WO2018008263A1 - バインダー組成物、電極合剤、電極、および非水電解質二次電池 - Google Patents
バインダー組成物、電極合剤、電極、および非水電解質二次電池 Download PDFInfo
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- WO2018008263A1 WO2018008263A1 PCT/JP2017/018694 JP2017018694W WO2018008263A1 WO 2018008263 A1 WO2018008263 A1 WO 2018008263A1 JP 2017018694 W JP2017018694 W JP 2017018694W WO 2018008263 A1 WO2018008263 A1 WO 2018008263A1
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- vinylidene fluoride
- fluoride copolymer
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- copolymer composition
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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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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
- C08F214/18—Monomers containing fluorine
- C08F214/22—Vinylidene fluoride
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L27/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers
- C08L27/02—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment
- C08L27/12—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
- C08L27/16—Homopolymers or copolymers or vinylidene fluoride
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
- C09J7/00—Adhesives in the form of films or foils
- C09J7/30—Adhesives in the form of films or foils characterised by the adhesive composition
- C09J7/38—Pressure-sensitive adhesives [PSA]
- C09J7/381—Pressure-sensitive adhesives [PSA] based on macromolecular compounds obtained by reactions involving only carbon-to-carbon unsaturated bonds
- C09J7/385—Acrylic 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
- 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
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
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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
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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
- H01M4/66—Selection of materials
- H01M4/665—Composites
- H01M4/667—Composites in the form of layers, e.g. 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
- 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
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
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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
- H01M4/52—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
- H01M4/624—Electric conductive fillers
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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 binder composition, an electrode mixture, an electrode, and a nonaqueous electrolyte secondary battery.
- Nonaqueous electrolyte secondary batteries are also used in hybrid vehicles combining secondary batteries and engines, and electric vehicles powered by secondary batteries, from the viewpoint of global environmental problems and energy saving. Applications are expanding.
- the electrode for a non-aqueous electrolyte secondary battery has a structure having a current collector and an electrode mixture layer formed on the current collector.
- the electrode mixture layer is generally applied on a current collector in a slurry state in which an electrode mixture containing an electrode active material, a conductive additive and a binder composition is dispersed in an appropriate solvent or dispersion medium. It is formed by volatilizing the medium.
- a vinylidene fluoride copolymer composition such as polyvinylidene fluoride (PVDF) is mainly used.
- PVDF is excellent in chemical resistance, weather resistance, and contamination resistance, and has excellent electrochemical stability, mechanical properties, slurry characteristics, and the like.
- PVDF has a problem that its adhesiveness with a metal foil which is a current collector of a battery is weak.
- Patent Document 1 discloses a battery electrode binder containing a vinylidene fluoride-based copolymer composition having a polar group.
- Patent Document 2 discloses a vinylidene fluoride copolymer derived from a vinylidene fluoride monomer and a certain kind of hydrophilic (meth) acrylic monomer (MA), and a hydrophilic (meth) acrylic monomer.
- a vinylidene fluoride copolymer containing 0.05 to 10 mol% of repeating units derived from the body (MA) and having a randomly distributed unit (MA) fraction of at least 40% is disclosed.
- the binder composition containing the vinylidene fluoride copolymer composition described in Patent Document 1 and the binder composition containing the vinylidene fluoride copolymer described in Patent Document 2 are included in the electrode mixture.
- the conductivity of the electrode mixture layer is low because the dispersibility of the conductive auxiliary agent is not sufficient.
- the present invention has been made in view of the above-described problems of the prior art, and its purpose is to provide sufficient adhesiveness in a binder composition using a vinylidene fluoride copolymer composition into which a polar group has been introduced. However, it is to provide a binder composition excellent in dispersibility of the conductive auxiliary agent.
- the binder composition includes a vinylidene fluoride copolymer composition
- the vinylidene fluoride copolymer composition includes a vinylidene fluoride and an acrylic monomer.
- the acrylic monomer is at least one selected from acrylic acid and methacrylic acid
- the vinylidene fluoride copolymer composition includes the vinylidene fluoride copolymer composition.
- the number average molecular weight of the vinylidene fluoride copolymer composition not adsorbed on the alumina after the adsorption relative to the number average molecular weight (Mn1) of the vinylidene fluoride copolymer composition before the adsorption (Mn2) (Mn2 / Mn1) is smaller than 2.
- a binder composition having sufficient adhesiveness and improved dispersibility of the conductive auxiliary agent.
- binder composition an electrode mixture, an electrode and a nonaqueous electrolyte secondary battery, and a method for producing the binder composition according to the present invention will be described in detail.
- the binder composition according to this embodiment is a composition used for binding an electrode active material to a current collector in an electrode in which an electrode mixture layer containing the electrode active material is formed on the current collector. is there.
- the binder composition according to the present embodiment includes a vinylidene fluoride copolymer composition.
- the binder composition may contain a solvent in addition to the vinylidene fluoride copolymer composition.
- the solvent may be a non-aqueous solvent or water.
- Non-aqueous solvents include, for example, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, trimethyl phosphate. Examples thereof include fate, acetone, and cyclohexanone. Two or more kinds of these solvents may be mixed and used.
- the “vinylidene fluoride copolymer composition” refers to a composition containing at least a copolymer (copolymer) of vinylidene fluoride and an acrylic monomer.
- the vinylidene fluoride copolymer composition include a homopolymer of vinylidene fluoride and a composition containing a copolymer of vinylidene fluoride and an acrylic monomer (copolymer).
- the acrylic monomer used for copolymerization with vinylidene fluoride is at least one selected from acrylic acid and methacrylic acid, and is preferably acrylic acid.
- the binder composition has a better adhesive property with the metal foil that is a battery current collector.
- the copolymer of vinylidene fluoride and an acrylic monomer may further contain other monomers in addition to the vinylidene fluoride and the acrylic monomer.
- the vinylidene fluoride copolymer composition may contain a plurality of types of copolymers of acrylic monomers and vinylidene fluoride having different compositions.
- the total amount of the acrylic monomer used for polymerization is not particularly limited, but is 0.05 to 5 parts by mass with respect to 100 parts by mass of vinylidene fluoride. It is preferably 0.1 to 3 parts by mass, more preferably 0.3 to 2 parts by mass.
