WO2013080938A1 - リチウムイオン二次電池用電極、リチウムイオン二次電池及びスラリー組成物、並びにリチウムイオン二次電池用電極の製造方法 - Google Patents
リチウムイオン二次電池用電極、リチウムイオン二次電池及びスラリー組成物、並びにリチウムイオン二次電池用電極の製造方法 Download PDFInfo
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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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- 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
- C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
- C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
- H01M4/623—Binders being polymers fluorinated polymers
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- 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
- C08F12/00—Homopolymers and 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 an aromatic carbocyclic ring
- C08F12/02—Monomers containing only one unsaturated aliphatic radical
- C08F12/04—Monomers containing only one unsaturated aliphatic radical containing one ring
- C08F12/14—Monomers containing only one unsaturated aliphatic radical containing one ring substituted by hetero atoms or groups containing heteroatoms
- C08F12/30—Sulfur
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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
- H01M2220/00—Batteries for particular applications
- H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
- H01M4/0404—Methods of deposition of the material by coating on electrode collectors
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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
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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
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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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to an electrode for a lithium ion secondary battery, a lithium ion secondary battery and a slurry composition, and a method for producing an electrode for a lithium ion secondary battery.
- the electrode is usually a liquid composition in which a polymer serving as a binder (binder) is dispersed or dissolved in a solvent such as water or an organic solvent, an electrode active material, and optionally conductive carbon or the like.
- a solvent such as water or an organic solvent
- an electrode active material such as silver, copper, and zinc.
- conductive carbon or the like a solvent
- the conductive material is mixed to obtain a slurry composition, and this slurry composition is applied to a current collector and dried.
- Japanese Patent No. 4438102 Japanese Patent Laid-Open No. 2003-308841 JP 2003-217573 A JP 2010-146870 A JP 2002-042819 A JP-A-2005-1000066
- the conventional electrode manufactured using water as a solvent has a problem in the adhesion of the electrode active material to the current collector. If the adhesiveness is low, the electrode active material cannot be held on the current collector, which may be a factor of reducing battery performance. In particular, storage characteristics and cycle characteristics in a high temperature environment may be deteriorated. For this reason, the technique which improves the adhesiveness of the electrode active material with respect to a collector is desired.
- the present invention was devised in view of the above problems, and is a lithium ion secondary battery excellent in adhesion of an electrode active material to a current collector, and excellent in storage characteristics and cycle characteristics in a high temperature environment;
- An object of the present invention is to provide a lithium ion secondary battery electrode capable of realizing a secondary battery; a slurry composition capable of producing the lithium ion secondary battery electrode; and a method of producing the lithium ion secondary battery electrode .
- the present inventor includes an electrode active material, an aromatic vinyl monomer unit, an unsaturated carboxylic acid monomer unit, and a crosslinkable monomer unit in a predetermined ratio.
- a lithium ion secondary battery electrode manufactured using a water-soluble polymer can improve the adhesion of the electrode active material to the current collector, and is a lithium ion secondary battery with excellent storage characteristics and cycle characteristics in a high temperature environment.
- the present invention has been completed by finding out that it can be realized. That is, the present invention is as follows.
- An electrode for a lithium ion secondary battery comprising an electrode active material and a water-soluble polymer,
- the water-soluble polymer comprises 1 to 30% by weight of an aromatic vinyl monomer unit, 20 to 60% by weight of an unsaturated carboxylic acid monomer unit, and 0.1 to about 0.1% by weight of a crosslinkable monomer unit.
- the electrode for lithium ion secondary batteries which is a copolymer containing 5 weight%.
- the water-soluble polymer further contains a fluorine-containing (meth) acrylic acid ester monomer unit, The electrode for a lithium ion secondary battery according to any one of [1] to [3], wherein a ratio of the fluorine-containing (meth) acrylic acid ester monomer unit is 1% by weight to 30% by weight.
- the content ratio of the water-soluble polymer is 0.1 to 30 parts by weight with respect to 100 parts by weight of the electrode active material, according to any one of [1] to [4].
- Electrode for lithium ion secondary battery [6] The lithium ion secondary battery electrode according to any one of [1] to [5], wherein the lithium ion secondary battery electrode further includes a particulate binder. [7] A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution and a separator, A lithium ion secondary battery, wherein at least one of the positive electrode and the negative electrode is the electrode for a lithium ion secondary battery according to any one of [1] to [6].
- a slurry composition for producing an electrode for a lithium ion secondary battery comprising an electrode active material and a water-soluble polymer,
- the water-soluble polymer comprises 1 to 30% by weight of an aromatic vinyl monomer unit, 20 to 60% by weight of an unsaturated carboxylic acid monomer unit, and 0.1 to about 0.1% by weight of a crosslinkable monomer unit.
- a slurry composition which is a copolymer comprising 5% by weight.
- a method for producing an electrode for a lithium ion secondary battery which comprises applying the slurry composition according to [8] onto a current collector and drying it.
- the electrode for a lithium ion secondary battery of the present invention can improve the adhesion of the electrode active material to the current collector, and can realize a lithium ion secondary battery excellent in storage characteristics and cycle characteristics in a high temperature environment.
- the lithium ion secondary battery of the present invention is excellent in storage characteristics and cycle characteristics in a high temperature environment.
- the slurry composition of the present invention it is possible to produce an electrode for a lithium ion secondary battery excellent in the adhesion of the electrode active material to the current collector, and thus a lithium ion secondary battery excellent in storage characteristics and cycle characteristics in a high temperature environment. It can be realized.
- the method for producing an electrode for a lithium ion secondary battery of the present invention the lithium ion secondary battery of the present invention can be produced.
- (meth) acryl means “acryl” or “methacryl”.
- (Meth) acrylate” means “acrylate” or “methacrylate”.
- positive electrode active material means an electrode active material for positive electrode
- negative electrode active material means an electrode active material for negative electrode.
- the “positive electrode active material layer” means an electrode active material layer provided on the positive electrode
- the “negative electrode active material layer” means an electrode active material layer provided on the negative electrode.
- a compound (including a polymer) is water-soluble means that an insoluble content is less than 0.5% by weight when 0.5 g of the compound is dissolved in 100 g of water at 25 ° C. .
- a compound being water-insoluble means that an insoluble content becomes 90% by weight or more when 0.5 g of the compound is dissolved in 100 g of water at 25 ° C.
- the electrode for a lithium ion secondary battery of the present invention includes an electrode active material and a water-soluble polymer.
- the electrode for a lithium ion secondary battery of the present invention comprises a current collector and an electrode active material layer provided on the current collector, and the electrode active material layer comprises an electrode active material and a water-soluble polymer. Including.
- Electrode active material examples include a positive electrode active material and a negative electrode active material.
- the positive electrode active material is an electrode active material used in the positive electrode, and is a material that transfers electrons in the positive electrode of the lithium ion secondary battery.
- As the positive electrode active material a material capable of inserting and removing lithium ions is usually used.
- Such positive electrode active materials are roughly classified into those made of inorganic compounds and those made of organic compounds.
- Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, transition metal sulfides, lithium-containing composite metal oxides of lithium and transition metals, and the like.
- Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.
- transition metal oxide examples include MnO, MnO 2 , V 2 O 5 , V 6 O 13 , TiO 2 , Cu 2 V 2 O 3 , amorphous V 2 O—P 2 O 5 , and MoO 3.
- MnO, V 2 O 5 , V 6 O 13 , and TiO 2 are preferable from the viewpoint of cycle stability and capacity.
- transition metal sulfide examples include TiS 2 , TiS 3 , amorphous MoS 2 , FeS, and the like.
- lithium-containing composite metal oxide examples include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.
- lithium-containing composite metal oxide having a layered structure examples include lithium-containing cobalt oxide (LiCoO 2 ), lithium-containing nickel oxide (LiNiO 2 ), lithium composite oxide of Co—Ni—Mn, Ni—Mn— Examples thereof include lithium composite oxides of Al and lithium composite oxides of Ni—Co—Al.
- lithium-containing composite metal oxide having a spinel structure examples include lithium manganate (LiMn 2 O 4 ) or Li [Mn 3/2 M] in which a part of Mn of lithium manganate is substituted with another transition metal. 1/2 ] O 4 (where M is Cr, Fe, Co, Ni, Cu, etc.).
- lithium-containing composite metal oxide having an olivine type structure examples include Li X MPO 4 (wherein M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti).
- Examples of the positive electrode active material made of an organic compound include conductive polymer compounds such as polyacetylene and poly-p-phenylene.
- a positive electrode active material made of a composite material in which an inorganic compound and an organic compound are combined may be used.
- a composite material covered with a carbon material may be produced by reducing and firing an iron-based oxide in the presence of a carbon source material, and this composite material may be used as a positive electrode active material.
- Iron-based oxides tend to have poor electrical conductivity, but can be used as a high-performance positive electrode active material by using a composite material as described above.
- positive electrode active material what carried out the element substitution of the said compound partially.
- mixture of said inorganic compound and an organic compound as a positive electrode active material.
- positive electrode active material one type may be used alone, or two or more types may be used in combination at any ratio.
- the volume average particle diameter of the positive electrode active material particles is preferably 1 ⁇ m or more, more preferably 2 ⁇ m or more, preferably 50 ⁇ m or less, more preferably 30 ⁇ m or less.
- the volume average particle diameter of the positive electrode active material particles is in the above range, it becomes easy to adjust the viscosity of the slurry composition to an appropriate viscosity that is easy to apply, and the slurry composition is uniformly applied.
- the obtained positive electrode can be obtained.
- the volume average particle diameter can be measured using a laser diffraction particle size distribution measuring apparatus.
- the negative electrode active material is an electrode active material used in the negative electrode, and is a material that transfers electrons in the negative electrode of the lithium ion secondary battery.
- a material that can occlude and release lithium is usually used. Examples of the material that can occlude and release lithium include a metal-based active material, a carbon-based active material, and an active material that combines these materials.
- the metal-based active material is an active material containing a metal, and usually contains an element capable of inserting lithium (also referred to as dope) in the structure, and the theoretical electric capacity per weight when lithium is inserted is 500 mAh.
- the upper limit of the theoretical electric capacity is not particularly limited, but may be, for example, 5000 mAh / g or less.
- the metal-based active material for example, lithium metal, a single metal that forms a lithium alloy and an alloy thereof, and oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like thereof are used.
- the single metal forming the lithium alloy examples include single metals such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, and Ti. Can be mentioned. Moreover, as a single metal alloy which forms a lithium alloy, the compound containing the said single metal is mentioned, for example. Among these, silicon (Si), tin (Sn), lead (Pb), and titanium (Ti) are preferable, and silicon, tin, and titanium are more preferable. Accordingly, a single metal of silicon (Si), tin (Sn), or titanium (Ti), an alloy containing these single metals, or a compound of these metals is preferable.
- the metallic active material may further contain one or more nonmetallic elements.
- SiO x C y capable of inserting and detaching lithium (also referred to as dedoping) at a low potential is preferable.
- SiO x C y can be obtained by firing a polymer material containing silicon.
- the range of 0.8 ⁇ x ⁇ 3 and 2 ⁇ y ⁇ 4 is preferably used in view of the balance between capacity and cycle characteristics.
- Lithium metal, elemental metal forming lithium alloy and oxides, sulfides, nitrides, silicides, carbides and phosphides of the alloys include oxides, sulfides, nitrides and silicides of lithium-insertable elements Products, carbides, phosphides and the like.
- an oxide is particularly preferable.
- a lithium-containing metal composite oxide containing an oxide such as tin oxide, manganese oxide, titanium oxide, niobium oxide, and vanadium oxide and a metal element selected from the group consisting of Si, Sn, Pb, and Ti atoms is used. .
- Li x Ti y M z O 4 As the lithium-containing metal composite oxide, a lithium titanium composite oxide represented by Li x Ti y M z O 4 (0.7 ⁇ x ⁇ 1.5, 1.5 ⁇ y ⁇ 2.3, 0 ⁇ z ⁇ 1.6, and M represents an element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb.), Li x Mn y M A lithium manganese composite oxide represented by z O 4 (x, y, z and M are the same as defined in the lithium titanium composite oxide). Among these, Li 4/3 Ti 5/3 O 4 , Li 1 Ti 2 O 4 , Li 4/5 Ti 11/5 O 4 , and Li 4/3 Mn 5/3 O 4 are preferable.
- an active material containing silicon is preferable as the metal-based active material.
- an active material containing silicon By using an active material containing silicon, the electric capacity of the lithium ion secondary battery can be increased.
- an active material containing silicon expands and contracts greatly with charge / discharge (for example, about 5 times).
- the active material containing silicon expands. And the deterioration of battery performance due to shrinkage can be prevented by the water-soluble polymer according to the present invention.
- SiO x , SiC and SiO x C y are preferable.
- SiO x , SiC and SiO x C y are preferable.
- Li insertion and desorption from Si (silicon) occurs at a high potential, and Li insertion and desorption from C (carbon) at a low potential. Is presumed to occur. For this reason, since expansion
- the carbon-based active material refers to an active material having carbon as a main skeleton into which lithium can be inserted, and examples thereof include a carbonaceous material and a graphite material.
- the carbonaceous material is generally a carbon material with low graphitization (ie, low crystallinity) obtained by carbonizing a carbon precursor by heat treatment at 2000 ° C. or lower. Although the minimum of the said heat processing is not specifically limited, For example, it is good also as 500 degreeC or more.
- Examples of the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitic carbon having a structure close to an amorphous structure typified by glassy carbon.
- Examples of the graphitizable carbon include carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers, pyrolytic vapor grown carbon fibers, and the like.
- MCMB is carbon fine particles obtained by separating and extracting mesophase microspheres generated in the process of heating pitches at around 400 ° C.
- the mesophase pitch-based carbon fiber is a carbon fiber using as a raw material mesophase pitch obtained by growing and coalescing the mesophase microspheres.
- Pyrolytic vapor-grown carbon fibers are (1) a method of pyrolyzing acrylic polymer fibers, etc., (2) a method of spinning by spinning a pitch, or (3) using nanoparticles such as iron as a catalyst.
- non-graphitizable carbon examples include phenol resin fired bodies, polyacrylonitrile-based carbon fibers, pseudo-isotropic carbon, furfuryl alcohol resin fired bodies (PFA), and hard carbon.
- the graphite material is a material having high crystallinity close to that of graphite obtained by heat-treating graphitizable carbon at 2000 ° C. or higher.
- the upper limit of the said heat processing temperature is not specifically limited, For example, it is good also as 5000 degrees C or less.
- Examples of the graphite material include natural graphite and artificial graphite.
- Examples of artificial graphite include artificial graphite mainly heat-treated at 2800 ° C. or higher, graphitized MCMB heat-treated at 2000 ° C. or higher, graphitized mesophase pitch-based carbon fiber heat-treated mesophase pitch-based carbon fiber at 2000 ° C. or higher, etc. Is mentioned.
- carbonaceous materials are preferable.
- the resistance of the lithium ion secondary battery can be reduced, and a lithium ion secondary battery having excellent input / output characteristics can be manufactured.
- the negative electrode active material one type may be used alone, or two or more types may be used in combination at any ratio.
- the negative electrode active material is preferably particle-sized.
- a higher density electrode can be formed during electrode molding.
- the volume average particle diameter of the particle is appropriately selected in consideration of other constituent elements of the lithium ion secondary battery, and is usually 0.1 ⁇ m or more, preferably 1 ⁇ m or more, more preferably It is 5 ⁇ m or more, usually 100 ⁇ m or less, preferably 50 ⁇ m or less, more preferably 20 ⁇ m or less.
- the 50% cumulative volume diameter of the negative electrode active material particles is usually 1 ⁇ m or more, preferably 15 ⁇ m or more, and usually 50 ⁇ m or less, preferably 30 ⁇ m or less, from the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics. It is.
- the 50% cumulative volume diameter can be obtained as a particle diameter at which the cumulative volume calculated from the small diameter side in the measured particle size distribution is 50% by measuring the particle size distribution by a laser diffraction method.
- the tap density of the negative electrode active material is not particularly limited, but 0.6 g / cm 3 or more is preferably used.
- the specific surface area of the negative electrode active material is usually 2 m 2 / g or more, preferably 3 m 2 / g or more, more preferably 5 m 2 / g or more, and usually 20 m 2 / g or less, preferably from the viewpoint of improving the output density. It is 15 m 2 / g or less, more preferably 10 m 2 / g or less.
- the specific surface area of the negative electrode active material can be measured by, for example, the BET method.
