Electrode binder polymer for nonaqueous electrochemical device, electrode binder composition for nonaqueous electrochemical device, electrode composition for nonaqueous electrochemical device, electrode for nonaqueous electrochemical device, nonaqueous electrochemical device, and nonaqueous secondary battery

Abstract

Provided is an electrode binder polymer for a nonaqueous electrochemical device, said electrode binder polymer being a copolymer that contains a constitutional unit derived from at least one monomer (1) of acrylonitrile and methacrylonitrile and a constitutional unit derived from at least one monomer (2) that is selected from the group consisting of an unsaturated carboxylic acid, an unsaturated carboxylic acid alkyl ester, and an unsaturated carboxylic acid amide, wherein the content of the constitutional unit derived from the monomer (2) is 0.1-4.9 mol% with respect to the total amount of constitutional units derived from the monomer (1) and the monomer (2), and the constitutional unit derived from the monomer (2) has a weight-average molecular weight of 10,000 to 450,000.

Description

Electrode binder polymer for non-aqueous electrochemical device, electrode binder composition for non-aqueous electrochemical device, electrode composition for non-aqueous electrochemical device, electrode for non-aqueous electrochemical device, non-aqueous electrochemical device, and non-aqueous secondary battery

[0001] The present disclosure relates to an electrode binder polymer for a non-aqueous electrochemical device, an electrode binder composition for a non-aqueous electrochemical device, an electrode composition for a non-aqueous electrochemical device, an electrode for a non-aqueous electrochemical device, a non-aqueous electrochemical device, and a non-aqueous secondary battery.

[0002] Organofluorine compounds have been used in a wide range of manufacturing and industrial applications due to their useful properties such as heat resistance, chemical resistance, and surface activity. For example, polyvinylidene fluoride resins are known to be used as binders for electrodes.

[0003] However, in recent years, ecotoxicity and human toxicity of organic fluorine compounds have been reported, and restrictions on the production and use of organic fluorine compounds have been tightened worldwide. Therefore, with regard to electrode binders, attempts have been made to develop binders with a low content of polyvinylidene fluoride resin or binders that do not contain polyvinylidene fluoride resin.

[0004] For example, Patent Documents 1 and 2 disclose the use of a polymer having structural units derived from acrylonitrile and a specific monomer as a binder for electrodes.

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2003-132893 Patent Document 2: Japanese Patent Application Laid-Open No. 2004-185826

[0006] However, the polymers having structural units derived from acrylonitrile and specific monomers disclosed in Patent Documents 1 and 2 above have problems in terms of practical application, such as a slow dissolution rate in a solvent and high swelling in an electrolyte solution.

[0007] The present disclosure has been made in view of the above, and relates to providing an electrode binder polymer for a non-aqueous electrochemical device, an electrode binder composition for a non-aqueous electrochemical device, an electrode composition for a non-aqueous electrochemical device, an electrode for a non-aqueous electrochemical device, a non-aqueous electrochemical device, and a non-aqueous secondary battery, which can provide a composition that has a high dissolution rate in a solvent, low swelling property with an electrolytic solution, and excellent coatability.

[0008] The present disclosure includes the following aspects. <1> An electrode binder polymer for a non-aqueous electrochemical device, which is a copolymer comprising structural units derived from at least one monomer (1) selected from acrylonitrile and methacrylonitrile, and structural units derived from at least one monomer (2) selected from the group consisting of an unsaturated carboxylic acid, an unsaturated carboxylic acid alkyl ester, and an unsaturated carboxylic acid amide, wherein the content of the structural units derived from monomer (2) is 0.1 mol % to 4.9 mol % relative to the total amount of the structural units derived from monomer (1) and monomer (2), and the weight-average molecular weight is 10,000 to 450,000. <2> The electrode binder polymer for a non-aqueous electrochemical device according to <1>, wherein the unsaturated carboxylic acid alkyl ester is at least one of methyl acrylate and methyl methacrylate. <3> The electrode binder polymer for a non-aqueous electrochemical device according to <1> or <2>, wherein the unsaturated carboxylic acid is at least one selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid. <4> The electrode binder polymer for a non-aqueous electrochemical device according to any one of <1> to <3>, wherein the monomer (2) has 5 or less carbon atoms. <5> An electrode binder composition for a non-aqueous electrochemical device, comprising the electrode binder polymer for a non-aqueous electrochemical device according to any one of <1> to <4>. <6> The electrode binder composition for a non-aqueous electrochemical device according to <5>, further comprising a solvent. <7> An electrode composition for a non-aqueous electrochemical device, comprising the electrode binder polymer for a non-aqueous electrochemical device according to any one of <1> to <4> and an active material. <8> The electrode composition for a non-aqueous electrochemical device according to <7>, wherein the active material is a positive electrode active material. <9> An electrode for a non-aqueous electrochemical device, comprising the electrode composition for a non-aqueous electrochemical device according to <7> or <8>. <10> A non-aqueous electrochemical device comprising the electrode for a non-aqueous electrochemical device according to <9>. <11> A non-aqueous secondary battery comprising the electrode for a non-aqueous electrochemical device according to <9> or <10>.

