Binder composition for heat-resistant layer of non-aqueous secondary battery, slurry composition for heat-resistant layer of non-aqueous secondary battery, heat-resistant layer for non-aqueous secondary battery, and non-aqueous secondary battery

Abstract

A binder composition for heat-resistant layers of nonaqueous secondary batteries, said binder composition containing a particulate polymer that contains from 1% by mass to 5% by mass of an acidic group-containing monomer unit and from 4.5% by mass to 25% by mass of a cyano group-containing monomer unit.

Description

Technical Field

[0001] The present invention relates to a binder composition for a heat-resistant layer of a non-aqueous secondary battery, a slurry composition for a heat-resistant layer of a non-aqueous secondary battery, a heat-resistant layer for a non-aqueous secondary battery, and a non-aqueous secondary battery.

Background Art

[0002] Non-aqueous secondary batteries such as lithium-ion secondary batteries (hereinafter, may be simply abbreviated as "secondary batteries") are small, lightweight, have a high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. And secondary batteries generally include battery members such as electrodes (positive electrodes and negative electrodes) and a separator that separates the positive electrode and the negative electrode. And as such battery members, battery members provided with a protective layer for improving heat resistance, that is, a heat-resistant layer, have been conventionally used.

[0003] Here, examples of the heat-resistant layer of the secondary battery include those formed by binding non-conductive particles with a binder. Such a heat-resistant layer is usually a slurry composition (hereinafter, referred to as a "slurry composition for a heat-resistant layer of a non-aqueous secondary battery" and may be abbreviated as a "slurry composition for a heat-resistant layer") in which non-conductive particles and a binder are dissolved or dispersed in a dispersion medium such as water. It is prepared by applying and drying this slurry composition for a heat-resistant layer on a substrate such as a separator substrate or an electrode substrate.

[0004] In recent years, in order to achieve further improvement in the performance of secondary batteries, improvement of the binder composition used for forming the heat-resistant layer has been attempted (for example, refer to Patent Document 1). Patent Document 1 discloses a binder composition for a non-aqueous secondary battery porous membrane containing a sulfosuccinic acid ester and / or its salt and water, in which the surface acid amount of the particulate polymer is within a predetermined range, and the ratio of the acid amount L in the liquid phase in the binder composition to the above surface acid amount is within a predetermined range. More specifically, Patent Document 1 describes that the particulate polymer preferably contains an acidic group-containing monomer unit in an amount of 0.1% by mass or more and 3% by mass or less, and may contain a (meth)acrylonitrile monomer unit. The binder composition of Patent Document 1 can exhibit heat resistance together with non-conductive particles, that is, can form a heat-resistant layer. And according to the binder composition of Patent Document 1, a porous membrane with a small amount of moisture can be formed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in recent years, while further performance improvement of secondary batteries has been demanded, the above conventional binder composition has room for improvement in terms of enhancing the adhesion between the heat-resistant layer formed using the binder composition and the base material (for example, a separator base material or an electrode base material) on which the heat-resistant layer is formed. More specifically, it has been required that the binder composition be capable of increasing the peel strength of the obtained heat-resistant layer to enhance the adhesion between the heat-resistant layer and the base material.

[0007] Therefore, an object of the present invention is to provide a binder composition for a non-aqueous secondary battery heat-resistant layer capable of preparing a slurry composition for a non-aqueous secondary battery heat-resistant layer that can form a heat-resistant layer with sufficiently high peel strength for a non-aqueous secondary battery. Another object of the present invention is to provide a slurry composition for a heat-resistant layer for a non-aqueous secondary battery, which can form a heat-resistant layer having a sufficiently high peel strength. Another object of the present invention is to provide a heat-resistant layer for a non-aqueous secondary battery having a sufficiently high peel strength, and a non-aqueous secondary battery including the heat-resistant layer.

Means for Solving the Problems

[0008] The present inventors have conducted intensive studies for the purpose of solving the above problems. As a result, the present inventors have found that when a binder composition containing a particulate polymer in which the content ratio of an acidic group-containing monomer unit is 1% by mass or more and 5% by mass or less and the content ratio of a cyano group-containing monomer unit is 4.5% by mass or more and 25% by mass or less is used, a heat-resistant layer having a sufficiently high peel strength can be formed, and thus completed the present invention.

[0009] That is, the present invention is intended to advantageously solve the above problems. The binder composition for a heat-resistant layer of a non-aqueous secondary battery of the present invention is a binder composition for a heat-resistant layer of a non-aqueous secondary battery containing a particulate polymer, wherein the particulate polymer contains an acidic group-containing monomer unit and a cyano group-containing monomer unit, and the content ratio of the acidic group-containing monomer unit in the particulate polymer is 1% by mass or more and 5% by mass or less, and the content ratio of the cyano group-containing monomer unit is 4.5% by mass or more and 25% by mass or less. Thus, according to the binder composition containing a particulate polymer in which the content ratio of the acidic group-containing monomer unit is 1% by mass or more and 5% by mass or less and the content ratio of the cyano group-containing monomer unit is 4.5% by mass or more and 25% by mass or less, a slurry composition capable of forming a heat-resistant layer having a sufficiently high peel strength can be prepared. Note that the fact that a polymer "contains a monomer unit" means that "the repeating unit derived from the monomer is contained in the polymer obtained using the monomer". In addition, the "content ratio" of a certain monomer unit in a polymer is 1 measurable by using nuclear magnetic resonance (NMR) methods such as 13 1H-NMR and

[0010] Here, in the binder composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention, it is preferable that the volume-average particle diameter of the particulate polymer is 0.30 μm or less. If the volume-average particle diameter of the particulate polymer is 0.30 μm or less, the heat shrinkage resistance of the resulting heat-resistant layer can be enhanced. Note that the "volume-average particle diameter" of the particulate polymer means "the particle diameter (D50) at which the cumulative volume calculated from the small-diameter side in the particle size distribution (volume basis) measured by the laser diffraction method becomes 50%".

[0011] Also, in the binder composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention, it is preferable that the acidic group-containing monomer unit contains a carboxylic acid group-containing monomer unit. If the acidic group-containing monomer unit in the particulate polymer contains a carboxylic acid group-containing monomer unit, the peel strength of the resulting heat-resistant layer can be further enhanced.

[0012] Furthermore, in the binder composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention, it is preferable that the particulate polymer further contains a crosslinkable monomer unit. If the particulate polymer contains a crosslinkable monomer unit in addition to the various monomer units described above, the rate characteristics of the resulting secondary battery can be enhanced.

[0013] And, in the binder composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention, it is preferable that the particulate polymer is a (meth)acrylate copolymer. If the particulate polymer is a (meth)acrylate copolymer, the peel strength of the resulting heat-resistant layer can be further enhanced. Note that in this specification, the "(meth)acrylate copolymer" means a copolymer in which the content ratio of the (meth)acrylate monomer unit in the copolymer is more than 50% by mass with respect to 100% by mass of all repeating units (all monomer units) contained in the copolymer. Also, in this specification, (meth)acrylic means acrylic or methacrylic.

[0014] Furthermore, the present invention aims to advantageously solve the above problems, and the slurry composition for a heat-resistant layer of a non-aqueous secondary battery of the present invention is characterized by including non-conductive particles and any one of the above-described binder compositions for a heat-resistant layer of a non-aqueous secondary battery. Thus, according to the slurry composition including non-conductive particles and any one of the above-described binder compositions, a heat-resistant layer having a sufficiently high peel strength can be formed.

