Binder for secondary battery functional layer, slurry composition for secondary battery functional layer, secondary battery functional layer, and secondary battery

Abstract

The purpose of the present invention is to provide a binder for a secondary battery functional layer, with which it is possible to form a functional layer having excellent heat shrinkage resistance, adhesion, and storage stability. The present invention is a binder for a secondary battery functional layer, the binder containing a particulate polymer, wherein the particulate polymer includes an acidic functional group-containing monomer unit and a reactive functional group-containing monomer unit containing a functional group that can react with the acidic functional group. The reactive functional group-containing monomer unit has a content ratio of 7 mass% to 30 mass%, where the total monomer units included in the particulate polymer are 100 mass%. A film formed from the particulate polymer after accelerated testing has an elastic modulus of 10 MPa or less.

Description

Binder for secondary battery functional layer, slurry composition for secondary battery functional layer, functional layer for secondary battery, and secondary battery

[0001] The present invention relates to a binder for a secondary battery functional layer, a slurry composition for a secondary battery functional layer, a functional layer for a secondary battery, and a secondary battery.

[0002] Secondary batteries such as lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Secondary batteries generally include battery components such as electrodes (positive and negative electrodes) and a separator that separates the positive and negative electrodes to prevent short circuits between them.

[0003] Here, as the battery component of the secondary battery, a component having a functional layer containing a binder and, optionally, particles (hereinafter referred to as "functional particles") blended to enable the battery component to exhibit a desired function is used. Specifically, as the separator of the secondary battery, a separator having an adhesive layer containing a binder or a porous membrane layer containing a binder and non-conductive particles as functional particles on a separator substrate is used. Furthermore, as the electrode of the secondary battery, an electrode having the above-mentioned adhesive layer or porous membrane layer on an electrode substrate formed by providing an electrode mixture layer on a current collector is used.

[0004] In order to further improve the performance of secondary batteries, attempts have been made to improve binders. For example, Patent Document 1 discloses a binder for non-aqueous secondary battery functional layers, which contains a particulate polymer containing (meth)acrylic acid alkyl ester monomer units, aromatic monovinyl monomer units, epoxy / N-methylol crosslinkable monomer units, and polyethylenically unsaturated crosslinkable monomer units in predetermined proportions, and which has a swelling degree in a non-aqueous electrolyte solution within a predetermined range. According to Patent Document 1, the use of this binder makes it possible to form a functional layer that exhibits excellent adhesion both before and after immersion in an electrolyte solution, and further makes it possible to improve the life characteristics of non-aqueous secondary batteries equipped with such a functional layer.

[0005] Patent No. 6515574

[0006] The functional layer formed using the binder of the above-mentioned conventional technology has room for improvement in heat shrinkage resistance. Also, the functional layer formed using the binder of the above-mentioned conventional technology has room for further improvement in adhesiveness of the functional layer. Furthermore, the functional layer formed using the binder is required to be resistant to deterioration in heat shrinkage resistance and adhesiveness even after a long period of time has passed, in other words, to have excellent storage stability.

[0007] Therefore, an object of the present invention is to provide a binder for a functional layer of a secondary battery capable of forming a functional layer having excellent heat shrinkage resistance, adhesion, and storage stability. Another object of the present invention is to provide a slurry composition for a functional layer of a secondary battery capable of forming a functional layer having excellent heat shrinkage resistance, adhesion, and storage stability. Another object of the present invention is to provide a functional layer for a secondary battery having excellent heat shrinkage resistance, adhesion, and storage stability. Another object of the present invention is to provide a secondary battery including the functional layer.

[0008] The present inventors have conducted extensive research with the aim of solving the above-mentioned problems, and have newly discovered that the above-mentioned problems can be solved by using a binder containing a particulate polymer having a predetermined composition and properties, thereby completing the present invention.

[0009] That is, the present invention aims to advantageously solve the above-mentioned problems. [1] The present invention provides a binder for a secondary battery functional layer containing a particulate polymer, wherein the particulate polymer contains an acidic functional group-containing monomer unit and a reactive functional group-containing monomer unit containing a functional group capable of reacting with the acidic functional group, the content of the reactive functional group-containing monomer unit being 7% by mass or more and 30% by mass or less when the total amount of all monomer units contained in the particulate polymer is taken as 100% by mass, and a film made of the particulate polymer after an accelerated test has an elastic modulus of 10 MPa or less. With such a binder for a secondary battery functional layer, a functional layer excellent in heat shrinkage resistance, adhesiveness, and storage stability can be formed. In this specification, "containing a monomer unit" means that "a polymer obtained using the monomer contains a repeating unit derived from the monomer." In this specification, the "content (mass%)" of each monomer unit (each repeating unit) contained in the polymer is 1 H-NMR and １３ The acid content can be measured using a nuclear magnetic resonance (NMR) method such as C-NMR. The type of acidic functional group-containing monomer unit is identified (qualitatively) using nuclear magnetic resonance (NMR), and the content ratio of the acidic functional group-containing monomer unit contained in the polymer is measured (quantitatively) using conductometric titration. Conductometric titration can measure the acid content by diluting the binder for the secondary battery functional layer to an appropriate concentration and titrating it with an aqueous sodium hydroxide solution and an aqueous hydrochloric acid solution. In this specification, "functional groups capable of reacting with acidic functional groups" include cyclic ether groups, hydroxyl groups, and amide groups. In this specification, the elastic modulus of a film made of a particulate polymer after an accelerated test can be measured according to the procedures and methods described in the Examples.

[0010] [2] In the binder for a secondary battery functional layer according to [1] above, the content of the acidic functional group-containing monomer unit is preferably 0.1% by mass or more and 1% by mass or less, when the total mass of all monomer units contained in the particulate polymer is taken as 100% by mass. When the content of the acidic functional group-containing monomer unit is equal to or more than the lower limit, when the total mass of all monomer units contained in the particulate polymer is taken as 100% by mass, the particulate polymer can be easily prepared and the storage stability of the functional layer can be improved. On the other hand, when the content of the acidic functional group-containing monomer unit is equal to or less than the upper limit, when the total mass of all monomer units contained in the particulate polymer is taken as 100% by mass, the storage stability of the functional layer can be improved.

[0011] [3] In the binder for a secondary battery functional layer according to [1] or [2] above, the particulate polymer preferably further contains a crosslinkable monomer unit, and the content of the crosslinkable monomer unit is more than 0% by mass and not more than 1.5% by mass, where the total amount of all monomer units contained in the particulate polymer is taken as 100% by mass. When the content of the crosslinkable monomer unit is equal to or greater than the lower limit, where the total amount of all monomer units contained in the particulate polymer is taken as 100% by mass, the cycle characteristics of the secondary battery can be improved. On the other hand, when the content of the crosslinkable monomer unit is equal to or less than the upper limit, where the total amount of all monomer units contained in the particulate polymer is taken as 100% by mass, the adhesiveness of the functional layer can be improved.

[0012] [4] In the binder for a secondary battery functional layer according to any one of [1] to [3] above, the particulate polymer preferably further contains a cyano group-containing monomer unit, and the content of the cyano group-containing monomer unit is preferably 2% by mass or more and 30% by mass or less, when the total mass of all monomer units contained in the particulate polymer is taken as 100% by mass. When the content of the cyano group-containing monomer unit is equal to or more than the lower limit, when the total mass of all monomer units contained in the particulate polymer is taken as 100% by mass, the adhesiveness of the functional layer can be improved. On the other hand, when the content of the cyano group-containing monomer unit is equal to or less than the upper limit, when the total mass of all monomer units contained in the particulate polymer is taken as 100% by mass, the cycle characteristics of the secondary battery can be improved.

[0013] [5] The binder for a secondary battery functional layer according to any one of [1] to [4] above preferably contains water and has a pH of 4 or more and 8 or less. When the pH of the binder for a secondary battery functional layer is within the above range, the storage stability of the functional layer can be improved. In this specification, the pH of the binder for a secondary battery functional layer can be measured according to the method described in the Examples.

[0014] [6] In the binder for a secondary battery functional layer according to any one of the above [1] to [5], the glass transition temperature of the particulate polymer is preferably 20°C or lower. When the glass transition temperature of the particulate polymer is equal to or lower than the upper limit, the adhesiveness of the functional layer can be improved. In this specification, the "glass transition temperature" of the particulate polymer can be measured using the method described in the examples of this specification.

[0015] [7] In the binder for a secondary battery functional layer according to any one of [1] to [6] above, the volume average particle diameter of the particulate polymer is preferably 0.1 μm or more and 0.2 μm or less. When the volume average particle diameter of the particulate polymer is equal to or greater than the lower limit, the cycle characteristics of the secondary battery can be improved. On the other hand, when the volume average particle diameter of the particulate polymer is equal to or less than the upper limit, the adhesiveness of the functional layer can be improved. In this specification, the term "volume average particle diameter" refers to the particle diameter at which the cumulative volume calculated from the smallest diameter side in the particle size distribution (volume basis) measured by laser diffraction is 50%.

[0016] [8] In the binder for a secondary battery functional layer according to any one of [1] to [7] above, the electrolyte swelling degree of the particulate polymer is preferably 3 to 5 times. When the electrolyte swelling degree of the particulate polymer is equal to or greater than the lower limit, the adhesion of the functional layer can be improved. On the other hand, when the electrolyte swelling degree of the particulate polymer is equal to or less than the upper limit, the cycle characteristics of the secondary battery can be improved. In this specification, the "electrolyte swelling degree" of the particulate polymer can be determined as the value (unit: times) obtained by immersing a film (binder film) formed from the particulate polymer in a specific non-aqueous electrolyte solution under predetermined conditions, dividing the weight after immersion by the weight before immersion. Specifically, the binder film can be formed using the method described in the examples of this specification, and the measurement can be performed using the measurement method described in the examples.

[0017] Another object of the present invention is to advantageously solve the above-mentioned problems, and [9] the present invention provides a slurry composition for a secondary battery functional layer, comprising the binder for a secondary battery functional layer according to any one of [1] to [8] above and functional particles. The above slurry composition can form a functional layer that is excellent in heat shrinkage resistance, adhesiveness, and storage stability.

