Classifications

• • 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
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
  • C08F214/18—Monomers containing fluorine
  • C08F214/22—Vinylidene fluoride
  • C08F214/225—Vinylidene fluoride with non-fluorinated comonomers
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D127/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers
  • C09D127/02—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment
  • C09D127/12—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C09D127/16—Homopolymers or copolymers of vinylidene fluoride
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/24—Electrically-conducting paints
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/60—Additives non-macromolecular
  • C09D7/61—Additives non-macromolecular inorganic
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
• • 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
  • C08F2800/00—Copolymer characterised by the proportions of the comonomers expressed
  • C08F2800/20—Copolymer characterised by the proportions of the comonomers expressed as weight or mass percentages
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/20—Oxides; Hydroxides
  • C08K3/22—Oxides; Hydroxides of metals
  • C08K2003/2293—Oxides; Hydroxides of metals of nickel
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K2201/00—Specific properties of additives
  • C08K2201/001—Conductive additives
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/02—Elements
  • C08K3/04—Carbon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to a binder for a positive electrode of a lithium ion secondary battery, an electrode mixture using the binder, an electrode, and a lithium ion secondary battery.
• PVDF polyvinylidene fluoride
• Patent Document 1 discloses a vinylidene fluoride polymer that has superior adhesiveness to metal foil than conventional vinylidene fluoride polymers.
• the present invention aims to provide a binder that is unlikely to cause gelation of the electrode mixture even when mixed with a positive electrode active material, and has sufficient adhesive properties even in a small amount, and an electrode mixture, an electrode, and a battery containing the binder. shall be.
• the present invention provides a binder for a positive electrode for a lithium ion secondary battery containing a vinylidene fluoride polymer, wherein the vinylidene fluoride polymer contains a constitutional unit derived from vinylidene fluoride and a carboxy group.
• a binder containing two or more types of structural units having the above-mentioned structure, and having a slurry viscosity ratio of 100% or less as determined by the following method.
• Viscosity ratio (%) (slurry viscosity after storage) / (slurry viscosity immediately after preparation) x 100
• the present invention also provides an electrode mixture containing the above binder and a positive electrode active material.
• the present invention provides an electrode in which an electrode mixture layer made of the above electrode mixture is provided on a current collector. Furthermore, the present invention provides a lithium ion secondary battery including the above electrode.
• the binder of the present invention hardly causes gelation even when mixed with a positive electrode active material containing nickel, and has sufficient adhesiveness even when used in a small amount. Therefore, it is possible to provide an electrode mixture that can be stably used over a long period of time, and also to provide high-capacity lithium ion secondary batteries and electrodes used therein.
• Binder As mentioned above, various vinylidene fluoride polymers have been used as binders for positive electrodes for lithium ion secondary batteries, but it has been desired to further improve their adhesive properties. Another problem is that when a vinylidene fluoride polymer is mixed with a positive electrode active material, especially a positive electrode active material with a high nickel ratio, gelation tends to occur.
• the positive electrode active material contains a base, and the positive electrode active material with a high nickel ratio contains a particularly large amount of base. Therefore, when vinylidene fluoride comes into contact with the positive electrode active material, the base accelerates the deterioration of the binder. Then, the deteriorated binder forms a crosslinked structure in the slurry-like electrode mixture (hereinafter also referred to as electrode mixture slurry), thereby causing the electrode mixture slurry to gel.
• electrode mixture slurry slurry-like electrode mixture
• the binder of the present invention contains a vinylidene fluoride-based polymer containing a constitutional unit derived from vinylidene fluoride and two or more types of constitutional units having a carboxy group. Further, the viscosity ratio of the slurry containing the vinylidene fluoride polymer is 100% or less, as measured by a specific method described below.
• the monomer copolymerizable with vinylidene fluoride has different copolymerizability with vinylidene fluoride depending on its structure.
