Components for constructing electrodes, terminal blocks, and secondary batteries.

Abstract

Invention details;

Description

Electrode-forming composition, electrode, and secondary battery

[0001] The present disclosure relates to an electrode-forming composition, an electrode, and a secondary battery.

[0002] Electrodes included in electrochemical devices such as lithium ion batteries can be formed, for example, by dissolving an electrode material and a binder in a solvent and applying the resulting composition to a current collector.

[0003] For example, Patent Document 1 describes an electrode-forming composition comprising a linear semi-crystalline copolymer [polymer (A)] containing repeating units derived from vinylidene fluoride (VDF) monomer and a hydrophilic (meth)acrylic monomer (MA) represented by a specific chemical formula, the copolymer [polymer (A)] containing 0.05 to 10 mol % of repeating units derived from the hydrophilic (meth)acrylic monomer (MA) and characterized by a fraction of randomly distributed units (MA) of at least 40%, a powdered electrode material, and, optionally, a conductivity-imparting additive and / or a viscosity modifier.

[0004] Patent Document 2 describes a polymer dope that contains a fluororesin and / or an aromatic polyamide resin and a β-alkoxypropionamide solvent represented by a specific chemical formula.

[0005] Patent Document 3 describes that a positive electrode for electrochemical cycling experiments was prepared by coating a slurry containing 92.5 wt % of a cathode active material suspended in N-ethyl-2-pyrrolidinone (NEP), 2 wt % of graphite, 2 wt % of Super C65 carbon black, and 3.5 wt % of polyvinylidene fluoride (PVdF) binder onto an aluminum foil.

[0006] JP 2010-525124 A JP 2011-184479 A JP 2021-508145 A

[0007] The present disclosure aims to provide an electrode-forming composition that contains a solvent different from conventional organic solvents, can be prepared very easily, has excellent slurry stability, and can form a coating layer that adheres firmly to metal foil and has excellent flexibility and conductivity. By using metal foil having such a coating layer as a battery electrode, it is possible to realize a battery that has a high high-temperature storage capacity retention rate, low gas generation, and is less likely to increase in resistance.

[0008] According to the present disclosure, there is provided an electrode-forming composition containing a copolymer containing vinylidene fluoride units and monomer units other than vinylidene fluoride, and a solvent represented by general formula (1).

[0009] General formula (1): (In the formula, R １ , R ２ and R ３ are independently H or a monovalent substituent, with the proviso that R １ , R ２ and R ３ The total number of carbon atoms in R is 6 or more, １ , R ２ and R ３ At least one of R is an organic group having a carbonyl group. １ , R ２ and R ３ Any two of them may be bonded to form a ring.)

[0010] In the electrode-forming composition of the present disclosure, the solvent is preferably a solvent represented by general formula (1a).

[0011] General formula (1a): (In the formula, R １ａ is a monovalent substituent, and R ２ａ and R ３ａ are independently H or a monovalent substituent, with the proviso that R １ａ , R ２ａ and R ３ａ The total number of carbon atoms in R is 5 or more. １ａ , R ２ａ and R ３ａ Any two of them may be bonded to form a ring.)

[0012] In the electrode-forming composition of the present disclosure, the solvent is preferably at least one selected from the group consisting of solvents represented by general formula (1b-1) and solvents represented by general formula (1b-2).

[0013] General formula (1b-1): (In the formula, R １ｂ is an alkyl group, an alkoxyalkyl group, an acylalkyl group, an alkenyl group, an amino group, or an aminoalkyl group; R ２ｂ and R ３ｂ are independently an alkyl group or an alkoxyalkyl group, and R １ｂ , R ２ｂ and R ３ｂ The total number of carbon atoms in R is 5 or more. ２ｂ and R ３ｂ are bonded to each other to form R ２ｂ and R ３ｂ may form a ring together with the nitrogen atom to which it is bonded, and the ring may contain an oxygen atom as a constituent atom.

[0014] General formula (1b-2): wherein ring A is a 5- or 6-membered amide ring, and R ４ｂ is an alkyl group, a cycloalkyl group, or an alkenyl group, and rings A and R ４ｂ The total number of carbon atoms is 5 or more.

[0015] In the electrode-forming composition of the present disclosure, the solvent is preferably at least one selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone, and N-butyl-2-pyrrolidone. In the electrode-forming composition of the present disclosure, the other monomer is preferably at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, (meth)acrylic acid, 2,3,3,3-tetrafluoropropene, hexafluoropropylene, and fluoroalkyl vinyl ether. In the electrode-forming composition of the present disclosure, the content of the other monomer units in the copolymer is preferably 0.0001 to 50.0 mol % based on the total monomer units. The electrode-forming composition of the present disclosure preferably further contains a powder electrode material. In the electrode-forming composition of the present disclosure, the powder electrode material preferably contains a lithium transition metal complex oxide. The electrode-forming composition of the present disclosure is preferably a positive electrode-forming composition.

[0016] The present disclosure also provides an electrode including a current collector and an electrode material layer formed from the electrode-forming composition and disposed on one or both sides of the current collector.

[0017] The present disclosure also provides a secondary battery including the above electrode.

[0018] According to the present disclosure, there is provided an electrode-forming composition that contains a solvent different from conventional organic solvents, which can be prepared very easily, has excellent slurry stability, and is capable of forming a coating layer that adheres firmly to a metal foil and is also excellent in flexibility and conductivity. By using a metal foil having such a coating layer as a battery electrode, it is possible to provide an electrode-forming composition that can realize a battery that has a high high-temperature storage capacity retention rate, a small amount of gas generation, and is less likely to increase in resistance.

[0019] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0020] The electrode-forming composition of the present disclosure contains a copolymer containing vinylidene fluoride (VdF) units and monomer units other than VdF, and a solvent having a specific chemical structure.

[0021] Patent Document 1 describes an electrode-forming composition containing a linear semi-crystalline copolymer including repeating units derived from vinylidene fluoride monomers and hydrophilic (meth)acrylic monomers represented by a specific chemical formula. In this electrode-forming composition, it is preferable to use, as the organic solvent, a nitrogen-containing organic solvent with greater dissolving power, such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), or N,N-dimethylacetamide (DMAc).

[0022] Furthermore, Patent Document 2 describes the use of a β-alkoxypropionamide solvent as the organic solvent for the electrode-forming composition, and Patent Document 3 describes the use of N-ethyl-2-pyrrolidinone. However, with the combinations of fluororesin and organic solvent described in Patent Documents 2 and 3, the fluororesin is difficult to dissolve or disperse in the organic solvent, and the resulting electrode-forming composition does not have sufficient slurry stability.

[0023] In the present disclosure, a copolymer containing VdF units and other monomer units other than VdF is used as a binder for an electrode-forming composition, and a solvent represented by general formula (1) is used as a solvent for the electrode-forming composition.

[0024] General formula (1): (In the formula, R １ , R ２ and R ３ are independently H or a monovalent substituent, with the proviso that R １ , R ２ and R ３ The total number of carbon atoms in R is 6 or more, １ , R ２ and R ３ At least one of R is an organic group having a carbonyl group. １ , R ２ and R ３ Any two of them may be bonded to form a ring.)

[0025] It has been found that the solvent represented by general formula (1) readily dissolves copolymers containing VdF and other monomer units at room temperature, similar to conventional organic solvents such as NMP. Therefore, the electrode-forming composition of the present disclosure can be prepared very easily. Furthermore, the electrode-forming composition of the present disclosure also has excellent slurry stability (the property of not increasing viscosity even after mixing with a powder electrode material) and can be easily applied to metal foils such as aluminum foil. Furthermore, the resulting coating layer firmly adheres to the metal foil and has excellent flexibility and conductivity. Furthermore, by using a metal foil having such a coating layer as a battery electrode, a battery with a high high-temperature storage capacity retention rate, low gas generation, and resistance increase can be realized.

[0026] <Copolymer> The copolymer contained in the electrode-forming composition of the present disclosure contains VdF units and other monomer units other than VdF. The other monomers may be fluorinated or non-fluorinated monomers. The copolymer contained in the electrode-forming composition of the present disclosure contains VdF units and other monomer units other than VdF, and therefore is more easily soluble in the solvent represented by general formula (1) than VdF homopolymers, which have traditionally been used as binders.

[0027] Examples of fluorinated monomers (excluding VdF) include tetrafluoroethylene (TFE), vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ethers, hexafluoropropylene (HFP), (perfluoroalkyl)ethylenes, 2,3,3,3-tetrafluoropropene, and trans-1,3,3,3-tetrafluoropropene.

[0028] The fluoroalkyl vinyl ether is preferably a fluoroalkyl vinyl ether having a fluoroalkyl group having 1 to 5 carbon atoms, and more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether).

[0029] Among these, the fluorinated monomer is preferably at least one selected from the group consisting of TFE, CTFE, 2,3,3,3-tetrafluoropropene, HFP, and fluoroalkyl vinyl ether, more preferably at least one selected from the group consisting of TFE and HFP, and particularly preferably TFE, because this allows the formation of an electrode material layer that is more excellent due to its flexibility and adhesion to the current collector, and allows the formation of a secondary battery that is more excellent due to its battery characteristics.

[0030] The fluorinated monomers (except VdF) may or may not have a polar group.

[0031] Examples of the non-fluorinated monomer include non-fluorinated monomers that do not have a polar group, such as ethylene and propylene, and non-fluorinated monomers that have a polar group (hereinafter sometimes referred to as polar group-containing monomers).

