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

The objective of the present invention is to provide a binder composition for a heat-resistant layer of a non-aqueous secondary battery, the binder composition being capable of preparing a slurry composition which is for a heat-resistant layer of a non-aqueous secondary battery, and from which a heat-resistant layer for a non-aqueous secondary battery can be formed which is excellent not only in terms of dispersion stability and coatability but also heat shrinkage. A binder composition according to the present invention is a binder composition which is for a heat-resistant layer of a non-aqueous secondary battery and contains a water-soluble polymer and water, wherein: the water-soluble polymer contains an amide group-containing monomer unit, an acid group-containing monomer unit, and a hydroxyl group-containing monomer unit; and in the water-soluble polymer, the content of the amide group-containing monomer unit is 63-98 mass%, and the content of the acid group-containing monomer unit is 1-20 mass%.

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 technology]

[0002] Non-aqueous secondary batteries such as lithium ion secondary batteries (hereinafter sometimes simply referred to as "secondary batteries") are small, lightweight, have high energy density, and are capable of repeated charging and discharging, 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. Conventionally, battery components that include a protective layer, i.e., a heat-resistant layer, for improving heat resistance have been used as such battery components.

[0003] Here, examples of the heat-resistant layer of a secondary battery include those formed by binding non-conductive inorganic particles such as alumina with a binder. Such a heat-resistant layer is usually formed by preparing a slurry composition in which non-conductive inorganic particles and a binder are dissolved or dispersed in a dispersion medium such as water (hereinafter referred to as a "non-aqueous slurry composition for a heat-resistant layer of a secondary battery" or sometimes abbreviated as a "slurry composition for a heat-resistant layer"). The slurry composition for a heat-resistant layer is then applied to a substrate such as a separator substrate or an electrode substrate, and dried.

[0004] In recent years, attempts have been made to improve the binder composition used in forming the heat-resistant layer in order to achieve further improvements in the performance of secondary batteries (see, for example, Patent Document 1). Specifically, Patent Document 1 discloses a binder composition for a porous membrane of a secondary battery, which contains a polycarboxylic acid having predetermined properties and water, and reports that the binder composition for a porous membrane of a secondary battery has high storage stability, and that a porous membrane for a secondary battery produced using the binder composition is easy to apply, and that a secondary battery having improved performance such as high-temperature cycle characteristics can be produced. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2015 / 129408 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in recent years, there has been a demand for further improvements in the performance of secondary batteries, and the conventional binder compositions have room for improvement in terms of improving the dispersion stability of a slurry composition prepared using the binder composition and further enhancing the coatability of the slurry composition.Furthermore, it has also been desired to further improve the heat shrinkage resistance of a heat-resistant layer obtained using the conventional binder composition.

[0007] Therefore, an object of the present invention is to provide a binder composition for a non-aqueous secondary battery heat-resistant layer that can prepare a slurry composition for a non-aqueous secondary battery heat-resistant layer that can form a non-aqueous secondary battery heat-resistant layer that has excellent dispersion stability and coatability as well as excellent resistance to thermal shrinkage. Another object of the present invention is to provide a slurry composition for a non-aqueous secondary battery heat-resistant layer that is excellent in dispersion stability and coatability, and is capable of forming a non-aqueous secondary battery heat-resistant layer that is excellent in heat shrinkage resistance. Another object of the present invention is to provide a heat-resistant layer for a non-aqueous secondary battery that has excellent resistance to heat shrinkage, and a non-aqueous secondary battery that includes the heat-resistant layer. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems, and have found that a slurry composition excellent in dispersion stability and coatability and a heat-resistant layer excellent in heat shrinkage resistance can be formed by using a binder composition containing a water-soluble polymer that contains amide group-containing monomer units, acid group-containing monomer units, and hydroxyl group-containing monomer units, with the contents of the amide group-containing monomer units and the acid group-containing monomer units each falling within a predetermined range, and water, thereby completing the present invention.

[0009] The present invention aims to advantageously solve the above-mentioned problems. The binder composition for a non-aqueous secondary battery heat-resistant layer of the present invention contains a water-soluble polymer and water. The water-soluble polymer contains amide group-containing monomer units, acid group-containing monomer units, and hydroxyl group-containing monomer units. The water-soluble polymer contains amide group-containing monomer units in an amount of 63% by mass to 98% by mass, and the acid group-containing monomer units in an amount of 1% by mass to 20% by mass. Thus, a binder composition containing a water-soluble polymer containing amide group-containing monomer units, acid group-containing monomer units, and hydroxyl group-containing monomer units, each in an amount within the above-mentioned ranges, and water, can be used to prepare a slurry composition with excellent dispersion stability and coatability. Furthermore, the slurry composition thus prepared can be used to successfully form a heat-resistant layer with excellent heat shrinkage resistance. In the present invention, the phrase "containing a monomer unit" means that "a polymer obtained using the monomer contains a repeating unit derived from the monomer." In the present invention, the "content ratio (mass%)" of each monomer unit (each repeating unit) contained in the polymer is 1 H-NMR and 13 It can be measured using nuclear magnetic resonance (NMR) techniques such as C-NMR.

[0010] In the binder composition for a heat-resistant layer of a non-aqueous secondary battery of the present invention, the content of the hydroxyl group-containing monomer unit in the water-soluble polymer is preferably 1% by mass or more and 25% by mass or less. If the content of the hydroxyl group-containing monomer unit in the water-soluble polymer is within the above range, the dispersion stability and coatability of the slurry composition can be further improved, and the heat shrinkage resistance of the heat-resistant layer can be further increased.

[0011] In addition, in the binder composition for a heat-resistant layer of a non-aqueous secondary battery of the present invention, the hydroxyl group-containing monomer unit is preferably a hydroxyl group-containing (meth)acrylamide monomer unit. If the hydroxyl group-containing monomer unit contained in the water-soluble polymer in the binder composition is a hydroxyl group-containing (meth)acrylamide monomer unit, the amount of moisture brought into the secondary battery by the heat-resistant layer can be reduced and the heat shrinkage resistance of the heat-resistant layer can be further improved. Furthermore, the cycle characteristics of the secondary battery can be improved. In the present invention, "(meth)acrylic" means acrylic and / or methacrylic.

[0012] In the binder composition for a heat-resistant layer of a non-aqueous secondary battery of the present invention, the molar ratio of the content of the hydroxyl group-containing monomer units to the content of the acid group-containing monomer units in the water-soluble polymer is preferably 0.70 or more. When the molar ratio of the content of the hydroxyl group-containing monomer units to the content of the acid group-containing monomer units in the water-soluble polymer (hereinafter sometimes abbreviated as "hydroxyl group / acid group molar ratio") is the above value or more, the dispersion stability and coatability of the slurry composition can be further improved. In the present invention, the "hydroxyl group / acid group molar ratio" is 1 H-NMR and 13 The content ratio (mol %) of the acid group-containing monomer unit and the content ratio (mol %) of the hydroxyl group-containing monomer unit are measured using a nuclear magnetic resonance (NMR) method such as C-NMR, and the hydroxyl group-containing monomer unit content can be calculated from these measured values.

[0013] In the binder composition for a heat-resistant layer of a nonaqueous secondary battery of the present invention, the water-soluble polymer preferably has a weight-average molecular weight of 200,000 or more and 2,000,000 or less. When the weight-average molecular weight of the water-soluble polymer contained in the binder composition is within the above range, the coatability of the slurry composition can be further improved and the heat shrinkage resistance of the heat-resistant layer can be further increased. In the present invention, the weight average molecular weight of the water-soluble polymer can be measured by gel permeation chromatography (GPC).

[0014] Here, the binder composition for a heat-resistant layer of a non-aqueous secondary battery of the present invention preferably further contains a particulate polymer. When the binder composition contains a particulate polymer, the adhesion between the heat-resistant layer obtained using the binder composition and the substrate can be improved. In addition, the cycle characteristics of the secondary battery can be improved.

[0015] The present invention also aims to advantageously solve the above-mentioned problems. The slurry composition for a non-aqueous secondary battery heat-resistant layer of the present invention is characterized by containing non-conductive inorganic particles and any of the binder compositions for a non-aqueous secondary battery heat-resistant layer described above. Thus, a slurry composition containing non-conductive inorganic particles and any of the binder compositions described above has excellent dispersion stability and coatability. Furthermore, the slurry composition can form a heat-resistant layer with excellent heat shrinkage resistance.

[0016] The present invention aims to advantageously solve the above-mentioned problems, and is characterized in that the heat-resistant layer for a non-aqueous secondary battery of the present invention is formed using the above-mentioned slurry composition for a heat-resistant layer for a non-aqueous secondary battery. As such, the heat-resistant layer formed from the above-mentioned slurry composition has excellent heat shrinkage resistance.

[0017] The present invention also aims to advantageously solve the above-mentioned problems, and the nonaqueous secondary battery of the present invention is characterized by including the heat-resistant layer for a nonaqueous secondary battery described above. In this way, the safety of a secondary battery including a battery component having the heat-resistant layer described above is sufficiently ensured. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery heat-resistant layer that can prepare a slurry composition for a non-aqueous secondary battery heat-resistant layer that is excellent in dispersion stability and coatability and is capable of forming a non-aqueous secondary battery heat-resistant layer that is excellent in heat shrinkage resistance. Furthermore, according to the present invention, it is possible to provide a slurry composition for a heat-resistant layer of a non-aqueous secondary battery, which can form a heat-resistant layer for a non-aqueous secondary battery that has excellent dispersion stability and coatability, and is also excellent in heat shrinkage resistance. According to the present invention, it is possible to provide a heat-resistant layer for a non-aqueous secondary battery that is excellent in heat shrinkage resistance, and a non-aqueous secondary battery that includes the heat-resistant layer. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described in detail. Here, the binder composition for a non-aqueous secondary battery heat-resistant layer of the present invention can be used to prepare a slurry composition for a non-aqueous secondary battery heat-resistant layer of the present invention. The slurry composition for a non-aqueous secondary battery heat-resistant layer of the present invention can be used to form a heat-resistant layer of a non-aqueous secondary battery such as a lithium-ion secondary battery. Furthermore, the heat-resistant layer for a non-aqueous secondary battery of the present invention is characterized by being formed from the slurry composition for a non-aqueous secondary battery heat-resistant layer of the present invention. Furthermore, the non-aqueous secondary battery of the present invention is characterized by having a heat-resistant layer for a non-aqueous secondary battery prepared using the slurry composition for a non-aqueous secondary battery heat-resistant layer 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 water-soluble polymer and water as a dispersion medium, and optionally further contains a particulate polymer and other components. Here, the binder composition of the present invention is characterized in that the water-soluble polymer contains an amide group-containing monomer unit, an acid group-containing monomer unit, and a hydroxyl group-containing monomer unit, and the content of the amide group-containing monomer unit is 63% by mass or more and 98% by mass or less, and the content of the acid group-containing monomer unit is 1% by mass or more and 20% by mass or less.