- the water-soluble polymer is a copolymer containing an aromatic vinyl monomer unit, an unsaturated carboxylic acid monomer unit, and a crosslinkable monomer unit in a specific ratio. Since the water-soluble polymer contains an aromatic vinyl monomer unit, an unsaturated carboxylic acid monomer unit, and a crosslinkable monomer unit in a specific ratio, the lithium ion secondary battery electrode of the present invention is Excellent adhesion of electrode active material to current collector.
- the water-soluble polymer may further contain a fluorine-containing (meth) acrylic acid ester monomer unit.
- a water-soluble polymer is usually interposed between electrode active materials and between an electrode active material and a current collector in an electrode for a lithium ion secondary battery, and binds the electrode active material and the current collector. Can be played.
- the water-soluble polymer is a slurry composition for producing an electrode for a lithium ion secondary battery, and usually has an action of uniformly dispersing an electrode active material and a particulate binder used as necessary, and The effect
- An aromatic vinyl monomer unit is a structural unit obtained by polymerizing an aromatic vinyl monomer.
- aromatic vinyl monomers include styrene, ⁇ -methyl styrene, vinyl toluene, divinyl benzene, and sodium p-styrene sulfonate. Of these, styrene and sodium p-styrenesulfonate are preferable. Therefore, as the aromatic vinyl monomer unit, a styrene monomer unit and a sodium styrenesulfonate monomer unit are preferable.
- an aromatic vinyl monomer and an aromatic vinyl monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the ratio of the aromatic vinyl monomer unit in the water-soluble polymer is preferably 1% by weight or more, more preferably 2% by weight or more, particularly preferably 5% by weight or more, and preferably 30% by weight or less. More preferably, it is 25 weight% or less, Most preferably, it is 20 weight% or less.
- the coating film can stably cover the electrode active material. Therefore, decomposition of the electrolytic solution can be suppressed, and high temperature storage characteristics and high temperature cycle characteristics of the lithium ion secondary battery can be improved.
- the reason why the adsorptivity of the aromatic vinyl monomer unit to the electrode active material can be increased is that the aromatic vinyl monomer unit has high hydrophobicity, and the hydrophobic part of the electrode active material This is probably because it can be adsorbed with high affinity.
- the ratio of the aromatic vinyl monomer unit in the water-soluble polymer can be adjusted by the ratio (charge ratio) of the aromatic vinyl monomer to the total monomers used for the polymerization of the water-soluble polymer.
- the ratio of the monomer units coincides with the ratio of the monomers (charge ratio).
- Unsaturated carboxylic acid monomer unit The unsaturated carboxylic acid monomer unit is a structural unit obtained by polymerizing an unsaturated carboxylic acid monomer.
- the unsaturated carboxylic acid monomer is a monomer having a carbon-carbon unsaturated bond and having a carboxyl group.
- the number of carboxyl groups contained in the unsaturated carboxylic acid monomer may be one or two or more.
- Examples of unsaturated carboxylic acid monomers include unsaturated monocarboxylic acids and derivatives thereof, unsaturated dicarboxylic acids and acid anhydrides, and derivatives thereof.
- unsaturated monocarboxylic acids include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid.
- unsaturated monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, ⁇ -acetoxyacrylic acid, ⁇ -trans-aryloxyacrylic acid, ⁇ -chloro- ⁇ -E-methoxyacrylic acid, and ⁇ -Derivatives of ethylenically unsaturated monocarboxylic acids, such as diaminoacrylic acid.
- unsaturated dicarboxylic acids include ethylenically unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid.
- unsaturated dicarboxylic acid anhydrides include acid anhydrides of ethylenically unsaturated dicarboxylic acids such as maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.
- Examples of derivatives of unsaturated dicarboxylic acids include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, methylallyl maleate; and diphenyl maleate, nonyl maleate, maleate Examples thereof include maleate esters such as decyl acid, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.
- unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferable. This is because the dispersibility of the water-soluble polymer in water can be further improved. Accordingly, the unsaturated carboxylic acid monomer unit is preferably an unsaturated monocarboxylic acid monomer unit. Moreover, an unsaturated carboxylic acid monomer and an unsaturated carboxylic acid monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the ratio of unsaturated carboxylic acid monomer units in the water-soluble polymer is preferably 20% by weight or more, more preferably 25% by weight or more, particularly preferably 30% by weight or more, and preferably 60% by weight or less. More preferably, it is 55% by weight or less, particularly preferably 50% by weight or less.
- the dispersion stability of the slurry composition can be improved. For this reason, it becomes possible to make the distribution of the electrode active material and the particulate binder in the electrode active material layer uniform and improve the adhesion.
- the hydrophilicity of the water-soluble polymer can be increased as described above, the affinity of the water-soluble polymer for the element having a hydrophilic group such as a current collector can be improved. For this reason, it becomes possible to improve adhesiveness also by this improvement in affinity.
- the ratio of the unsaturated carboxylic acid monomer unit in the water-soluble polymer can be adjusted by the ratio (charge ratio) of the unsaturated carboxylic acid monomer in the total monomers used for the polymerization of the water-soluble polymer.
- the ratio of the monomer units is the same as the ratio of the monomers (charge ratio).
- a crosslinkable monomer unit is a structural unit obtained by polymerizing a crosslinkable monomer.
- the crosslinkable monomer is a monomer that can form a crosslinked structure during or after polymerization by heating or energy ray irradiation.
- a monomer having thermal crosslinkability can be usually mentioned. More specifically, a monofunctional crosslinkable monomer having a thermally crosslinkable crosslinkable group and one olefinic double bond per molecule; a polyfunctional monomer having two or more olefinic double bonds per molecule.
- a functional crosslinkable monomer is mentioned.
- thermally crosslinkable groups examples include epoxy groups, N-methylolamide groups, oxetanyl groups, oxazoline groups, and combinations thereof.
- an epoxy group is more preferable in terms of easy adjustment of crosslinking and crosslinking density.
- crosslinkable monomer having an epoxy group as a thermally crosslinkable group and having an olefinic double bond examples include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl.
- Unsaturated glycidyl ethers such as ether; butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene Monoepoxides of dienes or polyenes such as; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; and glycidyl acrylate, glycidyl methacrylate, Glycidyl crotonate, Unsaturated carboxylic acids such as glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl este
- crosslinkable monomer having an N-methylolamide group as a thermally crosslinkable group and having an olefinic double bond have a methylol group such as N-methylol (meth) acrylamide (meta ) Acrylamides.
- crosslinkable monomer having an oxetanyl group as a thermally crosslinkable group and having an olefinic double bond examples include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) Acryloyloxymethyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, and 2-((meth) acryloyloxymethyl) ) -4-Trifluoromethyloxetane.
- crosslinkable monomer having an oxazoline group as a heat crosslinkable group and having an olefinic double bond examples include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2- Oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.
- crosslinkable monomers having two or more olefinic double bonds per molecule examples include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, and triethylene glycol di (meth).
- crosslinkable monomer ethylene dimethacrylate, allyl glycidyl ether, and glycidyl methacrylate are particularly preferable as the crosslinkable monomer.
- crosslinked monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the ratio of the crosslinkable monomer unit in the water-soluble polymer is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably 5% by weight. % Or less, more preferably 4% by weight or less, and particularly preferably 3% by weight or less.
- an electrode active material containing Si tends to have a large expansion and contraction associated with charging and discharging, the effect of suppressing the swelling of the electrode for a lithium ion secondary battery is obtained when an electrode active material containing Si is used. This is particularly noticeable.
- the rigidity of the main chain of a water-soluble polymer can be improved by making the ratio of the crosslinkable monomer unit in a water-soluble polymer more than the lower limit of the said range. Therefore, by combining the crosslinkable monomer unit and the unsaturated carboxylic acid monomer unit capable of improving the adhesion as described above at a predetermined ratio, a water-soluble polymer having an appropriate rigidity can be obtained. The water-soluble polymer can hold the electrode active material firmly.
- the ratio of the crosslinkable monomer unit in the water-soluble polymer can be equal to or less than the upper limit of the above range, the water-soluble polymer can be improved in water solubility and the dispersibility can be improved.
- the ratio of the crosslinkable monomer unit in the water-soluble polymer can usually be adjusted by the ratio (charge ratio) of the crosslinkable monomer in the total monomers used for the polymerization of the water-soluble polymer. The ratio of the monomer units coincides with the ratio of the monomers (charge ratio).
- the fluorine-containing (meth) acrylic acid ester monomer unit is a structural unit obtained by polymerizing a fluorine-containing (meth) acrylic acid ester monomer.
- Examples of the fluorine-containing (meth) acrylic acid ester monomer include monomers represented by the following formula (I).
- R 1 represents a hydrogen atom or a methyl group.
- R 2 represents a hydrocarbon group containing a fluorine atom.
- the carbon number of the hydrocarbon group is usually 1 or more and usually 18 or less.
- the number of fluorine atoms contained in R 2 may be one or two or more.
- fluorine-containing (meth) acrylic acid ester monomers represented by formula (I) include (meth) acrylic acid alkyl fluoride, (meth) acrylic acid fluoride aryl, and (meth) acrylic acid fluoride.
- Aralkyl is mentioned. Of these, alkyl fluoride (meth) acrylate is preferable.
- Such monomers include 2,2,2-trifluoroethyl (meth) acrylate, ⁇ - (perfluorooctyl) ethyl (meth) acrylate, 2,2, (meth) acrylic acid. 3,3-tetrafluoropropyl, (meth) acrylic acid 2,2,3,4,4,4-hexafluorobutyl, (meth) acrylic acid 1H, 1H, 9H-perfluoro-1-nonyl, (meth) 1H, 1H, 11H-perfluoroundecyl acrylate, perfluorooctyl (meth) acrylate, 3 [4 [1-trifluoromethyl-2,2-bis [bis (trifluoromethyl) fluoro (meth) acrylate] (Meth) acrylic acid perfluoroalkyl esters such as methyl] ethynyloxy] benzooxy] 2-hydroxypropyl.
- fluorine-containing (meth) acrylic acid ester monomer and fluorine-containing (meth) acrylic acid ester monomer unit may be used alone, or two or more types may be used in combination at any ratio. .
- the ratio of fluorine-containing (meth) acrylic acid ester monomer units in the water-soluble polymer is preferably 1% by weight or more, more preferably 2% by weight or more, particularly preferably 5% by weight or more, preferably 30% by weight. % Or less, more preferably 25% by weight or less, and particularly preferably 20% by weight or less.
- the ratio of the fluorine-containing (meth) acrylic acid ester monomer unit in the water-soluble polymer is not more than the upper limit of the above range, which is combined with the hydrophilicity improving effect by the unsaturated carboxylic acid monomer unit.
- the wettability of the water-soluble polymer with respect to the electrolytic solution can be improved.
- the low temperature output characteristic of the obtained lithium ion secondary battery can be improved.
- the ratio of the fluorine-containing (meth) acrylate monomer unit in the water-soluble polymer is the ratio of the fluorine-containing (meth) acrylate monomer to the total monomer used for the polymerization of the water-soluble polymer (
- the ratio of the monomer units is usually the same as the ratio of the monomers (feed ratio).
- the water-soluble polymer is not limited to the present invention. Any structural unit may be included as long as the effect of is not significantly impaired.
- arbitrary structural units include (meth) acrylic acid ester monomer units other than fluorine-containing (meth) acrylic acid ester monomer units, amide monomer units, olefin monomer units, halogen atom content Examples include monomer units, vinyl ester monomer units, vinyl ether monomer units, vinyl ketone monomer units, and heterocyclic-containing vinyl compound monomer units. Among these, (meth) acrylic acid ester monomer units are preferable.
- the (meth) acrylic acid ester monomer unit is a structural unit obtained by polymerizing a (meth) acrylic acid ester monomer.
- those containing fluorine are distinguished from (meth) acrylate monomers as fluorine-containing (meth) acrylate monomers.
- Examples of (meth) acrylic acid ester monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, Acrylic acid alkyl esters such as 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; and methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t -Butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl
- the (meth) acrylic acid ester monomer and the (meth) acrylic acid ester monomer unit may be used singly or in combination of two or more at an arbitrary ratio.
- the water-soluble polymer may have, in addition to each of the above structural units, a structural unit obtained by polymerizing a functional monomer such as a reactive surfactant monomer, Further, a structural unit obtained by polymerizing other copolymerizable monomers may be contained.
- the reactive surfactant monomer is a monomer having a polymerizable group that can be copolymerized with other monomers and having a surfactant group (hydrophilic group and hydrophobic group).
- the reactive surfactant unit obtained by polymerizing the reactive surfactant monomer is a structural unit that constitutes a part of the molecule of the water-soluble polymer and can function as a surfactant.
- the reactive surfactant monomer has a polymerizable unsaturated group, and this group also acts as a hydrophobic group after polymerization.
- the polymerizable unsaturated group that the reactive surfactant monomer has include a vinyl group, an allyl group, a vinylidene group, a propenyl group, an isopropenyl group, and an isobutylidene group.
- the type of the polymerizable unsaturated group may be one type or two or more types.
- the reactive surfactant monomer usually has a hydrophilic group as a portion that exhibits hydrophilicity.
- Reactive surfactant monomers are classified into anionic, cationic and nonionic surfactants depending on the type of hydrophilic group.
- anionic hydrophilic group examples include —SO 3 M, —COOM, and —PO (OH) 2 .
- M represents a hydrogen atom or a cation.
- cations include alkali metal ions such as lithium, sodium and potassium; alkaline earth metal ions such as calcium and magnesium; ammonium ions; ammonium ions of alkylamines such as monomethylamine, dimethylamine, monoethylamine and triethylamine; and Examples include ammonium ions of alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine.
- Examples of the cationic hydrophilic group include —Cl, —Br, —I, and —SO 3 ORX.
- RX represents an alkyl group.
- Examples of RX include methyl group, ethyl group, propyl group, and isopropyl group.
- nonionic hydrophilic group is —OH.
- Suitable reactive surfactant monomers include compounds represented by the following formula (II).
- R represents a divalent linking group. Examples of R include —Si—O— group, methylene group and phenylene group.
- R 3 represents a hydrophilic group. An example of R 3 includes —SO 3 NH 4 .
- n is an integer of 1 or more and 100 or less.
- Another example of a suitable reactive surfactant has a polymerized unit based on ethylene oxide and a polymerized unit based on butylene oxide, and further has an alkenyl group having a terminal double bond and —SO 3 NH 4 at the terminal.
- a compound for example, trade name “Latemul PD-104”, manufactured by Kao Corporation).
- a reactive surfactant monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the ratio is preferably 0.1 wt% or more, more preferably 0.2 wt% or more, particularly preferably 0.5 wt% or more, Preferably it is 15 weight% or less, More preferably, it is 10 weight% or less, Most preferably, it is 5 weight% or less.
- the dispersibility of the slurry composition for manufacturing the electrode for lithium ion secondary batteries can be improved by setting the ratio of the reactive surfactant unit in the water-soluble polymer to the lower limit value or more of the above range.
- the durability of the electrode active material layer can be improved by setting the ratio of the reactive surfactant unit in the water-soluble polymer to not more than the upper limit of the above range.
- the water-soluble polymer may have include structural units obtained by polymerizing the following monomers. That is, styrene monomers such as styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, ⁇ -methyl styrene and divinyl benzene; Amide monomers such as acrylamide and acrylamide-2-methylpropanesulfonic acid; ⁇ , ⁇ -unsaturated nitrile compound monomers such as acrylonitrile and methacrylonitrile; Olefin monomers such as ethylene and propylene; Vinyl chloride , Halogen atom-containing monomers such as vinylidene chloride; vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate;
- the water-soluble polymer may have, a structural unit obtained by polymerizing a monomer containing a sulfonic acid group (—SO 3 H) (hereinafter referred to as “sulfonic acid group-containing”).
- Monomer unit a structural unit obtained by polymerizing a monomer containing a phosphate group (—PO 3 H 2 ) (hereinafter referred to as“ phosphate group-containing monomer unit ”). May also be included).
- the sulfonic acid group-containing monomer examples include a sulfonic acid group-containing monomer having no functional group other than the sulfonic acid group or a salt thereof, a monomer containing an amide group and a sulfonic acid group, or a salt thereof And monomers containing a hydroxyl group and a sulfonic acid group, or salts thereof.
- these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Therefore, the water-soluble polymer may contain only one type of sulfonic acid group-containing monomer unit, or may contain two or more types in combination at any ratio.
