Electrode-forming composition, electrode, and secondary battery

Abstract

The present invention provides a composition for forming an electrode, the composition containing: a copolymer which contains a vinylidene fluoride unit and a monomer unit other than vinylidene fluoride; and a solvent which is represented by general formula (1) NR1R2R3 (wherein each of R1, R2 and R3 independently represents H or a monovalent substituent, provided that the total number of carbon atoms in R1, R2 and R3 is 6 or more; at least one of R1, R2 and R3 represents an organic group having a carbonyl group; and any two of R1, R2 and R3 may combine with each other to form a ring).

Description

[Technical Field]

[0001] This disclosure relates to an electrode-forming composition, an electrode, and a secondary battery. [Background technology]

[0002] The electrodes of electrochemical devices such as lithium-ion batteries can be formed, for example, by dissolving electrode material and 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 semicrystalline copolymer [polymer (A)] containing repeating units derived from vinylidene fluoride (VDF) monomer and hydrophilic (meth)acrylic monomer (MA) represented by a specific chemical formula, wherein the copolymer [polymer (A)] contains 0.05 to 10 mol% of repeating units derived from the hydrophilic (meth)acrylic monomer (MA) and is characterized by a fraction of at least 40% of randomly distributed units (MA), a powdered electrode material, and optionally, a conductivity-imparting additive and / or a viscosity modifier.

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

[0005] Patent Document 3 describes the preparation of a positive electrode for electrochemical cycle experiments by coating aluminum foil with a slurry containing 92.5% by mass of a cathode active substance suspended in N-ethyl-2-pyrrolidinone (NEP), 2% by mass of graphite, 2% by mass of super C65 carbon black, and 3.5% by mass of polyvinylidene fluoride (PVdF) binder. [Prior art documents] [Patent Documents]

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the present disclosure, there is provided an electrode-forming composition containing a solvent different from conventional organic solvents, which can be easily prepared, has excellent slurry stability, forms a coating layer that adheres strongly to a metal foil and is also excellent in flexibility and conductivity, and by using a metal foil provided with such a coating layer as an electrode of a battery, it is possible to realize a battery having a high high-temperature storage capacity retention rate, a small gas generation amount, and a low resistance increase tendency. The object is to provide an electrode-forming composition.

Means for Solving the Problems

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

[0009] General formula (1):

Chemical formula

[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): [ka] (In the formula, R 1a is a monovalent substituent, R 2a and R 3a R is independently an H or monovalent substituent, however R 1a , R 2a and R 3a The total number of carbon atoms is 5 or more. 1a , R 2a and R 3a (Two of these may be joined together to form a ring.)

[0012] In the electrode-forming composition of the present disclosure, it is preferable that the solvent is 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): [ka] (In the formula, R 1b R is an alkyl group, alkoxyalkyl group, acylalkyl group, alkenyl group, amino group, or aminoalkyl group. 2b and R 3b R is independently an alkyl group or an alkoxyalkyl group. 1b , R 2b and R 3b The total number of carbon atoms is 5 or more. 2b and R 3b They combine with each other, R 2b and R 3bIt may form a ring 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): [ka] (In the formula, ring A is a 5-membered or 6-membered amide ring, 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, it is preferable that the solvent is 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 compositions of this disclosure, it is preferable that the other monomer is at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, (meth)acrylic acid, 2,3,3,3-tetrafluoropropene, hexafluoropropylene, and fluoroalkyl vinyl ethers. In the electrode-forming composition of this disclosure, it is preferable that the content of other monomer units in the copolymer is 0.0001 to 50.0 mol% relative to the total monomer units. The electrode-forming composition of this disclosure preferably further contains a powder electrode material. In the electrode-forming composition of this disclosure, it is preferable that the powder electrode material contains a lithium transition metal composite oxide. The electrode-forming composition of this disclosure is preferably a positive electrode-forming composition.

[0016] Furthermore, the present disclosure provides an electrode comprising a current collector and an electrode material layer provided on one or both sides of the current collector and formed from the electrode-forming composition described above.

[0017] Furthermore, this disclosure provides a secondary battery comprising the electrodes described above. [Effects of the Invention]

[0018] According to this disclosure, an electrode-forming composition containing a solvent different from conventional organic solvents can be prepared very easily, has excellent slurry stability, adheres firmly to metal foil, and can form a coating layer that is also excellent in flexibility and conductivity. By using metal foil having such a coating layer as an electrode in a battery, it is possible to realize a battery with a high high-temperature storage capacity retention rate, low gas generation, and resistance that does not increase easily. [Modes for carrying out the invention]

[0019] The following describes specific embodiments of this disclosure in detail, but this disclosure is not limited to the embodiments described below.

[0020] The electrode-forming compositions of this disclosure contain copolymers containing vinylidene fluoride (VdF) units and other monomer units other than VdF, and solvents having a specific chemical structure.

[0021] Patent Document 1 describes an electrode-forming composition comprising a linear semicrystalline copolymer containing repeating units derived from vinylidene fluoride monomer and a hydrophilic (meth)acrylic monomer represented by a specific chemical formula. In this electrode-forming composition, it is preferable to use 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), as the organic solvent.

[0022] Furthermore, as an organic solvent for the electrode-forming composition, Patent Document 2 describes the use of a β-alkoxypropionamide solvent, 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 does not dissolve or disperse easily in the organic solvent, and the slurry stability of the resulting electrode-forming composition is not sufficient.

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

[0024] General formula (1): [ka] (In the formula, R 1 , R 2 and R 3 R is independently an H or monovalent substituent, however R 1 , R 2 and R 3 The total number of carbon atoms is 6 or more, R 1 , R 2 and R 3 At least one of them is an organic group having a carbonyl group. 1 , R 2 and R 3 (Two of these may be joined together to form a ring.)

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

[0026] <Copolymer> The copolymer contained in the electrode-forming composition of this disclosure contains VdF units and other monomer units other than VdF. The other monomers may be fluorinated monomers or non-fluorinated monomers. Because the copolymer contained in the electrode-forming composition of this disclosure contains other monomer units other than VdF in addition to VdF units, it dissolves more readily in the solvent represented by general formula (1) than VdF homopolymers that have been conventionally used as binders.

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

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

[0029] As the fluorinated monomer, at least one selected from the group consisting of TFE, CTFE, 2,3,3,3-tetrafluoropropene, HFP, and fluoroalkyl vinyl ether is preferred, more preferably at least one selected from the group consisting of TFE and HFP, and TFE is particularly preferred, because it can form an electrode material layer with even better flexibility and adhesion to the current collector, and can form a secondary battery with even better battery characteristics.