• vinylidene fluoride polymers that are copolymerized with two or more different monomers have complex structural units that are different from polymers that use only one type of monomer, polymers that use only one type of monomer, and polymers that blend two types of polymers. It has an array. Since this complex arrangement of structural units suppresses deterioration of the binder, it is thought that even if the vinylidene fluoride polymer and the positive electrode active material are mixed, the electrode mixture is difficult to gel. Furthermore, the vinylidene fluoride polymer contains a carboxy group derived from a structural unit having a carboxy group. The carboxy group can be bonded to a polar group present on the surface of the active material or current collector.
• the binder containing the vinylidene fluoride polymer has high adhesive strength to the active material and the current collector even in a small amount.
• the binder is very useful as a material for the electrode mixture layer of a lithium ion secondary battery.
• the vinylidene fluoride polymer and other components contained in the binder will be explained below.
• the binder may contain only one kind of the following vinylidene fluoride polymer, or may contain two or more kinds.
• the vinylidene fluoride polymer contains a structural unit derived from vinylidene fluoride and two or more of the following structural units having a carboxyl group.
• the vinylidene fluoride polymer may contain only two types of structural units having carboxyl groups described below, but it is preferable to contain three or more types from the viewpoint of suppressing gelation.
• the structural unit having a carboxy group may be, for example, a structural unit represented by formula (1).
• R 1 to R 3 each independently represent a hydrogen atom, a fluorine atom, a chlorine atom, or an alkyl group having 1 to 4 carbon atoms and which may have a substituent.
• the alkyl group may be linear or branched. Specific examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, and the like. Furthermore, examples of substituents on the alkyl group include halogen atoms and the like.
• R 1 to R 3 are more preferably a hydrogen atom or a methyl group, and particularly preferably a hydrogen atom.
• X in the above general formula (1) represents an alkylene group having 1 or more and 4 or less carbon atoms that may have a substituent.
• the alkylene group having 1 to 4 carbon atoms may be linear or branched.
• Specific examples of alkylene groups include methylene, ethylene, propylene, and butylene groups.
• substituents include halogen atoms and the like. From the viewpoint that the adhesion effect of the carboxy group is less likely to be inhibited by steric hindrance, it is preferable that the alkyl chain does not contain a substituent.
• any one or more of the structural units having two or more carboxy groups constituting the vinylidene fluoride polymer is a structural unit represented by the general formula (1)
• X of all the structural units represented by general formula (1) is a methylene group or Particularly preferred is ethylene group.
• n in the above general formula (1) is an integer of 0 or more and 5 or less, and 0 or 1 is more preferable.
• n in the structural unit represented by one type of general formula (1) is 0 or 1 from the viewpoint of suppressing gelation of the electrode mixture (from the viewpoint of satisfying the viscosity ratio of the slurry described below).
• n in at least one structural unit represented by general formula (1) is 1.
• the molecular weight of the structural unit having a carboxy group is preferably 70 or more and 600 or less, more preferably 100 or more and 400 or less, and even more preferably 100 or more and 250 or less. When the molecular weight is within this range, high adhesive strength can be maintained and gelation can be suppressed.
• the structural units having a carboxy group include, for example, methacrylic acid, acrylic acid, carboxymethyl methacrylate, carboxymethyl acrylate, carboxyethyl methacrylate, carboxyethyl acrylate, carboxypropyl methacrylate, carboxypropyl acrylate, carboxybutyl methacrylate, carboxybutyl acrylate, 2- ((2-(acryloyloxy)ethanoyl)oxy)ethanoic acid, 2-(((2-(acryloyloxy)ethanoyl)oxy)ethanoyl)oxy)ethanoic acid, 3-((3-(acryloyloxy)propanoyl) It can be a structural unit derived from oxy)propanoic acid, 3-((((3-(acryloyloxy)propanoyl)oxy)propanoyl)oxy)propanoic acid, and the like.