[0032] When a non-fluorinated monomer having a polar group is used, the polar group is introduced into the copolymer, thereby achieving even better adhesion between the coating layer and the metal foil. The polar group is preferably at least one selected from the group consisting of a carbonyl group-containing group, an epoxy group, a hydroxy group, a sulfonic acid group, a sulfate group, a phosphate group, an amino group, an amide group, and an alkoxy group, more preferably at least one selected from the group consisting of a carbonyl group-containing group, an epoxy group, and a hydroxy group, and even more preferably a carbonyl group-containing group. The hydroxy group does not include a hydroxy group that constitutes a part of the carbonyl group-containing group. The amino group is a monovalent functional group obtained by removing hydrogen from ammonia, a primary amine, or a secondary amine.

[0033] The carbonyl group-containing group is a functional group having a carbonyl group (-C(=O)-). As the carbonyl group-containing group, a group represented by the general formula: -COOR (R represents a hydrogen atom, an alkyl group or a hydroxyalkyl group) or a carboxylic acid anhydride group is preferred, and a group represented by the general formula: -COOR is more preferred. The number of carbon atoms in the alkyl group and hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3. Specific examples of the group represented by the general formula: -COOR include -COOCH ２ CH ２ OH, -COOCH ２ CH (CH ３ )OH, -COOCH(CH ３ ) CH ２ OH, -COOH, -COOCH ３ , -COOC ２ H ５ When the group represented by the general formula: -COOR is -COOH or contains -COOH, the -COOH may be a carboxylate such as a metal carboxylate or an ammonium carboxylate.

[0034] The carbonyl group-containing group may also be a group represented by the general formula: -X-COOR (where X is an atomic group having a main chain composed of 1 to 20 atoms and a molecular weight of 500 or less, and R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group). The alkyl group and the hydroxyalkyl group preferably have 1 to 16 carbon atoms, more preferably 1 to 6, and even more preferably 1 to 3 carbon atoms.

[0035] The amide group is preferably a group represented by the general formula: -CO-NRR' (R and R' independently represent a hydrogen atom or a substituted or unsubstituted alkyl group), or a bond represented by the general formula: -CO-NR"- (R" represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group).

[0036] Examples of the polar group-containing monomer include hydroxyalkyl (meth)acrylates such as hydroxyethyl acrylate and 2-hydroxypropyl acrylate; alkylidene malonic acid esters such as dimethyl methylidene malonate; vinyl carboxyalkyl ethers such as vinyl carboxymethyl ether and vinyl carboxyethyl ether; carboxyalkyl (meth)acrylates such as 2-carboxyethyl acrylate and 2-carboxyethyl methacrylate; (meth)acryloyloxyalkyl dicarboxylic acid esters such as acryloyloxyethyl succinate, acryloyloxypropyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, and methacryloyloxyethyl phthalate; monoesters of unsaturated dibasic acids such as maleic acid monomethyl ester, maleic acid monoethyl ester, citraconic acid monomethyl ester, and citraconic acid monoethyl ester; (In the formula, R １１ ~R １３ R independently represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. １４ represents a single bond or a hydrocarbon group having 1 to 8 carbon atoms. １ represents an inorganic cation and / or an organic cation; unsaturated dibasic acids such as maleic acid, maleic anhydride, citraconic acid, and citraconic anhydride; and the like.

[0037] The polar group-containing monomer unit that the copolymer may contain is preferably a unit based on the monomer (4) represented by the general formula (4).

[0038] In the general formula (4), Y １ represents an inorganic cation and / or an organic cation. Examples of inorganic cations include cations such as H, Li, Na, K, Mg, Ca, Al, and Fe. Examples of organic cations include NH ４ , N.H. ３ R １５ , N.H. ２ R １５ ２ , N.H.R. １５ ３ , N.R. １５ ４ (R １５Y independently represents an alkyl group having 1 to 4 carbon atoms. １ Examples include H, Li, Na, K, Mg, Ca, Al, and NH ４ are preferred, and H, Li, Na, K, Mg, Al, NH ４ is more preferred, and H, Li, Al, NH ４ is more preferred, and H is particularly preferred. For convenience, the symbols and valences of the specific inorganic cations and organic cations are omitted.

[0039] In general formula (4), R １１ ~R １３ R independently represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. The hydrocarbon group is a monovalent hydrocarbon group. The hydrocarbon group preferably has 4 or less carbon atoms. Examples of the hydrocarbon group include alkyl groups, alkenyl groups, alkynyl groups, etc. having the above carbon numbers, with methyl groups or ethyl groups being preferred. １１ and R １２ are preferably independently a hydrogen atom, a methyl group, or an ethyl group, and R １３ is preferably a hydrogen atom or a methyl group.

[0040] In general formula (4), R １４ represents a single bond or a hydrocarbon group having 1 to 8 carbon atoms. The hydrocarbon group is a divalent hydrocarbon group. The hydrocarbon group preferably has 4 or less carbon atoms. Examples of the hydrocarbon group include alkylene groups and alkenylene groups having the above carbon numbers, and among these, at least one selected from the group consisting of a methylene group, an ethylene group, an ethylidene group, a propylidene group, and an isopropylidene group is preferred, with a methylene group being more preferred.

[0041] As the monomer (4), at least one selected from the group consisting of (meth)acrylic acid and salts thereof, vinylacetic acid (3-butenoic acid) and salts thereof, 3-pentenoic acid and salts thereof, 4-pentenoic acid and salts thereof, 3-hexenoic acid and salts thereof, 4-heptenoic acid and salts thereof, and 5-hexenoic acid and salts thereof is preferred.

[0042] The other monomer is preferably at least one selected from the group consisting of TFE, CTFE, (meth)acrylic acid, 2,3,3,3-tetrafluoropropene, HFP, and fluoroalkyl vinyl ether. (Meth)acrylic acid includes acrylic acid and methacrylic acid.

[0043] The content of other monomer units in the copolymer is preferably 0.0001 to 50.0 mol%, more preferably 0.01 mol% or more, even more preferably 0.10 mol% or more, more preferably 45.0 mol% or less, even more preferably 40.0 mol% or less, and particularly preferably 35.0 mol% or less, based on the total monomer units.

[0044] The content of VdF units in the copolymer is 50.0 to 99.9999 mol%, more preferably 55.0 mol% or more, even more preferably 60.0 mol% or more, particularly preferably 65.0 mol% or more, more preferably 99.99 mol% or less, and even more preferably 99.90 mol% or less, based on the total monomer units.

[0045] When the copolymer contains a fluorinated monomer unit as another monomer unit, the content of the fluorinated monomer unit is preferably 0.0001 to 50.0 mol%, more preferably 2.0 mol% or more, even more preferably 3.0 mol% or more, particularly preferably 4.0 mol% or more, more preferably 45.0 mol% or less, even more preferably 40.0 mol% or less, particularly preferably 35.0 mol% or less, based on the total monomer units.

[0046] When the copolymer contains a fluorinated monomer unit as another monomer unit, the content of the VdF unit in the copolymer is 50.0 to 99.999 mol%, more preferably 55.0 mol% or more, even more preferably 60.0 mol% or more, particularly preferably 65.0 mol% or more, more preferably 98.0 mol% or less, even more preferably 97.0 mol% or less, particularly preferably 96.0 mol% or less, based on the total monomer units.

[0047] When the copolymer contains a non-fluorinated monomer unit such as a polar group-containing monomer as the other monomer unit, the content of the non-fluorinated monomer unit is preferably 0.0001 to 50.0 mol %, more preferably 0.01 mol % or more, even more preferably 0.10 mol % or more, more preferably 5.0 mol % or less, still more preferably 3.0 mol % or less, and particularly preferably 1.5 mol % or less, based on the total monomer units.

[0048] When the copolymer contains non-fluorinated monomer units as other monomer units, the content of VdF units in the copolymer is preferably 50.0 to 99.999 mol%, more preferably 95.0 mol% or more, even more preferably 97.0 mol% or more, particularly preferably 98.5 mol% or more, more preferably 99.99 mol% or less, and even more preferably 99.90 mol% or less, based on all monomer units.

[0049] In the present disclosure, the composition of the copolymer may be, for example, １９ In addition, when the copolymer contains a polar group-containing monomer unit as another monomer unit, the content of the polar group-containing monomer unit can be measured by acid-base titration of the acid group, for example, when the polar group is an acid group such as carboxylic acid.

[0050] The weight average molecular weight (polystyrene equivalent) of the copolymer is preferably 10,000 to 3,000,000, more preferably 30,000 or more, even more preferably 50,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, even more preferably 2,200,000 or less, and particularly preferably 2,000,000 or less. The weight average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0051] The number average molecular weight (polystyrene equivalent) of the copolymer is preferably 7,000 to 1,500,000, more preferably 21,000 or more, even more preferably 35,000 or more, more preferably 1,400,000 or less, still more preferably 1,200,000 or less, and particularly preferably 1,100,000 or less. The number average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0052] Examples of the copolymer include VdF / (meth)acrylic acid copolymer, VdF / TFE copolymer, VdF / HFP copolymer, VdF / fluoroalkyl vinyl ether copolymer, VdF / TFE / HFP copolymer, VdF / 2,3,3,3-tetrafluoropropene copolymer, VdF / TFE / 2,3,3,3-tetrafluoropropene copolymer, VdF / TFE / (meth)acrylic acid copolymer, VdF / HFP / (meth)acrylic acid copolymer, VdF / CTFE copolymer, and VdF / TFE / 4-pentenoic acid. copolymer, VdF / TFE / 3-butenoic acid copolymer, VdF / TFE / HFP / (meth)acrylic acid copolymer, VdF / TFE / HFP / 4-pentenoic acid copolymer, VdF / TFE / HFP / 3-butenoic acid copolymer, VdF / TFE / 2-carboxyethyl acrylate copolymer, VdF / TFE / HFP / 2-carboxyethyl acrylate copolymer, VdF / TFE / acryloyloxyethyl succinic acid copolymer, VdF / TFE / HFP / acryloyloxyethyl succinic acid copolymer, and the like.