[0030] Fluorinated monomers (except VdF) may or may not have polar groups.

[0031] Examples of non-fluorinated monomers include non-fluorinated monomers that do not have polar groups, such as ethylene and propylene, and non-fluorinated monomers that have polar groups (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 providing even better adhesion between the coated layer and the metal foil. The polar group is preferably at least one selected from the group consisting of carbonyl group-containing groups, epoxy groups, hydroxyl groups, sulfonic acid groups, sulfate groups, phosphoric acid groups, amino groups, amide groups, and alkoxy groups; more preferably at least one selected from the group consisting of carbonyl group-containing groups, epoxy groups, and hydroxyl groups; and even more preferably a carbonyl group-containing group. The hydroxyl group mentioned above does not include hydroxyl groups that constitute part of the carbonyl group-containing group. Furthermore, the amino group mentioned above is a monovalent functional group obtained by removing hydrogen from ammonia, a primary or secondary amine.

[0033] The carbonyl group-containing group mentioned above is a functional group having a carbonyl group (-C(=O)-). The carbonyl group-containing group is preferably a group represented by the general formula: -COOR (where R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group) or a carboxylic acid anhydride group, and more preferably a group represented by the general formula: -COOR. 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 groups represented by the general formula: -COOR include -COOCH2CH2OH, -COOCH2CH(CH3)OH, -COOCH(CH3)CH2OH, -COOH, -COOCH3, -COOC2H5, etc. If the group represented by the general formula: -COOR is -COOH or contains -COOH, then -COOH may be a carboxylate salt such as a metal carboxylate salt or an ammonium carboxylate salt.

[0034] Furthermore, the carbonyl group-containing group may also be a group represented by the general formula: -X-COOR (where X is an atomic group whose main chain consists of 1 to 20 atoms and has a molecular weight of 500 or less, and R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group). 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.

[0035] The amide group described above is preferably a group represented by the general formula: -CO-NRR' (where 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”- (where R represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group).

[0036] The above polar group-containing monomers include hydroxyalkyl (meth)acrylates such as hydroxyethyl acrylate and 2-hydroxypropyl acrylate; alkylidenemalonate esters such as dimethyl methylidenemalonate; 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 monomethyl maleate, monoethyl maleate, monomethyl citraconic acid, and monoethyl citraconic acid; general formula (4): [ka] (In the formula, R 11 ~R 13 R independently represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. 14 Y represents a single bond or a hydrocarbon group with 1 to 8 carbon atoms. 1 represents an inorganic cation and / or an organic cation. Examples include monomers represented by (4); unsaturated dibasic acids such as maleic acid, maleic anhydride, citraconic acid, and citraconic anhydride; etc.

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

[0038] In general formula (4), Y 1 '' represents inorganic cations and / or organic cations. Examples of inorganic cations include H, Li, Na, K, Mg, Ca, Al, and Fe. Examples of organic cations include NH4 and NH3R. 15 NH2R 15 2. NHR 15 3. NR 15 4(R15 Each independently represents an alkyl group having 1 to 4 carbon atoms. Examples of cations include Y. 1 Preferred cations are H, Li, Na, K, Mg, Ca, Al, and NH4; more preferred are H, Li, Na, K, Mg, Al, and NH4; even more preferred are H, Li, Al, and NH4; and particularly preferred is H. For convenience, specific examples of inorganic and organic cations are listed without symbols or valencies.

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

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

[0041] The monomer (4) is preferably at least one selected from the group consisting of (meth)acrylic acid and its salts, vinylacetic acid (3-butenic acid) and its salts, 3-pentenoic acid and its salts, 4-pentenoic acid and its salts, 3-hexenoic acid and its salts, 4-heptenoic acid and its salts, and 5-hexenoic acid and its salts.

[0042] Other preferred monomers include at least one selected from the group consisting of TFE, CTFE, (meth)acrylic acid, 2,3,3,3-tetrafluoropropene, HFP, and fluoroalkyl vinyl ethers. (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, relative to the total monomer units.

[0044] The VdF unit content of 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, relative to the total monomer units.

[0045] When the copolymer contains fluorinated monomer units as other monomer units, the content of fluorinated monomer units 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, and particularly preferably 35.0 mol% or less, relative to the total monomer units.

[0046] When the copolymer contains fluorinated monomer units as other monomer units, the VdF unit content of 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, and particularly preferably 96.0 mol% or less, based on the total monomer units.

[0047] When the copolymer contains non-fluorinated monomer units such as polar group-containing monomers as other monomer units, the content of non-fluorinated monomer units 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, even more preferably 3.0 mol% or less, and particularly preferably 1.5 mol% or less, relative to the total monomer units.

[0048] When the copolymer contains non-fluorinated monomer units as other monomer units, the VdF unit content of 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, relative to the total monomer units.

[0049] In this disclosure, the composition of the copolymer is, for example, 19 It can be measured by 1F-NMR. Furthermore, if the copolymer contains polar group-containing monomer units as other monomer units, the content of polar group-containing monomer units can be measured, for example, by acid-base titration of the acid group if the polar group is an acidic group such as a carboxylic acid.

[0050] The weight-average molecular weight (in 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 the solvent.

[0051] The number-average molecular weight (in 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, even 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 the solvent.

[0052] Examples of copolymers 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. Examples include copolymers, VdF / TFE / 3-butenoic acid copolymers, VdF / TFE / HFP / (meth)acrylic acid copolymers, VdF / TFE / HFP / 4-pentenoic acid copolymers, VdF / TFE / HFP / 3-butenoic acid copolymers, VdF / TFE / 2-carboxyethyl acrylate copolymers, VdF / TFE / HFP / 2-carboxyethyl acrylate copolymers, VdF / TFE / acryloyloxyethyl succinic acid copolymers, and VdF / TFE / HFP / acryloyloxyethyl succinic acid copolymers.

[0053] As the copolymer, 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 is preferred.

[0054] The VdF / TFE copolymer contains VdF units and TFE units. By using the VdF / TFE copolymer as the copolymer, an electrode-forming composition can be formed very easily, an electrode-forming composition with excellent slurry stability can be obtained, and a coating layer with excellent flexibility can be formed. The VdF unit content 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, relative to the total monomer units of the VdF / TFE copolymer. The TFE unit content 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, relative to the total monomer units of the VdF / TFE copolymer.