[0018]

[10] In the slurry composition for a secondary battery functional layer according to the above [9], the functional particles preferably include non-conductive particles. The slurry composition for a secondary battery functional layer containing non-conductive particles as functional particles can be suitably used for forming a porous membrane layer.

[0019]

[11] In the slurry composition for a secondary battery functional layer according to

[10] above, the ratio of the volume average particle diameter of the non-conductive particles to the volume average particle diameter of the particulate polymer is preferably 2.0 to 7.0 times. When the ratio of the volume average particle diameter of the non-conductive particles to the volume average particle diameter of the particulate polymer is equal to or greater than the lower limit, the adhesiveness of the functional layer can be further improved. On the other hand, when the ratio of the volume average particle diameter of the non-conductive particles to the volume average particle diameter of the particulate polymer is equal to or less than the upper limit, the heat shrinkage resistance of the functional layer can be further improved. Furthermore, the cycle characteristics of the secondary battery can be further improved.

[0020] Another object of the present invention is to advantageously solve the above-mentioned problems, and

[12] the present invention is a functional layer for a secondary battery formed using the slurry composition for a secondary battery functional layer according to any one of [9] to

[11] above. The functional layer for a secondary battery has excellent heat shrinkage resistance, adhesiveness, and storage stability.

[0021] Another object of the present invention is to advantageously solve the above-mentioned problems, and

[13] the present invention is a secondary battery including the functional layer for secondary batteries according to

[12] above. The secondary battery can exhibit excellent battery characteristics.

[0022] According to the present invention, a binder for a secondary battery functional layer can be provided, which can form a functional layer having excellent heat shrinkage resistance, adhesion, and storage stability. The present invention also provides a slurry composition for a secondary battery functional layer, which can form a functional layer having excellent heat shrinkage resistance, adhesion, and storage stability. The present invention also provides a functional layer for a secondary battery having excellent heat shrinkage resistance, adhesion, and storage stability. The present invention also provides a secondary battery including the functional layer.

[0023] Hereinafter, embodiments of the present invention will be described in detail. Herein, the binder for a secondary battery functional layer of the present invention (hereinafter, sometimes simply referred to as "binder") is used in the manufacture of any functional layer that performs functions such as reinforcement or adhesion in a secondary battery. For example, the binder of the present invention can be used to prepare a slurry composition for a secondary battery functional layer of the present invention (hereinafter, sometimes simply referred to as "slurry composition"). The slurry composition of the present invention can be used to form the above-mentioned functional layer. Furthermore, the functional layer for a secondary battery of the present invention (hereinafter, sometimes simply referred to as "functional layer") is formed from the slurry composition of the present invention. The secondary battery of the present invention includes the functional layer of the present invention. For example, the secondary battery of the present invention includes a positive electrode, a negative electrode, and a separator as battery components, and at least one of the above-mentioned battery components includes the functional layer of the present invention. That is, the secondary battery of the present invention includes a battery component having the functional layer of the present invention.

[0024] (Binder for Secondary Battery Functional Layer) The binder of the present invention contains a particulate polymer having a predetermined composition and properties, which will be described in detail below. The binder of the present invention is usually a composition in which the particulate polymer is dispersed in a solvent such as water. The binder of the present invention may further contain components other than the particulate polymer and the solvent (hereinafter referred to as "other components").

[0025] <Particulate Polymer> The particulate polymer is a component that functions as a binder, imparting adhesiveness to the functional layer formed using a slurry composition containing a binder, and also retaining components contained in the functional layer (e.g., functional particles such as non-conductive particles) so that they do not detach from the functional layer.

[0026] Here, the particulate polymer contains an acidic functional group-containing monomer unit and a reactive functional group-containing monomer (hereinafter sometimes simply referred to as a "reactive functional group-containing monomer") unit containing a functional group reactive with the acidic functional group, and the content of the reactive functional group-containing monomer unit is 7% by mass or more and 30% by mass or less, when the total amount of repeating units (total monomer units) contained in the particulate polymer is taken as 100% by mass. The particulate polymer may further contain other monomer units, in addition to the acidic functional group-containing monomer units and the reactive functional group-containing monomer units. Examples of the other monomer units include, but are not limited to, cyano group-containing monomer units, crosslinkable monomer units, and (meth)acrylic acid ester monomer units. In the binder of the present invention, the modulus of elasticity of a film made of the particulate polymer after an accelerated test is 10 MPa or less.

[0027] The binder of the present invention contains a particulate polymer having the above-described composition and properties, and therefore can impart excellent heat shrinkage resistance, adhesiveness, and storage stability to the functional layer. While the reasons for this are unclear, the following is presumed to be the case. First, the particulate polymer in the binder of the present invention contains an acidic functional group-containing monomer unit, which is presumed to result in excellent particle stability. Furthermore, the particulate polymer in the binder of the present invention contains a reactive functional group-containing monomer unit, which results in reactive functional groups present on the particle surface. These reactive functional groups are presumed to crosslink or interact with the surface of the separator substrate (e.g., a surface made hydrophilic by surface treatment) or other components contained in the functional layer. Furthermore, by setting the proportion of the reactive functional group-containing monomer unit in the particulate polymer within the above-described range, the crosslinking or interaction can be favorably achieved, stabilizing the layer structure of the functional layer and, as a result, improving the heat shrinkage resistance and adhesiveness of the functional layer. Furthermore, in the accelerated test of the particulate polymer, as in the examples described later, the particulate polymer is left to stand at 60°C for 14 days, and if the modulus of elasticity of the film made of the particulate polymer after such an accelerated test is 10 MPa or less, it is presumed that the number of crosslinks (degree of crosslinking) and interactions with other components in the functional layer are in a good state, in other words, the functional layer is maintained in a stable state, and therefore the storage stability is improved. For the above reasons, it is presumed that the binder of the present invention can impart excellent heat shrinkage resistance, adhesiveness, and storage stability to the functional layer.

[0028] <<Elastic Modulus of Film Made of Particulate Polymer After Accelerated Testing>> In the binder of the present invention, the elastic modulus of the film made of the particulate polymer after the accelerated test must be 10 MPa or less, preferably 7 MPa or less, and more preferably 5 MPa or less. As described above, if the elastic modulus of the film made of the particulate polymer after the accelerated test is equal to or less than the above upper limit, the storage stability of the functional layer can be improved. On the other hand, the elastic modulus of the film made of the particulate polymer after the accelerated test is, for example, 0.1 MPa or more, or may be 0.5 MPa or more, or may be 1 MPa or more. The elastic modulus of the film made of the particulate polymer after the accelerated test can be adjusted by changing the type and amount of the monomer used.

[0029] <<Elastic Modulus of Film Made of Particulate Polymer Before Accelerated Test>> The elastic modulus of the film made of the particulate polymer before the accelerated test is preferably 10 MPa or less, more preferably 7 MPa or less, even more preferably 5 MPa or less, and even more preferably 3 MPa or less. On the other hand, the elastic modulus of the film made of the particulate polymer before the accelerated test is, for example, 0.1 MPa or more, or may be 0.5 MPa or more, or may be 1 MPa or more.

[0030] <<Composition of Particulate Polymer>> [Acidic Functional Group-Containing Monomer Unit] Examples of the acidic functional group-containing monomer capable of forming the acidic functional group-containing monomer unit include a carboxyl group-containing monomer, a sulfonic acid group-containing monomer, and a phosphoric acid group-containing monomer.

[0031] Examples of carboxyl group-containing monomers include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters such as nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleates. Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride. Furthermore, as the carboxyl group-containing monomer, an acid anhydride that generates a carboxyl group upon hydrolysis can also be used.

[0032] Examples of sulfonic acid group-containing monomers include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, etc. In this specification, "(meth)allyl" means allyl and / or methallyl, and "(meth)acrylic" means acrylic and / or methacrylic.

[0033] Examples of the phosphate group-containing monomer include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, ethyl-(meth)acryloyloxyethyl phosphate, etc. In this specification, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0034] The above-listed acidic functional group-containing monomers may be used alone or in combination of two or more.

[0035] As the acidic functional group-containing monomer capable of forming the acidic functional group-containing monomer unit, from the viewpoint of further improving the particle stability of the particulate polymer, it is preferable to use a carboxyl group-containing monomer, more preferably to use a monocarboxylic acid, more preferably to use at least one monomer of acrylic acid and methacrylic acid, and even more preferably to use acrylic acid. That is, the particulate polymer preferably contains a carboxyl group-containing monomer unit, more preferably to contain a monocarboxylic acid unit, more preferably to contain at least one monomer unit of acrylic acid unit and methacrylic acid unit, and even more preferably to contain an acrylic acid unit.

[0036] The content ratio of the acidic functional group-containing monomer unit is preferably 0.1% by mass or more, preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.2% by mass or less, when all repeating units (total monomer units) contained in the particulate polymer are taken as 100% by mass. If the content ratio of the acidic functional group-containing monomer unit is equal to or greater than the lower limit when all monomer units contained in the particulate polymer are taken as 100% by mass, the preparation of the particulate polymer is easy and the storage stability of the functional layer can be improved. On the other hand, if the content ratio of the acidic functional group-containing monomer unit is equal to or less than the upper limit when all monomer units contained in the particulate polymer are taken as 100% by mass, the storage stability of the functional layer can be improved.

[0037] [Reactive Functional Group-Containing Monomer Unit] Examples of reactive functional group-containing monomers capable of forming reactive functional group-containing monomer units include cyclic ether group-containing monomers, hydroxyl group-containing monomers, and amide group-containing monomers.

[0038] The cyclic ether group-containing monomer is not particularly limited as long as it is a monomer containing a cyclic ether group, and examples thereof include a monomer containing an epoxy group (epoxy ring) (epoxy group-containing monomer) and a monomer containing an oxetanyl group (oxetane ring) (oxetanyl group-containing monomer). Among these, from the viewpoint of further improving the heat shrinkage resistance and adhesiveness of the functional layer, it is preferable to use an epoxy group-containing monomer. Examples of epoxy group-containing monomers include allyl glycidyl ether, glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl methacrylate, and 4-hydroxybutyl acrylate glycidyl ether. Examples of oxetanyl group-containing monomers include 3-((meth)acryloyloxymethyl)oxetane, 3-((meth)acryloyloxymethyl)-2-trifluoromethyloxetane, 3-((meth)acryloyloxymethyl)-2-phenyloxetane, 2-((meth)acryloyloxymethyl)oxetane, and 2-((meth)acryloyloxymethyl)-4-trifluoromethyloxetane. In this specification, "(meth)acrylate" means acrylate and / or methacrylate.