- the sulfonic acid group-containing monomer having no functional group other than the sulfonic acid group examples include a monomer sulfonated one of conjugated double bonds of a diene compound such as isoprene and butadiene, vinyl sulfonic acid, Examples thereof include styrene sulfonic acid, allyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, and sulfobutyl methacrylate.
- the salt lithium salt, sodium salt, potassium salt etc. are mentioned, for example. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- Examples of the monomer containing an amide group and a sulfonic acid group include 2-acrylamido-2-methylpropanesulfonic acid (AMPS).
- AMPS 2-acrylamido-2-methylpropanesulfonic acid
- salt lithium salt, sodium salt, potassium salt etc. are mentioned, for example. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- Examples of the monomer containing a hydroxyl group and a sulfonic acid group include 3-allyloxy-2-hydroxypropanesulfonic acid (HAPS).
- HAPS 3-allyloxy-2-hydroxypropanesulfonic acid
- salt lithium salt, sodium salt, potassium salt etc. are mentioned, for example. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- sulfonic acid group-containing monomers include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), monomers containing amide groups and sulfonic acid groups, or salts thereof. Is preferred.
- the ratio of the sulfonic acid group-containing monomer unit in the water-soluble polymer is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, while preferably 5% by weight or less, more preferably 3% by weight or less.
- the sulfonic acid group-containing monomer unit in the water-soluble polymer is contained in the water-soluble polymer within such a range, the dispersibility of the slurry composition for producing an electrode for a lithium ion secondary battery is improved.
- a cross-linked structure may be formed by the sulfonic acid group in the electrode active material layer, which increases the strength of the electrode active material layer, and also provides high temperature storage characteristics and low temperature output of the secondary battery. In some cases, the characteristics can be improved.
- the phosphoric acid group that the phosphoric acid group-containing monomer may have includes a monomer having a group —OP ( ⁇ O) (— OR 4 ) —OR 5 group (R 4 and R 5 are independently , Hydrogen atom, or any organic group), or a salt thereof.
- R 4 and R 5 are independently , Hydrogen atom, or any organic group
- Specific examples of the organic group as R 4 and R 5 include an aliphatic group such as an octyl group, an aromatic group such as a phenyl group, and the like.
- Examples of the phosphate group-containing monomer include compounds containing a phosphate group and an allyloxy group, and phosphate group-containing (meth) acrylic acid esters.
- Examples of the compound containing a phosphoric acid group and an allyloxy group include 3-allyloxy-2-hydroxypropane phosphoric acid.
- Examples of phosphoric acid group-containing (meth) acrylic acid esters include dioctyl-2-methacryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, monomethyl-2-methacryloyloxyethyl phosphate, dimethyl-2-methacryloyloxy Ethyl phosphate, monoethyl-2-methacryloyloxyethyl phosphate, diethyl-2-methacryloyloxyethyl phosphate, monoisopropyl-2-methacryloyloxyethyl phosphate, diisopropyl-2-methacryloyloxyethyl phosphate, mono n-butyl-2 -Methacryloyloxyethyl phosphate, di-n-butyl-2-methacryloyloxyethyl phosphate, monobutoxyethyl-2-methacryloyloxy
- a phosphate group containing monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, the water-soluble polymer may contain only one type of phosphate group-containing monomer unit, or may contain two or more types in combination at any ratio.
- the ratio of the phosphate group-containing monomer units in the water-soluble polymer is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, while preferably 10% by weight or less. Preferably it is 5 weight% or less.
- the phosphoric acid-containing monomer unit in the water-soluble polymer is based on the phosphoric acid group-containing monomer unit such as improved adhesion between the current collector and the electrode active material layer. An effect may be obtained.
- an appropriate degree of polymerization can be obtained in the polymerization of the water-soluble polymer, and the occurrence of undesirable effects such as a decrease in durability may be prevented.
- the weight average molecular weight of the water-soluble polymer is usually smaller than that of a polymer to be a particulate binder described later, preferably 100 or more, more preferably 500 or more, particularly preferably 1000 or more, preferably 500000 or less. Preferably it is 250,000 or less, Most preferably, it is 100,000 or less.
- the weight average molecular weight of the water-soluble polymer is equal to or higher than the lower limit of the above range, it is possible to form a stable protective layer that covers the electrode active material by increasing the strength of the water-soluble polymer. For this reason, for example, the dispersibility of the electrode active material and the high-temperature storage characteristics of the lithium ion secondary battery can be improved.
- a water-soluble polymer can be softened by setting it as the upper limit of the said range or less. For this reason, for example, suppression of the swelling of the electrode and improvement of the adhesion of the electrode active material layer to the current collector can be achieved.
- the weight average molecular weight of the water-soluble polymer is polystyrene using gel permeation chromatography (GPC) as a developing solvent, a solution obtained by dissolving 0.85 g / ml sodium nitrate in a 10% by volume aqueous solution of dimethylformamide. It can be obtained as a conversion value.
- the glass transition temperature of the water-soluble polymer is usually 0 ° C. or higher, preferably 5 ° C. or higher, and is usually 100 ° C. or lower, preferably 50 ° C. or lower. When the glass transition temperature of the water-soluble polymer is in the above range, both electrode adhesion and flexibility can be achieved.
- the glass transition temperature of the water-soluble polymer can be adjusted by combining various monomers.
- one type of water-soluble polymer may be used alone, or two or more types may be used in combination at any ratio.
- the amount of the water-soluble polymer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, particularly 100 parts by weight of the electrode active material.
- the amount is preferably 0.5 parts by weight or more, preferably 30 parts by weight or less, more preferably 25 parts by weight or less, and particularly preferably 20 parts by weight or less.
- the water-soluble polymer is, for example, a monomer composition containing an aromatic vinyl monomer, an unsaturated carboxylic acid monomer, a crosslinkable monomer, and an optional monomer as necessary in an aqueous solvent. Can be produced by polymerization. At this time, the ratio of each monomer in the monomer composition is usually the same as the ratio of structural units in the water-soluble polymer.
- the aqueous solvent is not particularly limited as long as it can dissolve the water-soluble polymer.
- an aqueous solvent having a boiling point at normal pressure of usually 80 ° C. or higher, preferably 100 ° C. or higher, and usually 350 ° C. or lower, preferably 300 ° C. or lower is used. Examples of the aqueous solvent will be given below. In the following examples, the number in parentheses after the solvent name is the boiling point (unit: ° C) at normal pressure, and the value after the decimal point is a value rounded off or rounded down.
- aqueous solvents examples include water (100); ketones such as diacetone alcohol (169) and ⁇ -butyrolactone (204); ethyl alcohol (78), isopropyl alcohol (82), and normal propyl alcohol (97).
- Alcohols propylene glycol monomethyl ether (120), methyl cellosolve (124), ethyl cellosolve (136), ethylene glycol tertiary butyl ether (152), butyl cellosolve (171), 3-methoxy-3-methyl-1-butanol (174) ), Ethylene glycol monopropyl ether (150), diethylene glycol monobutyl pyrether (230), triethylene glycol monobutyl ether (271), dipropylene glycol monomethyl ether (18) Glycol ethers, etc.); and 1,3-dioxolane (75), 1,4-dioxolane (101), ethers such as tetrahydrofuran (66) and the like.
- water is particularly preferable from the viewpoint that it is not flammable and easily obtains a water-soluble polymer.
- one type of aqueous solvent may be used alone, or two or more types may be used in combination at any ratio.
- water may be used as the main solvent, and an aqueous solvent other than the above-described water may be mixed and used within a range in which dissolution of the water-soluble polymer can be ensured.
- the polymerization method is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method may be used.
- a solution polymerization method any method such as ionic polymerization, radical polymerization, and living radical polymerization may be used.
- the polymerization temperature and the polymerization time can be arbitrarily selected depending on the polymerization method and the kind of the polymerization initiator. Usually, the polymerization temperature is about 30 ° C. or more, and the polymerization time is about 0.5 to 30 hours. Further, additives such as amines may be used as a polymerization aid.
- a reaction solution containing a water-soluble polymer is obtained by the method described above.
- the obtained reaction solution is usually acidic, and the water-soluble polymer is often dispersed in an aqueous solvent.
- the water-soluble polymer dispersed in the aqueous solvent as described above can be usually made soluble in the aqueous solvent by adjusting the pH of the reaction solution to, for example, 7 to 13.
- the water-soluble polymer may be taken out from the aqueous solution thus obtained.
- a slurry composition is produced using the water-soluble polymer dissolved in an aqueous solvent, and the electrode is formed using the slurry composition. Can be manufactured.
- the aqueous solution containing a water-soluble polymer in an aqueous solvent is usually acidic, and may be alkalized to pH 7 to pH 13 as necessary.
- the handleability of aqueous solution can be improved and the applicability
- Examples of the method for alkalinizing to pH 7 to pH 13 include alkali metal aqueous solutions such as lithium hydroxide aqueous solution, sodium hydroxide aqueous solution and potassium hydroxide aqueous solution; alkaline earth metal aqueous solutions such as calcium hydroxide aqueous solution and magnesium hydroxide aqueous solution; The method of mixing aqueous alkali solution, such as aqueous ammonia solution, is mentioned.
- One kind of the alkaline aqueous solution may be used alone, or two or more kinds may be used in combination at any ratio.
- the electrode for a lithium ion secondary battery of the present invention may contain a particulate binder.
- the particulate binder is usually contained in the electrode active material layer and has an effect of binding the electrode active material and the current collector.
- the electrode active material can be held more firmly in the lithium ion secondary battery electrode, so that the electrode active material is detached from the lithium ion secondary battery electrode. Can be further suppressed.
- the particulate binder can also bind particles other than the electrode active material usually contained in the electrode active material layer, and can also serve to maintain the strength of the electrode active material layer.
- the particulate binder has a particulate shape, the binding property is particularly high, and the deterioration of the capacity of the lithium ion secondary battery electrode due to repeated charge and discharge can be remarkably suppressed.
- the particulate binder can be used in a slurry composition for producing an electrode for a lithium ion secondary battery that can exist in a state in which the particle shape is maintained, but the electrode active material layer also has a state in which the particle shape is maintained. Those that can be present are preferred.
- the “state in which the particle state is maintained” does not have to be a state in which the particle shape is completely maintained, and may be in a state in which the particle shape is maintained to some extent.
- the compound that forms the particulate binder is not particularly limited as long as it is a compound that can bind the electrode active material and the electrode conductive material described later.
- a suitable particulate binder is a dispersion-type binder having a property of being dispersible in a solvent. Specific examples thereof include polymer compounds such as a fluoropolymer, a diene polymer, an acrylate polymer, a polyimide, a polyamide, and a polyurethane polymer.
- a fluoropolymer, a diene polymer, or an acrylate polymer is preferable, and a diene polymer or an acrylate polymer is more preferable in that the withstand voltage can be increased and the energy density of the electrochemical device can be increased.
- the diene polymer is a homopolymer of a conjugated diene; a copolymer of different types of conjugated dienes; a copolymer obtained by polymerizing a monomer mixture containing a conjugated diene, or a hydrogenated product thereof.
- the proportion of conjugated diene in the monomer mixture is usually 20% by weight or more, preferably 25% by weight or more.
- the diene polymer examples include conjugated diene homopolymers such as polybutadiene and polyisoprene; aromatic vinyl / conjugated diene copolymers such as carboxy-modified styrene / butadiene copolymer (SBR); Examples thereof include vinyl cyanide / conjugated diene copolymers such as acrylonitrile / butadiene copolymer (NBR); hydrogenated SBR, hydrogenated NBR, and the like.
- a conjugated diene may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the ratio of the conjugated diene monomer unit in the diene polymer is preferably 20% by weight or more, more preferably 30% by weight or more, preferably 60% by weight or less, more preferably 55% by weight or less.
- the acrylate polymer has a general formula (III): CH 2 ⁇ CR 6 —COOR 7 (in the general formula (III), R 6 represents a hydrogen atom or a methyl group, and R 7 represents an alkyl group or a cycloalkyl group.
- acrylate is preferable, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferable in that the strength of the electrode for a lithium ion secondary battery can be improved.
- these monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the ratio of monomer units obtained by polymerizing acrylic acid ester and / or methacrylic acid ester in the acrylate polymer is preferably 50% by weight or more, more preferably 70% by weight or more.
- the heat resistance of the particulate binder can be improved, and the electrode for a lithium ion secondary battery Can reduce the internal resistance.
- a carboxylic acid group-containing monomer copolymerizable with the compound represented by the general formula (III) is used. Also good.
- the carboxylic acid group-containing monomer include monobasic acid-containing monomers such as acrylic acid and methacrylic acid; dibasic acid-containing monomers such as maleic acid, fumaric acid, and itaconic acid. .
- a dibasic acid-containing monomer is preferable, and itaconic acid is particularly preferable in that the binding strength can be improved and the electrode strength can be improved.
- a carboxylic acid group containing monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the amount of the carboxylic acid group-containing monomer is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, particularly preferably 100 parts by weight of the compound represented by the general formula (III). 1 part by weight or more, preferably 50 parts by weight or less, more preferably 20 parts by weight or less, and particularly preferably 10 parts by weight or less.
- the amount of the carboxylic acid group-containing monomer is within this range, the binding property can be improved and the electrode strength can be improved.
- a nitrile group-containing monomer copolymerizable with the compound represented by the general formula (III) may be used.
- the nitrile group-containing monomer include acrylonitrile and methacrylonitrile. Among them, acrylonitrile is preferable in that the binding strength can be improved and the electrode strength can be improved.
- a nitrile group containing monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the amount of the nitrile group-containing monomer is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, and particularly preferably 1 part by weight with respect to 100 parts by weight of the compound represented by the general formula (III). It is at least 40 parts by weight, more preferably at most 30 parts by weight, particularly preferably at most 20 parts by weight. When the amount of the nitrile group-containing monomer is within this range, the binding property can be improved and the electrode strength can be improved.
- the weight average molecular weight of the polymer forming the particulate binder is preferably 10,000 or more, more preferably 20,000 or more, preferably 1,000,000 or less, more preferably 500,000 or less.
- the weight average molecular weight of the particulate binder can be determined by GPC as a value in terms of polystyrene using tetrahydrofuran as a developing solvent.
- the glass transition temperature (Tg) of the particulate binder is preferably 50 ° C. or lower, more preferably 0 ° C. or lower, and usually ⁇ 40 ° C. or higher.
- Tg glass transition temperature
- the polymer forming the particulate binder is insoluble in water. Therefore, the particulate binder is usually in the form of particles in the slurry composition for producing an electrode for a lithium ion secondary battery, and is included in the electrode for a lithium ion secondary battery while maintaining the particle shape.
- the number average particle diameter of the particulate binder is usually 0.01 ⁇ m or more, preferably 0.03 ⁇ m or more, more preferably 0.05 ⁇ m or more, and usually 1 ⁇ m or less, preferably 0.8 ⁇ m or less, more preferably 0.00. 5 ⁇ m or less.
- the number average particle diameter is a number average particle diameter calculated as an arithmetic average value obtained by measuring the diameters of 100 particulate binders randomly selected in a transmission electron micrograph.
- the shape of the particles may be either spherical or irregular.
- particulate binder may be used alone, or two or more kinds may be used in combination at any ratio.
- the amount of the particulate binder is usually 0.1 parts by weight or more, preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and usually 50 parts by weight or less, relative to 100 parts by weight of the electrode active material. Preferably it is 20 weight part or less, More preferably, it is 10 weight part or less.
- the particulate binder can be produced, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent to form polymer particles.
- the ratio of each monomer in the monomer composition is usually the same as the ratio of structural units in the particulate binder.
- aqueous solvent examples include those described in the method for producing a water-soluble polymer.
- any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method may be used.
- a polymerization method any method such as ionic polymerization, radical polymerization, and living radical polymerization may be used. Among them, it is easy to obtain a high molecular weight polymer, and since the polymer is obtained in the form of particles dispersed in water, no redispersion treatment is required, so that an electrode for a lithium ion secondary battery can be produced as it is.
- the emulsion polymerization method is particularly preferred from the viewpoint of production efficiency, such as being able to be used in the slurry composition.
- the emulsion polymerization method is usually performed by a conventional method. For example, it can be performed by the method described in “Experimental Chemistry Course” Vol. 28, (Publisher: Maruzen Co., Ltd., edited by The Chemical Society of Japan). That is, water, an additive such as a dispersant, an emulsifier, a crosslinking agent, a polymerization initiator, and a monomer are added to a sealed container equipped with a stirrer and a heating device so as to have a predetermined composition.