[0015] Here, in the slurry composition for a heat-resistant layer of a non-aqueous secondary battery of the present invention, it is preferable that the volume average particle diameter of the non-conductive particles is 0.7 μm or less. If the volume average particle diameter of the non-conductive particles is 0.7 μm or less, the heat shrinkage resistance of the obtained heat-resistant layer can be enhanced. Note that the volume average particle diameter of the non-conductive particles means "the particle diameter (D50) at which the cumulative volume calculated from the small-diameter side in the particle size distribution (volume basis) measured by the laser diffraction method becomes 50%".

[0016] Moreover, the present invention aims to advantageously solve the above problems, and the heat-resistant layer for a non-aqueous secondary battery of the present invention is characterized by being formed using the above-described slurry composition for a heat-resistant layer of a non-aqueous secondary battery. Thus, the heat-resistant layer formed from the above slurry composition has a sufficiently high peel strength.

[0017] Furthermore, the present invention aims to advantageously solve the above problems, and the non-aqueous secondary battery of the present invention is characterized by including the above-described heat-resistant layer for a non-aqueous secondary battery. Thus, the secondary battery including the battery member having the above-described heat-resistant layer has excellent battery characteristics.

Effects of the Invention

[0018] According to the present invention, it is possible to provide a binder composition for a heat-resistant layer of a non-aqueous secondary battery capable of preparing a slurry composition for a heat-resistant layer of a non-aqueous secondary battery that can form a heat-resistant layer for a non-aqueous secondary battery having a sufficiently high peel strength. Moreover, according to the present invention, it is possible to provide a slurry composition for a heat-resistant layer of a non-aqueous secondary battery that can form a heat-resistant layer for a non-aqueous secondary battery having a sufficiently high peel strength. According to the present invention, a heat-resistant layer for a non-aqueous secondary battery having a sufficiently high peel strength, and a non-aqueous secondary battery including the heat-resistant layer can be provided.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described in detail. Here, the binder composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention can be used for preparing the slurry composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention. And the slurry composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention can be used for forming the heat-resistant layer of a non-aqueous secondary battery such as a lithium-ion secondary battery. Further, the heat-resistant layer for the non-aqueous secondary battery of the present invention is characterized by being formed from the slurry composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention. Also, the non-aqueous secondary battery of the present invention is characterized by including a heat-resistant layer for the non-aqueous secondary battery prepared using the slurry composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention.

[0020] (Binder Composition for Heat-Resistant Layer of Non-Aqueous Secondary Battery) The binder composition of the present invention contains a particulate polymer, and optionally may further contain a dispersion medium and other components. Here, in the binder composition of the present invention, the above-mentioned particulate polymer contains an acidic group-containing monomer unit and a cyano group-containing monomer unit, and further, the content ratio of the acidic group-containing monomer unit in the particulate polymer is 1% by mass or more and 5% by mass or less, and the content ratio of the cyano group-containing monomer unit is 4.5% by mass or more and 25% by mass or less.

[0021] And since the binder composition of the present invention contains a particulate polymer that satisfies the above-described predetermined properties, the resulting heat-resistant layer can be adhered to the substrate with sufficient strength. As a result, the peel strength of the heat-resistant layer can be sufficiently increased. Thus, although the reason for obtaining the above effects by using the binder composition containing the above-described predetermined particulate polymer is not clear, within the above-described predetermined range, the acidic group-containing monomer unit and the cyano group-containing monomer unit are contained in the particulate polymer, so that the acidic group-containing monomer unit tends to be unevenly distributed near the surface of the particulate polymer, thereby increasing the stability of the particulate polymer and making it difficult to aggregate in the slurry composition, and it is presumed that this is due to the ability to exhibit good adhesive force to the adherend.

[0022] <Particulate polymer> The particulate polymer contained in the binder composition of the present invention is a component that can function as a binder in the heat-resistant layer formed using the slurry composition, imparts adhesiveness to the heat-resistant layer formed using the slurry composition containing the binder composition, and is a component that can hold the non-conductive particles contained in the heat-resistant layer so as not to detach from the heat-resistant layer. The particulate polymer is a water-insoluble particle formed of a predetermined polymer. In the present invention, the particle being "water-insoluble" 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 90% by mass or more.

[0023] Here, the particulate polymer contains an acidic group-containing monomer unit and a cyano group-containing monomer unit, and optionally may contain other monomer units. Hereinafter, the various monomer units will be described in detail.

[0024] <<Acidic group-containing monomer unit>> The acidic group-containing monomer unit is a monomer unit obtained by polymerizing an acidic group-containing monomer. Examples of the acidic group include -COOH group (carboxylic acid group); -SO3H group (sulfonic acid group); phosphoric acid groups such as -PO3H2 group and -PO(OH)(OR) group (R represents a hydrocarbon group); and other acidic functional groups. Therefore, examples of the acidic group-containing monomer capable of forming the acidic group-containing monomer unit include monomers having these acidic groups. Further, for example, monomers capable of generating an acidic group as described above by hydrolysis are also included as the acidic group-containing monomer. Specific examples of such acidic group-containing monomers include acid anhydrides capable of generating a carboxylic acid group by hydrolysis. The various acidic group-containing monomers listed below may be used alone or in combination of two or more in any ratio.

[0025] Examples of the monomer having a carboxylic acid group include monocarboxylic acids, dicarboxylic acids, acid anhydrides of dicarboxylic acids, and derivatives thereof. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, isocrotonic acid, and the like. Examples of the dicarboxylic acid include carboxylic acid group-containing monomers such as maleic acid, fumaric acid, itaconic acid, and methylmaleic acid. Examples of the acid anhydride of the dicarboxylic acid include maleic anhydride, acrylic anhydride, methylmaleic anhydride, dimethylmaleic anhydride, and the like.

[0026] Examples of the monomer having a sulfonic acid group include sulfonic acid group-containing monomers such as vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, 2-sulfonic acid ethyl (meth)acrylate, 2-acrylamido-2-methylpropane sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, and 2-(N-acryloyl)amino-2-methyl-1,3-propane-disulfonic acid.

[0027] Examples of monomers having a phosphate group such as a -PO3H2 group and a -PO(OH)(OR) group (where R represents a hydrocarbon group) include phosphate group-containing monomers such as 2-(meth)acryloyloxyethyl phosphate, methyl phosphate-2-(meth)acryloyloxyethyl, and ethyl phosphate-(meth)acryloyloxyethyl. In the present specification, (meth)acryloyl means acryloyl or methacryloyl.

[0028] In addition, salts of the above-mentioned various monomers can also be used as the acidic group-containing monomer. Among the above-mentioned acidic group-containing monomers, it is preferable to use a carboxylic acid group-containing monomer, and more preferably to use a monocarboxylic acid as described above. In particular, it is preferable to use at least one of acrylic acid and methacrylic acid. If the particulate polymer contains a carboxylic acid group-containing monomer unit formed using a carboxylic acid group-containing monomer as the acidic group-containing monomer unit, the peel strength of the resulting heat-resistant layer can be further increased.

[0029] The content ratio of the acidic group-containing monomer unit in the particulate polymer is preferably 1% by mass or more, more preferably 1.5% by mass or more, preferably 5% by mass or less, and more preferably 4% by mass or less, with the amount of all repeating units (all monomer units) contained in the particulate polymer being 100% by mass. If the content ratio of the acidic group-containing monomer unit in the particulate polymer is at least the above lower limit value, the peel strength of the resulting heat-resistant layer can be sufficiently increased. Also, if the content ratio of the acidic group-containing monomer unit in the particulate polymer is at most the above upper limit value, the heat shrinkage resistance of the resulting heat-resistant layer can be increased.

