Binders for non-aqueous electrolyte secondary batteries, electrode mixtures, electrodes, and non-aqueous electrolyte secondary batteries

Abstract

The objective of the present application is to provide a binder for a non-aqueous electrolyte secondary battery, the binder having high adhesiveness to an active material and a current collector, and having high flexibility to withstand bending in an electrode having a densified mixture layer. The binder for a non-aqueous electrolyte secondary battery that achieves said objective includes: a vinylidene fluoride polymer containing, as a main constituent, a structural unit derived from vinylidene fluoride; and an additive having a specific structure, wherein the mass ratio of the vinylidene fluoride polymer to the additive is 99 / 1-60 / 40.

Description

Technical Field

[0001] The present invention relates to a binder for a non-aqueous electrolyte secondary battery, an electrode binder, an electrode, and a non-aqueous electrolyte secondary battery.

Background Art

[0002] Polyvinylidene fluoride (PVDF) is widely used as a binder in the binder layer or the like of the electrode of a non-aqueous electrolyte secondary battery. From the viewpoint of improving the performance of the battery, the binder is required to have high adhesiveness to the active material and the current collector. For example, Patent Document 1 discloses that a binder composition containing a vinylidene fluoride copolymer obtained by copolymerizing vinylidene fluoride and carboxyethyl acrylate or the like and a non-aqueous solvent has excellent adhesiveness to the current collector.

[0003] In recent years, in order to increase the energy density of the battery, the density of the electrode binder layer has been increasing. Here, in order to increase the energy density of the battery, it is necessary to densely arrange the electrodes with a densified binder layer in the battery can body, and the electrodes are required to be bent into a desired shape. However, an electrode using a binder having excellent adhesiveness to the active material and the current collector has low flexibility, and when the electrode with a densified binder layer is bent, the binder layer may crack or the current collector foil may break, and the electrode may break.

[0004] Therefore, imparting flexibility to the electrode has been studied. Patent Document 2 discloses adding a compound having an enediol bond to the binder in the binder layer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] However, even with the electrode described in Patent Document 2, the flexibility of the electrode is still insufficient. Furthermore, the high adhesiveness required for the binder has not been addressed.

[0007] This invention has been made in view of the above problems. The objective is to provide a binder for non-aqueous electrolyte secondary batteries that combines high adhesion to the active material and current collector with high flexibility that can withstand bending in electrodes with a high-density composite layer. [Means for solving the problem]

[0008] The present invention provides a binder for non-aqueous electrolyte secondary batteries, comprising a vinylidene fluoride polymer whose main constituent component is a structural unit derived from vinylidene fluoride, and one or more additives selected from compounds represented by the following general formula (A), wherein the mass ratio of the vinylidene fluoride polymer to the additives is 99 / 1 to 60 / 40. [ka] (In general formula (A), X represents a divalent to 10-valent atomic group containing one or more atoms or structures selected from the group consisting of aromatic rings, cycloalkanes with polar groups, sulfur atoms, nitrogen atoms, and phosphorus atoms, and having a molecular weight of 300 or less; Y represents a divalent structure with a molecular weight of 200 or less that has an ether bond or an ester bond and is bonded to X via an ether bond or an ester bond; R represents an aliphatic hydrocarbon group whose main chain has 5 to 15 carbon atoms; and n represents an integer between 2 and 10.)

[0009] The present invention also provides an electrode mixture comprising the above-mentioned binder for non-aqueous electrolyte secondary batteries and an electrode active material.

[0010] The present invention also provides an electrode having a current collector and a composite layer provided on the current collector, the composite layer containing the non-aqueous electrolyte secondary battery binder and the electrode active material.

[0011] The present invention also provides a non-aqueous electrolyte secondary battery including the above-mentioned electrodes. [Effects of the Invention]

[0012] The binder for non-aqueous electrolyte secondary batteries of the present invention has high adhesion to the active material and current collector, and even when the electrode with a high-density composite layer is bent, the electrode containing the binder for non-aqueous electrolyte secondary batteries is less likely to break. [Modes for carrying out the invention]

[0013] In this specification, a numerical range indicated by "~" means a numerical range that includes the numbers written before and after "~".

[0014] 1. Binder for non-aqueous electrolyte secondary batteries The binder for non-aqueous electrolyte secondary batteries of the present invention (hereinafter also referred to as "binder") is suitable, for example, as a binder for the electrode mixture layer of a non-aqueous electrolyte secondary battery. However, the uses of the binder are not limited to this.

[0015] As mentioned above, binders used in the electrode mixture layer of non-aqueous electrolyte secondary batteries require high adhesion to the active material and current collector. On the other hand, increasing the binder's adhesion makes the electrode less flexible, and bending an electrode with a high-density mixture layer can cause the mixture layer to crack, the current collector to break, and the electrode to fracture. In other words, there was a trade-off between the binder's adhesion to the active material and current collector and the electrode's flexibility. The reason for this is thought to be as follows: When the binder is firmly bonded to the active material and current collector, it becomes difficult for the current collector to separate from the mixture layer. Electrodes with such firmly bonded components have low flexibility, and when bent, localized force is applied, making the electrode prone to fracture. Conversely, if the bond between the binder and the active material and current collector is weak, electrode fracture during bending is less likely, but the mixture layer is more likely to separate from the current collector. In either case, the performance of the non-aqueous electrolyte secondary battery deteriorates.

[0016] In contrast, the binder of the present invention contains, in a predetermined ratio, a vinylidene fluoride polymer whose main constituent component is a structural unit derived from vinylidene fluoride, and one or more additives selected from compounds represented by the following general formula (A). [ka] In the general formula (A) above, X represents a group of divalent to 10-valent atoms with a molecular weight of 300 or less, including aromatic rings, etc. Y represents a divalent structure with a molecular weight of 200 or less, bonded to X via ether or ester bonds. R represents an aliphatic hydrocarbon group with a main chain having 5 to 15 carbon atoms. n represents an integer between 2 and 10.

[0017] The additive represented by general formula (A) has polar or conjugated groups in the X and Y portions, and a nonpolar group in the R portion. Such additives also function as plasticizers for vinylidene fluoride polymers. For example, when mixed with vinylidene fluoride polymer, if the group represented by X is polar or conjugated, it can easily penetrate between the vinylidene fluoride polymer molecules. At the same time, if the group represented by R has an appropriate length, the intermolecular spacing of the vinylidene fluoride polymer widens sufficiently, increasing the flexibility of the vinylidene fluoride polymer. On the other hand, the above additive also functions to increase the adhesion strength between the binder and the active material or current collector. Increased flexibility of the vinylidene fluoride polymer improves the elongation at break of the binder, thus relieving stress in the mixture layer and increasing the adhesion strength between the binder and the active material or current collector.

[0018] In other words, the electrode having a composite layer containing the binder of the present invention is highly flexible, and even if the density of the composite layer is increased, for example, the electrode is less likely to break when bent. On the other hand, the adhesive strength between the binder and the active material or current collector is high, and delamination is less likely to occur. Therefore, it is possible to realize excellent battery characteristics. The components of the binder will be described below.