- a method may be used in which the composition is stirred to emulsify monomers and the like in water, and the temperature is increased while stirring to initiate polymerization. Or after emulsifying the said composition, it can put into an airtight container, and the method of starting reaction similarly can be used.
- polymerization initiator examples include, for example, lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide, and the like.
- a polymerization initiator may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- Emulsifiers, dispersants, polymerization initiators, and the like are generally used in these polymerization methods, and the amount used is generally the amount generally used.
- seed polymerization may be performed using seed particles.
- the pH of the aqueous dispersion of the particulate binder obtained by these methods may be adjusted to usually be in the range of 5 to 10, preferably 5 to 9.
- the pH adjustment may be performed by, for example, alkali metal (eg, Li, Na, K, Rb, Cs) hydroxide, ammonia, inorganic ammonium compound (eg, NH 4 Cl), organic amine compound (eg, ethanolamine, It can be carried out by mixing a basic aqueous solution containing diethylamine and the like with an aqueous dispersion of the particulate binder.
- alkali metal hydroxide eg, Li, Na, K, Rb, Cs
- ammonia eg, inorganic ammonium compound
- organic amine compound eg, ethanolamine
- the particulate binder may be a composite polymer particle composed of two or more kinds of polymers.
- the composite polymer particles are obtained, for example, by polymerizing at least one monomer component by a conventional method, then polymerizing at least one other monomer component and polymerizing by a conventional method (two-stage polymerization method). ) Or the like. In this way, by polymerizing the monomer stepwise, it is possible to obtain core-shell structured particles having a core layer present inside the particle and a shell layer covering the core layer.
- the electrode for a lithium ion secondary battery of the present invention may contain any component other than the above-described electrode active material, water-soluble polymer and particulate binder as long as the effects of the present invention are not significantly impaired.
- the electrode for a lithium ion secondary battery of the present invention may contain an electrode conductive material, a dispersant, a reinforcing material, a leveling agent, nanoparticles, and an additive.
- these optional components are contained in the electrode active material layer.
- arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- Examples of the electrode conductive material include conductive particles of carbon allotrope.
- Examples of the carbon allotrope forming such a conductive material for an electrode include conductive carbon material black such as furnace black, acetylene black, and ketjen black (registered trademark of Akzo Nobel Chemicals Bethlo Tenfen Note Shap). Is mentioned. Among these, acetylene black and furnace black are preferable.
- the electrically conductive material for electrodes may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the volume average particle diameter of the electrode conductive material is preferably smaller than the volume average particle diameter of the electrode active material.
- the specific range of the volume average particle diameter of the electrode conductive material is usually 0.001 ⁇ m or more, preferably 0.05 ⁇ m or more, more preferably 0.01 ⁇ m or more, and usually 10 ⁇ m or less, preferably 5 ⁇ m or less, more preferably 1 ⁇ m or less. When the volume average particle diameter of the electrode conductive material is within this range, high conductivity can be obtained with a smaller amount of use.
- the amount of the electrode conductive material is usually 0.1 parts by weight or more, preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and usually 50 parts by weight or less, with respect to 100 parts by weight of the electrode active material. , Preferably 15 parts by weight or less, more preferably 10 parts by weight or less.
- the amount of the electrode conductive material is within this range, the capacity of the lithium ion secondary battery can be increased, and the internal resistance of the electrode for the lithium ion secondary battery can be decreased.
- the dispersant examples include cellulosic polymers such as carboxymethylcellulose, methylcellulose, ethylcellulose, and hydroxypropylcellulose, and ammonium salts or alkali metal salts thereof; poly (meth) acrylates such as sodium poly (meth) acrylate; Examples include polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphate starch, casein, and various modified starches. Among these, a cellulose polymer is preferable, and carboxymethyl cellulose or an ammonium salt or an alkali metal salt thereof is particularly preferable.
- One of these dispersants may be used alone, or two or more thereof may be used in combination at any ratio.
- the amount of the dispersant is usually 0.1 parts by weight or more, preferably 0.5 parts by weight or more, more preferably 0.8 parts by weight or more, and usually 10 parts by weight with respect to 100 parts by weight of the electrode active material.
- the amount is preferably 5 parts by weight or less, more preferably 2 parts by weight or less.
- the reinforcing material for example, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used.
- One type of these reinforcing agents may be used alone, or two or more types may be used in combination at any ratio.
- a tough and flexible electrode for a lithium ion secondary battery can be obtained, and a lithium ion secondary battery exhibiting excellent long-term cycle characteristics can be realized.
- the amount of the reinforcing material is usually 0.01 parts by weight or more, preferably 1 part by weight or more, and usually 20 parts by weight or less, preferably 10 parts by weight or less, with respect to 100 parts by weight of the electrode active material.
- leveling agent examples include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants.
- surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants.
- One of these leveling agents may be used alone, or two or more thereof may be used in combination at any ratio.
- the amount of the leveling agent is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the electrode active material.
- the leveling agent is within the above range, the productivity, smoothness, and battery characteristics during electrode production are excellent.
- the dispersibility of an electrode active material etc. can be improved in the slurry composition for manufacturing the electrode for lithium ion secondary batteries by containing surfactant, and also the lithium ion secondary battery obtained by it The smoothness of the electrode can be improved.
- nanoparticles examples include particles such as fumed silica and fumed alumina. One kind of these nanoparticles may be used alone, or two or more kinds thereof may be used in combination at any ratio. When the nanoparticles are included, the thixotropy of the slurry composition for producing an electrode for a lithium ion secondary battery can be adjusted, thereby improving the leveling property of the obtained electrode for a lithium ion secondary battery. be able to.
- the amount of nanoparticles is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the electrode active material.
- the stability and productivity of the slurry composition for producing an electrode for a lithium ion secondary battery can be improved, and high battery characteristics can be realized.
- Examples of the additive include vinylene carbonate.
- An additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. By using the additive, for example, decomposition of the electrolytic solution can be suppressed.
- the amount of the additive is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the electrode active material.
- the electrode active material, the water-soluble polymer, and the components included as necessary are usually contained in the electrode active material layer.
- the electrode active material layer is usually provided on the surface of the current collector. At this time, the electrode active material layer may be provided on one side of the current collector, or may be provided on both sides.
- the current collector is not particularly limited as long as it has electrical conductivity and is electrochemically durable, but a metal material is preferable because it has heat resistance.
- the material for the current collector include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum.
- the current collector for the positive electrode is preferably aluminum
- the current collector for the negative electrode is preferably copper.
- the material of an electrical power collector may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 mm to 0.5 mm is preferable.
- the current collector is preferably used after the surface is roughened.
- the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method.
- a mechanical polishing method usually, a polishing cloth with an abrasive particle fixed thereto, a grindstone, an emery buff, a wire brush provided with a steel wire or the like is used.
- an intermediate layer may be formed on the surface of the current collector.
- the thickness of the electrode active material layer is usually 5 ⁇ m or more, preferably 20 ⁇ m or more, more preferably 30 ⁇ m or more, and usually 1000 ⁇ m or less, preferably 500 ⁇ m or less, more preferably 300 ⁇ m or less. When the thickness of the electrode active material layer is in the above range, load characteristics and cycle characteristics can be improved.
- the content ratio of the electrode active material in the electrode active material layer is preferably 85% by weight or more, more preferably 88% by weight or more, preferably 99% by weight or less, more preferably 97% by weight or less.
- the density of the electrode active material layer is usually 0.30 g / cm 3 or more, preferably 0.35 g / cm 3 or more, more preferably 0.40 g / cm 3 or more, and usually 10 g / cm 3 or less, preferably 8 .0g / cm 3 or less, more preferably 6.0 g / cm 3 or less.
- the amount of water in the electrode active material layer is preferably 1000 ppm or less, and more preferably 500 ppm or less.
- the amount of water can be measured by a known method such as the Karl Fischer method.
- Such a low water content can be achieved by appropriately adjusting the composition of the structural unit in the water-soluble polymer.
- the fluorine-containing (meth) acrylic acid ester monomer unit in the range of usually 0.5% by weight or more, preferably 1% by weight or more, and usually 20% by weight or less, preferably 10% by weight or less. , Moisture content can be reduced.
- the electrode for a lithium ion secondary battery of the present invention can be produced by, for example, a coating method or a powder molding method.
- the coating method refers to the surface of the current collector by preparing a slurry composition for producing an electrode for a lithium ion secondary battery, applying the slurry composition on the current collector, and drying the slurry composition.
- an electrode active material layer is formed on a lithium ion battery electrode.
- the powder molding method refers to preparing a slurry composition for producing an electrode for a lithium ion secondary battery, preparing composite particles containing an electrode active material and a water-soluble polymer from the slurry composition,
- This is a manufacturing method in which an electrode active material layer is formed by supplying composite particles onto a current collector and further rolling and forming as required to form an electrode for a lithium ion battery.
- the coating method is preferable in that the electrode active material layer has excellent adhesion to the current collector.
- the powder molding method is preferable in that the capacity of the electrode for the lithium ion secondary battery is high and the internal resistance is low, the process is simple, and the manufacturing cost is excellent.
- a slurry composition for producing an electrode for a lithium ion secondary battery is prepared.
- the slurry composition is a fluid composition containing an electrode active material, a water-soluble polymer, and a solvent.
- the electrode for a lithium ion secondary battery includes optional components such as a particulate binder, an electrode conductive material, a dispersant, a reinforcing material, a leveling agent, nanoparticles, and an additive
- the slurry composition also includes Include optional ingredients.
- the ratio of the electrode active material, the water-soluble polymer, and optional components in the slurry composition is usually the same as the ratio of each component contained in the electrode active material layer.
- solvent water may be used, an organic solvent may be used, or a combination of water and an organic solvent may be used. These solvents function as a solvent or a dispersion medium in the slurry composition, and can disperse the electrode active material, disperse the particulate binder, or dissolve the water-soluble polymer.
- organic solvent examples include alkyl alcohols such as methyl alcohol, ethyl alcohol and propyl alcohol; alkyl ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane and diglyme; diethylformamide, dimethylacetamide and N-methyl- Amides such as 2-pyrrolidone and dimethylimidazolidinone; sulfur solvents such as dimethyl sulfoxide and sulfolane; and the like.
- alcohols are preferable as the organic solvent.
- One of these may be used alone, or two or more of these may be used in combination at any ratio.
- water is preferable as the solvent because it is easy to dry the electrode active material layer and is excellent in environmental load.
- water is used as the solvent, in the slurry composition, a part of the water-soluble polymer is dissolved in water, but another part of the water-soluble polymer is adsorbed on the surface of the electrode active material, Since the electrode active material is covered with a stable layer of a water-soluble polymer, the dispersibility of the electrode active material in water can be improved. For this reason, the coating property of a slurry composition can be made favorable.
- the dispersibility of the particulate binder and the solubility of the water-soluble polymer can be adjusted depending on the amount or type of the organic solvent used in combination with water.
- the production efficiency can be improved.
- an organic solvent that dissolves the particulate binder and the water-soluble polymer is combined with water, the dispersion of the electrode active material is stabilized by adsorbing the particle binder and the water-soluble polymer on the surface of the electrode active material. Therefore, it is preferable.
- the amount of the solvent is such that the solid content in the slurry composition is usually 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more, and usually 90% by weight or less, preferably 85%. It is the range which becomes weight% or less, More preferably, it is 80 weight% or less. When the solid content concentration is in this range, each component is uniformly dispersed, which is preferable.
- the viscosity of the slurry composition is usually 10 mPa ⁇ s or more, preferably 30 mPa ⁇ s or more, more preferably 50 mPa ⁇ s or more, and usually 100,000 mPa ⁇ s or less, preferably 50,000 mPa ⁇ s at room temperature. Hereinafter, it is more preferably 20,000 mPa ⁇ s or less. When the viscosity is in this range, productivity can be increased.
- a slurry composition for producing an electrode for a lithium ion secondary battery can be produced by mixing an electrode active material, a water-soluble polymer and a solvent, and components used as necessary.
- the specific procedure at this time is arbitrary.
- the electrode active material, the water-soluble polymer, the electrode conductive material, and the particulate binder are used as a solvent.
- a method in which a water-soluble polymer is dissolved in a solvent, a particulate binder dispersed in a solvent is mixed, and then an electrode active material and a conductive material for an electrode are mixed; particles dispersed in a solvent For example, a method in which an electrode active material and an electrode conductive material are mixed in a binder and a water-soluble polymer dissolved in a solvent is mixed in the mixture.
- Examples of the mixing means include mixing equipment such as a ball mill, a sand mill, a bead mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a homomixer, and a planetary mixer.
- the mixing is usually carried out at room temperature to 80 ° C. for 10 minutes to several hours.
- the slurry composition of the present invention includes a water-soluble polymer containing an aromatic vinyl monomer unit, an unsaturated carboxylic acid monomer unit, and a crosslinkable monomer unit at a specific ratio, and thus has excellent dispersion stability. . Therefore, the slurry composition can be easily applied uniformly.
- Application method is not limited, and examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.
- a film of the slurry composition is formed on the surface of the current collector.
- membrane of a slurry composition can be suitably set according to the thickness of the target electrode active material layer.
- the electrode active material layer containing an electrode active material and a water-soluble polymer is formed in the surface of an electrical power collector, and the electrode for lithium ion secondary batteries of this invention is obtained.
- drying method examples include drying with warm air, hot air, low-humidity air or the like; vacuum drying; (far) drying method by irradiation with infrared rays or electron beams. Among these, a drying method by irradiation with far infrared rays is preferable.
- the drying temperature and the drying time are preferably a temperature and a time at which the solvent in the slurry composition applied to the current collector can be completely removed.
- the drying temperature is usually 100 ° C. or higher, preferably 120 ° C. or higher, and usually 300 ° C. or lower, preferably 250 ° C. or lower.
- drying time it is 10 minutes or more normally, Preferably it is 20 minutes or more, and is 100 hours or less normally, Preferably it is 20 hours or less.
- the electrode active material layer may be subjected to pressure treatment using, for example, a die press or a roll press as necessary.
- the porosity of the electrode active material layer can be lowered.
- the porosity is preferably 5% or more, more preferably 7% or more, preferably 30% or less, more preferably 20% or less.
- the polymer may be cured after the electrode active material layer is formed.
- a slurry composition for producing an electrode for a lithium ion secondary battery can be prepared.
- the slurry composition may be prepared in the same manner as the coating method.
- a solvent for the slurry composition it is preferable to use a combination of water and an organic solvent having a boiling point lower than that of water. Thereby, the drying speed can be increased during spray drying.
- composite particles are prepared from the slurry composition. Since the composite particles are prepared from the slurry composition, they are particles in which components such as an electrode active material and a water-soluble polymer contained in the slurry composition are integrated.
- the components such as the electrode active material and the particulate binder contained in the slurry composition do not exist as separate and independent particles, but a plurality of components such as the electrode active material and the particulate binder are combined.
- One particle is formed. Specifically, two or more particles (primary particles) are bonded, and secondary particles are formed as a lump of bonded primary particles.
- it is preferable that a plurality (preferably several to several tens) of electrode active materials are bound by a water-soluble polymer and a particulate binder used as necessary to form composite particles. .
- the adhesiveness of the electrode active material layer in the electrode for lithium ion secondary batteries can be made higher, and the internal resistance of the lithium ion secondary battery can be reduced.
- Composite particles can be produced by granulating the slurry composition.
- composite particle granulation methods include, for example, spray drying granulation method, rolling bed granulation method, compression granulation method, stirring granulation method, extrusion granulation method, crushing granulation method, fluidized bed granulation method.
- the granulation method include a granulation method, a fluidized bed multifunctional granulation method, a pulse combustion drying method, and a melt granulation method.
- the spray-drying granulation method is preferable because the composite particles in which the water-soluble polymer, the particulate binder used as necessary, and the electrode conductive material are unevenly distributed near the surface of the composite particles can be easily obtained.
- an electrode for a lithium ion secondary battery can be obtained with high productivity.
- the internal resistance of the lithium ion secondary battery electrode can be further reduced.
- the slurry composition is spray dried and granulated to obtain composite particles.
- Spray drying is performed by spraying and drying the slurry composition in hot air.
- An example of an apparatus used for spraying the slurry composition is an atomizer. There are two types of atomizers: a rotating disk method and a pressure method.
- the rotating disk system is a system in which a slurry composition is introduced almost at the center of a disk that rotates at high speed, and the slurry composition is released out of the disk by the centrifugal force of the disk, and the slurry composition is atomized at that time.
