Composition for electrochemical device functional layer, functional layer for electrochemical device, laminate for electrochemical device, and electrochemical device

Abstract

Provided is a composition for an electrochemical element functional layer, the composition including: a particulate polymer including a polymer A that includes (meth)acrylic acid ester monomer units and acidic-group-containing monomer units, and a polymer B that is different from said polymer A, the particulate polymer being such that the volume-average particle diameter is greater than 1.0 μm and no greater than 10.0 μm; a binder; and heat-resistant microparticles.

Description

[Technical Field]

[0001] The present invention relates to a composition for a functional layer of an electrochemical device, a functional layer for an electrochemical device, a laminate for an electrochemical device, and an electrochemical device. [Background technology]

[0002] Electrochemical devices such as lithium-ion secondary batteries and electric double-layer capacitors are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications.

[0003] Here, for example, a lithium ion secondary battery generally includes battery components such as a positive electrode, a negative electrode, and a separator that separates the positive electrode from the negative electrode to prevent short-circuiting between the positive electrode and the negative electrode.

[0004] In recent years, further improvements in electrochemical element components such as positive electrodes, negative electrodes, and separators have been investigated with the aim of further improving the performance of lithium-ion secondary batteries. In such improvements, attempts have been made to laminate layers (functional layers) on the separator substrate to exhibit desired functions such as heat resistance and adhesiveness. Specifically, for example, Patent Document 1 discloses a technique for forming, on a separator substrate, a functional layer for electrochemical devices, the functional layer comprising inorganic particles and a particulate polymer, the functional layer having a maximum surface height Sz of a predetermined value or more, and having protrusions containing the particulate polymer on the surface. Patent Document 2, for example, discloses that a secondary battery separator having excellent heat resistance, adhesiveness, and blocking resistance can be obtained by forming, on an organic separator layer, a heat-resistant layer and an adhesive layer containing a particulate polymer having a glass transition temperature of 10 to 100°C. Patent Document 3, for example, discloses a binder composition for a nonaqueous secondary battery porous membrane, the binder composition comprising a particulate polymer A and a particulate polymer B having a volume average particle diameter larger than that of the particulate polymer A, the particulate polymer A containing 50% to 90% by mass of (meth)acrylic acid alkyl ester monomer units, the particulate polymer B having a core-shell structure, and the core portion of the core-shell structure containing a nitrile group-containing monomer unit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 246394 [Patent Document 2] International Publication No. 2013 / 151144 [Patent Document 3] International Publication No. 2018 / 198940 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, from the viewpoint of further improving the manufacturing efficiency of electrochemical elements, functional layers provided on electrochemical element components are required to have both high levels of adhesion between components during the manufacturing process of the electrochemical element (hereinafter also referred to as "process adhesion") and high levels of blocking resistance. Note that the "blocking resistance" of a functional layer refers to the property of suppressing unintentional adhesion (blocking) when the functional layer is laminated with other components during the manufacturing process of the electrochemical element, not for the purpose of adhesion.

[0007] However, when a functional layer is formed according to the above-mentioned conventional techniques, it has not been possible to achieve both sufficiently high levels of process adhesion and blocking resistance in the resulting functional layer.

[0008] Therefore, an object of the present invention is to provide a composition for an electrochemical device functional layer that can provide a functional layer having both sufficiently high process adhesion and blocking resistance. Another object of the present invention is to provide a functional layer for an electrochemical device that has excellent process adhesion and blocking resistance, a laminate for an electrochemical device that includes such a functional layer for an electrochemical device, and an electrochemical device that includes such a laminate for an electrochemical device. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to achieve the above object, and have newly discovered that a functional layer formed using a composition for an electrochemical device functional layer, which comprises a particulate polymer A containing (meth)acrylic acid ester monomer units and acidic group-containing monomer units, a polymer B which is different from polymer A, and which has a volume average particle diameter of more than 1.0 μm and not more than 10.0 μm, a binder, and heat-resistant fine particles, has excellent process adhesion and blocking resistance, and have completed the present invention.

[0010] The present invention has an object to advantageously solve the above-mentioned problems, and provides a composition for an electrochemical device functional layer comprising a particulate polymer, a binder, and heat-resistant fine particles, wherein the particulate polymer comprises polymer A and polymer B, polymer A is a polymer containing (meth)acrylic acid ester monomer units and acidic group-containing monomer units, polymer B is a polymer having a different composition from polymer A, and the particulate polymer has a volume average particle diameter of more than 1.0 μm and not more than 10.0 μm. Thus, a composition for an electrochemical device functional layer comprising polymer A containing (meth)acrylic acid ester monomer units and acidic group-containing monomer units and polymer B, and a particulate polymer having a volume average particle diameter within a predetermined range, a binder, and heat-resistant fine particles, enables the formation of a functional layer with excellent process adhesion and blocking resistance. In this specification, "(meth)acrylic" means acrylic or methacrylic. In this specification, the volume average particle diameter of particles refers to the particle diameter D50 at which the cumulative volume calculated from the smallest diameter side by laser diffraction method becomes 50%, and can be measured by the method described in the examples. In addition, in this specification, when a polymer "contains a monomer unit," it means that "a polymer obtained using that monomer contains a structural unit derived from the monomer."

[0011] In the composition for an electrochemical device functional layer of the present invention, the acidic group-containing monomer unit of the polymer A is preferably a (meth)acrylic acid monomer unit. When the acidic group-containing monomer unit of the polymer A is a (meth)acrylic acid monomer unit, a functional layer having even more excellent process adhesion and blocking resistance can be formed.

[0012] In the composition for an electrochemical device functional layer of the present invention, the glass transition temperature of the polymer A is preferably 60° C. or higher and 85° C. or lower. When the glass transition temperature of the polymer A is within the above range, a functional layer having even more excellent process adhesion and blocking resistance can be formed. The glass transition temperature of the polymer can be measured according to the method described in the examples of this specification.

[0013] In the composition for an electrochemical device functional layer of the present invention, the acid value of the polymer A is preferably 0.5 mgKOH / g or more and 7 mgKOH / g or less. When the acid value of the polymer A is 0.5 mgKOH / g or more and 7 mgKOH / g or less, the slurry stability of the composition for a functional layer is improved, and the process adhesion and blocking resistance of the resulting functional layer can be further improved. The acid value of polymer A can be measured according to the method described in the examples of this specification.