[0009] According to the present disclosure, there are provided an electrode binder polymer for a non-aqueous electrochemical device, an electrode binder composition for a non-aqueous electrochemical device, an electrode composition for a non-aqueous electrochemical device, an electrode for a non-aqueous electrochemical device, a non-aqueous electrochemical device, and a non-aqueous secondary battery, which have a high dissolution rate in a solvent, low swelling with an electrolytic solution, and excellent coatability.

[0010] An embodiment of the present disclosure will be described in detail below. However, the present disclosure is not limited to the following embodiment. In the following disclosure, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0011] In the present disclosure, when a numerical range is indicated using "to", the numerical values ​​before and after "to" are included as the lower and upper limits, respectively. In the present disclosure, when a numerical range is described in stages, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in the present disclosure, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. In the present disclosure, when multiple substances corresponding to each component are present in the composition, the content of each component refers to the total content of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, when multiple elements are listed using "or", this does not exclude the combination of multiple elements unless a technical contradiction occurs, unless otherwise specified. In the present disclosure, when an element is described in the singular, this does not exclude the presence of multiple elements unless a technical contradiction occurs, unless otherwise specified. In the present disclosure, multiple exemplary embodiments described separately may be combined with each other to form a new embodiment, unless mutually contradictory.

[0012] <Electrode Binder Polymer for Non-Aqueous Electrochemical Device> The electrode binder polymer for a non-aqueous electrochemical device of the present disclosure (hereinafter also referred to as the "binder polymer of the present disclosure") is a copolymer containing: a structural unit derived from at least one monomer (1) selected from acrylonitrile and methacrylonitrile; and a structural unit derived from at least one monomer (2) selected from the group consisting of an unsaturated carboxylic acid, an unsaturated carboxylic acid alkyl ester, and an unsaturated carboxylic acid amide; the content of the structural unit derived from monomer (2) is 0.1 mol % to 4.9 mol % relative to the total amount of the structural units derived from monomer (1) and monomer (2); and the weight average molecular weight is 10,000 to 450,000.

[0013] The binder polymer of the present disclosure provides a composition that has a high dissolution rate in a solvent, low swelling with an electrolyte, and excellent coatability. The effect of the binder polymer of the present disclosure is presumed to be as follows. The structural unit derived from monomer (2) contained in the binder polymer of the present disclosure increases the dissolution rate in a solvent, but also increases the swelling rate with an electrolyte. However, the binder polymer of the present disclosure has a content of the structural unit derived from monomer (2) within a certain range, so that the binder polymer is excellent in both high dissolution rate in a solvent and low swelling with an electrolyte. Furthermore, if the weight-average molecular weight of the binder polymer is too high, the viscosity of the composition obtained from the binder polymer increases, and when the composition is coated, the leveling ability is low and the coating film is likely to have uneven thickness. However, since the weight average molecular weight of the binder polymer of the present disclosure is specified within a certain range, when a composition obtained from the binder polymer of the present disclosure is coated, the leveling property is high and the coating film is less likely to have uneven thickness, i.e., the coating property is excellent. Note that the present disclosure is not limited to the above-mentioned assumed mechanism.

[0014] <Constituent Units Derived from Monomer (1)> The binder polymer of the present disclosure contains constituent units derived from at least one monomer (1) selected from acrylonitrile and methacrylonitrile. Monomer (1) may be contained alone or in combination of two or more types. Monomer (1) is preferably acrylonitrile.

[0015] From the viewpoint of achieving both the dissolution rate in a solvent and the swelling property in an electrolyte solution, the content of the structural units derived from the monomer (1) is preferably 95.1 mol% to 99.9 mol% relative to the total amount of the structural units derived from the monomer (1) and the monomer (2), more preferably 96.0 mol% to 99.5 mol%, and even more preferably 96.5 mol% to 99.0 mol%. When the content of the structural units derived from the monomer (1) is 95.1 mol% or more relative to the total amount of the structural units derived from the monomer (1) and the monomer (2), the binder polymer has low swelling property in an electrolyte solution and is excellent. When the content of the structural units derived from the monomer (1) is 99.9 mol% or less relative to the total amount of the structural units derived from the monomer (1) and the monomer (2), the binder polymer has a high dissolution rate in a solvent and is excellent.

[0016] In the present disclosure, when a plurality of types of monomer (1) are present in the binder polymer of the present disclosure, the "content of constituent units derived from monomer (1)" refers to the total content of constituent units derived from the plurality of types of monomer (1). Similarly, when a plurality of types of monomer (2) are present in the binder polymer of the present disclosure, the "content of constituent units derived from monomer (2)" refers to the total content of constituent units derived from the plurality of types of monomer (2).

[0017] In the present disclosure, the content of constitutional units derived from a specific monomer in a polymer can be measured by NMR.

[0018] <Structural Unit Derived from Monomer (2)> The binder polymer of the present disclosure contains a structural unit derived from at least one monomer (2) selected from the group consisting of unsaturated carboxylic acids, unsaturated carboxylic acid alkyl esters, and unsaturated carboxylic acid amides. The monomer (2) may be contained alone or in combination of two or more.

[0019] From the viewpoint of preventing an increase in the degree of swelling, the number of carbon atoms in the monomer (2) is preferably 10 or less, more preferably 7 or less, and even more preferably 5 or less. The number of carbon atoms in the monomer (2) may be 2 or more, or may be 3 or more.