[0021] The binder composition of the present invention contains, in water, a water-soluble polymer that contains amide group-containing monomer units, acid group-containing monomer units, and hydroxyl group-containing monomer units, and the contents of the amide group-containing monomer units and the acid group-containing monomer units are within the above-mentioned ranges, and therefore, by using this binder composition, it is possible to prepare a slurry composition that is excellent in dispersion stability and coatability, and to form a heat-resistant layer that is excellent in heat shrinkage resistance. The reason why the above-mentioned effects are obtained by using a binder composition in which the above-mentioned water-soluble polymer is dissolved in water is not clear, but it is presumed to be as follows.

[0022] First, it is believed that the amide group-containing monomer units contained in the water-soluble polymer in the binder composition function as a main skeleton that imparts high rigidity to the water-soluble polymer, thereby improving the heat shrinkage resistance of the resulting heat-resistant layer. Furthermore, the acid group-containing monomer units contained in the water-soluble polymer in the binder composition bind to the non-conductive inorganic particles through electrostatic interactions in the slurry, thereby functioning as adsorption sites for the non-conductive inorganic particles. However, if the adsorption of the acid group-containing monomer units to the non-conductive inorganic particles is too strong, the non-conductive inorganic particles may aggregate, reducing the dispersion stability of the non-conductive inorganic particles in the slurry. Here, since the water-soluble polymer further contains hydroxyl group-containing monomer units, the hydration effect of the hydroxyl groups can suppress excessive adsorption of the acid group-containing monomer units to the non-conductive inorganic particles as described above. This is thought to improve the dispersion stability of the non-conductive inorganic particles in the slurry. Furthermore, a slurry composition with such excellent dispersion stability can be applied uniformly to a substrate without variation in the coating amount, and the resulting heat-resistant layer does not have any defects (streaks, uneven coating, repellency, etc.), so the slurry composition is also considered to have excellent coatability. Therefore, by using the binder composition of the present invention, a slurry composition excellent in dispersion stability and coatability can be obtained. Furthermore, a heat-resistant layer excellent in heat shrinkage resistance can be obtained by using a slurry composition prepared using the binder composition of the present invention.

[0023] <Water-soluble polymer> The water-soluble polymer contained in the binder composition for a non-aqueous secondary battery heat-resistant layer is a component that can contribute to improving the dispersion stability and coatability of the slurry composition in the slurry composition. The water-soluble polymer also functions as a binder in the heat-resistant layer formed using the slurry composition, imparting adhesiveness to the heat-resistant layer formed using the slurry composition containing the binder composition and preventing the non-conductive inorganic particles contained in the heat-resistant layer from detaching from the heat-resistant layer. In the present invention, a polymer being "water-soluble" means that when 0.5 g of the polymer is dissolved in 100 g of water at 25°C, the insoluble content is less than 1.0 mass %.

[0024] Here, the water-soluble polymer contains amide group-containing monomer units and acid group-containing monomer units in proportions within a predetermined range, and further contains hydroxyl group-containing monomer units. The water-soluble polymer may contain repeating units other than the amide group-containing monomer units, acid group-containing monomer units, and hydroxyl group-containing monomer units (hereinafter referred to as "other repeating units").

[0025] <<Amide group-containing monomer unit>> Examples of amide group-containing monomers capable of forming amide group-containing monomer units include N-vinylacetamide, (meth)acrylamide, dimethyl(meth)acrylamide, diethyl(meth)acrylamide, N-methoxymethyl(meth)acrylamide, and dimethylaminopropyl(meth)acrylamide. Among these, acrylamide and methacrylamide are preferred, and acrylamide is more preferred, from the viewpoint of further improving the heat shrinkage resistance of the heat-resistant layer. The amide group-containing monomers may be used alone or in combination of two or more. In the present invention, a monomer unit having both an amide group and a hydroxyl group is included in the "hydroxyl group-containing monomer unit" but is not included in the "amide group-containing monomer unit." In addition, in the present invention, a monomer unit having both an amide group and an acid group (such as a carboxylic acid group, a sulfonic acid group, or a phosphoric acid group) is included in the "acid group-containing monomer unit" but is not included in the "amide group-containing monomer unit."

[0026] The water-soluble polymer used in the present invention must have an amide group-containing monomer unit content of 63% to 98% by mass, where the total amount of all repeating units (total monomer units) in the water-soluble polymer is 100% by mass. The amide group-containing monomer unit content in the water-soluble polymer is preferably 67% by mass or more, more preferably 71% by mass or more, even more preferably 74% by mass or more, and preferably 95% by mass or less, and more preferably 90% by mass or less. If the amide group-containing monomer unit content in the water-soluble polymer is less than 63% by mass, the rigidity of the water-soluble polymer decreases, making it impossible to ensure sufficient heat shrinkage resistance of the heat-resistant layer. On the other hand, if the amide group-containing monomer unit content in the water-soluble polymer exceeds 98% by mass, the dispersion stability of the slurry composition decreases.

[0027] <<Acid group-containing monomer unit>> Examples of the acid group-containing monomer capable of forming the acid group-containing monomer unit include a carboxylic acid group-containing monomer, a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, etc. The acid group contained in the acid group-containing monomer unit may form a salt with an alkali metal, ammonia, etc.

[0028] Here, examples of the carboxylic acid group-containing monomer capable of forming the carboxylic acid group-containing monomer unit include monocarboxylic acids and derivatives thereof, dicarboxylic acids and acid anhydrides thereof, and derivatives thereof. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of the 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 maleate. Examples of the acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Furthermore, as the carboxylic acid group-containing monomer, an acid anhydride that generates a carboxylic acid group upon hydrolysis can also be used.

[0029] Furthermore, examples of sulfonic acid group-containing monomers capable of forming sulfonic acid group-containing monomer units include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid. In the present invention, "(meth)allyl" means allyl and / or methallyl.

[0030] Furthermore, examples of phosphate group-containing monomers capable of forming phosphate group-containing monomer units include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate. In the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0031] The acid group-containing monomers may be used singly or in combination of two or more. From the viewpoints of improving the adhesion between the heat-resistant layer and the substrate and further improving the coatability of the slurry composition, the acid group-containing monomer capable of forming the acid group-containing monomer unit is preferably a carboxylic acid group-containing monomer, more preferably a monocarboxylic acid, and even more preferably acrylic acid.

[0032] The water-soluble polymer used in the present invention must have an acid group-containing monomer unit content of 1% by mass or more and 20% by mass or less, preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, particularly preferably 7% by mass or more, preferably 16% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less, when the total amount of all repeating units (total monomer units) in the water-soluble polymer is taken as 100% by mass. If the acid group-containing monomer unit content in the water-soluble polymer is less than 1% by mass, the coatability of the slurry composition will be reduced. Furthermore, the adsorption force of the water-soluble polymer to the non-conductive inorganic particles will be reduced, making it impossible to ensure sufficient adhesion between the heat-resistant layer and the substrate. On the other hand, if the acid group-containing monomer unit content in the water-soluble polymer is more than 20% by mass, the dispersion stability of the slurry composition will be reduced.

[0033] <<Hydroxyl group-containing monomer units>> Examples of hydroxyl group-containing monomers capable of forming hydroxyl group-containing monomer units include hydroxyl group-containing (meth)acrylamide monomers such as N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, N-hydroxypropylacrylamide, N-hydroxymethylmethacrylamide, N-hydroxyethylmethacrylamide, and N-hydroxypropylmethacrylamide; and hydroxyl group-containing (meth)acrylate monomers such as 2-hydroxymethylacrylate, 2-hydroxyethylacrylate, 2-hydroxypropylacrylate, 2-hydroxybutylacrylate, 2-hydroxymethylmethacrylate, 2-hydroxyethylmethacrylate, 2-hydroxypropylmethacrylate, and 2-hydroxybutylmethacrylate. Among these, from the viewpoints of reducing the amount of moisture brought into the secondary battery by the heat-resistant layer, further increasing the heat shrinkage resistance of the heat-resistant layer, and improving the cycle characteristics of the secondary battery, hydroxyl group-containing (meth)acrylamide monomers are preferred, and N-hydroxyethylacrylamide and N-hydroxymethylacrylamide are more preferred. The hydroxyl group-containing monomers may be used alone or in combination of two or more. In the present invention, the term "(meth)acrylate" means acrylate and / or methacrylate.

[0034] Here, the water-soluble polymer contained in the binder composition of the present invention must contain a hydroxyl group-containing monomer unit, since if the water-soluble polymer does not contain a hydroxyl group-containing monomer unit, the dispersion stability and coatability of the slurry composition will be reduced. The content of the hydroxyl group-containing monomer units in the water-soluble polymer is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, particularly preferably 10% by mass or more, and preferably 25% by mass or less, more preferably 21% by mass or less, even more preferably 18% by mass or less, and particularly preferably 17% by mass or less, based on the total amount of repeating units (total monomer units) in the water-soluble polymer taken as 100% by mass. If the content of the hydroxyl group-containing monomer units in the water-soluble polymer is 1% by mass or more, the dispersion stability and coatability of the slurry composition can be further improved. On the other hand, if the content of the hydroxyl group-containing monomer units in the water-soluble polymer is 25% by mass or less, the heat shrinkage resistance of the heat-resistant layer can be further improved.