• structural units derived from carboxymethyl methacrylate, carboxymethyl acrylate, carboxyethyl methacrylate, carboxyethyl acrylate, carboxypropyl methacrylate, carboxypropyl acrylate, carboxybutyl methacrylate, carboxybutyl acrylate, etc. can be preferably used.
• the proportion of the above-mentioned carboxyl group-containing structural units in the vinylidene fluoride polymer is not particularly limited.
• the total amount of the structural units having a carboxyl group is preferably 0.1% by mass or more and 10% by mass or less, and 0.5% by mass or more and 5% by mass or less, based on the total amount of the structural units constituting the vinylidene fluoride polymer. It is more preferably at most 0.5% by mass and at most 2% by mass.
• the total proportion of structural units having a carboxyl group in the vinylidene fluoride polymer is 10% by mass or less, the crystallinity of the vinylidene fluoride polymer becomes high, and the binder (vinylidene fluoride polymer) The adhesive strength between the active material and the current collector tends to increase.
• the ratio of the total amount of the structural units having a carboxyl group is 0.1% by mass or more, a complex structural unit arrangement is sufficiently formed and deterioration of the binder is suppressed, so that the binder and the positive electrode active material are When mixed, gelation is unlikely to occur, and the viscosity ratio when made into a slurry, which will be described later, is likely to fall within a desired range.
• the amount of each structural unit having a carboxyl group is preferably 10% by mass or more, more preferably 20% by mass or more, based on the total amount of structural units having a carboxyl group.
• the proportion of individual structural units having carboxyl groups is 10% by mass or more, gelation is likely to be suppressed when mixed with a positive electrode active material containing nickel, as described above.
• the total amount of structural units having a carboxyl group and the amount of individual structural units can be determined by 19 F-NMR analysis, 1 H-NMR, or the like.
• the amount of vinylidene fluoride-derived structural units relative to all structural units in the vinylidene fluoride polymer is preferably 90% by mass or more and 99.9% by mass or less, and 95% by mass or more and 99.5% by mass or less. More preferably, it is 98% by mass or more and 99.5% by mass or less.
• the amount of constitutional units derived from vinylidene fluoride is 90% by mass or more, physical properties unique to vinylidene fluoride can be easily obtained.
• the amount of the vinylidene fluoride-derived structural units is 99.9% by mass or less, the total amount of the above-mentioned carboxyl group-containing structural units is relatively sufficient, and the binder (vinylidene fluoride polymer) and the active Increases adhesive strength with substances and current collectors.
• the amount of vinylidene fluoride-derived constitutional units in the vinylidene fluoride polymer can be determined, for example, by 19 F-NMR analysis.
• the vinylidene fluoride polymer may include structural units derived from vinylidene fluoride and structural units other than those having a carboxyl group (hereinafter referred to as ⁇ other compound-derived structural units'') to the extent that the objects and effects of the present invention are not impaired. (also referred to as "structural unit").
• the vinylidene fluoride polymer may contain only one type of structural unit derived from other compounds, or may contain two or more types of structural units. However, the total amount of vinylidene fluoride-derived structural units and carboxy group-containing structural units with respect to all structural units of the vinylidene fluoride polymer is preferably 90% by mass or more, more preferably 95% by mass or more.
• Examples of other compounds include fluorine-based monomers copolymerizable with vinylidene fluoride, hydrocarbon monomers such as ethylene and propylene, and monomers copolymerizable with the above general formula (1).
• fluorine-based monomers that can be copolymerized with vinylidene fluoride include perfluorinated vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, fluoroalkyl vinyl ether, and perfluoromethyl vinyl ether.
• Examples include alkyl vinyl ethers.
• Examples of the monomer copolymerizable with the general formula (1) include alkyl (meth)acrylate compounds represented by methyl (meth)acrylate.
• the vinylidene fluoride-based polymer may be one obtained by block polymerizing vinylidene fluoride and two or more precursors of the structural unit having a carboxy group, but it may be one obtained by random polymerization. More preferred.
