Binder, binder liquid, electrode mixture, electrode, intermediate layer, and battery

Abstract

The present invention enables the achievement of a binder which is excellent in terms of adhesion between materials that respectively constitute an electrode and an intermediate layer and adhesion between members that constitute a battery, and which is not likely to increase the resistance at an interface between materials. A binder according to the present invention contains a vinylidene fluoride copolymer which has a constituent unit derived from vinylidene fluoride and another constituent unit derived from a monomer other than vinylidene fluoride, wherein: the vinylidene fluoride copolymer has a cationic site and an anionic site; and the cationic site and the anionic site are present in the another constituent unit.

Description

Binders, binder solutions, electrode mixtures, electrodes, intermediate layers and batteries

[0001] The present invention relates to a binder, a binder liquid, an electrode mixture, an electrode, an intermediate layer, and a battery.

[0002] Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have high voltage and high energy density and are therefore used in a variety of applications, for example, as power sources for mobile electronic devices such as smartphones, electric vehicles, etc. Among non-aqueous electrolyte secondary batteries, all-solid-state batteries, which use a solid electrolyte, are known to have higher output and higher energy density than conventional batteries, which use a liquid electrolyte.

[0003] A typical electrode for a non-aqueous electrolyte secondary battery includes a current collector and an electrode mixture layer disposed on the current collector. The electrode mixture layer typically contains an electrode active material and a binder for adhering the electrode active material to the current collector. Conventionally, such binders have been vinylidene fluoride homopolymers (polyvinylidene fluoride) or vinylidene fluoride copolymers obtained by copolymerizing vinylidene fluoride with other monomers. These materials are also used as binders for intermediate layers of non-aqueous electrolyte secondary batteries.

[0004] For example, it is known that a vinylidene fluoride copolymer obtained by copolymerizing vinylidene fluoride with a monomer having a polar functional group has higher adhesive strength to constituent materials of non-aqueous electrolyte secondary batteries (e.g., current collectors, electrode active materials, etc.) than a vinylidene fluoride homopolymer. Patent Document 1 proposes a copolymer of vinylidene fluoride and a monoester of an unsaturated dibasic acid and a copolymer of vinylidene fluoride and vinylene carbonate.

[0005] Japanese Patent Application Publication No. 6-172452

[0006] However, since vinylidene fluoride polymers are not electrically conductive, there is a need to further improve the adhesiveness of vinylidene fluoride polymers so that the amount of vinylidene fluoride polymer used can be reduced to improve battery performance. Also, in all-solid-state batteries, there is room for improvement in reducing the resistance at the interfaces between the materials contained therein.

[0007] An object of one aspect of the present invention is to provide a binder that has excellent adhesion between materials constituting an electrode and an intermediate layer, and between components constituting a battery, and that is less likely to increase resistance at the interface between the materials.

[0008] In order to solve the above problems, a binder according to one embodiment of the present invention contains a vinylidene fluoride copolymer having a constituent unit derived from vinylidene fluoride and another constituent unit derived from a monomer other than vinylidene fluoride, the vinylidene fluoride copolymer having a cationic moiety and an anionic moiety, and the cationic moiety and the anionic moiety are present in the other constituent unit.

[0009] According to one aspect of the present invention, it is possible to realize a binder that has excellent adhesion between materials constituting an electrode and an intermediate layer, and between components constituting a battery, and that is less likely to increase resistance at the interface between the materials.

[0010] [Binder] A binder according to one embodiment of the present invention will be described in detail below. The binder according to this embodiment contains a vinylidene fluoride copolymer having structural units derived from vinylidene fluoride and other structural units derived from monomers other than vinylidene fluoride. The vinylidene fluoride copolymer has cationic moieties and anionic moieties. The cationic moieties and anionic moieties are present in the other structural units.

[0011] The structure of the cationic moiety is not particularly limited as long as it has cationic properties, and examples of the cationic moiety include a tertiary carbocation, a quaternary ammonium ion, a pyridinium ion, and a pyrrolidinium ion.

[0012] The structure of the anionic moiety is not particularly limited as long as it has an anionic property. For example, the anionic moiety may be —CO ２ - , -PO4 - - and -SO3 - Salts of these structures may also be used.

[0013] The anionic and cationic moieties may be contained in the vinylidene fluoride copolymer as structural units derived from zwitterionic monomers, or may be contained in the vinylidene fluoride copolymer as structural units derived from anionic and cationic monomers, respectively.

[0014] Here, vinylidene fluoride copolymers obtained by copolymerizing vinylidene fluoride with a monomer having a functional group such as a carboxy group have been conventionally known. Such vinylidene fluoride copolymers have carboxy groups in the anionic moieties derived from a monomer other than vinylidene fluoride. A binder containing a vinylidene fluoride copolymer that has only carboxy groups and does not have both anionic and cationic moieties can adhere to materials constituting electrodes and intermediate layers through hydrogen bonding. On the other hand, because the vinylidene fluoride copolymer has both cationic and anionic moieties, a binder containing the copolymer is more likely to form not only hydrogen bonds but also electrostatic interactions with materials constituting electrodes and intermediate layers. Therefore, such binders have excellent adhesive properties.

[0015] In this specification, "excellent adhesiveness" means superior adhesiveness compared to an electrode or intermediate layer prepared under similar conditions except that it does not contain the above-mentioned binder. Adhesion can be measured by a conventionally known method. For example, the 90° peel strength between an electrode mixture and a metal foil of an electrode prepared by applying an electrode mixture to a metal foil may be used as an indicator of the adhesiveness of the electrode mixture. Furthermore, for example, an intermediate layer prepared by applying an intermediate layer mixture to an intermediate layer substrate and an electrode may be bonded together, and the 90° peel strength between the intermediate layer mixture and the electrode may be used as an indicator of the adhesiveness of the intermediate layer mixture.

[0016] The other structural unit preferably includes a structural unit derived from a zwitterionic monomer copolymerizable with vinylidene fluoride. By copolymerizing the zwitterionic monomer with vinylidene fluoride, cationic and anionic moieties can be simultaneously introduced. Furthermore, the polymerization stability is higher than when an anionic monomer having an anionic moiety, a cationic monomer having a cationic moiety, and vinylidene fluoride are copolymerized.

[0017] The zwitterionic monomer may be a compound represented by formula (1):

[0018]

[0019] In formula (1), Ha, Hb, and Hc are each independently selected from hydrogen and an alkyl group having 1 to 4 carbon atoms. The alkyl group having 1 to 4 carbon atoms is a linear or branched alkyl group, and examples thereof include a methyl group, an ethyl group, a propyl group, a 1-methylethyl group, a butyl group, a 2-methylpropyl group, a 1-methylpropyl group, and a 1,1-dimethylethyl group. It is preferred that Ha, Hb, and Hc are each independently selected from hydrogen and a methyl group.