[0035] <<Other repeating units>> The other repeating units contained in the water-soluble polymer are not particularly limited. For example, the other repeating units include monomer units derived from known monomers, such as (meth)acrylic acid ester monomer units and crosslinkable monomer units, which will be described later in the section "particulate polymer." The water-soluble polymer may contain one type of other repeating unit, or two or more types. When all repeating units (all monomer units) contained in the water-soluble polymer are taken as 100% by mass, the content of other repeating units is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0% by mass.

[0036] <<Properties>> [Hydroxyl group / acid group molar ratio] Here, the molar ratio of the content of hydroxyl group-containing monomer units to the content of acid group-containing monomer units in the water-soluble polymer (hydroxyl group / acid group molar ratio) is preferably 0.70 or more, more preferably 0.80 or more, even more preferably 0.90 or more, and particularly preferably 1.00 or more. If the hydroxyl group / acid group molar ratio is 0.70 or more, the dispersion stability and coatability of the slurry composition can be further improved. In addition, the upper limit of the hydroxyl group / acid group molar ratio is not particularly limited, but can be, for example, 5.00 or less, 3.00 or less, or 2.63 or less.

[0037] [Weight average molecular weight] The water-soluble polymer used in the present invention preferably has a weight-average molecular weight of 200,000 or more, more preferably 300,000 or more, even more preferably 400,000 or more, and particularly preferably 500,000 or more, and preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less. If the water-soluble polymer has a weight-average molecular weight of 200,000 or more, the rigidity of the water-soluble polymer is improved, thereby further enhancing the heat shrinkage resistance of the heat-resistant layer. On the other hand, if the water-soluble polymer has a weight-average molecular weight of 2,000,000 or less, the viscosity of the slurry composition is reduced, thereby further improving the coatability of the slurry composition. The weight average molecular weight of the water-soluble polymer can be adjusted, for example, by changing the type and amount of the polymerization initiator and / or polymerization accelerator used in preparing the water-soluble polymer.

[0038] The water-soluble polymer contained in the binder composition of the present invention can interact appropriately with the non-conductive inorganic particles, making it possible to effectively control the proportion of water-soluble polymer adsorbed to the non-conductive inorganic particles in a slurry composition prepared using the binder composition. By effectively controlling the proportion of water-soluble polymer adsorbed to the non-conductive inorganic particles, the dispersion stability and coatability of the slurry composition, as well as the adhesion between the heat-resistant layer and the substrate, can be sufficiently improved. From the perspective of further improving the dispersion stability and coatability of the slurry composition while also enhancing the adhesion between the heat-resistant layer and the substrate, the proportion of water-soluble polymer adsorbed to the non-conductive inorganic particles is preferably 10% by mass or more and 60% by mass or less, assuming that the total amount of water-soluble polymer in the slurry composition is 100% by mass. Methods for measuring the proportion of the water-soluble polymer adsorbed to the non-conductive inorganic particles include, for example, a method in which the slurry composition is centrifuged, the non-conductive inorganic particles to which the water-soluble polymer is adsorbed are precipitated, and the weight loss behavior of the precipitate when heated is analyzed using Tg / DTA to calculate the proportion; and a method in which the slurry composition is centrifuged, and the concentration of the water-soluble polymer in the supernatant is quantified to calculate the proportion.

[0039] <<Method for preparing water-soluble polymers>> The water-soluble polymer described above is not particularly limited and can be prepared by any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. Furthermore, addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used as the polymerization method. The polymerization initiator, polymerization accelerator, emulsifier, dispersant, chain transfer agent, etc. used during polymerization can be those generally used, and the amounts used should be the amounts generally used. Among these, aqueous solution polymerization using water as the polymerization solvent is preferred because it does not require a solvent removal operation, the solvent is highly safe, and there is no problem of surfactant contamination.

[0040] When water is used as the polymerization solvent and the above-mentioned monomer composition is polymerized in water to prepare an aqueous solution containing a water-soluble polymer, it is preferable to adjust the pH of the aqueous solution after polymerization to 7 or more and 9 or less. This is because, if the obtained aqueous solution is neutralized to adjust the pH to within the above range, the viscosity stability of the slurry composition can be easily improved.

[0041] Here, the polymerization initiator that can be used for preparing the water-soluble polymer is not particularly limited, and includes known polymerization initiators such as sodium persulfate, ammonium persulfate, and potassium persulfate. Among them, ammonium persulfate is preferably used. The polymerization initiator may be used alone or in combination of two or more types in any ratio.

[0042] The polymerization accelerator is not particularly limited, and known reducing polymerization accelerators such as L-ascorbic acid, sodium hydrogen sulfite, and tetramethylethylenediamine can be used. Among these, L-ascorbic acid is preferred. One type of polymerization accelerator may be used alone, or two or more types may be used in combination at any ratio.

[0043] <Particulate polymer> The particulate polymer that may be optionally contained in the binder composition of the present invention is a component that functions as a binder, similar to the water-soluble polymer described above. When the binder composition contains the particulate polymer, the adhesion between the obtained heat-resistant layer and the substrate can be improved. The particulate polymer is a water-insoluble particle formed by 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 25°C, the insoluble content is 90 mass % or more.

[0044] Here, the particulate polymer is not particularly limited as long as it is a water-insoluble particulate polymer that can be dispersed in a dispersion medium such as water, but for example, a conjugated diene polymer, a fluorine-containing polymer, or an acrylic polymer can be used. Among these, it is preferable to use an acrylic polymer. If an acrylic polymer is used as the particulate polymer contained in the binder composition, it is possible to improve the adhesion between the heat-resistant layer and the substrate and also to increase the oxidation resistance of the battery component having the heat-resistant layer. The particulate polymer may be used alone or in combination of two or more kinds in any ratio.

[0045] <<Conjugated diene polymer>> Conjugated diene polymers are polymers containing conjugated diene monomer units. Specific examples of conjugated diene polymers include, but are not limited to, copolymers containing aromatic vinyl monomer units and aliphatic conjugated diene monomer units, such as styrene-butadiene copolymer (SBR), butadiene rubber (BR), isoprene rubber, acrylic rubber (NBR) (copolymers containing acrylonitrile units and butadiene units), and hydrogenated products thereof.

[0046] <<Fluorine-based polymers>> Specific examples of the fluorine-based polymer include, but are not limited to, polyvinylidene fluoride (PVdF) and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer.

[0047] <<Acrylic polymer>> The acrylic polymer is a polymer containing (meth)acrylic acid ester monomer units. The acrylic polymer may also contain repeating units other than (meth)acrylic acid ester monomer units. Such repeating units are not particularly limited, and preferred examples include hydrophilic group-containing monomer units and crosslinkable monomer units, but also include monomer units (other monomer units) other than (meth)acrylic acid ester monomer units, hydrophilic group-containing monomer units, and crosslinkable monomer units.

[0048] [(Meth)acrylic acid ester monomer unit] Examples of (meth)acrylic acid ester monomers that can form (meth)acrylic acid ester monomer units include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, and 2-ethylhexyl acrylate; and alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, and 2-ethylhexyl methacrylate. These may be used alone or in combination of two or more. Among these, n-butyl acrylate and 2-ethylhexyl acrylate are preferred as the (meth)acrylic acid ester monomer. Furthermore, the content of (meth)acrylic acid ester monomer units in the particulate polymer is preferably more than 50% by mass, more preferably 60% by mass or more, and is preferably 99% by mass or less, more preferably 97% by mass or less, when the amount of all repeating units (all monomer units) in the particulate polymer is 100% by mass.

[0049] [Hydrophilic group-containing monomer unit] Examples of hydrophilic group-containing monomers capable of forming hydrophilic group-containing monomer units include the "acid group-containing monomers" and "hydroxyl group-containing monomers" described in the "Water-soluble polymer" section. These may be used alone or in combination of two or more. Among these, it is preferable to use methacrylic acid as the hydrophilic group-containing monomer. The content ratio of the hydrophilic group-containing monomer units in the particulate polymer is preferably 1% by mass or more and 5% by mass or less, when the amount of all repeating units (all monomer units) in the particulate polymer is 100% by mass.

[0050] [Crosslinkable monomer unit] Examples of crosslinkable monomers that can form crosslinkable monomer units include glycidyl methacrylate, allyl glycidyl ether, ethylene glycol dimethacrylate, allyl (meth)acrylate, and divinylbenzene. These may be used alone or in combination of two or more. Among these, it is preferable to use allyl glycidyl ether and allyl methacrylate as the crosslinkable monomer. The content of the crosslinkable monomer units in the particulate polymer is preferably 1% by mass or more and 5% by mass or less, when the amount of all repeating units (all monomer units) in the particulate polymer is 100% by mass.

[0051] [Other monomer units] The other monomers capable of forming the other monomer units are not particularly limited as long as they are monomers other than the above-mentioned (meth)acrylic acid ester monomers, hydrophilic group-containing monomers, and crosslinkable monomers. Specific examples of the other monomers include α,β-unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile; and styrene-based monomers such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, and α-methylstyrene. These may be used alone or in combination of two or more. Among these, it is preferable to use acrylonitrile and styrene as the other polymer. The content ratio of other monomer units in the particulate polymer is preferably 1% by mass or more and 35% by mass or less, when the amount of all repeating units (all monomer units) in the particulate polymer is 100% by mass.

[0052] <<Properties>> [Glass transition temperature] Here, the glass transition temperature of the particulate polymer is preferably less than 20°C, more preferably less than 15°C. If the glass transition temperature of the particulate polymer is less than 20°C, the adhesion between the heat-resistant layer and the substrate can be improved. In addition, the lower limit of the glass transition temperature of the particulate polymer is not particularly limited, but can be, for example, more than -120°C or more than -60°C. In the present invention, the "glass transition temperature" of the particulate polymer can be measured by the method described in the examples of this specification. The glass transition temperature 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 preparing the particulate polymer.