[0020] From the viewpoint of achieving both a dissolution rate in a solvent and swelling properties with an electrolyte solution, the monomer (2) is preferably at least one of an unsaturated carboxylic acid and an unsaturated carboxylic acid alkyl ester, more preferably an unsaturated carboxylic acid or an unsaturated carboxylic acid alkyl ester, and even more preferably an unsaturated carboxylic acid or an unsaturated carboxylic acid alkyl ester.

[0021] (Unsaturated Carboxylic Acid) Examples of unsaturated carboxylic acids include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, and isocrotonic acid; and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid, mesaconic acid, glutaconic acid, and itaconic acid. The unsaturated carboxylic acids may be contained alone or in combination of two or more.

[0022] From the viewpoints of the dissolution rate in a solvent and the swelling property with an electrolyte solution, the unsaturated carboxylic acid is preferably at least one selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid, more preferably at least one of methacrylic acid and itaconic acid, and even more preferably itaconic acid.

[0023] (Unsaturated Carboxylic Acid Alkyl Esters) Examples of unsaturated carboxylic acid alkyl esters include: alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, and isobutyl acrylate; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, and isobutyl methacrylate; alkyl crotonates such as methyl crotonate, ethyl crotonate, n-propyl crotonate, isopropyl crotonate, n-butyl crotonate, t-butyl crotonate, and isobutyl crotonate; amino group-containing methacrylic acid esters such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; Examples of the unsaturated carboxylic acid alkyl ester include: acrylic acid esters containing an alkoxyl group, such as methoxypolyethylene glycol acrylate, ethoxypolyethylene glycol acrylate, ethoxydiethylene glycol acrylate, methoxydipropylene glycol acrylate, methoxyethyl acrylate, 2-ethoxyethyl acrylate, butoxyethyl acrylate, and phenoxyethyl acrylate; methacrylic acid esters containing an alkoxyl group, such as methoxypolyethylene glycol methacrylate, ethoxypolyethylene glycol methacrylate, methoxydiethylene glycol methacrylate, methoxydipropylene glycol methacrylate, methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, butoxyethyl methacrylate, and phenoxyethyl methacrylate; and alkyl acrylates and alkyl methacrylates having a phosphoric acid residue, sulfonic acid residue, boric acid residue, or the like in the alkyl group. The unsaturated carboxylic acid alkyl ester may be contained alone or in combination of two or more.

[0024] From the viewpoint of the dissolution rate in the solvent and swelling property with the electrolyte, the unsaturated carboxylic acid alkyl ester is preferably at least one of methyl acrylate and methyl methacrylate, and more preferably methyl acrylate or methyl methacrylate.

[0025] (Unsaturated Carboxylic Acid Amides) Examples of unsaturated carboxylic acid amides include acrylamide, methacrylamide, itaconic acid diamide, methylol acrylamide, butoxymethylol acrylamide, etc. The unsaturated carboxylic acid amides may be contained alone or in combination of two or more.

[0026] From the viewpoints of the dissolution rate in a solvent and swelling property with an electrolyte solution, the unsaturated carboxylic acid amide is preferably at least one selected from the group consisting of acrylamide, methacrylamide, and itaconic acid diamide, and more preferably acrylamide or methacrylamide.

[0027] (Content) The content of the structural units derived from the monomer (2) is 0.1 mol% to 4.9 mol% relative to the total amount of the structural units derived from the monomer (1) and the monomer (2). When the content of the structural units derived from the monomer (2) is 0.1 mol% or more relative to the total amount of the structural units derived from the monomer (1) and the monomer (2), the polymer dissolves quickly in a solvent and becomes excellent. When the content of the structural units derived from the monomer (2) is 4.9 mol% or less relative to the total amount of the structural units derived from the monomer (1) and the monomer (2), the polymer has low swelling property in an electrolyte solution and becomes excellent.

[0028] From the viewpoint of achieving both the dissolution rate in a solvent and the swelling property in an electrolyte solution, the content of the structural units derived from the monomer (2) is 0.1 mol % to 4.9 mol %, preferably 0.2 mol % to 4.5 mol %, and more preferably 0.3 mol % to 3.5 mol %, relative to the total amount of the structural units derived from the monomer (1) and the monomer (2).

[0029] When the binder polymer of the present disclosure contains a combination of two or more types of structural units derived from monomer (2), the content ratio of the structural units derived from monomer (2) in the binder polymer of the present disclosure is not particularly limited. For example, the content of the structural units derived from unsaturated carboxylic acid alkyl ester is preferably 20% to 1000%, more preferably 100% to 800%, and even more preferably 200% to 700%, on a molar basis relative to the content of the structural units derived from saturated carboxylic acid.

[0030] <Structural Units Derived from Monomers Other than Monomer (1) and Monomer (2)> The binder polymer of the present disclosure may contain structural units derived from monomers other than monomer (1) and monomer (2). The monomers other than monomer (1) and monomer (2) are not particularly limited, and known copolymerizable polymerizable unsaturated compounds can be used. Examples of monomers other than monomer (1) and monomer (2) include olefins (e.g., 1-olefins having 2 to 4 carbon atoms (ethylene, propylene, 1-butene, etc.)), vinyl compounds (e.g., vinyl acetate, vinyl chloride, vinyl sulfonic acid, maleic anhydride, N-vinylpyrrolidone, etc.), aromatic vinyl compounds (e.g., styrene, etc.), heterocyclic vinyl compounds (e.g., vinylpyridine, vinylimidazole, etc.), and the like. The monomers other than monomer (1) and monomer (2) may be contained alone or in combination of two or more.