[0019] • Polyvinylidene fluoride polymer A vinylidene fluoride polymer is a polymer whose main constituent component is a structural unit derived from vinylidene fluoride. The vinylidene fluoride polymer may be a homopolymer of vinylidene fluoride, or it may contain a homopolymer of vinylidene fluoride and a vinylidene fluoride polymer whose main constituent component is a structural unit derived from vinylidene fluoride. In this case, the vinylidene fluoride polymer may contain only one type of vinylidene fluoride polymer whose main constituent component is a structural unit derived from vinylidene fluoride, or it may contain two or more types. In this specification, "main constituent component is a structural unit derived from vinylidene fluoride" means that the amount of structural units derived from vinylidene fluoride exceeds 50% by mass relative to the total mass of all structural units constituting the vinylidene fluoride polymer. The amount of structural units derived from vinylidene fluoride is preferably 80% by mass or more, and more preferably 90% by mass or more, relative to the total mass of all structural units constituting the vinylidene fluoride polymer. When the amount of structural units derived from vinylidene fluoride in a vinylidene fluoride polymer is 90% by mass or more, the physical properties of the vinylidene fluoride polymer tend to fall within the desired range, and it becomes easier for it to bond with active materials, current collectors, and conductive additives. The amount of structural units derived from vinylide fluoride is, for example, 19 It can be identified by analysis using 1F-NMR, etc.

[0020] The vinylidene fluoride polymer may have structural units derived from compounds other than vinylidene fluoride (hereinafter also referred to as "other compounds"). That is, the vinylidene fluoride polymer may be a copolymer of vinylidene fluoride and other compounds. The type of other compound is not particularly limited and examples include unsaturated dibasic acids, unsaturated dibasic acid monoesters, alkyl vinyl halides, compounds represented by the following general formula (B-1), compounds represented by the following general formula (B-2), compounds represented by the following general formula (B-3), and the like.

[0021] As used herein, an unsaturated dibasic acid is an unsaturated dicarboxylic acid or a derivative thereof. Examples thereof include compounds in which two carboxyl groups are bonded by a linear or branched unsaturated alkylene group having 1 to 6 carbon atoms. More specific examples of the unsaturated dibasic acid include maleic acid, fumaric acid, itaconic acid, citraconic acid, and the like.

[0022] The unsaturated dibasic acid monoester is a monoester compound derived from the above unsaturated dibasic acid. Examples of the unsaturated dibasic acid monoester include maleic acid monomethyl ester, maleic acid monoethyl ester, citraconic acid monomethyl ester, citraconic acid monoethyl ester, and the like.

[0023] As used herein, a halogenated alkyl vinyl compound is a compound having one vinyl group and one or more halogenated alkyl groups, or a compound having one vinyl group and a halogen atom bonded to the vinyl group (excluding vinylidene fluoride). Examples of the halogenated alkyl vinyl compound include vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, fluoroalkyl vinyl ether, perfluoromethyl vinyl ether, and the like.

[0024] The general formula (B-1) is shown below. [Chemical formula] R in the above general formula (B-1) 11 , R 12 , and R 13 each independently represents a hydrogen atom, a fluorine atom, a chlorine atom, or an alkyl group having 1 to 5 carbon atoms. However, it is preferable that there is less steric hindrance during polymerization with vinylidene fluoride, and R 11 and R 12 are preferably hydrogen or an alkyl group having 1 to 3 carbon atoms, and more preferably hydrogen or a methyl group. In particular, both R 11 and R 12 are hydrogen, or R 11 and R12 It is preferable that only one of them is a methyl group.

[0025] In the above general formula (B-1), Z 1 This represents an atomic group in which the number of atoms in the main chain is 1 to 19 and the molecular weight is 472 or less. The molecular weight of the atomic group is preferably 14 to 172. Also, Z 1 The number of atoms in the main chain is preferably 1 to 14, and more preferably 1 to 9. 1 The number of atoms in the main chain refers to the number of atoms in the longest chain connecting the acryloyl group and the carboxyl group. 1 The main chain may be a hydrocarbon chain, but it may also contain nitrogen atoms, sulfur atoms, oxygen atoms, etc.

[0026] Examples of compounds represented by the above general formula (B-1) include 2-carboxyethyl (meth)acrylate; (meth)acryloyloxyethyl succinic acid; (meth)acryloyloxypropyl succinic acid; (meth)acryloyloxyethyl phthalic acid; (meth)acrylamide compounds such as N-carboxyethyl (meth)acrylamide; and thio(meth)acrylate compounds such as carboxyethyl thio(meth)acrylate. In this specification, (meth)acrylate refers to methacrylate, acrylate, or mixtures thereof; (meth)acrylic refers to methacrylic, acrylic, or mixtures thereof; and (meth)acryloyl refers to methacryloyl, acryloyl, or mixtures thereof.

[0027] The general formula (B-2) is shown below. [ka] In the above general formula (B-2), R 14 , R 15 , and R 16 Each of these independently represents a hydrogen atom, a fluorine atom, a chlorine atom, or an alkyl group having 1 to 5 carbon atoms. However, it is preferable that there is little steric hindrance during polymerization with vinylidene fluoride, and R 14 and R 15The hydrogen group is preferably a C1-C3 alkyl group, and more preferably a hydrogen group or a methyl group. In particular, R 14 and R 15 Both are hydrogen, or R 14 and R 15 It is preferable that only one of them is a methyl group.

[0028] In the above general formula (B-2), Z 2 This represents an atomic group in which the number of atoms in the main chain is 1 to 19 and the molecular weight is 484 or less. The molecular weight of the atomic group is preferably between 14 and 184. 2 The number of atoms in the main chain is preferably 1 to 14, and more preferably 1 to 9. 2 The number of atoms in the main chain refers to the number of atoms in the longest chain connecting the oxygen atom bonded to the carbon-carbon double bond with the carboxyl group. 2 The main chain may be a hydrocarbon chain, but it may also contain nitrogen atoms, sulfur atoms, oxygen atoms, etc.

[0029] Examples of compounds represented by the above general formula (B-2) include vinyl carboxyalkyl ethers such as vinyl carboxymethyl ether and vinyl carboxyethyl ether.

[0030] The general formula (B-3) is shown below. [ka] In the above general formula (B-3), R 17 , R 18 , and R 19 Each of these independently represents a hydrogen atom, a fluorine atom, a chlorine atom, or an alkyl group having 1 to 5 carbon atoms. However, it is preferable that there is little steric hindrance during polymerization with vinylidene fluoride, and R 17 and R 18 The hydrogen group is preferably a C1-C3 alkyl group, and more preferably a hydrogen group or a methyl group. In particular, R 17 and R 18 Both are hydrogen, or R 17 and R 18 It is preferable that only one of them is a methyl group.

[0031] In the general formula (B-3) above, E represents a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms that contains at least one hydroxyl group. Examples of hydrocarbon groups containing a hydroxyl group include the hydroxyethyl group and the hydroxypropyl group.

[0032] Examples of compounds represented by the above general formula (B-3) include acrylic acid, methacrylic acid, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methyl acrylate, and 2-hydroxypropyl methacrylate.

[0033] The vinylidene fluoride polymer may contain only one structural unit derived from other compounds, or it may contain two or more. Among the other compounds, structural units derived from acrylic acid, 2-hydroxyethyl acrylate, acryloyloxyethyl succinic acid, and acryloyloxypropyl succinic acid are preferred from the viewpoint of copolymerizability.

[0034] The amount of structural units derived from other compounds is preferably 20% by mass or less, and more preferably 10% by mass or less, relative to the total mass of all structural units constituting the vinylidene fluoride polymer. When the amount of structural units derived from other compounds in the vinylidene fluoride polymer is within the above range, the physical properties of the vinylidene fluoride polymer tend to fall within the desired range, and it becomes easier for it to bond with active materials, current collectors, and conductive additives.

[0035] The content of structural units derived from the above compound in the vinylidene fluoride copolymer is, for example, that of the vinylidene fluoride copolymer 19 It can be identified by analysis using F-NMR or FT-IR.

[0036] Here, the weight-average molecular weight of the vinylidene fluoride polymer is preferably 100,000 to 10,000,000, more preferably 200,000 to 5,000,000, and even more preferably 300,000 to 2,000,000. When the weight-average molecular weight of the vinylidene fluoride polymer is within this range, the physical properties of the vinylidene fluoride polymer tend to fall within the desired range, and it becomes easier for it to bond with active materials, current collectors, and conductive additives. The above weight-average molecular weight is a polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0037] • Additives The additive is a compound selected from the compounds represented by the following general formula (A). The additive may contain only one compound represented by the following general formula (A), or it may contain two or more compounds.