- the rotation speed of the disk depends on the size of the disk, and is usually 5,000 rpm or more, preferably 15,000 rpm or more, and usually 40,000 rpm or less, preferably 40,000 rpm or less. The lower the rotational speed of the disk, the larger the spray droplets and the larger the weight average particle diameter of the resulting composite particles.
- the rotating disk type atomizer there are a pin type and a vane type, and a pin type atomizer is particularly preferable.
- the pin-type atomizer is a kind of centrifugal spraying device using a spraying plate, and the spraying plate has a plurality of spraying rollers removably mounted on a concentric circle along its periphery between the upper and lower mounting disks. Consists of things. The slurry composition is introduced from the center of the spray disc, adheres to the spraying roller by centrifugal force, moves outward on the roller surface, and finally sprays away from the roller surface.
- the pressurization method is a method in which the slurry composition is pressurized and sprayed from a nozzle to be dried.
- the temperature of the sprayed slurry composition is usually room temperature, but it may be heated to room temperature or higher.
- the temperature of the hot air during spray drying is usually 80 ° C. or higher, preferably 100 ° C. or higher, and is usually 250 ° C. or lower, preferably 200 ° C. or lower.
- a hot air blowing method for example, a method in which the hot air and the spray direction flow in the horizontal direction, a method in which the hot air is sprayed at the top of the drying tower and descends with the hot air, a method in which the sprayed droplets and the hot air are in countercurrent contact A method in which sprayed droplets first flow in parallel with hot air, then drop by gravity and make countercurrent contact, and the like.
- the shape of the composite particles is preferably substantially spherical. That is, the sphericity of the composite particles is preferably 80% or more, and more preferably 90% or more.
- the value of (1 ⁇ (L1 ⁇ Ls) / La) ⁇ 100 is defined as sphericity (%).
- Ls represents the minor axis diameter of the composite particle
- Ll represents the major axis diameter of the composite particle
- La (Ls + Ll) / 2.
- the short axis diameter Ls and the long axis diameter Ll are values measured from a transmission electron micrograph image.
- the volume average particle diameter of the composite particles is usually 10 ⁇ m or more, preferably 20 ⁇ m or more, more preferably 30 ⁇ m or more, and usually 100 ⁇ m or less, preferably 80 ⁇ m or less, more preferably 60 ⁇ m or less.
- the obtained composite particles are supplied onto a current collector.
- a feeder is usually used.
- This feeder is preferably a quantitative feeder capable of supplying composite particles quantitatively.
- it can be quantitatively supplied that composite particles are continuously supplied using such a feeder, the supply amount is measured a plurality of times at regular intervals, and the average value m of the measured values and the standard deviation ⁇ m are obtained.
- the quantitative feeder examples include gravity feeders such as a table feeder and a rotary feeder; mechanical force feeders such as a screw feeder and a belt feeder. Of these, the rotary feeder is preferred.
- the composite particles supplied to the current collector are molded to form an electrode active material layer containing an electrode active material and a water-soluble polymer on the surface of the current collector.
- the electrode for the lithium ion secondary battery of the present invention Get.
- the current collector and the supplied composite particles are pressed with a pair of rolls to form, and an electrode active material layer is formed on the current collector as a layer of composite particles.
- the supplied composite particles are heated.
- the specific temperature of the supplied composite particles is preferably 40 ° C. or higher, more preferably 70 ° C. or higher, preferably 160 ° C. or lower, more preferably 140 ° C. or lower.
- the temperature of the composite particles is within this range, slippage of the composite particles on the roll surface is suppressed, and the composite particles are continuously and uniformly supplied to the roll. For this reason, an electrode active material layer having a uniform film thickness and small variations in electrode density can be obtained.
- the molding temperature is usually 0 ° C. to 200 ° C.
- the molding temperature is preferably higher than the melting point or glass transition temperature of the particulate binder, and more preferably 20 ° C. higher than the melting point or glass transition temperature.
- the forming speed by the roll is usually larger than 0.1 m / min, preferably 35 m / min or more, and preferably 70 m / min or less.
- the press linear pressure between the pair of rolls is usually 0.2 kN / cm or more, preferably 0.5 kN / cm or more, and usually 30 kN / cm or less, preferably 10 kN / cm or less.
- the arrangement of the pair of rolls is not particularly limited, but is preferably arranged substantially horizontally or substantially vertically.
- the current collector is continuously supplied between a pair of rolls, and the composite particles are supplied to at least one of the rolls so that the composite particles are supplied to the gap between the current collector and the rolls.
- the electrode active material layer can be formed by pressurization.
- the current collector is transported in the horizontal direction, the composite particles are supplied onto the current collector, the supplied composite particles are leveled with a blade or the like as necessary, and then the current collectors are paired.
- the electrode active material layer can be formed by supplying between the rolls and pressing.
- the electrode active material layer contains a curable polymer
- the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator.
- the lithium ion secondary battery of the present invention at least one of the positive electrode and the negative electrode is the electrode for the lithium ion secondary battery of the present invention. Since the lithium ion secondary battery of this invention is equipped with the electrode for lithium ion secondary batteries of this invention, it is excellent in the storage characteristic and cycling characteristics in a high temperature environment. Moreover, the lithium ion secondary battery of this invention can suppress the swelling of the electrode accompanying charging / discharging normally, and is excellent in a low temperature output characteristic.
- Electrolyte As the electrolytic solution, for example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent may be used.
- the lithium salt include LiPF 6 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlCl 4 , LiClO 4 , CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) 2 NLi , (CF 3 SO 2 ) 2 NLi, (C 2 F 5 SO 2 ) NLi, and other lithium salts.
- LiPF 6 , LiClO 4 , and CF 3 SO 3 Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used.
- One of these may be used alone, or two or more of these may be used in combination at any ratio.
- the amount of the supporting electrolyte is usually 1% by weight or more, preferably 5% by weight or more, and usually 30% by weight or less, preferably 20% by weight or less with respect to the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered, and the charging characteristics and discharging characteristics of the lithium ion secondary battery may be lowered.
- the solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte.
- the solvent include alkyl carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (MEC); Esters such as butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferred because high ion conductivity is easily obtained and the use temperature range is wide.
- a solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- an additive may be included in the electrolytic solution as necessary.
- carbonate compounds such as vinylene carbonate (VC) are preferable.
- An additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- electrolytic solution other than the above examples include a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolytic solution; an inorganic solid electrolyte such as lithium sulfide, LiI, and Li 3 N;
- separator As the separator, a porous substrate having a pore portion is usually used.
- separators include (a) a porous separator having pores, (b) a porous separator having a polymer coating layer formed on one or both sides, and (c) a porous resin coat containing inorganic ceramic powder. And a porous separator having a layer formed thereon. Examples of these are for solid polymer electrolytes such as polypropylene-based, polyethylene-based, polyolefin-based or aramid-based porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile or polyvinylidene fluoride hexafluoropropylene copolymer.
- a polymer film for a gel polymer electrolyte a separator coated with a gelled polymer coat layer; a separator coated with a porous film layer composed of an inorganic filler and an inorganic filler dispersant; and the like.
- the manufacturing method of the lithium ion secondary battery of the present invention is not particularly limited.
- the above-described positive electrode and negative electrode may be overlapped via a separator, and this may be wound or folded in accordance with the shape of the battery and placed in the battery container, and the electrolyte may be injected into the battery container and sealed.
- an expanded metal; an overcurrent prevention element such as a fuse or a PTC element; a lead plate or the like may be inserted to prevent an increase in pressure inside the battery or overcharge / discharge.
- the shape of the battery may be any of, for example, a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, and a flat type.
- Adhesion strength after measurement of high-temperature cycle characteristics After the evaluation of “3. High-temperature cycle characteristics” above, the cell of the lithium ion secondary battery was disassembled, and the electrode was taken out. Were dried under reduced pressure. The adhesion strength of the dried electrode was measured in the same manner as in “1. Adhesion strength”. However, the dimensions of the test piece were 40 mm in length and 10 mm in width.
- Example 1 (1-1. Production of water-soluble polymer) In a 5 MPa pressure vessel with a stirrer, 10 parts of sodium styrene sulfonate as an aromatic vinyl monomer, 35 parts of methacrylic acid as an unsaturated carboxylic acid monomer, 0.8 part of ethylene dimethacrylate as a crosslinkable monomer, fluorine-containing 10 parts of 2,2,2-trifluoroethyl methacrylate as a (meth) acrylic acid ester monomer, 44.2 parts of ethyl acrylate as an optional monomer, 150 parts of ion-exchanged water as a solvent, and excess as a polymerization initiator After 0.5 parts of potassium sulfate was added and sufficiently stirred, the polymerization was started by heating to 60 ° C.
- aqueous sodium hydroxide solution After adding 5% aqueous sodium hydroxide solution to the mixture containing the particulate binder and adjusting the pH to 8, the unreacted monomer is removed by heating under reduced pressure, and then cooled to 30 ° C. or lower to obtain a desired content. An aqueous dispersion containing a particulate binder was obtained.
- the aqueous solution containing the water-soluble polymer obtained in (1-1. Production of water-soluble polymer) was diluted with ion-exchanged water to adjust the concentration to 5%.
- a composition was obtained.
- the aqueous dispersion as the binder composition obtained in (1-2. Production of binder composition) was added to the mixed liquid.
- the amount of the binder composition was 2 parts by the amount of the particulate binder with respect to 100 parts of the total amount of the negative electrode active material.
- ion exchange water was added to adjust the final solid content concentration to 50% and mixed for 10 minutes. This was defoamed under reduced pressure to obtain a negative electrode slurry composition having good fluidity.
- the negative electrode slurry composition obtained in the above (1-3. Production of negative electrode slurry composition) is dried on a copper foil having a thickness of 20 ⁇ m, which is a current collector, with a comma coater, and the film thickness after drying is about 150 ⁇ m. It was applied and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, the negative electrode original fabric was obtained by heat-processing at 120 degreeC for 2 minute (s). This negative electrode original fabric was rolled with a roll press to obtain a negative electrode having a negative electrode active material layer thickness of 80 ⁇ m. The adhesion strength of the obtained negative electrode was measured.
- a 40% aqueous dispersion of an acrylate polymer having a glass transition temperature Tg of ⁇ 40 ° C. and a number average particle diameter of 0.20 ⁇ m was prepared.
- This acrylate polymer is a copolymer obtained by emulsion polymerization of a monomer mixture containing 78% by weight of 2-ethylhexyl acrylate, 20% by weight of acrylonitrile, and 2% by weight of methacrylic acid.
- the above positive electrode slurry composition was applied on a copper foil having a thickness of 20 ⁇ m as a current collector by a comma coater so that the film thickness after drying was about 200 ⁇ m and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, it heat-processed for 2 minutes at 120 degreeC, and obtained the positive electrode.
- the obtained lithium ion secondary battery was evaluated for high temperature storage characteristics, high temperature cycle characteristics, electrode plate swelling characteristics, adhesion strength after measurement of high temperature cycle characteristics, and low temperature output characteristics.
- Example 2 In the above (1-2. Production of binder composition), a 40% aqueous dispersion of an acrylate polymer similar to that used as the binder for the positive electrode of Example 1 was used as the aqueous dispersion containing the particulate binder. Using. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 3 In the above (1-2. Production of binder composition), an aqueous dispersion containing a diene polymer having a glass transition temperature of ⁇ 36 ° C. and a number average particle size of 0.15 ⁇ m as an aqueous dispersion containing a particulate binder. was used.
- This diene polymer is a copolymer obtained by emulsion polymerization of a monomer mixture containing 18.5% by weight of acrylonitrile, 78.5% by weight of 1,3-butadiene and 3% by weight of itaconic acid.
- a lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 4 In the above (1-1. Production of water-soluble polymer), the amount of sodium styrenesulfonate, which is an aromatic vinyl monomer, is changed to 2 parts, and the amount of ethyl acrylate, which is an optional monomer, is changed to 52 parts. Changed to 2 parts. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 5 In the above (1-1. Production of water-soluble polymer), the amount of sodium styrenesulfonate as an aromatic vinyl monomer was changed to 27 parts, and the amount of ethyl acrylate as an arbitrary monomer was changed to 27 parts. Changed to 2 parts. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 6 In the above (1-1. Production of water-soluble polymer), styrene was used in place of sodium styrenesulfonate as the aromatic vinyl monomer. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 7 In the above (1-1. Production of water-soluble polymer), the amount of unsaturated carboxylic acid monomer methacrylic acid was changed to 22 parts, and the amount of optional monomer ethyl acrylate 57. Changed to 2 parts. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 8 In the above (1-1. Production of water-soluble polymer), the amount of methacrylic acid as an unsaturated carboxylic acid monomer was changed to 58 parts, and the amount of ethyl acrylate as an arbitrary monomer was changed to 21. Changed to 2 parts. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 9 In the above (1-1. Production of water-soluble polymer), acrylic acid was used in place of methacrylic acid as the unsaturated carboxylic acid monomer. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 10 In the above (1-1. Production of water-soluble polymer), allyl glycidyl ether was used in place of ethylene dimethacrylate as the crosslinkable monomer. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 11 In the above (1-1. Production of water-soluble polymer), glycidyl methacrylate was used in place of ethylene dimethacrylate as the crosslinkable monomer. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 12 In the above (1-1. Production of water-soluble polymer), the amount of ethylene dimethacrylate as a crosslinkable monomer was changed to 0.1 part, and the amount of ethyl acrylate as an optional monomer was changed to 44 parts. Changed to 9 parts. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 13 In the above (1-1. Production of water-soluble polymer), the amount of ethylene dimethacrylate as a crosslinkable monomer was changed to 1.8 parts, and the amount of ethyl acrylate as an arbitrary monomer was changed to 43 parts. Changed to 2 parts. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 14 In the above (1-1. Production of water-soluble polymer), 2,2,2-trifluoroethyl methacrylate, which is a fluorine-containing (meth) acrylic acid ester monomer, is not used. The amount of certain ethyl acrylate was changed to 54.2 parts. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 15 In the above (1-1. Production of water-soluble polymer), the amount of 2,2,2-trifluoroethyl methacrylate which is a fluorine-containing (meth) acrylic acid ester monomer is changed to 2 parts, The amount of monomeric ethyl acrylate was changed to 52.2 parts. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 16 In the above (1-1. Production of water-soluble polymer), the amount of 2,2,2-trifluoroethyl methacrylate, which is a fluorine-containing (meth) acrylic acid ester monomer, was changed to 28 parts. The amount of monomeric ethyl acrylate was changed to 26.2 parts. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 17 In the above (1-2. Production of binder composition), when the aqueous solution containing the water-soluble polymer and the aqueous dispersion containing the particulate binder are mixed, the mixing ratio is equivalent to the solid content of the water-soluble polymer: Particulate binder was changed to 0.2: 2 (weight ratio). A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 18 In the above (1-2. Production of binder composition), when the aqueous solution containing the water-soluble polymer and the aqueous dispersion containing the particulate binder are mixed, the mixing ratio is equivalent to the solid content of the water-soluble polymer: Particulate binder was changed to 28: 2 (weight ratio). A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 19 In the above (1-3. Production of negative electrode slurry composition), 100 parts of artificial graphite (average particle size: 24.5 ⁇ m) having a specific surface area of 4 m 2 / g was used as the negative electrode active material, and SiO x (average particle size: 5 ⁇ m) was not used. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 20 In the above (1-3. Production of negative electrode slurry composition), the amount of artificial graphite as the negative electrode active material was changed to 50 parts, and the amount of SiO x was changed to 50 parts. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.
- Example 21 (21-1. Production of binder composition) As an aqueous dispersion containing a particulate binder, a 40% aqueous dispersion of an acrylate polymer similar to that used as the positive electrode binder of Example 1 was used. Except for the above, a binder composition was obtained in the same manner as in Example 1-2 (1-2. Production of binder composition).
- the positive electrode slurry composition obtained in (21-2. Production of positive electrode slurry composition) is dried on a copper foil having a thickness of 20 ⁇ m, which is a current collector, with a comma coater, and the film thickness after drying is about 120 ⁇ m. It was applied and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a positive electrode raw material.
- This positive electrode original fabric was rolled with a roll press to obtain a positive electrode having a positive electrode active material layer thickness of 75 ⁇ m. The adhesion strength of the obtained positive electrode was measured.
- the above-described negative electrode slurry composition was applied on a copper foil having a thickness of 20 ⁇ m as a current collector by a comma coater so that the film thickness after drying was about 100 ⁇ m and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, it heat-processed for 2 minutes at 120 degreeC, and obtained the negative electrode.