- the vinylidene fluoride copolymer of vinylidene fluoride and an acrylic monomer according to the present embodiment contains 99.95 to 95 mol% of a structural unit derived from vinylidene fluoride (provided that the structural unit is derived from vinylidene fluoride). And a structural unit derived from an acrylic monomer is preferably 100 mol%), more preferably 99.92 to 96.5 mol%, and more preferably 99.9 to 98 mol%. Is particularly preferred. Further, the structural unit derived from an acrylic monomer is preferably 0.05 to 5 mol%, more preferably 0.08 to 3.5 mol%, particularly preferably 0.1 to 2 mol%. preferable.
- the inherent viscosity of the vinylidene fluoride copolymer composition according to this embodiment is not particularly limited, but is preferably 1 dl / g or more and 5 dl / g or less, and is 1.5 dl / g or more and 4 dl / g or less. Is more preferably 1.6 dl / g or more and 3.5 dl / g or less.
- the inherent viscosity of the vinylidene fluoride copolymer composition is particularly preferably 1.7 dl / g or more and 3.5 dl / g or less in one example. When the inherent viscosity is 1 dl / g or more, the adhesiveness of the binder composition becomes better. Further, when the inherent viscosity is 5 dl / g or less, the decrease in the solid content of the slurry is further suppressed, and the productivity becomes better.
- the absorbance ratio A R of vinylidene fluoride copolymer composition according to the present embodiment is not particularly limited, but is preferably 0.1 to 0.7, 0.15 to 0.7 More preferably, it is 0.2 or more and 0.7 or less. Further, the absorbance ratio A R of vinylidene fluoride copolymer composition, in one example, it is preferable 0.15 to 0.6, or 0.2 to 0.5. When the absorbance ratio is 0.1 or more, the adhesiveness of the binder composition becomes better. Moreover, when the absorbance ratio is 0.7 or less, a decrease in crystallinity of the vinylidene fluoride copolymer composition can be suppressed. Absorbance ratio A R of vinylidene fluoride copolymer composition, for example, can be calculated by the method described in Examples set forth below.
- the melting point of the vinylidene fluoride copolymer composition according to this embodiment is preferably 160 ° C. or higher, and more preferably 165 ° C. or higher.
- the melting point of the vinylidene fluoride copolymer composition can be measured, for example, by the method described in Examples described later.
- the “melting point” is determined by a differential scanning calorimeter. Specifically, the endotherm obtained when the vinylidene fluoride copolymer composition is heated above the equilibrium melting point of polyvinylidene fluoride with a differential scanning calorimeter, then cooled to near room temperature, solidified, and heated again. The peak top of the endothermic peak having the largest area among the peaks is defined as the melting point.
- Examples of other monomers that can be included in the copolymer of vinylidene fluoride and acrylic monomer include, for example, fluorine monomers copolymerizable with vinylidene fluoride or hydrocarbon monomers such as ethylene and propylene. Moreover, the monomer copolymerizable with an acrylic monomer is mentioned.
- Examples of the fluorine-based monomer copolymerizable with vinylidene fluoride include perfluoroalkyl vinyl ethers represented by vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoromethyl vinyl ether. Etc.
- Examples of the monomer copolymerizable with the acrylic monomer include 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, (meth) acrylamide, glycidyl (meth) acrylate, acrylonitrile and the like.
- the said other monomer may be used individually by 1 type, and may use 2 or more types.
- the total amount of other monomers used for polymerization is not particularly limited, but relative to 100 parts by mass of vinylidene fluoride
- the content is preferably 0.01 to 30 parts by mass, more preferably 0.05 to 20 parts by mass, and still more preferably 0.1 to 10 parts by mass.
- the number average molecular weight ratio of the vinylidene fluoride copolymer composition refers to the vinylidene fluoride copolymer before adsorption between the alumina and the vinylidene fluoride copolymer composition when the vinylidene fluoride copolymer composition is adsorbed on alumina.
- the number average molecular weight ratio (Mn2 / Mn1) of the vinylidene fluoride copolymer composition according to this embodiment is smaller than 2.
- the number average molecular weight ratio (Mn2 / Mn1) of the vinylidene fluoride copolymer composition according to this embodiment is preferably 1.8 or less, more preferably 1.7 or less, and 1.6 or less. More preferably.
- the vinylidene fluoride copolymer composition when adsorbed on alumina, among the polymers contained in the vinylidene fluoride copolymer composition, a copolymer of an acrylic monomer and vinylidene fluoride is present. Preferentially adsorbed on alumina. That is, Mn2 is the number average molecular weight of the remaining polymer that was not adsorbed on alumina. Examples of the remaining polymer include a copolymer of vinylidene fluoride and an acrylic monomer that has not been adsorbed to alumina, and other polymers contained in the vinylidene fluoride copolymer composition. Examples of the other polymer include a homopolymer of vinylidene fluoride.
- Mn2 / Mn1 is an index indicating how polar functional groups are distributed with respect to the molecular weight distribution of the vinylidene fluoride copolymer composition. As Mn2 / Mn1 increases, the vinylidene fluoride copolymer having a polar group contained in the vinylidene fluoride copolymer composition is more biased toward the low molecular weight region with respect to the molecular weight distribution of the vinylidene fluoride copolymer composition. Indicates that
- the adsorption rate of the polymer to the solid surface is faster for the low molecular weight body.
- the vinylidene fluoride copolymer composition if the polar functional group is unevenly distributed in the low molecular weight region, the vinylidene fluoride copolymer composition having the polar functional group is preferentially adsorbed on the conductive aid, thereby assisting the conduction. The agent tends to aggregate.
- the number average molecular weight ratio Mn2 / Mn1 of the vinylidene fluoride copolymer composition in this embodiment is smaller than 2, in the molecular weight distribution of the vinylidene fluoride copolymer composition in this embodiment, polar groups derived from acrylic monomers Since the distribution of the vinylidene fluoride copolymer having a concentration in the low molecular weight region is suppressed, the dispersibility of the conductive additive is improved.
- the number average molecular weight ratio in the vinylidene fluoride copolymer composition according to this embodiment is estimated by the following method.