[0038] [ka] In general formula (A), X represents a group of atoms with a molecular weight of 300 or less and a valency of 2 to 10, containing one or more atoms or structures selected from the group consisting of aromatic rings, cycloalkanes with polar groups, sulfur atoms, nitrogen atoms, and phosphorus atoms.

[0039] The atomic group containing an aromatic ring, represented by X above, may contain only one aromatic ring or multiple aromatic rings. If the atomic group has multiple aromatic rings, they may be directly bonded or bonded via a linking group. Examples of linking groups that connect aromatic rings include alkyl groups with 6 or fewer carbon atoms. Specific examples of atomic groups containing aromatic rings include: [ka] (* represents a bond with the structure represented by Y), and includes naphthalene, anthracene, biphenyl, bibenzyl, etc. Note that, for convenience, only one bond is shown for each aromatic ring in the above formula, but an aromatic ring may have multiple bonds.

[0040] The atomic group containing a cycloalkane having a polar group represented by X above may contain only one cycloalkane having a polar group, or it may contain multiple cycloalkanes having a polar group. Examples of polar groups include hydroxyl groups, carboxyl groups, and epoxy groups. When the atomic group contains multiple cycloalkanes having polar groups, they may be directly bonded together or bonded together via linking groups. The linking groups that connect cycloalkanes having polar groups are the same as the linking groups that connect aromatic rings. Specific examples of atomic groups containing cycloalkanes having polar groups include: [ka] (* represents a bond with the structure represented by Y), and includes epoxycycloheptane, epoxycyclooctane, etc. For convenience, only one bond is shown in the above formula, but multiple bonds may be present.

[0041] Examples of atomic groups containing sulfur atoms represented by X above include ethylene sulfide, thietan, dithietan, tetrahydrothiophene, thiophene, etc. Examples of atomic groups containing nitrogen atoms represented by X above include azolidinedione, pyrrolidine, pyrrole, pyrazole, etc. Furthermore, examples of atomic groups containing phosphorus atoms represented by X above include: [ka] (* indicates a bond with the structure represented by Y), and includes phosphyran, phosphole, etc. Note that although three bonds are shown in the above structural formula for convenience, the number of bonds is not limited to three.

[0042] Among the above, the atomic group represented by X in general formula (A) is [ka] A structure selected from the group consisting of (* represents a bond with a structure represented by Y, and the number is not limited) is preferred, and it is more preferred to be an aromatic ring or a structure derived from bisphenol A.

[0043] On the other hand, Y in general formula (A) represents a divalent structure with a molecular weight of 200 or less that is bonded to X via an ether bond or an ester bond. It is preferable that the structure represented by Y is also bonded to the group represented by R via an ether bond or an ester bond. Therefore, it is preferable that the structure represented by Y is one of the divalent structures selected from the group consisting of an ester bond, an ether bond, a divalent structure having ester bonds at both ends, a divalent structure having ether bonds at both ends, or a divalent structure having an ester bond at one end and an ether bond at the other end.

[0044] Furthermore, the structure represented by Y is, [ka] It is more preferable that the structure be selected from the group consisting of (where m represents an integer between 1 and 3, inclusive).

[0045] On the other hand, in general formula (A), R represents an aliphatic hydrocarbon group whose main chain has 5 to 15 carbon atoms. R may consist only of linear chains, only of branched chains, or a combination of linear and branched chains. When R is branched, the main chain of R refers to the longest alkyl chain constituting R. Furthermore, multiple R groups contained in a single molecule may consist of aliphatic hydrocarbon groups with the same number of carbon atoms, or they may consist of aliphatic hydrocarbon groups with different numbers of carbon atoms.

[0046] Examples of aliphatic hydrocarbon groups represented by R include pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, and ethylhexyl groups. Among these, octyl, nonyl, decyl, dodecyl, or ethylhexyl groups are preferred from the viewpoint of plasticizing vinylidene fluoride polymers.

[0047] In general formula (A), n represents an integer between 2 and 10, preferably between 3 and 6.

[0048] Specific examples of compounds represented by the above general formula (A) include compounds represented by the following general formulas (A-1) to (A-4). [ka] In general formula (A-1), Y 1 Each of these independently represents the same structure as Y in the general formula (A) above, and R 1 Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A) above, and n represents an integer between 2 and 6. 1 These may be the same aliphatic hydrocarbon group or different aliphatic hydrocarbon groups.

[0049] The compound represented by the above general formula (A-1) is more preferably the compound represented by the following general formula (a-1). [ka] In general formula (a-1), R 1a Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A) above, and n represents an integer between 2 and 6. 1a These may be the same aliphatic hydrocarbon group or different aliphatic hydrocarbon groups.

[0050] [ka] In general formula (A-2), Y 2 and Y 3 Each of these independently represents the same structure as Y in the general formula (A) above, and R 2 , R 3 Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A) above. 2 and R 3 These may be the same aliphatic hydrocarbon group or different aliphatic hydrocarbon groups.

[0051] The compound represented by the above general formula (A-2) is more preferably the compound represented by the following general formula (a-2). [ka] In general formula (a-2), R 2a and R 3a Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A) above, and p and q independently represent integers from 1 to 3. 2a and R 3a These may be the same aliphatic hydrocarbon group or different aliphatic hydrocarbon groups.

[0052] [ka] In general formula (A-3), Y 4 and Y 5 Each of these independently represents the same structure as Y in the general formula (A) above, and R 4 , R 5 Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A) above. 4 and R 5 These may be the same aliphatic hydrocarbon group or different aliphatic hydrocarbon groups.

[0053] The compound represented by the above general formula (A-3) is more preferably the compound represented by the following general formula (a-3). [ka] In general formula (a-3), R 4a , R 5a Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A) above. 4a and R 5a These may be the same aliphatic hydrocarbon group or different aliphatic hydrocarbon groups. [ka] In general formula (A-4), Y 6 ~Y 8 Each of these independently represents the same structure as Y in the general formula (A) above, and R 6 ~R 8 Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A) above. 6 ~R 8 These may be the same aliphatic hydrocarbon group or different aliphatic hydrocarbon groups.

[0054] The compound represented by the above general formula (A-4) is more preferably the compound represented by the following general formula (a-4). [ka] In general formula (a-4), R 6a ~R 8a Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A) above. 6a ~R 8a These may be the same aliphatic hydrocarbon group or different aliphatic hydrocarbon groups.

[0055] Furthermore, more specific compounds of the above additives include trin-normal alkyl trimellitate (the number of carbon atoms in the alkyl group's main chain is between 5 and 15), triisoalkyl trimellitate (the number of carbon atoms in the alkyl group's main chain is between 5 and 15), tetran-normal alkyl pyromellitate (the number of carbon atoms in the alkyl group's main chain is between 5 and 15), tetraisoalkyl pyromellitate (the number of carbon atoms in the alkyl group's main chain is between 5 and 15), din-normal alkyl phthalate (the number of carbon atoms in the alkyl group's main chain is between 5 and 15), and diisoalkyl phthalate (alkyl This includes polyoxyethylene bisphenol A laurate ester (where the main chain of the group has 5 to 15 carbon atoms), triosalkyl phosphate (where the number of repeating oxyethylene groups is 1 to 3), triosalkyl phosphate (where the main chain of the alkyl group has 5 to 15 carbon atoms), triisoalkyl phosphate (where the main chain of the alkyl group has 5 to 15 carbon atoms), epoxycyclohexane diosalkyl (where the main chain of the alkyl group has 5 to 15 carbon atoms), epoxycyclohexane diisoalkyl (where the main chain of the alkyl group has 5 to 15 carbon atoms), etc. Among these, trimellitic trin-alkyl (the number of carbon atoms in the alkyl group's main chain is between 5 and 15), pyromellitic tetran-alkyl (the number of carbon atoms in the alkyl group's main chain is between 5 and 15), diisononyl phthalate, bisphenol A ethylene glycol ether dilaurylate, 4,5-epoxycyclohexane-1,2-dicarboxylate di2-ethylhexyl, and tri(2-ethylhexyl) phosphate are preferred when added, as they improve the flexibility of the electrode using the binder and enhance the adhesive strength to the active material and current collector.