[0031] The content of the structural units derived from monomers other than the monomer (1) and the monomer (2) is not particularly limited as long as the effects of the present disclosure are achieved, and may be 0 mol % to 50 mol %, 0 mol % to 25 mol %, or 0 mol % to 5 mol % relative to all structural units of the binder polymer of the present disclosure.

[0032] <Molecular Weight of Binder Polymer> The weight-average molecular weight of the binder polymer of the present disclosure is 10,000 to 450,000. When the weight-average molecular weight of the binder polymer of the present disclosure is 10,000 or more, it means that the binder polymer of the present disclosure is a polymer compound. When the weight-average molecular weight of the binder polymer of the present disclosure is 450,000 or less, the composition containing the binder polymer of the present disclosure does not become too viscous and has excellent coatability.

[0033] From the viewpoint of obtaining a composition with excellent coatability, the weight average molecular weight of the binder polymer of the present disclosure is more preferably 50,000 to 400,000, more preferably 100,000 to 380,000, and even more preferably 200,000 to 370,000.

[0034] In the present disclosure, the weight-average molecular weight of a polymer is determined by gel permeation chromatography (GPC). As an example of a measurement device, a GPC measurement device (HPLC-8320GPC EcoSEC, manufactured by Tosoh Corporation) can be used. In this case, a TSK gel α-M (manufactured by Tosoh Corporation) is used as the column, and a differential refractive index detector (HLC-8320 GPC RI detector, manufactured by Tosoh Corporation) is used as the detector. Dimethylformamide is used as the mobile phase, and lithium bromide and phosphoric acid are added as eluents to concentrations of 50 mM and 10 mM, respectively. Polystyrene (standard polystyrene kit PStQuick Kit-C, D, manufactured by Tosoh Corporation) is used as the standard substance.

[0035] <Method for Producing Binder Polymer> There are no particular limitations on the method for producing the binder polymer of the present disclosure, and known polymerization methods can be applied, with free radical polymerization being preferred.

[0036] When performing free radical polymerization, known polymerization methods such as solution polymerization, dispersion polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization can be used. In particular, solution polymerization or suspension polymerization is preferred from the viewpoint of productivity. The polymerization initiator and catalyst used in radical polymerization are not particularly limited, and examples thereof include azo compounds, organic peroxides, and redox catalysts such as persulfuric acid / sulfurous acid, chloric acid / sulfurous acid, or their sodium or ammonium salts. When using a redox initiator, a catalyst and / or a pH adjuster can be appropriately added to efficiently proceed with the redox reaction. Examples of catalysts include iron(II) sulfate, and examples of pH adjusters include concentrated sulfuric acid.

[0037] When solution polymerization is carried out, known solvents such as an aqueous zinc chloride solution, dimethyl sulfoxide, dimethylformamide, etc. can be used as the polymerization solvent. In particular, an aqueous zinc chloride solution or dimethyl sulfoxide is preferred because of the small number of side reactions.

[0038] <Electrode Binder Composition for Non-Aqueous Electrochemical Device> The electrode binder composition for a non-aqueous electrochemical device of the present disclosure (hereinafter also referred to as the "binder composition of the present disclosure") contains the binder polymer of the present disclosure.

[0039] <Binder polymer of the present disclosure> The binder polymer of the present disclosure contained in the binder composition of the present disclosure is as described above. From the viewpoint of achieving a balance between improving the binding strength of the electrode and increasing the presence rate of the active material in the electrode, the content of the binder polymer of the present disclosure in the binder composition of the present disclosure is preferably 0.5% by mass to 10% by mass, more preferably 1.0% by mass to 5% by mass, and even more preferably 1.5% by mass to 3% by mass.

[0040] <Solvent> The binder composition of the present disclosure may further contain a solvent. The solvent is not particularly limited as long as it can dissolve the binder polymer of the present disclosure, and examples thereof include amides such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, and N,N-dimethylformamide, acetone, water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol. From the viewpoint of easily dissolving the binder polymer of the present disclosure, NMP is preferred as the solvent. One type of solvent may be contained alone, or two or more types may be contained in combination.

[0041] From the viewpoint of obtaining fluidity that allows coating, the content of the solvent in the binder composition of the present disclosure is preferably 0% by mass to 99% by mass, more preferably 10% by mass to 70% by mass, and even more preferably 20% by mass to 60% by mass.

[0042] <Components Other Than the Binder Polymer and Solvent of the Present Disclosure> The binder composition of the present disclosure may contain components other than the binder polymer and solvent of the present disclosure. Examples of components other than the binder polymer and solvent of the present disclosure include polymers other than the binder polymer of the present disclosure, dispersants such as surfactants, wetting agents, antifoaming agents, pH adjusters, viscosity adjusters, and fluidizing agents.