- a 0.1% binder composition-NMP solution is prepared. While stirring this solution, slowly add alumina (eg, AKP3000). After alumina is added, it is stirred for a certain time and left to stand. Centrifuge the supernatant. GPC measurement is performed on the supernatant after centrifugation and the 0.1% binder composition-NMP solution before adding alumina, and the respective molecular weights are calculated.
- alumina eg, AKP3000
- the number average molecular weight of the vinylidene fluoride copolymer composition before being charged into alumina is Mn1
- the number average molecular weight of the vinylidene fluoride copolymer composition not being adsorbed on alumina after being charged into alumina is Mn2
- Mn2 relative to Mn1
- the number average molecular weight ratio (Mn2 / Mn1) which is the ratio, is determined. Since the amount of alumina to be added depends on the specific surface area of the alumina to be used, etc., it is not uniquely determined. It is preferable to adjust so that the area of the chromatogram is reduced by 60% or more after adsorption.
- the polar group since high adhesiveness is generally obtained by using a high molecular weight binder composition, the polar group contributes to efficiently exhibiting adhesiveness by suppressing the bias of the polar group to the low molecular weight region. To do. Thereby, the binder composition according to the present invention has an effect of being excellent in dispersibility of the conductive additive while having sufficient adhesiveness.
- Method for producing binder composition Although the manufacturing method of a binder composition is not specifically limited, In one example, the polymerization process of copolymerizing a vinylidene fluoride and an acrylic monomer and obtaining a vinylidene fluoride copolymer composition is included.
- the polymerization method of the vinylidene fluoride copolymer in the polymerization step is not particularly limited, and a conventionally known polymerization method can be used.
- the polymerization method include suspension polymerization, emulsion polymerization, solution polymerization and the like. Among them, aqueous suspension polymerization and emulsion polymerization are preferable from the viewpoint of ease of post-treatment, and aqueous suspension polymerization is particularly preferable. preferable.
- suspension polymerization In suspension polymerization, an oil-soluble polymerization initiator in water containing a stabilizer is dissolved in a water-insoluble monomer, which is mechanically stirred, suspended and dispersed, and heated. In this method, polymerization is performed in monomer droplets. In suspension polymerization, polymerization proceeds in monomer droplets, and a dispersion solution of binder composition fine particles is obtained. In suspension polymerization, a dispersion medium, a suspending agent, a polymerization initiator, and the like are used in addition to the monomer used for the polymerization of the vinylidene fluoride copolymer.
- the dispersion medium that can be used is not particularly limited, and a conventionally known dispersion medium can be used, but water is preferably used as the dispersion medium.
- suspending agent there is no limitation in particular as a suspending agent which can be used, A conventionally well-known thing can be used.
- the suspending agent include methyl cellulose, methoxylated methyl cellulose, propoxylated methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyethylene oxide, and gelatin.
- the addition amount of the suspending agent is preferably 0.005 to 1.0 part by mass, and 0.01 to 0.4 part by mass, when the total amount of all monomers used for copolymerization is 100 parts by mass. It is more preferable that
- Polymerization initiator There is no limitation in particular as a polymerization initiator which can be used, A conventionally well-known thing can be used.
- the polymerization initiator include diisopropyl peroxydicarbonate, dinormalpropyl peroxydicarbonate, dinormalheptafluoropropyl peroxydicarbonate, isobutyryl peroxide, di (chlorofluoroacyl) peroxide, and di (perfluoroacyl) peroxide. Examples thereof include oxide and t-butyl peroxypivalate.
- the addition amount of the polymerization initiator is preferably 0.05 to 5 parts by mass, more preferably 0.15 to 2 parts by mass, when the total amount of all monomers used for copolymerization is 100 parts by mass. preferable.
- a chain transfer agent may be used to adjust the degree of polymerization of the resulting vinylidene fluoride copolymer.
- the chain transfer agent include ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propyl aldehyde, ethyl propionate, and carbon tetrachloride.
- the addition amount of the chain transfer agent is preferably 0.1 to 5 parts by mass, with the total amount of all monomers used for copolymerization being 100 parts by mass, More preferably, it is 3 parts by mass.
- a buffer solution may be used as necessary.
- the buffer that can be used is not particularly limited, and conventionally known buffers can be used.
- Examples of the buffer include citrate buffer, phosphate buffer, citrate phosphate buffer, acetate buffer, borate buffer, and Tris buffer.
- the amount of the buffering agent constituting the buffer solution is preferably 0.01 to 5 parts by mass, with the total amount of all monomers used for copolymerization being 100 parts by mass, It is preferably ⁇ 3 parts by mass.
- the polymerization temperature T is appropriately selected according to the 10-hour half-life temperature T 10 of the polymerization initiator, and is usually selected in the range of T 10 ⁇ 20 ° C. ⁇ T ⁇ T 10 + 20 ° C.
- T 10 t- butyl peroxypivalate
- T 10 of diisopropyl peroxydicarbonate is 54.6 ° C. and 40.5 ° C. (see NOF Corporation Product Catalog). Therefore, in the polymerization using t-butyl peroxypivalate and diisopropyl peroxydicarbonate as the polymerization initiator, the polymerization temperatures T are 34.6 ° C. ⁇ T ⁇ 74.6 ° C. and 20.5 ° C. ⁇ T ⁇ 60.5, respectively. It is suitably selected within the range of ° C.
- the pressure during polymerization is usually under pressure, preferably 3 to 15 MPa-G.
- the polymerization time is not particularly limited, but is preferably 100 hours or less in consideration of productivity and the like.
- the electrode mixture which concerns on this embodiment contains the binder composition which concerns on this embodiment, an electrode active material, and a conductive support agent. Moreover, a solvent or a dispersion medium can be added as needed for adjusting the viscosity of the electrode mixture. An electrode can be produced by applying this electrode mixture to a current collector to form an electrode mixture layer.
- the electrode active material used in the electrode mixture in the present embodiment is not particularly limited.
- a conventionally known electrode active material for negative electrode (negative electrode active material) or electrode active material for positive electrode (positive electrode active material) ) can be used.
- the negative electrode active material include carbon materials, metal / alloy materials, and metal oxides. Among these, carbon materials are preferable. When such a carbon material is used, the energy density of the battery can be further increased.
- the positive electrode active material a lithium-based positive electrode active material containing at least lithium is preferable.