[0053] Among these, the copolymer is preferably at least one selected from the group consisting of VdF / TFE copolymer, VdF / CTFE copolymer, VdF / (meth)acrylic acid copolymer, VdF / 2,3,3,3-tetrafluoropropene copolymer, VdF / HFP copolymer, and VdF / fluoroalkyl vinyl ether copolymer.

[0054] The VdF / TFE copolymer contains VdF units and TFE units. By using a VdF / TFE copolymer as the copolymer, an electrode-forming composition can be formed very easily, and an electrode-forming composition with excellent slurry stability can be obtained, allowing for the formation of a coating layer with excellent flexibility. The content of VdF units is preferably 50.0 to 95.0 mol%, more preferably 55.0 mol% or more, even more preferably 60.0 mol% or more, more preferably 92.0 mol% or less, and even more preferably 89.0 mol% or less, based on the total monomer units of the VdF / TFE copolymer. The content of TFE units is preferably 50.0 to 5.0 mol%, more preferably 45.0 mol% or less, even more preferably 40.0 mol% or less, more preferably 8.0 mol% or more, and even more preferably 11.0 mol% or more, based on the total monomer units of the VdF / TFE copolymer.

[0055] The VdF / TFE copolymer may contain, in addition to VdF units and TFE units, units based on a monomer copolymerizable with VdF and TFE (excluding VdF and TFE). From the viewpoint of electrolyte swelling resistance, the content of units based on a monomer copolymerizable with VdF and TFE is preferably 3.0 mol% or less based on the total monomer units of the VdF / TFE copolymer.

[0056] Examples of the monomer copolymerizable with VdF and TFE include the above-mentioned fluorinated monomers, the above-mentioned non-fluorinated monomers, etc. Among them, the monomer copolymerizable with VdF and TFE is preferably at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers, and more preferably at least one selected from the group consisting of HFP, 2,3,3,3-tetrafluoropropene, and monomer (4).

[0057] The weight average molecular weight (polystyrene equivalent) of the VdF / TFE copolymer is preferably 50,000 to 2,000,000, more preferably 80,000 to 1,700,000, and even more preferably 100,000 to 1,500,000.

[0058] The number average molecular weight (polystyrene equivalent) of the VdF / TFE copolymer is 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and even more preferably 50,000 to 1,200,000.

[0059] The VdF / CTFE copolymer contains VdF units and CTFE units. By using a VdF / CTFE copolymer as the copolymer, an electrode-forming composition can be formed very easily, and a coating layer that adheres very strongly to a metal foil can be formed. The VdF unit content is preferably 80.0 to 98.0 mol%, more preferably 85.0 mol% or more, even more preferably 90.0 mol% or more, more preferably 97.5 mol% or less, and even more preferably 97.0 mol% or less, based on the total monomer units of the VdF / CTFE copolymer. The CTFE unit content is preferably 20.0 to 2.0 mol%, more preferably 15.0 mol% or less, even more preferably 10.0 mol% or less, more preferably 2.5 mol% or more, and even more preferably 3.0 mol% or more, based on the total monomer units of the VdF / CTFE copolymer.

[0060] The VdF / CTFE copolymer may contain, in addition to VdF units and CTFE units, units based on a monomer copolymerizable with VdF and CTFE (excluding VdF and CTFE). From the viewpoint of electrolyte swelling resistance, the content of units based on a monomer copolymerizable with VdF and CTFE is preferably 3.0 mol% or less based on the total monomer units of the VdF / CTFE copolymer.

[0061] Examples of the monomer copolymerizable with VdF and CTFE include the above-mentioned fluorinated monomers and the above-mentioned non-fluorinated monomers. Among them, the monomer copolymerizable with VdF and CTFE is preferably at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers, more preferably at least one selected from the group consisting of TFE, HFP, 2,3,3,3-tetrafluoropropene, and monomer (4), and even more preferably TFE.

[0062] The weight average molecular weight (polystyrene equivalent) of the VdF / CTFE copolymer is preferably 50,000 to 2,000,000, more preferably 80,000 to 1,700,000, and even more preferably 100,000 to 1,500,000.

[0063] The number average molecular weight (polystyrene equivalent) of the VdF / CTFE copolymer is preferably 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and even more preferably 50,000 to 1,200,000.

[0064] The VdF / (meth)acrylic acid copolymer contains VdF units and (meth)acrylic acid units. By using the VdF / (meth)acrylic acid copolymer as the copolymer, an electrode-forming composition can be formed very easily, and a coating layer that adheres very strongly to a metal foil can be formed. The content of the (meth)acrylic acid units is preferably 0.0001 to 5.0 mol %, more preferably 0.01 to 3.0 mol %, and even more preferably 0.10 to 1.5 mol %, based on the total monomer units.

[0065] The content of VdF units in the VdF / (meth)acrylic acid copolymer is preferably 95.0 to 99.9999 mol %, more preferably 97.0 to 99.99 mol %, and even more preferably 98.5 to 99.90 mol %, based on all monomer units.

[0066] The weight average molecular weight (polystyrene equivalent) of the VdF / (meth)acrylic acid copolymer is preferably 50,000 to 3,000,000, more preferably 80,000 or more, even more preferably 100,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, even more preferably 2,200,000 or less, particularly preferably 2,000,000 or less.

[0067] The number average molecular weight (polystyrene equivalent) of the VdF / (meth)acrylic acid copolymer is preferably 20,000 to 1,500,000, more preferably 40,000 or more, even more preferably 70,000 or more, particularly preferably 140,000 or more, more preferably 1,400,000 or less, even more preferably 1,200,000 or less, and particularly preferably 1,100,000 or less.

[0068] The VdF / 2,3,3,3-tetrafluoropropene copolymer contains VdF units and 2,3,3,3-tetrafluoropropene units. By using the VdF / 2,3,3,3-tetrafluoropropene copolymer as the copolymer, an electrode-forming composition can be formed very easily, and a coating layer with excellent flexibility and conductivity can be formed. The content of the VdF units, relative to the total monomer units of the VdF / 2,3,3,3-tetrafluoropropene copolymer, is preferably 50.0 to 98.0 mol%, more preferably 55.0 mol% or more, even more preferably 60.0 mol% or more, particularly preferably 65.0 mol% or more, more preferably 97.0 mol% or less, and even more preferably 96.0 mol% or less. The content of 2,3,3,3-tetrafluoropropene units is preferably 2.0 to 50.0 mol%, more preferably 3.0 mol% or more, even more preferably 4.0 mol% or more, more preferably 45.0 mol% or less, still more preferably 40.0 mol% or less, and particularly preferably 35.0 mol% or less, based on the total monomer units of the VdF / TFE copolymer.

[0069] The VdF / 2,3,3,3-tetrafluoropropene copolymer may contain, in addition to VdF units and 2,3,3,3-tetrafluoropropene units, units based on a monomer copolymerizable with VdF and 2,3,3,3-tetrafluoropropene (excluding VdF and 2,3,3,3-tetrafluoropropene). From the viewpoint of electrolyte swelling resistance, the content of units based on a monomer copolymerizable with VdF and 2,3,3,3-tetrafluoropropene is preferably 3.0 mol % or less based on all monomer units of the VdF / 2,3,3,3-tetrafluoropropene copolymer.

[0070] Examples of the monomer copolymerizable with VdF and 2,3,3,3-tetrafluoropropene include the above-mentioned fluorinated monomers and the above-mentioned non-fluorinated monomers. Among them, the monomer copolymerizable with VdF and 2,3,3,3-tetrafluoropropene is preferably at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers, and more preferably at least one selected from the group consisting of TFE, HFP, and monomer (4).

[0071] The weight average molecular weight (polystyrene equivalent) of the VdF / 2,3,3,3-tetrafluoropropene copolymer is preferably 10,000 to 2,000,000, more preferably 30,000 to 1,700,000, and even more preferably 5,000 to 1,500,000.

[0072] The number average molecular weight (polystyrene equivalent) of the VdF / 2,3,3,3-tetrafluoropropene copolymer is preferably 7,000 to 1,400,000, more preferably 21,000 to 1,300,000, and even more preferably 35,000 to 1,200,000.

[0073] The VdF / HFP copolymer contains VdF units and HFP units. By using the VdF / HFP copolymer as the copolymer, an electrode-forming composition can be formed very easily, and a coating layer that adheres very strongly to a metal foil can be formed. The content of the VdF units is preferably 80.0 to 98.0 mol%, more preferably 83.0 mol% or more, even more preferably 85.0 mol% or more, more preferably 97.0 mol% or less, and even more preferably 96.0 mol% or less, based on the total monomer units of the VdF / HFP copolymer. The content of the HFP units is preferably 20.0 to 2.0 mol%, more preferably 17.0 mol% or less, even more preferably 15.0 mol% or less, more preferably 3.0 mol% or more, and even more preferably 4.0 mol% or more, based on the total monomer units of the VdF / HFP copolymer.

[0074] The VdF / HFP copolymer may contain, in addition to VdF units and HFP units, units based on a monomer copolymerizable with VdF and HFP (excluding VdF and HFP). From the viewpoint of electrolyte swelling resistance, the content of units based on a monomer copolymerizable with VdF and HFP is preferably 3.0 mol % or less based on all monomer units of the VdF / HFP copolymer.

[0075] Examples of the monomer copolymerizable with VdF and HFP include the above-mentioned fluorinated monomers, the above-mentioned non-fluorinated monomers, etc. Among them, the monomer copolymerizable with VdF and HFP is preferably at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers, more preferably at least one selected from the group consisting of TFE, 2,3,3,3-tetrafluoropropene, and monomer (4), and even more preferably monomer (4).

[0076] The weight average molecular weight (polystyrene equivalent) of the VdF / HFP copolymer is preferably 50,000 to 2,000,000, more preferably 80,000 to 1,700,000, and even more preferably 100,000 to 1,500,000.