[0053] [Volume average particle size] The volume average particle diameter of the particulate polymer is preferably 0.1 μm or more, more preferably 0.15 μm or more, even more preferably 0.2 μm or more, particularly preferably 0.31 μm or more, and is preferably 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.5 μm or less. If the volume average particle diameter of the particulate polymer is 0.1 μm or more, 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 1 μm or less, the adhesion between the heat-resistant layer and the substrate can be improved. In the present invention, the term "volume average particle diameter" means "the particle diameter (D50) at which the cumulative volume calculated from the smallest diameter side in the particle size distribution (volume basis) measured by laser diffraction method becomes 50%." The volume average particle size 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 preparing the particulate polymer.

[0054] <<Method for preparing particulate polymer>> Here, the polymerization method for the particulate polymer is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. Furthermore, as the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used. Furthermore, polymerization solvents, emulsifiers, dispersants, polymerization initiators, chain transfer agents, etc. that can be used in the polymerization can be commonly used ones, and the amounts used can also be the amounts commonly used.

[0055] In the binder composition of the present invention, the content ratio of the water-soluble polymer to the particulate polymer is not particularly limited, but the proportion of the water-soluble polymer in the total content of the water-soluble polymer and the particulate polymer is preferably 15% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. If the proportion of the water-soluble polymer in the total content of the water-soluble polymer and the particulate polymer is 15% by mass or more, the heat shrinkage resistance of the heat-resistant layer can be further improved, and if it is 70% by mass or less, the adhesion between the heat-resistant layer and the substrate can be increased.

[0056] <Dispersion medium> The dispersion medium of the binder composition of the present invention is not particularly limited as long as it contains water. For example, the binder composition of the present invention may contain only water as the dispersion medium, or the dispersion medium may be a mixture of water and an organic solvent (e.g., esters, ketones, alcohols). The binder composition of the present invention may contain one type of organic solvent, or may contain two or more types of organic solvents.

[0057] <Other ingredients> In addition to the above-mentioned components, the binder composition of the present invention may contain a reinforcing agent, a leveling agent, a wetting agent, a dispersant, a viscosity modifier, an electrolyte additive, a preservative, an antifungal agent, an antifoaming agent, a polymerization inhibitor, and a binder other than the water-soluble polymer and particulate polymer of the present invention. These are not particularly limited as long as they do not affect the battery reaction, and known binders can be used. Furthermore, the other components may be used alone or in combination of two or more in any ratio.

[0058] The wetting agent is not particularly limited, and may be an ethylene oxide / propylene oxide surfactant (EO·PO-based surfactant), a fluorine-based surfactant, a silicone-based surfactant, etc. Among these, it is preferable to use an EO·PO-based surfactant or a fluorine-based surfactant, and it is more preferable to use an EO·PO-based surfactant. The dispersant is not particularly limited, and examples thereof include 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, and ammonium polycarboxylic acid sulfonic acid copolymers. Of these, sodium polyacrylate is preferably used. Specific examples of the components other than the wetting agent and dispersant described above are not particularly limited, but include those described in WO 2012 / 115096.

[0059] <Preparation of binder composition for non-aqueous secondary battery heat-resistant layer> The binder composition of the present invention can be prepared by mixing the above-mentioned water-soluble polymer and water, any particulate polymer, and other components by a known method. Specifically, the binder composition can be prepared by mixing the above-mentioned components using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix. When the water-soluble polymer and the optional particulate polymer are prepared by polymerization in an aqueous solvent, they can be mixed as they are in the form of an aqueous solution or aqueous dispersion to prepare a binder composition containing water as a solvent. Furthermore, the preparation of the binder composition and the preparation of the slurry composition described below may be carried out simultaneously, for example, by mixing the water-soluble polymer and the non-conductive inorganic particles and then adding any particulate polymer.

[0060] (Slurry composition for non-aqueous secondary battery heat-resistant layer) The slurry composition of the present invention is a composition used to form a heat-resistant layer, and contains non-conductive inorganic particles and the binder composition described above, and optionally further contains other components. That is, the slurry composition of the present invention usually contains non-conductive inorganic particles, a water-soluble polymer, and water as a dispersion medium, and optionally further contains a particulate polymer and other components. Furthermore, since the slurry composition of the present invention contains the binder composition described above, it has excellent dispersion stability and coatability, and by drying the slurry composition of the present invention on a substrate, a heat-resistant layer with excellent heat shrinkage resistance can be obtained.

[0061] <Non-conductive inorganic particles> Here, the non-conductive inorganic particles contained in the slurry composition for the heat-resistant layer are not particularly limited as long as they are particles made of an inorganic material that is stable and electrochemically stable in the use environment of the secondary battery. From this perspective, preferred examples of non-conductive inorganic particles include inorganic oxide particles such as aluminum oxide (alumina, Al2O3), aluminum oxide hydrate (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 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; clay particles such as talc and montmorillonite; etc. Among these, from the viewpoint of favorably adsorbing the water-soluble polymer and the particulate polymer and improving the adhesion between the heat-resistant layer and the substrate, particles made of alumina (alumina particles), particles made of boehmite (boehmite particles), and particles made of barium sulfate (barium sulfate particles) are preferred as non-conductive inorganic particles, with alumina particles and barium sulfate particles being more preferred. These particles may be subjected to element substitution, surface treatment, solid solution treatment, etc., as needed. These particles may be used alone or in combination of two or more types.

[0062] <Binder composition> As the binder composition, the above-described binder composition of the present invention containing a water-soluble polymer and water, as well as an optional particulate polymer and other components, is used. The content of the water-soluble polymer in the slurry composition is preferably 0.5 parts 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 inorganic particles, from the viewpoint of further improving the heat shrinkage resistance of the heat-resistant layer. The content of the water-soluble polymer in the slurry composition is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, in terms of solid content, per 100 parts by mass of the non-conductive inorganic particles, from the viewpoint of improving the cycle characteristics of the secondary battery. The content of the particulate polymer in the slurry composition is preferably 1 part by mass or more, more preferably 1.2 parts by mass or more, and even more preferably 1.4 parts by mass or more, in terms of solid content per 100 parts by mass of non-conductive inorganic particles, from the viewpoint of improving the adhesion between the heat-resistant layer and the substrate. Also, the content of the particulate polymer in the slurry composition is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 7 parts by mass or less, in terms of solid content per 100 parts by mass of non-conductive inorganic particles, from the viewpoint of improving the cycle characteristics of the secondary battery.

[0063] <Other ingredients> Other components that can be blended into the slurry composition are not particularly limited and include the same components as those that can be blended into the binder composition of the present invention. Note that the other components may be used alone or in combination of two or more in any ratio. The content of the wetting agent in the slurry composition is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, and preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less, per 100 parts by mass of non-conductive inorganic particles. By setting the content of the wetting agent to 0.01 parts by mass or more per 100 parts by mass of non-conductive inorganic particles, the wettability to the substrate is improved and the occurrence of repellency is suppressed, thereby further improving the coatability of the slurry composition. Furthermore, by setting the content of the wetting agent to 5 parts by mass or less per 100 parts by mass of non-conductive inorganic particles, the cycle characteristics of the secondary battery can be improved. The content of the dispersant in the slurry composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more, and preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less, per 100 parts by mass of the non-conductive inorganic particles. By setting the content of the dispersant to 0.1 parts by mass or more per 100 parts by mass of the non-conductive inorganic particles, the dispersion stability of the slurry composition can be further improved and the heat shrinkage resistance of the heat-resistant layer can be further enhanced. By setting the content of the dispersant to 5 parts by mass or less per 100 parts by mass of the non-conductive inorganic particles, the amount of moisture remaining in the heat-resistant layer formed using the slurry composition can be reduced, thereby improving the cycle characteristics of the secondary battery.

[0064] <Preparation of Slurry Composition for Non-Aqueous Secondary Battery Heat-Resistant Layer> The above-mentioned slurry composition can be prepared by mixing the above-mentioned components by a known mixing method, for example, using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix.

[0065] (Heat-resistant layer for non-aqueous secondary batteries) The heat-resistant layer of the present invention is formed from the above-mentioned slurry composition of the present invention, and can be formed, for example, 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 heat-resistant layer of the present invention is made of a dried product of the above-mentioned slurry composition, and usually contains at least non-conductive inorganic particles and a water-soluble polymer. Note that, since each component contained in the heat-resistant layer is the same as that contained in the above-mentioned slurry composition, the preferred ratio of each component is the same as the preferred ratio of each component in the slurry composition. 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, and therefore has excellent heat shrinkage resistance.

[0066] <Base material> Here, there is no limitation on the substrate to which the slurry composition is applied, and 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 heat-resistant layer, and the release substrate may be peeled off from the heat-resistant layer. In this way, the heat-resistant layer peeled off from the release substrate may be used as a free-standing film to form a battery component of a secondary battery. However, from the viewpoint of omitting the step of peeling off the heat-resistant layer and increasing the production 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 apply the slurry composition onto the separator substrate or the electrode substrate.

[0067] <<Separator substrate>> The separator substrate is not particularly limited, but 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.

[0068] <<Electrode base material>> The electrode substrates (positive electrode substrate and negative electrode substrate) are not particularly limited, but examples thereof include electrode substrates in which an electrode mixture layer containing an electrode active material and a binder is formed on a current collector. The current collector, the electrode active materials (positive electrode active material, negative electrode active material) and binders for the electrode composite layer (positive electrode composite layer binder, negative electrode composite layer binder), and the method for forming the electrode composite layer on the current collector may be known, for example, as described in JP 2013-145763 A.