[0039] Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate.

[0040] Examples of the amide group-containing monomer include N-vinylacetamide, (meth)acrylamide, dimethyl(meth)acrylamide, diethyl(meth)acrylamide, N-methoxymethyl(meth)acrylamide, and dimethylaminopropyl(meth)acrylamide.

[0041] Furthermore, as the reactive functional group-containing monomer, a monomer having two or more functional groups capable of reacting with an acidic functional group can also be used, and examples thereof include a monomer containing a hydroxyl group and an amide group. Examples of the monomer containing a hydroxyl group and an amide group include N-methylol(meth)acrylamide and hydroxyethyl(meth)acrylamide. In this specification, a monomer containing a hydroxyl group and an amide group is not included in either a hydroxyl group-containing monomer or an amide group-containing monomer.

[0042] The reactive functional group-containing monomers listed above may be used alone or in combination of two or more.

[0043] As the reactive functional group-containing monomer capable of forming the reactive functional group-containing monomer unit, from the viewpoint of further improving the adhesiveness of the functional layer and particularly further improving the heat shrinkage resistance of the functional layer, it is preferable to use a cyclic ether group-containing monomer, it is preferable to use an epoxy group-containing monomer, it is more preferable to use at least one monomer of allyl glycidyl ether and glycidyl (meth)acrylate, it is even more preferable to use at least one monomer of allyl glycidyl ether and glycidyl methacrylate. That is, the particulate polymer preferably contains a cyclic ether group-containing monomer unit, more preferably contains an epoxy group-containing monomer unit, it is even more preferable to contain at least one monomer unit of allyl glycidyl ether unit and glycidyl (meth)acrylate unit, it is even more preferable to contain at least one monomer unit of allyl glycidyl ether unit and glycidyl methacrylate unit.

[0044] The content of the reactive functional group-containing monomer unit must be 7% by mass or more, preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 18% by mass or more, when the total amount of all repeating units (total monomer units) contained in the particulate polymer is 100% by mass, and must be 30% by mass or less, preferably 25% by mass or less, more preferably 22% by mass or less, and even more preferably 20% by mass or less. When the content of the reactive functional group-containing monomer unit is equal to or greater than the lower limit above, when the total amount of all monomer units contained in the particulate polymer is 100% by mass, the heat shrinkage resistance of the functional layer can be improved. On the other hand, when the content of the reactive functional group-containing monomer unit is equal to or less than the upper limit above, when the total amount of all monomer units contained in the particulate polymer is 100% by mass, the adhesion of the functional layer can be improved.

[0045] In one embodiment, the particulate polymer preferably contains two or more types of reactive functional group-containing monomer units, and more preferably contains a cyclic ether group-containing monomer unit and a monomer unit containing a hydroxyl group and an amide group.

[0046] When the particulate polymer contains a cyclic ether group-containing monomer unit and a monomer unit containing a hydroxyl group and an amide group, the content of the cyclic ether group-containing monomer unit is preferably 6.9% by mass or more, more preferably 9.5% by mass or more, even more preferably 14.2% by mass or more, even more preferably 17% by mass or more, and preferably 25% by mass or less, more preferably 22% by mass or less, even more preferably 19.5% by mass or less, and even more preferably 18.5% by mass or less, when the total amount of all repeating units (total monomer units) contained in the particulate polymer is taken as 100% by mass. If the content of the cyclic ether group-containing monomer unit is equal to or greater than the lower limit above, the heat shrinkage resistance of the functional layer can be further improved. On the other hand, if the content of the cyclic ether group-containing monomer unit is equal to or less than the upper limit above, when the total amount of all monomer units contained in the particulate polymer is taken as 100% by mass, the adhesion of the functional layer can be further improved.

[0047] When the particulate polymer contains a cyclic ether group-containing monomer unit and a hydroxyl group- and amide group-containing monomer unit, the content of the hydroxyl group- and amide group-containing monomer unit is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.8% by mass or more, even more preferably 1% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2.5% by mass or less, and even more preferably 1.5% by mass or less, when the total mass of all repeating units (total monomer units) contained in the particulate polymer is taken as 100% by mass. If the content of the hydroxyl group- and amide group-containing monomer unit is equal to or greater than the above lower limit, the heat shrinkage resistance of the functional layer can be further improved. Furthermore, the cycle characteristics of the secondary battery can be improved. On the other hand, if the content ratio of the monomer units containing a hydroxyl group and an amide group is equal to or less than the upper limit above, when the total monomer units contained in the particulate polymer is taken as 100 mass%, the adhesion of the functional layer can be further improved.

[0048] In the particulate polymer, the content of the reactive functional group-containing monomer unit is preferably higher than the content of the acidic functional group-containing monomer unit, which can improve the heat shrinkage resistance and adhesiveness of the functional layer.

[0049] [Cyano Group-Containing Monomer Unit] In this specification, cyano group-containing monomers capable of forming cyano group-containing monomer units are not included in the above-mentioned acidic functional group-containing monomers and reactive functional group-containing monomers. Examples of cyano group-containing monomers that can be used include (meth)acrylonitriles such as acrylonitrile and methacrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; 2-cyanoethyl (meth)acrylates such as 2-cyanoethyl acrylate and 2-cyanoethyl methacrylate; and 2-cyanoethyl acrylamide. These may be used alone or in combination of two or more in any ratio. In this specification, "(meth)acrylonitrile" refers to acrylonitrile and / or methacrylonitrile.

[0050] As the cyano group-containing monomer capable of forming the cyano group-containing monomer unit, it is preferable to use (meth)acrylonitrile, and it is more preferable to use acrylonitrile, from the viewpoint of further improving the adhesiveness of the functional layer. That is, it is preferable that the particulate polymer contains a (meth)acrylonitrile unit, and it is more preferable that it contains an acrylonitrile unit.

[0051] The content of the cyano group-containing monomer unit is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 15% by mass or less, when the total repeating units (total monomer units) contained in the particulate polymer is taken as 100% by mass. If the content of the cyano group-containing monomer unit is equal to or greater than the lower limit above, when the total monomer units contained in the particulate polymer is taken as 100% by mass, the adhesion of the functional layer can be improved. On the other hand, if the content of the cyano group-containing monomer unit is equal to or less than the upper limit above, when the total monomer units contained in the particulate polymer is taken as 100% by mass, the internal resistance of the secondary battery can be prevented from increasing, and the cycle characteristics of the secondary battery can be improved.

[0052] [Crosslinkable Monomer Unit] A crosslinkable monomer capable of forming a crosslinkable monomer unit is a monomer capable of forming a crosslinked structure during or after polymerization by heating or irradiation with energy rays. In this specification, the crosslinkable monomer is not included in the above-mentioned acidic functional group-containing monomer, reactive functional group-containing monomer, and cyano group-containing monomer.

[0053] Examples of crosslinkable monomers include polyfunctional monomers having two or more polymerization reactive groups in the monomer. Examples of such polyfunctional monomers include divinyl monomers such as divinylbenzene, 1,3-butadiene, isoprene, and allyl methacrylate; di(meth)acrylic acid alkyl ester monomers such as ethylene dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate (EDMA), diethylene glycol diacrylate, and 1,3-butylene glycol diacrylate; and tri(meth)acrylic acid alkyl ester monomers such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate. These may be used alone or in combination of two or more.

[0054] As the crosslinkable monomer capable of forming the crosslinkable monomer unit, it is preferable to use at least one monomer of allyl methacrylate and ethylene glycol dimethacrylate from the viewpoint of improving the heat shrinkage resistance of the functional layer. Furthermore, as the crosslinkable monomer capable of forming the crosslinkable monomer unit, it is more preferable to use allyl methacrylate, since it can improve the heat shrinkage resistance of the functional layer and can improve the cycle characteristics of the secondary battery. That is, it is preferable that the particulate polymer contains at least one monomer unit of allyl methacrylate units and ethylene glycol dimethacrylate units, and it is preferable that it contains an allyl methacrylate unit.

[0055] The content of the crosslinkable monomer unit is preferably more than 0% by mass, more preferably 0.3% by mass or more, preferably 1.5% by mass or less, and more preferably 0.8% by mass or less, when the total repeating units (total monomer units) contained in the particulate polymer is taken as 100% by mass. If the content of the crosslinkable monomer unit is equal to or greater than the lower limit when the total monomer units contained in the particulate polymer is taken as 100% by mass, the cycle characteristics of the secondary battery can be improved. On the other hand, if the content of the crosslinkable monomer unit is equal to or less than the upper limit when the total monomer units contained in the particulate polymer is taken as 100% by mass, the adhesion of the functional layer can be improved.

[0056] [(Meth)acrylic acid ester monomer unit] In this specification, (meth)acrylic acid ester monomers capable of forming (meth)acrylic acid ester monomer units are not included in the above-mentioned acidic functional group-containing monomers, reactive functional group-containing monomers, cyano group-containing monomers, and crosslinkable monomers. Examples of the (meth)acrylic acid ester monomer include (meth)acrylic acid alkyl ester monomers and (meth)acrylic acid aryl ester monomers, but (meth)acrylic acid alkyl ester monomers are preferred from the viewpoint of improving the adhesion of the functional layer.

[0057] Examples of the (meth)acrylic acid alkyl ester monomer include acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate; and alkyl methacrylates such as ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, and glycidyl methacrylate. These may be used alone or in combination of two or more.

[0058] As the (meth)acrylic acid alkyl ester monomer, from the viewpoints of further improving the adhesiveness of the functional layer and improving heat shrinkage resistance, it is preferable to use at least one monomer of 2-ethylhexyl acrylate and butyl acrylate. That is, it is preferable that the particulate polymer contains at least one monomer unit of 2-ethylhexyl acrylate units and butyl acrylate units.