[0043] (Polymers Other than the Binder Polymer of the Present Disclosure) Examples of polymers other than the binder polymer of the present disclosure include polyvinylidene fluoride (PVDF)-based resins, wholly aromatic polyamides, polyamideimides, polyimides, polyethersulfones, polysulfones, polyetherketones, polyketones, polyetherimides, poly-N-vinylacetamide, polyacrylamide, copolymerized polyetherpolyamides, fluorine-based rubbers, acrylic resins, ethylene / methyl acrylate copolymers, ethylene / vinyl alcohol copolymers, acrylonitrile / butadiene copolymers and hydrogenated products thereof, styrene / butadiene copolymers, butadiene rubbers, ethylene / propylene / non-conjugated diene terpolymers (EPDM), cellulose, polyvinyl alcohol, and the like.

[0044] <Method for Producing Binder Composition> The method for producing the binder composition of the present disclosure is not particularly limited, and a known dissolution method can be applied. For example, the binder composition can be produced by adding the binder polymer of the present disclosure and any optional components such as a solvent, and mixing them by hand or using a mixer. Examples of the mixer that can be used include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer.

[0045] <Electrode Composition for Non-Aqueous Electrochemical Device> The electrode composition for a non-aqueous electrochemical device of the present disclosure (hereinafter also referred to as the "electrode composition of the present disclosure") contains the binder polymer of the present disclosure and an active material.

[0046] <Binder Polymer of the Present Disclosure> The binder polymer of the present disclosure contained in the electrode composition of the present disclosure has been described above.

[0047] <Active Material> The active material is preferably at least one of a positive electrode active material and a negative electrode active material, and is more preferably a positive electrode active material from the viewpoint of the reduction resistance of the binder polymer of the present disclosure.

[0048] The positive electrode active material is, for example, LiCoO ２ , LiNiO ２ , LiMn １／２ Ni １／２ O ２ , LiCo １／３ Mn １／３ Ni １／３ O ２ , LiMn ２ O ４ , LiFePO ４ , LiCo １／２ Ni １／２ O ２ , LiAl １／４ Ni ３／４ O ２ Lithium-containing transition metal oxides such as TiS ２ , TiS ３ , amorphous MoS ３ transition metal sulfides such as Cu ２ V ２ O ３ , amorphous V ２ O-P２ O ５ , MoO ３ , V ２ O ５ , V ６ O １３ transition metal oxides such as:

[0049] Examples of negative electrode active materials include materials that can electrochemically absorb lithium ions, and specific examples include carbon materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), pitch-based carbon fibers, and activated carbon; alloys of lithium with silicon, tin, aluminum, etc.; and Wood's alloy.

[0050] <Configuration of Electrode Composition of the Present Disclosure> The electrode composition of the present disclosure may be either a positive electrode composition or a negative electrode composition, and is preferably a positive electrode composition from the viewpoint of the reduction resistance of the binder polymer of the present disclosure.

[0051] <Method for producing the electrode composition of the present disclosure> The method for producing the electrode composition of the present disclosure is not particularly limited, and a known method can be applied, and the electrode composition can be produced using the binder composition of the present disclosure. For example, the electrode composition can be produced by mixing the binder composition of the present disclosure, an active material, and optionally, a conductive additive, etc., by hand mixing or using a mixer. Examples of the mixer that can be used include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer.

[0052] <Electrode for Non-Aqueous Electrochemical Device> An electrode for a non-aqueous electrochemical device according to the present disclosure (hereinafter also referred to as the “electrode of the present disclosure”) includes the electrode composition of the present disclosure. That is, the electrode of the present disclosure includes the binder polymer of the present disclosure and the active material.

[0053] <Configuration of Electrode of the Present Disclosure> The electrode of the present disclosure may be either a positive electrode or a negative electrode, and is preferably a positive electrode from the viewpoint of the reduction resistance of the binder polymer of the present disclosure.

[0054] An example of a positive electrode is a structure in which an active material layer containing a positive electrode active material and the binder polymer of the present disclosure is disposed on a current collector. Examples of current collectors include aluminum foil, titanium foil, stainless steel foil, and the like, each having a thickness of 5 μm to 30 μm. The active material layer may further include a conductive additive, a polymer other than the binder polymer of the present disclosure, a dispersant such as a surfactant, a wetting agent, an antifoaming agent, a pH adjuster, a viscosity adjuster, a fluidizing agent, and the like. Examples of conductive additives include carbon materials such as acetylene black, ketjen black, graphite powder, and ultrafine carbon fibers, conductive polymers, and metal powders.

[0055] An example of an embodiment of the negative electrode includes a structure in which an active material layer containing a negative electrode active material and the binder polymer of the present disclosure is disposed on a current collector. Examples of the current collector include copper foil, nickel foil, stainless steel foil, etc., each having a thickness of 5 μm to 30 μm. Alternatively, a metal lithium foil may be used as the negative electrode. The active material layer may further include a conductive additive, a polymer other than the binder polymer of the present disclosure, a dispersant such as a surfactant, a wetting agent, an antifoaming agent, a pH adjuster, a viscosity adjuster, a fluidizing agent, etc. Examples of conductive additives include carbon materials such as acetylene black, ketjen black, graphite powder, and ultrafine carbon fibers, conductive polymers, and metal powders.

[0056] <Method for manufacturing an electrode according to the present disclosure> The method for manufacturing an electrode according to the present disclosure is not particularly limited, and a known method can be applied, and the electrode can be manufactured using the electrode composition according to the present disclosure. For example, the electrode composition according to the present disclosure is applied to a current collector such as a metal foil, and then dried and / or rolled (i.e., pressed) to form an electrode in which an active material is dispersed and fixed in a matrix formed on the surface of the current collector.