• the vinylidene fluoride-based polymer is prepared by random polymerization, the uniformity of the polymer chain is improved, and the adhesion exhibited by the above-mentioned structural unit having a carboxy group is improved.
• the melting point of the vinylidene fluoride polymer is preferably 160°C or higher, more preferably 165°C or higher.
• the melting point of the vinylidene fluoride polymer can be determined by calorimetry using a differential scanning calorimeter (DSC). Specifically, the vinylidene fluoride polymer was heated from 30°C to 230°C at a rate of 10°C/min (first temperature rise), and then cooled from 230°C to 30°C at a rate of 10°C/min (1st temperature rise).
• the temperature is further increased from 30° C. to 230° C. at a rate of 10° C./min (second temperature raising). Then, the melting peak is identified by DSC.
• the maximum melting peak temperature observed during the second temperature increase is defined as the melting point of the vinylidene fluoride polymer.
• the inherent viscosity of the vinylidene fluoride polymer is preferably 0.5 dL/g or more and 5.0 dL/g or less, more preferably 1.0 dL/g or more and 4.0 dL/g or less, and 1.0 dL/g or more. Most preferably 3.5 dL/g or less.
• the inherent viscosity is 0.5 dL/g or more, the adhesive strength between the binder (vinylidene fluoride polymer) and the active material or current collector increases.
• the inherent viscosity is 5.0 or less, when an electrode slurry is produced, the slurry viscosity does not become too high and workability is excellent.
• the inherent viscosity ( ⁇ i ) is expressed as a logarithmic viscosity.
• 80 mg of vinylidene fluoride polymer is dissolved in 20 mL of N,N-dimethylformamide, and the viscosity is measured using an Ubbelohde viscometer in a constant temperature bath at 30°C. Then, from the obtained value, it is calculated based on the following formula.
• ⁇ i (1/C) ⁇ ln( ⁇ / ⁇ 0 )
• ⁇ is the viscosity of the solution
• ⁇ 0 is the viscosity of the solvent N,N-dimethylformamide alone
• C is the concentration of the vinylidene fluoride polymer in the solution, ie, 0.4 g/dL.
• the vinylidene fluoride polymer is prepared by combining vinylidene fluoride, two or more precursors of the structural unit represented by (1) above, and other compounds as necessary by a known method. It can be prepared by polymerization. Examples of methods for copolymerizing these include suspension polymerization, emulsion polymerization, solution polymerization, etc., but suspension polymerization is preferred from the viewpoints that it is easy to obtain a binder with high adhesive strength and there are few impurities.
• the binder may be composed only of the above-mentioned vinylidene fluoride polymer, but may also contain a non-aqueous solvent if necessary.
• the vinylidene fluoride polymer can be dissolved or dispersed, and the binder can be in a liquid state.
• non-aqueous solvents include, for example, polar solvents (polar solvents).
• polar solvents include amide compounds such as dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone; methanol, ethanol, isopropyl alcohol, 2-ethyl-1-hexanol, 1-nonanol, lauryl alcohol, tripropylene.
• Alcohols such as glycols; amine compounds such as o-toluidine, m-toluidine, and p-toluidine; 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; lactones such as ⁇ -butyrolactone and ⁇ -butyrolactone; Sulfoxide/sulfone compounds such as dimethyl sulfoxide and sulfolane are included.
• the binder may contain only one type of nonaqueous solvent, or may contain two or more types.
• the amount of the nonaqueous solvent in the binder is preferably 400 parts by mass or more and 5000 parts by mass or less, more preferably 500 parts by mass or more and 5000 parts by mass or less, based on 100 parts by mass of the vinylidene fluoride polymer.
• amount of the non-aqueous solvent in the binder is within this range, it is possible to uniformly disperse or dissolve the vinylidene fluoride polymer in the non-aqueous solvent.
