Electrode mixture, active material mixture, binder solution, production method for electrode mixture, production method for electrode, electrode, and secondary battery

Abstract

This electrode mixture comprises: an oxime; a vinylidene fluoride polymer having at least 50 mol% of a vinylidene fluoride-derived constitutional unit; an electrode active material; and carbon black having an average primary particle diameter of at most 30 nm.

Description

Electrode mixture, active material mixture, binder solution, method for manufacturing electrode mixture, method for manufacturing electrode, electrode, and secondary battery

[0001] The present invention relates to an electrode mixture, an active material mixture for an electrode mixture, a binder solution, a method for producing an electrode mixture, a method for producing an electrode, an electrode, and a secondary battery.

[0002] Electrodes for secondary batteries, including lithium-ion secondary batteries, have a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer is produced by applying a slurry-like electrode mixture containing a binder and an electrode active material to the current collector and drying the applied electrode mixture. A conductive additive such as carbon black may be blended into the electrode mixture to improve the electrical properties of the battery.

[0003] Electrode mixtures have a problem in that their viscosity increases over time after preparation. If the viscosity increases excessively, for example, gelling occurs, which significantly deteriorates the coatability of the electrode mixture. In response to this problem, Patent Document 1 describes that by blending an oxime into the electrode mixture, excessive thickening of the electrode mixture can be suppressed.

[0004] International Publication No. 2022 / 044538

[0005] As described in Patent Document 1, if excessive thickening of the electrode mixture can be suppressed, the coatability of the electrode mixture can be improved. On the other hand, if an attempt is made to suppress thickening of the electrode mixture, the adhesiveness of the produced electrode mixture layer to the current collector may decrease.

[0006] The present invention has been made in view of the above problems, and has an object to provide an electrode mixture that is unlikely to undergo excessive thickening over time and that is unlikely to reduce the adhesive strength of the produced electrode mixture layer to a current collector; an active material mixture and binder solution for producing the electrode mixture; a method for producing the electrode mixture; a method for producing an electrode using the electrode mixture; an electrode produced from the electrode mixture; and a secondary battery having the electrode.

[0007] One embodiment of the present invention for solving the above problems relates to the following electrode mixtures [1] to

[10] . [1] An electrode mixture containing an oxime, a vinylidene fluoride polymer having 50 mol % or more of structural units derived from vinylidene fluoride, an electrode active material, and carbon black having an average primary particle size of 30 nm or less. [2] The electrode mixture according to [1], wherein the oxime is an oxime represented by the following formula (1) or an oxime represented by the following formula (2): (In formula (1), R １ and R ２ R independently represents a functional group selected from the group consisting of a hydrogen atom, an aldehyde group, a nitrile group, an alkyl group having from 1 to 10 carbon atoms, an alkenyl group having from 2 to 10 carbon atoms, an alkynyl group having from 2 to 10 carbon atoms, a cycloalkyl group having from 3 to 10 carbon atoms, a cycloalkenyl group having from 3 to 10 carbon atoms, an aryl group having from 6 to 18 carbon atoms, an aralkyl group having from 7 to 14 carbon atoms, and a heterocyclic group having from 3 to 13 carbon atoms. １ and R ２ In the above groups, some or all of the hydrogen atoms may be substituted with a substituent selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, a hydroxyl group, and an amino group. When the functional group or the substituent has an alkyl group, the alkyl group may be linear, branched, or may have an ester bond. １ and R ２ may be bonded to each other to form a ring.) (In formula (2), R ３ and R ４ R independently represents a functional group selected from the group consisting of a hydrogen atom, an aldehyde group, a nitrile group, an alkyl group having from 1 to 10 carbon atoms, an alkenyl group having from 2 to 10 carbon atoms, an alkynyl group having from 2 to 10 carbon atoms, a cycloalkyl group having from 3 to 10 carbon atoms, a cycloalkenyl group having from 3 to 10 carbon atoms, an aryl group having from 6 to 18 carbon atoms, an aralkyl group having from 7 to 14 carbon atoms, and a heterocyclic group having from 3 to 13 carbon atoms. ３ and R ４In the functional groups R, some or all of the hydrogen atoms may be substituted with a substituent selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, a hydroxyl group, and an amino group. When the functional group or the substituent has an alkyl group, the alkyl group may be linear, branched, or may have an ester bond. ３ and R ４ may be bonded to each other to form a ring. X represents a single bond or an alkylene group having 1 to 5 carbon atoms. The alkylene group may be linear or branched. [3] The oxime represented by the formula (1) is １ and R ２ are independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and the alkyl group may be linear or branched; R １ and R ２ are oximes which may be bonded to each other to form a ring, and the oxime represented by the formula (2) is ３ and R ４ are independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and the alkyl group may be linear or branched; R ３ and R ４may bond to each other to form a ring, and X represents a single bond or an alkylene group having 1 to 5 carbon atoms, and the alkylene group may be linear or branched. The electrode mixture according to [2], wherein the oxime is an oxime represented by formula (2). [4] The electrode mixture according to [2] or [3], wherein the oxime is an oxime represented by formula (2). [5] The electrode mixture according to any of [1] to [4], wherein the content of the oxime is an amount such that the amount of hydroxyimino groups contained in the oxime per 1 g of the vinylidene fluoride polymer is 0.02 mmol / g or more and 0.80 mmol / g or less. [6] The electrode mixture according to any of [1] to [5], wherein the vinylidene fluoride polymer is a homopolymer of vinylidene fluoride. [7] The electrode mixture according to any one of [1] to [6], wherein the vinylidene fluoride polymer is a copolymer of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride. [8] The electrode mixture according to any one of [1] to [7], wherein the vinylidene fluoride polymer is a vinylidene fluoride polymer containing a constituent unit derived from a compound represented by the following formula (3): (In formula (3), R ５ represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a carboxyl group substituted with an alkyl group having 1 to 5 carbon atoms. ６ and R ７ R independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. ５ , R ６ or R ７When represents the alkyl group, the alkyl group may be linear or branched. Y represents a single bond or an atomic group having a main chain with 1 to 20 atoms and a molecular weight of 500 or less. [9] The electrode mixture according to any of [1] to [8], wherein the vinylidene fluoride polymer is a vinylidene fluoride polymer containing a structural unit derived from a (meth)acrylate monomer having no COOH group at its terminal.

[10] The electrode mixture according to any of [1] to [9], wherein the electrode active material is a lithium metal oxide represented by the following formula (4), which is a compound such that when extracted with water at 25°C by the extraction method specified in JIS K 5101-16-2 (2004), the pH of the extracted water is 10.5 or higher. LiNi ｘ Co ｙ M ｚ O ２ ... (4) (In formula (4), M is Mn or Al, 0<x<1, 0<y<1, 0<z<1, and x+y+z=1.)

[0008] Another embodiment of the present invention for solving the above problem relates to an active material mixture according to the following item

[11] :

[11] An active material mixture comprising: an oxime; an electrode active material; and carbon black having an average primary particle size of 30 nm or less.

[0009] Another embodiment of the present invention for solving the above problem relates to a binder solution as described below in

[12] :

[12] A binder solution for an electrode mixture containing an electrode active material and carbon black having an average primary particle size of 30 nm or less, the binder solution containing an oxime and a vinylidene fluoride polymer having a content of structural units derived from vinylidene fluoride of 50 mol % or more.

[0010] Another embodiment of the present invention for solving the above problem relates to a method for producing an electrode mixture as described below in

[13] :

[13] A method for producing an electrode mixture, comprising mixing an oxime, a vinylidene fluoride polymer containing 50 mol % or more of structural units derived from vinylidene fluoride, an electrode active material, and carbon black having an average primary particle size of 30 nm or less, and forming the mixture into a slurry.

[0011] Another embodiment of the present invention for solving the above problem relates to a method for manufacturing an electrode according to the following item

[14] .

[14] A method for manufacturing an electrode, comprising: applying the electrode mixture according to any one of items [1] to

[10] to a current collector; and drying the applied electrode mixture.