[0056] The mass ratio of the vinylidene fluoride polymer to the total amount of the additive is preferably 99 / 1 to 60 / 40, more preferably 98 / 2 to 80 / 20, and even more preferably 95 / 5 to 90 / 10. If the amount of the additive is above the lower limit, the electrode using the binder becomes flexible, and breakage of the electrode when bent becomes less likely. On the other hand, if it is below the upper limit, it becomes easier to obtain high adhesive strength.

[0057] ·others The binder may contain components other than the vinylidene fluoride polymer and additives mentioned above. Examples of these other components include polyisocyanate compounds having a blocked polyisocyanate group in which at least one isocyanate group is blocked (stabilized) with a blocking agent.

[0058] Blocked isocyanate groups are regenerated when heated, as the blocking agent dissociates (deblocks) the isocyanate groups. In terms of improving the adhesion strength of the binder to the active material and current collector, it is preferable that 60 mol% or more of the isocyanate groups are blocked by the blocking agent, more preferably 80 mol% or more of the isocyanate groups are blocked, and it is particularly preferable that all of the isocyanate groups of the polyisocyanate compound are blocked by the blocking agent.

[0059] The structure of polyisocyanate compounds is not particularly limited as long as they are compounds having multiple isocyanate groups. Examples include polymers of at least one diisocyanate selected from the group consisting of aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates, in which at least some of the isocyanate groups are blocked by a blocking agent.

[0060] On the other hand, the blocking agent only needs to have a structure that can bond to an isocyanate group and can be detached from the isocyanate group by heating or other means. Examples of blocking agents include oxime compounds, active methylene compounds, pyrazole compounds, mercaptan compounds, alcohol compounds, alkylphenol compounds, phenol compounds, acid amide compounds, acid imide compounds, imidazole compounds, urea compounds, amine compounds, and imide compounds. These can be the same compounds as known blocking agents.

[0061] The above-mentioned blocking agent is preferably detached by heating during drying after applying an electrode mixture containing a binder onto the current collector. From these viewpoints, the blocking agent is preferably an oxime compound, an activated methylene compound, or a pyrazole compound, and among these, methyl ethyl ketoxime, dimethyl malonate, diethyl malonate, ethyl acetoacetate, 3,5-dimethylpyrazole, and pyrazole are preferred.

[0062] The amount of polyisocyanate compound in the binder is not particularly limited, but it is preferable that the amount of polyisocyanate compound be 0.5 parts by mass or more and 50 parts by mass or less, and preferably 2 parts by mass or more and 40 parts by mass or less, per 100 parts by mass of vinylidene fluoride polymer. When the amount of polyisocyanate compound is 2 parts by mass or more, the adhesive strength of the binder to the active material and current collector increases. On the other hand, when the amount of polyisocyanate compound is 40 parts by mass or less, the amount of vinylidene fluoride polymer and additives increases relatively, and the flexibility of the electrode increases.

[0063] • Binder preparation method The method for preparing the binder is not particularly limited, and it can be produced by preparing the vinylidene fluoride polymer and mixing the vinylidene fluoride polymer with the additives and other components.

[0064] The form of the binder is not particularly limited and may be in powder or liquid form. Furthermore, the binder may contain a solvent, be dissolved in a solvent, or be dispersed in a solvent.

[0065] The solvent may be a non-aqueous solvent or water. 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, methyl ethyl ketone, ethyl acetate, n-butyl acetate, n-butanol, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and cyclohexanone. One of these solvents may be used, or two or more may be used in combination.

[0066] 2. Electrode mixture The binder described above can be used in an electrode mixture containing the binder described above and an electrode active material. The electrode mixture may further contain a conductive additive, a solvent, a dispersion medium, and other additives.

[0067] The electrode active material contained in the electrode mixture is not particularly limited, and for example, conventionally known active materials for negative electrodes (negative electrode active material) or positive electrodes (positive electrode active material) can be used.

[0068] Examples of the above-mentioned negative electrode active materials include carbon materials such as artificial graphite, natural graphite, non-graphitizable carbon, easily graphitizable carbon, activated carbon, or carbonized phenolic resin and pitch; metal and alloy materials such as Cu, Li, Mg, B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Cd, Ag, Zn, Hf, Zr, and Y; and metal oxides such as GeO, GeO2, SnO, SnO2, PbO, and PbO2. Materials with coatings applied to their surfaces are also included. The negative electrode active material may be a commercially available product.

[0069] On the other hand, examples of positive electrode active materials include lithium-based positive electrode active materials containing lithium. Examples of lithium-based positive electrode active materials include LiCoO2 and LiNi x Co 1-xComposite metal chalcogen compounds represented by the general formula LiMY2 (where M is one or more of transition metals such as Co, Ni, Fe, Mn, Cr, and V, and Y is a chalcogen element such as O and S) with 0 < x ≤ 1 for O2; composite metal oxides having a spinel structure such as LiMn2O4; and olivine-type lithium compounds such as LiFePO4; etc. are included. Also included are those with a coating applied to the surface of these active materials. Note that the positive electrode active material may be a commercially available product.

[0070] The amount of the active material contained in the electrode binder is appropriately selected according to its type, the function of the electrode, the type of the battery, etc., and is not particularly limited. However, in one example, it is preferably 50% by mass or more and 99.9% by mass or less based on the total amount of the above binder, electrode active material, and conductive assistant. When the amount of the active material is within this range, for example, a sufficient charge-discharge capacity can be obtained, and the battery performance is likely to be good.

[0071] Also, the conductive assistant is not particularly limited as long as it is a compound that can further enhance the conductivity between the active materials or between the active material and the current collector. Examples of the conductive assistant include acetylene black, ketjen black, carbon black, graphite powder, carbon nanofiber, carbon nanotube, and carbon fiber, etc.

[0072] The amount of the conductive assistant contained in the electrode binder is appropriately selected according to its type, the function of the electrode, the type of the battery, etc., and is not particularly limited, but can be arbitrarily set according to its type and the type of the battery. From the viewpoint of enhancing both the improvement of conductivity and the dispersibility of the conductive assistant, in one example, it 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 based on the total amount of the above binder, active material, and conductive assistant.

[0073] Also, the electrode binder may contain a solvent or the like. The type of the solvent is preferably a medium that can be removed by drying, and in addition to nonpolar solvents and low-polar solvents, polar solvents and ionic liquids are also included.

[0074] Examples of solvents include amide compounds such as dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; alcohols such as methanol, ethanol, isopropyl alcohol, 2-ethyl-1-hexanol, 1-nonanol, lauryl alcohol, and tripropylene glycol; amine compounds such as o-toluidine, m-toluidine, and p-toluidine; lactones such as γ-butyrolactone and δ-butyrolactone; sulfoxide and sulfone compounds such as dimethyl sulfoxide and sulfolane; and ionic liquids such as ethylmethylimidazolium salt, acetone, ethyl acetate, and butylmethylimidazolium salt.

[0075] The amount of solvent in the electrode mixture is not particularly limited, but it is preferably 20 to 150 parts by mass per 100 parts by mass of the active material described above.