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

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

[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 the VdF / CTFE copolymer as the copolymer, an electrode-forming composition can be formed very easily, and a coating layer that adheres extremely firmly to the 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, relative to 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, relative to the total monomer units of the VdF / CTFE copolymer.

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

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

[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 extremely firmly to the metal foil can be formed. The content of (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%, relative to the total monomer units.

[0065] The VdF unit content of 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%, relative to the total monomer units.

[0066] The weight-average molecular weight (in 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, and 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 VdF unit content 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, relative to the total monomer units of the VdF / 2,3,3,3-tetrafluoropropene copolymer. 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, even more preferably 40.0 mol% or less, and particularly preferably 35.0 mol% or less, relative to the total monomer units of the VdF / TFE copolymer.

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

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

[0071] The weight-average molecular weight (on a polystyrene basis) 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 extremely firmly to the metal foil can be formed. The VdF unit content 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, relative to the total monomer units of the VdF / HFP copolymer. The HFP unit content 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, relative to the total monomer units of the VdF / HFP copolymer.

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

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

[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 (polystyrene equivalent) 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 VdF unit content 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, relative to the total monomer units of the VdF / fluoroalkyl vinyl ether copolymer. The fluoroalkyl vinyl ether unit content 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, relative to the total monomer units of the VdF / fluoroalkyl vinyl ether copolymer.

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

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

[0081] The weight-average molecular weight (on a polystyrene basis) 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 (on a polystyrene basis) 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 copolymer content in the electrode-forming composition is preferably 0.1 to 20% by mass, more preferably 0.2 to 10% by mass, and even more preferably 0.5 to 3% by mass, relative to the mass of the electrode-forming composition.

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

[0085] General formula (1): [ka] (In the formula, R 1 , R 2 and R 3 These are independently H or monovalent substituents, However, R1 and R 2 and R 3 have a total carbon number of 6 or more, and R 1 and R 2 and R 3 at least one of which is an organic group having a carbonyl group. R 1 and R 2 and R 3 Any two of them may be bonded to form a ring.)

[0086] R 1 and R 2 2 and R 3 have a total carbon number of 6 or more. That is, R 1 and R [[ID=??]] 2 and R 3 are selected in terms of the type of the group so that the total carbon number becomes 6 or more. R 1 [[ID=??]] 2 ? and R 2 and R 3 The upper limit of the total carbon number of is not limited, but may be 16 or less, 14 or less, or 12 or less.

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

[0088] [[ID=??]] 1 R 1 and R 2 and R 3 at least one of which is an organic group having a carbonyl group. Preferred organic groups having a carbonyl group include an acyl group. As the acyl group, a group represented by the general formula: -CO-R 4 (wherein R 4 [[ID=??]] 4 ? is an alkyl group having 1 to 6 carbon atoms) is preferred. When the alkyl group has 3 or more carbon atoms, it may be linear or branched. When the alkyl group of R 4 has 2 or more carbon atoms, it may contain a heteroatom such as an oxygen atom or a nitrogen atom or a carbonyl group between carbon-carbon atoms. There seems to be some inconsistent or incorrect tags in the original text which have been marked with "??" in the translation for clarification. Please check and correct the original text if possible.

[0089] R 1 、R 2 and R 3 Any two of them may combine to form a ring. Further, as the ring-constituting atoms, hetero atoms such as an oxygen atom may be included. The ring is preferably a saturated ring. The number of members of the ring is not particularly limited, but 5-membered or 6-membered is preferred. Preferred rings include a pyrrolidine ring, an oxazoline ring, a piperidine ring or a morpholine ring.

[0090] As the solvent, a solvent represented by the general formula (1a) is preferred.

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

[0092] In general formula (1a), the total carbon number of R 1a , R[[ID=4⑧]] 2a and R 3a is 5 or more. That is, the types of the groups of R 1a , R 2a and R<00001`11>are selected so that the total carbon number becomes 5 or more. The upper limit of the total carbon number of R 1a , R 2a and R 3a is not limited, but may be 15 or less, 13 or less, or 11 or less.

[0093] In general formula (1a), R 1ais a monovalent substituent. Preferred monovalent substituents are alkyl groups, alkoxyalkyl groups, acylalkyl groups, alkenyl groups, amino groups, aminoalkyl groups, or cycloalkyl groups, and more preferably alkyl groups, alkoxyalkyl groups, acylalkyl groups, alkenyl groups, amino groups, or aminoalkyl groups.

[0094] In general formula (1a), R 2a and R 3a R is independently either H or a monovalent substituent. 2a and R 3a Among these, monovalent substituents are preferred independently. Preferred monovalent substituents are alkyl groups, alkoxyalkyl groups, acylalkyl groups, alkenyl groups, amino groups, aminoalkyl groups, or cycloalkyl groups, and more preferably alkyl groups, alkoxyalkyl groups, cycloalkyl groups, or alkenyl groups.

[0095] R 1a , R 2a and R 3a Any two of them may be joined together to form a ring. In particular, R 2a and R 3a They combine, R 2a and R 3a It is preferable that a ring is formed together with the nitrogen atom to which it is bonded. The ring may also contain heteroatoms such as oxygen atoms. The ring is preferably a saturated ring. The number of members in the ring is not particularly limited, but 5-membered or 6-membered rings are preferred. Preferred rings are pyrrolidine rings, oxazoline rings, piperidine rings, or morpholine rings.

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

[0097] General formula (1b-1): [ka] (In the formula, R 1bR is an alkyl group, alkoxyalkyl group, acylalkyl group, alkenyl group, amino group, or aminoalkyl group. 2b and R 3b R is independently an alkyl group or an alkoxyalkyl group. 1b , R 2b and R 3b The total number of carbon atoms is 5 or more. 2b and R 3b They combine with each other, R 2b and R 3b It may form a ring 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): [ka] (In the formula, ring A is a 5-membered or 6-membered amide ring, 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 is 5 or more. That is, R 1b , R 2b and R 3b The types of groups are selected such that the total number of carbon atoms is 5 or more. 1b , R 2b and R 3b There is no upper limit on the total number of carbon atoms, but it may be 15 or less, 13 or less, or 11 or less.

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

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

[0102] R 1b As for alkoxyalkyl groups, the general formula is: -R 1b1 -OR 1b2 (In the formula, R 1b1 R is an alkylene group having 1 to 5 carbon atoms. 1b2 A group represented by (where is an alkyl group having 1 to 5 carbon atoms) is preferred. If the alkyl group and alkylene group have 3 or more carbon atoms, they may be linear or branched.