[0014] In the composition for an electrochemical device functional layer of the present invention, the weight-average molecular weight of the polymer A is preferably 5,000 or more and 100,000 or less. When the weight-average molecular weight of the polymer A is 5,000 or more and 100,000 or less, a functional layer having even more excellent process adhesion and blocking resistance can be formed. The weight average molecular weight of polymer A can be measured according to the method described in the examples.

[0015] In the composition for an electrochemical device functional layer of the present invention, the particulate polymer preferably contains, based on the particulate polymer, 0.1 mass % to 10 mass % of the polymer A. When the proportion of the polymer A in the particulate polymer is within the above range, the slurry stability of the composition for a functional layer is improved, and the process adhesion and blocking resistance of the resulting functional layer can be further improved.

[0016] In the composition for an electrochemical device functional layer of the present invention, the polymer B preferably contains an aromatic vinyl monomer unit. When the polymer B contains an aromatic vinyl monomer unit, the process adhesion of the resulting functional layer can be further improved.

[0017] In the composition for an electrochemical device functional layer of the present invention, the heat-resistant fine particles are preferably inorganic fine particles, and the volume average particle diameter of the inorganic fine particles is preferably 2% to 25% of the volume average particle diameter of the particulate polymer. When the volume average particle diameter of the inorganic fine particles as the heat-resistant fine particles is 2% to 25% of the volume average particle diameter of the particulate polymer, a functional layer having excellent heat shrinkage resistance can be formed, and the output characteristics of the resulting electrochemical device can be improved.

[0018] In the composition for an electrochemical device functional layer of the present invention, the binder is preferably a polymer containing a (meth)acrylic acid ester monomer unit, the polymer having a different composition from that of the polymer A and the polymer B. If the binder is a polymer containing a (meth)acrylic acid ester monomer unit, the process adhesion of the functional layer can be further improved, and the electrochemical properties of the resulting electrochemical device can be improved.

[0019] The present invention also aims to advantageously solve the above-mentioned problems, and provides a functional layer for an electrochemical device, characterized in that it is formed using any one of the compositions for an electrochemical device functional layer described above. As described above, the functional layer formed using the composition for an electrochemical device functional layer of the present invention has excellent process adhesion and blocking resistance.

[0020] Preferably, the functional layer for electrochemical devices of the present invention has a structure in which the particulate polymer is partially embedded in a heat-resistant fine particle layer containing the heat-resistant fine particles, and the ratio of the volume average particle diameter of the particulate polymer to the thickness of the heat-resistant fine particle layer is 1.0 to 5.0. When the ratio of the volume average particle diameter of the particulate polymer to the thickness of the heat-resistant fine particle layer is 1.0 to 5.0, the process adhesion of the functional layer can be improved. The ratio of the volume average particle diameter of the particulate polymer to the thickness of the heat-resistant fine particle layer can be measured according to the method described in the examples of this specification.

[0021] The composition for an electrochemical device functional layer of the present invention may further contain, as the heat-resistant fine particles, organic fine particles having a volume average particle diameter of 50% to 150% of the volume average particle diameter of the particulate polymer, and having a glass transition temperature or melting point not exceeding 150° C. or not exceeding 200° C. If the composition for a functional layer further contains the specified organic fine particles, the blocking resistance of the resulting functional layer can be further improved.

[0022] In the composition for an electrochemical device functional layer of the present invention, the blending amount of the organic fine particles is preferably 20 parts by mass or more and 1,000 parts by mass or less relative to the particulate polymer. When the blending amount of the organic fine particles is within the above range, the blocking resistance and process adhesion of the resulting functional layer can be further improved.

[0023] In a functional layer for electrochemical devices formed using the composition for functional layer of the present invention, which contains organic fine particles as heat-resistant fine particles, the functional layer has a structure in which the particulate polymer and some of the organic fine particles as the heat-resistant fine particles are embedded in a heat-resistant fine particle layer containing the heat-resistant fine particles, and the ratio of the volume average particle diameter of the particulate polymer to the thickness of the heat-resistant fine particle layer is preferably 1.0 or more and 5.0 or less. A functional layer for electrochemical devices that satisfies these conditions has excellent blocking resistance while maintaining good process adhesion.

[0024] The present invention also aims to advantageously solve the above-mentioned problems, and provides a laminate for electrochemical devices comprising a substrate and a functional layer formed on the substrate using any one of the compositions for electrochemical device functional layers described above. Thus, a laminate for electrochemical devices comprising a functional layer formed using the composition for electrochemical device functional layers of the present invention has excellent process adhesion and blocking resistance.

[0025] The present invention has an object to advantageously solve the above-mentioned problems, and an electrochemical device of the present invention is characterized by including the above-mentioned laminate for electrochemical devices. An electrochemical device including the laminate for electrochemical devices of the present invention has excellent electrochemical properties. [Effects of the Invention]

[0026] According to the present invention, it is possible to provide a composition for an electrochemical device functional layer, which can provide a functional layer having both sufficiently high process adhesion and blocking resistance. Furthermore, according to the present invention, it is possible to provide a functional layer for an electrochemical device that has excellent process adhesion and blocking resistance, a laminate for an electrochemical device that includes such a functional layer for an electrochemical device, and an electrochemical device that includes such a laminate for an electrochemical device. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of the present invention will be described in detail. Here, the composition for an electrochemical device functional layer of the present invention (hereinafter also simply referred to as "functional layer composition") is used to form the functional layer for an electrochemical device of the present invention (hereinafter also simply referred to as "functional layer"). The laminate for an electrochemical device of the present invention comprises the functional layer of the present invention. Furthermore, the electrochemical device of the present invention is an electrochemical device comprising at least the laminate for an electrochemical device of the present invention.

[0028] (Composition for electrochemical device functional layer) The composition for an electrochemical device functional layer of the present invention contains a predetermined particulate polymer, a binder, and heat-resistant fine particles, and may further contain other components. By using the composition for a functional layer of the present invention, the resulting functional layer can achieve both sufficiently high levels of process adhesion and blocking resistance.

[0029] <Particulate polymer> As described in detail below, the particulate polymer contained in the functional layer composition includes polymer A containing (meth)acrylic acid ester monomer units and acidic group-containing monomer units, and polymer B having a different composition from polymer A, and the volume average particle diameter is within a predetermined range. After bonding components together via a functional layer formed using the functional layer composition, the particulate polymer may be in a particulate form or any other shape. The presence of polymer A and polymer B contained in the particulate polymer can be confirmed, for example, by detecting two peaks or shoulders when the functional layer composition is analyzed by GPC (Gel Permeation Chromatography).