[0059] The content of the (meth)acrylic acid ester monomer units is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less, when the total repeating units (total monomer units) contained in the particulate polymer is taken as 100% by mass. If the content of the (meth)acrylic acid ester monomer units is equal to or greater than the lower limit above, when the total monomer units contained in the particulate polymer is taken as 100% by mass, the adhesiveness of the functional layer can be improved. On the other hand, if the content of the (meth)acrylic acid ester monomer units is equal to or less than the upper limit above, when the total monomer units contained in the particulate polymer is taken as 100% by mass, the heat shrinkage resistance of the functional layer can be improved. Furthermore, the cycle characteristics of the secondary battery can be improved.

[0060] <<Glass Transition Temperature of Particulate Polymer>> The glass transition temperature of the particulate polymer is preferably 20°C or lower, more preferably 10°C or lower, and even more preferably 0°C or lower. If the glass transition temperature of the particulate polymer is equal to or lower than the above upper limit, the adhesiveness of the functional layer can be improved. On the other hand, the lower limit of the glass transition temperature of the particulate polymer is not particularly limited, but is usually −100°C or higher.

[0061] <<Electrolyte Swelling Degree of Particulate Polymer>> The electrolyte swelling degree of the particulate polymer is preferably 3 times or more, more preferably 3.5 times or more, and preferably 5 times or less, and more preferably 4.5 times or less. If the electrolyte swelling degree of the particulate polymer is equal to or greater than the lower limit, the adhesion of the functional layer can be improved. On the other hand, if the electrolyte swelling degree of the particulate polymer is equal to or less than the upper limit, an increase in the internal resistance of the secondary battery can be suppressed, and the cycle characteristics of the secondary battery can be improved. The electrolyte swelling degree of the particulate polymer can be adjusted by changing the type and amount of the monomer used and the polymerization reaction conditions (e.g., polymerization temperature, polymerization reaction time, etc.).

[0062] <<Volume Average Particle Diameter of Particulate Polymer>> The volume average particle diameter of the particulate polymer is preferably 0.1 μm or more, more preferably 0.12 μm or more, and preferably 0.2 μm or less, and more preferably 0.18 μm or less. If the volume average particle diameter of the particulate polymer is equal to or greater than the lower limit, the cycle characteristics of the secondary battery can be improved. On the other hand, if the volume average particle diameter of the particulate polymer is equal to or less than the upper limit, the adhesion of the functional layer can be improved.

[0063] <<Structure of Particulate Polymer>> The structure of the particulate polymer is not particularly limited and may be any of a block copolymer, a graft copolymer, a random copolymer, etc., but is preferably a random copolymer. Furthermore, the particulate polymer may have a core-shell structure comprising a core portion and a shell portion covering at least a part of the outer surface of the core portion, but preferably does not have a core-shell structure. Therefore, it is particularly preferable that the particulate polymer is a random copolymer without a core-shell structure. In this specification, when only one glass transition temperature is detected when the glass transition temperature of the particulate polymer is measured, it is determined to be "a random copolymer without a core-shell structure."

[0064] <<Preparation of Particulate Polymer>> The particulate polymer can be prepared by polymerizing a monomer composition containing the above-mentioned monomers. Here, the content ratio of each monomer in the monomer composition is usually the same as the content ratio of the monomer unit in the desired particulate polymer. The polymerization mode of the particulate polymer is not particularly limited, and for example, any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization may be used. However, emulsion polymerization is preferred because it allows easy adjustment of the volume average particle size of the particulate polymer. As the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, or living radical polymerization can be used. Furthermore, commonly used emulsifiers, dispersants, polymerization initiators, polymerization aids, etc. can be used in polymerization, and the amounts used are also commonly used amounts. When polymerizing the particulate polymer, it is preferable to lower the polymerization temperature below the polymerization temperature at any time from the start of polymerization to the end of polymerization to terminate the polymerization. In particular, the polymerization temperature at the end of the polymerization is preferably at least 10° C. lower than the temperature at the start of the polymerization, and more preferably at least 15° C. lower. When the polymerization temperature is lowered, a reducing agent such as ascorbic acid may be added.

[0065] <Solvent> As the solvent that can be contained in the binder of the present invention, known solvents capable of dispersing the above-mentioned particulate polymer can be used. Among them, it is preferable to use water as the solvent. Note that at least a part of the solvent that can be contained in the binder is not particularly limited, and can be the polymerization solvent used in preparing the particulate polymer.

[0066] <Solid content of binder for secondary battery functional layer> The solid content of the binder (particulate polymer, etc.) is preferably 30% by mass or more, more preferably 35% by mass or more, and preferably 50% by mass or less, and more preferably 45% by mass or less. If the solid content of the binder is equal to or greater than the lower limit, the particle stability of the particulate polymer can be improved, and as a result, the storage stability of the functional layer can be improved. On the other hand, if the solid content of the binder is equal to or less than the upper limit, excessive contact frequency between particles can be suppressed, and the storage stability of the functional layer can be improved.

[0067] <pH of binder for secondary battery functional layer> When the solvent is water, the pH of the binder is preferably 4 or more, more preferably 5 or more, and preferably 8 or less, more preferably 7 or less. When the pH of the binder is within the above range, the storage stability of the functional layer can be improved.

[0068] <Preparation of binder for secondary battery functional layer> The method for preparing the binder of the present invention is not particularly limited, but for example, when the particulate polymer is prepared in a solvent such as water and the particulate polymer is obtained as a dispersion, the dispersion of the particulate polymer may be used as the binder as it is, or other components may be added to the dispersion of the particulate polymer to form a binder. Here, examples of other components include the "other components" described later in the section "Slurry composition for secondary battery functional layer".

[0069] (Slurry composition for secondary battery functional layer) The slurry composition of the present invention is a composition used for forming a functional layer, and contains the above-mentioned binder and functional particles, and optionally further contains other components. That is, the slurry composition usually contains a particulate polymer, a solvent, and functional particles, and optionally further contains other components. Furthermore, since the slurry composition of the present invention contains the above-mentioned binder, a functional layer excellent in heat shrinkage resistance, adhesiveness, and storage stability can be obtained by drying the slurry composition of the present invention, for example, on a substrate.

[0070] <Binder> The binder used is the binder of the present invention described above. The amount of binder in the slurry composition is not particularly limited. The amount of binder in the slurry composition, calculated as solid content, is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and preferably 6 parts by mass or less, and more preferably 3 parts by mass or less, per 100 parts by mass of functional particles. If the amount of binder in the slurry composition is equal to or greater than the above lower limit, the adhesion of the functional layer can be improved. On the other hand, if the amount of binder in the slurry composition is equal to or less than the above upper limit, the heat shrinkage resistance of the functional layer can be improved.

[0071] <Functional Particles> Here, as the functional particles for making the functional layer exhibit the intended function, for example, when the functional layer is a porous membrane layer, non-conductive particles can be used. In particular, since the functional layer formed using the slurry composition of the present invention has excellent heat shrinkage resistance, the slurry composition of the present invention containing non-conductive particles as functional particles can be suitably used for forming a porous membrane layer that improves the heat resistance and strength of battery components.

[0072] <<Non-conductive particles>> The non-conductive particles that can be used in the porous membrane layer of the secondary battery are not particularly limited, and both inorganic fine particles and organic fine particles can be used, but inorganic fine particles are usually used. Among them, as the material of the non-conductive particles, a material that exists stably in the use environment of the secondary battery and is electrochemically stable is preferred. From this viewpoint, preferred examples of the material of the non-conductive particles include aluminum oxide (alumina), hydrated aluminum oxide (boehmite), silicon oxide, magnesium oxide (magnesia), calcium oxide, titanium oxide (titania), and BaTiO ３ Examples of suitable non-conductive particles include oxide particles such as ZrO and alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystalline particles such as silicon and diamond; sparingly soluble ionic crystalline particles such as barium sulfate, calcium fluoride and barium fluoride; and clay fine particles such as talc and montmorillonite. These particles may also be subjected to element substitution, surface treatment, solid solution formation, etc., as necessary. From the viewpoint of suppressing aggregation and improving the dispersibility of the slurry composition, it is preferable to use at least one non-conductive particle selected from the group consisting of alumina, boehmite, and barium sulfate, and it is more preferable to use non-conductive particles of at least one of alumina and barium sulfate. The non-conductive particles described above may be used singly or in combination of two or more types.

[0073] The volume average particle diameter of the non-conductive particles is preferably 0.1 μm or more, more preferably 0.3 μm or more, and preferably 1.5 μm or less, and more preferably 1.0 μm or less. If the volume average particle diameter of the non-conductive particles is equal to or greater than the lower limit, the adhesiveness of the functional layer can be improved. On the other hand, if the volume average particle diameter of the non-conductive particles is equal to or less than the upper limit, the air permeability of the functional layer is increased, thereby improving the electrolyte injectability of the functional layer and, as a result, improving the cycle characteristics of the secondary battery.

[0074] Here, the ratio of the volume average particle diameter of the non-conductive particles to the volume average particle diameter of the particulate polymer ("volume average particle diameter of non-conductive particles" / "volume average particle diameter of particulate polymer") is preferably 2.0 times or more, more preferably 2.5 times or more, and preferably 7.0 times or less, and more preferably 5.0 times or less. If the ratio of the volume average particle diameter of the non-conductive particles to the volume average particle diameter of the particulate polymer is equal to or greater than the above-mentioned lower limit, the adhesiveness of the functional layer can be further improved. On the other hand, if the ratio of the volume average particle diameter of the non-conductive particles to the volume average particle diameter of the particulate polymer is equal to or less than the above-mentioned upper limit, the heat shrinkage resistance of the functional layer can be further improved. In addition, the cycle characteristics of the secondary battery can be further improved.

[0075] <Other Components> The slurry composition may further contain other components in addition to the components described above. There are no particular limitations on the other components as long as they do not have an excessively unfavorable effect on the battery reaction in a secondary battery having a functional layer. The type of other component may be one type or two or more types. Examples of other components include surfactants, wetting agents, leveling agents, dispersants, electrolyte decomposition inhibitors, viscosity adjusters, etc.