- lithium-based positive electrode active material examples include a general formula LiMY 2 (M is Co, Ni, Fe, Mn, Cr, V, etc.) such as LiCoO 2 and LiNi x Co 1-x O 2 (0 ⁇ x ⁇ 1).
- Y is a chalcogen element such as O and S), a composite metal oxide having a spinel structure such as LiMn 2 O 4 , and an olivine-type lithium compound such as LiFePO 4 Can be mentioned.
- the conductive aid used in the electrode mixture in the present embodiment is not particularly limited, and for example, conventionally known materials such as carbon black, carbon fiber, and carbon nanotube can be used.
- the electrode mixture in this embodiment may contain components other than the above-described components.
- examples of other components include pigment dispersants such as polyvinyl pyrrolidone.
- the binder composition is preferably 0.1 to 10 parts by mass, and 0.3 to 6 parts by mass per 100 parts by mass in total of the binder composition and the electrode active material. It is more preferable that Further, the electrode active material is preferably 90 to 99.9 parts by mass, and more preferably 94 to 99.7 parts by mass.
- the content of the conductive auxiliary agent is preferably 0.1 to 10 parts by mass, preferably 0.3 to 5 parts by mass, where the total of the binder composition, the electrode active material, and the conductive auxiliary is 100 parts by mass. More preferred is 0.5 to 3 parts by mass.
- the binder composition, the electrode active material, and the conductive additive may be mixed so as to form a uniform slurry, and the order of mixing is not particularly limited.
- a binder composition contains a solvent, you may make it add an electrode active material etc. before adding a solvent to a vinylidene fluoride copolymer composition.
- an electrode active material and a solvent may be added to a vinylidene fluoride copolymer composition and mixed by stirring to obtain an electrode mixture.
- an electrode active material may be disperse
- the electrode according to the present embodiment has a configuration in which a layer formed from the electrode mixture according to the present embodiment is provided on a current collector.
- the electrode mixture layer may be formed on at least one surface of the current collector, and is preferably formed on both surfaces of the current collector.
- the current collector is a base material for electrodes and is a terminal for taking out electricity.
- the material of the current collector is not particularly limited, and conventionally known materials such as aluminum and copper can be used.
- the thickness of the current collector is not particularly limited, but is preferably 5 to 100 ⁇ m, and more preferably 5 to 20 ⁇ m.
- Electrode mixture layer is a layer obtained by apply
- the method of applying the electrode mixture is not particularly limited, and examples thereof include a method using a bar coater, a die coater, or a comma coater.
- the thickness of the electrode mixture layer is not particularly limited, but is usually 20 to 250 ⁇ m, preferably 20 to 150 ⁇ m.
- the basis weight of the electrode mixture layer is not particularly limited, but is usually 20 to 700 g / m 2 and preferably 30 to 500 g / m 2 .
- the drying temperature and drying time for forming the electrode mixture layer are usually 1 to 300 minutes at a temperature of 50 to 150 ° C.
- the pressure during drying is not particularly limited, but drying is usually performed under atmospheric pressure or reduced pressure.
- a press process may be performed.
- the pressure is usually 1 to 200 MPa-G.
- the nonaqueous electrolyte secondary battery according to the present embodiment includes the electrode according to the present embodiment.
- Examples of the nonaqueous electrolyte secondary battery according to this embodiment include a polymer battery including a gel electrolyte.
- Other members (for example, separators) in the nonaqueous electrolyte secondary battery are not particularly limited, and for example, conventionally used members can be used.
- the binder composition includes a vinylidene fluoride copolymer composition
- the vinylidene fluoride copolymer composition includes a copolymer of vinylidene fluoride and an acrylic monomer.
- the acrylic monomer is at least one selected from acrylic acid and methacrylic acid
- the vinylidene fluoride copolymer composition is adsorbed on alumina by the vinylidene fluoride copolymer composition.
- the ratio of the number average molecular weight (Mn2) of the vinylidene fluoride copolymer composition not adsorbed to the alumina after the adsorption to the number average molecular weight (Mn1) of the vinylidene fluoride copolymer composition before the adsorption (Mn2 / Mn1) ) Is less than 2.
- the melting point of the vinylidene fluoride copolymer composition is 160 ° C. or higher.
- an electrode mixture containing the binder composition according to the present invention, an electrode active material, and a conductive additive is also included in the present invention.
- an electrode including a layer formed from the electrode mixture according to the present invention on a current collector, and a nonaqueous electrolyte secondary battery including the electrode are also included in the present invention.
- electrodes were manufactured using various binder compositions according to the present invention, and a peel test and volume resistivity measurement were performed using the electrodes.
- adhered viscosity As described later, electrodes were manufactured using various binder compositions according to the present invention, and a peel test and volume resistivity measurement were performed using the electrodes.
- ⁇ i (1 / C) ⁇ ln ( ⁇ / ⁇ 0 )
- ⁇ 0 is the viscosity of N, N-dimethylformamide as a solvent
- C is 0.4 g / dl.
- Absorbance ratio A R Vinylidene fluoride copolymer composition was hot pressed at 230 ° C., to produce a press sheet of 30 mm ⁇ 30 mm.
- Absorbance ratio A R is determined by the following equation.
- a R A 1700-1800 / A 3023
- a 1700-1800 is the absorbance derived from the stretching vibration of the carbonyl group detected in the range of 1700-1800 cm ⁇ 1
- a 3023 is derived from the stretching vibration of CH detected in the vicinity of 3023 cm ⁇ 1 . Absorbance.
- Example 1 [Preparation of binder composition] In an autoclave with an internal volume of 2 liters, 930 g of ion-exchanged water as a dispersion medium, 0.2 g of Metroles SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a suspending agent, and 50 wt% t-diisopropyl peroxydi as a polymerization initiator A carbonate-fluorocarbon 225cb solution (3.2 g), vinylidene fluoride (400 g), and acrylic acid (0.2 g) were charged, and the temperature was raised to 26 ° C. over 1 hour. Next, 98 g of a 2 wt% aqueous acrylic acid solution was added over 9 hours while maintaining 26 ° C. The polymerization was completed when 25.7 hours had elapsed from the start of the temperature increase.
- the polymer slurry was heat treated at 95 ° C. for 60 minutes, dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a binder composition (vinylidene fluoride copolymer composition). It was.