[0076] The electrode mixture may further contain a dispersion medium, a dispersant, an adhesion aid, a thickener, etc., and known compounds can be used for these. The amounts of these are not particularly limited as long as they do not impair the purpose and effects of the present invention, but in one example, it is preferable that they be 15% by mass or less relative to the total amount of the active material and binder.

[0077] The electrode mixture may further contain additives such as phosphorus compounds, sulfur compounds, organic acids, amine compounds, and nitrogen compounds such as ammonium compounds; organic esters, various silane-based, titanium-based, and aluminum-based coupling agents; vinylidene fluoride polymers other than the vinylidene fluoride copolymers mentioned above, and resins such as polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and polyacrylonitrile (PAN). These are not particularly limited as long as they do not impair the purpose and effects of the present invention, but in one example, it is preferable that they be 15% by mass or less of the total amount of active material and binder.

[0078] The above electrode mixture may be prepared by mixing all the components at once, or by mixing some of the components first and then mixing the remaining components later.

[0079] The viscosity of the electrode mixture is not particularly limited, as long as it prevents dripping, uneven coating, and delayed drying after coating when applying the electrode mixture to obtain the mixture layer, and provides good workability and applicability for electrode fabrication. In one example, a viscosity of 0.1 Pa·s or more and 100 Pa·s or less is preferred. The viscosity of the electrode mixture is measured using an E-type viscometer or the like.

[0080] 3. Electrode The electrode mixture described above can be used to form the electrode layer of various non-aqueous electrolyte secondary batteries. The electrode of a non-aqueous electrolyte secondary battery includes, for example, a current collector and an electrode layer disposed on the current collector. In this case, the electrode mixture described above can be used to form the electrode layer. The electrode may be for a positive electrode or a negative electrode.

[0081] • Current collector The current collectors for the negative and positive electrodes are terminals for extracting electricity. The material of the current collector is not particularly limited, and metal foils or metal meshes made of aluminum, copper, iron, stainless steel, steel, nickel, titanium, etc., can be used. Alternatively, the metal foils or metal meshes may be applied to the surface of other media.

[0082] • Combination layer The composite layer is a layer obtained by applying the above-mentioned electrode composite onto the current collector and drying it. The composite layer may be formed on only one side of the current collector, or it may be arranged on both sides.

[0083] The components in the composite layer are appropriately selected depending on the type of non-aqueous electrolyte secondary battery. The composite layer usually only needs to contain the binder and active material described above, but it may also contain various additives such as conductive additives, dispersants, adhesion aids, and thickeners. These can be the same as those described for the electrode composite.

[0084] Here, the thickness of the mixture layer is not particularly limited, but in one example, 1 μm to 1000 μm is preferred. Also, the basis weight of the mixture layer formed on one side of the current collector is not particularly limited and can be any basis weight, but in one example, 50 to 1000 g / m² is preferred. 2 Preferably, 100-500 g / m 2 This is preferable.

[0085] • Formation of a combined layer The above-mentioned electrode mixture layer can be formed by the steps of applying the above-mentioned electrode mixture onto the current collector and drying it.

[0086] Furthermore, the method of applying the electrode mixture is not particularly limited, and methods such as the doctor blade method, reverse roll method, comma bar method, gravure method, air knife method, die coat method, and dip coat method can be applied.

[0087] Furthermore, after applying the electrode mixture, the solvent (dispersion medium) is dried by heating at an arbitrary temperature. In one example, the drying temperature is preferably 60°C to 500°C, and more preferably 80°C to 200°C. Drying may be performed multiple times at different temperatures. Drying may be performed under atmospheric pressure, under pressure, or under reduced pressure. Further heat treatment may be performed after drying. If the binder contains a polyisocyanate compound having a blocked polyisocyanate group, it is preferable to dry or heat treat at a temperature above the deblocking temperature of the blocking agent.

[0088] After applying and drying the electrode mixture described above, a pressing treatment may be performed. Pressing treatment can improve the electrode density. In one example, the pressing pressure is preferably 1 kPa or more and 10 GPa or less.

[0089] 4.Nonaqueous electrolyte secondary battery As described above, the binders and electrode mixtures can be used as electrodes for various non-aqueous electrolyte secondary batteries, etc., but they may also be used to form other layers of non-aqueous electrolyte secondary batteries. [Examples]

[0090] The following describes specific embodiments of the present invention along with comparative examples, but the present invention is not limited to these.

[0091] [Example 1] Preparation of polyvinylidene fluoride polymer A In a 2-liter autoclave, 1096 g of deionized water, 0.2 g of Metroze® 90SH-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), 2.2 g of 50% by mass diisopropyl peroxydicarbonate-Flon 225cb solution, 426 g of vinylidene fluoride (hereinafter also referred to as "VDF"), and an initial addition of 0.2 g of acryloyloxypropyl succinic acid (hereinafter also referred to as "APS") were charged. After raising the temperature to 26°C and maintaining the temperature at 26°C, a 6% by mass aqueous solution of APS was gradually added at a rate of 0.5 g / min. A total of 4.0 g of APS was added, including the initial amount. The resulting VDF / APS copolymer slurry was dehydrated, washed with water and dehydrated again, and dried at 80°C for 20 hours to obtain a polymer powder (vinylidene fluoride polymer A). The weight-average molecular weight was 800,000.

[0092] • Binder preparation 90 parts by mass of vinylidene fluoride polymer A and 10 parts by mass of trin-normal alkyl trimellitate (hereinafter also referred to as "TATM") shown below were mixed. [ka] (Each R independently represents an alkyl group with 8 carbon atoms or an alkyl group with 10 carbon atoms.)

[0093] [Example 2] The binder was prepared in the same manner as in Example 1, except that the additive used in the binder preparation was changed from TATM to tetran-alkyl pyromellitic acid (hereinafter also referred to as "TAPM") as shown below. [ka] (R represents an alkyl group with 8 carbon atoms or an alkyl group with 10 carbon atoms)

[0094] [Example 3] The binder was prepared in the same manner as in Example 1, except that the additive used in the binder preparation was changed from TATM to diisononyl phthalate (hereinafter also referred to as "DINP") as shown below. [ka] (R represents a nonyl group in all cases)

[0095] [Example 4] The binder was prepared in the same manner as in Example 1, except that the additive used in preparing the binder was changed from TATM to bisphenol A ethylene glycol ether dilaurylate (hereinafter also referred to as "BPDL") as shown below. [ka] (In all cases, R represents a lauryl group.)

[0096] [Example 5] The binder was prepared in the same manner as in Example 1, except that the additive used in the preparation of the binder was changed from TATM to 4,5-epoxycyclohexane-1,2-dicarboxylate di2-ethylhexyl (hereinafter also referred to as "EDOCH") as shown below. [ka] (In all cases, R represents a 2-ethylhexyl group.)

[0097] [Example 6] The binder was prepared in the same manner as in Example 1, except that the additive used in the binder preparation was changed from TATM to tri(2-ethylhexyl) phosphate (hereinafter also referred to as "TOF") as shown below. [ka] (In all cases, R represents a 2-ethylhexyl group.)

[0098] [Comparative Example 1] Without adding any additives, vinylidene fluoride polymer A was used as the binder.

[0099] [Comparative Example 2] The binder was prepared in the same manner as in Example 1, except that the additive used in the binder preparation was changed from TATM to dodecylbenzene (hereinafter also referred to as "DDB"). [ka] (R represents a dodecyl group)

[0100] [Comparative Example 3] The binder was prepared in the same manner as in Example 1, except that the additive used in preparing the binder was changed from TATM to hexyl benzoate (hereinafter also referred to as "HB") as shown below. [ka] (R represents a hexyl group) [Comparative Example 4] The binder was prepared in the same manner as in Example 1, except that the additive used in the binder preparation was changed from TATM to bis(2-ethylhexyl) azelaate (hereinafter also referred to as "DOZ") as shown below. [ka] (Each R represents a 2-ethylhexyl group.)