[0076] <<Viscosity Adjuster>> Here, from the viewpoint of further improving the heat shrinkage resistance of the functional layer, it is preferable to use a viscosity adjuster as another component. It is particularly preferable to use a water-soluble polymer as the viscosity adjuster. In this specification, the phrase "water-soluble" means that when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25°C, the insoluble content is less than 1 mass%. The water-soluble polymer is not particularly limited, but from the viewpoint of further improving the heat shrinkage resistance of the functional layer, it is preferable to use at least one water-soluble polymer selected from the group consisting of carboxymethyl cellulose and polyacrylamide.

[0077] The amount of viscosity modifier in the slurry composition is not particularly limited. The amount of water-soluble polymer in the slurry composition, in terms of solid content, is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 3 parts by mass or less, and more preferably 2 parts by mass or less, per 100 parts by mass of functional particles. If the amount of viscosity modifier in the slurry composition is equal to or greater than the above-mentioned lower limit, the heat shrinkage resistance of the functional layer can be further improved. On the other hand, if the amount of viscosity modifier in the slurry composition is equal to or less than the above-mentioned upper limit, sufficiently high coating stability can be ensured when the slurry composition is applied to a substrate to form a functional layer.

[0078] <<Dispersant>> Furthermore, from the viewpoint of improving the stability of the slurry composition, it is preferable to use a dispersant as another component. The dispersant is not particularly limited, and for example, sodium polyacrylate, acrylic acid / sulfonic acid monomer copolymer sodium salt, etc. can be used. Note that the dispersant is a component different from the viscosity modifier (water-soluble polymer, etc.) described above.

[0079] The amount of dispersant in the slurry composition is not particularly limited. The amount of dispersant in the slurry composition, in terms of solid content, is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and preferably 3 parts by mass or less, and more preferably 2 parts by mass or less, relative to 100 parts by mass of functional particles. If the amount of dispersant in the slurry composition is equal to or greater than the above lower limit, the stability of the slurry composition can be further improved. On the other hand, if the amount of dispersant in the slurry composition is equal to or less than the above upper limit, the coating stability can be sufficiently high when the slurry composition is applied to a substrate to form a functional layer.

[0080] <<Surfactant>> Furthermore, from the viewpoint of improving the coatability of the slurry composition, it is preferable to use a surfactant as another component. The surfactant is not particularly limited, and for example, a polyethylene glycol-type surfactant can be used. Note that the surfactant is a component different from the viscosity modifier (water-soluble polymer, etc.) and dispersant described above.

[0081] The amount of surfactant in the slurry composition is not particularly limited. The amount of surfactant in the slurry composition, in terms of solid content, is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 0.5 parts by mass or less, and more preferably 0.3 parts by mass or less, per 100 parts by mass of functional particles. If the amount of surfactant in the slurry composition is equal to or greater than the above lower limit, the coating properties of the slurry composition on the substrate can be sufficiently ensured. On the other hand, if the amount of surfactant in the slurry composition is equal to or less than the above upper limit, the adhesion of the functional layer can be sufficiently high.

[0082] <Solid content of slurry composition for secondary battery functional layer> The solid content of the slurry composition (particulate polymer, functional particles, other components, etc.) is preferably 20 mass % or more, more preferably 30 mass % or more, and preferably 60 mass % or less, more preferably 50 mass % or less. If the solid content of the slurry composition is within the above range, the viscosity of the slurry composition can be maintained at an appropriate level, and coating stability can be improved.

[0083] <Preparation of Slurry Composition for Secondary Battery Functional Layer> The method for preparing the slurry composition is not particularly limited. For example, when the slurry composition is a slurry composition for a porous membrane layer, the binder, non-conductive particles, and other components used as needed can be mixed in the presence of a solvent to prepare the slurry composition. The solvent used in preparing the slurry composition can be the solvent described above in the "Binder for Secondary Battery Functional Layer" section (e.g., water, etc.). The solvent used in preparing the slurry composition also includes the solvent contained in the binder. The mixing method is not particularly limited, and mixing can be performed using a commonly used stirrer or disperser.

[0084] (Functional layer for secondary battery) The functional layer of the present invention is a layer that performs functions such as reinforcement or adhesion in a secondary battery. Examples of the functional layer include a porous membrane layer that improves heat resistance and strength. The functional layer of the present invention is formed from the above-mentioned slurry composition of the present invention. For example, the functional layer can be formed by applying the above-mentioned slurry composition to the surface of a suitable substrate to form a coating film, and then drying the formed coating film. That is, the functional layer of the present invention is composed of a dried product of the above-mentioned slurry composition, and usually contains at least a particulate polymer and functional particles, and optionally further contains other components. Note that each component contained in the functional layer is the same as the preferred ratio of each component contained in the slurry composition, and therefore the preferred ratio of each component is the same as the preferred ratio of each component in the slurry composition.

[0085] Furthermore, the functional layer of the present invention is formed from the slurry composition of the present invention containing the binder of the present invention, and therefore has excellent heat shrinkage resistance, adhesiveness, and storage stability.

[0086] <Substrate> Here, there are no limitations on the substrate to which the slurry composition is applied. For example, a coating film of the slurry composition may be formed on the surface of a release substrate, the coating film may be dried to form a functional layer, and the release substrate may be peeled off from the functional layer. In this way, the functional layer peeled off from the release substrate can be used as a free-standing film to form a battery component for a secondary battery. However, from the viewpoint of omitting the step of peeling off the functional layer and improving the manufacturing efficiency of the battery component, it is preferable to use a separator substrate or an electrode substrate as the substrate. Specifically, it is preferable to form the functional layer by applying the slurry composition to the separator substrate or the electrode substrate. Furthermore, from the viewpoint of improving the adhesion between the formed functional layer and substrates such as the separator substrate and the electrode substrate, the surface of the above substrate may be subjected to a surface treatment such as a corona treatment or a plasma treatment to be hydrophilized.

[0087] <<Separator Substrate>> The separator substrate is not particularly limited, and examples thereof include known separator substrates such as organic separator substrates. The organic separator substrate is a porous member made of an organic material. Examples of the organic separator substrate include a microporous membrane or nonwoven fabric containing a polyolefin resin such as polyethylene or polypropylene, or an aromatic polyamide resin, and polyethylene microporous membranes and nonwoven fabrics are preferred because of their excellent strength.

[0088] <<Electrode Substrate>> The electrode substrate (positive electrode substrate and negative electrode substrate) is not particularly limited, but examples include an electrode substrate in which an electrode mixture layer containing electrode active material particles and a binder is formed on a current collector. A material that is electrically conductive and electrochemically durable is used as the current collector. Specifically, current collectors made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. can be used as the current collector. Copper foil is particularly preferred as the current collector used for the negative electrode. Aluminum foil is particularly preferred as the current collector used for the positive electrode. The above materials may be used alone or in combination of two or more types in any ratio. The electrode active material particles contained in the electrode mixture layer in the electrode substrate are not particularly limited, and known electrode active material particles can be used. Furthermore, any binder used for electrode mixture layers can be used as the binder contained in the electrode mixture layer of the electrode substrate.

[0089] <Method for forming a functional layer for a secondary battery> Examples of methods for forming a functional layer on a substrate such as the above-mentioned separator substrate or electrode substrate include the following: 1) A method in which the slurry composition of the present invention is applied to the surface of the substrate (in the case of an electrode substrate, the surface on the electrode composite layer side; the same applies hereinafter) and then dried; 2) A method in which a substrate is immersed in the slurry composition of the present invention and then dried; and 3) A method in which the slurry composition of the present invention is applied to a release substrate and dried to produce a functional layer, and the resulting functional layer is transferred to the surface of the substrate. Among these, method 1) is particularly preferred because it makes it easy to control the layer thickness of the functional layer. Method 1) specifically includes a step of applying the slurry composition to the substrate (application step) and a step of drying the slurry composition applied to the substrate to form a functional layer (drying step).

[0090] <<Coating Step>> In the coating step, the method for coating the slurry composition onto the substrate is not particularly limited, and examples thereof include a doctor blade method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

[0091] <<Drying Step>> In the drying step, the method for drying the slurry composition on the substrate is not particularly limited, and any known method can be used. Examples of drying methods include drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with infrared rays or electron beams. The drying conditions are not particularly limited, but the drying temperature is preferably 40°C to 150°C, and the drying time is preferably 2 minutes to 30 minutes.

[0092] The thickness of the functional layer formed is preferably 1 μm or more, more preferably 1.5 μm or more, and preferably 4 μm or less, and more preferably 3 μm or less. If the thickness of the functional layer is equal to or greater than the lower limit, the thermal shrinkage resistance of the functional layer can be sufficiently high. On the other hand, if the thickness of the functional layer is equal to or less than the upper limit, the internal resistance of the secondary battery can be reduced by thinning the functional layer, thereby improving the cycle characteristics of the secondary battery.

[0093] (Battery component having functional layer for secondary battery) Here, the battery component (separator and electrode) having a functional layer may have components other than the functional layer of the present invention and the substrate, as long as the effects of the present invention are not significantly impaired. Such components are not particularly limited, and examples thereof include a porous membrane layer that does not fall under the functional layer of the present invention. In addition, examples of layers that do not fall under the functional layer of the present invention include layers that do not contain functional particles but contain the particulate polymer and optionally other components, such as so-called adhesive layers. The battery component having the functional layer of the present invention has excellent heat shrinkage resistance, adhesiveness, and storage stability, and can also be well adhered to adjacent battery components.

[0094] (Secondary Battery) The secondary battery of the present invention includes the functional layer of the present invention described above. More specifically, the secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte solution, and the functional layer for a secondary battery described above is included in at least one of the battery components, the positive electrode, the negative electrode, and the separator. Note that, since the secondary battery of the present invention includes the functional layer of the present invention, which has excellent heat shrinkage resistance, adhesiveness, and storage stability, the secondary battery has a low heat shrinkage rate due to temperature changes, the battery components are well bonded together, and the heat shrinkage resistance and adhesiveness are unlikely to decrease even after a long period of time has passed, resulting in excellent battery characteristics such as cycle characteristics.

[0095] <Positive electrode, negative electrode, and separator> At least one of the positive electrode, negative electrode, and separator used in the secondary battery of the present invention is a battery component having the functional layer of the present invention described above. Note that the positive electrode, negative electrode, and separator not having the functional layer of the present invention are not particularly limited, and known positive electrodes, negative electrodes, and separators can be used.

