次電池の電極合剤用スラリー。
- フッ素ゴム粒子が、フッ化ビニリデンとヘキサフルオロプロピレンとの共重合体ゴムユニット、テトラフルオロエチレンとフッ化ビニリデンとヘキサフルオロプロピレンとの共重合体ゴムユニット、またはテトラフルオロエチレンとプロピレンとの共重合体ゴムユニットを含む請求項1記載の電極合剤用スラリー。
- フッ素ゴム粒子(C)が架橋されたフッ素ゴム粒子である請求項1または2記載の電極合剤用スラリー。
- フッ素ゴム粒子(C)の平均1次粒子径が0.1~2.0μmである請求項1~3のいずれかに記載の電極合剤用スラリー。
- 結着剤(B)が、ポリフッ化ビニリデン(B1)、および/または
組成式(B2):
(VDF)m(TFE)n(HFP)l
(式中、VDFはフッ化ビニリデン由来の構造単位;TFEはテトラフルオロエチレン由来の構造単位;HFPはヘキサフルオロプロピレン由来の構造単位;0.45≦m<1;0<n≦0.5;0≦l≦0.1。ただし、m+n+l=1)で示される含フッ素重合体(B2)を含む請求項1~4のいずれかに記載の電極合剤用スラリー。 - 結着剤(B2)が、式(B2)において、0.50≦m≦0.90、0.09≦n≦0.50および0≦l≦0.08。ただし、m+n+l=1)である含フッ素共重合体を含む請求項5記載の電極合剤用スラリー。
- 結着剤(B2)が、式(B2)において、lが0で、0.50≦m≦0.90および0.10≦n≦0.50。ただし、m+n=1)である二元含フッ素共重合体を含む請求項5記載の電極合剤用スラリー。
- 結着剤(B2)が、式(B2)において、0.50≦m≦0.90、0.09≦n≦0.49および0.01≦l≦0.04。ただし、m+n+l=1)である含フッ素共重合体を含む請求項5記載の電極合剤用スラリー。
- 結着剤(B)が、さらに、ポリフッ化ビニリデン(B1)および含フッ素重合体(B2)以外の溶剤可溶型熱可塑性樹脂(B3)を含む請求項5~8のいずれかに記載の電極合剤用スラリー。
- 結着剤(B3)が、ポリアクリル酸系重合体、ポリメタクリル酸系重合体、ポリイミド、ポリアミドおよびポリアミドイミドよりなる群から選ばれる少なくとも1種である請求項9記載の電極合剤用スラリー。
- 電極活物質(A)が正極活物質(A1)であり、式(A1):
LixM1 yM2 1-yO2
(式中、0.4≦x≦1;0.3≦y≦1;M1はNiおよびMnよりなる群から選ばれる少なくとも1種;M2はCo、AlおよびFeよりなる群から選ばれる少なくとも1種)で示されるリチウム含有複合金属酸化物を含む請求項1~10のいずれかに記載の電極合剤用スラリー。 - 電極活物質(A)がSiおよび/またはSnを含有する塩基性材料を含む負極活物質(A2)である請求項1~10のいずれかに記載の電極合剤用スラリー。
- さらに有機溶媒を含む請求項1~12のいずれかに記載の電極合剤用スラリー。
- 有機溶媒が、水分含有量が100ppm以下の有機溶媒である請求項13記載の電極合剤用スラリー。
- 固形分中に電極活物質(A)を70~98質量%、結着剤(B)を0.1~20質量%、およびフッ素ゴム粒子(C)を0.1~20質量%含む請求項1~14のいずれかに記載の電極合剤用スラリー。
- 請求項1~15のいずれかに記載の電極合剤用スラリーを集電体に塗工し乾燥して得られるリチウム二次電池の電極。
- 請求項16記載の電極を正極および/または負極とし、非水電解液を備えるリチウム二次電池。
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