[0057] The method for applying the electrode composition of the present disclosure to a current collector is not particularly limited. For example, application can be by a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, brush coating, etc. The amount to be applied is also not particularly limited, but is adjusted so that the thickness of the mixed layer containing the active material formed after drying is usually 0.005 to 5 mm, preferably 0.01 to 2 mm.

[0058] The drying method is not particularly limited, and examples thereof include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with far infrared rays, infrared rays, electron beams, etc. Drying conditions are adjusted so that the solvent is removed as quickly as possible within a speed range that does not cause stress concentration to cause cracks in the active material layer or peeling of the active material layer from the current collector. The rolling method is also not particularly limited, and the electrode may be stabilized by rolling the current collector after coating or drying. Examples of rolling methods include die pressing and roll pressing.

[0059] <<Non-aqueous Electrochemical Device>> The non-aqueous electrochemical device of the present disclosure includes the electrode of the present disclosure. The non-aqueous electrochemical device of the present disclosure may be a non-aqueous battery or a non-aqueous capacitor. The non-aqueous battery may be a non-aqueous primary battery or a non-aqueous secondary battery, preferably a non-aqueous secondary battery, and more preferably a non-aqueous lithium ion secondary battery.

[0060] The nonaqueous electrochemical device of the present disclosure may include, in addition to electrodes, an electrolyte solution, an exterior material, a separator, etc. The nonaqueous electrochemical device of the present disclosure has a structure in which, for example, a battery element in which a negative electrode and a positive electrode face each other with a separator interposed therebetween is enclosed in an exterior material together with an electrolyte solution.

[0061] (Electrolyte) The electrolyte is preferably a solution in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF ６ , LiBF ４ , LiClO ４Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted derivatives thereof; and cyclic esters such as γ-butyrolactone and γ-valerolactone; and the like, which may be used alone or in combination. A suitable electrolyte solution is a solution in which a cyclic carbonate and a chain carbonate are mixed in a mass ratio (cyclic carbonate:chain carbonate) of 20:80 to 40:60, and a lithium salt is dissolved in the range of 0.5 mol / L to 1.5 mol / L.

[0062] (Packaging Material) Examples of packaging materials include aluminum laminate film packs, metal cans, and coin cells.

[0063] (Separator) A known separator can be used as the separator. For example, a composite membrane having a porous substrate and a porous layer disposed on one or both sides of the porous substrate, or a single-layer membrane of the porous substrate itself may be used.

[0064] -Porous substrate- In the present disclosure, a porous substrate refers to a substrate having internal pores or voids. Examples of such substrates include microporous membranes; porous sheets made of fibrous materials, such as nonwoven fabrics and paper; and the like. The material of the porous substrate is preferably an electrically insulating material.

[0065] The porous substrate preferably contains a thermoplastic resin to impart a shutdown function to the porous substrate. The shutdown function refers to a function in which, when the battery temperature rises, the constituent materials dissolve and block the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery. The thermoplastic resin preferably has a melting point of less than 200°C. Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; and the like, with polyolefins being preferred.

[0066] -Porous Layer- The porous layer is a layer disposed on one or both sides of the porous substrate, has a large number of gaps or micropores, and allows gas or liquid to pass from one side to the other. The porous layer preferably contains at least one of inorganic particles and a binder resin. The porous layer may be configured by laminating multiple porous layers.

[0067] Examples of inorganic particles include metal oxide particles such as alumina and boehmite, metal hydroxide particles such as aluminum hydroxide and magnesium hydroxide, metal sulfate particles such as barium sulfate, metal carbonate particles such as calcium carbonate, metal nitride particles such as boron nitride, and clay mineral particles such as talc. Binder resins may be soluble in polar solvents, soluble in water, or dispersible in water. Examples of binder resins include polyamide, polyimide, polyamideimide, fluorine-based resins, acrylic resins, styrene-butadiene copolymers, and butadiene-acrylonitrile resins. These resins may be used alone or in combination of two or more.

[0068] <Method for Manufacturing the Non-Aqueous Electrochemical Device of the Present Disclosure> The method for manufacturing the non-aqueous electrochemical device of the present disclosure is not particularly limited, and any known method can be applied. For example, the non-aqueous electrochemical device can be manufactured by manufacturing a laminate in which a separator is disposed between a positive electrode and a negative electrode, placing the laminate in an exterior packaging material, injecting an electrolyte solution, and then sealing the exterior packaging material.

[0069] When manufacturing a laminate in which a separator is disposed between a positive electrode and a negative electrode, the method of disposing the separator between the positive electrode and the negative electrode may be a method of stacking at least one layer of a positive electrode, a separator, and a negative electrode in this order (so-called stack method), or a method of stacking a positive electrode, a separator, a negative electrode, and a separator in this order and winding them in the length direction.

[0070] The shape of the nonaqueous electrochemical device of the present disclosure may be any of coin, button, sheet, cylindrical, rectangular, flat, and the like.

[0071] The binder polymer, binder composition, electrode composition, electrode, nonaqueous electrochemical device, and nonaqueous secondary battery of the present disclosure will be described in more detail below with reference to examples. The materials, amounts used, ratios, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present disclosure. Therefore, the scope of the binder polymer, binder composition, electrode composition, electrode, nonaqueous electrochemical device, and nonaqueous secondary battery of the present disclosure should not be construed as being limited by the specific examples shown below.