[0020] In formula (1), Xa is an atomic group consisting of an atomic chain formed by bonding 2 to 6 atoms in a chain shape. Xa is a divalent atomic group. Xa is preferably an atomic chain formed by 2 to 6 atoms, and particularly preferably an atomic chain formed by 3 to 4 atoms. The atomic chain preferably contains 1 to 5 carbon atoms and at least one nitrogen atom or oxygen atom. Xa more preferably contains an alkylene group having 1 to 5 carbon atoms and one end of which is a nitrogen atom or an oxygen atom, and is preferably -NHCH ２ CH ２ CH ２ - or -OCH ２ CH ２ It is particularly preferred that -.

[0021] In formula (1), Xb is an atomic group consisting of an atomic chain formed by 1 to 5 atoms bonded in a chain shape. Xb is a divalent atomic group. Xb is preferably an atomic chain formed by 1 to 5 atoms, and more preferably an atomic chain formed by 1 to 4 atoms. The atomic chain contains 1 to 4 carbon atoms and may contain an oxygen atom (for example, one oxygen atom). Xb is more preferably an alkylene group having 1 to 4 carbon atoms.

[0022] In formula (1), Ya is an atomic group containing an ionic group. The ionic group preferably contains at least one element with high electronegativity. In this specification, "element with high electronegativity" refers to an element in Groups 15 to 17, such as a nonmetallic element in Groups 15 to 17. Ya is -N ＋ (-Za １ ) (-Za ２ )-, -O-P(=O)(-O － ) —O— or —S ＋ (-Za ３ )- is more preferred, and -N ＋ (-Za １ ) (-Za ２ )- or -O-P(=O)(-O － )-O- is particularly preferred. １ , Za ２ , and Za ３ are each independently selected from hydrogen, an alkyl group having 1 to 5 carbon atoms, or Xa-C(O)-C(Hc)=C(Ha)(Hb). The alkyl group having 1 to 5 carbon atoms is a linear or branched alkyl group. Xa and Ha to Hc are the same as those described above for Xa and Ha to Hc. Za １ , Za ２ , and Za ３ are each independently preferably an alkyl group having 1 to 3 carbon atoms or Xa-C(O)-C(Hc)=C(Ha)(Hb), and particularly preferably a methyl group or Xa-C(O)-C(Hc)=C(Ha)(Hb). １ , Za ２ , and Za ３ When Xa-C(O)-C(Hc)=C(Ha)(Hb) is included in formula (1), there are multiple Xa and multiple Ha to Hc, but it is preferable that each Xa, each Ha, each Hb, and each Hc is the same.

[0023] In formula (1), Yb is an atomic group containing an ionic group. The ionic group preferably contains at least one element having a high electronegativity. Yb is —N ＋ (-Zb １ ) (-Zb ２ ) (-Zb ３ ), -S＋ (-Zb ４ ) (-Zb ５ ), -O-P(=O)(-O － )-O(-Zb ６ ), -SO ３ － , -COO － , -SO ３ More preferably, it is -M or -COOM, and ＋ (-Zb １ ) (-Zb ２ ) (-Zb ３ ), -SO ３ － , -COO － It is particularly preferable that M is hydrogen or a metal ion, and it is preferable that M is easily ionized. １ , Zb ２ , Zb ３ , Zb ４ , Zb ５ and Zb ６ are each independently selected from hydrogen or an alkyl group having 1 to 5 carbon atoms. The alkyl group having 1 to 5 carbon atoms is a linear or branched alkyl group. １ , Zb ２ , Zb ３ , Zb ４ , Zb ５ and Zb ６ are each independently preferably an alkyl group having 1 to 3 carbon atoms, and particularly preferably a methyl group. Examples of metal ions used as M include lithium, sodium, potassium, calcium, and magnesium ions.

[0024] In formula (1), one of Ya and Yb is an anionic group, and the other is a cationic group. ＋ (-Za １ ) (-Za ２ ) - or -S ＋ (-Za ３ )-, Yb is -O-P(=O)(-O － )-O(-Zb ６ ), -SO ３ － , -COO － , -SO ３For example, Ya may be -O-P(=O)(-O － ) —O—, Yb is —N ＋ (-Zb １ ) (-Zb ２ ) (-Zb ３ ), or -S ＋ (-Zb ４ ) (-Zb ５ ) may also be used.

[0025] Examples of zwitterionic monomers include ammonio alkylene sulfonates, ammonio alkylene carboxylates, ammonio alkylene phosphonates, sulfonio alkylene carboxylates, and amine oxides. The zwitterionic monomers may also be the compounds shown in (1) to (8) below.

[0026]

[0027] The amounts of the monomer having an anionic moiety and the monomer having a cationic moiety introduced are not particularly limited. For example, the total amount of the monomer having an anionic moiety and the monomer having a cationic moiety introduced may be 0.05 wt % or more, preferably 0.08 wt % or more, and more preferably 0.15 wt % or more, relative to the total weight of the vinylidene fluoride copolymer. It is preferable that the total amount of the monomer having an anionic moiety and the monomer having a cationic moiety introduced in this ratio from the viewpoint of fully achieving the effects of the present invention. Furthermore, the total amount of the monomer having an anionic moiety and the monomer having a cationic moiety introduced in this ratio may be 10 wt % or less, preferably 5 wt % or less, and more preferably 2 wt % or less, relative to the total weight of the vinylidene fluoride copolymer. It is preferable that the total amount of the monomer having an anionic moiety and the monomer having a cationic moiety introduced in this ratio from the viewpoint of optimizing the reactivity with vinylidene fluoride.

[0028] The ratio of the monomer having an anionic moiety to the monomer having a cationic moiety introduced is not particularly limited. For example, it is preferable to introduce the monomer having an anionic moiety and the monomer having a cationic moiety into vinylidene fluoride so that the ratio of the amount of cationic moieties to the amount of anionic moieties in the resulting vinylidene fluoride copolymer (molar ratio: cationic moieties / anionic moieties) is in the range of 0.5 to 2.0. Furthermore, the ratio of the amount of cationic moieties to the amount of anionic moieties is more preferably in the range of 0.7 to 1.4, even more preferably in the range of 0.8 to 1.2, and even more preferably in the range of 0.9 to 1.1. Having the ratio of the anionic moieties and the cationic moieties introduced in this range is preferable from the viewpoint of further strengthening electrostatic interactions. Note that when both the anionic moieties and the cationic moieties are derived solely from zwitterionic monomers, the ratio of the amount of cationic moieties to the amount of anionic moieties in the resulting vinylidene fluoride copolymer (cationic moieties / anionic moieties) can be in the range of 0.5 to 2, or even 1.0.

[0029] Alternatively, a zwitterionic monomer containing both an anionic and cationic moiety may be copolymerized with vinylidene fluoride. Copolymerizing a zwitterionic monomer with vinylidene fluoride facilitates achieving a favorable ratio of anionic and cationic moieties. Furthermore, in order to adjust the ratio of anionic and cationic moieties introduced into the vinylidene fluoride copolymer, a monomer containing an anionic moiety or a monomer containing a cationic moiety may be copolymerized in addition to the zwitterionic monomer.