[0101] [Comparative Example 5] The binder was prepared in the same manner as in Example 1, except that the additive used in the binder preparation was changed from TATM to bis(2-ethylhexyl) adipate (hereinafter also referred to as "DOA") as shown below. [ka] (Each R represents a 2-ethylhexyl group.)

[0102] [Comparative Example 6] The binder was prepared in the same manner as in Example 1, except that the additive used in the binder preparation was changed from TATM to dibutyl phthalate (hereinafter also referred to as "DBP"). [ka] (R represents a butyl group in all cases)

[0103] [Comparative Example 7] The binder was prepared in the same manner as in Example 1, except that the additive used in the binder preparation was changed from TATM to tributyl trimellitate (hereinafter also referred to as "TBTM"). [ka] (Each R represents a butyl group.)

[0104] [Example 7] The binder was prepared in the same manner as in Example 1, except that 98 parts by mass of vinylidene fluoride polymer A and 2 parts by mass of TATM were mixed.

[0105] [Example 8] The binder was prepared in the same manner as in Example 1, except that 95 parts by mass of vinylidene fluoride polymer A and 5 parts by mass of TATM were mixed.

[0106] [Example 9] The binder was prepared in the same manner as in Example 1, except that 80 parts by mass of vinylidene fluoride polymer A and 20 parts by mass of TATM were mixed.

[0107] [Comparative Example 8] The binder was prepared in the same manner as in Example 1, except that 50 parts by mass of vinylidene fluoride polymer A and 50 parts by mass of TATM were mixed during the preparation of the binder.

[0108] [Example 10] Preparation of polyvinylidene fluoride polymer B In a 2-liter autoclave, 1075 g of deionized water, 0.4 g of methylcellulose, 420 g of vinylidene fluoride, and 1.9 g of diisopropyl peroxydicarbonate were charged and suspended polymerized at 25°C to obtain a slurry of vinylidene fluoride homopolymer. The obtained polymer slurry was dehydrated, washed with water, dehydrated again, and dried at 80°C for 20 hours to obtain polymer powder (vinylidene fluoride polymer B). The weight-average molecular weight was 1.1 million.

[0109] • Binder preparation A binder was obtained by mixing 90 parts by mass of vinylidene fluoride polymer B and 10 parts by mass of TATM.

[0110] [Comparative Example 9] Without adding any additives, vinylidene fluoride polymer B was used as the binder.

[0111] [Example 11] Preparation of polyvinylidene fluoride polymer C In a 2-liter autoclave, 1040 g of deionized water, 0.8 g of methylcellulose, 4 g of diisopropyl peroxydicarbonate, 2.5 g of ethyl acetate, 395 g of vinylidene fluoride, and 4 g of monomethyl maleate (hereinafter also referred to as "MMM") were charged. Suspension polymerization was carried out at 28°C to obtain a polymer slurry of vinylidene fluoride copolymer (VDF / MMM). The obtained polymer slurry was dehydrated, washed with water and dehydrated again, and dried at 80°C for 20 hours to obtain polymer powder (vinylidene fluoride polymer C). The weight-average molecular weight was 300,000.

[0112] • Binder preparation A binder was obtained by mixing 90 parts by mass of vinylidene fluoride polymer C with 10 parts by mass of TATM.

[0113] [Comparative Example 10] Without adding any additives, vinylidene fluoride polymer C was used as the binder.

[0114] [Example 12] Preparation of polyvinylidene fluoride polymer D In a 2-liter autoclave, 900 g of deionized water, 0.4 g of Metroze® 90SH-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), 4 g of 50 wt% perbutyl perpivalate-Flon 225cb solution, 396 g of vinylidene fluoride, and an initial addition of 0.2 g of acrylic acid (hereinafter also referred to as "AA") were charged. After raising the temperature to 50°C, a 3 wt% AA aqueous solution was continuously supplied to the reaction vessel under conditions of maintaining a constant pressure during polymerization. A total of 1.96 g of AA was added, including the initial amount. The resulting vinylidene fluoride copolymer (VDF / AA) polymer slurry was dehydrated, washed with water and dehydrated again, and dried at 80°C for 20 hours to obtain polymer powder (vinylidene fluoride polymer D). The weight-average molecular weight was 800,000.

[0115] • Binder preparation A binder was obtained by mixing 90 parts by mass of vinylidene fluoride polymer D with 10 parts by mass of TATM.

[0116] [Comparative Example 11] Without adding any additives, vinylidene fluoride polymer D was used as the binder.

[0117] [Example 13] Preparation of polyvinylidene fluoride polymer E A commercially available polyvinylidene fluoride polymer E (Solvay Corporation, product name Solef 5130, with polyvinylidene fluoride as the main component) was prepared.

[0118] • Binder preparation A binder was obtained by mixing 90 parts by mass of vinylidene fluoride polymer E with 10 parts by mass of TATM.

[0119] [Comparative Example 12] Without adding any additives, vinylidene fluoride polymer E was used as the binder.

[0120] [Example 14] • Binder preparation A binder was obtained by mixing 81 parts by mass of vinylidene fluoride polymer A, 9 parts by mass of block polyisocyanate (BPNCO, manufactured by Asahi Kasei Chemicals, Duranate (trademark registered) TPA-B80E), and 10 parts by mass of TATM.

[0121] [Comparative Example 13] The binder was prepared in the same manner as in Example 14, except that TATM was not added during the preparation of the binder.

[0122] [evaluation] • Evaluation of molecular weight using GPC The molecular weight of the vinylidene fluoride polymer was measured as the weight-average molecular weight in polystyrene terms for a solution of vinylidene fluoride polymer dissolved in N-methylpyrrolidone (hereinafter also referred to as "NMP") at a concentration of 0.1% by weight, using gel permeation chromatography (GPC-900 shodex KD-806M column, JASCO Corporation).

[0123] Preparation of binder solution Each of the above binders was added to 93.5 parts by mass of NMP, and the mixture was stirred with a magnetic stirrer to prepare the binder solutions corresponding to the above-described examples and comparative examples.

[0124] • Electrode fabrication An electrode mixture was prepared by mixing 23 parts by mass of the above binder solution, 100 parts by mass of the positive electrode active material LiCoO2 (lithium cobalt oxide) (hereinafter also referred to as "LCO"), 2 parts by mass of the conductive additive Super-P (manufactured by Imerys Graphite Carbon Co., Ltd.), and 13 parts by mass of NMP. The electrode mixture was applied to one or both sides of an aluminum foil and dried to obtain an electrode. Hereinafter, an electrode obtained by applying the electrode mixture to both sides of an aluminum foil will be referred to as a double-sided coated electrode, and an electrode obtained by applying the electrode mixture to only one side of an aluminum foil will be referred to as a single-sided coated electrode.

[0125] • Calculation of electrode density The electrode density was determined by the following measurement method. The double-sided coated electrode and current collector were each cut to a length of 50 mm and a width of 20 mm, and their weights were measured using an electronic balance. The weight of the positive electrode mixture layer was calculated from the difference between the obtained electrode weight and the current collector weight. The thickness of the double-sided coated electrode and current collector was measured at five points using a micrometer. The difference between the obtained average electrode thickness and the average current collector thickness was taken as the thickness of the positive electrode mixture layer, and the volume of the positive electrode mixture layer was calculated by multiplying this thickness by the electrode area. The electrode density of the positive electrode mixture layer was calculated by dividing the weight of the mixture layer of the positive electrode mixture layer by the obtained volume of the positive electrode mixture layer.