[0069] <Method for forming heat-resistant layer> The following methods can be used to form a heat-resistant layer on a substrate such as the separator substrate or electrode substrate. 1) A method in which the slurry composition of the present invention is applied to the surface of a substrate (in the case of an electrode substrate, the surface on the electrode mixture layer side; the same applies hereinafter) and then dried; 2) a method of immersing a substrate in the slurry composition of the present invention and then drying the same; and 3) A method in which the slurry composition of the present invention is applied to a release substrate, dried to produce a heat-resistant layer, and the resulting heat-resistant layer is transferred to the surface of the substrate. Among these, the method 1) is particularly preferred because it allows for easy control of the thickness of the heat-resistant layer. Specifically, the method 1) includes a step of applying a slurry composition onto a substrate (application step) and a step of drying the slurry composition applied onto the substrate to form a heat-resistant layer (drying step).

[0070] <<Coating process>> 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.

[0071] <<Drying process>> 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 the drying method include drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with infrared rays or electron beams.

[0072] (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 solution, and the heat-resistant layer is included in at least one of the positive electrode, the negative electrode, and the separator, which are battery components.

[0073] <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 heat-resistant layer of the present invention described above. Note that the positive electrode, negative electrode, and separator not having the heat-resistant layer of the present invention are not particularly limited, and known positive electrodes, negative electrodes, and separators can be used.

[0074] <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 lithium-ion secondary batteries, a lithium salt is used as the supporting electrolyte. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, CF4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. Among these, LiPF6, LiClO4, and CF3SO3Li are preferred because they are easily soluble in solvents and exhibit a high degree of dissociation. One type of electrolyte may be used alone, or two or more types may be used in combination. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0075] 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), and ethyl methyl carbonate (EMC) are preferred; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. Mixtures of these solvents may also be used. Among these, carbonates are preferred because of their high dielectric constant and wide stable potential range. The concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate. Known additives may also be added to the electrolytic solution.

[0076] <Method of manufacturing non-aqueous secondary battery> The nonaqueous secondary battery of the present invention can be produced, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the stack as necessary according to the battery shape, 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 member with a heat-resistant layer. To prevent internal pressure increases and overcharging / discharging, etc., in the secondary battery, a fuse, an overcurrent protection element such as a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. The shape of the secondary battery may be any type, such as a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, or a flat type. [Example]

[0077] The present invention will be specifically described 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. In addition, in a polymer produced by polymerizing multiple types of monomers, the ratio of a monomer unit formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of the certain monomer to all the monomers used in the polymerization of the polymer, unless otherwise specified. In the examples and comparative examples, the weight-average molecular weight of the water-soluble polymer, the glass transition temperature and volume-average particle size of the particulate polymer, the dispersion stability and coatability of the slurry composition for the heat-resistant layer, the heat shrinkage resistance of the heat-resistant layer, the adhesion between the heat-resistant layer and the substrate, and the cycle characteristics of the secondary battery were evaluated by the following methods. <Weight-average molecular weight of water-soluble polymer> The aqueous solutions containing the water-soluble polymers prepared in the Examples and Comparative Examples were diluted to a concentration of 0.5%. Caustic soda was then added until the pH reached 10-12, and the solution was immersed in a water bath at 80°C or higher for 1 hour. The solution was then diluted to 0.025% with the eluent described below to prepare a sample. The sample was analyzed by gel permeation chromatography under the following conditions to determine the weight-average molecular weight of the water-soluble polymer. Apparatus: Gel permeation chromatograph GPC (instrument No. GPC-26) Detector: Differential refractive index detector RI (manufactured by Showa Denko K.K., product name "RI-201", sensitivity 32) Column: 2 TSKgel GMPWXL (φ7.8 mm x 30 cm, Tosoh Corporation) Eluent: 0.1M Tris buffer (pH 9, 0.1M potassium chloride added) Flow rate: 0.7mL / min Column temperature: 40℃ Injection volume: 0.2mL Standard samples: Monodisperse polyethylene oxide (PEO) and polyethylene glycol (PEG) manufactured by Tosoh Corporation and Sigma-Aldrich LLC <Glass transition temperature of particulate polymer> The measurement sample was a powdered sample obtained by drying an aqueous dispersion containing particulate polymer at 25°C for 48 hours. A 10 mg sample was weighed into an aluminum pan and measured using a differential scanning calorimetry (DSC) analyzer (manufactured by SII Nanotechnology Inc., product name "EXSTAR DSC6220") at a temperature range of -100°C to 200°C at a heating rate of 20°C / min, according to the conditions specified in JIS Z8703. A differential scanning calorimetry (DSC) curve was obtained. An empty aluminum pan was used as a reference. The temperature at which the differential signal (DDSC) peaked during this heating process was determined as the glass transition temperature (°C). Since multiple peaks were observed, the temperature with the largest displacement was determined as the glass transition temperature of the particulate polymer. <Volume average particle size of particulate polymer> The volume-average particle size of the particulate polymer was measured by laser diffraction. Specifically, an aqueous dispersion containing the prepared particulate polymer (adjusted to a solids concentration of 0.1% by mass) was used as a sample. The particle size distribution (volume basis) was measured using a laser diffraction particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name "LS-13 320"), and the particle size D50 at which the cumulative volume calculated from the smallest diameter side reached 50% was taken as the volume-average particle size. <Dispersion Stability of Slurry Composition for Heat-Resistant Layer> 1 kg of the slurry composition for the heat-resistant layer prepared in the examples and comparative examples was placed in a 1 L plastic bottle and left to stand for 10 days. The left-standing plastic bottle was stirred for 30 minutes with a mix rotor. After stirring, the slurry composition for the heat-resistant layer in the plastic bottle was sampled from within the top 1 cm, and the solid concentration of the supernatant sampled was measured. In addition, after stirring, the slurry composition in the plastic bottle was extracted, and the presence or absence of adhesion to the bottom of the plastic bottle was confirmed, and evaluated as follows. A: The solid concentration of the supernatant after stirring is 39.5% or more, and there is no adhesion to the bottom of the plastic bottle. B: The solid concentration of the supernatant after stirring is 39.5% or more, but adhesion to the bottom of the plastic bottle is observed. C: The solid concentration of the supernatant after stirring is less than 39.5%. <Coatability of Slurry Composition for Heat-Resistant Layer> The appearance of the heat-resistant layers formed from the slurry compositions for heat-resistant layers prepared in the examples and comparative examples was visually observed and evaluated as follows. A: An area of ​​30cm x 30cm or more where no agglomerates, streaks, and / or repellencies are observed. B: The area where no agglomerates, streaks, and / or repellencies are observed is 10cm x 10cm or more but less than 30cm x 30cm. C: The area where no clumps, streaks, and / or repellencies are observed is less than 10 cm x 10 cm. <Heat shrinkage resistance of heat-resistant layer> The separators with heat-resistant layers produced in the examples and comparative examples were cut into squares measuring 12 cm wide x 12 cm long, and a square with a side length of 10 cm was drawn inside each 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 the 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 shrink 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 <Adhesion between heat-resistant layer and substrate> The separators with heat-resistant layers prepared in the examples and comparative examples were cut into a 10 mm wide x 50 mm long test piece. Next, a SUS plate with double-sided tape (Nitto Denko Corporation, No. 5608) attached was prepared, and the heat-resistant layer of each 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 peel angle was 180°, and the peel strength was measured. A higher peel strength indicates better adhesion between the heat-resistant layer and the substrate. A: Peel strength 60N / m or more B: Peel strength 30N / m or more and less than 60N / m C: Peel strength less than 30N / m <Cycle characteristics of secondary batteries> The lithium ion secondary batteries produced in the examples and comparative examples were allowed to stand for 24 hours in an environment at 25° C. Thereafter, at 25° C., they were 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 then 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 cycle was repeated in a 25°C environment, and the capacity C1 after 300 cycles was measured. The capacity retention rate ΔC = (C1 / C0) × 100 (%) was calculated and evaluated according to the following criteria. A higher 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 and less than 85% C: Capacity retention rate ΔC is less than 75%