[0096] <Electrolyte> As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. For example, in a lithium ion secondary battery, a lithium salt is used as the supporting electrolyte. For example, LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２ ) ２ Among them, LiPF is preferred because it is easily soluble in solvents and shows a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO３ Li is preferred. Note that one type of electrolyte may be used alone, or two or more types may be used in combination. Generally, the use of a supporting electrolyte with a higher degree of dissociation tends to result in higher lithium ion conductivity, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0097] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, in lithium ion secondary batteries, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC) are suitable. esters such as γ-butyrolactone and methyl formate are also suitable. Ethers such as 1,2-dimethoxyethane and tetrahydrofuran are also suitable. Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide are also suitable. Mixtures of these solvents may also be used. Among these, carbonates are preferred due to their high dielectric constant and wide stable potential range. Generally, the lower the viscosity of the solvent used, the higher the lithium ion conductivity. Therefore, the lithium ion conductivity can be adjusted by the type of solvent. The concentration of the electrolyte in the electrolyte can be adjusted as appropriate. Known additives may also be added to the electrolyte.

[0098] <Method for Manufacturing Secondary Battery> The secondary battery of the present invention described above can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the stack as necessary, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. At least one of the positive electrode, negative electrode, and separator is a battery component having the functional layer of the present invention. If necessary, the battery container may contain an expanded metal, a fuse, an overcurrent prevention element such as a PTC element, a lead plate, or the like, to prevent pressure buildup within the battery and overcharging and discharging. The shape of the battery may be, for example, a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, or the like.

[0099] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. Furthermore, in a polymer produced by copolymerizing multiple types of monomers, the proportion of a repeating unit (monomer unit) formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of that certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified. In the examples and comparative examples, the measurement and evaluation of various attributes were carried out according to the following methods.

[0100] <Volume Average Particle Diameter of Particulate Polymer> The volume average particle diameter of the particulate polymer was measured by a laser diffraction method. Specifically, first, an aqueous dispersion (adjusted to a solid content of 0.1% by mass) containing the prepared particulate polymer was used as a sample. Then, in the particle size distribution (volume basis) measured using a laser diffraction particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name "LS-13 320"), the particle diameter D50 at which the cumulative volume calculated from the smallest diameter side reached 50% was taken as the volume average particle diameter.

[0101] <Glass Transition Temperature of Particulate Polymer> The prepared dispersion containing the particulate polymer was pre-dried for 3 days in an environment of 50% relative humidity and 23 to 26°C temperature to form a pre-film having a thickness of 2±0.5 mm. The pre-film was dried for 10 hours in a vacuum dryer at a temperature of 120°C. Thereafter, the dried film was used as a sample and the glass transition temperature (°C) was measured using a differential scanning calorimeter (DSC7200, manufactured by SII Corporation) in accordance with JIS K7121 under conditions of a measurement temperature of -100°C to 180°C and a heating rate of 5°C / min.

[0102] <Electrolyte Swelling Degree> The prepared aqueous dispersion containing the particulate polymer was dried under an environment of 50% relative humidity and 23 to 25°C temperature, and formed into a film with a thickness of approximately 0.1 mm. The formed film was cut into a piece of approximately 2 cm square, and its weight (weight before immersion) was measured. Then, it was immersed in an electrolyte solution at a temperature of 60°C for 72 hours. The immersed film was pulled out, the electrolyte solution was wiped off, and the weight (weight after immersion) was immediately measured, and the value of (weight after immersion) / (weight before immersion) × 100 (%) was taken as the electrolyte swelling degree. The electrolyte solution was a 3:7 (weight ratio) mixed solvent of ethylene carbonate and ethyl methyl carbonate with LiPF ６ A solution in which the above was dissolved at a concentration of 1 mol / L was used.

[0103] <Measurement of pH of binder> The pH of the prepared aqueous dispersion (binder) containing the particulate polymer was measured at 25°C using a pH meter F-21 manufactured by Horiba, Ltd., after calibrating a glass electrode with buffer solutions of pH 4, pH 7, and pH 9.

[0104] <Elastic modulus of film made of particulate polymer after accelerated test> The prepared aqueous dispersion containing the particulate polymer was left to stand at 60°C for 14 days to carry out an accelerated test. The aqueous dispersion containing the particulate polymer after the accelerated test was air-dried at a relative humidity of 50% and a temperature of 25°C to prepare a film. The obtained film was sliced ​​into 2 µm sections using a microtome. The film elastic modulus of the obtained sections was measured using an atomic force microscope (AFM) in FV mode. The median value of the measurement results was used as the evaluation result. The device (atomic force microscope) used was a "FastScan" product manufactured by Bruker.

[0105] <Elastic modulus of film made of particulate polymer before accelerated test> Before the accelerated test, an aqueous dispersion containing a particulate polymer was air-dried at a relative humidity of 50% and a temperature of 25°C to prepare a film. The obtained film was sliced ​​into 2 µm sections using a microtome. The obtained sections were measured for the film elastic modulus using an atomic force microscope (AFM) in FV mode. The median value of the measurement results was used as the evaluation result. The device (atomic force microscope) used was a product name "FastScan" manufactured by Bruker.

[0106] <Adhesion of Functional Layer for Secondary Battery> Separators with functional layers prepared in the Examples and Comparative Examples were each cut into a 10 mm wide x 50 mm long test piece. Next, a stainless steel plate with double-sided tape (Nitto Denko Corporation, No. 5608) attached was prepared, and the functional layer surface of the test piece was attached to the double-sided tape. One end of the separator substrate was then pulled at a speed of 50 mm / min so that the peeling surface was at a 180° angle, and the peel strength was measured. The adhesion of the functional layer was evaluated according to the following criteria. Higher peel strength indicates better adhesion. A: Peel strength of 15 N / m or more; B: Peel strength of 5 N / m or more but less than 15 N / m; C: Peel strength less than 5 N / m.

[0107] <Heat Shrinkage Resistance of Functional Layer for Secondary Battery> Each separator with a functional layer produced in the Examples and Comparative Examples was cut into a square with sides of 12 cm, and a square with sides of 10 cm was drawn inside the square to prepare a test piece. The test piece was then placed in a thermostatic chamber at 150°C and left for 1 hour, after which the change in area of ​​the square drawn inside (= {(area of ​​square before leaving - area of ​​square after leaving) / area of ​​square before leaving} × 100%) was calculated as the heat shrinkage rate and evaluated according to the following criteria. A smaller heat shrinkage rate indicates better heat shrinkage resistance of the functional layer. A: Heat shrinkage rate less than 10% B: Heat shrinkage rate 10% or more but less than 20% C: Heat shrinkage rate 20% or more

[0108] <Storage Stability of Secondary Battery Functional Layer> The separators with functional layers prepared in the examples and comparative examples were left standing in a thermostatic chamber at 40°C for 90 days. The adhesiveness and heat shrinkage resistance of the separators with functional layers were then measured using the same procedures as described above. The adhesiveness and heat shrinkage resistance of the functional layers after 90 days of standing were evaluated according to the same criteria as described above. The evaluation results of adhesiveness and heat shrinkage resistance before 90 days of standing (i.e., the evaluation results for "adhesion" and "heat shrinkage resistance") were compared with the evaluation results of adhesiveness and heat shrinkage resistance after 90 days of standing, and the results were evaluated according to the following criteria: A: No change in the evaluation results of both adhesiveness and heat shrinkage resistance before and after 90 days of standing; B: The evaluation results of either adhesiveness or heat shrinkage resistance decreased by one level before and after 90 days of standing; C: The evaluation results of both adhesiveness and heat shrinkage resistance decreased by one level before and after 90 days of standing, or the evaluation results of either adhesiveness or heat shrinkage resistance decreased by two levels before and after 90 days of standing.

[0109] <Cycle Characteristics of Secondary Battery> The fabricated lithium ion secondary battery was left standing for 24 hours in an environment at 25°C. Thereafter, at 25°C, it was charged to 4.2 V (cutoff condition: 0.02 C) using a constant voltage-constant current (CC-CV) method at a charge rate of 1 C, and discharged to 3.0 V using a constant current (CC) method at a discharge rate of 1 C, and the initial capacity C0 was measured. Furthermore, the same charge-discharge operation was repeated in an environment at 25°C, and the capacity C1 after 300 cycles was measured. Then, the capacity retention rate ΔC = (C1 / C0) × 100 (%) was calculated and evaluated according to the following criteria. A higher value of this capacity retention rate indicates less decrease in discharge capacity and better cycle characteristics. A: Capacity retention rate ΔC is 85% or more. B: Capacity retention rate ΔC is 75% or more but less than 85%. C: Capacity retention rate ΔC is less than 75%.

[0110] Example 1 Preparation of Aqueous Dispersion (Binder) Containing Particulate Polymer To a reactor equipped with a stirrer, 90 parts of ion-exchanged water, 0.05 parts of sodium dodecylbenzenesulfonate (manufactured by Kao Chemical Corporation, "Neopelex G-15") as an emulsifier, and 0.23 parts of ammonium persulfate as a polymerization initiator were supplied, and the gas phase was replaced with nitrogen gas, followed by heating to 70°C. Meanwhile, in a separate vessel, 50 parts of ion-exchanged water, 0.2 parts of sodium dodecylbenzenesulfonate ("Neopelex G-15" manufactured by Kao Chemical Corporation) as an emulsifier, 70 parts of butyl acrylate (BA) as a (meth)acrylic acid ester monomer, 10 parts of acrylonitrile (AN) as a cyano group-containing monomer, 17.8 parts of allyl glycidyl ether (AGE) and 2 parts of N-methylolacrylamide (NMA) as reactive functional group-containing monomers, and 0.2 parts of acrylic acid (AA) as an acidic functional group-containing monomer were mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor over 3 hours to carry out polymerization. The reaction was carried out at 70°C during the addition. After the addition was completed, the reaction solution was cooled to 50°C, and 0.2 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, product name "Perbutyl O") as a polymerization initiator was added, and 0.1 parts of ascorbic acid as a reducing agent was added. The mixture was stirred for 3 hours to terminate the reaction, thereby producing an aqueous dispersion (binder) containing a particulate polymer. The pH of the obtained binder was adjusted to pH 6 using 10% aqueous ammonia. The solid content of the binder was 40%. Various attributes of the obtained binder were measured. The results are shown in Table 1.