[0126] • Measurement of fracture electrode density Double-sided coated electrodes, cut to a length of 50 mm and a width of 20 mm, were pressed using a roll press to adjust the electrode density as appropriate, and used as measurement samples. Using a tensile testing machine (Orientec Co., Ltd. UNIVERSAL TESTING INSTRUMENT MODEL: STB-1225), the measurement samples were bent at a head speed of 30 mm / min and a compression test was performed. The bent portion of the measurement sample was opened, and fracture was determined by whether or not light could pass through from behind. The minimum electrode density at which fracture occurred was defined as the fracture electrode density and used as an indicator of electrode flexibility. Furthermore, compared to a comparative example without additives, the following criteria were used to evaluate the electrode flexibility as a ratio to the fracture electrode density. A higher fracture electrode density compared to the comparative example indicates superior electrode flexibility. Examples 1-9 and comparative examples 2-8 were compared with comparative example 1. Example 10 was compared with comparative example 9, Example 11 with comparative example 10, Example 12 with comparative example 11, Example 13 with comparative example 12, and Example 14 with comparative example 13. ◎: Breaking electrode density is 3% or higher compared to the comparative example. ○: Rupture electrode density is 1% or more but less than 3% compared to the comparative example. ×: Breaking electrode density is less than 1% compared to the comparative example.

[0127] • Measurement of peel strength A single-sided coated electrode cut to a length of 50 mm and a width of 20 mm was used as the measurement sample. In accordance with JIS K6854-1, a tensile testing machine (Orientec Co., Ltd. UNIVERSAL TESTING INSTRUMENT MODEL: STB-1225) was used to perform a 90-degree peel test at a head speed of 10 mm / min, and the peel strength (gf / mm) was measured. Furthermore, the peel strength was evaluated against a comparative example that did not contain additives according to the following criteria as a ratio to the peel strength. Examples 1 to 9 and comparative examples 2 to 8 were compared with comparative example 1. Example 10 was compared with comparative example 9, Example 11 with comparative example 10, Example 12 with comparative example 11, Example 13 with comparative example 12, and Example 14 with comparative example 13. ○: Peel strength reduction is within 15% compared to the comparative example. ×: Peel strength decreased by 15% or more compared to the comparative example.

[0128] [Table 1]

[0129] As shown in Table 1 above, when the mass ratio of the vinylidene fluoride polymer to the additive of a predetermined structure was 99 / 1 to 60 / 40 (Examples 1 to 9), the fracture electrode density improved in all cases compared to Comparative Example 1, which did not contain the additive, and the peel strength was also sufficiently high. In contrast, when there was no group corresponding to X in the general formula (A) above (Comparative Examples 4 and 5), the peel strength was low. On the other hand, when there was no group corresponding to Y (Comparative Example 2), or when there was only one atomic group represented by YR (Comparative Example 3), both the fracture electrode density and peel strength were low. Furthermore, even when there was a group corresponding to X, when the number of carbon atoms in the alkyl group (R) of the additive was small (Comparative Examples 6 and 7), although the fracture electrode density improved, the peel strength was low because the plasticization of the vinylidene fluoride polymer was insufficient. On the other hand, when there was too much additive (Comparative Example 8), although the electrode flexibility was high and it was possible to improve the fracture electrode density, the peel strength decreased.

[0130] Furthermore, even when the type of vinylidene fluoride polymer was changed, when the mass ratio with the additive of the predetermined structure was 99 / 1 to 60 / 40 (Examples 10 to 13), the fracture electrode density was improved compared to Comparative Examples 9 to 12, and the peel strength was also sufficiently high.

[0131] Furthermore, in Example 14, where blocked polyisocyanate was added, the peel strength was very high. In this case as well, the fracture electrode density was improved and the peel strength was sufficiently high compared to Comparative Example 13, which did not contain any additives.

[0132] [Example 15] 6.5 parts by mass of the binder prepared in Example 1 were added to 93.5 parts by mass of NMP and stirred with a magnetic stirrer to prepare a binder solution. 30.8 parts by mass of this binder solution and Li as the active material were added. 1.0 Ni 0.85 Co 0.1 Al 0.05 An electrode mixture was prepared by mixing 100 parts by mass of O2 (hereinafter also referred to as "NCA") with 2 parts by mass of Super-P (manufactured by Imerys Graphite Carbon Corporation) and 5.8 parts by mass of NMP as conductive additives. The resulting electrode mixture was coated onto aluminum foil and dried to obtain an electrode. The fracture electrode density and the peel strength of the composite layer were measured for the electrode in question in the same manner as described above. The fracture electrode density and peel strength were evaluated based on Comparative Example 14 described below.

[0133] [Comparative Example 14] Except for not adding TATM when preparing the binder, the electrodes were formed in the same manner as in Example 15, and the fracture electrode density and the peel strength of the composite layer were measured for the electrodes in the same manner as described above.

[0134] [Example 16] 8.5 parts by mass of the binder prepared in Example 10 were added to 91.5 parts by mass of NMP and stirred with a magnetic stirrer to prepare a binder solution. 47.6 parts by mass of this binder solution was mixed with 100 parts by mass of LiFePO4 (lithium iron phosphate (hereinafter also referred to as "LFP")) as an active material, and 3 parts by mass of Super-P (manufactured by Imerys Graphite Carbon Co., Ltd.) and 3 parts by mass of NMP as conductive additives to prepare an electrode mixture. The obtained electrode mixture was coated onto aluminum foil and dried to obtain an electrode. The fracture electrode density and the peel strength of the mixture layer were measured for the electrode in the same manner as described above. The fracture electrode density and peel strength were evaluated based on Comparative Example 15 described below.

[0135] [Comparative Example 15] Except for not adding TATM when preparing the binder, the electrodes were formed in the same manner as in Example 16, and the fracture electrode density and the peel strength of the composite layer were measured for the electrodes in the same manner as described above.

[0136] [Example 17] 6.5 parts by mass of the binder prepared in Example 1 were added to 93.5 parts by mass of NMP and stirred with a magnetic stirrer to prepare a binder solution. 30.8 parts by mass of this binder solution and Li as the active material were added. 1.00 Ni 0.8 Co 0.1 Mn 0.1 An electrode mixture was prepared by mixing 100 parts by mass of O2 (hereinafter also referred to as "NCM") with 2 parts by mass of Super-P (manufactured by Imerys Graphite Carbon Co., Ltd.) and 5.8 parts by mass of NMP as conductive additives. The prepared electrode mixture was applied to aluminum foil and dried to obtain an electrode. The fracture electrode density and the peel strength of the mixture layer were measured for the electrode in the same manner as described above. The fracture electrode density and peel strength were evaluated based on Comparative Example 16 described below.

[0137] [Comparative Example 16] Except for not adding TATM when preparing the binder, the electrodes were formed in the same manner as in Example 17, and the fracture electrode density and the peel strength of the composite layer were measured for the electrodes in the same manner as described above.

[0138] [Table 2]

[0139] As shown in Table 2 above, even when the active material was changed, when the mass ratio of vinylidene fluoride polymer to the additive of the predetermined structure was 99 / 1 to 60 / 40 (Examples 15 to 17), the fracture electrode density was improved in all cases compared to Comparative Examples 14 to 16, in which no additive was added, and the peel strength was also sufficiently high.

[0140] This application claims priority under Japanese Patent Application No. 2021-013550, filed on 29 January 2021. All provisions of the said application are incorporated herein by reference. [Industrial applicability]

[0141] The binder for non-aqueous electrolyte secondary batteries of the present invention makes it possible to provide an electrode that combines high adhesion with high flexibility that can withstand bending in an electrode with a high-density composite layer.