[0030] The amount of zwitterionic monomer introduced is not particularly limited. For example, the amount of zwitterionic monomer introduced may be 0.05 wt % or more, preferably 0.08 wt % or more, and more preferably 0.15 wt % or more, relative to the total weight of the vinylidene fluoride copolymer. This proportion of the amount of zwitterionic monomer introduced is preferred from the viewpoint of fully obtaining the effects of the zwitterionic monomer. Furthermore, the amount of zwitterionic monomer introduced may be 10 wt % or less, preferably 5 wt % or less, and more preferably 2 wt % or less, relative to the total weight of the vinylidene fluoride copolymer. This proportion of the amount of zwitterionic monomer introduced is preferred from the viewpoint of optimizing reactivity with vinylidene fluoride.

[0031] When the vinylidene fluoride copolymer according to this embodiment is used in a non-aqueous electrolyte secondary battery, the amount of zwitterionic monomer introduced may be 5 wt % or less, preferably 2 wt % or less, and more preferably 1 wt % or less, based on the total weight of the vinylidene fluoride copolymer. The amount of zwitterionic monomer introduced in this proportion is preferable from the viewpoint of ease of handling during production. The amount of zwitterionic monomer introduced is, for example, １ H-NMR and １９ It can be identified by F-NMR.

[0032] The vinylidene fluoride copolymer may contain a structural unit derived from any monomer in addition to the structural units derived from vinylidene fluoride and the other structural units described above. For example, the vinylidene fluoride copolymer may contain a structural unit derived from a fluorine-containing monomer copolymerizable with vinylidene fluoride.

[0033] The fluorine-containing monomer is C ｎ H （２ｎ＋１－ｙ） F ｙ or a compound (excluding vinylidene fluoride) in which at least one fluorine atom is bonded to a carbon atom having a double bond, the compound being represented by the formula: where n is an integer of 0 or more, and y is an integer of 1 or more and (2n+1) or less.

[0034] Examples of the fluorine-containing monomer include vinyl fluoride, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, fluoroalkyl vinyl ether, perfluoroalkyl vinyl ether, etc. From the viewpoint of increasing the flexibility of the electrode, the fluorine-containing monomer is preferably selected from tetrafluoroethylene, hexafluoropropylene, and chlorotrifluoroethylene.

[0035] When a fluorine-containing monomer is introduced, the amount of the fluorine-containing monomer introduced is not particularly limited. For example, when a vinylidene fluoride copolymer is used in combination with an electrolyte solution, the amount of the fluorine-containing monomer introduced may be 0% by weight or more, preferably 1% by weight or more, more preferably 2% by weight or more, and even more preferably 3% by weight or more, relative to the total weight of the vinylidene fluoride copolymer. When the amount of the fluorine-containing monomer introduced is within this range, the flexibility of the electrode and intermediate layer can be improved. Furthermore, the amount of the fluorine-containing monomer introduced may be 20% by weight or less, preferably 15% by weight or less, and even more preferably 10% by weight or less, relative to the total weight of the vinylidene fluoride copolymer. When the amount of the fluorine-containing monomer introduced is within this range, the vinylidene fluoride copolymer does not dissolve in the electrolyte solution, and the adhesion between the materials constituting the electrode and intermediate layer, as well as the adhesion between the components constituting the battery, can be improved. When a vinylidene fluoride copolymer is used in combination with a solid electrolyte, the amount may be 20% by weight or more, preferably 22% by weight or more, and even more preferably 25% by weight or more. When the amount of the fluorine-containing monomer introduced is within this range, the affinity with the low-polarity solvent used in the preparation of the electrode and the intermediate layer is increased, and the preparation of the electrode and the intermediate layer is facilitated. Furthermore, the amount of the fluorine-containing monomer introduced may be 70 wt% or less, preferably 50 wt% or less, and more preferably 45 wt% or less, based on the total weight of the vinylidene fluoride copolymer. When the amount of the fluorine-containing monomer introduced is within this range, the adhesion between the materials constituting the electrode and the intermediate layer, and the adhesion between other members constituting the battery, is enhanced. The amount of the fluorine-containing monomer introduced may be, for example, １９ It can be identified by F-NMR.

[0036] The vinylidene fluoride copolymer may contain a crosslinked structure in its structure, and in order to obtain the crosslinked structure, a crosslinking reaction may be carried out using a polyfunctional monomer.

[0037] The molecular weight (Mw) of the vinylidene fluoride copolymer is preferably 100,000 or more, more preferably 200,000 or more, and even more preferably 250,000 or more, from the viewpoint of ensuring the adhesiveness of the binder. Also, the molecular weight (Mw) of the vinylidene fluoride copolymer is preferably 5,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,500,000 or less, from the viewpoint of ensuring the solubility and dispersibility in the solvent used to prepare the electrode and intermediate layer.

[0038] The average primary particle diameter of the vinylidene fluoride copolymer may be, for example, 1 nm to 500 μm, 10 nm to 10 μm, or 100 nm to 1 μm. From the viewpoint of productivity, the average primary particle diameter of the vinylidene fluoride copolymer is particularly preferably 100 nm to 0.5 μm. The average primary particle diameter can be calculated, for example, by regularization analysis of dynamic light scattering.

[0039] When used in combination with an electrolytic solution, the vinylidene fluoride copolymer preferably has a melting point of 130° C. or higher, more preferably 140 to 180° C. When used in combination with a solid electrolyte, the copolymer may not exhibit a melting point, but a melting point of 130° C. or lower is preferred.

[0040] (Preparation of vinylidene fluoride copolymer) The method for preparing the vinylidene fluoride copolymer contained in the binder is not particularly limited, and may be performed by a conventionally known method such as suspension polymerization, emulsion polymerization, solution polymerization, bulk polymerization, etc. From the viewpoint of ease of post-treatment, etc., suspension polymerization and emulsion polymerization are preferred, and emulsion polymerization is more preferred from the viewpoint of excellent reactivity between vinylidene fluoride and cationic monomers and anionic monomers or zwitterionic monomers.

[0041] In emulsion polymerization, first, vinylidene fluoride, a monomer other than vinylidene fluoride, and if necessary, other monomers, a liquid medium, an emulsifier, and a polymerization initiator soluble in the liquid medium are mixed in an autoclave to polymerize a vinylidene fluoride copolymer.

[0042] The medium used in the emulsion polymerization can be selected from liquids in which vinylidene fluoride is sparingly soluble, such as water.

[0043] The emulsifier used in the emulsion polymerization is not particularly limited as long as it can form micelles in a liquid medium and can stably disperse the synthesized polymer in the liquid medium, and any known emulsifier can be used. For example, the emulsion polymerization may be soap-free emulsion polymerization, mini-emulsion polymerization, or seed emulsion polymerization.

[0044] The emulsifier may be any of nonionic emulsifiers, cationic emulsifiers, anionic emulsifiers, amphoteric emulsifiers, and reactive emulsifiers, or a combination of these may be used. Specific examples of emulsifiers include fluorine-based emulsifiers and non-fluorine-based emulsifiers conventionally used in emulsion polymerization of polyvinylidene fluoride. Fluorine-based emulsifiers include fully fluorinated emulsifiers and partially fluorinated emulsifiers. These emulsifiers may be used alone or in combination of two or more. Among them, perfluoroalkylsulfonic acids and their salts, perfluoroalkylcarboxylic acids and their salts, fluorine-based emulsifiers having a fluorocarbon chain or a fluoropolyether chain, and non-fluorine-based emulsifiers such as polyoxyethylene alkyl ethers and polyoxyalkylene alkyl ethers are preferred from the viewpoint of polymerization stability. Furthermore, monomers having a cationic moiety, monomers having an anionic moiety, or zwitterionic monomers may be used as reactive emulsifiers.