[0103] R 1b The acylalkyl group is of the general formula: -R 1b3 -CO-R 1b4 (In the formula, R 1b3 R is an alkylene group having 1 to 5 carbon atoms. 1b4 A group represented by (where is an alkyl group having 1 to 5 carbon atoms) is preferred. If the alkyl group and alkylene group have 3 or more carbon atoms, they may be linear or branched.

[0104] R 1b The alkenyl group is, in general formula: -R 1b5 -CR 1b6 =CR 1b7 (In the formula, R 1b5 R is a single bond or an alkylene group having 1 to 5 carbon atoms. 1b6 and R 1b7 The group is preferably one that is independently represented by H or an alkyl group having 1 to 5 carbon atoms. If the alkyl group and alkylene group have 3 or more carbon atoms, they may be linear or branched. A vinyl group is preferred as the alkenyl group.

[0105] R 1b The amino groups and aminoalkyl groups are monovalent functional groups obtained by removing hydrogen from ammonia, primary or secondary amines. 1b If it is an amino group, R 1bIt can form an amide bond with the carbonyl group to which it is bonded.

[0106] R 1b The amino group is of the general formula: -N-(R 1b8 )2(wherein, R 1b8 A group represented by (where is H or an alkyl group having 1 to 5 carbon atoms) is preferred. If the alkyl group has 3 or more carbon atoms, it may be linear or branched. As the amino group, -N-(CH3)2 or -N-(C2H5)2 is preferred.

[0107] R 1b The aminoalkyl group is, in general formula: -R 1b9 -N-(R 1b8 )2(wherein, R 1b9 R is an alkylene group having 1 to 5 carbon atoms. 1b8 A group represented by (where is H or an alkyl group having 1 to 5 carbon atoms) is preferred. If the alkyl group and alkylene group have 3 or more carbon atoms, they may be linear or branched.

[0108] In general formula (1b-1), R 2b and R 3b These are independently alkyl groups or alkoxyalkyl groups.

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

[0110] R 2b and R 3b As for alkoxyalkyl groups, the general formula is: -R 2b1 -OR 2b2 (In the formula, R 2b1 R is an alkylene group having 1 to 5 carbon atoms. 2b2 A group represented by (where is an alkyl group having 1 to 5 carbon atoms) is preferred. If the alkyl group and alkylene group have 3 or more carbon atoms, they may be linear or branched.

[0111] R 2b and R 3b They combine with each other, R 2b and R 3b The nitrogen atom to which it is bonded may form a ring, and the ring may contain 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-membered or 6-membered rings are preferred. Preferred rings are pyrrolidine rings, oxazoline rings, piperidine rings, or morpholine rings.

[0112] In general formula (1b-2), rings A and R 4b The total number of carbon atoms is 5 or more. That is, rings A and R 4b The types of rings and groups are selected such that the total number of carbon atoms is 5 or more. Rings A and R 4b There is no upper limit on the total number of carbon atoms, but it may be 15 or less, 13 or less, or 11 or less.

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

[0114] R 4b This 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. If the alkyl group has 3 or more carbon atoms, it may be linear or branched.

[0116] R 4b As the cycloalkyl group, a cycloalkyl group having 3 to 10 carbon atoms is preferred. As the cycloalkyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, or a cyclooctyl group is preferred.

[0117] R 4b The alkenyl group is, in general formula: -R 4b1 -CR 4b2 =CR 4b3 (In the formula, R 4b1 R is a single bond or an alkylene group having 1 to 5 carbon atoms. 4b2 and R 4b3 The group is preferably one that is independently represented by H or an alkyl group having 1 to 5 carbon atoms. If the alkyl group and alkylene group have 3 or more carbon atoms, they may be linear or branched. A vinyl group is preferred as the alkenyl group.

[0118] As a solvent, 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-dimethylacetacetamide, N-octyl-2-pyrrolidone, and N,N-diethylacetamide is preferred.

[0119] As a solvent, at least one 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 a solvent, the amount of gas generated in the resulting battery tends to be suppressed. In particular, using an electrode-forming composition containing N-ethyl-2-pyrrolidone (NEP) as a solvent tends to result in a higher retention rate of high-temperature storage capacity of the resulting battery. 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 not to increase significantly.

[0120] The amount of solvent in the electrode-forming composition is determined considering factors such as the ease of application to the current collector and the ability to form a thin film after drying. Typically, the ratio of copolymer to solvent is 0.5:99.5 to 20:80 by mass.

[0121] <Other ingredients> The electrode-forming composition of this disclosure preferably further contains a powder electrode material.

[0122] The powder electrode material is a powder electrode material used in batteries, and preferably contains an electrode active material. The electrode active material is divided into a positive electrode active material and a negative electrode active material. In the case of lithium-ion secondary batteries, there are no particular restrictions on the positive electrode active material as long as it is electrochemically capable of intercalating and releasing 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 preferable that the positive electrode active material is 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 metals used in lithium transition metal composite oxides are preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples of lithium transition metal composite oxides include lithium-cobalt composite oxides such as LiCoO2, lithium-nickel composite oxides such as LiNiO2, lithium-manganese composite oxides such as LiMnO2, LiMn2O4, and Li2MnO3, and those in which some of the transition metal atoms that make up the main body of these lithium transition metal composite oxides are substituted with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, and Si. Examples of the above substitutions include lithium-nickel-manganese composite oxides, lithium-nickel-cobalt-aluminum composite oxides, lithium-nickel-cobalt-manganese composite oxides, lithium-manganese-aluminum composite oxides, lithium-titanium composite oxides, and more specifically, LiNi 0.5 Mn 0.5 O2, LiLiLi 0.85 Co 0.10 Al0.05 O2, LiLiLi 0.33 Co 0.33 Mn 0.33 O2, LiLiLi 0.5 Mn 0.3 Co 0.2 O2, LiLiLi 0.6 Mn 0.2 Co 0.2 O2, LiLiLi 0.8 Mn 0.1 Co 0.1 O2, LiMn 1.8 Al 0.2 O4, LiMn 1.5 Ni 0.5 O4, Li4Ti5O 12 Li Limited 0.82 Co 0.15 Al 0.03 Examples include O2.