- the obtained lithium ion secondary battery was evaluated for high temperature storage characteristics, high temperature cycle characteristics, electrode plate swelling characteristics, adhesion strength after measurement of high temperature cycle characteristics, and low temperature output characteristics.
- Example 22 In the above (21-2. Production of positive electrode slurry composition), lithium manganate having a volume average particle diameter of 15 ⁇ m was used as the positive electrode active material. A lithium ion secondary battery was produced and evaluated in the same manner as in Example 21 except for the above items.
- Example 23 (23-1. Production of negative electrode)
- the negative electrode slurry composition obtained in Example 1 (1-3. Production of negative electrode slurry composition) was spray dried and granulated to obtain spherical composite particles having a volume average particle diameter of 47 ⁇ m and a sphericity of 91%.
- the spray-drying granulation uses a spray dryer (OC-16; manufactured by Okawara Chemical Co., Ltd.), a rotating disk type atomizer (diameter 65 mm), a rotational speed of 25,000 rpm, a hot air temperature of 150 ° C., and a particle recovery outlet. The temperature was 90 ° C.
- the composite particles are supplied together with a 20 ⁇ m-thick copper foil to a roll (roll temperature rough surface heat roll; manufactured by Hirano Giken Co., Ltd.) (roll temperature: 100 ° C., press linear pressure: 3.9 kN / cm).
- a sheet-shaped electrode material was formed at a speed of 20 m / min.
- This electrode original fabric was rolled with a roll press to obtain a secondary battery negative electrode having a layer configuration of (copper foil) / (negative electrode active material layer) and a thickness of the negative electrode active material layer of 80 ⁇ m.
- the adhesion strength of the obtained negative electrode was measured.
- the negative electrode was replaced with the negative electrode obtained in the above (23-1. Production of negative electrode) in place of that obtained in Example 1-4 (1-4. Production of negative electrode). 1-5. Production of Positive Electrode) to (1-7. Lithium Ion Secondary Battery) were produced and evaluated for lithium ion secondary batteries.
- Example 24 (24-1. Production of positive electrode)
- the cathode slurry composition obtained in Example 21 (21-2. Production of cathode slurry composition) was spray-dried and granulated to obtain spherical composite particles having a volume average particle size of 53 ⁇ m and a sphericity of 94%.
- the spray-drying granulation uses a spray dryer (OC-16; manufactured by Okawara Chemical Co., Ltd.), a rotating disk type atomizer (diameter 65 mm), a rotational speed of 25,000 rpm, a hot air temperature of 150 ° C., and a particle recovery outlet. The temperature was 90 ° C.
- the composite particles are supplied together with a 20 ⁇ m-thick copper foil to a roll (roll temperature rough surface heat roll; manufactured by Hirano Giken Co., Ltd.) (roll temperature: 100 ° C., press linear pressure: 3.9 kN / cm).
- a sheet-shaped electrode material was formed at a speed of 20 m / min. This raw electrode roll was rolled with a roll press to obtain a secondary battery positive electrode having a layer configuration of (copper foil) / (positive electrode active material layer) and a positive electrode active material layer thickness of 75 ⁇ m. The adhesion strength of the obtained positive electrode was measured.
- Comparative Example 8 What was prepared in Comparative Example 7 instead of the aqueous solution containing the water-soluble polymer obtained in (1-1. Production of water-soluble polymer) in (21-1. Production of binder composition). Was used. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 21 except for the above items.
- Example 20 uses a negative electrode active material having a large degree of expansion and contraction.
- the peel strength obtained in Example 20 should be evaluated as sufficiently high peel strength considering that the negative electrode active material is used as a material having a large degree of expansion and contraction. Should be evaluated as being played.
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Abstract
Description
すなわち、本発明は以下の通りである。
前記水溶性重合体が、芳香族ビニル単量体単位1重量%~30重量%、不飽和カルボン酸単量体単位20重量%~60重量%及び架橋性単量体単位0.1重量%~5重量%を含む共重合体である、リチウムイオン二次電池用電極。
〔2〕 前記芳香族ビニル単量体単位が、スチレン単量体単位又はスチレンスルホン酸ナトリウム単量体単位である、〔1〕記載のリチウムイオン二次電池用電極。
〔3〕 前記不飽和カルボン酸単量体単位が、不飽和モノカルボン酸単量体単位である、〔1〕又は〔2〕記載のリチウムイオン二次電池用電極。
〔4〕 前記水溶性重合体が、さらにフッ素含有(メタ)アクリル酸エステル単量体単位を含み、
前記フッ素含有(メタ)アクリル酸エステル単量体単位の比率が、1重量%~30重量%である、〔1〕~〔3〕のいずれか一項に記載のリチウムイオン二次電池用電極。
〔5〕 前記水溶性重合体の含有割合が、電極活物質100重量部に対して、0.1重量部~30重量部である、〔1〕~〔4〕のいずれか一項に記載のリチウムイオン二次電池用電極。
〔6〕 前記リチウムイオン二次電池用電極が、さらに粒子状バインダーを含む、〔1〕~〔5〕のいずれか一項に記載のリチウムイオン二次電池用電極。
〔7〕 正極、負極、電解液及びセパレータを備えるリチウムイオン二次電池であって、
正極及び負極の少なくとも一方が、〔1〕~〔6〕のいずれか一項に記載のリチウムイオン二次電池用電極である、リチウムイオン二次電池。
〔8〕 電極活物質及び水溶性重合体を含む、リチウムイオン二次電池用電極を製造するためのスラリー組成物であって、
前記水溶性重合体が、芳香族ビニル単量体単位1重量%~30重量%、不飽和カルボン酸単量体単位20重量%~60重量%及び架橋性単量体単位0.1重量%~5重量%を含む共重合体である、スラリー組成物。
〔9〕 〔8〕記載のスラリー組成物を、集電体上に塗布し、乾燥することを含む、リチウムイオン二次電池用電極の製造方法。
本発明のリチウムイオン二次電池は、高温環境における保存特性及びサイクル特性に優れる。
本発明のスラリー組成物によれば、集電体に対する電極活物質の密着性に優れるリチウムイオン二次電池用電極を製造でき、ひいては高温環境における保存特性及びサイクル特性に優れるリチウムイオン二次電池を実現しうる。
本発明のリチウムイオン二次電池用電極の製造方法によれば、本発明のリチウムイオン二次電池を製造しうる。
本発明のリチウムイオン二次電池用電極は、電極活物質及び水溶性重合体を含む。通常、本発明のリチウムイオン二次電池用電極は、集電体と当該集電体上に設けられた電極活物質層とを備え、この電極活物質層が電極活物質及び水溶性重合体を含む。
電極活物質としては、正極活物質と負極活物質とが挙げられる。
正極活物質は、正極において用いられる電極活物質であり、リチウムイオン二次電池の正極において電子の受け渡しをする物質である。正極活物質としては、通常、リチウムイオンの挿入及び脱離が可能な物質が用いられる。このような正極活物質は、無機化合物からなるものと有機化合物からなるものとに大別される。
また、上記の無機化合物と有機化合物との混合物を正極活物質として用いてもよい。
正極活物質は、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。
炭素質材料は、一般的には、炭素前駆体を2000℃以下で熱処理して炭素化させた、黒鉛化の低い(即ち、結晶性の低い)炭素材料である。前記の熱処理の下限は特に限定されないが、例えば500℃以上としてもよい。
水溶性重合体は、芳香族ビニル単量体単位と、不飽和カルボン酸単量体単位と、架橋性単量体単位とを、特定の比率で含む共重合体である。水溶性重合体が芳香族ビニル単量体単位と不飽和カルボン酸単量体単位と架橋性単量体単位とを特定の比率で組み合わせて含むので、本発明のリチウムイオン二次電池用電極は、集電体に対する電極活物質の密着性に優れる。また、水溶性重合体は、更にフッ素含有(メタ)アクリル酸エステル単量体単位を含んでいてもよい。
芳香族ビニル単量体単位は、芳香族ビニル単量体を重合して得られる構造単位である。芳香族ビニル単量体の例としては、スチレン、α-メチルスチレン、ビニルトルエン、ジビニルベンゼン、及びp-スチレンスルホン酸ナトリウムが挙げられる。中でも、スチレン及びp-スチレンスルホン酸ナトリウムが好ましい。したがって、芳香族ビニル単量体単位としては、スチレン単量体単位及びスチレンスルホン酸ナトリウム単量体単位が好ましい。
また、芳香族ビニル単量体及び芳香族ビニル単量体単位は、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。
芳香族ビニル単量体単位の比率を前記範囲の下限値以上とすることにより、水溶性重合体の電極活物質に対する吸着性を高めることができるので、電極活物質同士の密着性や電極活物質と集電体との密着性を高め、電極活物質を電極活物質層に安定して保持することが可能となる。また、通常、リチウムイオン二次電池用電極において、水溶性重合体は電極活物質の表面に被膜を形成しうる。この際、水溶性重合体の電極活物質に対する吸着性が高いことにより、前記の被膜は電極活物質を安定して覆うことが可能である。したがって、電解液の分解を抑制して、リチウムイオン二次電池の高温保存特性及び高温サイクル特性を向上させることができる。ここで、芳香族ビニル単量体単位の電極活物質に対する吸着性を高めることができる理由は、芳香族ビニル単量体単位は高い疎水性を有し、電極活物質の疎水性の部位に対して高い親和性で吸着しうるためと推察される。
一方、芳香族ビニル単量体単位の比率を前記範囲の上限値以下とすることにより、水溶性重合体の疎水性が過剰に高くなることを抑制し、水溶性重合体に水溶性を発現させることができる。
水溶性重合体における芳香族ビニル単量体単位の比率は、水溶性重合体の重合に用いる全単量体に占める芳香族ビニル単量体の比率(仕込み比)により調整することができ、通常は、前記単量体単位の比率は、前記単量体の比率(仕込み比)と一致する。
不飽和カルボン酸単量体単位は、不飽和カルボン酸単量体を重合して得られる構造単位である。不飽和カルボン酸単量体は、炭素-炭素不飽和結合を有し、且つ、カルボキシル基を有する単量体である。ここで、不飽和カルボン酸単量体が有するカルボキシル基の数は、1つでもよく、2つ以上でもよい。
不飽和モノカルボン酸の誘導体の例としては、2-エチルアクリル酸、イソクロトン酸、α-アセトキシアクリル酸、β-trans-アリールオキシアクリル酸、α-クロロ-β-E-メトキシアクリル酸、及びβ-ジアミノアクリル酸等の、エチレン性不飽和モノカルボン酸の誘導体が挙げられる。
不飽和ジカルボン酸の酸無水物の例としては、無水マレイン酸、アクリル酸無水物、メチル無水マレイン酸、及びジメチル無水マレイン酸等の、エチレン性不飽和ジカルボン酸の酸無水物が挙げられる。
不飽和ジカルボン酸の誘導体の例としては、メチルマレイン酸、ジメチルマレイン酸、フェニルマレイン酸、クロロマレイン酸、ジクロロマレイン酸、フルオロマレイン酸等のマレイン酸メチルアリル;並びにマレイン酸ジフェニル、マレイン酸ノニル、マレイン酸デシル、マレイン酸ドデシル、マレイン酸オクタデシル、マレイン酸フルオロアルキル等のマレイン酸エステルが挙げられる。
また、不飽和カルボン酸単量体及び不飽和カルボン酸単量体単位は、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。
水溶性重合体における不飽和カルボン酸単量体単位の比率を前記範囲の下限値以上とすることにより、水溶性重合体の親水性を高め、水溶性重合体が水に溶解しうるようにできる。また、リチウムイオン二次電池用電極を製造するためのスラリー組成物において、水溶性重合体と電極活物質及び粒子状バインダーとの静電反発作用により、電極活物質及び粒子状バインダーの偏り及び凝集を抑制して、当該スラリー組成物の分散安定性を向上させることができる。このため、電極活物質層における電極活物質及び粒子状バインダーの分布を均一化して、密着性を向上させることが可能となる。さらに、前記のように水溶性重合体の親水性を高めることができるので、集電体等の親水基を有する要素に対する水溶性重合体の親和性を向上させることができる。このため、この親和性の向上によっても、密着性を向上させることが可能となる。
一方、水溶性重合体における不飽和カルボン酸単量体単位の比率を前記範囲の上限値以下とすることにより、リチウムイオン二次電池において水溶性重合体のカルボキシル基と電解液との過度の接触を避けることができ、リチウムイオン二次電池の耐久性を向上させることができる。
水溶性重合体における不飽和カルボン酸単量体単位の比率は、水溶性重合体の重合に用いる全単量体に占める不飽和カルボン酸単量体の比率(仕込み比)により調整することができ、通常は、前記単量体単位の比率は、前記単量体の比率(仕込み比)と一致する。
架橋性単量体単位は、架橋性単量体を重合して得られる構造単位である。また、架橋性単量体は、加熱又はエネルギー線照射により、重合中又は重合後に架橋構造を形成しうる単量体である。架橋性単量体の例としては、通常は、熱架橋性を有する単量体を挙げることができる。より具体的には、熱架橋性の架橋性基及び1分子あたり1つのオレフィン性二重結合を有する単官能の架橋性単量体;1分子あたり2つ以上のオレフィン性二重結合を有する多官能の架橋性単量体が挙げられる。
また、架橋性単量体及び架橋性単量体単位は、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。