[0030] <<Cyano group-containing monomer unit>> The cyano group-containing monomer unit is a monomer unit obtained by polymerizing a cyano group-containing monomer. Examples of the cyano group-containing monomer that can form the cyano group-containing monomer unit include α,β-unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile. These can be used alone or in combination of two or more in any ratio.

[0031] The content ratio of the cyano group-containing monomer unit in the particulate polymer is preferably 4.5% by mass or more, more preferably 6% by mass or more, preferably 25% by mass or less, and more preferably 22% by mass or less, with respect to 100% by mass of the total repeating units contained in the particulate polymer. If the content ratio of the cyano group-containing monomer unit in the particulate polymer is at least the above lower limit value, the rate characteristics of the resulting secondary battery can be enhanced. Further, if the content ratio of the cyano group-containing monomer unit in the particulate polymer is at most the above upper limit value, the peel strength of the resulting heat-resistant layer can be sufficiently enhanced.

[0032] <<Other monomer units>> The other monomer units are not particularly limited, and examples thereof include crosslinkable monomer units, (meth)acrylate monomer units, ethylenically unsaturated carboxylic acid amide monomer units, aromatic vinyl monomer units, fluorine atom-containing monomer units, and aliphatic conjugated diene monomer units.

[0033] [Crosslinkable monomer unit] The crosslinkable monomer unit is a structural unit having a structure formed by polymerizing a crosslinkable monomer. The crosslinkable monomer is a monomer that can form a crosslinked structure during or after polymerization, triggered by heating or irradiation with energy rays, etc. More specifically, examples of the crosslinkable monomer unit include a crosslinkable monomer having a thermally crosslinkable crosslinkable group and one olefinic double bond per molecule (hereinafter sometimes referred to as "crosslinkable monomer 1"); a crosslinkable monomer having two or more olefinic double bonds per molecule (hereinafter sometimes referred to as "crosslinkable monomer 2"), etc. These may be used alone or in combination of two or more in any ratio. It should be noted that the crosslinkable monomer unit does not include those corresponding to the various monomer units described above and below.

[0034] Examples of the thermally crosslinkable crosslinkable groups that may be contained in the crosslinkable monomer 1 include an epoxy group, a methylol group, an oxetanyl group, an oxazoline group, and combinations thereof. Specific examples of the crosslinkable monomer 1 include glycidyl acrylate and glycidyl methacrylate (thermally crosslinkable crosslinkable group: epoxy group); (meth)acrylamides having a methylol group such as N-methylol(meth)acrylamide (thermally crosslinkable crosslinkable group: methylol group). Among them, it is preferable to use N-methylol(meth)acrylamide, and it is more preferable to use N-methylol acrylamide.

[0035] Furthermore, examples of the crosslinkable monomer 2 include allyl (meth)acrylate, allyl (meth)acrylate ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and the like. In the present specification, (meth)acrylate means acrylate or methacrylate. Among them, allyl (meth)acrylate is preferable, and allyl methacrylate is more preferable.

[0036] When the particulate polymer contains a crosslinkable monomer unit, the content ratio of the crosslinkable monomer unit in the particulate polymer is preferably 0.001% by mass or more and 10% by mass or less, with the amount of all repeating units contained in the particulate polymer being 100% by mass. If the content ratio of the crosslinkable monomer unit in the particulate polymer is at least the above lower limit value, the rate characteristics of the resulting secondary battery can be improved.

[0037] [(Meth)acrylate monomer unit] (Meth)acrylic acid ester monomer units are monomer units obtained by polymerizing (meth)acrylic acid ester monomers. Examples of alkyl (meth)acrylate monomers that can form (meth)acrylic acid ester monomer units include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, hexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate, benzyl acrylate, and other acrylates; methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate, benzyl methacrylate, and other methacrylates. These may be used alone or in combination of two or more in any ratio. Among them, as the (meth)acrylic acid ester monomer, n-butyl acrylate and 2-ethylhexyl acrylate are preferred.

[0038] When the particulate polymer contains (meth)acrylic acid ester monomer units, the content ratio of the (meth)acrylic acid ester monomer units in the particulate polymer is preferably more than 50% by mass, more preferably 60% by mass or more, preferably 93% by mass or less, and more preferably 90% by mass or less, with the amount of all repeating units (all monomer units) contained in the particulate polymer being 100% by mass. If the content ratio of the (meth)acrylic acid ester monomer units in the particulate polymer is within the above range, the peel strength of the resulting heat-resistant layer can be further increased.

[0039] [Ethylenically unsaturated carboxylic acid amide monomer unit] The ethylenically unsaturated carboxylic acid amide monomer unit is a monomer unit obtained by polymerizing an ethylenically unsaturated carboxylic acid amide monomer. Examples of the ethylenically unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methoxymethylacrylamide, and N-methoxymethylmethacrylamide. Among them, acrylamide and methacrylamide are preferred, and acrylamide is more preferred. These may be used alone or in combination of two or more in any ratio.

[0040] When the particulate polymer contains an ethylenically unsaturated carboxylic acid amide monomer unit, the content ratio of the ethylenically unsaturated carboxylic acid amide monomer unit in the particulate polymer is preferably 1% by mass or more, more preferably 2% by mass or more, preferably 10% by mass or less, and more preferably 8% by mass or less, with the amount of all repeating units (all monomer units) contained in the particulate polymer being 100% by mass. If the content ratio of the ethylenically unsaturated carboxylic acid amide monomer unit in the particulate polymer is within the above range, the peel strength of the resulting heat-resistant layer can be increased.

[0041] [Aromatic vinyl monomer unit] The aromatic vinyl monomer unit is a monomer unit obtained by polymerizing an aromatic vinyl monomer. The aromatic vinyl monomer is not particularly limited, and examples include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene. These aromatic vinyl monomers may be used alone or in combination of two or more in any ratio. Among them, styrene is preferred as the aromatic vinyl monomer.

[0042] [Fluorine atom-containing monomer unit] The fluorine atom-containing monomer unit is a monomer unit obtained by polymerizing a fluorine atom-containing monomer. Examples of the fluorine atom-containing monomer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, vinyl chloride fluoride, vinyl fluoride, perfluoroalkyl vinyl ether, and the like. These may be used alone or in combination of two or more in any ratio.

[0043] [Aliphatic conjugated diene monomer unit] The aliphatic conjugated diene monomer unit is a monomer unit obtained by polymerizing an aliphatic conjugated diene monomer. Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, and the like. These may be used alone or in combination of two or more in any ratio.

[0044] [Properties] [Volume average particle diameter] Further, the volume average particle diameter of the particulate polymer is preferably 0.08 μm or more, more preferably 0.10 μm or more, preferably 0.30 μm or less, more preferably 0.25 μm or less, still more preferably 0.20 μm or less, and particularly preferably 0.18 μm or less. If the volume average particle diameter of the particulate polymer is at least the above lower limit value, it is possible to suppress an excessive decrease in the air permeability of the resulting heat-resistant layer. Further, if the volume average particle diameter of the particulate polymer is at most the above upper limit value, it is possible to enhance the heat shrinkage resistance of the resulting heat-resistant layer. The volume average particle diameter of the particulate polymer can be adjusted, for example, by changing the type and amount of the monomer, polymerization initiator, and / or polymerization accelerator used in the preparation of the particulate polymer.