[0124] Preferred transition metals for lithium-containing transition metal phosphate compounds include V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples of lithium-containing transition metal phosphate compounds include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, cobalt phosphates such as LiCoPO4, and those in which some of the transition metal atoms that make up the main component of these lithium transition metal phosphate compounds are substituted with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si.

[0125] In particular, from the viewpoint of high voltage, high energy density, or charge / discharge cycle characteristics, LiCoO2, LiNiO2, LiMn2O4, LiNi 0.82 Co 0.15 Al 0.03 O2, LiLiLi 0.33 Mn 0.33 Co 0.33 O2, LiLiLi 0.5 Mn 0.3 Co 0.2 O2, LiLiLi 0.6 Mn 0.2 Co 0.2 O2, LiLiLi 0.8 Mn 0.1 Co 0.1O2 and LiFePO4 are preferred.

[0126] Furthermore, lithium-nickel composite oxides are preferred as lithium transition metal composite oxides, and the general formula is (7): General formula (7): Li y Ni 1-x M x O2 (In the formula, x is 0.01 ≤ x ≤ 0.5, y is 0.9 ≤ y ≤ 1.2, and M represents a metal atom (excluding Li and Ni).) Lithium-nickel composite oxides represented by [formula] are more preferable. Lithium transition metal composite oxides with such a high nickel content are beneficial for increasing the capacity of secondary batteries.

[0127] In general formula (7), x is a coefficient that satisfies 0.01 ≤ x ≤ 0.5, and more preferably 0.05 ≤ x ≤ 0.4, and even more preferably 0.10 ≤ x ≤ 0.3, in order to obtain a secondary battery with higher capacity.

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

[0129] LiNi 0.80 Co 0.15 Al 0.05 O2, LiLiLi 0.82 Co 0.15 Al 0.03 O2, LiLiLi 0.33 Mn 0.33 Co 0.33 O2, LiLiLi 0.5 Mn 0.3 Co 0.2 O2, LiLiLi 0.6 Mn 0.2 Co 0.2 O2, LiLiLi0.8 Mn 0.1 Co 0.1 O2 and LiNi 0.90 Mn 0.05 Co 0.05 Preferably, at least one selected from the group consisting of O2, and LiNi 0.82 Co 0.15 Al 0.03 O2, LiLiLi 0.6 Mn 0.2 Co 0.2 O2 and LiNi 0.8 Mn 0.1 Co 0.1 At least one selected from the group consisting of O2 is more preferable.

[0130] Furthermore, it is also possible to use positive electrode active materials in which a substance with a different composition from the main component of the positive electrode active material is attached to its surface. Examples of surface-attached substances 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-adhering substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent and impregnating them into the positive electrode active material, followed by drying; dissolving or suspending a surface-adhering substance precursor in a solvent and impregnating it into the positive electrode active material, then reacting it by heating or other means; or adding it to the positive electrode active material precursor and simultaneously firing it.

[0132] The amount of surface-adhered material is preferably 0.1 ppm or more, more preferably 1 ppm or more, even more preferably 10 ppm or more, and 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-adhered material can suppress the oxidation reaction of the non-aqueous electrolyte on the surface of the positive electrode active material, thereby improving battery life. However, if the amount of adhesion is too small, the effect will not be fully realized, and if it is too large, it may hinder the movement of lithium ions in and out, potentially increasing resistance.

[0133] The particle shapes of the positive electrode active material can be conventionally shaped, such as lumpy, polyhedral, spherical, ellipsoidal, plate-shaped, needle-shaped, or columnar. However, among these, it is preferable that the active material is composed of primary particles that aggregate to form secondary particles, and that these secondary particles are spherical or ellipsoidal in shape. Normally, in electrochemical elements, the active material in the electrode expands and contracts with charging and discharging, making it susceptible to deterioration such as destruction of the active material or breakage of the conductive path due to this stress. Therefore, it is preferable to have an active material in which primary particles aggregate to form secondary particles rather than a single-particle active material consisting only of primary particles, as this reduces the stress of expansion and contraction and prevents deterioration. Furthermore, spherical or ellipsoidal particles are preferable to plate-shaped equiaxially oriented particles because they require less orientation during electrode molding, resulting in less expansion and contraction of the electrode during charging and discharging, and they are also easier to mix uniformly with the conductive agent when manufacturing the electrode.

[0134] The tap density of the positive electrode active material is typically 1.3 g / cm³. 3 Preferably 1.5 g / cm³ 3 More preferably 1.6 g / cm³ 3 In summary, the most preferred amount is 1.7 g / cm³. 3The above is a summary. If the tap density of the positive electrode active material falls below the above lower limit, the amount of dispersion medium required during the formation of the positive electrode material layer increases, as does the amount of conductive agent and copolymer required, which may restrict the packing rate of the positive electrode active material into the positive electrode material layer and limit the battery capacity. By using metal composite oxide powder with a high tap density, a high-density positive electrode material layer can be formed. Generally, a higher tap density is preferable and there is no particular upper limit, but if it is too high, the diffusion of lithium ions using the non-aqueous electrolyte as a medium within the positive electrode material layer becomes the rate-limiting factor, and the load characteristics tend to deteriorate, so it is usually 2.5 g / cm³. 3 Preferably, 2.4 g / cm³ 3 The following applies:

[0135] The tap density of the positive electrode active material was determined by passing it through a sieve with a mesh size of 300 μm over 20 cm. 3 After dropping the sample into the tapping cell to fill the cell volume, a powder density analyzer (for example, TapDenser manufactured by Seishin Corporation) is used to perform 1000 taps with a stroke length of 10 mm. 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 (or secondary particle diameter if primary particles aggregate to form secondary particles) is typically 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, most preferably 3 μm or more, and typically 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, and most preferably 15 μm or less. If it falls below the lower limit, it may not be possible to obtain a high bulk density product, and if it exceeds the upper limit, the diffusion of lithium within the particles will take longer, which may lead to a decrease in battery performance or problems such as streaking when manufacturing the positive electrode of the battery, i.e., when the active material and conductive agent or copolymer are slurryed with a solvent and applied as a thin film. Here, by mixing two or more positive electrode active materials with different median diameters d50, the packing performance during positive electrode manufacturing can be further improved.