[0072] In the following description, syntheses, treatments, manufacturing, etc. were carried out at room temperature (25° C.±3° C.) unless otherwise specified.

[0073] <Preparation of Binder Polymer> (Example 1) A 1 L separable flask was charged with 449.54 parts by mass of ion-exchanged water deoxygenated by nitrogen blowing, 0.05 parts by mass of concentrated sulfuric acid as a pH adjuster, and 0.0005 parts by mass of iron (II) sulfate as a catalyst. A nitrogen atmosphere was created inside the separable flask while stirring, and the separable flask was immersed in a water bath adjusted to 50°C. 49.50 parts by mass of acrylonitrile as monomer (1) and 0.50 parts by mass of itaconic acid as monomer (2) were added. After confirming that the internal temperature of the separable flask had reached 48°C or higher, 0.37 parts by mass of a 50% aqueous solution of ammonium hydrogensulfite and 0.15 parts by mass of ammonium peroxodisulfate were added as polymerization initiators. After the addition, the separable flask was maintained at 50°C for 1 hour to carry out a polymerization reaction. After the reaction was completed, white particles were collected from the reaction mixture by filtration, thoroughly washed with ion-exchanged water, and then dried overnight in an electric dryer at 70° C. to obtain a binder polymer. The copolymerization components of the obtained binder polymer were 99.6 mol % of acrylonitrile and 0.4 mol % of itaconic acid, which was the same ratio as the charged amount in terms of mass.

[0074] (Examples 2 to 5 and Comparative Examples 1 to 5) Binder polymers of Examples 2 to 5 and Comparative Examples 1 to 5 were obtained in the same manner as in Example 1, except that the compositions of Monomer (1) and Monomer (2) were changed as shown in Table 1.

[0075] (Comparative Examples 6 and 7) Binder polymers of Comparative Examples 6 and 7 were obtained in the same manner as in Example 1, except that the compositions of Monomer (1) and Monomer (2) were changed as shown in Table 2 and the polymerization reaction time was changed to a longer time.

[0076] <Evaluation of Binder Polymer> [Dissolution Rate of Binder Polymer in Solvent] 15 parts by mass of each of the binder polymer powders of Examples 1 to 5 and Comparative Examples 1 to 5 was added to a bottle containing 85 parts by mass of N-methyl-2-pyrrolidone as a solvent, and the sealed bottle was mixed while rotating in an environment of 25°C to obtain each binder polymer solution. The time required for the dissolved residue to become invisible after mixing was taken as the dissolution time, and the dissolution rate was evaluated on a four-point scale according to the following criteria: A: The dissolution time was less than 1 day. B: The dissolution time was 1 day or more but less than 7 days. C: The dissolution time was 7 days or more but less than 14 days. D: The dissolution time was 14 days or more.

[0077] The results of the dissolution rate are shown in Table 1. The binder polymers of Examples 1 to 5 were excellent in dissolution rate in the solvent.

[0078] [Swelling of binder polymer by electrolyte solution] The binder polymer solution was cast onto a glass plate and dried to prepare a 4 cm square cast film. The mass of the cast film was measured in a dry environment at 25°C, immersed in the electrolyte solution in a container, and the container was sealed. After 72 hours, the cast film was pulled out, the attached liquid was wiped off, and the mass was measured again. The electrolyte solution was 1 M (mol / L) LiPF ６ - Ethylene carbonate / ethyl methyl carbonate (= 3 / 7 [mass ratio]) was used. The value of (mass after immersion) / (mass before immersion) was taken as the swelling degree, and the swelling property was evaluated on a four-point scale according to the following criteria: A: Swelling degree is less than 1.1. B: Swelling degree is 1.1 or more and less than 1.2. C: Swelling degree is 1.2 or more and less than 1.3. D: Swelling degree is 1.3 or more.

[0079] The results of the swelling property are shown in Table 1. The binder polymers of Examples 1 to 5 were excellent in that they had low swelling property with the electrolyte solution.

[0080] [Weight-average molecular weight of binder polymer] The weight-average molecular weight of the binder polymer was determined by gel permeation chromatography (GPC). A GPC measurement device (HPLC-8320GPC EcoSEC, manufactured by Tosoh Corporation) was used as the measurement device. A TSK gel α-M column (manufactured by Tosoh Corporation) was used as the column, and a differential refractive index detector (HLC-8320 GPC RI detector, manufactured by Tosoh Corporation) was used as the detector. Dimethylformamide was used as the mobile phase, and lithium bromide and phosphoric acid were added as eluents to concentrations of 50 mM and 10 mM, respectively. Polystyrene (standard polystyrene kit PStQuick Kit-C, D, manufactured by Tosoh Corporation) was used as the standard substance. The measurement results of the weight-average molecular weight are shown in Table 2.

[0081] <Preparation of Electrode Composition> Lithium cobalt oxide (LiCoO ２ 94 parts by mass of the powder, 3 parts by mass of acetylene black as a conductive additive, 3 parts by mass of the binder polymer, and an appropriate amount of N-methyl-2-pyrrolidone as a solvent were kneaded together to prepare electrode compositions for positive electrodes.