[0045] [Degree of swelling in the electrolytic solution] The particulate polymer preferably has a swelling degree with respect to the electrolytic solution of 2 times or more, more preferably 4.5 times or more, still more preferably 5 times or more, preferably 11 times or less, more preferably 10 times or less, and still more preferably 9 times or less. If the swelling degree of the particulate polymer is at least the above lower limit value, the rate characteristics of the resulting secondary battery can be enhanced. If the swelling degree of the particulate polymer is at most the above upper limit value, the adhesiveness of the particulate polymer can be enhanced. In the present specification, the "swelling degree" of the particulate polymer is the swelling degree with respect to an electrolytic solution (a solution obtained by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a mass ratio of 3:7), and can be measured by the method described in the examples.

[0046] <<Method for preparing particulate polymer>> Here, the polymerization method of the particulate polymer is not particularly limited, and for example, any method such as solution polymerization method, suspension polymerization method, bulk polymerization method, emulsion polymerization method may be used. Also, as the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, living radical polymerization can be used. And general polymerization solvents, emulsifiers, dispersants, polymerization initiators, chain transfer agents, etc. that can be used in the polymerization can be used, and the amount used can also be the generally used amount.

[0047] In the binder composition of the present invention, the content of the particulate polymer is not particularly limited.

[0048] <Dispersion medium> Examples of the dispersion medium that can optionally be contained in the binder composition of the present invention include water, organic solvents (for example, esters, ketones, alcohols), and mixtures thereof. The binder composition of the present invention may contain one kind of organic solvent or may contain two or more kinds of organic solvents. Among them, water is preferable as the dispersion medium.

[0049] <Other components> The binder composition of the present invention may contain a water-soluble polymer, a reinforcing material, a leveling agent, a wetting agent, a dispersant, a viscosity modifier, an electrolyte additive, a preservative, a fungicide, an antifoaming agent, a polymerization inhibitor, and a binder other than the particulate polymer as described above. These are not particularly limited as long as they do not affect the battery reaction, and known ones can be used. Further, the other components may be used alone or in combination of two or more in any ratio.

[0050] The water-soluble polymer that the binder composition for the heat-resistant layer of the non-aqueous secondary battery may optionally contain is a component that can function as a viscosity modifier in the binder composition and in the slurry composition containing such a binder composition. Note that the polymer being "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 1.0 mass%.

[0051] As the water-soluble polymer, various thickening polysaccharides can be used without particular limitation. As the thickening polysaccharides, it is preferable to use carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, polyvinyl alcohol, polyacrylic acid or salts thereof, and it is particularly preferable to use carboxymethyl cellulose or a salt thereof. Examples of the carboxymethyl cellulose salt include sodium salt, ammonium salt and the like. The thickening polysaccharides may be used alone or in combination of two or more in any ratio.

[0052] Further, as the wetting agent that the binder composition for the heat-resistant layer of the non-aqueous secondary battery may optionally contain, ethylene oxide·propylene oxide-based surfactants (EO·PO-based surfactants), fluorine-based surfactants, silicone-based surfactants and the like can be used without particular limitation. Among them, it is preferable to use EO·PO-based surfactants and fluorine-based surfactants, and it is more preferable to use EO·PO-based surfactants. In addition, as the dispersant, there is no particular limitation, and polycarboxylic acids such as polyacrylic acid, sodium polycarboxylates such as sodium polyacrylate, ammonium polycarboxylates such as ammonium polyacrylate, polycarboxylic acid sulfonic acid copolymers, sodium polycarboxylic acid sulfonic acid copolymers, ammonium polycarboxylic acid sulfonic acid copolymers, etc. can be used. Among them, it is preferable to use sodium polyacrylate. Specific examples of other components other than the wetting agent and dispersant described above are not particularly limited, and for example, those described in International Publication No. 2012 / 115096 can be mentioned.

[0053] <Preparation of Binder Composition for Heat-Resistant Layer of Non-Aqueous Secondary Battery> And the binder composition of the present invention can be prepared by mixing the above-mentioned particulate polymer with any other components, if necessary, by a known method. Specifically, the binder composition can be prepared by mixing the above components using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a colloid mill, an ultrasonic disperser, a homogenizer, a planetary mixer, or a film mixer. In addition, for example, when the particulate polymer is prepared by polymerization in an aqueous solution, the state of the aqueous dispersion of the particulate polymer can be used as the binder composition as it is.

[0054] (Slurry Composition for Heat-Resistant Layer of Non-Aqueous Secondary Battery) The slurry composition of the present invention is a composition used for forming a heat-resistant layer, contains non-conductive inorganic particles and the above-mentioned binder composition, and optionally further contains other components. That is, the slurry composition of the present invention usually contains non-conductive particles, particulate polymers, and a dispersion medium, and optionally further contains other components. And since the slurry composition of the present invention contains the above-mentioned binder composition, a heat-resistant layer with a sufficiently high peel strength can be formed.

[0055] <Non-Conductive Particles> Here, the non-conductive particles contained in the heat-resistant layer slurry composition are not particularly limited, and include particles made of inorganic materials (i.e., non-conductive inorganic particles) and particles made of organic materials (i.e., non-conductive organic particles) that stably exist and are electrochemically stable in the usage environment of the secondary battery. Among them, non-conductive inorganic particles are preferred. Preferred examples of non-conductive inorganic particles include inorganic oxide particles such as aluminum oxide (alumina, Al2O3), hydrated aluminum oxide (boehmite, AlOOH), gibbsite (Al(OH)3), silicon oxide, magnesium oxide (magnesia), magnesium hydroxide, calcium oxide, titanium oxide (titania), barium titanate (BaTiO3), ZrO, and alumina-silica composite oxides; nitride particles such as aluminum nitride and boron nitride; covalent crystal particles such as silicon and diamond; sparingly soluble ionic crystal particles such as barium sulfate, calcium fluoride, and barium fluoride; clay fine particles such as talc and montmorillonite; and the like. Among these, from the viewpoint of improving the adhesion between the heat-resistant layer and the substrate, as the non-conductive particles, particles made of alumina (alumina particles), particles made of boehmite (boehmite particles), particles made of titania (titania particles), and particles made of barium sulfate (barium sulfate particles) are preferred, alumina particles, boehmite particles, and barium sulfate particles are more preferred, and alumina particles and barium sulfate particles are even more preferred. In addition, these particles may be subjected to element substitution, surface treatment, solid solution formation, etc. as necessary. Also, these particles may be used alone or in combination of two or more.

[0056] Note that the non-conductive organic particles are organic compounds different from the particulate polymer as the binder. That is, the non-conductive organic particles do not have binding properties. Preferred examples of the non-conductive organic particles include various cross-linked polymer particles such as cross-linked polymethyl methacrylate, cross-linked polystyrene, cross-linked polydivinylbenzene, styrene-divinylbenzene copolymer cross-linked products, polystyrene, polyimide, polyamide, polyamideimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate, and heat-resistant polymer particles such as polysulfone, polyacrylonitrile, polyaramide, polyacetal, and thermoplastic polyimide. Further, as the non-conductive organic particles, modified products and derivatives thereof can also be used. These particles may be used alone or in combination of two or more. Note that the glass transition temperature of the organic particles as the non-conductive particles is preferably higher than 20°C and usually 350°C or lower. The glass transition temperature of the organic particles can be measured according to JIS K7121.