[0077] The number average molecular weight (in terms of polystyrene) of the VdF / HFP copolymer is preferably 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and even more preferably 50,000 to 1,200,000.

[0078] The VdF / fluoroalkyl vinyl ether copolymer contains VdF units and fluoroalkyl vinyl ether units. The content of VdF units is preferably 80.0 to 98.0 mol%, more preferably 83.0 mol% or more, even more preferably 85.0 mol% or more, more preferably 97.0 mol% or less, and even more preferably 96.0 mol% or less, based on the total monomer units of the VdF / fluoroalkyl vinyl ether copolymer. The content of fluoroalkyl vinyl ether units is preferably 20.0 to 2.0 mol%, more preferably 17.0 mol% or less, even more preferably 15.0 mol% or less, more preferably 3.0 mol% or more, and even more preferably 4.0 mol% or more, based on the total monomer units of the VdF / fluoroalkyl vinyl ether copolymer.

[0079] The VdF / fluoroalkyl vinyl ether copolymer may contain, in addition to VdF units and fluoroalkyl vinyl ether units, units based on a monomer copolymerizable with VdF and fluoroalkyl vinyl ether (excluding VdF and fluoroalkyl vinyl ether). From the viewpoint of electrolyte swelling resistance, the content of units based on a monomer copolymerizable with VdF and fluoroalkyl vinyl ether is preferably 3.0 mol% or less based on the total monomer units of the VdF / fluoroalkyl vinyl ether copolymer.

[0080] Examples of the monomer copolymerizable with VdF and fluoroalkyl vinyl ether include the above-mentioned fluorinated monomers, the above-mentioned non-fluorinated monomers, etc. Among them, the monomer copolymerizable with VdF and fluoroalkyl vinyl ether is preferably at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers, more preferably at least one selected from the group consisting of TFE, 2,3,3,3-tetrafluoropropene, and monomer (4), and even more preferably monomer (4).

[0081] The weight average molecular weight (polystyrene equivalent) of the VdF / fluoroalkyl vinyl ether copolymer is preferably 50,000 to 2,000,000, more preferably 80,000 to 1,700,000, and even more preferably 100,000 to 1,500,000.

[0082] The number average molecular weight (in terms of polystyrene) of the VdF / fluoroalkyl vinyl ether copolymer is preferably 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and even more preferably 50,000 to 1,200,000.

[0083] The content of the copolymer in the electrode-forming composition is preferably 0.1 to 20 mass %, more preferably 0.2 to 10 mass %, and even more preferably 0.5 to 3 mass %, relative to the mass of the electrode-forming composition.

[0084] <Solvent> The solvent contained in the electrode-forming composition of the present disclosure is represented by general formula (1): The solvent used in the present disclosure is preferably a solvent that is liquid at 20°C.

[0085] General formula (1): (In the formula, R １ , R ２ and R ３ are independently H or a monovalent substituent, provided that R １ , R ２ and R ３ The total number of carbon atoms in R is 6 or more, １ , R ２ and R ３ At least one of R is an organic group having a carbonyl group.１ , R ２ and R ３ Any two of them may be bonded to form a ring.)

[0086] R １ , R ２ and R ３ The total number of carbon atoms in R is 6 or more. １ , R ２ and R ３ The types of groups are selected so that the total number of carbon atoms in R is 6 or more. １ , R ２ and R ３ The upper limit of the total carbon number is not limited, but may be 16 or less, 14 or less, or 12 or less.

[0087] R １ , R ２ and R ３ are independently H or a monovalent substituent. The monovalent substituent is preferably an alkyl group, an alkoxyalkyl group, an acylalkyl group, an alkenyl group, an amino group, an aminoalkyl group, or a cycloalkyl group.

[0088] R １ , R ２ and R ３ At least one of the above is an organic group having a carbonyl group. The organic group having a carbonyl group is preferably an acyl group. The acyl group is represented by the general formula: -CO-R ４ (In the formula, R ４ is an alkyl group having 1 to 6 carbon atoms). When the alkyl group has 3 or more carbon atoms, it may be linear or branched. ４ When the alkyl group has two or more carbon atoms, it may contain a heteroatom such as an oxygen atom or a nitrogen atom, or a carbonyl group between the carbon atoms.

[0089] R １ , R ２ and R ３Any two of these may be bonded to form a ring. The ring may contain a heteroatom such as an oxygen atom as a constituent atom. The ring is preferably a saturated ring. The number of members in the ring is not particularly limited, but 5 or 6 members are preferred. The ring is preferably a pyrrolidine ring, an oxazoline ring, a piperidine ring, or a morpholine ring.

[0090] The solvent is preferably a solvent represented by general formula (1a).

[0091] General formula (1a): (In the formula, R １ａ is a monovalent substituent, and R ２ａ and R ３ａ are independently H or a monovalent substituent, with the proviso that R １ａ , R ２ａ and R ３ａ The total number of carbon atoms in R is 5 or more. １ａ , R ２ａ and R ３ａ Any two of them may be bonded to form a ring.)

[0092] In general formula (1a), R １ａ , R ２ａ and R ３ａ The total number of carbon atoms in R is 5 or more. １ａ , R ２ａ and R ３ａ The type of each group is selected so that the total number of carbon atoms in R is 5 or more. １ａ , R ２ａ and R ３ａ The upper limit of the total carbon number is not limited, but may be 15 or less, 13 or less, or 11 or less.

[0093] In general formula (1a), R １ａ is a monovalent substituent. The monovalent substituent is preferably an alkyl group, an alkoxyalkyl group, an acylalkyl group, an alkenyl group, an amino group, an aminoalkyl group, or a cycloalkyl group, and more preferably an alkyl group, an alkoxyalkyl group, an acylalkyl group, an alkenyl group, an amino group, or an aminoalkyl group.

[0094] In general formula (1a), R ２ａ and R ３ａare independently H or a monovalent substituent. ２ａ and R ３ａ As the monovalent substituent, an alkyl group, an alkoxyalkyl group, an acylalkyl group, an alkenyl group, an amino group, an aminoalkyl group, or a cycloalkyl group is preferable, and an alkyl group, an alkoxyalkyl group, a cycloalkyl group, or an alkenyl group is more preferable.

[0095] R １ａ , R ２ａ and R ３ａ Any two of R may be bonded to form a ring. ２ａ and R ３ａ is bonded to form R ２ａ and R ３ａ is preferably bonded to a nitrogen atom to form a ring. The ring may contain a heteroatom such as an oxygen atom as a constituent atom. The ring is preferably a saturated ring. The number of members in the ring is not particularly limited, but 5 or 6 members are preferred. The ring is preferably a pyrrolidine ring, oxazoline ring, piperidine ring, or morpholine ring.

[0096] The solvent is more preferably at least one selected from the group consisting of solvents represented by general formula (1b-1) and solvents represented by general formula (1b-2).

[0097] General formula (1b-1): (In the formula, R １ｂ is an alkyl group, an alkoxyalkyl group, an acylalkyl group, an alkenyl group, an amino group, or an aminoalkyl group; R ２ｂ and R ３ｂ are independently an alkyl group or an alkoxyalkyl group, and R １ｂ , R ２ｂ and R ３ｂ The total number of carbon atoms in R is 5 or more. ２ｂ and R ３ｂ are bonded to each other to form R ２ｂ and R ３ｂ may form a ring together with the nitrogen atom to which it is bonded, and the ring may contain an oxygen atom as a constituent atom.

[0098] General formula (1b-2): wherein ring A is a 5- or 6-membered amide ring, and R ４ｂ is an alkyl group, a cycloalkyl group, or an alkenyl group, and rings A and R ４ｂ The total number of carbon atoms is 5 or more.

[0099] In general formula (1b-1), R １ｂ , R ２ｂ and R ３ｂ The total number of carbon atoms in R is 5 or more. １ｂ , R ２ｂ and R ３ｂ The type of each group is selected so that the total number of carbon atoms in R is 5 or more. １ｂ , R ２ｂ and R ３ｂ The upper limit of the total carbon number is not limited, but may be 15 or less, 13 or less, or 11 or less.

[0100] In general formula (1b-1), R １ｂ is an alkyl group, an alkoxyalkyl group, an acylalkyl group, an alkenyl group, an amino group, or an aminoalkyl group.

[0101] R １ｂ The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms. When the alkyl group has 3 or more carbon atoms, it may be linear or branched.

[0102] R １ｂ The alkoxyalkyl group of the general formula: -R １ｂ１ -O-R １ｂ２ (In the formula, R １ｂ１ is an alkylene group having 1 to 5 carbon atoms, R １ｂ２ is an alkyl group having 1 to 5 carbon atoms). When the alkyl group or alkylene group has 3 or more carbon atoms, it may be linear or branched.

[0103] R １ｂ The acylalkyl group of the general formula: -R １ｂ３ -CO-R １ｂ４ (In the formula, R １ｂ３ is an alkylene group having 1 to 5 carbon atoms, R １ｂ４is an alkyl group having 1 to 5 carbon atoms). When the alkyl group or alkylene group has 3 or more carbon atoms, it may be linear or branched.

[0104] R １ｂ The alkenyl group of the general formula: -R １ｂ５ -CR １ｂ６ =CR １ｂ７ (In the formula, R １ｂ５ is a single bond or an alkylene group having 1 to 5 carbon atoms, R １ｂ６ and R １ｂ７ are independently H or an alkyl group having 1 to 5 carbon atoms. When the alkyl group or alkylene group has 3 or more carbon atoms, it may be linear or branched. As the alkenyl group, a vinyl group is preferred.

[0105] R １ｂ The amino group of the aminoalkyl group is a monovalent functional group formed by removing a hydrogen atom from ammonia, a primary amine, or a secondary amine. １ｂ is an amino group, R １ｂ can form an amide bond with the carbonyl group to which it is attached.