[0045] The amount of emulsifier to be added can be selected arbitrarily, but is preferably 0.0001 to 10 parts by mass when the total amount of the monomers used in the polymerization is taken as 100 parts by mass.

[0046] The polymerization initiator is not particularly limited as long as it is a compound capable of polymerizing the monomers. Examples of polymerization initiators include known water-soluble peroxides, water-soluble azo compounds, and redox initiators. Examples of water-soluble peroxides include ammonium persulfate and potassium persulfate. Examples of water-soluble azo compounds include 2,2'-azobis-isobutyronitrile (AIBN) and 2,2'-azobis-2-methylbutyronitrile (AMBN). Examples of redox initiators include ascorbic acid-hydrogen peroxide. These initiators can be used alone or in combination of two or more. Among these, water-soluble peroxides are preferred from the viewpoint of reactivity. When the total amount of monomers used in the polymerization is 100 parts by mass, the total amount of polymerization initiators is preferably 0.01 to 5 parts by mass.

[0047] If necessary, a chain transfer agent may be used to adjust the molecular weight of the resulting vinylidene fluoride copolymer. Examples of the chain transfer agent include ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propylaldehyde, ethyl propionate, and carbon tetrachloride.

[0048] If necessary, a pH adjuster may be used, such as an electrolyte substance having a buffering capacity, such as sodium dihydrogen phosphate, disodium hydrogen phosphate, or potassium dihydrogen phosphate, or a basic substance, such as sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, or ammonia.

[0049] If necessary, additives may be added, such as dispersion stabilizers, anti-settling agents, anti-mold agents, wetting agents, and preservatives.

[0050] The reaction temperature may be appropriately selected depending on the type of initiator, etc. It is preferably 10 to 150°C, more preferably 20 to 120°C.

[0051] The pressure inside the autoclave during polymerization may be adjusted appropriately from the viewpoints of productivity and safety, and is preferably 0.5 to 20 MPa, more preferably 1 to 10 MPa.

[0052] For dehydration, drying and washing of the polymer obtained after polymerization, any known method may be used, or a combination of several known methods may be used.

[0053] [Binder Liquid] A binder liquid according to one embodiment of the present invention will be described in detail below. The binder liquid contains a binder containing the above-mentioned vinylidene fluoride copolymer and any solvent capable of dissolving or dispersing the vinylidene fluoride copolymer. The binder liquid preferably contains a binder and either water or an organic solvent. As the binder liquid, latex produced by emulsion polymerization may be appropriately diluted and used, or the binder may be re-dispersed after drying.

[0054] From the viewpoint of drying property and safety of the electrode, the boiling point of the solvent is preferably 50°C or more and 250°C or less, more preferably 60°C or more and 230°C or less, and even more preferably 90°C or more and 210°C or less.

[0055] When a vinylidene fluoride copolymer is used in combination with an electrolyte solution, water or an organic solvent can be used as the solvent. Examples of organic solvents include N-methyl-2-pyrrolidone (hereinafter also referred to as NMP), N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoamide, dioxane, tetramethylurea, triethyl phosphate, trimethyl phosphate, acetone, cyclohexanone, methyl ethyl ketone, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0056] When a vinylidene fluoride copolymer is used in combination with a solid electrolyte (e.g., a sulfide-based solid electrolyte), an organic solvent can be used as the solvent. From the viewpoint of suppressing degradation of the solid electrolyte, the solvent is preferably an organic solvent, and a solvent with low hydrophilicity is particularly preferable. Examples of such organic solvents include ethyl acetate, ethyl butyrate, butyl acetate, butyl butyrate, isopropyl acetate, amyl acetate, isobutyl isobutyrate, ethyl propionate, methyl isobutyl ketone, dipropyl ketone, dibutyl ketone, diisobutyl ketone, tetrahydrofuran, dioxane, anisole, toluene, xylene, tetralin, and trimethylbenzene. These may be used alone or in combination of two or more.

[0057] [Electrode Mixture] An electrode mixture (electrode slurry) according to one embodiment of the present invention will be described in detail below. The electrode mixture according to this embodiment contains the above-described binder liquid and an active material. The electrode mixture may further contain any electrolyte.

[0058] The electrode mixture can be an electrode mixture for a positive electrode or an electrode mixture for a negative electrode by changing the type of active material etc. depending on the type of current collector to be coated.

[0059] (Active Material) In this specification, the term "active material" refers to both a positive electrode active material used in a positive electrode and a negative electrode active material used in a negative electrode.

[0060] As the positive electrode active material, a known positive electrode active material can be used. For example, a lithium-based positive electrode active material containing lithium is preferred. As the lithium-based positive electrode active material, for example, LiCoO ２ , LiNiO ２ , 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), LiNi Ｘ Co １－Ｘ O ２(0<x≦1) ２ (M is at least one transition metal such as Co, Ni, Fe, Mn, Cr, and V; Y is a chalcogen element such as O and S), LiMnO ２ , LiMn ２ O ４ and LiFePO ４ LiMaPO etc. ４ (wherein Ma is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr), Li ２ MnO ３ -LiMbO ２ (wherein Mb is one or more elements selected from Mn, Co, and Ni), and lithium titanate (Li ４ Ti ５ O1 ２ ), titanium oxide (TiO ２ ), Li ｓ Ni ｔ Co ｕ Al ｖ O ２ (0.9<s<1.3, 0.9<t+u+v<1.1), etc. Also included are positive electrode active materials whose surfaces are coated with an oxide layer such as lithium niobate, lithium titanate, and lithium phosphate.

[0061] As the negative electrode active material, a known negative electrode active material can be used. In particular, it is preferable to use a negative electrode active material capable of absorbing and releasing lithium ions. Examples of such a negative electrode active material include lithium alloys, metal oxides, carbon materials such as graphite and hard carbon, silicon and silicon alloys, and Li ４ Ti ５ O １２ etc.

[0062] (Electrolyte) As the electrolyte, any known electrolyte can be used. For example, an electrolytic solution or a solid electrolyte can be used.

[0063] As the electrolyte, a known electrolyte can be used. In particular, it is preferable that the electrolyte has high lithium ion conductivity and is electrochemically stable. As such an electrolyte, a liquid in which an electrolyte salt is dissolved in a non-aqueous solvent or an ionic liquid can be used.

[0064] The solid electrolyte is not particularly limited as long as it is a solid compound having ion conductivity, and conventionally known inorganic solid electrolytes and polymer solid electrolytes can be used. Examples of inorganic solid electrolytes include oxide-based solid electrolytes, sulfide-based solid electrolytes, nitride-based solid electrolytes, and complex hydride solid electrolytes. Examples of polymer solid electrolytes include gel-based electrolytes and intrinsic polymer electrolytes.