[0057] The volume average particle diameter of the non-conductive particles is preferably 0.7 μm or less, more preferably 0.5 μm or less, and even more preferably 0.4 μm or less. If the volume average particle diameter of the non-conductive particles is below the above upper limit value, the heat shrinkage resistance of the resulting heat-resistant layer can be enhanced. Note that the volume average particle diameter of the non-conductive particles can usually be 0.05 μm or more. The volume average particle diameter of the non-conductive particles can be measured by applying a laser analysis method according to JIS Z 8825 to the non-conductive particles pretreated according to JIS Z 8824.

[0058] <Binder composition> As the binder composition, the binder composition of the present invention described above is used. Incidentally, from the viewpoint of suppressing excessive decrease in the air permeability of the resulting heat-resistant layer, the content of the above-described predetermined particulate polymer in the slurry composition is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and still more preferably 6 parts by mass or less in terms of solid content per 100 parts by mass of the non-conductive particles. Further, from the viewpoint of further enhancing the peel strength of the resulting heat-resistant layer, the content of the predetermined particulate polymer in the slurry composition is preferably 1 part by mass or more, more preferably 1.2 parts by mass or more, and still more preferably 1.5 parts by mass or more in terms of solid content per 100 parts by mass of the non-conductive particles. Incidentally, when the slurry composition contains a water-soluble polymer which is an optional component described later, it is preferable that the content of the particulate polymer is more than the content of the water-soluble polymer.

[0059] <Other components> Examples of other components that can be incorporated into the slurry composition include the same components as those that can be incorporated into the binder composition of the present invention without particular limitation. The other components may be used alone or in combination of two or more in any ratio. And, from the viewpoint of improving the heat shrinkage resistance of the resulting heat-resistant layer, the content of the water-soluble polymer as an optional component in the slurry composition is preferably 0.5 part by mass or more, more preferably 1 part by mass or more in terms of solid content per 100 parts by mass of the non-conductive particles (particularly, non-conductive inorganic particles). Further, from the viewpoint of suppressing excessive decrease in the air permeability of the resulting heat-resistant layer, the content of the water-soluble polymer as an optional component in the slurry composition is preferably 5 parts by mass or less, more preferably 4 parts by mass or less in terms of solid content per 100 parts by mass of the non-conductive particles (particularly, non-conductive inorganic particles). In addition, the content of the wetting agent, which is an optional component in the slurry composition, is preferably 0.01 part by mass or more, preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and still more preferably 1 part by mass or less per 100 parts by mass of the non-conductive particles (particularly non-conductive inorganic particles). If the content of the wetting agent is not less than the above lower limit value, the peel strength of the resulting heat-resistant layer can be further increased. Also, if the content of the wetting agent is not more than the above upper limit value, the cycle characteristics of the secondary battery can be improved. Furthermore, the content of the dispersant, which is an optional component in the slurry composition, is preferably 0.1 part by mass or more, preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and still more preferably 1 part by mass or less per 100 parts by mass of the non-conductive particles (particularly non-conductive inorganic particles). If the content of the dispersant is not less than the above lower limit value, the heat shrinkage resistance of the heat-resistant layer can be increased. Also, if the content of the dispersant is not more than the above upper limit value, the rate characteristics of the secondary battery can be improved.

[0060] <Preparation of Slurry Composition for Heat-Resistant Layer of Non-Aqueous Secondary Battery> The above-described slurry composition can be prepared by mixing the above components by a known mixing method as described above in the section <Preparation of Binder Composition for Heat-Resistant Layer of Non-Aqueous Secondary Battery>.

[0061] (Heat-Resistant Layer for Non-Aqueous Secondary Battery) The heat-resistant layer of the present invention is formed from the above-described slurry composition of the present invention. For example, after applying the above-described slurry composition to the surface of a suitable substrate to form a coating film, the formed coating film is dried to form the heat-resistant layer. That is, the heat-resistant layer of the present invention is composed of the dried product of the above-described slurry composition and usually contains at least non-conductive particles and a particulate polymer. Since each component contained in the heat-resistant layer was contained in the above slurry composition, the preferred abundance ratio of each of these components is the same as the preferred abundance ratio of each component in the slurry composition. And since the heat-resistant layer of the present invention is formed from the slurry composition of the present invention containing the binder composition of the present invention, the peel strength is sufficiently high.

[0062] <Substrate> Here, there is no limitation 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, and the coating film may be dried to form a heat-resistant layer, and the release substrate may be peeled off from the heat-resistant layer. Thus, the heat-resistant layer peeled off from the release substrate can also be used as a self-supporting film for forming battery members of a secondary battery. However, from the viewpoint of omitting the step of peeling the heat-resistant layer and improving the manufacturing efficiency of battery members, it is preferable to use a separator substrate or an electrode substrate as the substrate. Specifically, it is preferable to apply the slurry composition on a separator substrate or an electrode substrate, and it is more preferable to apply it on a separator substrate.

[0063] <<Separator Substrate>> The separator substrate is not particularly limited, and known separator substrates such as organic separator substrates can be mentioned. The organic separator substrate is a porous member made of an organic material. Examples of the organic separator substrate include microporous membranes or non-woven fabrics containing polyolefin resins such as polyethylene and polypropylene, and aromatic polyamide resins. Microporous membranes or non-woven fabrics made of polyethylene are preferable because of their excellent strength.

[0064] <<Electrode Substrate>> The electrode substrate (positive electrode substrate and negative electrode substrate) is not particularly limited, and examples thereof include an electrode substrate in which an electrode mixture layer containing an electrode active material and a binder is formed on a current collector. Known materials can be used for the current collector, the electrode active materials (positive electrode active material, negative electrode active material) in the electrode mixture layer, and the binders for the electrode mixture layer (binder for positive electrode mixture layer, binder for negative electrode mixture layer), and the method for forming the electrode mixture layer on the current collector. For example, those described in JP-A-2013-145763 can be mentioned.

[0065] <Method for Forming Heat-Resistant Layer> As methods for forming a heat-resistant layer on substrates such as the above-described separator substrate and electrode substrate, the following methods can be mentioned. 1) A method in which the slurry composition of the present invention is applied to the surface of the substrate (in the case of the electrode substrate, the surface on the side of the electrode composite layer; the same applies hereinafter), and then dried; 2) A method in which the 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 onto a release substrate, dried to produce a heat-resistant layer, and the obtained heat-resistant layer is transferred onto the surface of the substrate. Among these, the method of 1) is particularly preferable because it is easy to control the layer thickness of the heat-resistant layer. The method of 1) specifically includes a step of applying the slurry composition onto the substrate (coating step) and a step of drying the slurry composition applied onto the substrate to form a heat-resistant layer (drying step).

[0066] <<Coating step>> And in the coating step, there is no particular limitation on the method of applying the slurry composition onto the substrate. For example, methods such as the doctor blade method, reverse roll method, direct roll method, gravure method, extrusion method, and brush coating method can be mentioned.

[0067] <<Drying step>> Also, in the drying step, there is no particular limitation on the method of drying the slurry composition on the substrate, and known methods can be used. Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with infrared rays or electron beams.