[0012] Another embodiment of the present invention for solving the above problems relates to electrodes according to the following

[15] to

[17] .

[15] An electrode manufactured by the manufacturing method described in

[14] .

[16] The electrode according to

[15] , wherein the electrode mixture layer manufactured from the electrode mixture has a peel strength from the current collector, measured by a 90° peel test, that is 80% or more of the peel strength from the current collector of an electrode manufactured under the same manufacturing conditions from an electrode mixture having the same composition but not containing an oxime.

[17] An electrode having a current collector and an electrode mixture layer, wherein the electrode mixture layer contains an oxime, a vinylidene fluoride polymer having 50 mol % or more of structural units derived from vinylidene fluoride, an electrode active material, and carbon black having an average primary particle size of 30 nm or less.

[0013] Another embodiment of the present invention for solving the above problems relates to a secondary battery according to the following item

[18] :

[18] A secondary battery having the electrode according to item

[17] .

[0014] According to the present invention, there are provided an electrode mixture that is unlikely to undergo excessive thickening over time and that is unlikely to reduce the adhesive strength of the produced electrode mixture layer to a current collector, an active material mixture and a binder solution for producing the electrode mixture, a method for producing the electrode mixture, a method for producing an electrode using the electrode mixture, an electrode produced from the electrode mixture, and a secondary battery having the electrode.

[0015] [Electrode Mixture] One embodiment of the present invention relates to an electrode mix to be applied to a current collector to produce an electrode.

[0016] The electrode mixture contains an oxime, a vinylidene fluoride polymer containing 50 mol % or more of constituent units derived from vinylidene fluoride, an electrode active material, and carbon black having an average primary particle size of 30 nm or less.

[0017] (Oxime) Oxime reduces the initial viscosity of the electrode mixture and also suppresses an increase in viscosity over time.

[0018] An oxime is a compound in which the oxygen atom of the carbonyl group of an aldehyde or ketone is replaced with a hydroxyimino group (=NOH). The oxime may be an oxime derived from an aldehyde (RCH=NOH) or a oxime derived from a ketone (R'RC=NOH).

[0019] The type of oxime is not particularly limited. Examples of oximes include acetone oxime (acetoxime), 2-butanone oxime (methyl ethyl ketone oxime), methyl isopropyl ketone oxime, methyl tertiary butyl ketone oxime, ditertiary butyl ketone oxime, 2-pentanone oxime, 3-pentanone oxime, 1-cyclohexyl-1-propanone oxime, formaldehyde oxime, acetaldoxime (acetaldehyde oxime), butyraldoxime (benzaldehyde oxime), benzaloxime (benzaldehyde oxime), acetophenone oxime, benzophenone oxime, 4-hydroxyacetophenone oxime, cyclopropanone oxime, cyclobutanone oxime, cyclopentanone oxime, cyclohexanone oxime, Examples include cycloheptanone oxime, cyclooctanone oxime, cyclononanone oxime, cyclodecanone oxime, cyclododecanone oxime, benzoquinone dioxime, benzoquinone monooxime, 2,3-butanedione monooxime, acetamide oxime, 3-hydroxy-3-methyl-2-butanone oxime, α-benzoin oxime, 1,3-dihydroxyacetone oxime, 2-isonitrosopropiophenone, dimethylglyoxime, methylethylglyoxime, diethylglyoxime, diphenylglyoxime, benzophenone dioxime, piperidone oxime, 2,4-pentanedione dioxime, 2-diethyl ether oxime, ethyl acetohydroxime, and ethyl cyanoglyoxylate oxime.

[0020] The oxime may be a polymer containing a hydroxyimino group (hereinafter also simply referred to as an "oxime polymer") or an oligomer containing a hydroxyimino group (hereinafter also simply referred to as an "oxime oligomer").

[0021] Oxime polymers and oxime oligomers can be synthesized by polymerizing a monomer or oligomer containing a hydroxyimino group, or by reacting a polymer or oligomer having a ketone group in the backbone with hydroxyamine. Examples of polymers having a ketone group in the backbone include poly(methyl vinyl ketone), polyketone (PK), polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), and polyether ketone ether ketone ketone (PEKEKK). Specific examples of oxime polymers and oxime oligomers include poly(methyl vinyl oxime).

[0022] These oximes may be used alone or in combination of two or more.

[0023] These oximes can be oximes represented by the following formula (1) or oximes represented by the following formula (2).

[0024]

[0025] In formula (1), R １ and R ２ R independently represent a functional group that is a hydrogen atom, an aldehyde group, a nitrile group, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a cycloalkenyl group having 3 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, an aralkyl group having 7 to 14 carbon atoms, or a heterocyclic group having 3 to 13 carbon atoms. Each of the alkyl groups may be linear, branched, or have an ester bond. １ and R ２ may be bonded to each other to form a ring.

[0026] The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and even more preferably 1 to 2 carbon atoms. The alkenyl group preferably has 2 to 10 carbon atoms, more preferably 2 to 6 carbon atoms, and even more preferably 2 to 4 carbon atoms. The alkynyl group preferably has 2 to 10 carbon atoms, more preferably 2 to 6 carbon atoms, and even more preferably 2 to 4 carbon atoms. The cycloalkyl group preferably has 3 to 10 carbon atoms, more preferably 3 to 7 carbon atoms, and even more preferably 5 to 7 carbon atoms. The aryl group preferably has 6 to 18 carbon atoms, more preferably 6 to 10 carbon atoms, and even more preferably 6 to 8 carbon atoms. The aralkyl group preferably has 7 to 14 carbon atoms, more preferably 7 to 11 carbon atoms, and even more preferably 7 to 9 carbon atoms. The heterocyclic group preferably has 3 to 13 carbon atoms, more preferably 3 to 10 carbon atoms, and even more preferably 3 to 8 carbon atoms.

[0027]

[0028] In formula (2), R ３ and R ４ R independently represent a functional group that is a hydrogen atom, an aldehyde group, a nitrile group, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a cycloalkenyl group having 3 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, an aralkyl group having 7 to 14 carbon atoms, or a heterocyclic group having 3 to 13 carbon atoms. Each of the alkyl groups may be linear, branched, or have an ester bond. ３ and R ４ may be bonded to each other to form a ring.

[0029] The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and even more preferably 1 to 2 carbon atoms. The alkenyl group preferably has 2 to 10 carbon atoms, more preferably 2 to 6 carbon atoms, and even more preferably 2 to 4 carbon atoms. The alkynyl group preferably has 2 to 10 carbon atoms, more preferably 2 to 6 carbon atoms, and even more preferably 2 to 4 carbon atoms. The cycloalkyl group preferably has 3 to 10 carbon atoms, more preferably 3 to 7 carbon atoms, and even more preferably 5 to 7 carbon atoms. The aryl group preferably has 6 to 18 carbon atoms, more preferably 6 to 10 carbon atoms, and even more preferably 6 to 8 carbon atoms. The aralkyl group preferably has 7 to 14 carbon atoms, more preferably 7 to 11 carbon atoms, and even more preferably 7 to 9 carbon atoms. The heterocyclic group preferably has 3 to 13 carbon atoms, more preferably 3 to 10 carbon atoms, and even more preferably 3 to 8 carbon atoms.

[0030] X represents a single bond or an alkylene group having from 1 to 5 carbon atoms. The alkylene group may be linear or branched.

[0031] From the viewpoint of more effectively suppressing a decrease in the adhesive strength of the electrode mixture layer to the current collector, the oxime represented by formula (1) is preferably R １ and R ２ are preferably independently a hydrogen atom or an oxime group representing an alkyl group having 1 to 5 carbon atoms. The alkyl group may be linear or branched. １ and R ２ may be bonded to each other to form a ring. １ or R ２ When the alkyl groups constituting the formula (I) are linear or branched, one or both of the alkyl groups preferably has 1 or more and 3 or less carbon atoms, more preferably 1 or more and 2 or less carbon atoms, and even more preferably 1 carbon atom.