[0030] <<Polymer A>> Polymer A is required to contain (meth)acrylic acid ester monomer units and acidic group-containing monomer units, and may optionally contain other monomer units. That is, polymer A is required to contain both or at least one of acrylic acid ester monomer units and methacrylic acid ester monomer units, and also to contain acidic group-containing monomer units. By containing these predetermined monomer units, polymer A can form a functional layer that is excellent in process adhesion and blocking resistance.

[0031] [(Meth)acrylic acid ester monomer unit] Examples of (meth)acrylic acid ester monomers that can form the (meth)acrylic acid ester monomer unit include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylates such as n-butyl acrylate and t-butyl acrylate, octyl acrylates such as pentyl acrylate, hexyl acrylate, heptyl acrylate and 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate. alkyl esters; and methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, butyl methacrylates such as n-butyl methacrylate and t-butyl methacrylate, octyl methacrylates such as pentyl methacrylate, hexyl methacrylate, heptyl methacrylate and 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, and other methacrylic acid alkyl esters. Among these, n-butyl acrylate, 2-ethylhexyl acrylate, and methyl methacrylate are preferred. These (meth)acrylic acid ester monomers may be used singly or in combination of two or more kinds in any ratio.

[0032] The content of (meth)acrylic acid ester monomer units in polymer A is preferably 5% by mass or more, more preferably 50% by mass or more, and preferably 99.9% by mass or less, based on 100% by mass of all repeating units contained in polymer A. If the content of (meth)acrylic acid ester monomer units in polymer A is equal to or greater than the above-mentioned lower limit, the process adhesion of the resulting functional layer can be further improved. If the content of (meth)acrylic acid ester monomer units is equal to or less than the above-mentioned upper limit, the slurry stability can be increased.

[0033] [Acidic group-containing monomer unit] Examples of acidic group-containing monomers that can be used to form the acidic group-containing monomer units include monomers having a carboxylic acid group, monomers having a sulfonic acid group, monomers having a phosphoric acid group, and monomers having a hydroxyl group. Among these, the acidic group-containing monomer units of polymer A are preferably monomer units having a carboxylic acid group, and more preferably (meth)acrylic acid monomer units. When the acidic group-containing monomer units of polymer A are monomer units having a carboxylic acid group, particularly (meth)acrylic acid monomer units, a functional layer having even more excellent process adhesion and blocking resistance can be formed.

[0034] Examples of the monomer having a carboxylic acid group include monocarboxylic acids and dicarboxylic acids. Examples of the monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of the dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and p-styrenesulfonic acid, as well as salts thereof. In this specification, "(meth)allyl" means allyl and / or methallyl, and "(meth)acrylic" means acrylic and / or methacrylic. Furthermore, examples of the monomer having a phosphate group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate. In this specification, the term "(meth)acryloyl" means acryloyl and / or methacryloyl. Examples of the monomer having a hydroxyl group include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate. These acidic group-containing monomers may be used alone or in combination of two or more kinds in any ratio.

[0035] The content of the acidic group-containing monomer units in polymer A is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, based on 100% by mass of all repeating units contained in polymer A. If the content of the acidic group-containing monomer units in polymer A is equal to or greater than the above-mentioned lower limit, the slurry stability of the functional layer composition can be improved, and the blocking resistance of the resulting functional layer can be further improved. Furthermore, if the content of the acidic group-containing monomer units in polymer A is equal to or less than the above-mentioned upper limit, the stability during the preparation of the particulate polymer can be improved.

[0036] [Other monomer units] The monomer that can be used to constitute the other monomer unit is not particularly limited, and for example, an aromatic vinyl monomer described below can be used as a monomer that can be used to form an [aromatic vinyl monomer unit] that can be contained in polymer B.

[0037] The content of the other monomer units in polymer A is not particularly limited, but is preferably 95% by mass or less, assuming that the total repeating units contained in polymer A is 100% by mass. Alternatively, it may be 0% by mass, i.e., polymer A may not contain any other monomer units.

[0038] <<Glass transition temperature of polymer A>> The glass transition temperature of polymer A is preferably 60°C or higher, more preferably 70°C or higher, and preferably 85°C or lower, more preferably 77°C or lower. When the glass transition temperature of polymer A is equal to or higher than the above lower limit, the blocking resistance of the resulting functional layer can be improved. When the glass transition temperature of polymer A is equal to or lower than the above upper limit, the process adhesion of the resulting functional layer can be further improved. The glass transition temperature of the polymer A can be adjusted by changing the composition of the polymer A.

[0039] <<Acid value of polymer A>> The acid value of polymer A is preferably 0.5 mgKOH / g or more, more preferably 1.0 mgKOH / g or more, even more preferably 1.5 mgKOH / g or more, and preferably 7.0 mgKOH / g or less, more preferably 6.0 mgKOH / g or less, and even more preferably 4.0 mgKOH / g or less. If the acid value of polymer A is equal to or greater than the above-mentioned lower limit, the slurry stability of the functional layer composition can be improved, and the blocking resistance and process adhesion of the resulting functional layer can be further improved. If the acid value of polymer A is equal to or less than the above-mentioned upper limit, the stability of the particulate polymer can be improved. The acid value of polymer A can be controlled based on the blending ratio of the acidic group-containing monomer unit blended when preparing polymer A.

[0040] <<Weight average molecular weight of polymer A>> The weight-average molecular weight of polymer A is preferably 5,000 or more, more preferably 6,000 or more, and even more preferably 7,000 or more, and is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 45,000. If the weight-average molecular weight of polymer A is equal to or greater than the above-mentioned lower limit, the blocking resistance of the functional layer can be further improved. If the weight-average molecular weight of polymer A is equal to or less than the above-mentioned upper limit, the process adhesion of the functional layer can be further improved. The weight-average molecular weight of polymer A can be controlled based on the composition ratio of the monomers added during polymerization of polymer A, the amount of polymerization initiator, and the like.

[0041] <<Polymer A content>> The content of polymer A in the particulate polymer is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.5% by mass or more, and preferably 10% by mass or less, more preferably 8.0% by mass or less, and even more preferably 5.0% by mass or less, based on the particulate polymer. When the content of polymer A is equal to or greater than the lower limit, the slurry stability of the functional layer composition can be improved and the blocking resistance of the functional layer can be further improved. When the content of polymer A is equal to or less than the upper limit, the process adhesion of the functional layer can be further improved.