[0082] <Evaluation of Electrode Composition> [Coatability of Electrode Composition] The obtained electrode composition for the positive electrode was applied to a 20 μm thick aluminum foil using a roll coater and dried to obtain a positive electrode film. The coating film surface of the positive electrode film, which was 100 mm wide and 500 mm long, was visually observed, and the coatability was evaluated on a four-point scale based on the following criteria. Note that when the coatability of the electrode composition is poor, unevenness in thickness occurs in the coating film, and uneven shading is observed in the appearance. A: The entire coating film surface is uniform and no uneven shading is observed. B: Uneven shading is observed over an area of ​​less than 1 / 16 of the entire coating film surface. C: Uneven shading is observed over an area of ​​1 / 16 to less than 1 / 8 of the entire coating film surface. D: Uneven shading is observed over an area of ​​1 / 8 or more of the entire coating film surface.

[0083] The results of the coatability are shown in Table 2. When the binder polymers of the present disclosure in Examples 1 to 5, each having a weight-average molecular weight of 450,000 or less, were used in the electrode compositions, the coatability was good. On the other hand, when a polymer having a weight-average molecular weight of more than 450,000 was used in the electrode compositions in Comparative Examples 6 and 7, the coatability was poor.

[0084] <Preparation of Nonaqueous Electrochemical Device> (Examples 6 to 10) The positive electrode films using the binder polymers of Examples 1 to 5 obtained in the above <Evaluation of Electrode Composition> were further pressed to form positive electrodes. Metallic lithium foil was used as a negative electrode. A polyethylene microporous film (thickness: 8 μm, porosity: 36%) was sandwiched between these positive and negative electrodes as a separator, and the resulting battery was placed in a coin cell as an exterior material. An electrolyte solution was then injected and sealed to obtain a nonaqueous lithium-ion secondary battery (one embodiment of the nonaqueous electrochemical device of the present disclosure). The electrolyte solution was 1 M (mol / L) LiPF ６ Ethylene carbonate / ethyl methyl carbonate (=3 / 7 [mass ratio]) was used. All of these coin cell fabrication operations were carried out in an Ar atmosphere.

[0085] [Performance of Nonaqueous Lithium-Ion Secondary Battery] The performance of the nonaqueous lithium-ion secondary battery was evaluated by the capacity development rate, which is the ratio of the 0.2 C constant current discharge capacity of the battery to the actual capacity of 150 mAh / g of the lithium cobalt oxide. The discharge cutoff voltage was 2.5 V. Charging was performed at a constant current and voltage of 0.2 C and 4.2 V. The results are shown in Table 3. The capacity development rates of the nonaqueous lithium-ion secondary batteries of Examples 6 to 10 were 95.8%, 95.1%, 96.3%, 96.5%, and 95.9%, respectively. That is, the nonaqueous lithium-ion secondary batteries of Examples 6 to 10 were able to fully utilize the capacity of the lithium cobalt oxide and were practical as nonaqueous lithium-ion secondary batteries.

[0086]

[0087]

[0088]

[0089] From the above, the binder polymers of Examples 1 to 5 were binder polymers that achieved a good balance between high dissolution rate in solvents and low swelling with electrolyte solutions, and furthermore, were binder polymers that could yield compositions with excellent coatability. The nonaqueous electrochemical devices of Examples 6 to 10 also had excellent capacity development rates.

[0090] The disclosure of Japanese Patent Application No. 2024-074124, filed on April 30, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. An electrode binder polymer for a non-aqueous electrochemical device, which is a copolymer comprising structural units derived from at least one monomer (1) selected from acrylonitrile and methacrylonitrile, and structural units derived from at least one monomer (2) selected from the group consisting of unsaturated carboxylic acids, unsaturated carboxylic acid alkyl esters, and unsaturated carboxylic acid amides, wherein the content of the structural units derived from monomer (2) is 0.1 mol % to 4.9 mol % relative to the total amount of structural units derived from monomer (1) and monomer (2), and the weight-average molecular weight is 10,000 to 450,000.

2. The electrode binder polymer for a non-aqueous electrochemical device according to claim 1, wherein the unsaturated carboxylic acid alkyl ester is at least one of methyl acrylate and methyl methacrylate.

3. An electrode binder polymer for a non-aqueous electrochemical device according to claim 1 or 2, wherein the unsaturated carboxylic acid is at least one selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid.

4. An electrode binder polymer for a non-aqueous electrochemical device according to claim 1 or 2, wherein the number of carbon atoms in the monomer (2) is 5 or less.

5. An electrode binder composition for a non-aqueous electrochemical device, comprising the electrode binder polymer for a non-aqueous electrochemical device according to claim 1 or 2.

6. The electrode binder composition for a non-aqueous electrochemical device according to claim 5, further comprising a solvent.

7. An electrode composition for a non-aqueous electrochemical device, comprising the electrode binder polymer for a non-aqueous electrochemical device according to claim 1 or 2, and an active material.

8. The electrode composition for a non-aqueous electrochemical device according to claim 7, wherein the active material is a positive electrode active material.

9. An electrode for a non-aqueous electrochemical device comprising the electrode composition for a non-aqueous electrochemical device according to claim 7.

10. A non-aqueous electrochemical device comprising the electrode of claim 9.

11. A non-aqueous secondary battery comprising an electrode of the non-aqueous electrochemical device according to claim 9.

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