[0065] The oxide-based solid electrolyte is not particularly limited, but examples thereof include perovskite-type LLTO, garnet-type LLZ, NASICON-type compounds, LISICON-type compounds, LIPON-type compounds, and β-alumina-type compounds.

[0066] The sulfide-based solid electrolyte is not particularly limited, but includes a solid electrolyte containing Li, A (A is at least one of P, Si, Ge, Al, and B), and S, and the sulfide-based solid electrolyte may further contain a halogen element. Other examples include LGPS-type compounds, argyrodite-type compounds, amorphous compounds, and Li-P-S-based compounds.

[0067] These solid electrolytes may contain only one of the above electrolytes, or may contain two or more of them.

[0068] (Other Components) The electrode mixture may contain components other than the binder solution, active material, and electrolyte (hereinafter also referred to as "other components"), as long as the effects of the present invention are not impaired. Examples of other components include a conductive aid, a thickener, an anti-settling agent, a dispersion stabilizer, an adhesion aid, a lubricant, and a viscosity adjuster.

[0069] [Intermediate Layer Mix] An intermediate layer mix (intermediate layer slurry) according to one embodiment of the present invention will be described in detail below. The intermediate layer mix according to this embodiment contains the binder liquid described above. As the intermediate layer mix, the binder liquid described above may be used as is, or may be diluted with the solvent for the binder liquid. The intermediate layer mix may further contain any electrolyte and filler.

[0070] (Electrolyte) As the electrolyte, the same electrolytes as those described above in the description of the electrode mixture can be used.

[0071] (Filler) The filler is not particularly limited, but may be an inorganic filler or an organic filler. Inorganic fillers are preferred from the viewpoint of heat resistance, etc. Examples of inorganic fillers include oxides, hydroxides, carbonates, sulfates, nitrides, clay minerals, and boehmite. These fillers may be contained in one type or in two or more types.

[0072] (Other Components) The intermediate layer mixture may contain other components in addition to the binder liquid, electrolyte, and filler, as long as the effects of the present invention are not impaired.

[0073] [Electrode] An electrode according to one embodiment of the present invention will be described in detail below. The electrode according to this embodiment contains the binder described above. When the electrode contains a binder, it is intended that any of the components of the electrode contains a binder.

[0074] The electrode may have a current collector and an electrode mixture layer formed on the surface of the current collector. Here, the electrode mixture layer can be obtained by applying an electrode mixture containing the binder described above onto the current collector and drying it.

[0075] The current collector is not particularly limited, and may be, for example, a metal foil or metal steel such as aluminum, copper, iron, stainless steel, steel, nickel, or titanium. Alternatively, the current collector may be a metal foil or metal steel applied to the surface of another medium.

[0076] [Intermediate Layer] An intermediate layer according to one embodiment of the present invention will be described in detail below. The intermediate layer according to this embodiment contains the binder described above. In this specification, the intermediate layer refers to a layer located between the positive electrode and the negative electrode in a battery. The intermediate layer may be in direct contact with the positive electrode and the negative electrode, or another layer may be interposed between the intermediate layer and the positive electrode and / or the negative electrode.

[0077] The configuration of the intermediate layer is not particularly limited. For example, the intermediate layer may be a layer obtained by drying the intermediate layer slurry described above, or may be a layer obtained by coating or impregnating a separator substrate with the slurry and then drying it. Examples of separator substrates include porous substrates and nonwoven fabrics.

[0078] [Battery] A battery according to one embodiment of the present invention will be described in detail below. The battery according to this embodiment contains the binder described above. The battery according to this embodiment includes the electrode or intermediate layer described above. That is, the battery according to this embodiment contains the binder described above in the electrode or intermediate layer described above. The battery according to this embodiment may be, for example, a nonaqueous electrolyte battery. Such a battery is preferable because it has excellent adhesion between the materials constituting the electrode and intermediate layer, and between the components constituting the battery, and is less likely to increase resistance at the interface between the materials. In this specification, the "resistance at the interface between materials" can be determined based on the ionic conductivity of the battery.

[0079] [Summary] A binder according to Aspect 1 of the present invention contains a vinylidene fluoride copolymer having a structural unit derived from vinylidene fluoride and another structural unit derived from a monomer other than vinylidene fluoride, the vinylidene fluoride copolymer having a cationic moiety and an anionic moiety, the cationic moiety and the anionic moiety being present in the other structural unit. This structure is preferable from the viewpoint of realizing a binder that has excellent adhesion between materials constituting an electrode and an intermediate layer, and between components constituting a battery, and that is less likely to increase resistance at the interface between materials.

[0080] The binder according to the second aspect of the present invention may have a composition in which the ratio of the amount of cationic moieties to the amount of anionic moieties is 0.5 or more and 2 or less.

[0081] The binder according to Aspect 3 of the present invention may be configured in accordance with Aspect 1 or 2 above, so that the other constituent unit includes a constituent unit derived from a zwitterionic monomer copolymerizable with vinylidene fluoride.

[0082] The binder according to Aspect 4 of the present invention may be configured as in Aspect 3 above, wherein the zwitterionic monomer is a compound represented by formula (1).

[0083] In formula (1), Ha, Hb, and Hc are each independently selected from hydrogen and an alkyl group having 1 to 4 carbon atoms; Xa is an atomic group consisting of an atomic chain formed by 2 to 6 atoms bonded in a chain, and the atomic chain of Xa contains 1 to 4 carbon atoms and at least one nitrogen atom or oxygen atom; Xb is an atomic group consisting of an atomic chain formed by 1 to 5 atoms bonded in a chain, and the atomic chain of Xb contains 1 to 4 carbon atoms; Ya is an atomic group containing an ionic group; Yb is an atomic group containing an ionic group; one of Ya and Yb is an anionic group, and the other is a cationic group.

[0084] A binder according to Aspect 5 of the present invention may be configured as in Aspect 4 above, wherein in formula (1), Ha, Hb, and Hc are each independently selected from hydrogen and a methyl group; Xa is an atomic group consisting of an atomic chain formed by 3 to 4 atoms bonded in a chain; and Xb is an atomic group consisting of an atomic chain formed by 1 to 4 atoms bonded in a chain.

[0085] A binder according to a sixth aspect of the present invention is the binder according to the fourth or fifth aspect, wherein in the formula (1), Ya is —N ＋ (-Za １ ) (-Za ２ )-, -O-P(=O)(-O － ) —O—, or —S ＋ (-Za ３ )- and Za １ , Za ２ , and Za ３are each independently selected from hydrogen or an alkyl group having 1 to 5 carbon atoms; Yb is —N ＋ (-Zb １ ) (-Zb ２ ) (-Zb ３ ), -S ＋ (-Zb ４ ) (-Zb ５ ), -O-P(=O)(-O － )-O(-Zb ６ ), -SO ３ － , -COO － , -SO ３ M, or -COOM, and Zb １ , Zb ２ , Zb ３ , Zb ４ , Zb ５ and Zb ６ are each independently selected from hydrogen or an alkyl group having 1 to 5 carbon atoms, and M is hydrogen or a metal ion.