[0111] <Preparation of Slurry Composition> The slurry composition was prepared using alumina particles (AKP-3000 manufactured by Sumitomo Chemical Co., Ltd., volume average particle diameter D50 = 0.7 μm) as non-conductive particles (functional particles), acrylic acid / sulfonic acid monomer copolymer sodium salt (product name "AQUALIC GL366" manufactured by Nippon Shokubai Co., Ltd.) as a dispersant, carboxymethyl cellulose with an etherification degree of 0.8 to 1.0 (product name "1220" manufactured by Daicel FineChem Co., Ltd.) as a viscosity modifier, and polyethylene glycol surfactant (NOPTEX ED-052 manufactured by San Nopco) as a surfactant. The viscosity of a 1% aqueous solution of the viscosity modifier was 10 to 20 mPa·s. First, 100 parts of the non-conductive particles and 0.5 parts of the dispersant were mixed with ion-exchanged water and processed for 1 hour in a bead mill (LMZ015 manufactured by Ashizawa Finetech Co., Ltd.) to obtain a dispersion. Furthermore, an aqueous dispersion containing a particulate polymer in an amount of 3 parts in terms of solid content, a 4% aqueous solution of carboxymethyl cellulose in an amount of 1.5 parts in terms of solid content, and 0.2 parts of a polyethylene glycol surfactant were mixed to prepare a slurry composition with a solid content of 40% by mass.

[0112] <Preparation of Separator with Functional Layer on One Side> A polyethylene separator substrate (manufactured by Asahi Kasei Corporation, product name "ND412", thickness: 12 μm) was prepared. The slurry composition prepared above was applied to the surface of the prepared separator substrate and dried at a temperature of 50°C for 3 minutes to obtain a separator with a functional layer on one side (functional layer thickness: 3 μm). The resulting separator with functional layer was evaluated for adhesion, heat shrinkage resistance, and storage stability. The results are shown in Table 1.

[0113] <Preparation of Negative Electrode> In a 5 MPa pressure vessel equipped with a stirrer, 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3.5 parts of itaconic acid as a carboxylic acid group-containing monomer, 63.5 parts of styrene as an aromatic vinyl monomer, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator were placed and thoroughly stirred. The solution was heated to 50 ° C to initiate polymerization. When the polymerization conversion rate reached 96%, the solution was cooled to stop the polymerization reaction, and a mixture containing a particulate binder (styrene-butadiene copolymer) was obtained. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust the pH to 8, and unreacted monomer was removed by heated vacuum distillation. The mixture from which the unreacted monomer had been removed was then cooled to 30 ° C or below to obtain an aqueous dispersion containing a binder for the negative electrode. 48.75 parts of artificial graphite (theoretical capacity: 360 mAh / g) as a negative electrode active material, 48.75 parts of natural graphite (theoretical capacity: 360 mAh / g), and 1 part of carboxymethyl cellulose as a thickener (solid content equivalent) were added to a planetary mixer. The mixture was then diluted with ion-exchanged water to a solid content of 60%, and then kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts of the aqueous dispersion containing the negative electrode binder (solid content equivalent) were added, and the mixture was kneaded for 40 minutes at a rotation speed of 40 rpm. Then, ion-exchanged water was added to the mixture to a viscosity of 3000±500 mPa·s (measured with a Brookfield viscometer at 25°C and 60 rpm), thereby preparing a negative electrode composite layer slurry composition. The negative electrode composite layer slurry composition was applied to the surface of a 15 μm thick copper foil current collector using a comma coater in an amount of 11±0.5 mg / cm ２ The copper foil coated with the slurry composition for the negative electrode composite layer was then transported at a speed of 400 mm / min through an oven at 80°C for 2 minutes and then through an oven at 110°C for 2 minutes to dry the slurry composition on the copper foil, thereby obtaining a negative electrode blank having a negative electrode composite layer formed on a current collector. The negative electrode composite layer side of the prepared negative electrode blank was then roll-pressed under a temperature of 25±3°C and a linear pressure of 11 t (tons), resulting in a negative electrode composite layer density of 1.60 g / cm. ３Thereafter, the negative electrode was left to stand for one week in an environment of a temperature of 25±3° C. and a relative humidity of 50±5%.

[0114] <Preparation of Positive Electrode> A Co—Ni—Mn lithium composite oxide active material NMC111 (LiNi) was used as a positive electrode active material in a planetary mixer. １ / ３ Co １ / ３ Mn １ / ３ O ２ 96 parts of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., product name "HS-100") as a conductive material, 2 parts of polyvinylidene fluoride (manufactured by Kureha Chemical Industry Co., Ltd., product name "KF-1100") as a binder were added, and N-methyl-2-pyrrolidone (NMP) as a dispersion medium was added and mixed so that the total solids content was 67%, to prepare a slurry composition for a positive electrode composite layer. Subsequently, the obtained slurry composition for a positive electrode composite layer was applied to a 20 μm-thick aluminum foil current collector using a comma coater in a coating amount of 20±0.5 mg / cm. ２ The slurry composition on the aluminum foil was then dried by transporting the aluminum foil at a speed of 200 mm / min through an oven at 90°C for 2 minutes and then through an oven at 120°C for 2 minutes, thereby obtaining a positive electrode blank with a positive electrode composite layer formed on the current collector. Thereafter, the positive electrode composite layer side of the prepared positive electrode blank was roll-pressed under a temperature of 25±3°C and a linear pressure of 14 t (tons), resulting in a positive electrode composite layer density of 3.40 g / cm. ３ Thereafter, the positive electrode was left for one week in an environment of a temperature of 25±3° C. and a relative humidity of 50±5%.

[0115] <Preparation of Secondary Battery> The pressed positive electrode obtained above was cut into a 4 cm x 4 cm square, and the pressed negative electrode was cut into a 4.2 cm x 4.2 cm square. The functional layer-equipped separator obtained above was cut into a 5 cm x 5 cm square. Next, the functional layer-coated surface of the cut-out functional layer-equipped separator was placed on the positive electrode composite layer of the pressed positive electrode. Furthermore, the pressed negative electrode composite layer was placed on the side of the placed functional layer-equipped separator that was not in contact with the positive electrode, thereby obtaining a battery component laminate (positive electrode / functional layer / separator substrate / negative electrode). Next, the resulting laminate was wrapped in an aluminum packaging exterior as the battery exterior, and an electrolyte solution (solvent: ethylene carbonate (EC) / diethyl carbonate (DEC) / vinylene carbonate (VC) (volume ratio = 68.5 / 30 / 1.5), electrolyte: LiPF6 with a concentration of 1 mol / L) was poured into the battery so that no air remained. The opening of the aluminum packaging exterior was heat-sealed at a temperature of 150°C, and the aluminum packaging exterior was hermetically closed to produce a 40 mAh stacked lithium-ion secondary battery. The cycle characteristics of this lithium-ion secondary battery were evaluated. The results are shown in Table 1.

[0116] (Example 2) In the preparation of an aqueous dispersion containing a particulate polymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that a monomer composition was obtained by changing acrylic acid as the acidic functional group-containing monomer to methacrylic acid. The results are shown in Table 1.

[0117] (Example 3) In the preparation of an aqueous dispersion containing a particulate polymer, allyl glycidyl ether was used as the reactive functional group-containing monomer to obtain a monomer composition, and the other operations, measurements, and evaluations were carried out in the same manner as in Example 2. The results are shown in Table 1.

[0118] (Example 4) In the preparation of an aqueous dispersion containing a particulate polymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 3, except that the cyano group-containing monomer was changed from acrylonitrile to methacrylonitrile to obtain a monomer composition. The results are shown in Table 1.

[0119] (Example 5) In preparing an aqueous dispersion containing a particulate polymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that a monomer composition was obtained by mixing 0.2 parts of sodium dodecylbenzenesulfonate ("Neopelex G-15" manufactured by Kao Chemical Corporation) as an emulsifier, 70 parts of butyl acrylate as a (meth)acrylic acid ester monomer, 10 parts of acrylonitrile as a cyano group-containing monomer, 18 parts of allyl glycidyl ether and 1.4 parts of N-methylolacrylamide as reactive functional group-containing monomers, 0.2 parts of methacrylic acid as an acidic functional group-containing monomer, and 0.4 parts of ethylene glycol dimethacrylate as a crosslinkable monomer. The results are shown in Table 1.

[0120] (Example 6) In the preparation of an aqueous dispersion containing a particulate polymer, allyl glycidyl ether as a reactive functional group-containing monomer was changed to glycidyl methacrylate, and ethylene glycol dimethacrylate as a crosslinkable monomer was changed to allyl methacrylate to obtain a monomer composition, and various operations, measurements, and evaluations were carried out in the same manner as in Example 5. The results are shown in Table 1.