- the resulting polymer yield 96%, inherent viscosity eta i is 3.04dl / g, absorbance ratio A R was 0.28.
- Binder composition, N-methyl-2-pyrrolidone (NMP), and Ketjen black (Carbon ECP, manufactured by Lion Specialty Chemicals Co., Ltd.) as a conductive additive are added to a polyethylene cup and kneaded with Shinky AR-310. (1500 rpm, 1 minute) to obtain a paste.
- the electrode active material lithium cobaltate, manufactured by Nippon Chemical Industry Co., Ltd., Cell Seed C5H
- NMP was added and kneaded (1500 rpm, 2 minutes) so that the viscosity could be applied, thereby preparing an electrode mixture (kneading A).
- the addition amount (part) of the binder composition was 1.5 parts when the electrode active material was 100 parts.
- the obtained electrode mixture was applied onto a 15 ⁇ m-thick aluminum foil as a current collector with a bar coater and dried at 110 ° C. for 30 minutes in a nitrogen atmosphere using a thermostatic bath.
- a single-side coated electrode having a basis weight of 200 g / m 2 was produced.
- Example 2 [Preparation of binder composition]
- 900 g of ion-exchanged water as a dispersion medium 900 g
- 0.4 g of Metroles 90SH-100 manufactured by Shin-Etsu Chemical Co., Ltd.
- 50 wt% t-butylperoxypi 50 wt% t-butylperoxypi as a polymerization initiator 3.0 g of Valate-Freon 225cb solution, 400 g of vinylidene fluoride, and 0.2 g of acrylic acid as a monomer were charged, and the temperature was raised to 50 ° C. over 2 hours.
- the polymer slurry was heat treated at 95 ° C. for 60 minutes, dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a binder composition.
- the resulting polymer yield was 79%, the inherent viscosity eta i is 2.96dl / g, absorbance ratio A R was 0.28.
- the electrode was manufactured in the same manner as in Example 1.
- Example 3 [Preparation of binder composition] In an autoclave with an internal volume of 2 liters, 900 g of ion-exchanged water as a dispersion medium, 0.4 g of Metroles 90SH-100 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a cellulose-based suspending agent, and 50 wt% t-butylperoxypi as a polymerization initiator 4.0 g of Valate-Freon 225cb solution, 400 g of vinylidene fluoride, and 0.2 g of acrylic acid as a monomer were charged, and the temperature was raised to 50 ° C. over 2 hours.
- Metroles 90SH-100 manufactured by Shin-Etsu Chemical Co., Ltd.
- 50 wt% t-butylperoxypi as a polymerization initiator
- Valate-Freon 225cb solution 400 g of vinylidene fluoride, and 0.2 g of acrylic acid as
- the polymer slurry was heat treated at 95 ° C. for 60 minutes, dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a binder composition.
- the resulting polymer yield was 79%, the inherent viscosity eta i is 2.51dl / g, absorbance ratio A R was 0.29.
- the electrode was manufactured in the same manner as in Example 1.
- Example 4 [Preparation of binder composition] The binder composition was prepared in the same manner as in Example 3.
- Electrode active material lithium cobaltate, Nippon Chemical Industry Co., Ltd., Cellseed C-10
- Ketjen Black Lion Specialty Chemicals Co., Ltd., carbon ECP
- the electrode active material lithium cobaltate, Nippon Chemical Industry Co., Ltd., Cellseed C-10
- Ketjen Black Lion Specialty Chemicals Co., Ltd., carbon ECP
- the binder composition was added here and kneaded (1500 rpm, 2 minutes).
- NMP was added and kneaded (1500 rpm, 2 minutes) so that the viscosity could be applied, thereby preparing an electrode mixture (kneading B).
- the addition amount (part) of the binder composition was 2 parts when the electrode active material was 100 parts.
- the electrode was manufactured in the same manner as in Example 1.
- the polymer slurry was heat treated at 95 ° C. for 60 minutes, dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a binder composition.
- the resulting polymer yield was 53%
- the inherent viscosity eta i is 2.59dl / g
- absorbance ratio A R was 0.83.
- the electrode was manufactured in the same manner as in Example 1.
- a 0.1 wt% binder composition-NMP solution was prepared. While sufficiently stirring 5 g of this solution, 0.8 g of AKP3000 (Sumitomo Chemical High-Purity Alumina) was slowly added. After adding AKP3000, the mixture was stirred for 2.5 hours and allowed to stand overnight. The supernatant was collected and centrifuged. GPC measurement was performed on the supernatant after centrifugation and the 0.1% binder composition-NMP solution before adding alumina, and the respective number average molecular weights were calculated.
- AKP3000 Suditomo Chemical High-Purity Alumina
- the number average molecular weight of the vinylidene fluoride copolymer composition before being charged into alumina is Mn1
- the number average molecular weight of the vinylidene fluoride copolymer composition not being adsorbed on alumina after being charged into alumina is Mn2
- Mn2 relative to Mn1
- the vinylidene fluoride copolymer composition was hot-pressed at 230 ° C. to produce a 30 mm ⁇ 30 mm press sheet, and about 10 mg was cut out from the produced press sheet and used as a measurement sample.
- the measurement sample was put in an aluminum sample pan and measured using a differential scanning calorimeter (DSC) manufactured by Mettler Toledo. The measurement condition is that the measurement sample is heated to 230 ° C. and held for 10 minutes. Thereafter, it is cooled to 30 ° C. at 10 K / min and held for 10 minutes. Thereafter, the temperature was raised to 230 ° C. at 10 K / min. The peak top temperature of the largest endothermic peak obtained at the second temperature increase was taken as the melting point.
- DSC differential scanning calorimeter
- Table 1 shows the results of the inherent viscosity, peel strength, volume resistivity, and number average molecular weight ratio of each example and each comparative example.
- Table 2 shows the melting points of the vinylidene fluoride copolymer compositions used in Examples 1 to 3 and Comparative Example 1.