[0032] In addition, from the viewpoint of more effectively suppressing a decrease in the adhesive strength of the electrode mixture layer to the current collector or further increasing the adhesive strength, R １ and R ２ The total number of carbon atoms in each of these is preferably 1 or more and 3 or less, more preferably 1 or more and 2 or less, and even more preferably 1.

[0033] In addition, from the viewpoint of more effectively suppressing a decrease in the adhesive strength of the electrode mixture layer to the current collector or further increasing the adhesive strength, R １ and R ２ are preferably bonded to each other to form a ring. The number of carbon atoms constituting the ring is preferably 3 or more and 12 or less, and more preferably 4 or more and 8 or less.

[0034] Represented by formula (1), R １ or R ２ represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, examples of the oxime include acetoxime, 2-butanone oxime, methyl isopropyl ketone oxime, methyl tertiary butyl ketone oxime, ditertiary butyl ketone oxime, 2-pentanone oxime, formaldehyde oxime, acetaldoxime, butylaldoxime, cyclopropanone oxime, cyclobutanone oxime, cyclopentanone oxime, cyclohexanone oxime, cycloheptanone oxime, cyclooctanone oxime, cyclononanone oxime, and cyclodecanone oxime.

[0035] In addition, from the viewpoint of more effectively suppressing a decrease in the adhesive strength of the electrode mixture layer to the current collector, the oxime represented by formula (2) is preferably R ３ and R ４ are preferably independently a hydrogen atom or an oxime group representing an alkyl group having 1 to 5 carbon atoms. The alkyl group may be linear or branched. ３ and R ４ may be bonded to each other to form a ring. ３ or R ４When the alkyl groups constituting the formula (I) are linear or branched, one or both of the alkyl groups preferably has 1 or more and 3 or less carbon atoms, more preferably 1 or more and 2 or less carbon atoms, and even more preferably 1 carbon atom.

[0036] Furthermore, from the viewpoint of more effectively suppressing a decrease in the adhesive strength of the electrode mixture layer to the current collector or further increasing the adhesive strength, X is preferably an alkylene group having 1 to 5 carbon atoms, more preferably an alkylene group having 1 to 3 carbon atoms, and even more preferably an alkylene group having 1 carbon atom.

[0037] Represented by formula (2), R ３ and R ４ Examples of oximes in which represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms include dimethylglyoxime, methylethylglyoxime, diethylglyoxime, 2,4-pentanedionedioxime, and the like.

[0038] From the viewpoint of more effectively suppressing a decrease in the adhesive strength of the electrode mixture layer to the current collector or further increasing the adhesive strength, the oxime is represented by the formula (1), １ and R ２ are independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, or an oxime represented by formula (2), ３ and R ４ are preferably oximes in which R are independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. ３ and R ４ are more preferably oximes in which each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

[0039] In the oxime represented by formula (1) and the oxime represented by formula (2), some or all of the hydrogen atoms of the alkyl group may be substituted with an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, a hydroxyl group, or an amino group.

[0040] The content of oxime in the electrode mixture is preferably such that the amount of hydroxyimino groups contained in the oxime is 0.005 mmol to 5.00 mmol, more preferably 0.01 mmol to 3.00 mmol, even more preferably 0.02 mmol to 0.80 mmol, and particularly preferably 0.20 mmol to 0.80 mmol, per 1 g of vinylidene fluoride polymer. The greater the amount of hydroxyimino groups, the more effectively the initial viscosity of the electrode mixture can be reduced and the more effectively the increase in viscosity over time can be suppressed. On the other hand, by setting the amount of hydroxyimino groups to 3.00 mmol or less, 0.80 mmol or less, or to 0.20 mmol or more per 1 g of vinylidene fluoride polymer, the adhesion strength of the electrode mixture layer to the current collector can be further improved.

[0041] The content of the oxime in the electrode mixture is preferably such that the amount of hydroxyimino groups contained in the oxime is 0.0075 mmol to 7.50 mmol, more preferably 0.015 mmol to 4.50 mmol, even more preferably 0.03 mmol to 1.20 mmol, and particularly preferably 0.30 mmol to 1.20 mmol per 100 g of active material. The greater the amount of hydroxyimino groups, the more effectively the initial viscosity of the electrode mixture can be reduced and the more effectively the increase in viscosity over time can be suppressed. On the other hand, by setting the amount of hydroxyimino groups to 4.50 mmol or less, 1.20 mmol or less, or to 0.30 mmol or more per 100 g of active material, the adhesion strength of the electrode mixture layer to the current collector can be further improved.

[0042] The presence and amount of oxime in the electrode mixture can be determined by mass spectrometry (P&T-GCMS, solvent extraction-GCMS, etc.), nuclear magnetic resonance spectrometry ( １ H-NMR, 13 The compound can be analyzed by spectroscopy (e.g., C-NMR).

[0043] (Vinylidene fluoride polymer) The vinylidene fluoride polymer acts as a binder for binding the electrode active material onto the current collector.

[0044] A vinylidene fluoride polymer is a polymer containing structural units derived from vinylidene fluoride as a main structural component. Specifically, the vinylidene fluoride polymer contains structural units derived from vinylidene fluoride in an amount of 50 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more. The upper limit of the amount of structural units derived from vinylidene fluoride is not particularly limited, but can be 100 mol%.

[0045] The vinylidene fluoride polymer may be a homopolymer of vinylidene fluoride, or a copolymer of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride.

[0046] When the vinylidene fluoride polymer is a copolymer, it may be a copolymer of vinylidene fluoride with any known monomer copolymerizable with vinylidene fluoride.

[0047] When the vinylidene fluoride polymer is a copolymer, it preferably contains a structural unit derived from a compound represented by the following formula (3).

[0048]

[0049] In formula (3), R ５ represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a carboxyl group substituted with an alkyl group having 1 to 5 carbon atoms. ６ and R ７ R independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. ５ , R ６ or R ７ When R represents the alkyl group, the alkyl group may be linear or branched. ５ and R ６ is preferably a substituent with little steric hindrance. ５ and R ６are each independently preferably hydrogen or an alkyl group having 1 to 3 carbon atoms, more preferably hydrogen or a methyl group.

[0050] Y in formula (3) is a single bond or an atomic group having 1 to 20 atoms in the main chain and a molecular weight of 500 or less. The atomic group more preferably has a molecular weight of 200 or less. The lower limit of the molecular weight of the atomic group is not particularly limited, but is usually 15. The smaller the molecular weight of the atomic group, the more unlikely the electrode mixture is to gel. In this specification, the "number of atoms in the main chain" refers to the ratio of the carboxyl group written to the right of Y in formula (3) to the group (R ５ R ６ C=CR ７ -) with the fewest number of atoms. Y may be linear or branched containing a functional group as a side chain. When Y has a side chain, it may have only one side chain or may have multiple side chains. When Y is a single bond, the compound represented by formula (3) is a compound in which the carboxyl group is not bonded to R ７ It has a structure in which it is directly bonded to the carbon atom bonded to

[0051] Examples of the compound represented by formula (3) include acrylic acid (AA), methacrylic acid, 2-carboxyethyl acrylate (CEA), 2-carboxyethyl methacrylate, maleic acid monomethyl ester, acryloyloxyethyl succinate (AES), acryloyloxypropyl succinate (APS), methacryloyloxyethyl succinate, and methacryloyloxypropyl succinate, etc. These compounds may be used alone or in combination.

[0052] When vinylidene fluoride polymer is a copolymer, it may have a structural unit derived from other compounds than the compound represented by formula (3).Examples of the other compounds include vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene (HFP), and perfluoroalkyl vinyl ethers such as perfluoromethyl vinyl ether, (meth)acrylate monomers that do not have a COOH group at the end, such as glycidyl (meth)acrylate and methyl (meth)acrylate, as well as unsaturated dibasic acids such as maleic acid, fumaric acid, and citraconic acid, and esters of unsaturated dibasic acids such as maleic acid monomethyl ester, maleic acid monoethyl ester, citraconic acid monomethyl ester, and citraconic acid monoethyl ester.These compounds may be used alone or in combination of two or more. When the vinylidene fluoride polymer is a copolymer, it may be a copolymer with only the compound represented by formula (3), or may be a copolymer with only the other compound, or may be a copolymer with both the compound represented by formula (3) and the other compound.