[0121] (Example 7) In the preparation of an aqueous dispersion containing a particulate polymer, the amount of butyl acrylate as a (meth)acrylic acid ester monomer was changed to 53 parts, and the amount of acrylonitrile as a cyano group-containing monomer was changed to 27 parts to obtain a monomer composition, and other operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0122] (Example 8) In the preparation of an aqueous dispersion containing a particulate polymer, the amount of butyl acrylate as a (meth)acrylic acid ester monomer was changed to 76 parts, and the amount of acrylonitrile as a cyano group-containing monomer was changed to 4 parts to obtain a monomer composition, and the various operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0123] (Example 9) In the preparation of an aqueous dispersion containing a particulate polymer, the amount of butyl acrylate as a (meth)acrylic acid ester monomer was changed to 60 parts, and the amount of glycidyl methacrylate as a reactive functional group-containing monomer was changed to 28 parts to obtain a monomer composition, and other than that, various operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0124] (Example 10) In the preparation of an aqueous dispersion containing a particulate polymer, the amount of butyl acrylate as a (meth)acrylic acid ester monomer was changed to 80 parts, and the amount of glycidyl methacrylate as a reactive functional group-containing monomer was changed to 8 parts to obtain a monomer composition, and other operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0125] (Example 11) In the preparation of an aqueous dispersion containing a particulate polymer, the amount of N-methylolacrylamide as a reactive functional group-containing monomer was changed to 0.9 parts, the amount of methacrylic acid as an acidic functional group-containing monomer was changed to 0.8 parts, and the amount of allyl methacrylate as a crosslinkable monomer was changed to 0.3 parts to obtain a monomer composition, and the various operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0126] (Example 12) In the preparation of the aqueous dispersion containing the particulate polymer, the amount of methacrylic acid as the acidic functional group-containing monomer was changed to 0.1 parts, and the amount of allyl methacrylate as the crosslinkable monomer was changed to 0.5 parts to obtain a monomer composition, and the various operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0127] (Example 13) In the preparation of an aqueous dispersion containing a particulate polymer, the amount of butyl acrylate as a (meth)acrylic acid ester monomer was changed to 67.8 parts, the amount of N-methylolacrylamide as a reactive functional group-containing monomer was changed to 3 parts, and the amount of allyl methacrylate as a crosslinkable monomer was changed to 1 part to obtain a monomer composition, and other operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0128] (Example 14) In the preparation of an aqueous dispersion containing a particulate polymer, the amount of butyl acrylate as a (meth)acrylic acid ester monomer was changed to 71.1 parts, the amount of N-methylolacrylamide as a reactive functional group-containing monomer was changed to 0.5 parts, and the amount of allyl methacrylate as a crosslinkable monomer was changed to 0.2 parts to obtain a monomer composition, and the various operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0129] (Example 15) In preparing the aqueous dispersion containing the particulate polymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 6, except that the pH was adjusted to 4.5. The results are shown in Table 1.

[0130] (Example 16) In preparing the aqueous dispersion containing the particulate polymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 6, except that the pH was adjusted to 7.5. The results are shown in Table 1.

[0131] (Example 17) In the preparation of the aqueous dispersion containing the particulate polymer, the amount of the emulsifier charged in advance into the reactor was changed from 0.05 parts to 0 parts (i.e., no emulsifier was charged into the reactor), and the volume average particle diameter of the particulate polymer was adjusted to 0.18 μm, and various operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0132] (Example 18) In the preparation of the aqueous dispersion containing the particulate polymer, the amount of the emulsifier previously charged into the reactor was changed from 0.05 parts to 0.1 parts, and the volume average particle diameter of the particulate polymer was adjusted to 0.12 μm, except that various operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0133] (Example 19) In preparing the slurry composition, various operations, measurements, and evaluations were carried out in the same manner as in Example 6, except that the alumina particles used as the non-conductive particles were replaced with boehmite (APYRAL AOH60, manufactured by Nabaltec, volume average particle diameter D50 = 0.9 μm). The results are shown in Table 1.

[0134] (Example 20) In preparing the slurry composition, various operations, measurements, and evaluations were carried out in the same manner as in Example 6, except that the alumina particles used as the non-conductive particles were replaced with barium sulfate (TS-3, manufactured by Takehara Chemical Industry Co., Ltd., volume average particle diameter D50 = 0.6 μm). The results are shown in Table 1.

[0135] (Example 21) In preparing the slurry composition, various operations, measurements, and evaluations were carried out in the same manner as in Example 6, except that carboxymethyl cellulose was replaced with anionic polyacrylamide (Polystron 117, manufactured by Arakawa Chemical Industries, Ltd.) as the viscosity modifier. The results are shown in Table 1.

[0136] (Comparative Example 1) In the preparation of an aqueous dispersion containing a particulate polymer, the amount of butyl acrylate as a (meth)acrylic acid ester monomer was changed to 50 parts, and the amount of allyl glycidyl ether as a reactive functional group-containing monomer was changed to 38 parts to obtain a monomer composition, and the various operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0137] (Comparative Example 2) In preparing an aqueous dispersion containing a particulate polymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that a monomer composition was obtained by mixing 0.2 parts of sodium dodecylbenzenesulfonate ("Neopelex G-15" manufactured by Kao Chemical Corporation) as an emulsifier, 93.6 parts of butyl acrylate as a (meth)acrylic acid ester monomer, 2 parts of acrylonitrile as a cyano group-containing monomer, 2 parts of allyl glycidyl ether as a reactive functional group-containing monomer, 2 parts of methacrylic acid as an acidic functional group-containing monomer, and 0.4 parts of ethylene glycol dimethacrylate as a crosslinkable monomer. The results are shown in Table 1.

[0138] (Comparative Example 3) In the preparation of an aqueous dispersion containing a particulate polymer, the amount of butyl acrylate as a (meth)acrylic acid ester monomer was changed to 77.6 parts, the amount of acrylonitrile as a cyano group-containing monomer was changed to 10 parts, and the amount of allyl glycidyl ether as a reactive functional group-containing monomer was changed to 10 parts to obtain a monomer composition, and other than that, various operations, measurements, and evaluations were carried out in the same manner as in Comparative Example 2. The results are shown in Table 1.

[0139] (Comparative Example 4) In preparing an aqueous dispersion containing a particulate polymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that a monomer composition was obtained by mixing 0.2 parts of sodium dodecylbenzenesulfonate (manufactured by Kao Chemical Corporation, "Neopelex G-15") as an emulsifier, 70 parts of butyl acrylate as a (meth)acrylic acid ester monomer, 10 parts of acrylonitrile as a cyano group-containing monomer, and 18 parts of glycidyl methacrylate and 2 parts of N-methylolacrylamide as reactive functional group-containing monomers. The results are shown in Table 1.

[0140] (Comparative Example 5) In the preparation of an aqueous dispersion containing a particulate polymer, the amount of butyl acrylate as a (meth)acrylic acid ester monomer was changed to 65.8 parts, the amount of N-methylolacrylamide as a reactive functional group-containing monomer was changed to 4 parts, and the amount of allyl methacrylate as a crosslinkable monomer was changed to 2 parts to obtain a monomer composition, and other operations, measurements, and evaluations were carried out in the same manner as in Example 6. The results are shown in Table 1.

[0141] In Table 1 shown below, "BA" represents a butyl acrylate unit, "AN" represents an acrylonitrile unit, "MAN" represents a methacrylonitrile unit, "AA" represents an acrylic acid unit, "MAA" represents a methacrylic acid unit, "AGE" represents an allyl glycidyl ether unit, "GMA" represents a glycidyl methacrylate unit, "NMA" represents an N-methylolacrylamide unit, "EDMA" represents an ethylene glycol dimethacrylate unit, "AMA" represents an allyl methacrylate unit, and "COO / SO ３ "[Na]" indicates acrylic acid / sulfonic acid monomer copolymer sodium salt, "CMC" indicates carboxymethyl cellulose, "PAA" indicates polyacrylamide, "PEG type" indicates that the surfactant is polyethylene glycol type, "elastic modulus after accelerated test" indicates the elastic modulus of the film made of the particulate polymer after the accelerated test, and "elastic modulus before accelerated test" indicates the elastic modulus of the film made of the particulate polymer before the accelerated test.

[0142]

[0143] As is clear from Table 1, by using the binders of Examples 1 to 21, it is possible to form functional layers that are excellent in heat shrinkage resistance, adhesiveness, and storage stability.

[0144] According to the present invention, a binder for a secondary battery functional layer can be provided, which can form a functional layer having excellent heat shrinkage resistance, adhesion, and storage stability. The present invention also provides a slurry composition for a secondary battery functional layer, which can form a functional layer having excellent heat shrinkage resistance, adhesion, and storage stability. The present invention also provides a functional layer for a secondary battery having excellent heat shrinkage resistance, adhesion, and storage stability. The present invention also provides a secondary battery including the functional layer.

Claims

1. A binder for a secondary battery functional layer containing particulate polymer, The particulate polymer comprises an acidic functional group-containing monomer unit and a reactive functional group-containing monomer unit containing a functional group that can react with an acidic functional group. The content ratio of the reactive functional group-containing monomer units is 7% by mass or more and 30% by mass or less, when the total monomer units contained in the particulate polymer are taken as 100% by mass. A binder for a secondary battery functional layer, wherein the elastic modulus of the film made of the particulate polymer after accelerated testing is 10 MPa or less.

2. The binder for a secondary battery functional layer according to claim 1, wherein the content of the acidic functional group-containing monomer units is 0.1% by mass or more and 1% by mass or less, when the total monomer units contained in the particulate polymer are taken as 100% by mass.

3. The particulate polymer further comprises crosslinkable monomer units, The binder for a secondary battery functional layer according to claim 1, wherein the content of the crosslinkable monomer units is greater than 0% by mass and less than or equal to 1.5% by mass, when the total monomer units contained in the particulate polymer are taken as 100% by mass.

4. The particulate polymer further comprises cyano group-containing monomer units, The binder for a secondary battery functional layer according to claim 1, wherein the content of the cyano group-containing monomer units is 2% by mass or more and 30% by mass or less, when the total monomer units contained in the particulate polymer are taken as 100% by mass.

5. A binder for a secondary battery functional layer according to claim 1, which contains water and has a pH of 4 or higher and 8 or lower.

6. The binder for a secondary battery functional layer according to claim 1, wherein the glass transition temperature of the particulate polymer is 20°C or lower.

7. The binder for a secondary battery functional layer according to claim 1, wherein the volume-average particle diameter of the particulate polymer is 0.1 μm or more and 0.2 μm or less.

8. The binder for the functional layer of a secondary battery according to claim 1, wherein the degree of electrolyte swelling of the particulate polymer is 3 times or more and 5 times or less.

9. A slurry composition for a secondary battery functional layer, comprising a binder for a secondary battery functional layer according to any one of claims 1 to 8 and functional particles.

10. The slurry composition for a secondary battery functional layer according to claim 9, wherein the functional particles include non-conductive particles.

11. The slurry composition for a secondary battery functional layer according to claim 10, wherein the ratio of the volume-average particle diameter of the non-conductive particles to the volume-average particle diameter of the particulate polymer is 2.0 times or more and 7.0 times or less.

12. A functional layer for a secondary battery, formed using the slurry composition for a functional layer of a secondary battery described in claim 9.

13. A secondary battery comprising the functional layer for a secondary battery as described in claim 12.