• the binder may further contain other resins such as acrylic resin, fillers such as inorganic fillers, various additives, etc., as long as the objects and effects of the present invention are not impaired.
• the binder has a viscosity ratio of the slurry determined by the following method of 100% or less, preferably 80% or less, and 50% or less. % or less is more preferable.
• the viscosity ratio is 100% or less, the electrode mixture described below becomes stable. The viscosity ratio largely depends on the type and structure of the vinylidene fluoride polymer.
• the viscosity ratio test is performed on the vinylidene fluoride polymer by removing only the vinylidene fluoride polymer from the binder. That is, if the binder contains a nonaqueous solvent, a resin other than the vinylidene fluoride polymer, a filler, various additives, etc., these are removed and the following test is performed. In addition, when the binder contains a plurality of vinylidene fluoride polymers, the test is conducted in a state where these are mixed.
• Viscosity ratio (%) (slurry viscosity after storage) / (slurry viscosity immediately after preparation) x 100
• the electrode active material (NCA811) is placed in ultrapure water in an amount 50 times the mass of the electrode active material (NCA811). Then, it is stirred for 10 minutes using a magnetic stirrer at a rotation speed of 600 rpm. The pH of the solution is measured using a pH meter MODEL F-21 manufactured by Horiba, Ltd., and the measured pH is defined as the pH of NCA811.
• Electrode mixture The binder described above and a positive electrode active material can be mixed to form an electrode mixture for producing a positive electrode of a lithium ion secondary battery.
• the electrode mixture may further contain a conductive aid, a solvent, other additives, and the like.
• the type of positive electrode active material is not particularly limited, and a general lithium-based positive electrode active material containing lithium can be used.
• a lithium-based positive electrode active material for example, the following general formula (2) LiMxO2 ...( 2 ) Examples include lithium metal oxides represented by:
• M represents at least one metal element including Ni, and the metal element other than Ni is preferably selected from the group consisting of Co, Al, Fe, Mn, Cr and V.
• Ni it is more preferable to further contain one or more selected from the group consisting of Co, Mn, and Al.
• the lithium metal oxide represented by the above formula (2) when the total of the metal elements constituting M is 100 mol%, it is preferable to contain 55 mol% or more of Ni, and 70% or more of Ni. It is more preferable to include. In the above general formula (2), 0.5 ⁇ x ⁇ 1.5, more preferably 0.7 ⁇ x ⁇ 1.3.
• the positive electrode active material may be one obtained by coating the surface of the above compound. Furthermore, the positive electrode active material may be a commercially available product.
• Examples of the composition of the lithium-based positive electrode active material represented by the above general formula (2) and other lithium-based positive electrode active materials include Li 1.0 Ni 0.8 Co 0.2 O 2 , Li 1.0 Ni 0.5 Mn 0.5 O 2 , Li 1.00 Ni 0.35 Co 0.34 Mn 0.34 O 2 (NCM111), Li 1.00 Ni 0.52 Co 0.20 Mn 0.30 O 2 (NCM523), Li 1.00 Ni 0.50 Co 0.30 Mn 0.20 O 2 (NCM532), Li 1.00 Ni 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), Li 1.00 Ni 0.83 Co 0.12 Mn 0.05 O 2 (NCM811), Li 1.00 Ni 0.85 Co 0.15 Al 0.05 O 2 (NCA811), LiCoO 2 (LCO), and Includes LiFePO 4 (LFP) and the like.
• the positive electrode active material may include a plurality of different types of lithium-based positive electrode active materials.
• LiNix Co y Mn Z O 2 (x, y and z are the same as in the above specific example), or LiNix Co y Mn Z O 2 (x, y, and z are as shown in the above specific example).
• LiNix Co y Al z O 2 (x, y, and z are as shown in the above specific example).
• the amount of the positive electrode active material contained in the electrode mixture is appropriately selected depending on the use of the electrode mixture, but the amount of the positive electrode active material contained in the electrode mixture is 40 It is preferably at least 99.9% by mass. When the amount of the positive electrode active material is within this range, for example, sufficient charge/discharge capacity can be obtained, and battery performance tends to be good.