[0042] <<Polymer B>> Polymer B is a polymer having a different composition from the above-mentioned polymer A. The composition of polymer B is not particularly limited as long as it is different from that of polymer A. Polymer B may contain, for example, aromatic vinyl monomer units, as well as other monomer units that may include (meth)acrylic acid ester monomer units and crosslinkable monomer units. In particular, from the viewpoint of further improving the process adhesion of the resulting functional layer, it is preferable that polymer B contains aromatic vinyl monomer units.

[0043] [Aromatic vinyl monomer unit] The aromatic vinyl monomer that can be used to form the aromatic vinyl monomer unit is not particularly limited, and examples thereof include styrene, α-methylstyrene, butoxystyrene, vinylnaphthalene, etc. Among these, styrene is preferred. These aromatic vinyl monomers may be used alone or in combination of two or more at any ratio.

[0044] The content of aromatic vinyl monomer units in polymer B is preferably 20% by mass or more, preferably 90% by mass or less, and more preferably 85% by mass or less, based on 100% by mass of all repeating units contained in polymer B. When the content of aromatic vinyl monomer units in polymer B is within the above range, good adhesion between the functional layer and the substrate can be achieved.

[0045] [(Meth)acrylic acid ester monomer unit] Examples of (meth)acrylic acid ester monomers that can form (meth)acrylic acid ester monomer units include those mentioned above. Among them, octyl acrylates such as 2-ethylhexyl acrylate are preferred. These (meth)acrylic acid ester monomers may be used alone or in combination of two or more in any ratio.

[0046] The content of the (meth)acrylic acid ester monomer units in polymer B is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 80% by mass or less, and more preferably 75% by mass or less, based on 100% by mass of all repeating units contained in polymer B. When the content of the (meth)acrylic acid ester monomer units in polymer B is equal to or greater than the above-mentioned lower limit, the glass transition temperature of polymer B can be prevented from decreasing excessively, and the blocking resistance of the resulting functional layer can be improved. When the content of the (meth)acrylic acid ester monomer units is equal to or less than the above-mentioned upper limit, the adhesion between the functional layer and the substrate can be improved.

[0047] [Crosslinkable monomer unit] Examples of monomers capable of forming crosslinkable monomer units include polyfunctional monomers having two or more polymerization reactive groups. Examples of such polyfunctional monomers include divinyl compounds such as allyl methacrylate and divinylbenzene; di(meth)acrylic acid ester compounds such as diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, and 1,3-butylene glycol diacrylate; tri(meth)acrylic acid ester compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate; and ethylenically unsaturated monomers containing epoxy groups such as allyl glycidyl ether and glycidyl methacrylate. These may be used alone or in combination of two or more. Among these, ethylene glycol dimethacrylate is preferred.

[0048] The content of the crosslinkable monomer unit in polymer B is preferably 0.05% by mass or more and 2% by mass or less, with the total mass of all repeating units contained in polymer B being 100% by mass. When the content of the crosslinkable monomer unit in polymer B is within the above range, the process adhesion of the resulting functional layer can be improved.

[0049] [Monomer units other than those listed above] Examples of monomers that can be used to form monomer units other than those mentioned above (in other words, monomer units other than aromatic vinyl monomer units, (meth)acrylic acid ester monomer units, and crosslinkable monomer units) include acidic group-containing monomers.

[0050] The acidic group-containing monomer that can be used to form the acidic group-containing monomer unit is not particularly limited, and the above-mentioned monomers can be used.

[0051] The content of the other monomer units in polymer B is not particularly limited, but is preferably 10% by mass or less, assuming that the total repeating units contained in polymer A is 100% by mass of the other monomer units. Alternatively, it may be 0% by mass, i.e., polymer A may not contain any other monomer units.

[0052] In particular, it is preferable that polymer B does not contain any acidic group-containing monomer units, or if it does contain any, the content of the acidic group-containing monomer units is less than 0.1 mass %. If the content of the acidic group-containing monomer units in polymer B is equal to or less than the above upper limit, the stability during production of the particulate polymer can be improved.

[0053] <<Glass transition temperature of polymer B>> The glass transition temperature of polymer B is preferably 20°C or higher, more preferably 30°C or higher, even more preferably 40°C or higher, even more preferably 45°C or higher, and is preferably 100°C or lower, more preferably 80°C or lower, and even more preferably 70°C or lower. When the glass transition temperature of polymer B is at least the above lower limit, the blocking resistance of the resulting functional layer can be improved. Furthermore, when the glass transition temperature of polymer B is at most the above upper limit, the process adhesion of the resulting functional layer can be further improved. The "glass transition temperature" of polymer B can be measured according to the method described in the Examples. The glass transition temperature of polymer B can be adjusted by changing the composition of polymer B. More specifically, for example, the glass transition temperature of polymer B can be increased by increasing the amount of crosslinkable monomer units used in preparing polymer B.

[0054] <<Acid value of polymer B>> The acid value of polymer B is preferably lower than that of polymer A, more specifically, preferably less than 0.5 mgKOH / g. There is no particular limitation on the lower limit of the acid value of polymer B. If the acid value of polymer B is lower than that of polymer A, the slurry stability of the functional layer composition can be improved, and the blocking resistance and process adhesion of the resulting functional layer can be further improved.

[0055] <<Structure of particulate polymer>> The particulate polymer preferably has a structure in which polymer A is unevenly distributed on the surface side relative to the center side. Such a structure is not particularly limited, as long as the frequency of polymer A is higher on the surface side than on the center side of the particulate polymer. If polymer A is unevenly distributed on the surface side of the particulate polymer, the slurry stability of the functional layer composition can be improved, and the process adhesion and blocking resistance of the resulting functional layer can be further improved. The reason for this is unclear, but it is presumed that if polymer A is unevenly distributed on the surface side of the particulate polymer, a relatively large amount of polymer A containing acidic group-containing monomer units is present on the surface of the particulate polymer, which can cause electrostatic repulsion between the particulate polymers. This is thought to make the particulate polymers less likely to aggregate and settle in the functional layer composition, thereby improving slurry stability. Furthermore, when a functional layer is formed, the presence of particulate polymers with a volume average particle diameter of 1.0 μm or more on the surface of the functional layer is thought to make it less likely for the functional layers to block each other due to the electrostatic repulsion between the particulate polymers when multiple functional layers are placed in contact with each other.