[0106] R １ｂ The amino group of the general formula: -N-(R １ｂ８ ) ２ (In the formula, R １ｂ８ is H or an alkyl group having 1 to 5 carbon atoms). When the alkyl group has 3 or more carbon atoms, it may be linear or branched. As the amino group, -N-(CH ３ ) ２ or -N-(C ２ H ５ ) ２ is preferred.

[0107] R １ｂ The aminoalkyl group of the general formula: -R １ｂ９ -N-(R １ｂ８ ) ２ (In the formula, R １ｂ９ is an alkylene group having 1 to 5 carbon atoms, R １ｂ８is H or an alkyl group having 1 to 5 carbon atoms. When the alkyl group or alkylene group has 3 or more carbon atoms, it may be linear or branched.

[0108] In general formula (1b-1), R ２ｂ and R ３ｂ is independently an alkyl group or an alkoxyalkyl group.

[0109] R ２ｂ and R ３ｂ The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms. When the alkyl group has 3 or more carbon atoms, it may be linear or branched.

[0110] R ２ｂ and R ３ｂ The alkoxyalkyl group of the general formula: -R ２ｂ１ -O-R ２ｂ２ (In the formula, R ２ｂ１ is an alkylene group having 1 to 5 carbon atoms, R ２ｂ２ is an alkyl group having 1 to 5 carbon atoms). When the alkyl group or alkylene group has 3 or more carbon atoms, it may be linear or branched.

[0111] R ２ｂ and R ３ｂ are bonded to each other to form R ２ｂ and R ３ｂ may form a ring together with the nitrogen atom to which it is bonded, and may contain an oxygen atom as a constituent atom of the ring. The ring is preferably a saturated ring. The number of members in the ring is not particularly limited, but 5 or 6 members are preferred. The ring is preferably a pyrrolidine ring, oxazoline ring, piperidine ring, or morpholine ring.

[0112] In general formula (1b-2), ring A and R ４ｂ The total number of carbon atoms in ring A and R is 5 or more. ４ｂ The types of rings and groups are selected so that the total number of carbon atoms in ring A and R is 5 or more. ４ｂ The upper limit of the total carbon number is not limited, but may be 15 or less, 13 or less, or 11 or less.

[0113] Ring A is a 5- or 6-membered amide ring. Therefore, ring A is composed of a carbon atom, a nitrogen atom, and an alkylene group having 3 to 4 carbon atoms. The hydrogen atoms bonded to the carbon atoms of the alkylene group constituting ring A may or may not be substituted with a substituent, but it is preferable that they are not substituted with a substituent. Examples of the substituent include an alkyl group such as a methyl group.

[0114] R ４ｂ is an alkyl group, a cycloalkyl group, or an alkenyl group.

[0115] R ４ｂ The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms. When the alkyl group has 3 or more carbon atoms, it may be linear or branched.

[0116] R ４ｂ The cycloalkyl group is preferably a cycloalkyl group having a carbon number of 3 to 10. The cycloalkyl group is preferably a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, or a cyclooctyl group.

[0117] R ４ｂ The alkenyl group of the general formula: -R ４ｂ１ -CR ４ｂ２ =CR ４ｂ３ (In the formula, R ４ｂ１ is a single bond or an alkylene group having 1 to 5 carbon atoms, R ４ｂ２ and R ４ｂ３ are independently H or an alkyl group having 1 to 5 carbon atoms. When the alkyl group or alkylene group has 3 or more carbon atoms, it may be linear or branched. As the alkenyl group, a vinyl group is preferred.

[0118] The solvent is preferably at least one selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone (NEP), N-butyl-2-pyrrolidone (NBP), acryloylmorpholine, N-cyclohexyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 3-butoxy-N,N-dimethylpropanamide, N,N,N',N'-tetraethylurea, N,N-dimethylacetoacetamide, N-octyl-2-pyrrolidone, and N,N-diethylacetamide.

[0119] Among these, at least one solvent selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone, and N-butyl-2-pyrrolidone is more preferred. In particular, when an electrode-forming composition containing 3-methoxy-N,N-dimethylpropanamide is used as the solvent, the amount of gas generated by the resulting battery tends to be suppressed. In particular, when an electrode-forming composition containing N-ethyl-2-pyrrolidone (NEP) is used as the solvent, the high-temperature storage capacity retention rate of the resulting battery tends to be high. In particular, when an electrode-forming composition containing N-butyl-2-pyrrolidone (NBP) is used as the solvent, the resistance of the resulting battery tends to be less likely to increase.

[0120] The amount of solvent in the electrode-forming composition is determined in consideration of the coatability onto the current collector, the thin film formability after drying, etc. Usually, the ratio of copolymer to solvent is 0.5:99.5 to 20:80 by mass.

[0121] <Other Components> The electrode-forming composition of the present disclosure preferably further contains a powdered electrode material.

[0122] The powder electrode material is a powder electrode material used in batteries and preferably contains an electrode active material. Electrode active materials are divided into positive electrode active materials and negative electrode active materials. In the case of lithium-ion secondary batteries, the positive electrode active material is not particularly limited as long as it is capable of electrochemically absorbing and desorbing lithium ions, but lithium composite oxides are preferred, and lithium transition metal composite oxides are more preferred. Lithium-containing transition metal phosphate compounds are also preferred as the positive electrode active material. It is also preferred that the positive electrode active material be a substance containing lithium and at least one transition metal, such as a lithium transition metal composite oxide or a lithium-containing transition metal phosphate compound.

[0123] The transition metal of the lithium transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc., and a specific example of the lithium transition metal composite oxide is LiCoO ２ Lithium-cobalt composite oxides such as LiNiO ２ Lithium-nickel composite oxides such as LiMnO ２ , LiMn ２ O ４ , Li ２ MnO ３ and lithium-manganese composite oxides in which a part of the transition metal atoms that constitute the main part of these lithium transition metal composite oxides has been substituted with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, etc. Examples of the above-mentioned substituted oxides include lithium-nickel-manganese composite oxide, lithium-nickel-cobalt-aluminum composite oxide, lithium-nickel-cobalt-manganese composite oxide, lithium-manganese-aluminum composite oxide, and lithium-titanium composite oxide, and more specifically, LiNi ０．５ Mn ０．５ O ２ , LiNi ０．８５ Co ０．１０ Al ０．０５ O ２ , LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ , LiNi ０．５ Mn ０．３ Co ０．２O ２ , LiNi ０．６ Mn ０．２ Co ０．２ O ２ , LiNi ０．８ Mn ０．１ Co ０．１ O ２ , LiMn １．８ Al ０．２ O ４ , LiMn １．５ Ni ０．５ O ４ , Li ４ Ti ５ O １２ , LiNi ０．８２ Co ０．１５ Al ０．０３ O ２ etc.

[0124] The transition metal of the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, or the like. Specific examples of the lithium-containing transition metal phosphate compound include LiFePO ４ , Li ３ Fe ２ (P.O. ４ ) ３ , LiFeP ２ O ７ Iron phosphates such as LiCoPO ４ and lithium transition metal phosphate compounds in which a part of the transition metal atoms constituting the main component of these compounds is substituted with another metal such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, or Si.

[0125] In particular, from the viewpoint of high voltage, high energy density, charge / discharge cycle characteristics, etc., LiCoO ２ , LiNiO ２ , LiMn ２ O ４ , LiNi ０．８２ Co ０．１５ Al ０．０３ O ２ , LiNi ０．３３ Mn ０．３３ Co ０．３３ O ２ , LiNi ０．５ Mn ０．３Co ０．２ O ２ , LiNi ０．６ Mn ０．２ Co ０．２ O ２ , LiNi ０．８ Mn ０．１ Co ０．１ O ２ , LiFePO ４ is preferred.

[0126] As the lithium transition metal composite oxide, a lithium-nickel composite oxide is preferred, and the lithium transition metal composite oxide is represented by the general formula (7): ｙ Ni １－ｘ M ｘ O ２ (wherein x is 0.01≦x≦0.5, y is 0.9≦y≦1.2, and M represents a metal atom (excluding Li and Ni).) Such lithium transition metal composite oxides with a high nickel content are useful for increasing the capacity of secondary batteries.

[0127] In the general formula (7), x is a coefficient satisfying 0.01≦x≦0.5, and since a secondary battery with an even higher capacity can be obtained, it is preferable that 0.05≦x≦0.4, and more preferably 0.10≦x≦0.3.

[0128] In general formula (7), examples of the metal atom of M include V, Ti, Cr, Mn, Fe, Co, Cu, Al, Zn, Mg, Ga, Zr, Si, etc. Preferred metal atoms of M are transition metals such as V, Ti, Cr, Mn, Fe, Co, and Cu, or combinations of the above transition metals with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mg, Ga, Zr, and Si.

[0129] Lithium transition metal composite oxides with a high nickel content include LiNi ０．８０ Co ０．１５ Al ０．０５ O ２ , LiNi ０．８２ Co ０．１５ Al ０．０３ O ２ , LiNi ０．３３ Mn ０．３３ Co０．３３ O ２ , LiNi ０．５ Mn ０．３ Co ０．２ O ２ , LiNi ０．６ Mn ０．２ Co ０．２ O ２ , LiNi ０．８ Mn ０．１ Co ０．１ O ２ , and LiNi ０．９０ Mn ０．０５ Co ０．０５ O ２ At least one selected from the group consisting of LiNi is preferred. ０．８２ Co ０．１５ Al ０．０３ O ２ , LiNi ０．６ Mn ０．２ Co ０．２ O ２ , and LiNi ０．８ Mn ０．１ Co ０．１ O ２ At least one selected from the group consisting of:

[0130] Furthermore, a substance having a different composition from the substance constituting the main positive electrode active material may be attached to the surface of the positive electrode active material. Examples of the surface-attached substance include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide, sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate, and carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate.