[0053] When the vinylidene fluoride polymer is a copolymer with a compound represented by formula (3), the modification amount (the ratio of the number of moles of structural units derived from the compound represented by formula (3) to the number of moles of all structural units contained in the vinylidene fluoride polymer) is preferably 0.01 mol % or more and 10 mol % or less, more preferably 0.1 mol % or more and 5 mol % or less, and even more preferably 0.2 mol % or more and 1 mol % or less. In addition, the amount of constituent units derived from vinylidene fluoride in the vinylidene fluoride polymer (the ratio of the number of moles of constituent units derived from vinylidene fluoride to the number of moles of all constituent units contained in the vinylidene fluoride polymer) is preferably 90 mol% or more and 99.99 mol% or less, more preferably 95 mol% or more and 99.90 mol% or less, even more preferably 99.00 mol% or more and 99.80 mol% or less, and particularly preferably 99.50 mol% or more and 99.80 mol% or less. When the modification amount is within the above range, the change in the viscosity of the electrode mixture after storage relative to the viscosity of the electrode mixture immediately after preparation is reduced, and the viscosity of the electrode mixture can be more stabilized.

[0054] The amount of modification of vinylidene fluoride polymer and the amount of constituent units derived from vinylidene fluoride are １ H NMR spectrum or １９ It can be determined by F NMR spectrum or neutralization titration.

[0055] Commercially available vinylidene fluoride polymers may be used. Examples of commercially available vinylidene fluoride polymers include KF#7300, KF#9100, KF#9700, KF#7500, and KF#9400 manufactured by Kureha Corporation.

[0056] The inherent viscosity (ηi) of the vinylidene fluoride polymer is not particularly limited, but is preferably 0.5 dL / g or more and 5.0 dL / g or less, more preferably 1.0 dL / g or more and 4.5 dL / g or less, and even more preferably 1.5 dL / g or more and 4.0 dL / g or less. When the inherent viscosity is in the above range, thickness unevenness during coating is less likely to occur, making it easier to fabricate an electrode.

[0057] The inherent viscosity (ηi) is calculated by the following method. 80 mg of vinylidene fluoride polymer is dissolved in 20 mL of N,N-dimethylformamide to prepare a polymer solution. The viscosity η of the prepared polymer solution is measured using an Ubbelohde viscometer in a thermostatic bath at 30°C. The inherent viscosity (ηi) is then calculated from the following formula: ｉ ) is calculated. ｉ =(1 / C)・ln(η / η ０ ) In the above formula, η ０ is the viscosity of the solvent N,N-dimethylformamide, and C is the concentration of vinylidene fluoride polymer in the prepared polymer solution (0.4 g / dL).

[0058] The polymerization method for vinylidene fluoride polymers is not particularly limited, and conventionally known polymerization methods can be used. Examples of polymerization methods include suspension polymerization, emulsion polymerization, solution polymerization, etc. Among these, aqueous suspension polymerization or emulsion polymerization is preferred because of ease of post-treatment, and aqueous suspension polymerization is more preferred.

[0059] The content of vinylidene fluoride polymer in the electrode mixture can be 0.2 mass% or more and 20 mass% or less, preferably 0.2 mass% or more and 10 mass% or less, and more preferably 0.2 mass% or more and 4 mass% or less, relative to the total amount of solids in the electrode mixture.

[0060] (Electrode Active Material) The electrode active material takes in or releases ions such as lithium ions, thereby enabling the secondary battery to be charged and discharged.

[0061] The electrode active material may be a positive electrode active material or a negative electrode active material.

[0062] The positive electrode active material is not particularly limited, but is preferably a lithium metal oxide.

[0063] Examples of lithium metal oxides include LiMnO ２ , LiMn ２ O ４ , LiCoO ２ , LiNiO ２ , LiNi ｘ Co １－ｘ O２ (0<x<1), LiNi ｘ Co ｙ Mn １－ｘ－ｙ O ２ (0<x<1, 0<y<1), LiNi ｘ Co ｙ Al １－ｘ－ｙ O ２ (0<x<1, 0<y<1), LiM ａ P.O. ４ (However, M ａ is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr).

[0064] From the viewpoint of increasing the capacity density and thereby increasing the capacity of the secondary battery, the positive electrode active material is preferably a lithium metal compound containing Ni, and from the viewpoint of suppressing crystal structure changes during charge / discharge processes and stabilizing cycle characteristics, the positive electrode active material is more preferably a lithium metal compound containing Ni and Co.

[0065] From the viewpoint of increasing the charging potential of the secondary battery and further improving the cycle characteristics, the positive electrode compound is preferably a lithium metal oxide (ternary lithium metal oxide) represented by the following formula (4).

[0066] LiNi ｘ Co ｙ M ｚ O ２ ...(4)

[0067] In formula (4), M is Mn or Al, 0<x<1, 0<y<1, 0<z<1, and x+y+z=1.

[0068] Examples of ternary lithium metal oxides include Li １．００ Ni ０．５ Co ０．２ Mn ０．３ O ２ (NCM523), Li １．００ Ni ０．６ Co ０．２ Mn ０．２ O ２ (NCM622), Li １．００ Ni ０．８ Co ０．１ Mn ０．1 O ２(NCM811), and Li １．００ Ni ０．８ Co ０．１５ Al ０．０５ O ２ (NCA811), etc. These ternary lithium metal oxides are preferably compounds that, when extracted with water at room temperature (25°C) according to the extraction method specified in JIS K 5101-16-2 (2004), result in an extraction water pH of 10.5 or higher. Such ternary lithium metal oxides are likely to dehydrofluorinate vinylidene fluoride polymers, which can easily cause the electrode mixture to thicken. However, the electrode mixture according to this embodiment can suppress the increase in viscosity by using an oxime.

[0069] Specifically, the pH of the extracted water is a value obtained by adding the electrode active material to ultrapure water in an amount 50 times the weight of the electrode active material, stirring the mixture with a magnetic stirrer at a rotation speed of 600 rpm for 10 minutes, and measuring the pH of the extracted water using a pH meter, Model: F-21, manufactured by Horiba, Ltd.

[0070] An electrode mixture containing a positive electrode active material having a pH of 10.5 or higher contains a large amount of base, which easily deteriorates vinylidene fluoride and causes viscosity increase. Therefore, in order to prevent the thickening of the electrode mixture slurry and the resulting gelation, it is usually necessary to remove the base by washing the positive electrode active material with water. In contrast, the electrode mixture according to this embodiment is less likely to thicken or gel, even when using a positive electrode active material containing a large amount of base. Therefore, the electrode mixture according to this embodiment does not require washing the positive electrode active material with water during production.

[0071] The negative electrode active material is not particularly limited, and known materials such as carbon materials, metal / alloy materials, and metal oxides can be used. Among these, carbon materials are preferred from the viewpoint of further increasing the energy density of the secondary battery. Examples of the carbon materials include artificial graphite, natural graphite, non-graphitizable carbon, and easily graphitizable carbon.

[0072] These electrode active materials may be used alone or in combination of two or more.

[0073] The content of vinylidene fluoride and electrode active material in the electrode mixture is preferably such that the amount of vinylidene fluoride is 0.2 parts by mass or more and 15 parts by mass or less, and more preferably 0.5 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of the electrode active material.

[0074] The content of the electrode active material in the electrode mixture is preferably 40% by mass or more and 99.9% by mass or less relative to the total amount of solids in the electrode mixture. When the amount of the electrode active material is within this range, for example, a sufficient charge / discharge capacity is obtained, and the battery performance is likely to be good.

[0075] (Carbon Black) Carbon black can be used as a so-called conductive aid that improves the conductivity of electrodes due to its conductive properties.