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Abstract
Description
本実施形態に係るバインダー組成物は、電極活物質を含む電極合剤層が集電体上に形成されてなる電極において、電極活物質を集電体に結着させるために用いられる組成物である。本実施形態に係るバインダー組成物は、フッ化ビニリデン共重合体組成物を含む。なおバインダー組成物は、フッ化ビニリデン共重合体組成物以外に溶媒を含んでいてもよい。溶媒は、非水溶媒であってもよいし、水であってもよい。非水溶媒としては、例えば、N‐メチルピロリドン、N,N‐ジメチルホルムアミド、N,N‐ジメチルアセトアミド、ジメチルスルホキシド、ヘキサメチルホスフォアミド、ジオキサン、テトラヒドロフラン、テトラメチルウレア、トリエチルホスフェイト、トリメチルホスフェイト、アセトン、およびシクロヘキサノンなどを挙げることができる。これらの溶媒は2種類以上を混合して用いてもよい。
本実施形態において「フッ化ビニリデン共重合体組成物」とは、少なくともフッ化ビニリデンとアクリル単量体との共重合体(コポリマー)を含む組成物を指す。フッ化ビニリデン共重合体組成物としては、例えば、フッ化ビニリデンの単独重合体(ホモポリマー)、およびフッ化ビニリデンとアクリル単量体との共重合体(コポリマー)を含む組成物などが挙げられる。フッ化ビニリデンとの共重合に用いられるアクリル単量体は、アクリル酸およびメタクリル酸から選ばれる少なくとも1種類以上であり、好ましくはアクリル酸である。アクリル単量体はカルボキシ基を有しており、カルボキシ基は金属との接着性を有する官能基であるため、バインダー組成物は電池の集電体である金属箔との接着性がより良好となる。なおフッ化ビニリデンとアクリル単量体との共重合体は、フッ化ビニリデンとアクリル単量体とに加えて、さらに他の単量体を含んでいてもよい。また、フッ化ビニリデン共重合体組成物には、組成が異なる複数種の、アクリル単量体とフッ化ビニリデンとの共重合体が含まれていてもよい。
フッ化ビニリデンとアクリル単量体との共重合体に含まれ得る他の単量体として、例えばフッ化ビニリデンと共重合可能なフッ素系単量体あるいはエチレン、プロピレン等の炭化水素系単量体、またアクリル単量体と共重合可能な単量体が挙げられる。フッ化ビニリデンと共重合可能なフッ素系単量体としては、例えば、フッ化ビニル、トリフルオロエチレン、テトラフルオロエチレン、クロロトリフルオロエチレン、ヘキサフルオロプロピレン、およびペルフルオロメチルビニルエーテルに代表されるペルフルオロアルキルビニルエーテル等を挙げることができる。アクリル単量体と共重合可能な単量体としては、2-ヒドロキシエチル(メタ)アクリレート、ヒドロキシプロピル(メタ)アクリレート、(メタ)アクリルアミド、グリシジル(メタ)アクリレート、およびアクリロニトリル等が挙げられる。なお、上記他の単量体は、1種単独で用いてもよく、2種以上を用いてもよい。
本実施形態に係るフッ化ビニリデン共重合体組成物における数平均分子量比について以下に説明する。
バインダー組成物の製造方法は、特に限定されないが、一例において、フッ化ビニリデンとアクリル単量体とを共重合し、フッ化ビニリデン共重合体組成物を得る重合工程を含む。
懸濁重合は、安定剤などを含む水中で油溶性の重合開始剤を非水溶性の単量体に溶かし、これを機械的に攪拌し、懸濁および分散させて加温することにより、その単量体液滴中で重合を行う方法である。懸濁重合では、単量体液滴中で重合が進行し、バインダー組成物微粒子の分散溶液が得られる。懸濁重合において、フッ化ビニリデン共重合体の重合に用いられる単量体の他に、分散媒体、懸濁剤、および重合開始剤等が用いられる。
用いることができる分散媒体としては特に限定はなく、従来公知のものを用いることができるが、分散媒体として水を用いることが好ましい。
用いることができる懸濁剤としては特に限定はなく、従来公知のものを用いることができる。懸濁剤としては、例えば、メチルセルロース、メトキシ化メチルセルロース、プロポキシ化メチルセルロース、ヒドロキシエチルセルロース、ヒドロキシプロピルセルロース、ポリビニルアルコール、ポリエチレンオキシド、およびゼラチン等を挙げることができる。
用いることができる重合開始剤としては特に限定はなく、従来公知のものを用いることができる。重合開始剤としては、例えば、ジイソプロピルペルオキシジカーボネート、ジノルマルプロピルペルオキシジカーボネート、ジノルマルヘプタフルオロプロピルペルオキシジカーボネート、イソブチリルペルオキサイド、ジ(クロロフルオロアシル)ペルオキサイド、ジ(ペルフルオロアシル)ペルオキサイド、およびt-ブチルペルオキシピバレート等を挙げることができる。
懸濁重合において、得られるフッ化ビニリデン共重合体の重合度を調節するために、連鎖移動剤を用いてもよい。連鎖移動剤としては、例えば、酢酸エチル、酢酸メチル、炭酸ジエチル、アセトン、エタノール、n-プロパノール、アセトアルデヒド、プロピルアルデヒド、プロピオン酸エチル、および四塩化炭素等を挙げることができる。
重合温度Tは、重合開始剤の10時間半減期温度T10に応じて適宜選択され、通常はT10-20℃≦T≦T10+20℃の範囲で選択される。例えば、t‐ブチルペルオキシピバレートおよびジイソプロピルペルオキシジカーボネートのT10はそれぞれ、54.6℃および40.5℃(日油株式会社製品カタログ参照)である。したがって、t‐ブチルペルオキシピバレートおよびジイソプロピルペルオキシジカーボネートを重合開始剤として用いた重合では、重合温度Tはそれぞれ34.6℃≦T≦74.6℃および20.5℃≦T≦60.5℃の範囲で適宜選択される。
本実施形態に係る電極合剤は、本実施形態に係るバインダー組成物と電極活物質と導電助剤とを含有する。また、電極合剤の粘度調整のため必要に応じて溶媒または分散媒を適宜追加することができる。この電極合剤を集電体に塗布して電極合剤層を形成することにより電極を作製することができる。