[0137] In this disclosure, the median diameter d50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using the HORIBA LA-920 as the particle size distribution analyzer, a 0.1% by mass aqueous solution of sodium hexametaphosphate is used as the dispersion medium during measurement, and the measurement is performed after ultrasonic dispersion for 5 minutes with a measurement refractive index of 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, 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. Exceeding the above upper limit makes it difficult to form spherical secondary particles, which can adversely affect powder packing properties and significantly reduce the specific surface area, potentially leading to a decrease in battery performance such as output characteristics. Conversely, below the above lower limit usually results in problems such as poor reversibility of charge and discharge due to underdeveloped crystals. The primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, it is determined by taking a photograph at 10,000x magnification, finding the longest value of the intercept between the left and right boundaries of the primary particle with respect to a horizontal line for any 50 primary particles, and taking the average value.

[0139] The BET specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g or more, preferably 0.3m 2 / g or more, more preferably 0.4m 2 For values ​​of / g or more, 4.0m 2 Less than or equal to / g, preferably 2.5m 2 / g or less, more preferably 1.5m 2 It is less than / g. If the BET specific surface area is smaller than this range, battery performance tends to decrease, and if it is larger, it becomes difficult to increase the tap density, which can easily cause problems with coating when forming the positive electrode material layer.

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

[0141] For the production of positive electrode active materials, general methods for producing inorganic compounds are used. In particular, various methods can be considered for producing spherical or ellipsoidal active materials. For example, a method is to dissolve or grind and disperse transition metal raw materials such as transition metal nitrates and sulfates, and raw materials of other elements as needed, in a solvent such as water, adjust the pH while stirring to produce and recover spherical precursors, dry them as needed, and then add a Li source such as LiOH, Li2CO3, or LiNO3 and calcine at a high temperature to obtain the active material. Alternatively, a method is to dissolve or grind transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, and oxides, and raw materials of other elements as needed, in a solvent such as water. One method involves dispersing the material, drying and molding it with a spray dryer or the like to form a spherical or ellipsoidal precursor, adding a Li source such as LiOH, Li2CO3, or LiNO3, and firing it at a high temperature to obtain the active material. Another method involves dissolving or pulverizing and dispersing transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, or oxides, a Li source such as LiOH, Li2CO3, or LiNO3, and raw materials of other elements as needed, in a solvent such as water, drying and molding the mixture with a spray dryer or the like to form a spherical or ellipsoidal precursor, and firing it at a high temperature to obtain the active material.

[0142] In this disclosure, the positive electrode active material powder may be used alone, or two or more powders with 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 is electrochemically capable of intercalating and releasing lithium ions. Examples include carbonaceous materials, metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alloys such as elemental lithium and lithium-aluminum alloy, and metals that can form alloys with lithium, such as Sn and Si. These may be used individually or in any combination and ratio of two or more. Among these, carbonaceous materials or lithium composite oxides are preferred from a safety standpoint.

[0144] As for the metal composite oxide, there are no particular limitations as long as it can intercalate and release lithium, but it is preferable from the viewpoint of high current density charge-discharge characteristics that it contains titanium and / or lithium as constituent components.

[0145] As for carbonaceous materials, (1) Natural graphite, (2) Artificial carbonaceous materials and artificial graphitic materials; carbonaceous materials {for example, natural graphite, coal coke, petroleum coke, coal pitch, petroleum pitch, or these pitches that have been oxidized, needle coke, pitch coke and carbon materials which have been partially graphitized, furnace black, acetylene black, pitch-based carbon fibers and other pyrolysis products of organic materials, and carbonizable organic materials (for example, coal tar pitch from soft pitch to hard pitch, or coal-based heavy oil such as carbonized liquefied oil, straight-run heavy oil such as atmospheric residue and vacuum residue, crude oil, ethylene tar and other cracked petroleum heavy oil produced as by-products during the pyrolysis of naphtha, etc., as well as 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, terfe Polyphenylene (such as nyl), polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, immobilized products thereof, nitrogen-containing organic polymers such as polyacrylonitrile and polypyrrole, sulfur-containing organic polymers such as polythiophene 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, thermosetting resins such as furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin, and carbonized organic materials obtained by dissolving these or carbonizable organic materials in low molecular weight organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane, and carbonized materials obtained by heat-treating these carbonized materials once or more at a temperature range of 400 to 3200°C. (3) A carbonaceous material having a negative electrode material layer consisting of at least two different types of carbonaceous materials having different crystalline properties and / or an interface where these different crystalline carbonaceous materials are in contact, (4) A carbonaceous material having a negative electrode material layer consisting of at least two different orientations of carbonaceous material and / or an interface where the carbonaceous material with different orientations is in contact, Those selected from this range are preferable because they offer 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) is preferably 40% by mass or more in the electrode-forming composition in order to increase the capacity of the resulting electrode.

[0147] The above powder electrode material may further contain a conductive agent. Examples of conductive agents include carbon blacks such as acetylene black and Ketjenblack, carbon materials such as graphite, carbon fibers, carbon nanotubes, carbon nanohorns, and graphene.

[0148] The ratio of powder electrode material (active material and conductive agent) to the copolymer described above in the electrode-forming composition is usually around 80:20 to 99.5:0.5 by mass ratio, and is determined considering the retention of powder components, adhesion to the current collector, and the 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 polyamide-imide resins, styrene rubber, butadiene rubber, and styrene-butadiene rubber.

[0150] The electrode-forming composition may contain dispersants such as resins with surfactant properties, cationic surfactants, or nonionic surfactants to improve slurry stability.

[0151] One method for preparing an electrode-forming composition is to disperse and mix the powder electrode material in a solution or dispersion obtained by dissolving or dispersing a copolymer 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, thus creating a thin-film electrode. Alternatively, the copolymer and the powder electrode material may be mixed first, and then a solvent may be added to prepare the electrode-forming composition.

[0152] The electrode-forming compositions of this disclosure can be suitably used as materials for forming electrodes in batteries such as secondary batteries and capacitors. The battery may be a primary battery, a rechargeable battery (secondary battery), or an energy storage element. The battery may also be a non-aqueous electrolyte battery. Non-aqueous electrolyte batteries include all batteries that have an electrolyte and a power generation element. Examples of non-aqueous 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 this disclosure may be a positive electrode-forming composition used for the production of a positive electrode, or a negative electrode-forming composition used for the production of a negative electrode. The electrode material layer formed from the electrode-forming composition of this disclosure may be a positive electrode material layer or a negative electrode material layer.

[0154] <Electrode> The electrode of this disclosure comprises a current collector and an electrode material layer. The electrode material layer is formed using the electrode forming composition of this disclosure and may be provided on one side of the current collector or on both sides.