[0076] The carbon black is not particularly limited, and may be any of furnace black, ketjen black, channel black, acetylene black, thermal black, etc. Among these, acetylene black is preferred because it is easy to reduce metal components as impurities.

[0077] The carbon black may be subjected to an oxidation treatment or graphitization treatment. The oxidation-treated carbon black may have oxygen-containing polar functional groups, such as phenol groups, quinone groups, carboxyl groups, and carbonyl groups, on its surface.

[0078] The carbon black is a particle having an average primary particle diameter of 30 nm or less. By using such small-particle carbon black in combination with an oxime, it is possible to more effectively suppress or even increase the adhesive strength of the electrode mixture layer to the current collector. From the above viewpoint, the average primary particle diameter of the carbon black is preferably 26 nm or less, and more preferably 24 nm or less. The lower limit of the average primary particle diameter of the carbon black is not particularly limited, but can be 5 nm or more.

[0079] The average primary particle diameter of carbon black is the average value of particle diameters measured based on photographs taken with a transmission electron microscope or the like. Specifically, five images were taken at 100,000 magnification using a transmission electron microscope JEM-2000FX (manufactured by JEOL Ltd.), and the particle diameters of 200 or more randomly selected primary particles were determined by image analysis, and the number average was calculated. The primary particle diameter refers to the circle-equivalent diameter of the primary particles.

[0080] The carbon black may be in the form of secondary particles in which primary particles are linked in a chain or cluster shape. The specific surface area of ​​the secondary particles measured by the BET method is 20 m ２ / g or more 1500m ２ / g or less, and 2 / g or more 1500m 2 / g or less is more preferable, and 100m 2 / g or more 1000m 2 / g or less is more preferable, and 100m 2 / g or more 500m 2 The larger the specific surface area of ​​the carbon black, the more effectively it is possible to suppress a decrease in the adhesive strength of the electrode mixture layer to the current collector, or to increase the adhesive strength.

[0081] The content of carbon black in the electrode mixture is preferably 0.1% by mass to 15% by mass or less, more preferably 0.1% by mass to 7% by mass or less, and even more preferably 0.1% by mass to 5% by mass or less, relative to the total amount of solids in the electrode mixture.

[0082] (Non-aqueous solvent) The electrode mixture is preferably a slurry containing a non-aqueous solvent.

[0083] Examples of non-aqueous solvents include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, trimethyl phosphate, acetone, ethyl acetate, n-butyl acetate, n-butanol, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and cyclohexanone. Of these, N-methylpyrrolidone is preferred. These non-aqueous solvents may be used alone or in combination.

[0084] The content of the non-aqueous solvent in the electrode mixture is not particularly limited, but is preferably, for example, 20 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the electrode active material.

[0085] (Other Substances) The electrode mixture may contain a binder other than vinylidene fluoride polymer, a conductive aid other than carbon black, a pigment dispersant, a dispersion stabilizer, an adhesive aid, a thickener, various coupling agents, and the like.

[0086] Examples of conductive additives other than carbon black include carbonaceous materials such as carbon nanotubes, graphite fine powder and graphite fiber, and metal fine powder and metal fiber such as nickel and aluminum.

[0087] Examples of pigment dispersants include polyvinylpyrrolidone and the like.

[0088] The content of these other substances in the electrode mixture is preferably 15 mass % or less based on the total amount of solids in the electrode mixture.

[0089] [Electrode Mixture] The electrode mixture can be produced by mixing the above-mentioned components and forming a slurry.

[0090] The method for adding each component during mixing is not particularly limited. The vinylidene fluoride polymer, the electrode active material, the carbon black, the oxime, and the non-aqueous solvent may be added separately to a mixing vessel, or a plurality of these components may be mixed in advance, and the resulting premixture may be added to the mixing vessel.

[0091] For example, the vinylidene fluoride polymer may be prepared in advance as a liquid premix (solution or dispersion) containing the vinylidene fluoride polymer and a non-aqueous solvent. The vinylidene fluoride polymer may also be prepared in advance as a powder premix obtained by powder-mixing with an electrode active material or carbon black, or as a liquid premix (dispersion) to which a non-aqueous solvent is further added. An oxime may also be added and mixed in advance with these liquid components.

[0092] The electrode active material may be prepared in advance as a liquid pre-mixture active material mixture (dispersion) containing the electrode active material and a non-aqueous solvent. The electrode active material may also be prepared in advance as a pre-mixture active material mixture by mixing with carbon black. The electrode active material and carbon black may be prepared as a powder pre-mixture active material mixture obtained by powder mixing, or as a liquid pre-mixture active material mixture (dispersion) to which a non-aqueous solvent is further added. An oxime may be further added and mixed in advance to these liquid pre-mixture active material mixtures.

[0093] Alternatively, the carbon black may be prepared in advance as a liquid pre-mixture (dispersion) containing the carbon black and a non-aqueous solvent, and the oxime may be further added and mixed into this liquid pre-mixture.

[0094] The order in which these components are added to the mixing vessel is not particularly limited.

[0095] The method for preparing the slurry is not particularly limited, and any known method can be used.

[0096] The obtained electrode mixture contains a vinylidene fluoride polymer, an electrode active material, carbon black having an average primary particle size of 30 nm or less, an oxime, and a non-aqueous solvent. The electrode mixture preferably has a viscosity of 1,000 mPa·s or more and 30,000 mPa·s or less immediately after preparation, and more preferably 1,000 mPa·s or more and 20,000 mPa·s or less. Furthermore, the electrode mixture preferably has a viscosity of 1,000 mPa·s or more and 50,000 mPa·s or less, and more preferably 1,000 mPa·s or more and 20,000 mPa·s or less after storage at 40°C for 7 days after preparation in a nitrogen atmosphere. The viscosity immediately after preparation and the viscosity after storage can be adjusted by adjusting the amount of oxime added, etc.

[0097] [Electrode] The electrode mixture can be used to prepare an electrode mixture layer contained in an electrode by applying it to a current collector and drying it.

[0098] The current collector is the base material of the electrode and also serves as a terminal for extracting electricity. The current collector can be made of metal such as iron, stainless steel, steel, copper, aluminum, nickel, and titanium. The current collector can be in the form of a foil or a mesh. For example, when preparing a positive electrode, the current collector is preferably an aluminum foil. The thickness of the current collector is preferably 5 μm or more and 100 μm or less, and more preferably 5 μm or more and 20 μm or less.

[0099] The electrode mixture can be applied to the current collector by a known method such as a bar coater, die coater, or comma coater. Drying can be performed, for example, at a temperature of 50°C or higher and 170°C or lower, preferably 50°C or higher and 170°C or lower. The electrode mixture layer can be formed by applying and drying the current collector on both sides of the current collector, or on only one side of the current collector. After application and drying, the formed electrode mixture layer can be pressed to increase its density.

[0100] The thickness of the electrode mixture layer can be, for example, 20 μm or more and 600 μm or less, and preferably 20 μm or more and 350 μm or less. The basis weight of the electrode mixture layer is, for example, 20 g / m ２ 700g / m or more２ and 20 g / m ２ More than 500g / m ２ It can be as follows:

[0101] The obtained electrode mixture has a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer contains a vinylidene fluoride polymer, an electrode active material, and carbon black having an average primary particle size of 30 nm or less. The oxime may be completely volatilized during drying, or the oxime may remain on the electrode. The amount of the oxime remaining is not particularly limited, but it is preferred that the oxime is 0 μg / m or less. ２ More than (or above the detection limit) 500 μg / m ２ It can be as follows:

[0102] The formed electrode can be a positive electrode when the electrode active material is a positive electrode active material, and can be a negative electrode when the electrode active material is a negative electrode active material.

[0103] [Other Embodiments] It goes without saying that the above-described embodiments are exemplary embodiments of the present invention, and the present invention may include embodiments other than the above-described embodiments within the scope of its core technical concept.

[0104] The present invention will be described in detail based on examples, but the present invention is not limited to these examples.