水溶性重合体における架橋性単量体単位の比率を前記範囲の下限値以上とすることにより、電解液による水溶性重合体の膨潤を抑制し、リチウムイオン二次電池用電極の膨らみを抑制できる。一般にSiを含む電極活物質は充放電に伴う膨張及び収縮が大きい傾向があるので、前記のリチウムイオン二次電池用電極の膨らみを抑制できる効果は、Siを含む電極活物質を用いた場合に特に顕著である。また、水溶性重合体における架橋性単量体単位の比率を前記範囲の下限値以上としたことにより、水溶性重合体の主鎖の剛性を高めることができる。したがって、架橋性単量体単位と、上述したように密着性を高める作用を奏しうる不飽和カルボン酸単量体単位とを所定の比率で組み合わせることにより、適度の剛性を有する水溶性重合体とし、かかる水溶性重合体によって電極活物質を強固に保持できる。これにより、電極活物質が電極から容易に脱離しないようにできるので、高温保存特性及び高温サイクル特性を向上させることができる。
一方、水溶性重合体における架橋性単量体単位の比率を前記範囲の上限値以下とすることにより、水溶性重合体の水に対する可溶性を高め、分散性を良好にすることができる。
水溶性重合体における架橋性単量体単位の比率は、通常、水溶性重合体の重合に用いる全単量体に占める架橋性単量体の比率(仕込み比)により調整することができ、通常は、前記単量体単位の比率は、前記単量体の比率(仕込み比)と一致する。
フッ素含有(メタ)アクリル酸エステル単量体単位は、フッ素含有(メタ)アクリル酸エステル単量体を重合して得られる構造単位である。フッ素含有(メタ)アクリル酸エステル単量体としては、例えば、下記の式(I)で表される単量体が挙げられる。
前記の式(I)において、R2は、フッ素原子を含有する炭化水素基を表す。炭化水素基の炭素数は、通常1以上であり、通常18以下である。また、R2が含有するフッ素原子の数は、1個でもよく、2個以上でもよい。
水溶性重合体におけるフッ素含有(メタ)アクリル酸エステル単量体単位の比率を前記範囲の下限値以上とすることにより、水溶性重合体に、電解液に対する反発力を与えることができ、膨潤度を適切な範囲内とすることができる。
一方、水溶性重合体におけるフッ素含有(メタ)アクリル酸エステル単量体単位の比率を前記範囲の上限値以下とすることにより、不飽和カルボン酸単量体単位による親水性の向上効果と組み合わさって、水溶性重合体の電解液に対する濡れ性を向上させることができる。これにより、イオン伝導度が高まるので、得られるリチウムイオン二次電池の低温出力特性を向上させることができる。
水溶性重合体におけるフッ素含有(メタ)アクリル酸エステル単量体単位の比率は、水溶性重合体の重合に用いた全単量体に占めるフッ素含有(メタ)アクリル酸エステル単量体の比率(仕込み比)により調整することができ、通常は、前記単量体単位の比率は、前記単量体の比率(仕込み比)と一致する。
任意の構造単位の例としては、フッ素含有(メタ)アクリル酸エステル単量体単位以外の(メタ)アクリル酸エステル単量体単位、アミド単量体単位、オレフィン類単量体単位、ハロゲン原子含有単量体単位、ビニルエステル類単量体単位、ビニルエーテル類単量体単位、ビニルケトン類単量体単位、及び複素環含有ビニル化合物単量体単位などが挙げられる。中でも、(メタ)アクリル酸エステル単量体単位が好ましい。
好適な反応性界面活性剤の別の例としては、エチレンオキシドに基づく重合単位及びブチレンオキシドに基づく重合単位を有し、さらに末端に、末端二重結合を有するアルケニル基及び-SO3NH4を有する化合物(例えば、商品名「ラテムルPD-104」、花王株式会社製)を挙げることができる。
反応性界面活性剤単量体は、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。
ここで、水溶性重合体の重量平均分子量は、ゲルパーミエーションクロマトグラフィー(GPC)によって、ジメチルホルムアミドの10体積%水溶液に0.85g/mlの硝酸ナトリウムを溶解させた溶液を展開溶媒としたポリスチレン換算の値として求めうる。
また、水系溶媒は1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。例えば、主溶媒として水を使用して、水溶性重合体の溶解が確保可能な範囲において上記記載の水以外の水系溶媒を混合して用いてもよい。
また、アミン類などの添加剤を重合助剤として用いてもよい。
本発明のリチウムイオン二次電池用電極は、粒子状バインダーを含んでいてもよい。粒子状バインダーは、通常は電極活物質層に含まれて、電極活物質及び集電体を結着させる作用を奏する。水溶性重合体に加えて粒子状バインダーを含むことにより、リチウムイオン二次電池用電極では、電極活物質を更に強固に保持できるので、リチウムイオン二次電池用電極からの電極活物質の脱離を更に抑制できる。また、粒子状バインダーは通常は電極活物質層に含まれる電極活物質以外の粒子をも結着し、電極活物質層の強度を維持する役割も果たしうる。特に、粒子状バインダーは、その形状が粒子形状であることにより、結着性が特に高く、リチウムイオン二次電池用電極の容量低下及び充放電の繰り返しによる劣化を顕著に抑えることができる。粒子状バインダーは、リチウムイオン二次電池用電極を製造するためのスラリー組成物中で粒子形状を保持した状態で存在できるものを用いうるが、電極活物質層においても粒子形状を保持した状態で存在できるものが好ましい。本発明において、「粒子状態を保持した状態」とは、完全に粒子形状を保持した状態である必要はなく、その粒子形状をある程度保持した状態であればよい。
前記単量体混合物における共役ジエンの割合は通常20重量%以上、好ましくは25重量%以上である。前記ジエン重合体の具体例としては、ポリブタジエンやポリイソプレンなどの共役ジエン単独重合体;カルボキシ変性されていてもよいスチレン・ブタジエン共重合体(SBR)などの芳香族ビニル・共役ジエン共重合体;アクリロニトリル・ブタジエン共重合体(NBR)などのシアン化ビニル・共役ジエン共重合体;水素化SBR、水素化NBR等が挙げられる。なお、共役ジエンは、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。ジエン重合体における共役ジエン単量体単位の割合は、好ましくは20重量%以上、より好ましくは30重量%以上であり、好ましくは60重量%以下、より好ましくは55重量%以下である。
一般式(III)で表される化合物の具体例としては、アクリル酸エチル、アクリル酸プロピル、アクリル酸イソプロピル、アクリル酸n-ブチル、アクリル酸イソブチル、アクリル酸t-ブチル、アクリル酸n-アミル、アクリル酸イソアミル、アクリル酸n-ヘキシル、アクリル酸2-エチルヘキシル、アクリル酸ヘキシル、アクリル酸ノニル、アクリル酸ラウリル、アクリル酸ステアリルなどのアクリレート;メタクリル酸エチル、メタクリル酸プロピル、メタクリル酸イソプロピル、メタクリル酸n-ブチル、メタクリル酸イソブチル、メタクリル酸t-ブチル、メタクリル酸n-アミル、メタクリル酸イソアミル、メタクリル酸n-ヘキシル、メタクリル酸2-エチルヘキシル、メタクリル酸オクチル、メタクリル酸イソデシル、メタクリル酸ラウリル、メタクリル酸トリデシル、メタクリル酸ステアリルなどのメタアクリレート等が挙げられる。これらの中でも、アクリレートが好ましく、アクリル酸n-ブチルおよびアクリル酸2-エチルヘキシルが、リチウムイオン二次電池用電極の強度を向上できる点で、特に好ましい。また、これらの単量体は、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。
本発明のリチウムイオン二次電池用電極は、上述した電極活物質、水溶性重合体及び粒子状バインダー以外にも、本発明の効果を著しく損なわない限り任意の成分を含んでいてもよい。例えば、本発明のリチウムイオン二次電池用電極は、電極用導電材、分散剤、補強材、レベリング剤、ナノ粒子及び添加剤を含んでいてもよい。通常、これらの任意の成分は電極活物質層に含まれる。また、任意の成分は、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。
電極活物質及び水溶性重合体、並びに必要に応じて含まれる成分は、上述したように、通常、電極活物質層に含まれる。電極活物質層は、通常、集電体の表面に設けられる。この際、電極活物質層は、集電体の片面に設けられていてもよく、両面に設けられていてもよい。
集電体は、電極活物質層との接着強度を高めるため、表面に予め粗面化処理して使用することが好ましい。粗面化方法としては、例えば、機械的研磨法、電解研磨法、化学研磨法などが挙げられる。機械的研磨法においては、通常、研磨剤粒子を固着した研磨布紙、砥石、エメリバフ、鋼線などを備えたワイヤーブラシ等が使用される。また、電極活物質層の接着強度及び導電性を高めるために、集電体の表面に中間層を形成してもよい。
このような低い水分量は、水溶性重合体中の構造単位の組成を適宜調整することにより達成しうる。特に、フッ素含有(メタ)アクリル酸エステル単量体単位を通常0.5重量%以上、好ましくは1重量%以上、また、通常20重量%以下、好ましくは10重量%以下の範囲にすることにより、水分量を低減することができる。
本発明のリチウムイオン二次電池用電極は、例えば、塗布法又は粉体成型法により製造しうる。
ここで、塗布法とは、リチウムイオン二次電池用電極を製造するためのスラリー組成物を用意し、そのスラリー組成物を集電体上に塗布し、乾燥させることにより、集電体の表面に電極活物質層を形成して、リチウムイオン電池用電極を得る製造方法である。
また、粉体成型法とは、リチウムイオン二次電池用電極を製造するためのスラリー組成物を用意し、そのスラリー組成物から電極活物質及び水溶性重合体を含む複合粒子を調製し、その複合粒子を集電体上に供給し、所望により更にロールプレスして成形することにより電極活物質層を形成して、リチウムイオン電池用電極を得る製造方法である。
これらのうち、電極活物質層の集電体に対する密着性に優れる点では塗布法が好ましい。また、リチウムイオン二次電池用電極の容量が高く内部抵抗が低く、さらにプロセスが簡単で製造コストに優れる点では粉体成型法が好ましい。
塗布法においては、まず、リチウムイオン二次電池用電極を製造するためのスラリー組成物を用意する。スラリー組成物は、電極活物質、水溶性重合体及び溶媒を含む流体状の組成物である。また、リチウムイオン二次電池用電極が例えば粒子状バインダー、電極用導電材、分散剤、補強材、レベリング剤、ナノ粒子及び添加剤等の任意の成分を含む場合には、スラリー組成物にも任意の成分を含ませる。スラリー組成物における電極活物質、水溶性重合体及び任意の成分の比率は、通常は、電極活物質層に含まれる各成分の比率と同様にする。
また、特に粒子状バインダー及び水溶性重合体を溶解する有機溶媒を水と組み合わせると、粒子バインダー及び水溶性重合体が電極活物質の表面に吸着することにより、電極活物質の分散が安定化するので、好ましい。
乾燥温度と乾燥時間は、集電体に塗布したスラリー組成物中の溶媒を完全に除去できる温度と時間が好ましい。具体的な範囲を挙げると、乾燥温度は通常100℃以上、好ましくは120℃以上であり、通常300℃以下、好ましくは250℃以下である。また、乾燥時間としては、通常10分以上、好ましくは20分以上であり、通常100時間以下、好ましくは20時間以下である。
粉体成型法においては、まず、リチウムイオン二次電池用電極を製造するためのスラリー組成物を用意しうる。スラリー組成物は、塗布法と同様にして用意してもよい。ただし、スラリー組成物の溶媒としては、水と、水よりも沸点の低い有機溶媒とを組み合わせて用いることが好ましい。これにより、噴霧乾燥時に、乾燥速度を速くすることができる。
スラリー組成物の噴霧に用いる装置としては、例えばアトマイザーが挙げられる。アトマイザーは、回転円盤方式と加圧方式との二種類の装置がある。
また、噴霧乾燥時の熱風の温度は、通常80℃以上、好ましくは100℃以上であり、通常250℃以下、好ましくは200℃以下である。
ロールによる成形速度は、通常0.1m/分より大きく、好ましくは35m/分以上、また、好ましくは70m/分以下である。
さらに、一対のロール間のプレス線圧は、通常0.2kN/cm以上、好ましくは0.5kN/cm以上であり、通常30kN/cm以下、好ましくは10kN/cm以下である。
本発明のリチウムイオン二次電池は、正極、負極、電解液及びセパレータを備える。また、本発明のリチウムイオン二次電池においては、正極及び負極の少なくとも一方が、本発明のリチウムイオン二次電池用電極である。
本発明のリチウムイオン二次電池は、本発明のリチウムイオン二次電池用電極を備えるので、高温環境における保存特性及びサイクル特性に優れる。また、本発明のリチウムイオン二次電池は、通常、充放電に伴う電極の膨らみを抑制でき、また、低温出力特性に優れる。
電解液としては、例えば、非水系の溶媒に支持電解質としてリチウム塩を溶解したものを使用してもよい。リチウム塩としては、例えば、LiPF6、LiAsF6、LiBF4、LiSbF6、LiAlCl4、LiClO4、CF3SO3Li、C4F9SO3Li、CF3COOLi、(CF3CO)2NLi、(CF3SO2)2NLi、(C2F5SO2)NLiなどのリチウム塩が挙げられる。特に溶媒に溶けやすく高い解離度を示すLiPF6、LiClO4、CF3SO3Liは好適に用いられる。これらは1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。
セパレーターとしては、通常、気孔部を有する多孔性基材を用いる。セパレーターの例を挙げると、(a)気孔部を有する多孔性セパレーター、(b)片面または両面に高分子コート層が形成された多孔性セパレーター、(c)無機セラミック粉末を含む多孔質の樹脂コート層が形成された多孔性セパレーター、などが挙げられる。これらの例としては、ポリプロピレン系、ポリエチレン系、ポリオレフィン系、またはアラミド系多孔性セパレーター、ポリビニリデンフルオリド、ポリエチレンオキシド、ポリアクリロニトリルまたはポリビニリデンフルオリドヘキサフルオロプロピレン共重合体などの固体高分子電解質用またはゲル状高分子電解質用の高分子フィルム;ゲル化高分子コート層がコートされたセパレーター;無機フィラーと無機フィラー用分散剤とからなる多孔膜層がコートされたセパレーター;などが挙げられる。
本発明のリチウムイオン二次電池の製造方法は、特に限定されない。例えば、上述した正極と負極とをセパレーターを介して重ね合わせ、これを電池形状に応じて巻く、折るなどして電池容器に入れ、電池容器に電解液を注入して封口してもよい。さらに、必要に応じてエキスパンドメタル;ヒューズ、PTC素子などの過電流防止素子;リード板などを入れ、電池内部の圧力上昇、過充放電の防止をしてもよい。電池の形状は、例えば、ラミネートセル型、コイン型、ボタン型、シート型、円筒型、角形、扁平型などいずれであってもよい。
以下の説明において、量を表す「%」及び「部」は、別に断らない限り重量基準である。また、以下に説明する操作は、別に断らない限り、常温及び常圧の条件において行った。
1.密着強度
実施例および比較例で製造した電極を、長さ100mm、幅10mmの長方形に切り出して試験片とした。この試験片を、電極活物質層の表面を下にして、電極活物質層の表面にセロハンテープを貼り付けた。この際、セロハンテープとしてはJIS Z1522に規定されるものを用いた。また、セロハンテープは試験台に固定しておいた。その後、集電体の一端を鉛直上方に引張り速度50mm/分で引っ張って剥がしたときの応力を測定した。この測定を3回行い、その平均値を求めて、当該平均値をピール強度とした。ピール強度が大きいほど、電極活物質層の集電体への結着力が大きいこと、すなわち、密着強度が大きいことを示す。
実施例および比較例で製造したラミネート型セルのリチウムイオン二次電池を24時間静置した後に、25℃環境下、充電レート0.1Cにて、4.2Vまで充電し、放電レート0.1Cにて、3.0Vまで放電することにより、初期容量C0を測定した。さらに、25℃環境下、充電レート0.1Cにて4.2Vまで充電し、その後、60℃で7日間保存した後、25℃環境下、放電レート0.1Cにて、3.0Vまで放電することにより、高温保存後の容量C1を測定した。高温保存特性は、ΔCS=C1/C0×100(%)で示す容量維持率ΔCSにて評価した。この容量維持率ΔCSの値が高いほど、高温保存特性に優れることを示す。
実施例および比較例で製造したラミネート型セルのリチウムイオン二次電池を24時間静置した後に、25℃環境下、充電レート0.1Cにて、4.2Vまで充電し、放電レート0.1Cにて、3.0Vまで放電することにより、初期容量C0を測定した。さらに、60℃の環境下で、充電レート0.1Cにて、4.2Vまで充電し、放電レート0.1Cにて、3.0Vまで放電する充放電サイクルを100回(100サイクル)繰り返し、100サイクル後の容量C2を測定した。高温サイクル特性は、ΔCC=C2/C0×100(%)で示す容量維持率ΔCCにて評価した。この容量維持率ΔCCの値が高いほど、高温サイクル特性に優れることを示す。
前記の「2.高温保存特性」の評価の後でリチウムイオン二次電池のセルを解体し、電極の極板の厚みd1を測定した。リチウムイオン二次電池のセルの作製前における電極の極板の厚みをd0として、電極の極板膨らみ率((d1-d0)/d0)×100(%)を算出した。この値が低いほど、極板膨らみ特性に優れることを示す。
前記の「3.高温サイクル特性」の評価の後でリチウムイオン二次電池のセルを解体し、電極を取り出し、これを、60℃、24時間、0.1MPa以下の減圧下で乾燥させた。乾燥させた電極について「1.密着強度」と同様にして密着強度を測定した。但し、試験片の寸法は長さ40mm、幅10mmとした。
実施例および比較例で製造したラミネート型セルのリチウムイオン二次電池を24時間静置した後に、25℃の環境下で、0.1C、5時間の充電操作を行い、このときの電圧V0を測定した。その後、-25℃の環境下で、0.1Cの放電の操作を行い、放電開始10秒後の電圧V10を測定した。低温出力特性は、ΔV=V0-V10で示す電圧変化ΔVにて評価した。この電圧変化ΔVの値が小さいほど、低温出力特性に優れることを示す。
(1-1.水溶性重合体の製造)
攪拌機付き5MPa耐圧容器に、芳香族ビニル単量体としてスチレンスルホン酸ナトリウム10部、不飽和カルボン酸単量体としてメタクリル酸35部、架橋性単量体としてエチレンジメタクリレート0.8部、フッ素含有(メタ)アクリル酸エステル単量体として2,2,2-トリフルオロエチルメタクリレート10部、任意の単量体としてエチルアクリレート44.2部、溶媒としてイオン交換水150部、及び重合開始剤として過硫酸カリウム0.5部を入れ、十分に攪拌した後、60℃に加温して重合を開始した。
重合転化率が96%になった時点で冷却し反応を停止して、水溶性重合体を含む混合物を得た。上記水溶性重合体を含む混合物に、10%アンモニア水を添加して、pH8に調整し、所望の水溶性重合体を含む水溶液を得た。
攪拌機付き5MPa耐圧容器に、1,3-ブタジエン33部と、メタクリル酸1.5部と、スチレン65.5部と、乳化剤としてドデシルベンゼンスルホン酸ナトリウム4部と、イオン交換水150部と、重合開始剤として過硫酸カリウム0.5部とを入れ、十分に攪拌した後、50℃に加温して重合を開始した。
重合転化率が96%になった時点で冷却し反応を停止して、粒子状バインダー(スチレンブタジエンゴム)を含む混合物を得た。上記粒子状バインダーを含む混合物に、5%水酸化ナトリウム水溶液を添加して、pH8に調整後、加熱減圧蒸留によって未反応単量体の除去を行った後、30℃以下まで冷却し、所望の粒子状バインダーを含む水分散液を得た。