• the binder even when the binder is mixed with the positive electrode active material described above, especially the positive electrode active material containing a relatively large amount of Ni, gelation does not easily occur. Furthermore, the binder exhibits high adhesiveness to the positive electrode active material and the like. Therefore, the ratio of the solid content derived from the binder to the total amount of the solid content derived from the binder (the total amount excluding components that volatilize during curing), the active material, and the conductive additive is set to be, for example, 0.2% by mass or more and 20% by mass or less. It is also possible to do this. The amount of solid content derived from the binder is more preferably 0.2% by mass or more and 10% by mass or less, and even more preferably 0.2% by mass or more and 4% by mass or less.
• the conductive additive contained in the electrode mixture is not particularly limited as long as it is a compound that can further enhance the conductivity between the positive electrode active materials or between the positive electrode active material and the current collector.
• conductive aids include acetylene black, Ketjenblack, carbon black, graphite powder, graphene, carbon nanofibers, carbon nanotubes, carbon fibers, and the like.
• the amount of the conductive additive contained in the electrode mixture is appropriately selected depending on its type. From the viewpoint of improving both the conductivity and the dispersibility of the conductive aid, it is preferably 0.1% by mass or less than 15% by mass based on the total amount of the solid content derived from the binder, the positive electrode active material, and the conductive aid. , more preferably 0.1% by mass or more and 7% by mass or less, further preferably 0.1% by mass or more and 5% by mass or less.
• the electrode mixture may contain a solvent different from the nonaqueous solvent contained in the binder.
• the solvent can be selected from non-aqueous solvents that can be included in the binder described above.
• the total amount of solvent in the electrode mixture (including the amount of non-aqueous solvent in the binder) is not particularly limited, but is usually preferably 20 parts by mass or more and 150 parts by mass or less based on 100 parts by mass of the above-mentioned active material.
• the electrode mixture may further contain a dispersant, an adhesion aid, a thickener, etc., and known compounds can be used as these. These amounts are not particularly limited as long as they do not impair the objects and effects of the present invention, but are preferably 15% by mass or less based on the total amount of solid content derived from the binder and active material.
• electrode mixtures include nitrogen compounds such as phosphorus compounds, sulfur compounds, organic acids, amine compounds, and ammonium compounds; organic esters, various silane-based, titanium-based, and aluminum-based coupling agents; and the above-mentioned vinylidene fluoride-based coupling agents. It may further contain additives such as resins other than polymers such as vinylidene fluoride polymer, polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and polyacrylonitrile (PAN). These are not particularly limited as long as they do not impair the objects and effects of the present invention, but are preferably 15% by mass or less based on the total amount of the solid content derived from the binder and the positive electrode active material.
• nitrogen compounds such as phosphorus compounds, sulfur compounds, organic acids, amine compounds, and ammonium compounds
• organic esters various silane-based, titanium-based, and aluminum-based coupling agents
• vinylidene fluoride-based coupling agents may further
• the electrode mixture may be prepared by mixing all the components at once, or may be prepared by mixing some of the components first and then mixing the remaining components.
• the viscosity of the electrode mixture can prevent dripping, uneven coating, and delayed drying after coating when applying the electrode mixture to form the electrode mixture layer, and improves workability when preparing the electrode mixture layer. It is not particularly limited as long as it has a viscosity that provides good coating properties.
• the viscosity (slurry viscosity) measured with a B-type viscometer at 20°C and 6 rpm is preferably 100 mPa ⁇ s or more and 100,000 mPa ⁇ s or less, and 1000 mPa ⁇ s or more and 80,000 mPa ⁇ s or less. More preferably, it is particularly preferably 2000 mPa ⁇ s or more and 70000 mPa ⁇ s or less.