[0131] These surface-attaching substances can be attached to the surface of the positive electrode active material by, for example, a method of dissolving or suspending the surface-attaching substance precursor in a solvent, adding the substance to the positive electrode active material by impregnation, and drying the solvent; a method of dissolving or suspending the surface-attaching substance precursor in a solvent, adding the substance to the positive electrode active material by impregnation, and then reacting the substance by heating or the like; a method of adding the substance to the positive electrode active material precursor and simultaneously baking the substance; or the like.

[0132] The amount of the surface-attached substance is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more by mass relative to the positive electrode active material, and is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less by mass relative to the positive electrode active material. The surface-attached substance can suppress the oxidation reaction of the nonaqueous electrolyte on the surface of the positive electrode active material and improve the battery life, but if the amount of attachment is too small, the effect will not be fully exerted, and if it is too large, the movement of lithium ions into and out of the positive electrode active material will be hindered, which may increase the resistance.

[0133] The particle shape of the positive electrode active material may be a block, polyhedron, sphere, ellipsoid, plate, needle, column, or the like, as conventionally used. Among these, those formed by aggregation of primary particles to form secondary particles, with the secondary particles being spherical or ellipsoidal, are preferred. Typically, electrochemical devices experience expansion and contraction of the active material in the electrode during charging and discharging, which can lead to deterioration, such as destruction of the active material or disconnection of the conductive path, due to stress. Therefore, a material formed by aggregation of primary particles to form secondary particles is preferred over a single-particle active material consisting of only primary particles, as this relieves the stress of expansion and contraction and prevents deterioration. Furthermore, spherical or ellipsoidal particles are preferred over plate-like equiaxially oriented particles because they are less oriented during electrode molding, resulting in less expansion and contraction of the electrode during charging and discharging, and are also more easily mixed uniformly with the conductive agent during electrode fabrication.

[0134] The tap density of the positive electrode active material is usually 1.3 g / cm ３ or more, preferably 1.5 g / cm ３ More preferably, 1.6 g / cm ３ or more, most preferably 1.7 g / cm ３That is all. If the tap density of the positive electrode active material is below the above lower limit, the amount of dispersion medium required when forming the positive electrode material layer increases, and the amounts of conductive agent and copolymer required also increase, which may restrict the filling rate of the positive electrode active material in the positive electrode material layer and limit the battery capacity. By using a metal composite oxide powder with a high tap density, a high-density positive electrode material layer can be formed. Generally, the higher the tap density, the more preferable it is, and there is no particular upper limit. However, if it is too high, the diffusion of lithium ions in the positive electrode material layer using the nonaqueous electrolyte as a medium becomes rate-limiting, which may lead to a decrease in load characteristics. Therefore, the tap density is usually set to 2.5 g / cm. ３ or less, preferably 2.4 g / cm ３ The following is the result.

[0135] The tap density of the positive electrode active material is determined by passing it through a sieve with an opening of 300 μm and measuring 20 cm ３ After dropping a sample into the tapping cell to fill the cell volume, tapping is performed 1,000 times with a stroke length of 10 mm using a powder density measuring device (for example, Tap Denser manufactured by Seishin Enterprise Co., Ltd.), and the density obtained from the volume and weight of the sample at that time is defined as the tap density.

[0136] The median diameter d50 of the positive electrode active material particles (the secondary particle diameter when primary particles are aggregated to form secondary particles) is usually 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, and most preferably 3 μm or more, and usually 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, and most preferably 15 μm or less. Below the lower limit, a high bulk density product may not be obtained. Above the upper limit, the diffusion of lithium within the particles takes time, resulting in a decrease in battery performance. Also, problems such as streaking may occur when preparing a battery positive electrode, i.e., when the active material, conductive agent, copolymer, etc. are slurried with a solvent and applied as a thin film. Mixing two or more positive electrode active materials with different median diameters d50 can further improve the filling properties during positive electrode preparation.

[0137] The median diameter d50 in the present disclosure is measured using a known laser diffraction / scattering particle size distribution analyzer. When using a HORIBA LA-920 particle size distribution analyzer, the measurement is performed using a 0.1% by mass aqueous solution of sodium hexametaphosphate as the dispersion medium, and after ultrasonic dispersion for 5 minutes, the measurement is performed with a measurement refractive index set to 1.24.

[0138] When primary particles aggregate to form secondary particles, the average primary particle diameter of the positive electrode active material is typically 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.08 μm or more, and most preferably 0.1 μm or more, and typically 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and most preferably 0.6 μm or less. If the average diameter exceeds the upper limit, it is difficult to form spherical secondary particles, which can adversely affect powder packing and significantly reduce the specific surface area, potentially resulting in a decrease in battery performance, such as output characteristics. Conversely, if the average diameter is below the lower limit, problems such as poor charge / discharge reversibility due to underdeveloped crystals can occur. The primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, the average diameter is determined by taking a 10,000x magnification photograph of 50 random primary particles and calculating the longest intercept of a horizontal line at the left and right boundaries of the primary particles.

[0139] The BET specific surface area of ​​the positive electrode active material is 0.2 m ２ / g or more, preferably 0.3m ２ / g or more, more preferably 0.4m ２ / g or more, 4.0m ２ / g or less, preferably 2.5m ２ / g or less, more preferably 1.5m ２ If the BET specific surface area is smaller than this range, the battery performance is likely to deteriorate, whereas if it is larger, it becomes difficult to increase the tap density, which may easily cause problems with the coating properties when forming the positive electrode material layer.

[0140] The BET specific surface area is defined as a value measured by a surface area meter (for example, a fully automatic surface area measuring device manufactured by Ohkura Riken) using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3, after which the sample is pre-dried at 150°C for 30 minutes under a nitrogen flow, by a nitrogen adsorption BET single-point method based on a gas flow method.

[0141] As a method for producing a positive electrode active material, a general method for producing an inorganic compound is used. In particular, various methods can be considered for producing a spherical or oval-spherical active material. For example, a transition metal raw material such as a transition metal nitrate or sulfate, and optionally raw materials of other elements, are dissolved or pulverized and dispersed in a solvent such as water, and the pH is adjusted while stirring to produce and recover a spherical precursor, which is then dried as necessary, and then dispersed in a solvent such as LiOH, Li ２ CO ３ , LiNO ３ a method of adding a Li source such as LiOH or LiO, and baking at a high temperature to obtain an active material; a method of dissolving or pulverizing and dispersing transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, and oxides, and, if necessary, raw materials of other elements, in a solvent such as water, and drying and molding the resulting material using a spray dryer or the like to obtain a spherical or oval-spherical precursor, to which LiOH, Li, ２ CO ３ , LiNO ３ and the like, and calcining at high temperature to obtain an active material. Also, a method of adding a transition metal source material such as a transition metal nitrate, sulfate, hydroxide, or oxide, and LiOH, Li ２ CO ３ , LiNO ３ and the like, and, if necessary, raw materials of other elements, in a solvent such as water, and then drying and molding the resulting solution using a spray dryer or the like to form a spherical or oval spherical precursor, which is then fired at a high temperature to obtain an active material.

[0142] In the present disclosure, one type of positive electrode active material powder may be used alone, or two or more types having different compositions or different powder properties may be used in any combination and ratio.

[0143] The negative electrode active material is not particularly limited as long as it can electrochemically absorb and release lithium ions, and examples thereof include carbonaceous materials, metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alone, lithium alloys such as lithium-aluminum alloys, and metals capable of forming alloys with lithium, such as Sn and Si. These may be used alone or in any combination and ratio of two or more. Among these, carbonaceous materials or lithium composite oxides are preferably used from the viewpoint of safety.

[0144] The metal composite oxide is not particularly limited as long as it is capable of absorbing and releasing lithium, but it is preferable that the metal composite oxide contains titanium and / or lithium as a constituent component from the viewpoint of high current density charge / discharge characteristics.

[0145] Examples of carbonaceous materials include: (1) natural graphite, (2) artificial carbonaceous substances and artificial graphitic substances; carbonaceous substances (for example, natural graphite, coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, or oxidized versions of these pitches, needle coke, pitch coke, and carbon materials obtained by partially graphitizing these pitches, furnace black, acetylene black, pitch-based carbon fiber, and other organic pyrolysis products; carbonizable organic substances (for example, coal tar pitch ranging from soft pitch to hard pitch, coal-based heavy oils such as carbonized liquefied oil, atmospheric residue, vacuum residue, straight-run heavy oils, cracked petroleum heavy oils such as ethylene tar produced as a by-product during the thermal decomposition of crude oil, naphtha, etc.); aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, and phenanthrene; N-ring compounds such as phenazine and acridine; S-ring compounds such as thiophene and bithiophene; biphenyl, terphenyl; carbonaceous materials obtained by heat-treating at least once in the range of 400 to 3200°C any of the following: polyphenylenes such as phenylenes, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insolubilized products thereof, nitrogen-containing organic polymers such as polyacrylonitrile and polypyrrole, sulfur-containing organic polymers such as polythiophenes and polystyrene, natural polymers such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, and polysaccharides represented by saccharose, thermoplastic resins such as polyphenylene sulfide and polyphenylene oxide, and thermosetting resins such as furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin), and charcoals thereof, or solutions of carbonizable organic substances dissolved in low-molecular organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane, and charcoals thereof; (3) a carbonaceous material in which the negative electrode layer is made of carbonaceous matter having at least two or more different types of crystallinity and / or has an interface where carbonaceous matter of the different crystallinity contacts, and (4) a carbonaceous material in which the negative electrode layer is made of carbonaceous matter having at least two or more different types of orientation and / or has an interface where carbonaceous matter of the different orientations contacts, is preferred because it has a good balance between initial irreversible capacity and high current density charge / discharge characteristics.