[0086] The binder liquid according to Aspect 7 of the present invention may be configured in any one of Aspects 1 to 6 above, further comprising the binder and either water or an organic solvent.

[0087] An electrode mixture according to Aspect 8 of the present invention may contain the binder liquid according to Aspect 7 above and an active material.

[0088] The intermediate layer mixture according to Aspect 9 of the present invention may contain the binder liquid according to Aspect 7 above.

[0089] The electrode according to aspect 10 of the present invention may contain the binder according to any one of aspects 1 to 6 above.

[0090] The intermediate layer according to the eleventh aspect of the present invention may contain the binder according to any one of the first to sixth aspects.

[0091] The battery according to the twelfth aspect of the present invention may be configured to contain any one of the binders according to the first to sixth aspects.

[0092] A battery according to Aspect 13 of the present invention may include the electrode according to Aspect 10.

[0093] The battery according to the fourteenth aspect of the present invention may be configured to include the intermediate layer according to the eleventh aspect.

[0094] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0095] [Examples] The abbreviations and full names of the compounds used in the following examples are shown in Table 1. In the table, zwitterions (1) to (8) correspond to the compounds of formulas (1) to (8) given as specific examples of the zwitterionic monomers described above.

[0096]

[0097] Example 1: A 2-L autoclave was charged with 300 parts by mass of ion-exchanged water and degassed by bubbling with nitrogen for 30 minutes. Next, 0.006 parts by mass of polyoxyalkylene alkyl ether was added as an emulsifier, and the pressure was increased to 4.5 MPa, followed by nitrogen substitution three times. Then, 30 parts by mass of VDF was added to the autoclave. The temperature was raised to 80°C while stirring. A 5% by mass aqueous solution of APS was then added to the autoclave so that the APS content was 0.06 parts by mass, and polymerization was initiated. The internal pressure at this time was set to 2.5 MPa. Immediately after the initiation of polymerization, 70 parts by mass of VDF were continuously added so that the internal pressure was maintained at 2.5 MPa at the start of polymerization. Furthermore, while VDF was being continuously added, a 1% by mass solution of AcEAS was continuously added in parallel so that the AcEAS content was 0.5 parts by mass. After the addition was completed, the polymerization was completed when the pressure dropped to 1.5 MPa, yielding a latex (resin composition).

[0098] The obtained latex was coagulated in a 0.5% by mass calcium chloride solution, washed with water, and then dried at 60° C. to obtain a vinylidene fluoride copolymer.

[0099] [Example 2] Polymerization was carried out in the same manner as in Example 1 to obtain a latex (resin composition), except that the amount of VDF added to the autoclave before the start of polymerization was changed from 30 parts by mass to 27 parts by mass, 3 parts by mass of HFP was further added, and the amount of AcEAS added after the start of polymerization was changed from 0.5 parts by mass to 0.1 parts by mass. The obtained latex was treated in the same manner as in Example 1 to obtain a vinylidene fluoride copolymer.

[0100] [Example 3] A latex (resin composition) was obtained by polymerization in the same manner as in Example 2, except that 0.5 parts by mass of AmPAP was used instead of 0.1 parts by mass of AcEAS added after the initiation of polymerization. The obtained latex was treated in the same manner as in Example 1, to obtain a vinylidene fluoride copolymer.

[0101] [Example 4] Polymerization was carried out in the same manner as in Example 2, except that 0.5 parts by mass of AmPAS was used instead of 0.1 parts by mass of AcEAS added after the initiation of polymerization, to obtain a latex (resin composition). The obtained latex was treated in the same manner as in Example 1 to obtain a vinylidene fluoride copolymer.

[0102] [Example 5] Polymerization was carried out in the same manner as in Example 2, except that the amount of AcEAS added after the initiation of polymerization was changed from 0.1 part by mass to 0.5 part by mass, to obtain a latex (resin composition). The obtained latex was treated in the same manner as in Example 1, to obtain a vinylidene fluoride copolymer.

[0103] [Example 6] A latex (resin composition) was obtained by polymerization in the same manner as in Example 2, except that 0.5 parts by mass of MaEPC was used instead of 0.1 parts by mass of AcEAS added after the initiation of polymerization. The obtained latex was treated in the same manner as in Example 1, to obtain a vinylidene fluoride copolymer.

[0104] [Example 7] Polymerization was carried out in the same manner as in Example 2 to obtain a latex (resin composition), except that the amount of ion-exchanged water in the autoclave before the start of polymerization was changed from 300 parts by mass to 350 parts by mass, the amount of VDF added was changed from 27 parts by mass to 5 parts by mass, the amount of HFP added was changed from 3 parts by mass to 37 parts by mass, the amount of AcEAS added after the start of polymerization was changed from 0.5 parts by mass to 0.1 parts by mass, and the amount of VDF continuously added immediately after the start of polymerization was changed from 70 parts by mass to 58 parts by mass. The obtained latex was treated in the same manner as in Example 1 to obtain a vinylidene fluoride copolymer.

[0105] [Example 8] Polymerization was carried out in the same manner as in Example 2, except that the amount of ion-exchanged water in the autoclave before the start of polymerization was changed from 300 parts by mass to 350 parts by mass, the amount of VDF added was changed from 27 parts by mass to 5 parts by mass, the amount of HFP added was changed from 3 parts by mass to 37 parts by mass, 0.1 parts by mass of MaEAPS was added after the start of polymerization instead of 0.1 parts by mass of AcEAS, and the amount of VDF continuously added immediately after the start of polymerization was changed from 70 parts by mass to 58 parts by mass, to obtain a latex (resin composition). The obtained latex was treated in the same manner as in Example 1, to obtain a vinylidene fluoride copolymer.

[0106] [Example 9] Polymerization was carried out in the same manner as in Example 2 to obtain a latex (resin composition), except that the amount of ion-exchanged water in the autoclave before the start of polymerization was changed from 300 parts by mass to 350 parts by mass, the amount of VDF added was changed from 27 parts by mass to 5 parts by mass, the amount of HFP added was changed from 3 parts by mass to 37 parts by mass, 0.1 parts by mass of MaEABS was added after the start of polymerization instead of 0.1 parts by mass of AcEAS, and the amount of VDF continuously added immediately after the start of polymerization was changed from 70 parts by mass to 58 parts by mass. The obtained latex was treated in the same manner as in Example 1 to obtain a vinylidene fluoride copolymer.

[0107] [Example 10] Before the start of polymerization, the amount of ion-exchanged water in the autoclave was changed from 300 parts by mass to 350 parts by mass, the amount of VDF added was changed from 27 parts by mass to 5 parts by mass, the amount of HFP added was changed from 3 parts by mass to 37 parts by mass, 0.1 parts by mass of BMaEAPS was added after the start of polymerization instead of 0.1 parts by mass of AcEAS, and the amount of VDF continuously added immediately after the start of polymerization was changed from 70 parts by mass to 58 parts by mass. Polymerization was carried out in the same manner as in Example 2 to obtain a latex (resin composition). The obtained latex was treated in the same manner as in Example 1 to obtain a vinylidene fluoride copolymer.