• the viscosity of the electrode mixture (slurry viscosity) in this specification is a value measured 2 minutes after the start of rotation using the B-type rotational viscometer.
• Electrode (positive electrode) of the lithium ion secondary battery of the present invention may include an electrode mixture layer made of the above-mentioned electrode mixture, for example, a current collector and a positive electrode disposed on the current collector. , and the above-mentioned electrode mixture layer.
• a current collector is a terminal for extracting electricity.
• the material of the current collector is not particularly limited, and metal foil or metal mesh of aluminum, copper, iron, stainless steel, steel, nickel, titanium, etc. can be used. Alternatively, a layer containing carbon black or the like may be formed on the surface of another medium, or the medium may be coated with the above-mentioned metal foil or metal mesh.
• the electrode mixture layer is a layer formed by applying a composition containing a binder and a positive electrode active material (for example, the above-mentioned electrode mixture) onto a current collector and drying it.
• the electrode mixture layer may be formed only on one surface of the current collector, or may be arranged on both surfaces.
• the electrode mixture layer contains at least the above-mentioned binder-derived solid content (vinylidene fluoride polymer) and active material, and optionally contains various conductive aids, dispersants, adhesion aids, thickeners, etc. It further includes additives and the like. These are the same as those explained for the electrode mixture.
• the thickness of the electrode mixture layer is not particularly limited, but in one example, it is preferably 1 ⁇ m or more and 1000 ⁇ m or less.
• the basis weight of the electrode mixture layer formed on one surface of the current collector is not particularly limited and can be any desired basis weight, but in one example, 50 g/m 2 or more and 1000 g /m 2 or less is preferable, and 100 g/m 2 or more and 500 g/m 2 or less is more preferable.
• the electrode mixture layer can be formed by applying the electrode mixture on the current collector and drying it.
• the method for applying the electrode mixture is not particularly limited, and the doctor blade method, reverse roll method, comma bar method, gravure method, air knife method, die coating method, dip coating method, etc. can be applied.
• the electrode mixture After applying the electrode mixture, it is heated at an arbitrary temperature to dry the non-aqueous solvent.
• the drying temperature is preferably 60°C or higher and 500°C or lower, more preferably 80°C or higher and 200°C or lower. Heating may be performed multiple times at different temperatures.
• the solvent in the mixture may be dried under atmospheric pressure, increased pressure, or reduced pressure. Further heat treatment may be performed after drying.
• a press treatment may be further performed.
• the electrode density can be improved.
• the press pressure is preferably 1 kPa or more and 10 GPa or less.
• Lithium ion secondary battery The binder and electrode mixture described above can be used to form the electrode (positive electrode) of lithium ion secondary batteries, etc., as described above, but they can also be used to form other layers of lithium ion secondary batteries. May be used for
• the inherent viscosity of the vinylidene fluoride polymer was measured as follows. First, 80 mg of vinylidene fluoride polymer was dissolved in 20 mL of N,N-dimethylformamide, and the viscosity was measured using an Ubbelohde viscometer in a constant temperature bath at 30°C. Then, the inherent viscosity ( ⁇ i ) of the vinylidene fluoride polymer was calculated from the obtained value based on the following formula.
• ⁇ i (1/C) ⁇ ln( ⁇ / ⁇ 0 )
• ⁇ is the viscosity of the solution
• ⁇ 0 is the viscosity of the solvent N,N-dimethylformamide alone
• C is the concentration of the vinylidene fluoride polymer in the solution, ie, 0.4 g/dL.
• Electrodes produced in Examples and Comparative Examples described below were cut out to a length of 100 mm and a width of 20 mm. Then, using a tensile tester (ORIENTE CHSIA-1150 manufactured by UNIVERSAL TESTING MACHINE) according to JIS F6854-1, a 90° peel test was performed at a head speed of 10 mm/min to measure the peel strength.