[0155] The electrode of this disclosure comprises an electrode material layer formed using the electrode-forming composition of this disclosure, and therefore exhibits excellent flexibility and conductivity, with 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 / cm³. 3 More preferably 2.5 to 4.5 g / cm³ 3 That is the case.

[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, preferably 170 μm or less, and more preferably 150 μm or less, in order to obtain even higher battery characteristics. The thickness of the electrode material layer may also be 85 μm or less, or less than 69 μm.

[0159] The thickness of the electrode material layer can be measured using a micrometer. In this 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 current collectors for the electrodes of this disclosure include metal foils or metal meshes made of iron, stainless steel, copper, aluminum, nickel, titanium, etc., with aluminum foil being preferred.

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

[0162] The amount of electrode-forming composition applied to the current collector is preferably 10 mg / cm². 2 The above is more preferable, and more preferably 17.5 mg / cm³ 2 The above is preferable to 60 mg / cm³. 2 The following is more preferable: 50 mg / cm³ 2 The following applies: The amount of electrode-forming composition applied is the dry weight of the electrode-forming composition per unit area.

[0163] <Secondary battery> Furthermore, this disclosure provides a secondary battery comprising the electrodes described above.

[0164] The secondary battery of this disclosure has electrodes formed using the electrode-forming composition of this disclosure, and therefore has a high high-temperature storage capacity retention rate, low gas generation, and resistance does not easily increase.

[0165] The secondary battery of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and it is preferable that one or both of the positive electrode and the negative electrode are the above-described electrodes. Further, the secondary battery of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and it is preferable that the positive electrode is the above-described electrode. Also, 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 known solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate can be used. Any conventionally known electrolyte can also be used, and LiClO4, LiAsF6, LiPF6, LiBF4, LiCl, LiBr, CH3SO3Li, CF3SO3Li, cesium carbonate, etc. can be used.

[0167] The electrode of the present disclosure is excellent in flexibility and conductivity, the current collector and the electrode material layer are sufficiently adhered, and it can form a secondary battery with excellent battery characteristics. Therefore, it can be suitably used as an electrode for a wound-type secondary battery. Further, the secondary battery of the present disclosure may be a wound-type secondary battery.

[0168] The electrode of the present disclosure is useful not only for a lithium-ion secondary battery using the above-described liquid electrolyte for a non-aqueous electrolyte secondary battery but also for a polymer electrolyte lithium secondary battery. It is also useful for an electric double layer capacitor.

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

Examples

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

[0171] Each value in the examples was measured by the following method.

[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 the 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 the 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 performed with a 0.1 N aqueous NaOH solution until the acidity was completely neutralized at a neutralization transition of approximately -270 mV. From the measurement results, the amount of polar group-containing monomer units contained in 1 g of copolymer was determined, and the content of polar group-containing monomer units was calculated.

[0174] (Weight average molecular weight) Measurements were taken using gel permeation chromatography (GPC). A Tosoh AS-8010, CO-8020, and column (three GMHHR-H columns connected in series) and a Shimadzu RID-10A were used. Dimethylformamide (DMF) was used as the solvent, flowing at a rate of 1.0 ml / min. The data (reference: polystyrene) were used for calculation.

[0175] Comparative Example 1 (Preparation of electrode-forming composition (binding agent solution)) The PVdF (VdF homopolymer) listed in Table 1 was added to 3-methoxy-N,N-dimethylpropanamide to a concentration of 8% by mass, and the mixture was stirred at 25°C or 50°C for 24 hours. The dissolution of PVdF was observed and evaluated according to the following criteria.

[0176] <Solubility> 1. Does not dissolve 2. Dissolve within 12 hours to 24 hours by heating (50°C). 3. Dissolve within 12 hours by heating (50°C). 4. Dissolve at room temperature (25°C) for more than 12 hours but within 24 hours. 5. Dissolve at room temperature (25°C) within 12 hours.

[0177] (Preparation of electrode-forming composition (positive electrode mixture slurry)) To the binder solution obtained above, add the positive electrode active material (NMC622(LiNi 0.6 Mn 0.2 Co 0.2 O2) and a conductive agent (acetylene black) were added and thoroughly mixed with a stirrer to prepare the 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% by 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 of 400% or more 2. Viscosity increase rate is 350% or more but less than 400% 3. Viscosity increase rate is 300% or more but less than 350% 4. Viscosity increase rate is 200% or more but less than 300% 5. Viscosity increase rate is less than 200%

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

[0180] (Fabrication of a positive electrode with a positive electrode material layer on one side) The obtained positive electrode active material was uniformly applied onto one side of a positive electrode current collector (aluminum foil with a thickness of 20 μm) such that the coating amount was 22.5 mg / cm 2 After 3-methoxy-N,N-dimethylpropanamide was completely volatilized, a positive electrode comprising a positive electrode material layer and a positive electrode current collector was fabricated by applying a pressure of 10 t using a roll press machine.

[0181] (Fabrication of a positive electrode having positive electrode material layers on both sides) The obtained positive electrode active material was uniformly applied onto both sides of a positive electrode current collector (aluminum foil with a thickness of 20 μm) such that the coating amount was 30.0 mg / cm per side 2 After 3-methoxy-N,N-dimethylpropanamide was completely volatilized, a positive electrode comprising a positive electrode material layer and a positive electrode current collector was fabricated by applying a pressure of 6 t using a roll press machine.

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

[0183] <Flexibility of the positive electrode> A test piece of 2 cm × 20 cm was fabricated by cutting out a positive electrode having positive electrode material layers on both sides. Using a cylindrical mandrel bending tester (manufactured by Allgood), after clamping and fixing the test piece to the tester with a mandrel of 3 mm in diameter set, the roller was brought close to the test piece, and when the handle was evenly rotated 180° over a period of 1 - 2 seconds, the positive electrode material layer was visually confirmed and evaluated according to the following criteria. 2: No cracks were observed. 1: Cracks were observed, but no breakage of the positive electrode material layer was observed. 0: The positive electrode material layer was broken.

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

[0185] (Preparation of electrolyte solution) A non-aqueous electrolyte was obtained by mixing ethylene carbonate, a high dielectric constant solvent, and ethyl methyl carbonate, a low viscosity solvent, in a volume ratio of 30 to 70, adding LiPF6 to a concentration of 1.0 mol / liter, and then adding 2% by mass of vinylene carbonate.