本実施形態における電極合剤において用いられる電極活物質は、特に限定されるものではなく、例えば、従来公知の負極用の電極活物質(負極活物質)または正極用の電極活物質(正極活物質)を用いることができる。負極活物質としては、例えば、炭素材料、金属・合金材料、および金属酸化物などが挙げられるが、中でも炭素材料が好ましい。このような炭素材料を使用すると、電池のエネルギー密度をより高くすることができる。正極活物質としては、少なくともリチウムを含むリチウム系正極活物質が好ましい。リチウム系正極活物質としては例えば、LiCoO2、LiNixCo1-xO2(0≦x≦1)等の一般式LiMY2(Mは、Co、Ni、Fe、Mn、Cr、V等の遷移金属の少なくとも一種:YはO、S等のカルコゲン元素)で表わされる複合金属カルコゲン化合物、LiMn2O4などのスピネル構造をとる複合金属酸化物、およびLiFePO4などのオリビン型リチウム化合物等が挙げられる。
本実施形態における電極合剤において用いられる導電助剤は、特に限定されるものではなく、例えば、カーボンブラック、カーボンファイバー、およびカーボンナノチューブ等の従来公知のものを用いることができる。
本実施形態における電極合剤は、上述の成分以外の他の成分を含んでいてもよい。他の成分としては、例えば、ポリビニルピロリドンなどの顔料分散剤等を挙げることができる。
本実施形態に係る電極合剤においては、バインダー組成物と電極活物質との合計100質量部あたり、バインダー組成物は0.1~10質量部であることが好ましく、0.3~6質量部であることがより好ましい。また電極活物質は90~99.9質量部であることが好ましく、94~99.7質量部であることがより好ましい。導電助剤の含有量は、バインダー組成物と電極活物質と導電助剤との合計を100質量部とすると、0.1~10質量部であることが好ましく、0.3~5質量部であることがより好ましく、0.5~3質量部であることがさらに好ましく。
本実施形態に係る電極合剤の製造方法は、例えば、バインダー組成物、電極活物質、導電助剤を均一なスラリーとなるように混合すればよく、混合する際の順序は特に限定されない。さらに、バインダー組成物が溶媒を含む場合、フッ化ビニリデン共重合体組成物に溶媒を加える前に、電極活物質などを加えるようにしてもよい。
本実施形態に係る電極は、本実施形態に係る電極合剤から形成された層が集電体上に設けられた構成である。電極合剤層は、集電体の少なくとも一方の面に形成されていればよく、集電体の両方の面に形成されていることが好ましい。
集電体は電極の基材であり、電気を取り出すための端子である。集電体の材質としては、特に限定されるものではなく、アルミニウムおよび銅などの従来公知のものを用いることができる。
電極合剤層は、上述した電極合剤を集電体に塗布して、乾燥させることにより得られる層である。電極合剤の塗布方法としては特に限定はなく、バーコーター、ダイコーター、またはコンマコーターで塗布する等の方法が挙げられる。
本実施形態に係る非水電解質二次電池は、本実施形態に係る電極を備えるものである。本実施形態に係る非水電解質二次電池としては、例えば、ゲル電解質を含むポリマー電池等も含まれる。非水電解質二次電池における他の部材(例えば、セパレータ)については特に限定されるものでなく、例えば、従来用いられている部材を用いることができる。
本発明に係るバインダー組成物では、当該バインダー組成物はフッ化ビニリデン共重合体組成物を含み、当該フッ化ビニリデン共重合体組成物は、フッ化ビニリデンとアクリル単量体との共重合体を含み、当該アクリル単量体はアクリル酸およびメタクリル酸から選ばれる少なくとも1種類以上であり、当該フッ化ビニリデン共重合体組成物は、当該フッ化ビニリデン共重合体組成物をアルミナに吸着させた場合に、当該吸着前のフッ化ビニリデン共重合体組成物の数平均分子量(Mn1)に対する、当該吸着後のアルミナに吸着されなかったフッ化ビニリデン共重合体組成物の数平均分子量(Mn2)の比(Mn2/Mn1)が、2より小さい。
インヘレント粘度ηiを算出するために、フッ化ビニリデン共重合体組成物80mgを20mlのN,N‐ジメチルホルムアミドに溶解することによって重合体溶液を作製する。当該重合体溶液の粘度ηを、30℃の恒温槽内においてウベローデ粘度計を用いて測定する。インヘレント粘度ηiは、当該粘度ηを用いて下記式によって求められる。
上記式において、η0は溶媒であるN,N‐ジメチルホルムアミドの粘度、Cは0.4g/dlである。
吸光度比ARを算出するために、フッ化ビニリデン共重合体組成物を、230℃で熱プレスして、30mm×30mmのプレスシートを作製する。作製したプレスシートのIRスペクトルを、赤外分光光度計FT-730(株式会社堀場製作所製)を用いて、1500cm-1~4000cm-1範囲で測定する。吸光度比ARは、下記式によって求められる。
上記式において、A1700-1800は1700~1800cm-1の範囲で検出されるカルボニル基の伸縮振動に由来の吸光度であり、A3023は3023cm-1付近に検出されるCHの伸縮振動に由来の吸光度である。
[バインダー組成物の調製]
内容量2リットルのオートクレーブに、分散媒としてイオン交換水930g、セルロース系懸濁剤としてメトローズSM‐100(信越化学工業(株)製)0.2g、重合開始剤として50wt%t‐ジイソプロピルペルオキシジカーボネート‐フロン225cb溶液3.2g、フッ化ビニリデン400g、および単量体としてアクリル酸0.2gを仕込み、26℃まで1時間かけて昇温した。次に、26℃を維持しながら、2wt%のアクリル酸水溶液を9時間かけて98g添加した。昇温開始から25.7時間経過した時点で重合を終了した。
バインダー組成物とN‐メチル‐2‐ピロリドン(NMP)、導電助剤としてケッチェンブラック(ライオン・スペシャリティ・ケミカルズ(株)製、カーボンECP)をポリエチレン製カップに加え、シンキー製AR‐310で混練(1500rpm、1分)しペースト状とした。ここに電極活物質(コバルト酸リチウム、日本化学工業製、セルシードC5H)と必要に応じてNMPを加え混練(1500rpm、2分)した。さらに、塗工可能な粘度となるようにNMPを加え混練(1500rpm、2分)することで電極合剤を作製した(混練A)。
得られた電極合剤を、集電体である厚さ15μmのアルミニウム箔上にバーコーターで塗布し、これを恒温槽を用いて、窒素雰囲気下にて110℃で30分間乾燥して、片面目付け量が200g/m2の片面塗工電極を作製した。