[0105] 1. Preparation of vinylidene fluoride polymer 1-1. Preparation of VDF / APS copolymer A 2-liter autoclave was charged with 1,096 g of ion-exchanged water, 0.2 g of Metrose 90SH-100 (Shin-Etsu Chemical Co., Ltd.), 2.2 g of a 50 wt % diisopropyl peroxydicarbonate-Flon 225cb solution, 426 g of vinylidene fluoride, and an initial amount of 0.2 g of acryloyloxypropyl succinic acid (APS). After heating to 26°C over 1 hour, the temperature was maintained at 26°C, and a 6 wt % aqueous APS solution was gradually added at a rate of 0.5 g / min. The resulting polymer slurry was dehydrated and dried to obtain a vinylidene fluoride copolymer containing polar groups (VDF / APS copolymer). A total of 4.0 g of APS was added, including the amount initially added.

[0106] 1-2. Preparation of VDF / AA Copolymer: A 2-liter autoclave was charged with 524 g of ion-exchanged water, 0.4 g of Metrose 90SH-100 (Shin-Etsu Chemical Co., Ltd.), 4 g of a 50 wt % perbutyl perpivalate-Flon 225cb solution, 396 g of vinylidene fluoride, and an initial amount of 0.2 g of acrylic acid (AA), and heated to 50°C. A 1 wt % aqueous AA solution was continuously fed into the reaction vessel while maintaining constant pressure during polymerization. The resulting polymer slurry was dehydrated and dried to obtain vinylidene fluoride copolymer (VDF / AA). A total of 3.96 g of AA was added, including the amount initially added.

[0107] 2. Preparation of electrode mixture 2-1. Preparation of electrode mixture 1 NCA811 was used as the electrode active material. Carbon black (Denka Black Li-435, manufactured by Denka Co., Ltd., average primary particle size: 23 nm) was added to NCA811, and the powders were mixed.

[0108] The VDF / APS copolymer obtained in Preparation Example 1 and pentanedione dioxime were dissolved in N-methyl-2-pyrrolidone (NMP) to prepare a binder solution. The amount of pentanedione dioxime added was adjusted so that the solution contained 6 wt % vinylidene fluoride polymer and 0.22 mmol of pentanedione dioxime per 1 g of vinylidene fluoride polymer. The amount of hydroxyimino groups in the pentanedione dioxime per 1 g of vinylidene fluoride polymer was 0.44 mmol.

[0109] NCA811, carbon black, and a binder solution were kneaded to prepare electrode mixture 1. Specifically, the binder solution was added to the carbon black to give a solids concentration of 11.3 wt%, and primary kneading was performed at 2000 rpm for 1 minute. Next, NCA811 was added, and secondary kneading was performed at 2000 rpm for 2 minutes. Furthermore, the binder solution and NMP were added to give a solids concentration of 71.0 wt%, and tertiary kneading was performed at 2000 rpm for 3 minutes to obtain electrode mixture 1. The weight ratio of the electrode active material, carbon black, and VDF / APS copolymer in electrode mixture 1 (electrode active material:carbon black:VDF / APS copolymer) was 100:1.5:1.5.

[0110] 2-2. Preparation of electrode mixture 2 Electrode mixture 2 was prepared in the same manner as electrode mixture 1, except that pentanedionedioxime was changed to dimethylglyoxime and the amount of dimethylglyoxime in the binder solution was 0.22 mmol per 1 g of vinylidene fluoride polymer. In electrode mixture 2, the amount of hydroxyimino groups in dimethylglyoxime per 1 g of vinylidene fluoride polymer was 0.44 mmol.

[0111] 2-3. Preparation of electrode mixture 3 Electrode mixture 3 was prepared in the same manner as electrode mixture 1, except that pentanedionedioxime was changed to dimethylglyoxime and the amount of dimethylglyoxime in the binder solution was 0.055 mmol per 1 g of vinylidene fluoride polymer. In electrode mixture 3, the amount of hydroxyimino groups in dimethylglyoxime per 1 g of vinylidene fluoride polymer was 0.11 mmol.

[0112] 2-4. Preparation of electrode mixture 4 Electrode mixture 4 was prepared in the same manner as electrode mixture 1, except that pentanedione dioxime was changed to 2-butanone oxime and the amount of 2-butanone oxime in the binder solution was 0.44 mmol per 1 g of vinylidene fluoride polymer. In electrode mixture 4, the amount of hydroxyimino groups in 2-butanone oxime per 1 g of vinylidene fluoride polymer was 0.44 mmol.

[0113] 2-5. Preparation of electrode mixture 5 Electrode mixture 5 was prepared in the same manner as electrode mixture 1, except that pentanedione dioxime was changed to 2-butanone oxime and the amount of 2-butanone oxime in the binder solution was 0.11 mmol per 1 g of vinylidene fluoride polymer. In electrode mixture 5, the amount of hydroxyimino groups in 2-butanone oxime per 1 g of vinylidene fluoride polymer was 0.11 mmol.

[0114] 2-6. Preparation of electrode mixture 6 Electrode mixture 6 was prepared in the same manner as electrode mixture 1, except that pentanedione dioxime was changed to 2-butanone oxime and the amount of 2-butanone oxime in the binder solution was 0.02 mmol per 1 g of vinylidene fluoride polymer. In electrode mixture 6, the amount of hydroxyimino groups in 2-butanone oxime per 1 g of vinylidene fluoride polymer was 0.02 mmol.

[0115] 2-7. Preparation of electrode mixture 7 Electrode mixture 7 was prepared in the same manner as electrode mixture 1, except that pentanedionedioxime was changed to acetaldehyde oxime and the amount of acetaldehyde oxime in the binder solution was 0.44 mmol per 1 g of vinylidene fluoride polymer. In electrode mixture 7, the amount of hydroxyimino groups possessed by acetaldehyde oxime per 1 g of vinylidene fluoride polymer was 0.44 mmol.

[0116] 2-8. Preparation of electrode mixture 8 Electrode mixture 8 was prepared in the same manner as in the preparation of electrode mixture 1, except that pentanedione dioxime was changed to cyclohexanone oxime and the amount of cyclohexanone oxime in the binder solution was 0.44 mmol per 1 g of vinylidene fluoride polymer. In electrode mixture 8, the amount of hydroxyimino groups in cyclohexanone oxime per 1 g of vinylidene fluoride polymer was 0.44 mmol.

[0117] 2-9. Preparation of Electrode Mix 9 Electrode mix 9 was prepared in the same manner as electrode mix 1, except that the VDF / APS copolymer was changed to a VDF / AA copolymer, pentanedionedioxime was changed to dimethylglyoxime, and the amount of dimethylglyoxime in the binder solution was 0.22 mmol per 1 g of vinylidene fluoride polymer. In electrode mix 9, the amount of hydroxyimino groups in dimethylglyoxime per 1 g of vinylidene fluoride polymer was 0.44 mmol.

[0118] 2-10. Preparation of Electrode Mixture 10 Electrode mix 10 was prepared in the same manner as in the preparation of electrode mix 1, except that pentanedionedioxime was not added to the binder solution.

[0119] 2-11. Preparation of electrode mixture 11 Electrode mixture 11 was prepared in the same manner as electrode mixture 1, except that the carbon black was changed to Denka Black Li-400 (manufactured by Denka Co., Ltd., average primary particle diameter: 48 nm), pentanedione dioxime was changed to 2-butanone oxime, the amount of 2-butanone oxime in the binder solution was 0.44 mmol per 1 g of vinylidene fluoride polymer, and the solids concentration of the electrode mixture was 75%. In electrode mixture 11, the amount of hydroxyimino groups in 2-butanone oxime per 1 g of vinylidene fluoride polymer was 0.44 mmol.