[0068] <Thickness of the heat-resistant layer> The thickness of the heat-resistant layer is preferably 4 μm or less, more preferably 3 μm or less, still more preferably 2.5 μm or less, and particularly preferably 2 μm or less. Note that the thickness of the heat-resistant layer is not particularly limited, but can be, for example, 0.2 μm or more. If the thickness of the heat-resistant layer is below the above upper limit value, the rate characteristics of the obtained secondary battery can be improved. Also, if the thickness of the heat-resistant layer is above the above lower limit value, such a heat-resistant layer is excellent in heat shrinkage resistance.

[0069] (Non-aqueous secondary battery) The secondary battery of the present invention includes the heat-resistant 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, and the above-described heat-resistant layer is included in at least one of the positive electrode, the negative electrode, and the separator which are battery members.

[0070] (Positive electrode, negative electrode, and separator) At least one of the positive electrode, the negative electrode, and the separator used in the secondary battery of the present invention is a battery member including the heat-resistant layer of the present invention described above. Note that, as the positive electrode, the negative electrode, and the separator not including the heat-resistant layer of the present invention, known positive electrodes, negative electrodes, and separators can be used without particular limitation.

[0071] (Electrolyte) As the electrolyte, usually, an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent is used. As the supporting electrolyte, for example, a lithium salt is used in a lithium-ion secondary battery. Examples of the lithium salt include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, (C2F5SO2)NLi, and the like. Among them, LiPF6, LiClO4, and CF3SO3Li are preferable because they are easily soluble in the solvent and show a high degree of dissociation. Note that the electrolyte may be used alone or in combination of two or more. Usually, the higher the degree of dissociation of the supporting electrolyte used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted according to the type of the supporting electrolyte.

[0072] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, in a lithium-ion secondary battery, alkyl carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; etc. are preferably used. A mixture of these solvents may also be used. Among them, carbonates are preferred because they have a high dielectric constant and a wide stable potential region. Note that the concentration of the electrolyte in the electrolyte can be adjusted as appropriate. Further, known additives such as vinylene carbonate (VC) may be added to the electrolyte.

[0073] <Method for manufacturing a non-aqueous secondary battery> The non-aqueous secondary battery of the present invention can be manufactured, for example, by laminating a positive electrode and a negative electrode with a separator interposed therebetween, winding, folding, etc. according to the battery shape as necessary, placing them in a battery container, and injecting an electrolyte into the battery container and sealing it. Note that at least one of the positive electrode, negative electrode, and separator is made of a member with a heat-resistant layer. In order to prevent an increase in the internal pressure of the secondary battery, overcharge / discharge, etc., an overcurrent prevention element such as a fuse or a PTC element, an expandable metal, a lead plate, etc. may be provided as necessary. The shape of the secondary battery may be, for example, a coin type, button type, sheet type, cylindrical type, rectangular type, flat type, etc., any of which is acceptable.

Examples

[0074] Hereinafter, the present invention will be specifically described 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. Also, in a polymer produced by polymerizing a plurality of types of monomers, the proportion of the monomer unit formed by polymerizing a certain monomer in the polymer is usually the same as the ratio (charge ratio) of the certain monomer in all the monomers used for polymerizing the polymer, unless otherwise specified. And in the examples and comparative examples, the measurement and evaluation of various attributes were carried out according to the following methods.

[0075] <Volume average particle diameter of the particulate polymer> The volume average particle diameter of the particulate polymers prepared in the examples and comparative examples was measured by the laser diffraction method. Specifically, an aqueous dispersion (adjusted to a solid content concentration of 0.1% by mass) containing the measurement object (particulate polymer) was used as a sample. Then, in the particle size distribution (volume basis) measured using a laser diffraction particle size distribution measuring device (manufactured by Beckman Coulter, product name "LS-13 320"), the particle diameter D50 at which the cumulative volume calculated from the small diameter side becomes 50% was taken as the volume average particle diameter. <Degree of swelling in the electrolytic solution> The particulate polymers prepared in the examples and comparative examples were formed into films about 0.1 mm thick, cut into pieces about 2 cm square to obtain test pieces, and the mass of such test pieces (mass before immersion) was measured. Then, the test pieces were immersed in the electrolytic solution at 60 °C for 72 hours. The immersed test pieces were pulled out, the electrolytic solution was wiped off, and the mass (mass after immersion) was measured immediately. The value of (mass after immersion) / (mass before immersion) was taken as the degree of swelling. As the electrolytic solution, a solution in which LiPF6 was dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a mass ratio of 3:7 was used. The smaller the value of the obtained degree of swelling, the higher the electrolytic solution resistance of the particulate polymer. <Water solubility of the particulate polymer> The particulate polymers prepared in the examples and comparative examples were dissolved in 100 g of water at a temperature of 25 °C with 0.5 g of the polymer. In all the examples and comparative examples, it was confirmed that the insoluble content was 90% by mass or more.

[0076] <Adhesion of the heat-resistant layer for non-aqueous secondary batteries> The separators with heat-resistant layers prepared in the examples and comparative examples were each cut into pieces with a width of 10 mm and a length of 50 mm to obtain test pieces. Next, a SUS (stainless steel) plate with a double-sided tape (manufactured by Nitto Denko Corporation, No. 5608) attached was prepared, and the heat-resistant layer side of the above test piece was attached to both sides of the double-sided tape. Then, the peel strength was measured when one end of the separator substrate was pulled and peeled off at a speed of 50 mm / min so that the peel surface became 180°, and the evaluation was carried out according to the following criteria. The higher the peel strength, the higher the adhesion between the separator substrate and the heat-resistant layer. A: Peel strength of 40 N / m or more B: Peel strength of 30 N / m or more and less than 40 N / m C: Peel strength of 20 N / m or more and less than 30 N / m D: Peel strength of less than 20 N / m <Increase value of air permeability> For the separator substrate used in the manufacture of the separator with heat-resistant layer and the prepared separator with heat-resistant layer, the Gurley value (sec / 100cc) was measured using a digital type Okaiken air permeability and smoothness tester (manufactured by Asahi Seiko Co., Ltd., EYO-5-1M-R). Specifically, from the Gurley value G0 of the "separator substrate" and the Gurley value G1 of the manufactured "separator with heat-resistant layer", the increase amount ΔG of the Gurley value (=G1 - G0) was obtained and evaluated according to the following criteria. The smaller the increase amount ΔG of this Gurley value, the better the ion conductivity of the separator. A: The increase amount of the Gurley value is less than 70 seconds / 100cc B: The increase amount of the Gurley value is 70 seconds / 100cc or more and less than 100 seconds / 100cc C: The increase amount of the Gurley value is 100 seconds / 100cc or more <Heat shrinkage of heat-resistant layer for non-aqueous secondary battery> The separators with heat-resistant layers prepared in the examples and comparative examples were cut into squares with a width of 12 cm and a length of 12 cm. A square with a side length of 10 cm was drawn inside such a square to obtain a test piece. Then, the test piece was placed in a constant-temperature bath at 150 °C and left for 1 hour. After that, the area change of the square drawn inside (={(area of the square before standing - area of the square after standing) / area of the square before standing}×100%) was determined as the heat shrinkage rate and evaluated according to the following criteria. The smaller this heat shrinkage rate, the better the heat shrinkage resistance of the heat-resistant layer. A: Heat shrinkage rate is less than 10% B: Heat shrinkage rate is 10% or more and less than 20% C: Heat shrinkage rate is 20% or more <Rate characteristics of non-aqueous secondary batteries> Regarding the lithium-ion secondary batteries prepared in the examples and comparative examples, they were charged to 4.3 V by a constant current method of 0.1 C and then discharged to 3.0 V at 0.1 C to obtain the 0.1 C discharge capacity. Then, they were charged to 4.3 V at 0.1 C and then discharged to 3.0 V at 4 C to obtain the 2 C discharge capacity. These measurements were performed on 10 cells of the lithium-ion secondary battery, and the average values of each measurement were designated as the 0.1 C discharge capacity a and the 2 C discharge capacity b. The capacity retention rate represented by the ratio (b / a (%)) of the 2 C discharge capacity b to the 0.1 C discharge capacity a was determined, and the rate characteristics were evaluated according to the following criteria. The higher the value of the capacity retention rate, the better the rate characteristics. A: Capacity retention rate is 90% or more B: Capacity retention rate is 60% or more and less than 90% C: Capacity retention rate is less than 60%