[0078] Example 1 <Preparation of aqueous solution containing water-soluble polymer> A 10-L flask equipped with a septum was charged with 6,335 g of ion-exchanged water and 190 g of a 2.0% aqueous solution of L-ascorbic acid (a polymerization accelerator). The flask was heated to 40°C and purged with nitrogen gas at a flow rate of 100 mL / min. Next, 939.8 g (74.0%) of acrylamide (an amide group-containing monomer), 127.0 g (10.0%) of acrylic acid (an acid group-containing monomer), and 203.2 g (16.0%) of N-hydroxyethylacrylamide (a hydroxyl group-containing monomer) were mixed and injected into the flask via syringe. 200 g of a 5.0% aqueous solution of ammonium persulfate (a polymerization initiator) was then added to the flask via syringe, and the reaction temperature was set to 60°C. After 2 hours, to further increase the reaction conversion, 100 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 95 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After another 2 hours, 100 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 95 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After 2 hours, 34 g of a 5% aqueous solution of sodium nitrite as a reaction terminator was added to the flask and stirred. The flask was then cooled to 40°C and an air atmosphere was created, and the pH of the system was adjusted to 8.0 using an 8% aqueous solution of lithium hydroxide to prepare an aqueous solution containing a water-soluble polymer. The weight average molecular weight of the resulting water-soluble polymer was then measured, and the results are shown in Table 1. <Preparation of aqueous dispersion containing particulate polymer> To a reactor equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 parts of sodium lauryl sulfate (manufactured by Kao Chemical Corporation, product name "EMAL (registered trademark) 2F") as an emulsifier, and 0.5 parts of ammonium persulfate were supplied, the gas phase was replaced with nitrogen gas, and the temperature was raised to 60°C. Meanwhile, in a separate vessel, 50 parts of ion-exchanged water, 0.5 parts of sodium dodecylbenzenesulfonate, 94.2 parts of n-butyl acrylate as a (meth)acrylic acid ester monomer, 2 parts of methacrylic acid as a hydrophilic group-containing monomer, 0.3 parts of allyl methacrylate and 1.5 parts of allyl glycidyl ether as crosslinkable monomers, and 2 parts of acrylonitrile as other monomers were mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor over 4 hours to carry out polymerization. The reaction was carried out at 60°C during the addition. After the addition was completed, the mixture was stirred for an additional 3 hours at 70°C to terminate the reaction, yielding an aqueous dispersion containing a particulate polymer. The glass transition temperature and volume average particle size of the resulting particulate polymer were measured. The results are shown in Table 1. <Preparation of Slurry Composition for Non-Aqueous Secondary Battery Heat-Resistant Layer> Alumina particles (manufactured by Nippon Light Metal Co., Ltd., product name "LS-256", volume average particle size: 0.5 μm) were prepared as non-conductive inorganic particles, and sodium polyacrylate (manufactured by Toagosei Co., Ltd., product name "Aron T-50") was prepared as a dispersant. A mixture of 100 parts non-conductive inorganic particles, 0.5 parts dispersant, and ion-exchanged water was processed for 1 hour in a bead mill (manufactured by Ashizawa Finetech Co., Ltd., product name "LMZ015") to obtain a dispersion. Furthermore, 2 parts (solids) of the aqueous solution containing the water-soluble polymer obtained as described above, 4 parts (solids) of the aqueous dispersion containing the particulate polymer obtained as described above, and 0.3 parts of an ethylene oxide / propylene oxide surfactant (manufactured by San Nopco Co., Ltd., product name "Noptex ED-052") serving as a wetting agent were mixed to prepare a slurry composition for a heat-resistant layer with a solids concentration of 40%. This slurry composition for a heat-resistant layer also contained a binder composition for a heat-resistant layer. In this example, the slurry composition for a heat-resistant layer and the binder composition for a heat-resistant layer were simultaneously prepared. The dispersion stability and coatability of the slurry composition for the heat-resistant layer thus obtained were evaluated, and the results are shown in Table 1. <Separator production> A polyethylene separator substrate (manufactured by Asahi Kasei Corporation, product name "ND412", thickness: 12 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 a temperature of 50°C for 3 minutes to obtain a separator having a heat-resistant layer on one side (thickness of the heat-resistant layer: 2.5 μm). The heat shrinkage resistance of the heat-resistant layer thus obtained and the adhesion between the heat-resistant layer and the separator substrate were evaluated. The results are shown in Table 1. <Formation of the negative electrode> A 5 MPa pressure vessel equipped with a stirrer was charged with 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. After thorough stirring, the mixture was heated to 50°C to initiate polymerization. The polymerization reaction was stopped by cooling when the polymerization conversion reached 96%, yielding a mixture containing a particulate binder (styrene-butadiene copolymer). The mixture was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution, and unreacted monomer was removed by heated vacuum distillation. The mixture was then cooled to below 30°C to yield an aqueous dispersion containing a negative electrode binder. A planetary mixer was charged with 48.75 parts of artificial graphite (theoretical capacity: 360 mAh / g) and 48.75 parts of natural graphite (theoretical capacity: 360 mAh / g) as negative electrode active materials, and 1 part (solids equivalent) of carboxymethyl cellulose as a thickener. The mixture was then diluted with ion-exchanged water to a solids concentration of 60% and kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts (solids equivalent) of the aqueous dispersion containing the negative electrode binder obtained as described above was added and kneaded for 40 minutes at a rotation speed of 40 rpm. Ion-exchanged water was then 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 slurry composition for a negative electrode composite layer. The above slurry composition for the negative electrode composite layer 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 2Thereafter, the copper foil coated with the slurry composition for a 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 blank in which a negative electrode composite layer was formed on a current collector. Thereafter, the negative electrode composite layer side of the prepared negative electrode blank was roll-pressed under conditions of a temperature of 25±3°C and a linear pressure of 11 t (tons), so that the density of the negative electrode composite layer became 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%. <Formation of the positive electrode> The planetary mixer uses a Co-Ni-Mn 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 ethanol (O2), 2 parts of acetylene black (manufactured by Denka Co., Ltd., product name "HS-100") as a conductive material, and 2 parts of polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., product name "KF-1100") as a positive electrode binder, and further adding and mixing N-methyl-2-pyrrolidone (NMP) as a dispersion medium so that the total solids concentration was 67%. Next, the obtained slurry composition for the positive electrode composite layer was applied to a 20 μm thick aluminum foil current collector using a comma coater in an amount of 20±0.5 mg / cm 2 The coating was applied so that The aluminum foil was then transported at a speed of 200 mm / min through an oven at a temperature of 90°C for 2 minutes and then through an oven at a temperature of 120°C for 2 minutes to dry the slurry composition on the aluminum foil, thereby obtaining a positive electrode substrate having 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 conditions of a temperature of 25±3°C and a linear pressure of 14 tonnes, until the density of the positive electrode composite layer became 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%. <Fabrication of lithium-ion secondary batteries> A wound cell (equivalent to a discharge capacity of 520 mAh) was fabricated using the negative electrode, positive electrode, and separator described above and placed in an aluminum package. The aluminum package was then filled with a 1.0 M LiPF solution (solvent: a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3:7, additive: vinylene carbonate at 2% by volume) as the electrolyte. The aluminum package was then heat-sealed at 150°C to seal the opening, completing the fabrication of a lithium-ion secondary battery. The cycle characteristics of this lithium-ion secondary battery were evaluated. The results are shown in Table 1.

[0079] Example 2 The aqueous solution containing the water-soluble polymer, the aqueous dispersion containing the particulate polymer, the slurry composition for the heat-resistant layer, the negative electrode, the positive electrode, the separator, and the lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that the amount of acrylamide as the amide group-containing monomer, the amount of acrylic acid as the acid group-containing monomer, and the amount of N-hydroxyethylacrylamide as the hydroxyl group-containing monomer were changed to 889.0 g (70.0%), 152.4 g (12.0%), and 228.6 g (18.0%), respectively, during the preparation of the aqueous solution containing the water-soluble polymer. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0080] Example 3 The aqueous solution containing the water-soluble polymer, the aqueous dispersion containing the particulate polymer, the slurry composition for the heat-resistant layer, the negative electrode, the positive electrode, the separator, and the lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that the amount of acrylamide as the amide group-containing monomer, the amount of acrylic acid as the acid group-containing monomer, and the amount of N-hydroxyethylacrylamide as the hydroxyl group-containing monomer were changed to 825.5 g (65.0%), 139.7 g (11.0%), and 304.8 g (24.0%), respectively, during the preparation of the aqueous solution containing the water-soluble polymer. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0081] Example 4 The aqueous solution containing the water-soluble polymer, the aqueous dispersion containing the particulate polymer, the slurry composition for the heat-resistant layer, the negative electrode, the positive electrode, the separator, and the lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that the amount of acrylamide as the amide group-containing monomer, the amount of acrylic acid as the acid group-containing monomer, and the amount of N-hydroxyethylacrylamide as the hydroxyl group-containing monomer were changed to 825.5 g (65.0%), 38.1 g (3.0%), and 406.4 g (32.0%), respectively, during the preparation of the aqueous solution containing the water-soluble polymer. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0082] Example 5 The aqueous solution containing the water-soluble polymer, the aqueous dispersion containing the particulate polymer, the slurry composition for the heat-resistant layer, the negative electrode, the positive electrode, the separator, and the lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that the amount of acrylamide as the amide group-containing monomer, the amount of acrylic acid as the acid group-containing monomer, and the amount of N-hydroxyethylacrylamide as the hydroxyl group-containing monomer were changed to 806.45 g (63.5%), 215.9 g (17.0%), and 247.65 g (19.5%), respectively, during the preparation of the aqueous solution containing the water-soluble polymer. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0083] Example 6 The aqueous solution containing the water-soluble polymer, the aqueous dispersion containing the particulate polymer, the slurry composition for the heat-resistant layer, the negative electrode, the positive electrode, the separator, and the lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that the amount of acrylamide as the amide group-containing monomer, the amount of acrylic acid as the acid group-containing monomer, and the amount of N-hydroxyethylacrylamide as the hydroxyl group-containing monomer were changed to 1219.2 g (96.0%), 17.78 g (1.4%), and 33.02 g (2.6%), respectively, during the preparation of the aqueous solution containing the water-soluble polymer. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0084] Example 7 The aqueous solution containing the water-soluble polymer, the aqueous dispersion containing the particulate polymer, the slurry composition for the heat-resistant layer, the negative electrode, the positive electrode, the separator, and the lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that the amount of acrylamide as the amide group-containing monomer, the amount of acrylic acid as the acid group-containing monomer, and the amount of N-hydroxyethylacrylamide as the hydroxyl group-containing monomer were changed to 939.8 g (74.0%), 203.2 g (16.0%), and 127.0 g (10.0%), respectively, during the preparation of the aqueous solution containing the water-soluble polymer. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0085] Example 8 The aqueous solution containing the water-soluble polymer, the aqueous dispersion containing the particulate polymer, the slurry composition for the heat-resistant layer, the negative electrode, the positive electrode, the separator, and the lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that the amount of acrylamide as the amide group-containing monomer, the amount of acrylic acid as the acid group-containing monomer, and the amount of N-hydroxyethylacrylamide as the hydroxyl group-containing monomer were changed to 939.8 g (74.0%), 63.5 g (5.0%), and 266.7 g (21.0%), respectively, during the preparation of the aqueous solution containing the water-soluble polymer. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0086] Example 9 An aqueous dispersion containing a particulate polymer, a slurry composition for a heat-resistant layer, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that an aqueous solution containing a water-soluble polymer prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of aqueous solution containing water-soluble polymer> A 10-L flask equipped with a septum was charged with 6,335 g of ion-exchanged water and 95 g of a 2.0% aqueous solution of L-ascorbic acid (as a polymerization accelerator). The flask was heated to 40°C and purged with nitrogen gas at a flow rate of 100 mL / min. Next, 939.8 g (74.0%) of acrylamide (as an amide group-containing monomer), 127.0 g (10.0%) of acrylic acid (as an acid group-containing monomer), and 203.2 g (16.0%) of N-hydroxyethylacrylamide (as a hydroxyl group-containing monomer) were mixed and injected into the flask via syringe. Then, 100 g of a 5.0% aqueous solution of ammonium persulfate (as a polymerization initiator) was added to the flask via syringe, and the reaction temperature was set to 60°C. After 2 hours, to further increase the reaction conversion, 50 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 47.5 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After another 2 hours, 50 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 47.5 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After 2 hours, 34 g of a 5% aqueous solution of sodium nitrite as a reaction terminator was added to the flask and stirred. The flask was then cooled to 40°C and an air atmosphere was created, and the pH of the system was adjusted to 8.0 using an 8% aqueous solution of lithium hydroxide to prepare an aqueous solution containing a water-soluble polymer.