[0120] 2-12. Preparation of electrode mixture 12 Electrode mixture 12 was prepared in the same manner as electrode mixture 1, except that the carbon black was changed to Denka Black Li-400 (manufactured by Denka Co., Ltd., average primary particle diameter: 48 nm), pentanedione dioxime was changed to 2-butanone oxime, the amount of 2-butanone oxime in the binder solution was 0.11 mmol per 1 g of vinylidene fluoride polymer, and the solids concentration of the electrode mixture was 75%. In electrode mixture 12, the amount of hydroxyimino groups in 2-butanone oxime per 1 g of vinylidene fluoride polymer was 0.11 mmol.

[0121] 2-13. Preparation of electrode mixture 13 Electrode mixture 13 was prepared in the same manner as electrode mixture 1, except that the carbon black was changed to Denka Black Li-400 (manufactured by Denka Co., Ltd., average primary particle diameter: 48 nm), pentanedione dioxime was changed to 2-butanone oxime, the amount of 2-butanone oxime in the binder solution was 0.02 mmol per 1 g of vinylidene fluoride polymer, and the solids concentration of the electrode mixture was 75%. In electrode mixture 13, the amount of hydroxyimino groups in 2-butanone oxime per 1 g of vinylidene fluoride polymer was 0.02 mmol.

[0122] 2-14. Preparation of electrode mixture 14 Electrode mixture 14 was prepared in the same manner as electrode mixture 1, except that the carbon black was changed to Denka Black Li-400 (manufactured by Denka Co., Ltd., average primary particle diameter: 48 nm), pentanedionedioxime was changed to dimethylglyoxime, the amount of dimethylglyoxime in the binder solution was 0.22 mmol per 1 g of vinylidene fluoride polymer, and the solids concentration of the electrode mixture was 75%. In electrode mixture 14, the amount of hydroxyimino groups possessed by dimethylglyoxime per 1 g of vinylidene fluoride polymer was 0.44 mmol.

[0123] 2-15. Preparation of electrode mixture 15 Electrode mixture 15 was prepared in the same manner as electrode mixture 1, except that the carbon black was changed to Denka Black Li-400 (manufactured by Denka Co., Ltd., average primary particle diameter: 48 nm), pentanedionedioxime was changed to dimethylglyoxime, the amount of dimethylglyoxime in the binder solution was 0.055 mmol per 1 g of vinylidene fluoride polymer, and the solids concentration of the electrode mixture was 75%. In electrode mixture 15, the amount of hydroxyimino groups in dimethylglyoxime per 1 g of vinylidene fluoride polymer was 0.11 mmol.

[0124] 2-16. Preparation of electrode mixture 16 Electrode mixture 16 was prepared in the same manner as electrode mixture 1, except that the carbon black was changed to Denka Black Li-400 (manufactured by Denka Co., Ltd., average primary particle diameter: 48 nm), pentanedionedioxime was changed to dimethylglyoxime, the amount of dimethylglyoxime in the binder solution was 0.01 mmol per 1 g of vinylidene fluoride polymer, and the solids concentration of the electrode mixture was 75%. In electrode mixture 16, the amount of hydroxyimino groups in dimethylglyoxime per 1 g of vinylidene fluoride polymer was 0.02 mmol.

[0125] 2-17. Preparation of Electrode Mix 17 Electrode mix 17 was prepared in the same manner as electrode mix 1, except that the carbon black was changed to Denka Black Li-400 (manufactured by Denka Co., Ltd., average primary particle diameter: 48 nm), pentanedionedioxime was changed to diacetoxymonoxime, the amount of diacetoxymonoxime in the binder solution was 0.44 mmol per 1 g of vinylidene fluoride polymer, and the solids concentration of the electrode mix was 75%. In electrode mix 17, the amount of hydroxyimino groups possessed by diacetoxymonoxime per 1 g of vinylidene fluoride polymer was 0.44 mmol.

[0126] 2-18. Preparation of electrode mixture 18 Electrode mixture 18 was prepared in the same manner as electrode mixture 1, except that the carbon black was changed to Denka Black Li-400 (manufactured by Denka Co., Ltd., average primary particle diameter: 48 nm), pentanedionedioxime was changed to diacetoxymonoxime, the amount of diacetoxymonoxime in the binder solution was 0.11 mmol per 1 g of vinylidene fluoride polymer, and the solids concentration of the electrode mixture was 75%. In electrode mixture 18, the amount of hydroxyimino groups in the diacetoxymonoxime per 1 g of vinylidene fluoride polymer was 0.11 mmol.

[0127] 2-19. Preparation of Electrode Mix 19 Electrode mix 19 was prepared in the same manner as electrode mix 1, except that the carbon black was changed to Denka Black Li-400 (manufactured by Denka Co., Ltd., average primary particle diameter: 48 nm), pentanedionedioxime was changed to diacetoxymonoxime, the amount of diacetoxymonoxime in the binder solution was 0.02 mmol per 1 g of vinylidene fluoride polymer, and the solids concentration of the electrode mix was 75%. In electrode mix 19, the amount of hydroxyimino groups possessed by diacetoxymonoxime per 1 g of vinylidene fluoride polymer was 0.02 mmol.

[0128] 2-20. Preparation of electrode mixture 20 An electrode mixture 20 was prepared in the same manner as in the preparation of electrode mixture 1, except that the carbon black was changed to Denka Black Li-400 (manufactured by Denka Company Ltd., average primary particle diameter: 48 nm), pentanedione dioxime was not added to the binder solution, and the solids concentration of the electrode mixture was 75%.

[0129] 3. Measurement 3-1. pH of Electrode Active Material The pH of the electrode active material (NCA811) was the pH of the water when the electrode active material was extracted with water at room temperature (25°C). Extraction of the electrode active material into water was performed using the extraction method specified in JIS K 5101-16-2 (2004). Specifically, the electrode active material was placed in ultrapure water in an amount 50 times the weight of the electrode active material, and stirred with a magnetic stirrer at a rotation speed of 600 rpm for 10 minutes, and the pH of the solution was measured using a pH meter Model F-21 manufactured by Horiba, Ltd. The pH after extraction when NCA811 was extracted with water was 11.5.

[0130] 3-2. Inherent viscosity (ηi) of vinylidene fluoride polymer A polymer solution was prepared by dissolving 80 mg of vinylidene fluoride polymer in 20 mL of N,N-dimethylformamide. The viscosity η of the prepared polymer solution was measured using an Ubbelohde viscometer in a thermostatic bath at 30°C. The inherent viscosity (ηi) was then calculated using the following formula: ηi = (1 / C) · ln(η / η0) In the above formula, η0 is the viscosity of the N,N-dimethylformamide solvent, and C is the concentration (0.4 g / dL) of the vinylidene fluoride polymer in the prepared polymer solution.

[0131] The inherent viscosity of the VDF / APS copolymer was 2.5 dL / g, and the inherent viscosity of the VDF / AA copolymer was 2.5 dL / g.

[0132] 4. Evaluation 4-1. Viscosity Using an E-type viscometer, the viscosity was measured at 25°C and a shear rate of 2 s －１ The viscosity was measured at 100°C. Specifically, the slurry (electrode mixture) was charged into the measuring device, waited for 60 seconds, and then the rotor was rotated to measure the viscosity. At this time, the value 300 seconds after the start of rotor rotation was taken as the slurry viscosity. For each electrode mixture prepared, the viscosity immediately after preparation and the viscosity after storage at 40°C in a nitrogen atmosphere for 7 days (168 hours) were measured.

[0133] Each electrode mixture prepared was applied to a 15 μm thick aluminum foil current collector using a bar coater, and the resulting film was subjected to primary drying in a thermostatic chamber under a nitrogen atmosphere at 110°C for 30 minutes. This was then subjected to secondary drying under a nitrogen atmosphere at 130°C for 2 hours to obtain a film with a coating weight of approximately 250 g / m. ２ As a result, an electrode (electrode peeling measurement sample) was obtained.

[0134] The prepared electrode was cut into a length of 100 mm and a width of 20 mm, and a 90° peel test of the electrode mixture layer was performed at a head speed of 10 mm / min using a tensile tester (ORIENTE CHSIA-1150 manufactured by UNIVERSAL TESTING MACHINE) in accordance with JIS F6854-1 to measure the peel strength.