[0056] In one example, the particulate polymer may have a core-shell structure comprising a core portion and a shell portion covering at least a portion of the outer surface of the core portion. The "core-shell structure" of the particulate polymer can be confirmed by observing the particulate polymer using a scanning electron microscope. Here, the shell portion may entirely or partially cover the outer surface of the core portion. Furthermore, when the particulate polymer has a core-shell structure, it is preferable that the shell portion is made of polymer A. In this case, it is also preferable that the core portion is made of polymer B. If the particulate polymer is a core-shell polymer having a shell portion made of polymer A, it is considered that the slurry stability of the functional layer composition is improved and the process adhesion and blocking resistance of the obtained functional layer can be further improved.

[0057] <<Volume average particle size of particulate polymer>> The particulate polymer must have a volume average particle diameter of 1.0 μm or more and 10.0 μm or less, preferably 2.0 μm or more, more preferably 2.5 μm or more, even more preferably 3.0 μm or more, preferably 9.0 μm or less, more preferably 8.0 μm or less, and even more preferably 7.5 μm or less. When the volume average particle diameter of the particulate polymer is within the above range, the process adhesiveness of the resulting functional layer can be further improved. Although the reason for this is unclear, when the volume average particle diameter of the particulate polymer is equal to or greater than the above lower limit, a portion of the particulate polymer can be protruded from the surface of the functional layer, thereby improving the process adhesiveness of the functional layer surface. Furthermore, when the volume average particle diameter of the particulate polymer is equal to or less than the above upper limit, the particulate polymer can be prevented from falling off the functional layer during formation, thereby improving the process adhesiveness of the resulting functional layer. The volume average particle size of the particulate polymer can be adjusted, for example, by changing the type and amount of metal hydroxide used when preparing the particulate polymer.

[0058] [Preparation of particulate polymer] The particulate polymer can be prepared by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous solvent such as water. Here, the proportion of each monomer in the monomer composition is usually the same as the proportion of each monomer unit in the particulate polymer.

[0059] The polymerization method is not particularly limited, and any of methods such as suspension polymerization, emulsion polymerization aggregation, and pulverization can be used. Among them, from the viewpoint of simplicity and cost-effectiveness, suspension polymerization and emulsion polymerization aggregation are preferred, and suspension polymerization is more preferred. Furthermore, any of reactions such as radical polymerization and living radical polymerization can be used as the polymerization reaction.

[0060] [Other compounding agents] Further, the monomer composition used in preparing the particulate polymer may contain other additives such as a chain transfer agent, a polymerization regulator, a polymerization reaction retarder, a reactive fluidizing agent, a filler, a flame retardant, an antioxidant, and a colorant in any blending amount.

[0061] Here, as an example, a method for preparing a particulate polymer by suspension polymerization will be described. According to the polymerization method exemplified below, a particulate polymer having a structure in which polymer A is unevenly distributed on the surface side can be efficiently produced.

[0062] [Preparation of particulate polymers by suspension polymerization] (1) Preparation of Polymer A and Preparation of Monomer Composition of Polymer B First, polymer A is prepared by polymerizing polymer A according to a standard method. Also, a monomer composition (B) having a composition corresponding to the composition of polymer B is prepared. At this time, various monomers are blended according to the composition of polymer B, and further, other blending ingredients are added as necessary. (2) Droplet formation Next, a colloidal dispersion containing a dispersion stabilizer is prepared, and the polymer A and monomer composition (B) obtained above are added thereto, followed by the addition of a polymerization initiator to form a mixed liquid, and mixed droplets containing the polymer A and the monomer composition (B) are formed in the colloidal dispersion containing the dispersion stabilizer. Here, the method for forming the mixed droplets is not particularly limited, and examples thereof include a method of shear stirring using a disperser such as an emulsifying disperser.

[0063] Examples of the polymerization initiator used in this case include oil-soluble polymerization initiators such as t-butylperoxy-2-ethylhexanoate and azobisisobutyronitrile, etc. Examples of the dispersion stabilizer include metal oxides such as magnesium hydroxide, and sodium dodecylbenzenesulfonate.

[0064] (3) Polymerization After the mixed droplets are formed, the temperature of the water containing the formed mixed droplets is raised to initiate polymerization. The polymerization is continued until the polymerization conversion rate is sufficiently increased, thereby forming a particulate polymer in the water. The polymerization reaction temperature is preferably 50°C or higher and 95°C or lower. The polymerization reaction time is preferably 1 hour or higher and 10 hours or lower, preferably 8 hours or lower, and more preferably 6 hours or lower.

[0065] (4) Washing, filtering, dehydration and drying process After the polymerization is completed, the water containing the particulate polymer is washed, filtered, and dried in a conventional manner to obtain the particulate polymer.

[0066] <Binding material> The binder binds the heat-resistant particles together in the functional layer. Examples of binders include known polymers used as binders, such as conjugated diene polymers, acrylic polymers, polyvinylidene fluoride (PVDF), and polyvinyl alcohol (PVOH). One binder may be used alone, or two or more binders may be used in combination. Preferred binders are water-insoluble polymers that are dispersible in a dispersion medium such as water, such as conjugated diene polymers, acrylic polymers, and polyvinylidene fluoride (PVDF). Conjugated diene polymers and acrylic polymers are more preferred, and acrylic polymers containing (meth)acrylic acid ester monomer units are even more preferred. When the binder is an acrylic polymer containing (meth)acrylic acid ester monomer units, the process adhesion of the functional layer can be further improved, and the electrochemical properties of the resulting electrochemical device can be improved. In the present invention, a polymer 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. These binders may be used singly or in combination of two or more kinds in any ratio.

[0067] Here, the conjugated diene polymer refers to a polymer containing conjugated diene monomer units. Specific examples of the conjugated diene polymer 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), acrylic rubber (NBR) (copolymers containing acrylonitrile units and butadiene units), and hydrogenated products thereof.

[0068] The acrylic polymer that can be preferably used as the binder is not particularly limited, and examples thereof include a polymer containing the above-mentioned crosslinkable monomer unit, a (meth)acrylic acid ester monomer unit, and an acidic group-containing monomer unit.

[0069] The proportion of (meth)acrylic acid ester monomer units in the acrylic polymer is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 58% by mass or more, and preferably 98% by mass or less, more preferably 97% by mass or less, even more preferably 96% by mass or less. By making the proportion of (meth)acrylic acid ester monomer units equal to or greater than the lower limit of the above range, the process adhesion of the functional layer can be improved. On the other hand, by making it equal to or less than the upper limit, the electrochemical properties of an electrochemical device including the functional layer can be further improved.