[0146] The content of the electrode active material (positive electrode active material or negative electrode active material) in the electrode-forming composition is preferably 40 mass % or more in order to increase the capacity of the resulting electrode.

[0147] The powder electrode material may further contain a conductive agent, such as carbon blacks such as acetylene black and ketjen black, carbon materials such as graphite, carbon fiber, carbon nanotubes, carbon nanohorns, and graphene.

[0148] The ratio of the powder electrode material (active material and conductive agent) to the above-mentioned copolymer in the electrode-forming composition is usually about 80:20 to 99.5:0.5 by mass, and is determined taking into consideration the retention of the powder components, adhesion to the current collector, and conductivity of the electrode.

[0149] The electrode-forming composition may contain, for example, acrylic resins such as polyacrylic acid, polymethacrylate, and polymethyl methacrylate, polyimide, polyamide, and polyamideimide resins, styrene rubber, butadiene rubber, and styrene-butadiene rubber.

[0150] The electrode-forming composition may contain a dispersant such as a resin having a surface-active effect, a cationic surfactant, or a nonionic surfactant in order to improve the slurry stability.

[0151] The electrode-forming composition can be prepared by dispersing and mixing the powder electrode material in a solution or dispersion in which the copolymer is dissolved or dispersed in a solvent. The resulting electrode-forming composition is then uniformly applied to a current collector such as a metal foil or metal mesh, dried, and pressed as necessary to form a thin electrode material layer on the current collector, resulting in a thin-film electrode. Alternatively, the copolymer and the electrode material powder may be mixed first, and then a solvent may be added to prepare the electrode-forming composition.

[0152] The electrode-forming composition of the present disclosure can be suitably used as a material for forming electrodes of batteries such as secondary batteries and capacitors. The battery may be a primary battery, a storage battery (secondary battery), or a storage element. The battery may be a nonaqueous electrolyte battery. Nonaqueous electrolyte batteries include all batteries equipped with an electrolyte and a power generation element. Examples of nonaqueous electrolyte batteries include lithium ion primary batteries, lithium ion secondary batteries, nickel-metal hydride batteries, lithium ion capacitors, and electric double layer capacitors.

[0153] The electrode-forming composition of the present disclosure may be a positive electrode-forming composition used to prepare a positive electrode, or may be a negative electrode-forming composition used to prepare a negative electrode. The electrode material layer formed from the electrode-forming composition of the present disclosure may be a positive electrode material layer or a negative electrode material layer.

[0154] The electrode of the present disclosure includes a current collector and an electrode material layer. The electrode material layer is formed using the electrode-forming composition of the present disclosure and may be provided on one side or both sides of the current collector.

[0155] The electrode of the present disclosure includes an electrode material layer formed using the electrode-forming composition of the present disclosure, and therefore has excellent flexibility and conductivity, sufficient adhesion between the current collector and the electrode material layer, and can form a secondary battery with excellent battery characteristics.

[0156] The density of the electrode material layer is preferably 2.0 to 5.0 g / cm ３ and more preferably 2.5 to 4.5 g / cm ３ is.

[0157] The density of the electrode material layer can be calculated from the mass and volume of the electrode material layer.

[0158] The thickness of the electrode material layer is preferably 20 μm or more, more preferably 30 μm or more, even more preferably 40 μm or more, particularly preferably 45 μm or more, and preferably 170 μm or less, more preferably 150 μm or less, because even better battery characteristics can be obtained. The thickness of the electrode material layer may also be 85 μm or less, or may be less than 69 μm.

[0159] The thickness of the electrode material layer can be measured with a micrometer. In the present disclosure, the thickness of the electrode material layer is the thickness per side when the electrode material layer is provided on both sides of the current collector.

[0160] Examples of the current collector provided in the electrode of the present disclosure include metal foils or metal meshes made of iron, stainless steel, copper, aluminum, nickel, titanium, etc., and among these, aluminum foil is preferred.

[0161] The electrode of the present disclosure can be suitably produced by a production method in which the electrode-forming composition of the present disclosure is applied to a current collector. After the electrode-forming composition is applied, the coating film may be dried and the resulting dried coating film may be pressed.

[0162] The amount of the electrode-forming composition applied to the current collector is preferably 10 mg / cm ２ More preferably, 17.5 mg / cm ２ or more, preferably 60 mg / cm ２ More preferably, it is 50 mg / cm or less. ２ The coating amount of the electrode-forming composition is the dry weight of the electrode-forming composition per unit area.

[0163] <Secondary Battery> The present disclosure also provides a secondary battery including the above-described electrode.

[0164] The secondary battery of the present disclosure includes an electrode formed using the electrode-forming composition of the present disclosure, and therefore has a high high-temperature storage capacity retention rate, a low amount of gas generation, and is less likely to increase in resistance.

[0165] The secondary battery of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and preferably one or both of the positive electrode and the negative electrode are the above-described electrodes. The secondary battery of the present disclosure also includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and preferably the positive electrode is the above-described electrode. A separator may be interposed between the positive electrode and the negative electrode.

[0166] The non-aqueous electrolyte is not particularly limited, but one or more of known solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate can be used. Any of the conventionally known electrolytes can be used, and LiClO ４ , LiAsF ６ , LiPF ６ , LiBF ４ , LiCl, LiBr, CH ３ SO ３ Li, CF ３ SO ３ Li, cesium carbonate, etc. can be used.

[0167] The electrode of the present disclosure has excellent flexibility and conductivity, has sufficient adhesion between the current collector and the electrode material layer, and can form a secondary battery with excellent battery characteristics, and therefore can be suitably used as an electrode for a wound-type secondary battery. In addition, the secondary battery of the present disclosure may be a wound-type secondary battery.

[0168] The electrode of the present disclosure is useful for nonaqueous electrolyte secondary batteries, not only for the lithium ion secondary batteries using the liquid electrolyte described above, but also for polymer electrolyte lithium secondary batteries, and is also useful for electric double layer capacitors.

[0169] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0170] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0171] The values ​​in the examples were measured by the following methods.

[0172] (Polymer Composition) The compositions of the copolymer and PVdF were measured by solution NMR. Measurement device: Varian VNMRS400 Resonance frequency: 376.04 (Sfrq) Pulse width: 30° (pw=6.8)

[0173] (Content of polar group-containing monomer units in polymer) The content of polar group-containing monomer units (acrylic acid units) was measured by acid-base titration of the carboxyl group. Specifically, approximately 0.5 g of copolymer was dissolved in acetone at a temperature of 70-80°C. 5 ml of water was added dropwise under vigorous stirring to avoid coagulation of the copolymer. Titration was carried out with a 0.1 N NaOH aqueous solution until complete neutralization of the acidity at a neutral transition of approximately -270 mV. From the measurement results, the amount of the polar group-containing monomer units contained in 1 g of copolymer was determined, and the content of the polar group-containing monomer units was calculated.

[0174] (Weight-average molecular weight) was measured by gel permeation chromatography (GPC) using Tosoh AS-8010, CO-8020, a column (three GMHHR-H columns connected in series) and Shimadzu RID-10A, and was calculated from data measured using dimethylformamide (DMF) as a solvent at a flow rate of 1.0 ml / min (reference: polystyrene).

[0175] Comparative Example 1 (Preparation of Electrode-Forming Composition (Binder Solution)) PVdF (VdF homopolymer) shown in Table 1 was added to 3-methoxy-N,N-dimethylpropanamide so as to give a concentration of 8 mass %, and the mixture was stirred at 25°C or 50°C for 24 hours. The state in which the PVdF dissolved was observed, and evaluated according to the following criteria.

[0176] <Solubility> 1. Not soluble. 2. Dissolves within 24 hours or more after heating (50°C). 3. Dissolves within 12 hours after heating (50°C). 4. Dissolves within 24 hours or more after heating (25°C). 5. Dissolves within 12 hours at room temperature (25°C).

[0177] (Preparation of electrode-forming composition (positive electrode mixture slurry)) The binder solution obtained above was mixed with a positive electrode active material (NMC622 (LiNi ０．６ Mn ０．２ Co ０．２ O ２) and a conductive agent (acetylene black) were added and thoroughly mixed with a stirrer to prepare a positive electrode mixture. The mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode mixture was 97 / 1.5 / 1.5. The solid content concentration in the positive electrode mixture was 75 mass%. The viscosity change rate of the obtained positive electrode mixture slurry was measured and evaluated according to the following criteria.

[0178] <Slurry stability> 1. Viscosity increase rate is 400% or more. 2. Viscosity increase rate is 350% or more and less than 400%. 3. Viscosity increase rate is 300% or more and less than 350%. 4. Viscosity increase rate is 200% or more and less than 300%. 5. Viscosity increase rate is less than 200%.

[0179] The viscosity increase rate was measured by the following method. Using a Brookfield DV2T type viscometer, the viscosity of the positive electrode mixture was measured 10 minutes after the start of measurement under the conditions of 25°C, spindle LV-04(64), and a rotation speed of 6 rpm. The viscosity increase rate (Xn) was calculated using the following formula from the viscosity (η0) of the positive electrode mixture measured immediately after preparation and the viscosity (ηn) 24 hours after preparation of the positive electrode mixture. Xn = ηn / η0 × 100 [%]

[0180] (Preparation of a Positive Electrode Having a Positive Electrode Material Layer on One Side) The obtained positive electrode mixture was applied to one side of a positive electrode current collector (aluminum foil having a thickness of 20 μm) in an amount of 22.5 mg / cm ２ After the 3-methoxy-N,N-dimethylpropanamide was completely evaporated, a pressure of 10 tons was applied using a roll press to press the mixture, thereby producing a positive electrode including a positive electrode material layer and a positive electrode current collector.