[0135] Regarding the peel strength of the electrode mixture layer in electrodes prepared from each electrode mixture containing oxime, the percentage change (%) relative to the peel strength of the electrode mixture layer in an electrode prepared from an electrode mixture containing the same vinylidene fluoride polymer, the same electrode active material, and the same carbon black but without the addition of oxime (when a VDF / APS copolymer was used as the vinylidene fluoride polymer, either electrode mixture 10 or electrode mixture 20 was used; when a VDF / AA copolymer was used as the vinylidene fluoride polymer, an electrode mixture prepared separately using the VDF / AA copolymer was used) was calculated. From the obtained percentage change, the peel strength was evaluated according to the following criteria.

[0136] ◎ Peel strength is improved (change rate is 100% or more) ○ Peel strength is almost the same (change rate is 80% or more but less than 100%) × Peel strength is decreased (change rate is less than 80%)

[0137] The types of electrode active materials used in the preparation of electrode mixtures 1 to 20, the average primary particle diameter of carbon black, the amounts (weight ratios) of comonomers in polyvinylidene fluoride (PVDF), the types and amounts of oximes added, and the evaluation results are shown in Tables 1 and 2. The amount of oxime added indicates the amount of hydroxyimino groups per 1 g of PVDF.

[0138]

[0139]

[0140] As is clear from Tables 1 and 2, an electrode mixture containing an oxime, a vinylidene fluoride polymer in which the amount of constituent units derived from vinylidene fluoride is 50 mol % or more, an electrode active material, and carbon black having an average primary particle size of 30 nm or less was less likely to thicken and the adhesive strength of the electrode mixture layer to the current collector was less likely to decrease.

[0141] This application claims priority from Japanese Patent Application No. 2023-182455, filed October 24, 2023. The subject matter described in the specification and claims of that application as originally filed is incorporated herein by reference.

[0142] The electrode mixture according to the present invention is less likely to thicken, and can more effectively prevent a decrease in the adhesive strength of the electrode mixture layer to the current collector, or can produce an electrode mixture layer with higher adhesive strength.

Claims

1. An electrode mixture comprising: an oxime; a vinylidene fluoride polymer having a content of constituent units derived from vinylidene fluoride of 50 mol % or more; an electrode active material; and carbon black having an average primary particle diameter of 30 nm or less.

2. The electrode mixture according to claim 1, wherein the oxime is an oxime represented by the following formula (1) or an oxime represented by the following formula (2): (In formula (1), R １ and R ２ R independently represents a functional group selected from the group consisting of a hydrogen atom, an aldehyde group, a nitrile group, an alkyl group having from 1 to 10 carbon atoms, an alkenyl group having from 2 to 10 carbon atoms, an alkynyl group having from 2 to 10 carbon atoms, a cycloalkyl group having from 3 to 10 carbon atoms, a cycloalkenyl group having from 3 to 10 carbon atoms, an aryl group having from 6 to 18 carbon atoms, an aralkyl group having from 7 to 14 carbon atoms, and a heterocyclic group having from 3 to 13 carbon atoms. １ and R ２ In these groups, some or all of the hydrogen atoms may be substituted with a substituent selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, a hydroxyl group, and an amino group. When the functional group or the substituent has an alkyl group, the alkyl group may be linear or branched, or may have an ester bond. R １ and R ２ may be bonded to each other to form a ring.) (In formula (2), R ３ and R ４ R independently represents a functional group selected from the group consisting of a hydrogen atom, an aldehyde group, a nitrile group, an alkyl group having from 1 to 10 carbon atoms, an alkenyl group having from 2 to 10 carbon atoms, an alkynyl group having from 2 to 10 carbon atoms, a cycloalkyl group having from 3 to 10 carbon atoms, a cycloalkenyl group having from 3 to 10 carbon atoms, an aryl group having from 6 to 18 carbon atoms, an aralkyl group having from 7 to 14 carbon atoms, and a heterocyclic group having from 3 to 13 carbon atoms. ３ and R ４ In the functional groups, some or all of the hydrogen atoms may be substituted with a substituent selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, a hydroxyl group, and an amino group. When the functional group or the substituent has an alkyl group, the alkyl group may be linear or branched, or may have an ester bond. R ３ and R ４ may be bonded to each other to form a ring. X represents a single bond or an alkylene group having 1 to 5 carbon atoms. The alkylene group may be linear or branched.

3. The oxime represented by the formula (1) is R １ and R ２ each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, the alkyl group may be linear or branched; R １ and R ２ are oximes which may be bonded to each other to form a ring, and the oxime represented by the formula (2) is ３ and R ４ each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, the alkyl group may be linear or branched; R ３ and R ４ may be bonded to each other to form a ring, X represents a single bond or an alkylene group having 1 to 5 carbon atoms, and the alkylene group is an oxime that may be linear or branched.

4. The electrode mixture according to claim 2, wherein the oxime is an oxime represented by formula (2).

5. The electrode mixture according to claim 1, wherein the content of the oxime is an amount such that the amount of hydroxyimino groups contained in the oxime per 1 g of the vinylidene fluoride polymer is 0.02 mmol / g or more and 0.80 mmol / g or less.

6. The electrode mixture according to claim 1, wherein the vinylidene fluoride polymer is a homopolymer of vinylidene fluoride.

7. The electrode mixture according to claim 1, wherein the vinylidene fluoride polymer is a copolymer of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride.

8. The electrode mixture according to claim 1, wherein the vinylidene fluoride polymer is a vinylidene fluoride polymer containing a structural unit derived from a compound represented by the following formula (3): (In formula (3), R ５ R represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a carboxyl group substituted with an alkyl group having 1 to 5 carbon atoms. ６ and R ７ R independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. ５ , R ６ Or R ７ When represents the alkyl group, the alkyl group may be linear or branched. Y represents a single bond or an atomic group having a main chain with 1 to 20 atoms and a molecular weight of 500 or less.

9. The electrode mixture according to claim 1, wherein the vinylidene fluoride polymer is a vinylidene fluoride polymer containing a structural unit derived from a (meth)acrylate monomer having no COOH group at its terminal.

10. The electrode mixture according to claim 1, wherein the electrode active material is a lithium metal oxide represented by the following formula (4), and when extracted with water at 25°C according to the extraction method specified in JIS K 5101-16-2 (2004), the pH of the extracted water is 10.5 or more. ｘ Co ｙ M ｚ O ２ ... (4) (In formula (4), M is Mn or Al, 0<x<1, 0<y<1, 0<z<1, and x+y+z=1.) 11. An active material mixture comprising: an oxime; an electrode active material; and carbon black having an average primary particle size of 30 nm or less.

12. A binder solution for an electrode mixture containing an electrode active material and carbon black having an average primary particle diameter of 30 nm or less, the binder solution containing an oxime and a vinylidene fluoride polymer having 50 mol % or more of structural units derived from vinylidene fluoride.

13. A method for producing an electrode mixture, comprising mixing an oxime, a vinylidene fluoride polymer having 50 mol % or more of constituent units derived from vinylidene fluoride, an electrode active material, and carbon black having an average primary particle diameter of 30 nm or less, and forming the mixture into a slurry.

14. A method for manufacturing an electrode, comprising the steps of: applying the electrode mixture according to any one of claims 1 to 10 to a current collector; and drying the applied electrode mixture.

15. An electrode produced by the method of claim 14.

16. The electrode according to claim 15, wherein the electrode mixture layer produced from the electrode mixture has a peel strength from the current collector measured by a 90° peel test that is 80% or more of the peel strength from the current collector of an electrode mixture layer produced under the same production conditions from an electrode mixture having the same composition except that it does not contain an oxime.

17. An electrode comprising a current collector and an electrode mixture layer, the electrode mixture layer containing an oxime, a vinylidene fluoride polymer having a content of constituent units derived from vinylidene fluoride of 50 mol % or more, an electrode active material, and carbon black having an average primary particle diameter of 30 nm or less.

18. A secondary battery comprising the electrode according to claim 17.

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