[0077] (Example 1) <Preparation of an aqueous dispersion containing particulate polymer A> 90 parts of ion-exchanged water, 0.05 part of sodium dodecylbenzenesulfonate (manufactured by Kao Chemical Co., Ltd., "Neoperex G-15") as an emulsifier, and 0.23 part of ammonium persulfate were respectively supplied to a reactor equipped with a stirrer. The gas phase part was replaced with nitrogen gas, and the temperature was raised to 70 °C. On one hand, 50 parts of ion-exchanged water, 0.1 part of sodium dodecylbenzenesulfonate as an emulsifier, 2.5 parts of methacrylic acid (MAA) as an acidic functional group-containing monomer, 10 parts of acrylonitrile (AN) as a cyano group-containing monomer, and as other monomers, 85.3 parts of n-butyl acrylate (BA) as a (meth)acrylate monomer, 0.2 part of allyl methacrylate (AMA) as a crosslinkable monomer, and 2.0 parts of acrylamide (AAm) as an ethylenically unsaturated carboxylic acid amide monomer were mixed in another container to obtain a monomer composition. This monomer composition was continuously added to the reactor over 4 hours for polymerization. During the addition, the reaction was carried out at 80°C. After the addition was completed, stirring was continued at 80°C for 3 hours to complete the reaction, and an aqueous dispersion (binder composition for heat-resistant layer) containing particulate polymer A was produced. For the obtained particulate polymer A, the volume average particle diameter and the degree of swelling in the electrolyte were measured or calculated according to the above. The results are shown in Table 1. The obtained particulate polymer A was a (meth)acrylate copolymer (ACL) in which the content ratio of the butyl acrylate unit, which is an acrylate monomer unit, was 85.3% by mass. <Preparation of Slurry Composition for Heat-Resistant Layer> As non-conductive particles, alumina particles (manufactured by Sumitomo Chemical Co., Ltd., AKP-30, volume average particle diameter D50 (catalog value): 0.3 μm) were used, sodium polyacrylate (manufactured by Toagosei Co., Ltd., Aron T-50) was used as a dispersant, and carboxymethyl cellulose (manufactured by Daicel Finechem Co., Ltd., D1220) with an etherification degree of 0.8 to 1.0 was used as a water-soluble polymer. The viscosity of a 1% aqueous solution of the water-soluble polymer was 10 to 20 mPa·s. 100 parts of non-conductive particles, 0.5 part of a dispersant, and ion-exchanged water were mixed and processed with a bead mill (LMZ015, manufactured by Asazawa Fine Tech Co., Ltd.) for 1 hour to obtain a dispersion liquid. Further, 3 parts of the binder composition for the heat-resistant layer prepared as described above in an amount equivalent to the solid content of the particulate polymer A, 1.5 parts of a 4% aqueous solution of carboxymethyl cellulose in an amount equivalent to the solid content, and 0.3 part of an ethylene oxide-propylene oxide-based surfactant (manufactured by San Nopco Ltd., Noptex ED-052) as a wetting agent were mixed to prepare a slurry composition for the heat-resistant layer with a solid content concentration of 40% by mass. <Fabrication of a separator with a heat-resistant layer provided on one side> A separator substrate made of polyethylene (manufactured by Asahi Kasei Corporation, ND509, thickness: 9 μm) was prepared. The slurry composition for the heat-resistant layer prepared above was applied to the surface of the prepared separator substrate and dried at 50°C for 3 minutes to obtain a separator with a heat-resistant layer (thickness of the heat-resistant layer: 2 μm) provided on one side. Using the obtained separator with a heat-resistant layer, the increase value of air permeability, the adhesion of the heat-resistant layer, and the heat shrinkage were evaluated according to the above. The results are shown in Table 1. <Fabrication of the negative electrode> Into a 5 MPa pressure-resistant container equipped with a stirrer, 33 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 63.5 parts of styrene, 0.4 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator were put. After sufficiently stirring, the mixture was heated to 50°C to start polymerization. When the polymerization conversion rate reached 96%, it was cooled to stop the polymerization reaction, and a mixture containing particulate binder (styrene-butadiene copolymer) was obtained. A 5% aqueous sodium hydroxide solution was added to the above mixture to adjust the pH to 8, and then unreacted monomers were removed by heating under reduced pressure distillation. Thereafter, the mixture was cooled to 30°C or lower to obtain an aqueous dispersion containing a binder for the negative electrode. Into a planetary mixer, 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 in terms of solid content were added. Further, the mixture was diluted with ion-exchanged water so that the solid content concentration was 60%, and then kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts of the negative electrode binder obtained as described above in terms of solid content were added, and kneaded for 40 minutes at a rotation speed of 40 rpm. Then, ion-exchanged water was added so that the viscosity was 3000±500 mPa·s (measured with a B-type viscometer at 25°C and 60 rpm), to prepare a slurry composition for a negative electrode mixture layer. The negative electrode mixture layer slurry composition was applied to the surface of a 15 μm-thick copper foil current collector with a comma coater in an amount of 11±0.5 mg / cm 2 Thereafter, the copper foil coated with the slurry composition for the negative electrode composite layer was transported at a speed of 400 mm / min through an oven at a temperature of 80° C. for 2 minutes and then through an oven at a temperature of 110° C. for 2 minutes to dry the slurry composition on the copper foil, thereby obtaining a negative electrode raw sheet in which a negative electrode composite layer was formed on a current collector. Thereafter, the negative electrode composite layer side of the produced negative electrode blank was roll-pressed under conditions of a temperature of 25±3°C and a linear pressure of 11 t (tons) to obtain a negative electrode composite layer density of 1.60 g / cm 3 Thereafter, the negative electrode was left for one week in an environment of a temperature of 25±3° C. and a relative humidity of 50±5%. <Preparation of positive electrode> The planetary mixer is equipped with the lithium composite oxide active material NMC111, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A slurry composition for a positive electrode composite layer was prepared by adding 96 parts of ethyl acetate (O2, 96 parts), 2 parts of acetylene black (HS-100, manufactured by Denka Co., Ltd.) as a conductive material, and 2 parts of polyvinylidene fluoride (KF-1100, manufactured by Kureha Chemical Co., Ltd.) as a binder, and further adding and mixing N-methyl-2-pyrrolidone (NMP) as a dispersion medium so that the total solids concentration was 67%. Subsequently, the obtained slurry composition for the positive electrode composite layer was applied onto a 20-μm-thick aluminum foil serving as a current collector using a comma coater so that the coating amount was 20 ± 0.5 mg / cm 2 was achieved. Furthermore, the slurry composition on the aluminum foil was dried by transporting it at a speed of 200 mm / min for 2 minutes in an oven at 90°C and then for 2 minutes in an oven at 120°C, thereby obtaining a positive electrode precursor in which a positive electrode composite layer was formed on the current collector. Thereafter, the positive electrode composite layer side of the produced positive electrode precursor was roll-pressed under the conditions of a linear pressure of 14 t (ton) in an environment at a temperature of 25 ± 3°C to obtain a positive electrode with a positive electrode composite layer density of 3.40 g / cm 3 Thereafter, the positive electrode was left standing for 1 week in an environment at a temperature of 25 ± 3°C and a relative humidity of 50 ± 5%. <Fabrication of Secondary Battery> Using the above negative electrode, positive electrode, and separator, a wound cell (equivalent to a discharge capacity of 520 mAh) was fabricated and placed inside an aluminum packaging material. Thereafter, a 1.0 M LiPF6 solution (solvent: ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (mass ratio) mixed solvent, additive: 2% by volume (solvent ratio) vinylene carbonate contained) was filled inside the aluminum packaging material as an electrolytic solution. Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing was performed at a temperature of 150°C to close the aluminum packaging material, and a lithium-ion secondary battery was manufactured. Using this lithium-ion secondary battery, rate characteristics were evaluated. The results are shown in Table 1.