[0181] (Preparation of a positive electrode having a positive electrode material layer on both sides) The obtained positive electrode mixture was applied to both sides of a positive electrode current collector (aluminum foil having a thickness of 20 μm) in an amount of 30.0 mg / cm 2 per side. ２ After the 3-methoxy-N,N-dimethylpropanamide was completely evaporated, a pressure of 6 tons was applied using a roll press to press the mixture, thereby producing a positive electrode including a positive electrode material layer and a positive electrode current collector.

[0182] <Adhesion between the positive electrode material layer of the positive electrode and the positive electrode current collector> A 1.2 cm × 7.0 cm test piece was prepared by cutting out a positive electrode having a positive electrode material layer on one side. The positive electrode material layer side of the test piece was fixed to a movable jig with double-sided tape, and the tape was then attached to the surface of the positive electrode current collector. The peel strength was measured using an autograph to measure the stress (N / cm) when the tape was pulled at a 90-degree angle at a speed of 100 mm / min. A 1 N load cell was used for the autograph.

[0183] <Positive Electrode Flexibility> A 2 cm x 20 cm test piece was prepared by cutting a positive electrode having a positive electrode material layer on both sides. Using a cylindrical mandrel bending tester (manufactured by Allgood Co.), a 3 mm diameter mandrel was set in the tester, and the test piece was clamped and fixed with the main clamp. A roller was then brought close to the test piece, and the handle was rotated evenly 180° over 1 to 2 seconds. The positive electrode material layer was visually inspected and evaluated according to the following criteria: 2: No cracks were observed; 1: Cracks were observed, but no fracture of the positive electrode material layer was observed; 0: The positive electrode material layer was fractured.

[0184] <Conductivity> The positive electrode mixture was applied to a PET film using a doctor blade, and then dried, and the surface resistance of the coating was measured using a Loresta GP (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) (in accordance with JIS K7194).

[0185] (Preparation of Electrolyte Solution) Ethylene carbonate, a high-dielectric constant solvent, and ethyl methyl carbonate, a low-viscosity solvent, were mixed in a volume ratio of 30:70, and LiPF ６ was added to give a concentration of 1.0 mol / L, and 2 mass % of vinylene carbonate was added thereto to obtain a non-aqueous electrolyte solution.

[0186] (Fabrication of Lithium Ion Secondary Battery) A positive electrode having a positive electrode material layer on one side was cut into a shape having a coated portion (positive electrode material layer) 50 mm wide and 30 mm long and an uncoated portion 5 mm wide and 9 mm long.

[0187] To 98 parts by mass of artificial graphite, 1 part by mass of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose: 1% by mass) and 1 part by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50% by mass) were added as thickeners and binders, and the mixture was mixed in a disperser to form a slurry. The resulting slurry was applied to a copper foil of 20 μm in thickness, dried, and rolled in a press. The foil was then cut into a shape having a coated portion (negative electrode material layer) of 52 mm in width and 32 mm in length and an uncoated portion of 5 mm in width and 9 mm in length to form a negative electrode.

[0188] The positive electrode and the negative electrode were arranged to face each other with a 20 μm-thick microporous polyethylene film (separator) interposed therebetween, and the nonaqueous electrolyte solution obtained above was poured into the battery. After the nonaqueous electrolyte solution had sufficiently permeated the separator and the like, the battery was sealed, pre-charged, and aged to prepare a lithium ion secondary battery (aluminum laminate cell).

[0189] The resulting lithium ion secondary battery was evaluated for its high temperature storage capacity retention rate, gas amount change rate, and resistance increase rate.

[0190] [Initial Characteristic Evaluation] The lithium ion secondary battery was sandwiched between plates and pressurized, and then charged to 4.2 V at a constant current equivalent to 0.2 C at 25 ° C., and then discharged to 3.0 V at a constant current of 0.2 C. This was repeated for two cycles to stabilize the battery. In the third cycle, the battery was charged to 4.2 V at a constant current of 0.2 C, then charged at a constant voltage of 4.2 V until the current value reached 0.05 C, and then discharged to 3.0 V at a constant current of 0.2 C. In the fourth cycle, the battery was charged to 4.2 V at a constant current of 0.2 C, then charged at a constant voltage of 4.2 V until the current value reached 0.05 C, and then discharged to 3.0 V at a constant current of 0.2 C to determine the initial discharge capacity. The battery was then charged to 4.2 V at a constant current of 0.2 C, and then charged at a constant voltage of 4.2 V until the current value reached 0.05 C, and the initial resistance was measured. Here, 1C represents the current value that discharges the battery's reference capacity in 1 hour, 5C represents five times that current value, 0.1C represents 1 / 10 of that current value, and 0.2C represents 1 / 5 of that current value.

[0191] [High-Temperature Storage Test] After the initial characteristic evaluation, the lithium-ion secondary battery was stored at a high temperature of 85°C for 36 hours. After the battery was sufficiently cooled, the volume of the battery was measured using the Archimedes method, and the gas volume change rate was calculated from the volume change before and after high-temperature storage. Next, the battery was discharged at 0.5C to 3V at 25°C, and the remaining capacity after high-temperature storage was calculated. The high-temperature storage capacity retention rate (%) was calculated based on the following formula. The battery was further charged to 4.2V at a constant current of 0.2C, then charged at a constant voltage of 4.2V until the current value reached 0.05C, and then discharged at 0.5C to 3V. The battery was then charged to 4.2V at a constant current of 0.2C, and then charged at a constant voltage of 4.2V until the current value reached 0.05C. The resistance after high-temperature storage was measured, and the resistance increase rate (%) was calculated based on the following formula. High-temperature storage capacity retention rate (%) = (remaining capacity) / (initial discharge capacity) x 100 Gas volume change rate (%) = (volume after high-temperature storage (ml)) / (volume before high-temperature storage (ml)) x 100 Resistance increase rate (%) = (resistance after high-temperature storage (Ω)) / (initial resistance (Ω)) x 100

[0192] Examples 1 to 18 Electrode-forming compositions (binder solutions and positive electrode mixture slurries) were prepared in the same manner as in Comparative Example 1, except that copolymers (copolymers containing VdF units and other monomer units other than VdF) shown in Table 1 were used instead of PVdF (VdF homopolymer). Positive electrodes and lithium ion secondary batteries were fabricated and evaluated in the same manner as in Comparative Example 1.

[0193] The results are shown in Table 1.

[0194]

[0195] "Other monomer (α)" in Tables 1 to 4 refers to the type of other monomer (α) that forms the other monomer unit in a copolymer containing VdF units and other monomer units other than VdF. Also, "composition (mol %)" in Table 1 refers to the content (mol %) of VdF units and the content (mol %) of other monomer (α) units in PVdF (homopolymer) and the copolymer.

[0196] Examples 19 to 52 and Comparative Examples 2 to 10 Electrode-forming compositions (binder solutions and positive electrode mixture slurries) were prepared in the same manner as in Comparative Example 1 and Examples 1 to 18, except that the solvents shown in Tables 2 to 4 were used instead of 3-methoxy-N,N-dimethylpropanamide, and positive electrodes and lithium ion secondary batteries were fabricated and evaluated in the same manner as in Comparative Example 1. The results are shown in Tables 2 to 4.

[0197]

[0198]

[0199]

Claims

DEPCT6725 / 03 / 25671. Components for the construction of an electrode consisting of a copolymer composed of vinylidine fluoride units and units of other monomers other than vinylidine fluoride and a solvent, represented by the general formula (1). General formula (1):(chemical formula) where each R1, R2 and R3 are independently H or monovalent substituents, provided that the total number of carbon atoms of R1, R2 and R3 is 6 or more, and at least one of R1, R2 and R3 is an organic group with a carbonyl group, and any two of R1, R2 and R3 form bonds.

2. Components for the formation of an electrode according to claim 1, where the solvent is the solvent represented by the general formula (1a): General formula (1a): (chemical formula) where R1a is a monovalent substituent, R2a and R3a each are independent of H or monovalent substituents, provided that the total number of carbon atoms of R1a, R2a and R3a is 5 or more, and any two R1a, R2a and R3a bond together in a manner that is selective or absent to form a ring. 3.The components for constructing the electrodes according to claim 1 or 2, where at least one solvent is chosen from a group of solvents represented by general formulas (1b-1) and solvents represented by general formulas (1b-2). General formula (1b-1): (chemical formula) where R1b is an alkyl, alkoxyalkyl, acylalkyl, alkenyl, amino, or aminoalkyl group, R2b and R3b each independently are alkyl or alkoxyalkyl groups, and the total number of carbon atoms of R1b, R2b and R3b are R3b has 5 or more atoms and R2b and R3b form selective bonds to each other to form a ring with the nitrogen atom to which R2b and R3b are attached, and the ring has oxygen atoms as its constituents in a selective manner. General formula (1b-2):(chemical formula)where ring A is a 5 or 6 member amide ring, R4b is an alkyl, cycloalkyl or alkenyl group, and the total number of carbon atoms of rings A and R4b is 5 or more.4.The components for electrode construction under any of the claims 1 through 3, where at least one solvent is selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone and N-butyl-2-pyrrolidone.

5. The components for electrode construction under any of the claims 1 through 4, where at least one other monomer is selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, (meth)acrylic acid, 2,3,3,3-tetrafluoropropine, hexafluoroethylene.

6. Electrode construction components under any of Patents 1 through 5, where the amount of other monomer units in the copolymer is between 0.0001 and 50.0 mol / % based on the total monomer units.

7. Electrode construction components under any of Patents 1 through 6, which are further incorporated with powdered electrode material.

8. Electrode construction components under Patent 7, where the powdered electrode material incorporates oxides of lithium transition metal compounds. 9.

10. An electrode consisting of a current receiver and electrode material layers provided on one or each of the two sides of the current receiver and constructed from the electrode elements under any of the claims 1 through 9.

11. A secondary battery consisting of electrodes under claim 10.