Claims

1. A vinylidene fluoride polymer whose main constituent component is a structural unit derived from vinylidene fluoride, One or more additives selected from the compounds represented by the following general formula (A) and the compounds represented by the following general formula (A-4), Includes, The mass ratio of the vinylidene fluoride polymer to the additive is 99 / 1 to 80 / 20. The aforementioned vinylidene fluoride polymer vinylidene fluoride and At least one compound selected from the group consisting of unsaturated dibasic acids, unsaturated dibasic acid monoesters, alkyl vinyl halides, compounds represented by the following general formula (B-1), compounds represented by the following general formula (B-2), and compounds represented by the following general formula (B-3), Including the polymer, A binder for the composite layer of non-aqueous electrolyte secondary batteries. 【Chemistry 1】 (In general formula (A), X represents a group of divalent to decavalent atoms that contains one or more structures selected from the group consisting of aromatic rings and cycloalkanes having polar groups, and has a molecular weight of 300 or less. Y represents a divalent structure with a molecular weight of 200 or less, containing an ether bond or ester bond and bonded to X via an ether bond or ester bond. R represents an aliphatic hydrocarbon group whose main chain has 5 to 15 carbon atoms. n represents an integer between 2 and 10 (inclusive). 【Chemistry 2】 (In general formula (A-4), Y ６ ~Y ８ Each of these independently represents a divalent structure with a molecular weight of 200 or less, containing either an ether bond or an ester bond, and bonded to a phosphorus atom via an ether bond or an ester bond. R ６ ~R ８ Each of these independently represents an aliphatic hydrocarbon group with a main chain having 5 to 15 carbon atoms. 【Transformation 3】 (In general formula (B-1), R11, R12, and R13 each independently represent a hydrogen atom, a fluorine atom, a chlorine atom, or an alkyl group having 1 to 5 carbon atoms. (Z1 represents an atomic group in which the number of atoms in the main chain is between 1 and 19 and the molecular weight is 472 or less.) 【Chemistry 4】 (In general formula (B-2), R14, R15, and R16 each independently represent a hydrogen atom, a fluorine atom, a chlorine atom, or an alkyl group having 1 to 5 carbon atoms. (Z2 represents an atomic group in which the number of atoms in the main chain is between 1 and 19, and the molecular weight is 484 or less.) 【Transformation 5】 (In general formula (B-3), R17, R18, and R19 each independently represent a hydrogen atom, a fluorine atom, a chlorine atom, or an alkyl group having 1 to 5 carbon atoms. E represents a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms, which may contain a hydroxyl group.

2. A vinylidene fluoride polymer having structural units derived from vinylidene fluoride as its main constituent component, One or more additives selected from the compounds represented by the following general formula (A) and the compounds represented by the following general formula (A-4), Includes, The mass ratio of the vinylidene fluoride polymer to the additive is 99 / 1 to 80 / 20. A binder for the composite layer of non-aqueous electrolyte secondary batteries. 【Transformation 6】 (In general formula (A), X, Y, R, and n satisfy one of the combinations shown in (i) to (iii) below) (i) X represents a divalent to 10-valent atomic group containing one or more cycloalkanes having polar groups and having a molecular weight of 300 or less; Y represents a divalent structure with a molecular weight of 200 or less that contains an ether bond or an ester bond and is bonded to X via an ether bond or an ester bond; R represents an aliphatic hydrocarbon group whose main chain has 5 to 15 carbon atoms; and n represents an integer between 2 and 10. (ii) X represents a divalent to 10-valent atomic group having one or more structures selected from the group consisting of aromatic rings and cycloalkanes having polar groups, and having a molecular weight of 300 or less; Y represents a divalent structure having a molecular weight of 200 or less, containing an ether bond and bonded to X via an ether bond or ester bond; R represents an aliphatic hydrocarbon group having 5 to 15 carbon atoms in the main chain; and n represents an integer between 2 and 10. (iii) X represents a divalent to 10-valent atomic group containing one or more aromatic rings and having a molecular weight of 300 or less; Y represents a divalent structure with a molecular weight of 200 or less that contains an ether bond and is bonded to X via an ether bond or ester bond; R represents an aliphatic hydrocarbon group whose main chain has 5 to 15 carbon atoms; and n represents an integer between 3 and 10. 【Transformation 7】 (In general formula (A-4), Y6 to Y8 each independently represent a divalent structure with a molecular weight of 200 or less, containing either an ether bond or an ester bond, and bonded to the phosphorus atom via an ether bond or an ester bond. R6 to R8 each independently represent an aliphatic hydrocarbon group with a main chain having 5 to 15 carbon atoms.

3. In the general formula (A) above, Y is a divalent structure selected from the group consisting of an ester bond, an ether bond, a divalent structure having ester bonds at both ends, a divalent structure having ether bonds at both ends, and a divalent structure having an ester bond at one end and an ether bond at the other end. A binder for the composite layer of a non-aqueous electrolyte secondary battery according to claim 1 or 2.

4. In the general formula (A) above, Y is an ether bond, an ester bond, and 【Transformation 8】 It is one of the structures selected from the group consisting of (where m represents an integer between 1 and 3, inclusive), A binder for the composite layer of a non-aqueous electrolyte secondary battery according to claim 3.

5. In the general formula (A) above, X comprises an aromatic ring or a cycloalkane having a polar group, and Y has an ester bond. A binder for the composite layer of a non-aqueous electrolyte secondary battery according to claim 1 or 2.

6. The compound represented by the general formula (A) is a compound represented by any of the following general formulas (A-1) to (A-3). A binder for the composite layer of a non-aqueous electrolyte secondary battery according to claim 1. 【Chemistry 9】 (In general formula (A-1), Y １ Each of these independently represents the same structure as Y in the general formula (A), R １ Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A), n represents an integer between 2 and 6 (inclusive). 【Chemistry 10】 (In general formula (A-2), Y ２ and Y ３ Each of these independently represents the same structure as Y in the general formula (A), R ２ , R ３ each independently represents an aliphatic hydrocarbon group identical to R in the general formula (A)) 【Chemistry 11】 (In general formula (A-3), Y ４ and Y ５ Each of these independently represents the same structure as Y in the general formula (A), R ４ , R ５ Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A) above.

7. The compound represented by the general formula (A) is a compound represented by any of the following general formulas (a-1) to (a-3). A binder for the composite layer of a non-aqueous electrolyte secondary battery according to claim 6. 【Chemistry 12】 (In general formula (a-1), R １ａ Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A), n represents an integer between 2 and 6 (inclusive). 【Chemistry 13】 (In general formula (a-2), R ２ａ and R ３ａ Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A), (p and q each independently represent integers between 1 and 3.) 【Chemistry 14】 (In general formula (a-3), R ４ａ , R ５ａ Each of these independently represents the same aliphatic hydrocarbon group as R in the general formula (A) above.

8. The compound represented by the general formula (A-4) is the compound represented by the following general formula (a-4): A binder for the composite layer of a non-aqueous electrolyte secondary battery according to claim 1 or 2. 【Chemistry 15】 (In general formula (a-4), R ６ａ ~R ８ａ Each of these independently corresponds to R in the general formula (A-4) ６ ~R ８ (Represents the same aliphatic hydrocarbon group as)

9. The present invention further includes polyisocyanate compounds in which at least some isocyanate groups are blocked by a blocking agent. A binder for the composite layer of a non-aqueous electrolyte secondary battery according to any one of claims 1 to 8.

10. A binder for the composite layer of a non-aqueous electrolyte secondary battery according to any one of claims 1 to 9, Electrode active material and, Electrode mixture.

11. The device comprises a current collector and a composite layer provided on the current collector, which includes a binder for the composite layer of a non-aqueous electrolyte secondary battery according to any one of claims 1 to 9 and an electrode active material. electrode.

12. Including the electrode according to claim 11, Nonaqueous electrolyte secondary battery.

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