[0108] [Example 11] Polymerization was carried out in the same manner as in Example 2, except that the amount of ion-exchanged water in the autoclave before the start of polymerization was changed from 300 parts by mass to 350 parts by mass, the amount of VDF added was changed from 27 parts by mass to 5 parts by mass, the amount of HFP added was changed from 3 parts by mass to 37 parts by mass, 0.1 parts by mass of MaEAA was added after the start of polymerization instead of 0.1 parts by mass of AcEAS, and the amount of VDF continuously added immediately after the start of polymerization was changed from 70 parts by mass to 58 parts by mass, to obtain a latex (resin composition). The obtained latex was treated in the same manner as in Example 1, to obtain a vinylidene fluoride copolymer.

[0109] [Example 12] Polymerization was carried out in the same manner as in Example 7, except that the amount of AcEAS added in parallel while VDF was continuously added was changed from 0.1 parts by mass to 1.2 parts by mass, to obtain a latex (resin composition). The obtained latex was treated in the same manner as in Example 1, to obtain a vinylidene fluoride copolymer.

[0110] Comparative Example 1 A latex (resin composition) was obtained by polymerization in the same manner as in Example 1, except that AcEAS, which was to be added in parallel during the continuous addition of VDF, was not added. The obtained latex was treated in the same manner as in Example 1, to obtain a vinylidene fluoride homopolymer.

[0111] [Comparative Example 2] Polymerization was carried out in the same manner as in Example 2, except that AcEAS, which was to be added in parallel during the continuous addition of VDF, was not added, to obtain a latex (resin composition). The obtained latex was treated in the same manner as in Example 1, to obtain a vinylidene fluoride copolymer.

[0112] Comparative Example 3 A latex (resin composition) was obtained by polymerization in the same manner as in Example 7, except that AcEAS, which was to be added in parallel during the continuous addition of VDF, was not added. The obtained latex was treated in the same manner as in Example 1, to obtain a vinylidene fluoride copolymer.

[0113] Table 2 below shows the raw materials and their mass ratios for each sample prepared in the above-mentioned Examples and Comparative Examples.

[0114] [Evaluation] The physical properties of each of the polymers obtained in the above-mentioned Examples and Comparative Examples were measured by the following methods.

[0115] (Average primary particle diameter) The average primary particle diameter of vinylidene fluoride copolymer was calculated by regularization analysis of the latex after polymerization by dynamic light scattering method. Specifically, it was measured using DelsaMaxCORE manufactured by BECKMAN COULTER in accordance with JIS Z 8828. Then, of two peaks, large and small, obtained by regularization analysis, the larger peak was taken as the average primary particle diameter.

[0116] (HFP introduction amount) The mass fraction of the structural unit derived from the fluorine-containing alkyl vinyl compound in the vinylidene fluoride copolymer (here, the HFP introduction amount) was measured using an LNM-ECZR 600 MHz FT-NMR manufactured by JEOL. １９ The F-NMR measurement was used to calculate the F-NMR spectra. Specifically, 40 mg of vinylidene fluoride copolymer was dissolved in 750 μL of DMF-d7, dimethyl sulfoxide-d6, or acetone-d6 to prepare a measurement sample. １９ Among the peaks obtained by F-NMR measurement, CF derived from HFP structural units ３ The peaks in the part correspond to two peaks around -70 to -80 ppm, and are CF derived from VDF structural units and HFP structural units (all structural units). ２ The peak in this region corresponds to a peak at or below -90 ppm. Therefore, the amount of HFP introduced was calculated from the integrated values ​​of these peaks and the molecular weights of VDF and HFP according to the following formula (1).

[0117] Amount of HFP introduced [mol%] = {(CF ３Peak integral value / 3) / (CF ２ Peak integral value / 2)}×100 Amount of HFP introduced [wt %]=[(Amount of HFP introduced [mol %]×Molecular weight of HFP) / {(100−Amount of HFP introduced [mol %])×Molecular weight of VDF+Amount of HFP introduced [mol %]×Molecular weight of HFP}]×100...Equation (1)

[0118] (Amount of Zwitterionic Monomer Introduction) The mass fraction of other structural units in the vinylidene fluoride copolymer (here, the amount of zwitterionic monomer introduction) was measured using an LNM-ECZR 600 MHz FT-NMR spectrometer manufactured by JEOL. １ Specifically, 10 mg of vinylidene fluoride copolymer and 1 mg of triphenylmethane as an internal standard were dissolved in 750 μL of DMF-d7, dimethyl sulfoxide-d6, or acetone-d6 to prepare a measurement sample. １ Among the peaks obtained by H-NMR, when DMF-d7 was used, the CH(-Ph) of triphenylmethane ３ The peak of the AcEAS structural unit -C(=O)-O-CH (Peak A) corresponds to 5.5 to 5.8 ppm. ２ The peak of the - moiety (Peak B) corresponds to a peak in the vicinity of 4.4 to 4.7 ppm. The peak of the -C(=O)-NH- moiety (Peak C) derived from the AmPAP or AmPAS structural unit corresponds to a peak in the vicinity of 8.1 to 8.4 ppm. The peak of the -CH moiety derived from the MaEPC structural unit corresponds to a peak in the vicinity of 8.1 to 8.4 ppm. ２ -O-P(=O)(-O － )-O-CH ２ The peak of the - moiety (peak D) corresponds to a peak in the vicinity of 4.0 to 4.3 ppm. ＋ -CH adjacent to ２ The negative peak (Peak E) corresponds to a peak near 3.65 to 3.8 ppm. Therefore, the amounts of AcEAS, AmPAP, AmPAS, and MaEPC introduced relative to VDF were calculated from the integrals of each peak and the molecular weights of the zwitterionic monomer and internal standard using the following equations (2) to (4). The integrals of Peaks B, C, and D were calculated relative to the integral of Peak A, which was set to 1.

[0119] Amount of AcEAS introduced [wt %] = {(amount of standard added / molecular weight of internal standard) × (integral value of Peak B / 2) × molecular weight of zwitterionic monomer / amount of polymer added} × 100 ... Equation (2) Amount of AmPAP or AmPAS introduced [wt %] = {(amount of standard added / molecular weight of internal standard) × integral value of Peak C × molecular weight of zwitterionic monomer / amount of polymer added} × 100 ... Equation (3) Amount of MaEPC introduced [wt %] = {(amount of standard added / molecular weight of internal standard) × (integral value of Peak D / 4) × molecular weight of zwitterionic monomer / amount of polymer added} × 100 ... Equation (4) Amount of MaEAPS, MaEABS, or MaEAA introduced [wt %] = {(amount of standard substance added / molecular weight of internal standard substance) × (integral value of Peak E / 4) × molecular weight of zwitterionic monomer / amount of polymer added} × 100 ... Equation (5) Amount of BMaEAPS introduced [wt %] = {(amount of standard substance added / molecular weight of internal standard substance) × (integral value of Peak E / 6) × molecular weight of zwitterionic monomer / amount of polymer added} × 100 ... Equation (6)

[0120] [Results] The solid content concentration, average primary particle size, amount of HFP introduced, and amount of zwitterionic monomer introduced for each polymer obtained in the Examples and Comparative Examples are shown in Table 3 below.