[0186] (Manufacturing of lithium-ion secondary batteries) A positive electrode, which has a positive electrode material layer on one side, was cut into a shape having a coated portion (positive electrode material layer) with a width of 50 mm and a length of 30 mm, and an uncoated portion with a width of 5 mm and a length of 9 mm.

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

[0188] The positive and negative electrodes described above were placed facing each other via a 20 μm thick microporous polyethylene film (separator), the non-aqueous electrolyte obtained above was injected, and after the non-aqueous electrolyte had sufficiently permeated the separator, etc., it was sealed, pre-charged and aged to produce a lithium-ion secondary battery (aluminum laminate cell).

[0189] The high-temperature storage capacity retention rate, gas volume change rate, and resistance increase rate of the obtained lithium-ion secondary batteries were evaluated.

[0190] [Initial characteristic evaluation] A lithium-ion secondary battery was charged to 4.2V at 25°C with a constant current equivalent to 0.2C while sandwiched between plates and under pressure. It was then discharged to 3.0V with a constant current of 0.2C. This process was repeated for two cycles to stabilize the battery. For the third cycle, the battery was charged to 4.2V with a constant current of 0.2C, then charged at a constant voltage of 4.2V until the current reached 0.05C, and then discharged to 3.0V with a constant current of 0.2C. Subsequently, for the fourth cycle, the battery was charged to 4.2V with a constant current of 0.2C, then charged at a constant voltage of 4.2V until the current reached 0.05C, and then discharged to 3.0V with a constant current of 0.2C to determine its initial discharge capacity. Afterward, the battery was charged to 4.2V with a constant current of 0.2C, then charged at a constant voltage of 4.2V until the current reached 0.05C, and its initial resistance was measured. Here, 1C represents the current value that discharges the battery's standard capacity in one hour, 5C represents five times that current value, 0.1C represents one-tenth of that current value, and 0.2C represents one-fifth of that current value.

[0191] [High-temperature storage test] Lithium-ion secondary batteries, after initial characteristic evaluation, were stored at a high temperature of 85°C for 36 hours. After the batteries had cooled sufficiently, their volume was measured using the Archimedes method, and the gas volume change rate was determined from the volume change before and after high-temperature storage. Next, the battery was discharged to 3V at 0.5C at 25°C to determine the remaining capacity after high-temperature storage, and the high-temperature storage capacity retention rate (%) was calculated based on the following formula. Furthermore, it was charged to 4.2V with a constant current of 0.2C, then charged again at a constant voltage of 4.2V until the current value was 0.05C, and then discharged to 3V at 0.5C. After that, it was charged to 4.2V with a constant current of 0.2C, then charged again at a constant voltage of 4.2V until the current value was 0.05C, and the resistance after high-temperature storage was measured, and the resistance increase rate (%) was calculated based on the following formula. High temperature storage capacity maintenance rate (%) = (residual capacity) / (initial discharge capacity) × 100 Gas volume change rate (%) = (Volume after high-temperature storage (ml)) / (Volume before high-temperature storage (ml)) × 100 Resistance increase rate (%) = (Resistance after high-temperature storage (Ω)) / (Initial resistance (Ω)) × 100

[0192] Examples 1-18 An electrode-forming composition (binding agent solution and positive electrode slurry) was prepared in the same manner as in Comparative Example 1, except that a copolymer (a copolymer containing VdF units and other monomer units other than VdF) listed in Table 1 was used instead of PVdF (VdF homopolymer). A positive electrode and a lithium-ion secondary battery were then fabricated and evaluated in the same manner as in Comparative Example 1.

[0193] The results are shown in Table 1.

[0194] [Table 1]

[0195] The term "other monomers (α)" in Tables 1-4 refers to the types of other monomers (α) that form other monomer units in copolymers containing VdF units and other monomer units other than VdF. Furthermore, the term "composition (mol%)" in Table 1 refers to the content (mol%) of VdF units and other monomer (α) units in the PVdF (homopolymer) and copolymer.

[0196] Examples 19-52, Comparative Examples 2-10 Except for using the solvents listed in Tables 2-4 instead of 3-methoxy-N,N-dimethylpropanamide, electrode-forming compositions (binding agent solution and positive electrode mixture slurry) were prepared in the same manner as in Comparative Example 1 and Examples 1-18. Positive electrodes and lithium-ion secondary batteries were then fabricated and evaluated in the same manner as in Comparative Example 1. The results are shown in Tables 2-4.

[0197] [Table 2]

[0198] Table 3

[0199] Table 4

Claims

1. An electrode-forming composition comprising a copolymer containing vinylidene fluoride units and other monomer units other than vinylidene fluoride, and at least one solvent selected from the group consisting of a solvent represented by general formula (1b-1) and a solvent represented by general formula (1b-2), An electrode-forming composition wherein the monomer other than vinylidene fluoride is at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, (meth)acrylic acid, 2,3,3,3-tetrafluoropropene, hexafluoropropylene, and fluoroalkyl vinyl ether. General formula (1b-1): 【Chemistry 13】 (wherein, R １ｂ is an alkoxyalkyl group represented by the general formula: -R １ｂ１ -O-R １ｂ２ (wherein, R １ｂ１ is an alkylene group having 1 to 3 carbon atoms, R １ｂ２ is an alkyl group having 1 to 3 carbon atoms), and R ２ｂ and R ３ｂ are each independently an alkyl group having 1 to 3 carbon atoms, and the total number of carbon atoms of R １ｂ , R ２ｂ and R ３ｂ is 5 or more.) General formula (1b-2): 【Chemistry 14】 (In the formula, ring A is a 5-membered amide ring, R ４ｂ This is an alkyl group having 2 to 4 carbon atoms, and rings A and R ４ｂ The total number of carbon atoms is 5 or more.

2. The electrode-forming composition according to claim 1, wherein the solvent is at least one selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone, and N-butyl-2-pyrrolidone.

3. The electrode-forming composition according to claim 1 or 2, wherein the content of other monomer units in the copolymer is 0.0001 to 50.0 mol% relative to the total monomer units.

4. The electrode-forming composition according to claim 1 or 2, further comprising a powder electrode material.

5. The electrode-forming composition according to claim 4, wherein the powder electrode material contains a lithium transition metal composite oxide.

6. The electrode forming composition according to claim 1 or 2, which is a composition for forming a positive electrode.

7. An electrode comprising a current collector and an electrode material layer provided on one or both sides of the current collector, formed from the electrode-forming composition described in claim 1 or 2.

8. A secondary battery comprising the electrode described in claim 7.

Images