[0087] Example 10 An aqueous dispersion containing a particulate polymer, a slurry composition for a heat-resistant layer, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that an aqueous solution containing a water-soluble polymer prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of aqueous solution containing water-soluble polymer> A 10-L flask equipped with a septum was charged with 6,335 g of ion-exchanged water and 285 g of a 2.0% aqueous solution of L-ascorbic acid (a polymerization accelerator). The flask was heated to 40°C and purged with nitrogen gas at a flow rate of 100 mL / min. Next, 939.8 g (74.0%) of acrylamide (an amide group-containing monomer), 127.0 g (10.0%) of acrylic acid (an acid group-containing monomer), and 203.2 g (16.0%) of N-hydroxyethylacrylamide (a hydroxyl group-containing monomer) were mixed and injected into the flask via syringe. 300 g of a 5.0% aqueous solution of ammonium persulfate (a polymerization initiator) was then added to the flask via syringe, and the reaction temperature was set to 60°C. After 2 hours, to further increase the reaction conversion, 150 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 142.5 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After another 2 hours, 150 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 142.5 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After 2 hours, 34 g of a 5% aqueous solution of sodium nitrite as a reaction terminator was added to the flask and stirred. The flask was then cooled to 40 °C and an air atmosphere was created. The pH of the system was adjusted to 8.0 using an 8% aqueous solution of lithium hydroxide, and an aqueous solution containing a water-soluble polymer was prepared.

[0088] Example 11 An aqueous dispersion containing a particulate polymer, a slurry composition for a heat-resistant layer, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that an aqueous solution containing a water-soluble polymer prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of aqueous solution containing water-soluble polymer> A 10-L flask equipped with a septum was charged with 6335 g of ion-exchanged water and 66.5 g of a 2.0% aqueous solution of L-ascorbic acid (a polymerization accelerator). The flask was heated to 40°C and purged with nitrogen gas at a flow rate of 100 mL / min. Next, 939.8 g (74.0%) of acrylamide (an amide group-containing monomer), 127.0 g (10.0%) of acrylic acid (an acid group-containing monomer), and 203.2 g (16.0%) of N-hydroxyethylacrylamide (a hydroxyl group-containing monomer) were mixed and injected into the flask via syringe. 75 g of a 5.0% aqueous solution of ammonium persulfate (a polymerization initiator) was then added to the flask via syringe, and the reaction temperature was set to 60°C. After 2 hours, to further increase the reaction conversion, 35 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 33.3 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After another 2 hours, 35 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 33.3 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After 2 hours, 34 g of a 5% aqueous solution of sodium nitrite as a reaction terminator was added to the flask and stirred. The flask was then cooled to 40°C and an air atmosphere was created, and the pH of the system was adjusted to 8.0 using an 8% aqueous solution of lithium hydroxide to prepare an aqueous solution containing a water-soluble polymer.

[0089] Example 12 When preparing the aqueous solution containing the water-soluble polymer, the amount of acrylamide as the amide group-containing monomer was changed to 933.45 g (73.5%), and the amount of acrylic acid as the acid group-containing monomer was changed to 120.65 g (9.5%). Furthermore, 215.9 g (17.0%) of 2-hydroxyethyl methacrylate was used instead of 203.2 g (16.0%) of N-hydroxyethyl acrylamide as the hydroxyl group-containing monomer. Furthermore, when preparing the slurry composition for the heat-resistant layer, the amount of the aqueous dispersion containing the particulate polymer was changed to 3 parts in terms of solids. Otherwise, the aqueous solution containing the water-soluble polymer, the aqueous dispersion containing the particulate polymer, the slurry composition for the heat-resistant layer, the negative electrode, the positive electrode, the separator, and the lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0090] Example 13 When preparing the aqueous solution containing the water-soluble polymer, 2-hydroxyethyl acrylate was used instead of N-hydroxyethyl acrylamide as the hydroxyl group-containing monomer. Furthermore, when preparing the slurry composition for the heat-resistant layer, the amount of the aqueous dispersion containing the particulate polymer was changed to 3 parts in terms of solids. Otherwise, the aqueous solution containing the water-soluble polymer, the aqueous dispersion containing the particulate polymer, the slurry composition for the heat-resistant layer, the negative electrode, the positive electrode, the separator, and the lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

[0091] Example 14 An aqueous solution containing a water-soluble polymer, a slurry composition for a heat-resistant layer, a negative electrode, a positive electrode, a separator, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that the aqueous dispersion containing a particulate polymer was not added during the preparation of the slurry composition for a heat-resistant layer, and the amount of the aqueous solution containing a water-soluble polymer was changed to 4 parts in terms of solid content. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

[0092] Example 15 In preparing the slurry composition for the heat-resistant layer, the amount of the aqueous dispersion containing the particulate polymer was changed to 1.3 parts in terms of solid content, but the aqueous solution containing the water-soluble polymer, the aqueous dispersion containing the particulate polymer, the slurry composition for the heat-resistant layer, the negative electrode, the positive electrode, the separator, and the lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1. Then, evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0093] Example 16 An aqueous solution containing a water-soluble polymer, a slurry composition for a heat-resistant layer, a negative electrode, a positive electrode, a separator, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that an aqueous dispersion containing a particulate polymer prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2. <Preparation of aqueous dispersion containing particulate polymer> 70 parts of ion-exchanged water and 0.5 parts of ammonium persulfate were fed into a reactor equipped with a stirrer, the gas phase was replaced with nitrogen gas, and the temperature was raised to 60° C. Meanwhile, in a separate vessel, 50 parts of ion-exchanged water, 0.5 parts of polyoxyethylene lauryl ether (manufactured by Kao Chemical Corporation, product name "Emulgen (registered trademark) 120") as an emulsifier, 65 parts of 2-ethylhexyl acrylate as a (meth)acrylic acid ester monomer, 30 parts of styrene as other monomers, 1.7 parts of allyl glycidyl ether and 0.3 parts of allyl methacrylate as crosslinkable monomers, and 3 parts of methacrylic acid as a hydrophilic group-containing monomer were mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor over 4 hours to carry out polymerization. During the continuous addition, the reaction was carried out at 70°C. After the continuous addition was completed, the mixture was stirred at 80°C for another 3 hours to terminate the reaction, thereby obtaining an aqueous dispersion of a particulate polymer. The obtained aqueous dispersion of the particulate polymer was cooled to 25°C, and then an aqueous sodium hydroxide solution was added thereto to adjust the pH to 8.0, and then steam was introduced to remove unreacted monomers. Thereafter, while adjusting the solid content concentration with ion-exchanged water, the mixture was filtered through a 200 mesh (opening: approximately 77 µm) stainless steel wire mesh to obtain an aqueous dispersion containing the particulate polymer (solid content concentration: 40%).

[0094] Example 17 An aqueous solution containing a water-soluble polymer, a slurry composition for a heat-resistant layer, a negative electrode, a positive electrode, a separator, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that an aqueous dispersion containing a particulate polymer prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2. <Preparation of aqueous dispersion containing particulate polymer> 70 parts of ion-exchanged water, 0.20 parts of polyoxyethylene lauryl ether (manufactured by Kao Chemical Corporation, product name "Emulgen 120") as an emulsifier, and 0.5 parts of ammonium persulfate were each supplied to a reactor equipped with a stirrer, the gas phase was replaced with nitrogen gas, and the temperature was raised to 60°C. Meanwhile, in a separate vessel, 50 parts of ion-exchanged water, 0.5 parts of polyoxyethylene lauryl ether (manufactured by Kao Chemical Corporation, product name "Emulgen 120") as an emulsifier, 70 parts of 2-ethylhexyl acrylate as a (meth)acrylic acid ester monomer, 25 parts of styrene as other monomers, 1.7 parts of allyl glycidyl ether and 0.3 parts of allyl methacrylate as crosslinkable monomers, and 3 parts of methacrylic acid as a hydrophilic group-containing monomer were mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor over 4 hours to carry out polymerization. During the continuous addition, the reaction was carried out at 70°C. After the continuous addition was completed, the mixture was stirred at 80°C for another 3 hours to terminate the reaction, thereby obtaining an aqueous dispersion of a particulate polymer. The obtained aqueous dispersion of the particulate polymer was cooled to 25°C, and then an aqueous sodium hydroxide solution was added thereto to adjust the pH to 8.0, and then steam was introduced to remove unreacted monomers. Thereafter, while adjusting the solid content concentration with ion-exchanged water, the mixture was filtered through a 200 mesh (opening: approximately 77 µm) stainless steel wire mesh to obtain an aqueous dispersion containing the particulate polymer (solid content concentration: 40%).

[0095] Example 18 An aqueous solution containing a water-soluble polymer, an aqueous dispersion containing a particulate polymer, a slurry composition for a heat-resistant layer, a negative electrode, a positive electrode, a separator, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that barium sulfate particles (manufactured by Takehara Chemical Industry Co., Ltd., product name "TS-3", volume average particle diameter: 0.5 μm) were used instead of alumina particles as the non-conductive inorganic particles when preparing the slurry composition for a heat-resistant layer. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

[0096] (Comparative Example 1) Except for using an aqueous solution containing a water-soluble polymer prepared as follows, an aqueous dispersion containing a particulate polymer, a slurry composition for a heat-resistant layer, a negative electrode, a positive electrode, a separator, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2. <Preparation of aqueous solution containing water-soluble polymer> A 10 L flask equipped with a septum was charged with a monomer composition consisting of 895.0 g (89.5%) of acrylamide and 15.0 g (1.5%) of dimethylacrylamide as amide group-containing monomers, and 90.0 g (9.0%) of acrylic acid as an acid group-containing monomer, as well as 3650 g of ion-exchanged water and 50 g of isopropyl alcohol. The atmosphere in the flask was purged with nitrogen gas at a flow rate of 100 mL / min. Next, 70 g of a 5% aqueous ammonium persulfate solution and 30 g of a 5% aqueous sodium bisulfite solution were added to the flask with stirring. The mixture was then heated from room temperature to 80 °C and maintained at that temperature for 3 hours. 1620 g of ion-exchanged water was then added, and the pH was adjusted to 8 with 10% aqueous sodium hydroxide solution, yielding an aqueous solution containing a water-soluble polymer.