[バインダー組成物の調製]
内容量2リットルのオートクレーブに、分散媒としてイオン交換水900g、セルロース系懸濁剤としてメトローズ90SH‐100(信越化学工業(株)製)0.4g、重合開始剤として50wt%t‐ブチルペルオキシピバレート‐フロン225cb溶液3.0g、フッ化ビニリデン400g、および単量体としてアクリル酸0.2gを仕込み、50℃まで2時間かけて昇温した。次に、50℃を維持しながら、0.3wt%のアクリル酸水溶液を重合圧力が一定となる速度で徐々に添加した。アクリル酸は、初期に添加した量を含めて、全量で2.0gを添加した。重合は、アクリル酸水溶液の添加終了と同時に停止した。昇温開始から重合停止までの時間は、合計9.8時間であった。
電極合剤の製造法は、実施例1と同様の方法で行った。
電極の製造は、実施例1と同様の方法で行った。
[バインダー組成物の調製]
内容量2リットルのオートクレーブに、分散媒としてイオン交換水900g、セルロース系懸濁剤としてメトローズ90SH‐100(信越化学工業(株)製)0.4g、重合開始剤として50wt%t‐ブチルペルオキシピバレート‐フロン225cb溶液4.0g、フッ化ビニリデン400g、および単量体としてアクリル酸0.2gを仕込み、50℃まで2時間かけて昇温した。次に、50℃を維持しながら、0.3wt%のアクリル酸水溶液を重合圧力が一定となる速度で徐々に添加した。アクリル酸は、初期に添加した量を含めて、全量で2.0gを添加した。重合は、アクリル酸水溶液の添加終了と同時に停止した。昇温開始から重合停止までの時間は、合計9.4時間であった。
電極合剤の製造法は、実施例1と同様の方法で行った。
電極の製造は、実施例1と同様の方法で行った。
[バインダー組成物の調製]
バインダー組成物の調製は、実施例3と同様の方法で行った。
電極活物質(コバルト酸リチウム、日本化学工業製、セルシードC‐10)と導電助剤としてケッチェンブラック(ライオン・スペシャリティ・ケミカルズ株式会社製、カーボンECP)をポリエチレン製カップに加え、シンキー製AR‐310で混練(1500rpm、1分)した。ここにバインダー組成物を加え混練(1500rpm、2分)した。さらに、塗工可能な粘度となるようにNMPを加え混練(1500rpm、2分)することで電極合剤を作製した(混練B)。
電極の製造は、実施例1と同様の方法で行った。
[バインダー組成物の調製]
内容量2リットルのオートクレーブに、分散媒としてイオン交換水900g、セルロース系懸濁剤としてメトローズ90SH‐100(信越化学工業(株)製)0.4g、重合開始剤として50wt%t‐ブチルペルオキシピバレート‐フロン225cb溶液2.6g、フッ化ビニリデン400g、および単量体としてアクリル酸0.8gを仕込み、50℃まで2時間かけて昇温した。次に、50℃を維持しながら、1wt%のアクリル酸水溶液を重合圧力が一定となる速度で徐々に添加した。アクリル酸は、初期に添加した量を含めて、全量で4.0gを添加した。重合は、アクリル酸水溶液の添加終了と同時に停止した。昇温開始から重合停止までの時間は、合計14.6時間であった。
電極合剤の製造法は、実施例1と同様の方法で行った。
電極の製造は、実施例1と同様の方法で行った。
本実施例において、数平均分子量比は、次の方法にて推定した。
溶媒 10mM LiBr‐NMP溶液
カラム KD‐806M×2本
測定温度 40℃
流速 1ml/min
検出器 RI検出器
インジェクト量 100μl
実施例1~4、および比較例1で得られた片面塗工電極を、長さ100mm、幅20mmに切り出し、JIS K‐6854‐1に準じて引張試験機(ORIENTEC社製「STA‐1150 UNIVERSAL TESTING MACHINE」)を使用し、ヘッド速度10mm/分で90度剥離試験を行い、剥離強度を評価した。
実施例1~4、および比較例1で得られた片面塗工電極を長さ30mm、幅30mmに切り出し、塗工面をOPPテープに貼り付け、アルミニウム箔を剥がし測定サンプルとした。測定にはロレスタGP MCP‐T610(三菱化学製)(プローブ:PSP(4端子法))を使用し、体積抵抗率を評価した。
融点を算出するために、フッ化ビニリデン共重合体組成物を、230℃で熱プレスして、30mm×30mmのプレスシートを作製し、作製したプレスシートから約10mgを切り出し測定サンプルとした。測定サンプルをアルミ製サンプルパンに入れ、Mettler Toledo製の示差走査熱量計(DSC)を用いて測定した。測定条件は、測定サンプルを230℃まで昇温し10分間保持する。その後、10K/minで30℃まで冷却し10分間保持する。その後、230℃まで10K/minで昇温した。2度目の昇温時に得られる最も大きな吸熱ピークのピークトップ温度を融点とした。
Claims (5)
- 電極活物質を集電体に結着させるために用いられるバインダー組成物であって、
当該バインダー組成物はフッ化ビニリデン共重合体組成物を含み、
当該フッ化ビニリデン共重合体組成物は、フッ化ビニリデンとアクリル単量体との共重合体を含み、
当該アクリル単量体は、アクリル酸およびメタクリル酸から選ばれる少なくとも1種類以上であり、
当該フッ化ビニリデン共重合体組成物は、当該フッ化ビニリデン共重合体組成物をアルミナに吸着させた場合に、当該吸着前のフッ化ビニリデン共重合体組成物の数平均分子量(Mn1)に対する、当該吸着後のアルミナに吸着されなかったフッ化ビニリデン共重合体組成物の数平均分子量(Mn2)の比(Mn2/Mn1)が、2より小さいことを特徴とするバインダー組成物。 - 上記フッ化ビニリデン共重合体組成物の融点が160℃以上であることを特徴とする請求項1の記載のバインダー組成物。
- 請求項1または2に記載のバインダー組成物と電極活物質と導電助剤とを含むことを特徴とする電極合剤。
- 請求項3に記載の電極合剤から形成された層を集電体上に備えていることを特徴とする電極。
- 請求項4に記載の電極を備えていることを特徴とする非水電解質二次電池。
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