ディスパー付きのプラネタリーミキサーに、負極活物質として比表面積4m2/gの人造黒鉛(体積平均粒子径:24.5μm)90部及びSiOx(信越化学社製;体積平均粒子径5μm)10部と、分散剤としてカルボキシメチルセルロースの1%水溶液(第一工業製薬株式会社製「BSH-12」)を固形分相当で1部とを加え、イオン交換水で固形分濃度55%に調整した後、25℃で60分混合した。次に、イオン交換水で固形分濃度52%に調整した後、さらに25℃で15分混合し混合液を得た。
上記(1-3.負極スラリー組成物の製造)で得られた負極スラリー組成物を、コンマコーターで、集電体である厚さ20μmの銅箔の上に、乾燥後の膜厚が150μm程度になるように塗布し、乾燥させた。この乾燥は、銅箔を0.5m/分の速度で60℃のオーブン内を2分間かけて搬送することにより行った。その後、120℃にて2分間加熱処理して負極原反を得た。この負極原反をロールプレスで圧延して、負極活物質層の厚みが80μmの負極を得た。
得られた負極について、密着強度を測定した。
正極用のバインダーとして、ガラス転移温度Tgが-40℃で、個数平均粒子径が0.20μmのアクリレート重合体の40%水分散体を用意した。このアクリレート重合体は、アクリル酸2-エチルヘキシル78重量%、アクリロニトリル20重量%、及びメタクリル酸2重量%を含む単量体混合物を乳化重合して得られた共重合体である。
単層のポリプロピレン製セパレーター(幅65mm、長さ500mm、厚さ25μm、乾式法により製造、気孔率55%)を、5cm×5cmの正方形に切り抜いた。
電池の外装として、アルミニウム包材外装を用意した。上記(1-5.正極の製造)で得られた正極を、4cm×4cmの正方形に切り出し、集電体側の表面がアルミニウム包材外装に接するように配置した。正極の正極活物質層の面上に、上記(1-6.セパレーターの用意)で得られた正方形のセパレーターを配置した。さらに、上記(1-4.負極の製造)で得られた負極を、4.2cm×4.2cmの正方形に切り出し、これをセパレーター上に、負極活物質層側の表面がセパレーターに向かい合うよう配置した。これに、電解液として濃度1.0MのLiPF6溶液(溶媒はEC/DEC=1/2(体積比)の混合溶媒)を充填した。さらに、アルミニウム包材の開口を密封するために、150℃のヒートシールをしてアルミニウム外装を閉口し、リチウムイオン二次電池を製造した。
前記の(1-2.バインダー組成物の製造)において、粒子状バインダーを含む水分散液として、実施例1の正極用のバインダーとして用いたものと同様のアクリレート重合体の40%水分散体を用いた。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-2.バインダー組成物の製造)において、粒子状バインダーを含む水分散液として、ガラス転移温度が-36℃、数平均粒子径が0.15μmのジエン重合体を含む水分散液を用いた。このジエン重合体は、アクリロニトリル18.5重量%、1,3-ブタジエン78.5重量%及びイタコン酸3重量%を含む単量体混合物を乳化重合して得られる共重合体である。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、芳香族ビニル単量体であるスチレンスルホン酸ナトリウムの量を2部に変更し、任意の単量体であるエチルアクリレートの量を52.2部に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、芳香族ビニル単量体であるスチレンスルホン酸ナトリウムの量を27部に変更し、任意の単量体であるエチルアクリレートの量を27.2部に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、芳香族ビニル単量体として、スチレンスルホン酸ナトリウムの代わりにスチレンを用いた。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、不飽和カルボン酸単量体であるメタクリル酸の量を22部に変更し、任意の単量体であるエチルアクリレートの量を57.2部に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、不飽和カルボン酸単量体であるメタクリル酸の量を58部に変更し、任意の単量体であるエチルアクリレートの量を21.2部に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、不飽和カルボン酸単量体として、メタクリル酸の代わりにアクリル酸を用いた。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、架橋性単量体として、エチレンジメタクリレートの代わりにアリルグリシジルエーテルを用いた。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、架橋性単量体として、エチレンジメタクリレートの代わりにグリシジルメタクリレートを用いた。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、架橋性単量体であるエチレンジメタクリレートの量を0.1部に変更し、任意の単量体であるエチルアクリレートの量を44.9部に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、架橋性単量体であるエチレンジメタクリレートの量を1.8部に変更し、任意の単量体であるエチルアクリレートの量を43.2部に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、フッ素含有(メタ)アクリル酸エステル単量体である2,2,2-トリフルオロエチルメタクリレートを使用せず、任意の単量体であるエチルアクリレートの量を54.2部に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、フッ素含有(メタ)アクリル酸エステル単量体である2,2,2-トリフルオロエチルメタクリレートの量を2部に変更し、任意の単量体であるエチルアクリレートの量を52.2部に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、フッ素含有(メタ)アクリル酸エステル単量体である2,2,2-トリフルオロエチルメタクリレートの量を28部に変更し、任意の単量体であるエチルアクリレートの量を26.2部に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-2.バインダー組成物の製造)において、水溶性重合体を含む水溶液と粒子状バインダーを含む水分散液とを混合する際、混合比を、固形分相当で水溶性重合体:粒子状バインダー=0.2:2(重量比)に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-2.バインダー組成物の製造)において、水溶性重合体を含む水溶液と粒子状バインダーを含む水分散液とを混合する際、混合比を、固形分相当で水溶性重合体:粒子状バインダー=28:2(重量比)に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-3.負極スラリー組成物の製造)において、負極活物質として比表面積4m2/gの人造黒鉛(平均粒子径:24.5μm)100部を用い、SiOx(平均粒子径:5μm)を用いなかった。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-3.負極スラリー組成物の製造)において、負極活物質である人造黒鉛の量を50部に変更し、SiOxの量を50部に変更した。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
(21-1.バインダー組成物の製造)
粒子状バインダーを含む水分散液として、実施例1の正極用のバインダーとして用いたのと同様のアクリレート重合体の40%水分散体を用いた。以上の事項以外は、実施例1の(1-2.バインダー組成物の製造)と同様にして、バインダー組成物を得た。
負極活物質の代わりに正極活物質として体積平均粒子径10μmのコバルト酸リチウム100部を用いた。また、前記(1-2.バインダー組成物の製造)で得られたバインダー組成物の代わりに前記(21-1.バインダー組成物の製造)で得られたバインダー組成物を用いた。以上の事項以外は、実施例1の(1-3.負極スラリー組成物の製造)と同様にして、正極スラリー組成物を得た。
前記(21-2.正極スラリー組成物の製造)で得られた正極スラリー組成物を、コンマコーターで、集電体である厚さ20μmの銅箔の上に、乾燥後の膜厚が120μm程度になるように塗布し、乾燥させた。この乾燥は、銅箔を0.5m/分の速度で60℃のオーブン内を2分間かけて搬送することにより行った。その後、120℃にて2分間加熱処理して正極原反を得た。この正極原反をロールプレスで圧延して、正極活物質層の厚みが75μmの正極を得た。
得られた正極について、密着強度を測定した。
負極用のバインダーとして、実施例1の正極用のバインダーとして用いたのと同様のアクリレート重合体の40%水分散体を用意した。
電池の外装として、アルミニウム包材外装を用意した。上記(21-4)で得られた負極を、4cm×4cmの正方形に切り出し、集電体側の表面がアルミニウム包材外装に接するように配置した。負極の負極活物質層の面上に、実施例1と同様の正方形のセパレーターを配置した。さらに、上記(21-3)で得られた正極を、4.2cm×4.2cmの正方形に切り出し、これをセパレーター上に、正極活物質層側の表面がセパレーターに向かい合うよう配置した。これに、電解液として濃度1.0MのLiPF6溶液(溶媒はEC/DEC=1/2(体積比)の混合溶媒)を充填した。さらに、アルミニウム包材の開口を密封するために、150℃のヒートシールをしてアルミニウム外装を閉口し、リチウムイオン二次電池を製造した。
前記(21-2.正極スラリー組成物の製造)において、正極活物質として体積平均粒子径15μmのマンガン酸リチウムを用いた。以上の事項以外は実施例21と同様にして、リチウムイオン二次電池を製造し、評価した。
(23-1.負極の製造)
実施例1の(1-3.負極スラリー組成物の製造)で得られた負極スラリー組成物の噴霧乾燥造粒を行い、体積平均粒子径47μm、球形度91%の球状の複合粒子を得た。前記の噴霧乾燥造粒は、スプレー乾燥機(OC-16;大川原化工機社製)を使用し、回転円盤方式のアトマイザー(直径65mm)の回転数25,000rpm、熱風温度150℃、粒子回収出口の温度が90℃の条件で行った。
得られた負極について、密着強度を測定した。
負極として、実施例1の(1-4.負極の製造)で得られたものに代えて上記(23-1.負極の製造)で得られたものを用いた他は、実施例1の(1-5.正極の製造)~(1-7.リチウムイオン二次電池)と同様にして、リチウムイオン二次電池を作製し、評価した。
(24-1.正極の製造)
実施例21の(21-2.正極スラリー組成物の製造)で得られた正極スラリー組成物の噴霧乾燥造粒を行い、体積平均粒子径53μm、球形度94%の球状の複合粒子を得た。前記の噴霧乾燥造粒は、スプレー乾燥機(OC-16;大川原化工機社製)を使用し、回転円盤方式のアトマイザー(直径65mm)の回転数25,000rpm、熱風温度150℃、粒子回収出口の温度が90℃の条件で行った。
得られた正極について、密着強度を測定した。
正極として、実施例21の(21-3.正極の製造)で得られたものに代えて上記(24-1.正極の製造)で得られたものを用いた他は、実施例21の(21-4.負極の製造)~(21-5.リチウムイオン二次電池)と同様にして、リチウムイオン二次電池を作製し、評価した。
前記の(1-2.バインダー組成物の製造)において、水溶性重合体を含む水溶液を混合せず、粒子状バインダーを含む水分散液をそのままバインダー組成物とした。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-2.バインダー組成物の製造)において、上記(1-1.水溶性重合体の製造)で得られた水溶性重合体の代わりに、ポリアクリル酸ナトリウム(重量平均分子量250000)を用いた。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、芳香族ビニル単量体としてスチレンスルホン酸ナトリウムの代わりにスチレン50部を用い、メタクリル酸の代わりに無水マレイン酸50部を用い、エチレンジメタクリレート、2,2,2-トリフルオロエチルメタクリレート及びエチルアクリレートを用いなかった。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、芳香族ビニル単量体としてスチレンスルホン酸ナトリウムの代わりにスチレン50部を用い、不飽和カルボン酸単量体であるメタクリル酸の量を10部に変更し、任意の単量体としてエチルアクリレートの代わりにアクリロニトリル40部を用い、エチレンジメタクリレート及び2,2,2-トリフルオロエチルメタクリレートを用いなかった。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、芳香族ビニル単量体としてスチレンスルホン酸ナトリウムの代わりにスチレン10部を用い、不飽和カルボン酸単量体であるメタクリル酸の量を40部に変更し、任意の単量体としてエチルアクリレートの代わりにアクリロニトリル50部を用い、エチレンジメタクリレート及び2,2,2-トリフルオロエチルメタクリレートを用いなかった。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、芳香族ビニル単量体としてスチレンスルホン酸ナトリウムの代わりにスチレン10部を用い、不飽和カルボン酸単量体であるメタクリル酸の量を40部に変更し、架橋性単量体としてエチレンジメタクリレートの代わりにグリシジルメタクリレート10部を用い、任意の単量体としてエチルアクリレートの代わりにアクリロニトリル40部を用い、2,2,2-トリフルオロエチルメタクリレートを用いなかった。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(1-1.水溶性重合体の製造)において、芳香族ビニル単量体としてスチレンスルホン酸ナトリウムの代わりにスチレン10部を用い、不飽和カルボン酸単量体であるメタクリル酸の量を40部に変更し、任意の単量体としてエチルアクリレートの代わりにアクリロニトリル50部を用い、エチレンジメタクリレート及び2,2,2-トリフルオロエチルメタクリレートを用いなかった。また、前記の(1-3.負極スラリー組成物の製造)において、負極活物質として比表面積4m2/gの人造黒鉛(平均粒子径:24.5μm)100部を用い、SiOx(平均粒子径:5μm)を用いなかった。以上の事項以外は、実施例1と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の(21-1.バインダー組成物の製造)において、水溶性重合体を含む水溶液として上記(1-1.水溶性重合体の製造)で得られたものの代わりに比較例7で製造したものを用いた。以上の事項以外は、実施例21と同様にして、リチウムイオン二次電池を製造し、評価した。
前記の実施例及び比較例の結果を、以下の表1~表8に示す。下記の表において用いた略称の対応は、以下の通りである。
SBR:スチレンブタジエンゴム
ACR:アクリルゴム
NBR:アクリロニトリルブタジエンゴム
NaSS:スチレンスルホン酸ナトリウム
ST:スチレン
MAA:メタクリル酸
AA:アクリル酸
EDMA:エチレンジメタクリレート
AGE:アリルグリシジルエーテル
GMA:グリシジルメタクリレート
3FM:2,2,2-トリフルオロエチルメタクリレート
EA:エチルアクリレート
AN:アクリロニトリル
LCO:コバルト酸リチウム
LMO:マンガン酸リチウム
実施例と比較例とを比べると、比較例よりも実施例の方が、ピール強度が高く、また高温保存特性及び高温サイクル特性に優れることが分かる。ここで、負極に係る実施例1~20及び23と、正極に係る実施例21、22及び24とのいずれにおいても良好な結果が得られていることから、前記の効果は、正極及び負極のいずれにおいても奏しうることが分かる。さらに、塗布法に係る実施例1~22と、粉体成型法に係る実施例23及び24のいずれにおいても良好な結果が得られていることから、前記の効果は、塗布法及び粉体成型法のいずれにおいても奏しうることがわかる。
Claims (9)
- 電極活物質及び水溶性重合体を含むリチウムイオン二次電池用電極であって、
前記水溶性重合体が、芳香族ビニル単量体単位1重量%~30重量%、不飽和カルボン酸単量体単位20重量%~60重量%及び架橋性単量体単位0.1重量%~5重量%を含む共重合体である、リチウムイオン二次電池用電極。 - 前記芳香族ビニル単量体単位が、スチレン単量体単位又はスチレンスルホン酸ナトリウム単量体単位である、請求項1記載のリチウムイオン二次電池用電極。
- 前記不飽和カルボン酸単量体単位が、不飽和モノカルボン酸単量体単位である、請求項1又は2記載のリチウムイオン二次電池用電極。
- 前記水溶性重合体が、さらにフッ素含有(メタ)アクリル酸エステル単量体単位を含み、
前記フッ素含有(メタ)アクリル酸エステル単量体単位の比率が、1重量%~30重量%である、請求項1~3のいずれか一項に記載のリチウムイオン二次電池用電極。 - 前記水溶性重合体の含有割合が、電極活物質100重量部に対して、0.1重量部~30重量部である、請求項1~4のいずれか一項に記載のリチウムイオン二次電池用電極。
- 前記リチウムイオン二次電池用電極が、さらに粒子状バインダーを含む、請求項1~5のいずれか一項に記載のリチウムイオン二次電池用電極。
- 正極、負極、電解液及びセパレータを備えるリチウムイオン二次電池であって、
正極及び負極の少なくとも一方が、請求項1~6のいずれか一項に記載のリチウムイオン二次電池用電極である、リチウムイオン二次電池。 - 電極活物質及び水溶性重合体を含む、リチウムイオン二次電池用電極を製造するためのスラリー組成物であって、
前記水溶性重合体が、芳香族ビニル単量体単位1重量%~30重量%、不飽和カルボン酸単量体単位20重量%~60重量%及び架橋性単量体単位0.1重量%~5重量%を含む共重合体である、スラリー組成物。 - 請求項8記載のスラリー組成物を、集電体上に塗布し、乾燥することを含む、リチウムイオン二次電池用電極の製造方法。
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CN104011919B (zh) | 2017-09-01 |
US20140342226A1 (en) | 2014-11-20 |
JP6070570B2 (ja) | 2017-02-01 |
US9461308B2 (en) | 2016-10-04 |
CN104011919A (zh) | 2014-08-27 |
KR20140106614A (ko) | 2014-09-03 |
KR101991924B1 (ko) | 2019-06-21 |
JPWO2013080938A1 (ja) | 2015-04-27 |
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