[0070] The proportion of crosslinkable monomer units in the acrylic polymer is preferably 0.1% by mass or more, more preferably 1.0% by mass or more, and preferably 3.0% by mass or less, more preferably 2.5% by mass or less. By making the proportion of crosslinkable monomer units equal to or greater than the above limit, the electrochemical properties of an electrochemical device including a functional layer can be further improved. By making the proportion of crosslinkable monomer units equal to or less than the above upper limit, the adhesiveness of the functional layer can be increased.

[0071] The proportion of the acid group-containing monomer units in the acrylic polymer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. By making the proportion of the acid group-containing monomer units equal to or greater than the above-mentioned lower limit, the dispersibility of the binder in the functional layer composition and in the functional layer can be improved, and the electrochemical properties of an electrochemical device including the functional layer can be sufficiently improved. Furthermore, by making the proportion of the acid group-containing monomer units equal to or less than the above-mentioned upper limit, the amount of residual moisture in the functional layer can be reduced, and the electrochemical properties of an electrochemical device can be sufficiently improved.

[0072] The acrylic polymer may contain other monomer units.

[0073] <<Glass transition temperature of binder>> The glass transition temperature (Tg) of the binder is preferably -100°C or higher, more preferably -90°C or higher, even more preferably -80°C or higher, and preferably less than 30°C, more preferably 20°C or lower, and even more preferably 15°C or lower. If the glass transition temperature of the binder is above the lower limit, the adhesiveness and strength of the functional layer can be increased. On the other hand, if the glass transition temperature of the binder is below the upper limit, the flexibility of the functional layer can be increased.

[0074] [Binder content] The content of the binder is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.5 parts by mass or more, and preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the heat-resistant fine particles. If the content of the binder is equal to or greater than the lower limit, the particulate polymer can be sufficiently prevented from falling off the functional layer, and the adhesiveness of the functional layer can be sufficiently increased. On the other hand, if the content of the binder is equal to or less than the upper limit, a decrease in the ionic conductivity of the functional layer can be suppressed, and a decrease in the rate characteristics of the electrochemical device can be suppressed.

[0075] The binder is not particularly limited and can be prepared, for example, by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous solvent such as water. Here, the ratio of each monomer in the monomer composition is usually the same as the ratio of each monomer unit in the binder.

[0076] The polymerization method and polymerization reaction are not particularly limited, and for example, the polymerization methods and polymerization reactions exemplified above as the polymerization methods for the particulate polymer can be used.

[0077] Furthermore, the binder may be in a particulate or non-particulate form, but from the viewpoint of effectively preventing the components contained in the functional layer from falling off, it is preferable that the binder be in a particulate form.

[0078] When the binder is particulate, the volume average particle diameter of the binder may be, for example, 0.1 μm or more and 0.5 μm or less. If the volume average particle diameter of the binder is within this range, the heat shrinkage resistance and process adhesion of the resulting functional layer and the output characteristics of the resulting secondary battery can be further improved.

[0079] <<Heat-resistant fine particles>> Here, the heat-resistant fine particles contained in the functional layer are not particularly limited, and examples thereof include fine particles made of inorganic materials (i.e., inorganic fine particles) and fine particles made of organic materials (i.e., organic fine particles) that are stable and electrochemically stable in the environment in which the electrochemical element is used. As the heat-resistant fine particles, inorganic fine particles and organic fine particles may be used alone, but it is preferable to use inorganic fine particles and organic fine particles in combination.

[0080] [Inorganic fine particles] Examples of inorganic fine 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; and clay fine particles such as talc and montmorillonite. These particles may be subjected to element substitution, surface treatment, solid solution formation, etc., as necessary. The inorganic fine particles may be used singly or in combination of two or more.

[0081] [Organic fine particles] Unlike the above-mentioned specific particulate polymer and binder, the organic fine particles are fine particles made of a polymer that does not have adhesive properties. Examples of organic fine particles include various crosslinked polymer particles such as crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked products, polystyrene, polyimide, polyamide, polyamideimide, melamine resin, phenolic resin, and benzoguanamine-formaldehyde condensate; heat-resistant polymer particles such as polysulfone, polyacrylonitrile, polyaramid, polyacetal, and thermoplastic polyimide; and modified products and derivatives thereof. The organic fine particles may be used alone or in combination of two or more. Preferred organic fine particles are crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, and styrene-divinylbenzene copolymer crosslinked products. That is, it is preferred that the organic fine particles contain a crosslinkable monomer unit. The crosslinkable monomer unit is not particularly limited, and the above-mentioned units can be used. Among these, ethylene glycol dimethacrylate units are preferred as the crosslinkable monomer units contained in the organic fine particles. The content of the crosslinkable monomer units in the organic fine particles is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, and may be 100% or 95% by mass or less, assuming that the total repeating units contained in the organic fine particles is 100% by mass. If the content of the crosslinkable monomer units contained in the organic fine particles is equal to or more than the above lower limit, the blocking resistance of the resulting functional layer can be improved.

[0082] As described above, the organic fine particles are composed of a polymer that does not have adhesive properties. Specifically, when the polymer that constitutes the organic fine particles has a glass transition temperature, the glass transition temperature is preferably 150°C or higher, more preferably above 200°C. Additionally or alternatively, the polymer that constitutes the organic fine particles preferably does not have a glass transition temperature or melting point in a temperature range of 200°C or lower. To determine whether a functional layer composition contains organic fine particles as heat-resistant fine particles in addition to the particulate polymer that is an essential component of the present invention, the functional layer composition is heated for a predetermined time (e.g., at 100°C for 30 minutes) to a temperature higher than the glass transition temperatures of polymer A and polymer B that constitute the particulate polymer. Then, when the particle diameter is measured according to the volume average particle diameter measurement method described in the Examples of this specification, whether a peak is detected or not can be verified.

[0083] When the content of the organic fine particles is equal to or greater than the lower limit, the blocking resistance of the resulting functional layer can be further improved. When the content of the organic fine particles is equal to or less than the upper limit, the process adhesion of the resulting functional layer can be further improved.

[0084] Among the heat-resistant fine particles described above, from the viewpoint of further improving the heat resistance of the functional layer, it is preferable to contain inorganic fine particles, and it is even more preferable to contain at least one of particles made of alumina (alumina particles), particles made of boehmite (boehmite particles), particles made of barium sulfate (barium sulfate particles), and particles made of magnesium hydroxide (magnesium hydroxide particles).