[0121]

[0122] [Adhesion Test] NCM811 (manufactured by PoSco) as a positive electrode active material and carbon black (Super-P) as a conductive additive were weighed out to a ratio of 100 / 1 (by weight) and mixed with a spatula. Then, the mixture was kneaded at 800 rpm for 1 minute using a conditioning mixer MX-201 (manufactured by Thinky Corporation).

[0123] Each polymer prepared in the above examples and comparative examples was weighed into a screw bottle, and an organic solvent was added and heated and stirred at 80 ° C to prepare a 5% by mass binder solution. The binder solution was added so that the ratio of positive electrode active material / conductive additive / binder was 100 / 1 / 2.5 (wt%) and mixed with a spatula. The mixture was then kneaded for 3 minutes at 2000 rpm using a conditioning mixer, and an appropriate organic solvent was added and kneaded for 1 minute at 2000 rpm using a conditioning mixer to prepare an electrode mixture (electrode slurry). This electrode mixture was applied to an Al foil with a 250 μm spacer, dried at 80 ° C for 1.5 hours, and then dried at 130 ° C for 2 hours to prepare an electrode. The electrode was cut into a 5 cm x 2 cm piece and pressed at a pressure of 4 MPa to prepare a test specimen.

[0124] The 90° peel strength between the electrode mixture and the Al foil of the prepared electrode was measured using a Tensilon universal material testing machine (manufactured by A&D Co., Ltd.) to evaluate the adhesion. The head speed was 10 mm / min. Table 4 shows the types of organic solvents used in each example and comparative example, and the results of the adhesion test.

[0125]

[0126] [Evaluation of Ionic Conductivity] In a glove box under an argon atmosphere, an argyrodite-type sulfide solid electrolyte (manufactured by Ampcera, composition formula Li ６ P.S. ５Br) and carbon black (Super-P) as a conductive additive were weighed out so that the solid electrolyte:conductive additive ratio was 76 / 20 (wt%) and mixed with a spatula. Next, each polymer prepared in the above-mentioned Examples and Comparative Examples was weighed into a screw bottle, and butyl butyrate was added and heated and stirred at 80 ° C to prepare an 8 mass% binder solution. The binder solution was added to the mixture of solid electrolyte and conductive additive so that the solid electrolyte:conductive additive:binder ratio was 76 / 20 / 4 (wt%), and the mixture was kneaded for 3 minutes at 2000 rpm using a conditioning mixer MX-201 (manufactured by Thinky Corporation). Further, butyl butyrate was added as needed and kneaded for 1 minute at 2000 rpm using a conditioning mixer. The electrode mixture thus prepared was applied to an Al foil with a 250 μm spacer provided, dried at 80 ° C. for 10 minutes under reduced pressure, and then dried at 130 ° C. for 10 minutes under reduced pressure. The resulting film was punched out with a 10 mm diameter die to form an intermediate layer. This intermediate layer was placed in an electrochemical measurement cell, and metallic indium (10 Φ) and metallic lithium (3 Φ) were placed on the coated side of the intermediate layer. A Cu mesh plate was placed on top of the Li-In electrode and pressurized at 200 MPa for 3 seconds to form a measurement cell.

[0127] The ionic conductivity of the fabricated cell was measured in a thermostatic chamber at 25°C using an impedance analyzer (Model 1287A) manufactured by Solartron Analytical and a VSP-300 manufactured by Biologic. The voltage amplitude was 10 mV, and the frequency range was 1 MHz to 1 Hz. In the obtained Cole-Cole plot, the real value at the intersection of the half-arc component and the approximate straight line component was regarded as the resistance value, and the ionic conductivity of the intermediate layer was calculated using the following formula. The results are shown in Table 5. Ionic conductivity (mS / cm) = 1000 × sample thickness (cm) ÷ sample area (cm) ２ ) ÷ resistance value (Ω)

[0128]

[0129] The present invention can be used as a constituent material for non-aqueous electrolyte secondary batteries.

Claims

1. A binder comprising a vinylidene fluoride copolymer having structural units derived from vinylidene fluoride and other structural units derived from a monomer other than vinylidene fluoride, wherein the vinylidene fluoride copolymer has cationic moieties and anionic moieties, and the cationic moieties and the anionic moieties are present in the other structural units.

2. The binder according to claim 1, wherein the ratio of cationic moieties to anionic moieties is 0.5 or more and 2.0 or less.

3. The binder according to claim 1, wherein the other structural units include structural units derived from zwitterionic monomers copolymerizable with vinylidene fluoride.

4. The binder of claim 3, wherein the zwitterionic monomer is a compound represented by formula (1). In formula (1), Ha, Hb, and Hc are each independently selected from hydrogen and an alkyl group having 1 to 4 carbon atoms; Xa is an atomic group consisting of an atomic chain formed by 2 to 6 atoms bonded in a chain, and the atomic chain of Xa contains 1 to 5 carbon atoms and at least one nitrogen atom or oxygen atom; Xb is an atomic group consisting of an atomic chain formed by 1 to 5 atoms bonded in a chain, and the atomic chain of Xb contains 1 to 4 carbon atoms; Ya is an atomic group containing an ionic group; Yb is an atomic group containing an ionic group; one of Ya and Yb is an anionic group, and the other is a cationic group.

5. The binder according to claim 4, wherein in formula (1), Ha, Hb, and Hc are each independently selected from hydrogen and a methyl group; Xa is an atomic group consisting of an atomic chain formed by 3 to 4 atoms bonded in a chain; and Xb is an atomic group consisting of an atomic chain formed by 1 to 4 atoms bonded in a chain.

6. In the formula (1), Ya is -N ＋ (-Za １ ) (-Za ２ )-, -O-P(=O)(-O － ) —O—, or —S ＋ (-Za ３ )- and Za １ , Za ２ , and Za ３ are each independently selected from hydrogen or an alkyl group having 1 to 5 carbon atoms; Yb is —N ＋ (-Zb １ ) (-Zb ２ ) (-Zb ３ ), -S ＋ (-Zb ４ ) (-Zb ５ ), -O-P(=O)(-O － )-O(-Zb ６ ), -SO ３ － , -COO － , -SO ３ M, or -COOM, and Zb １ , Zb ２ , Zb ３ , Zb ４ , Zb ５ and Zb ６ are each independently selected from hydrogen or an alkyl group having 1 to 5 carbon atoms, and M is hydrogen or a metal ion.

7. A binder liquid containing the binder according to any one of claims 1 to 6 and either water or an organic solvent.

8. An electrode mixture containing the binder liquid according to claim 7 and an active material.

9. An intermediate layer mixture containing the binder liquid according to claim 7.

10. An electrode containing a binder according to any one of claims 1 to 6.

11. An intermediate layer containing a binder according to any one of claims 1 to 6.

12. A battery containing the binder of any one of claims 1 to 6.

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