• a tensile tester ORIENTE CHSIA-1150 manufactured by UNIVERSAL TESTING MACHINE
• a vinylidene fluoride polymer solution was added to the mixture of NCA811 and carbon black, and kneaded. Specifically, the above solution was added so that the solid content concentration was 81.5% by mass, and primary kneading was performed at 2000 rpm for 2.5 minutes. Then, the remaining above solution and NMP were added to make the solid content concentration 75% by mass. Then, secondary kneading was performed at 2000 rpm for 3 minutes to obtain a slurry. Note that after the first kneading and the second kneading, the slurry was allowed to cool until the temperature reached 40°C.
• the above slurry was prepared in an environment of 22°C and a dew point of -30°C or more and -40°C or less.
• the mass ratio of the electrode active material, carbon black, and vinylidene fluoride polymer in the obtained slurry was 100:2:2 in this order.
• Viscosity ratio (%) (slurry viscosity after storage) / (slurry viscosity immediately after preparation) x 100
• NCA811 average particle diameter measured by laser diffraction/diffusion method of aqueous dispersion: 12.5 ⁇ m, specific surface area measured by BET 1-point method: 0.24 m 2 /g, pH measured by the above method: 11.6
• ⁇ N-Methyl-2-pyrrolidone water content: less than 500 ppm
• ⁇ Carbon black SuperP (registered trademark) manufactured by Timcal Japan
• average particle diameter measured by electron microscope analysis 40 nm
• specific surface area measured by BET 1-point method 60 m 2 /g
• the above vinylidene fluoride polymer A (binder) was dissolved in NMP to prepare a vinylidene fluoride polymer solution containing 8% by mass of vinylidene fluoride polymer A. Then, NMP was added to the mixture of NCA811 and carbon black, and the mixture was kneaded. Specifically, a vinylidene fluoride polymer solution was added so that the solid content concentration was 83.7% by mass, and primary kneading was performed at 2000 rpm for 4 minutes. Next, a vinylidene fluoride polymer solution was further added to make the solid content concentration 73.5% by mass, and secondary kneading was performed at 2000 rpm for 3 minutes to obtain an electrode mixture.
• the obtained electrode mixture was coated on a 15 ⁇ m thick aluminum foil serving as a current collector using a bar coater, and was primarily dried at 110° C. for 30 minutes in a constant temperature bath under a nitrogen atmosphere. Next, secondary drying was performed at 130° C. for 2 hours in a nitrogen atmosphere to obtain an electrode (electrode peel measurement sample) with a basis weight of about 250 g/m 2 .
• the mass ratio of the electrode active material, carbon black, and vinylidene fluoride polymer in the obtained electrode mixture was 100:2:1.5 in this order.
• Example 2 An electrode mixture and an electrode were obtained in the same manner as in Example 1, except that the binder was changed to vinylidene fluoride polymer B.
• Example 3 An electrode mixture and an electrode were obtained in the same manner as in Example 1, except that the binder was changed to vinylidene fluoride polymer F.
• Example 2 An electrode mixture and an electrode were obtained in the same manner as in Example 1, except that the binder was changed to a blend of vinylidene fluoride polymer C and vinylidene fluoride polymer D at a weight ratio of 3:7.
• Example 6 An electrode mixture and an electrode were obtained in the same manner as in Example 1, except that the binder was changed to a blend of vinylidene fluoride polymer D and vinylidene fluoride polymer G at a weight ratio of 4:6.
• the binder contains a vinylidene fluoride polymer containing a constitutional unit derived from vinylidene fluoride and two or more types of constitutional units having a carboxyl group, it has high peel strength and The anti-oxidation resistance was good (Examples 1 to 3).
• the binder of the present invention is mixed with a positive electrode active material containing a large amount of nickel, there is little deterioration or thickening. Further, the binder has good adhesive strength even in a small amount. Therefore, the binder, the electrode mixture, and the electrode containing the binder are very useful for manufacturing lithium ion secondary batteries.

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