[0085] [Properties of heat-resistant particles] The inorganic fine particles serving as heat-resistant fine particles preferably have a volume-average particle diameter of 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.25 μm or more, and preferably 1.5 μm or less, more preferably 1.0 μm or less, and even more preferably 0.8 μm or less. When the volume-average particle diameter of the inorganic fine particles serving as heat-resistant fine particles is 0.1 μm or more, a decrease in the ionic conductivity of the functional layer due to excessively dense packing of the inorganic fine particles serving as heat-resistant fine particles in the functional layer can be suppressed, allowing the electrochemical device to exhibit excellent rate characteristics. On the other hand, when the volume-average particle diameter of the inorganic fine particles serving as heat-resistant fine particles is 1.5 μm or less, even when the functional layer is thinned, the device component comprising a laminate including the functional layer can fully exhibit excellent heat resistance. Therefore, the capacity of the electrochemical device can be increased while ensuring sufficient heat resistance of the device component. Furthermore, the organic fine particles serving as heat-resistant fine particles preferably have a volume average particle diameter of 3.0 μm or more, more preferably 4.0 μm or more, even more preferably 5.0 μm or more, and preferably 12.0 μm or less, and more preferably 10.0 μm or less. If the volume average particle diameter of the organic particles serving as heat-resistant fine particles is equal to or greater than the above-mentioned lower limit, the blocking resistance of the resulting functional layer can be further improved. If the volume average particle diameter of the organic particles serving as heat-resistant fine particles is equal to or less than the above-mentioned upper limit, the process adhesion of the resulting functional layer can be improved.

[0086] <Volume average particle size ratio of heat-resistant fine particles to particulate polymer> The volume average particle diameter of the inorganic fine particles as heat-resistant fine particles is preferably 2% or more, more preferably 2.5% or more, and even more preferably 3% or more, and preferably 25% or less, more preferably 20% or less, and even more preferably 15% or less, of the volume average particle diameter of the particulate polymer described above. When the ratio of the volume average particle diameters of the inorganic fine particles as heat-resistant fine particles to the particulate polymer is equal to or greater than the lower limit, an increase in the internal resistance of the resulting electrochemical device can be suppressed, thereby improving the rate characteristics. Furthermore, when the ratio of the volume average particle diameters of the inorganic fine particles as heat-resistant fine particles to the particulate polymer is equal to or less than the upper limit, the heat shrinkage resistance of the functional layer can be further improved. Furthermore, the volume average particle diameter of the organic fine particles as heat-resistant fine particles is preferably 50% or more, more preferably 70% or more, and preferably 150% or less, and more preferably 130% or less, of the volume average particle diameter of the particulate polymer described above. If the ratio of the volume average particle diameters of the organic fine particles as heat-resistant fine particles to the particulate polymer is equal to or greater than the above-mentioned lower limit, the deformation of the particulate polymer protruding from the surface of the functional layer can be suppressed, thereby further improving the blocking resistance of the resulting functional layer. If the ratio of the volume average particle diameters of the organic fine particles as heat-resistant fine particles to the particulate polymer is equal to or less than the above-mentioned upper limit, the blocking resistance of the resulting functional layer can be sufficiently ensured while improving the process adhesion.

[0087] <Content of inorganic fine particles as heat-resistant fine particles> The content of inorganic fine particles as heat-resistant fine particles is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, and preferably 98 parts by mass or less, and more preferably 95 parts by mass or less, based on 100 parts by mass of the total content of the particulate polymer and the inorganic fine particles as heat-resistant fine particles. When the content of inorganic fine particles as heat-resistant fine particles is equal to or greater than the above-mentioned lower limit, the heat shrinkage resistance, deformation resistance, and blocking resistance of the resulting functional layer can be improved. When the content of inorganic fine particles as heat-resistant fine particles is equal to or less than the above-mentioned upper limit, the process adhesion and deformation resistance of the resulting functional layer can be improved.

[0088] <Content of organic fine particles when inorganic fine particles and organic fine particles are used in combination as heat-resistant fine particles> When organic fine particles are used in combination with inorganic fine particles as the heat-resistant fine particles, the content of the organic fine particles is preferably 20 parts by mass or more, more preferably 50 parts by mass or more, more preferably 90 parts by mass or more, and preferably 1000 parts by mass or less, more preferably 800 parts by mass or less, even more preferably 500 parts by mass or less, and even more preferably 400 parts by mass or less, per 100 parts by mass of the particulate polymer. When the blending ratio of the organic fine particles to the particulate polymer is equal to or greater than the lower limit, the resulting functional layer can have improved process adhesion while sufficiently ensuring blocking resistance. Furthermore, when the blending ratio of the organic fine particles to the particulate polymer is equal to or less than the upper limit, the resulting functional layer can have even improved process adhesion. This allows the resulting electrochemical device to have even better electrochemical properties, such as cycle characteristics and rate characteristics.

[0089] When inorganic and organic particles are used in combination as heat-resistant particles, the inorganic particles can particularly contribute to improving the heat resistance of the resulting functional layer, and the organic particles can particularly contribute to improving the blocking resistance of the resulting functional layer.

[0090] <Other ingredients> The functional layer composition may contain any other components in addition to the components described above. The other components are not particularly limited as long as they do not affect the electrochemical reaction in the electrochemical element, and examples thereof include known additives such as dispersants, viscosity modifiers (thickeners), and wetting agents. These other components may be used alone or in combination of two or more.

[0091] For example, a viscosity modifier (thickener) may be a water-soluble polymer. Note that a polymer is "water-soluble" when 0.5 g of the polymer is dissolved in 100 g of water at 25°C, and the insoluble content is less than 1.0 mass %.

[0092] The water-soluble polymer is not particularly limited, and various thickening polysaccharides can be used. Preferred thickening polysaccharides include carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, and salts thereof. Furthermore, various synthetic polymers can be used as the water-soluble polymer. Preferred synthetic polymers include polyvinyl alcohol, poly(meth)acrylic acid, poly(meth)acrylic acid derivatives, poly(meth)acrylamide, poly(meth)acrylamide derivatives, and copolymers thereof or salts thereof, with poly(meth)acrylic acid, poly(meth)acrylic acid derivatives, poly(meth)acrylamide, poly(meth)acrylamide derivatives, or salts thereof being particularly preferred. Examples of salts of water-soluble polymers include lithium salts, sodium salts, and ammonium salts. The water-soluble polymer may be used alone or in combination of two or more kinds in any ratio.

[0093] <Method for preparing composition for electrochemical device functional layer> The method for preparing the composition for the functional layer is not particularly limited, and can be prepared, for example, by mixing the above-mentioned particulate polymer, binder, heat-resistant fine particles, water as a dispersion medium, and other components used as needed. When the particulate polymer or binder is prepared by polymerizing a monomer composition in an aqueous solvent, the particulate polymer or binder may be mixed with other components as is in the form of an aqueous dispersion. When the particulate polymer or binder is mixed in the form of an aqueous dispersion, the water in the aqueous dispersion may be used as the dispersion medium.