[0078] (Examples 2 to 6, 8 to 9, 12 to 13) In synthesizing the particulate polymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the composition of the monomer composition used for polymerization was changed as necessary so that the types and content ratios of various monomer units, particle diameters, and swelling degrees with respect to the electrolytic solution in the obtained particulate polymer were as shown in Table 1. The results are shown in Table 1. In Table 1, for each particulate polymer prepared in these examples, which had a composition different from that of Example 1, they were respectively denoted as particulate polymers B to F, J to K, and L to N.

[0079] (Example 7) In synthesizing the particulate polymer I, the polymerization conditions of the monomer composition were changed (specifically, the amount of the emulsifier charged into the reactor was changed to 0.02 parts) so that the particle diameter of the resulting particulate polymer I would be as shown in Table 1. Except for this point, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0080] (Example 10) In the step of [[PREPARATION OF HEAT-RESISTANT LAYER SLURRY COMPOSITION]], various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that larger-diameter alumina particles (manufactured by Sumitomo Chemical Co., Ltd., AKP-3000, volume-average particle diameter D50 (catalog value): 0.7 μm) were used as the non-conductive particles. The results are shown in Table 1.

[0081] (Example 11) In the step of [[PREPARATION OF HEAT-RESISTANT LAYER SLURRY COMPOSITION]], various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the non-conductive particles used were changed from alumina particles to barium sulfate particles (manufactured by Takehara Chemical Co., Ltd., TS-2, volume-average particle diameter D50 (catalog value): 0.3 μm). The results are shown in Table 1.

[0082] (Comparative Examples 1 to 4) In synthesizing the particulate polymer, except that the composition of the monomer composition used for polymerization was changed as necessary so that the types and content ratios of various monomer units, the particle diameter, and the degree of swelling with respect to the electrolytic solution in the resulting particulate polymer would be as shown in Table 1 respectively, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1. In Table 1, for each of these particulate polymers prepared in these comparative examples, which have compositions different from that of Example 1, they are respectively designated as particulate polymers O to R.

[0083] In Table 1 shown below, 「MAA」 represents a methacrylic acid unit, 「AN」 represents an acrylonitrile unit, "AMA" represents an allyl methacrylate unit, "BA" represents an n-butyl acrylate unit, "Aam" represents an acrylamide unit, "ACL" represents a (meth)acrylic acid ester copolymer, "CMC" represents carboxymethyl cellulose, "MAN" represents a methacrylonitrile unit, "AA" represents an acrylic acid unit, "NMA" represents an N-methylolacrylamide unit, "2EHA" represents a 2-ethylhexyl acrylate unit, "MMA" represents a methyl methacrylate unit, "Al2O3" represents alumina particles, "BaSO4" represents barium sulfate particles.

[0084] [Table 1]

[0085] From Table 1, in Examples 1 to 13 using a binder composition containing a particulate polymer in which the acidic group-containing monomer unit is contained in a proportion of 1% by mass or more and 5% by mass or less, and the cyano group-containing monomer unit is contained in a proportion of 4.5% by mass or more and 25% by mass or less, it can be seen that a heat-resistant layer with sufficiently high peel strength and high adhesion to the substrate was obtained. Further, it can be seen that the heat-resistant layers of Examples 1 to 13 were capable of exhibiting excellent rate characteristics in secondary batteries. On the other hand, in Comparative Examples 1 to 4 using a binder composition containing a particulate polymer in which the content ratio of the cyano group-containing monomer unit or the hydroxyl group-containing monomer unit does not satisfy the above-specified range, it can be seen that a heat-resistant layer with sufficiently high peel strength could not be formed, and the adhesion of such a heat-resistant layer to the substrate was insufficient.

Industrial Applicability

[0086] According to the present invention, it is possible to provide a binder composition for a heat-resistant layer of a non-aqueous secondary battery capable of preparing a slurry composition for a heat-resistant layer of a non-aqueous secondary battery that can form a heat-resistant layer for a non-aqueous secondary battery having a sufficiently high peel strength. Further, according to the present invention, it is possible to provide a slurry composition for a heat-resistant layer of a non-aqueous secondary battery that can form a heat-resistant layer for a non-aqueous secondary battery having a sufficiently high peel strength. And, according to the present invention, it is possible to provide a heat-resistant layer for a non-aqueous secondary battery having a sufficiently high peel strength, and a non-aqueous secondary battery including the heat-resistant layer.

Claims

1. A binder composition for a heat-resistant layer of a non-aqueous secondary battery, comprising a particulate polymer, wherein the particulate polymer contains an acidic group-containing monomer unit, a cyano group-containing monomer unit, and an ethylenically unsaturated carboxylic acid amide monomer unit, in the particulate polymer, the content ratio of the acidic group-containing monomer unit is 1% by mass or more and 5% by mass or less, the content ratio of the cyano group-containing monomer unit is 4.5% by mass or more and 25% by mass or less, and further, the content ratio of the ethylenically unsaturated carboxylic acid amide monomer unit is 1% by mass or more, the ethylenically unsaturated carboxylic acid amide monomer unit is at least one of an acrylamide monomer unit, a methacrylamide monomer unit, an N-methoxymethylacrylamide monomer unit, and an N-methoxymethylmethacrylamide monomer unit, A binder composition for a heat-resistant layer of a non-aqueous secondary battery.

2. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 1, wherein the volume average particle diameter of the particulate polymer is 0.30 μm or less.

3. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 1 or 2, wherein the acidic group-containing monomer unit contains a carboxylic acid group-containing monomer unit.

4. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to any one of claims 1 to 3, wherein the particulate polymer further contains a crosslinkable monomer unit.

5. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to any one of claims 1 to 4, wherein the particulate polymer is a (meth)acrylate copolymer.

6. A slurry composition for a heat-resistant layer of a non-aqueous secondary battery, comprising non-conductive particles and the binder composition for a heat-resistant layer of a non-aqueous secondary battery according to any one of claims 1 to 5.

7. The slurry composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 6, wherein the volume average particle diameter of the non-conductive particles is 0.7 μm or less.

8. A heat-resistant layer for a non-aqueous secondary battery, formed using the slurry composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 6 or 7.

9. A non-aqueous secondary battery, comprising the heat-resistant layer for a non-aqueous secondary battery according to claim 8.

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