[0097] (Comparative Example 2) An aqueous solution containing a water-soluble polymer, an aqueous dispersion containing a particulate polymer, a slurry composition for a heat-resistant layer, a negative electrode, a positive electrode, a separator, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that, when preparing the aqueous solution containing a water-soluble polymer, acrylic acid as the acid group-containing monomer and N-hydroxyethylacrylamide as the hydroxyl group-containing monomer were not added, and the amount of acrylamide as the amide group-containing monomer was changed to 1,270 g (100%). Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

[0098] (Comparative Example 3) Except for using an aqueous solution containing a water-soluble polymer prepared as follows, an aqueous dispersion containing a particulate polymer, a slurry composition for a heat-resistant layer, a negative electrode, a positive electrode, a separator, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2. <Preparation of aqueous solution containing water-soluble polymer> A 10-L flask equipped with a septum was charged with 6335 g of ion-exchanged water and 95 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator, heated to 40°C, and the flask was purged with nitrogen gas at a flow rate of 100 mL / min. Next, 635.0 g (50.0%) of acrylamide and 127.0 g (10.0%) of methacrylamide as amide group-containing monomers, 317.5 g (25.0%) of acrylic acid and 63.5 g (5.0%) of 2-acrylamido-2-methylpropanesulfonic acid as acid group-containing monomers, 63.5 g (5.0%) of 2-hydroxyethyl methacrylate as a hydroxyl group-containing monomer, and 63.5 g (5.0%) of methacrylonitrile as other monomers were mixed and injected into the flask with a syringe. Next, 100 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator was added to the flask via syringe, and the reaction temperature was set to 60°C. After two hours, 50 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 47.5 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added to further increase the reaction conversion rate. After another two hours, 50 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 47.5 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After two hours, 34 g of a 5% aqueous solution of sodium nitrite as a reaction terminator was added to the flask and stirred. The flask was then cooled to 40°C and replaced with an air atmosphere, and the pH of the system was adjusted to 8.0 using an 8% aqueous solution of lithium hydroxide.

[0099] Comparative Example 4 Except for using an aqueous solution containing a water-soluble polymer prepared as follows, an aqueous dispersion containing a particulate polymer, a slurry composition for a heat-resistant layer, a negative electrode, a positive electrode, a separator, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2. <Preparation of aqueous solution containing water-soluble polymer> A 10-L flask equipped with a septum was charged with 6,335 g of ion-exchanged water and 95 g of a 2.0% aqueous solution of L-ascorbic acid (a polymerization accelerator). The flask was heated to 40°C and purged with nitrogen gas at a flow rate of 100 mL / min. Next, 571.5 g (45.0%) of acrylamide (an amide group-containing monomer), 317.5 g (25.0%) of acrylic acid (an acid group-containing monomer), and 381.0 g (30.0%) of N-hydroxyethylacrylamide (a hydroxyl group-containing monomer) were mixed and injected into the flask via syringe. Then, 100 g of a 5.0% aqueous solution of ammonium persulfate (a polymerization initiator) was added to the flask via syringe, and the reaction temperature was set to 60°C. After 2 hours, to further increase the reaction conversion, 50 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 47.5 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After another 2 hours, 50 g of a 5.0% aqueous solution of ammonium persulfate as a polymerization initiator and 47.5 g of a 2.0% aqueous solution of L-ascorbic acid as a polymerization accelerator were added. After 2 hours, 34 g of a 5% aqueous solution of sodium nitrite as a reaction terminator was added to the flask and stirred. The flask was then cooled to 40°C and an air atmosphere was created, and the pH of the system was adjusted to 8.0 using an 8% aqueous solution of lithium hydroxide to prepare an aqueous solution containing a water-soluble polymer.

[0100] (Comparative Example 5) The aqueous solution containing the water-soluble polymer, the aqueous dispersion containing the particulate polymer, the slurry composition for the heat-resistant layer, the negative electrode, the positive electrode, the separator, and the lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that the amount of acrylamide as the amide group-containing monomer, the amount of acrylic acid as the acid group-containing monomer, and the amount of N-hydroxyethylacrylamide as the hydroxyl group-containing monomer were changed to 946.15 g (74.5%), 6.35 g (0.5%), and 317.5 g (25.0%), respectively, during the preparation of the aqueous solution containing the water-soluble polymer. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

[0101] In addition, in Tables 1 and 2 shown below, "AAm" indicates an acrylamide unit; "DMAAm" indicates a dimethylacrylamide unit, "MAAm" indicates a methacrylamide unit; "AA" represents an acrylic acid unit; "ATBS" indicates a 2-acrylamido-2-methylpropanesulfonic acid unit; "HEAAm" indicates an N-hydroxyethylacrylamide unit; "HEMA" indicates 2-hydroxyethyl methacrylate units; "HEA" indicates 2-hydroxyethyl acrylate units; "MAN" represents a methacrylonitrile unit; "BA" indicates n-butyl acrylate units; "2EHA" indicates 2-ethylhexyl acrylate units, "MAA" indicates a methacrylic acid unit, "AGE" represents an allyl glycidyl ether unit, "AMA" indicates an allyl methacrylate unit; "AN" indicates an acrylonitrile unit; "ST" indicates a styrene unit; "Al2O3" indicates alumina particles, "BaSO4" refers to barium sulfate particles.

[0102] [Table 1]

[0103] [Table 2]

[0104] Tables 1 and 2 show that in Examples 1 to 18, which used binder compositions containing water-soluble polymers containing amide group-containing monomer units, acid group-containing monomer units, and hydroxyl group-containing monomer units, and in which the content ratios of the amide group-containing monomer units and the acid group-containing monomer units were within the respective specified ranges, slurry compositions with excellent dispersion stability and coatability and heat-resistant layers with excellent heat shrinkage resistance were formed. Furthermore, the heat-resistant layers of Examples 1 to 18 exhibited excellent adhesion to the substrate and were capable of providing secondary batteries with excellent cycle characteristics. On the other hand, in Comparative Example 1, which used a binder composition containing a water-soluble polymer consisting only of amide group-containing monomer units and acid group-containing monomer units, it was found that the dispersion stability and coatability of the slurry composition were not sufficiently ensured. Furthermore, in Comparative Example 2, which used a binder composition containing a water-soluble polymer consisting only of amide group-containing monomer units, the dispersion stability and coatability of the slurry composition were not sufficiently ensured, and it was found that a heat-resistant layer with excellent adhesion to the substrate could not be formed. Furthermore, in Comparative Example 3, which used a binder composition containing a water-soluble polymer in which the content ratios of amide group-containing monomer units and acid group-containing monomer units were outside the specified ranges, it was found that the dispersion stability and coatability of the slurry composition were not sufficiently ensured, and a heat-resistant layer with excellent heat shrinkage resistance could not be formed. Furthermore, in Comparative Example 4, which used a binder composition containing a water-soluble polymer in which the content ratios of amide group-containing monomer units and acid group-containing monomer units were outside the specified ranges, it was found that the dispersion stability of the slurry composition was not sufficiently ensured and a heat-resistant layer with excellent heat shrinkage resistance could not be formed. Furthermore, in Comparative Example 5, which used a binder composition containing a water-soluble polymer with a content ratio of acid group-containing monomer units outside the specified range, it was found that the coating properties of the slurry composition were not sufficiently ensured, and a heat-resistant layer with excellent adhesion to the substrate could not be formed. [Industrial Applicability]

[0105] According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery heat-resistant layer that can prepare a slurry composition for a non-aqueous secondary battery heat-resistant layer that is excellent in dispersion stability and coatability and is capable of forming a non-aqueous secondary battery heat-resistant layer that is excellent in heat shrinkage resistance. Furthermore, according to the present invention, it is possible to provide a slurry composition for a heat-resistant layer of a non-aqueous secondary battery, which can form a heat-resistant layer for a non-aqueous secondary battery that has excellent dispersion stability and coatability, and is also excellent in heat shrinkage resistance. According to the present invention, it is possible to provide a heat-resistant layer for a non-aqueous secondary battery that is excellent in heat shrinkage resistance, and a non-aqueous secondary battery that includes the heat-resistant layer.

Claims

1. A binder composition for a non-aqueous secondary battery heat-resistant layer, comprising a water-soluble polymer and water, the water-soluble polymer comprises an amide group-containing monomer unit, an acid group-containing monomer unit, and a hydroxyl group-containing monomer unit; the water-soluble polymer has a content of the amide group-containing monomer unit of 63% by mass or more and 98% by mass or less, and a content of the acid group-containing monomer unit of 1% by mass or more and 20% by mass or less, the water-soluble polymer has a molar ratio of the content of the hydroxyl group-containing monomer units to the content of the acid group-containing monomer units of 0.70 or more and 5.00 or less.

2. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 1 , wherein the content of the hydroxyl group-containing monomer unit in the water-soluble polymer is 1% by mass or more and 25% by mass or less.

3. 3. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 1, wherein the hydroxyl group-containing monomer unit is a hydroxyl group-containing (meth)acrylamide monomer unit.

4. 4. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 1, wherein the water-soluble polymer has a weight-average molecular weight of 200,000 or more and 2,000,000 or less.

5. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to any one of claims 1 to 4, further comprising a particulate polymer.

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

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

8. A non-aqueous secondary battery comprising the heat-resistant layer for a non-aqueous secondary battery according to claim 7 .

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