[0094] Here, the method for mixing the above-mentioned components is not particularly limited, but in order to efficiently disperse each component, it is preferable to use a disperser as a mixing device. The disperser is preferably a device that can uniformly disperse and mix the above-mentioned components. Examples of dispersers include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer.

[0095] Furthermore, it is preferable to premix the above-mentioned specific particulate polymer with a dispersant such as a nonionic surfactant, an anionic surfactant, a cationic surfactant, or an amphoteric surfactant before mixing it with the heat-resistant fine particles and the binder. Among these, anionic surfactants are preferably used as the dispersant. Specific examples of anionic surfactants include sulfate ester salts of higher alcohols such as sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecyl sulfate, ammonium dodecyl sulfate, sodium octyl sulfate, sodium decyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, and sodium octadecyl sulfate; alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate, sodium laurylbenzenesulfonate, and sodium hexadecylbenzenesulfonate; and aliphatic sulfonates such as sodium laurylsulfonate, sodium dodecylsulfonate, and sodium tetradecylsulfonate. The amount of dispersant blended is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, and preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, and even more preferably 0.3 parts by mass or less, relative to 100 parts by mass of the particulate polymer. When the amount of dispersant blended is equal to or greater than the lower limit, uneven distribution of the particulate polymer in the functional layer can be suppressed, and the cycle characteristics of the resulting electrochemical device can be improved. When the amount of dispersant blended is equal to or less than the upper limit, an increase in the internal resistance of the resulting electrochemical device can be suppressed, and deterioration of the rate characteristics can be suppressed.

[0096] (functional layer for electrochemical elements) The functional layer for an electrochemical device can be formed, for example, on a suitable substrate using the functional layer composition described above. The functional layer contains at least the particulate polymer, binder, and heat-resistant fine particles described above, as well as other components used as needed. The components contained in the functional layer are those contained in the functional layer composition described above, and the preferred ratios of the components are the same as the preferred ratios of the components in the functional layer composition. Because the functional layer of the present invention is formed using the functional layer composition described above, it has excellent process adhesion and blocking resistance. The functional layer is not particularly limited and can be formed according to the method described in the section (Laminate for an electrochemical device).

[0097] In the functional layer formed using the functional layer composition, a plurality of heat-resistant fine particles are usually arranged so as to be stacked in the thickness direction of the functional layer. The plurality of heat-resistant fine particles are stacked in the thickness direction of the functional layer to form a layer (hereinafter also referred to as a "heat-resistant fine particle layer"). The functional layer has a structure in which a portion of the particulate polymer described above is embedded in the heat-resistant fine particle layer.

[0098] The thickness of the layer formed by stacking the heat-resistant fine particles in the thickness direction of the functional layer is preferably 0.5 μm or more, more preferably 0.8 μm or more, even more preferably 1 μm or more, and preferably 6 μm or less, more preferably 5 μm or less, and even more preferably 4 μm or less. If the thickness of the heat-resistant fine particle layer is equal to or greater than the above lower limit, the heat resistance of the functional layer is extremely good. On the other hand, if the thickness of the heat-resistant fine particle layer is equal to or less than the above upper limit, the ion diffusibility of the functional layer can be ensured, and the rate characteristics of the electrochemical device can be further improved.

[0099] [Ratio of volume average particle diameter of particulate polymer to thickness of heat-resistant particle layer] Furthermore, the ratio of the volume average particle diameter of the particulate polymer to the thickness of the heat-resistant fine particle layer (volume average particle diameter of the particulate polymer / thickness of the heat-resistant fine particle layer) is preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.5 or more, and preferably 5.0 or less, more preferably 3.5 or less. If the ratio of the volume average particle diameter of the particulate polymer to the thickness of the heat-resistant fine particle layer is above the above lower limit, the particulate polymer is more likely to protrude from the surface of the heat-resistant fine particles on the thickness direction surface of the functional layer, thereby exhibiting good adhesiveness. If the ratio of the volume average particle diameter of the particulate polymer to the thickness of the heat-resistant fine particle layer is below the above upper limit, the particulate polymer has more adhesion points, thereby exhibiting good adhesiveness.

[0100] (Laminate for electrochemical devices) The electrochemical device laminate includes a substrate and a functional layer for an electrochemical device formed on the substrate using the above-described functional layer composition. The functional layer for an electrochemical device contains at least the above-described particulate polymer, binder, and heat-resistant fine particles, as well as other components used as needed. The components contained in the functional layer are those contained in the above-described functional layer composition, and the preferred abundance ratios of the components are the same as the preferred abundance ratios of the components in the functional layer composition. The electrochemical device laminate includes a functional layer formed using the above-described functional layer composition, and therefore has excellent process adhesion and blocking resistance.

[0101] <Base material> The substrate may be appropriately selected depending on the type of electrochemical element member in which the laminate of the present invention is used. For example, when the laminate of the present invention is used as a separator, a separator substrate is used as the substrate. For example, when the laminate of the present invention is used as an electrode, an electrode substrate is used as the substrate.

[0102] <<Separator substrate>> The separator substrate is not particularly limited, and examples thereof include known separator substrates such as organic separator substrates, which are porous members made of organic materials, and examples of organic separator substrates include microporous membranes or nonwoven fabrics containing polyolefin resins such as polyethylene, polypropylene, polybutene, and polyvinyl chloride, and aromatic polyamide resins. Among these, a microporous film made of a polyolefin resin is preferred from the viewpoint that the ratio of the electrode active material in the electrochemical device can be increased to increase the capacity per volume. The thickness of the separator substrate can be any thickness, preferably 5 μm or more and 30 μm or less, more preferably 5 μm or more and 20 μm or less, and even more preferably 5 μm or more and 18 μm or less.

[0103] <<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 is formed on a current collector. Here, the current collector, the electrode active materials (positive electrode active material, negative electrode active material) and binders for the electrode composite layer (binders for the positive electrode composite layer, binders for the negative electrode composite layer) in the electrode composite layer, and the method for forming the electrode composite layer on the current collector may be known, and for example, the method described in JP 2013-145763 A may be used.

[0104] <Method of manufacturing laminate> The method for producing the laminate of the present invention is not particularly limited, and for example, a method of forming a functional layer on a release sheet and transferring the functional layer onto a substrate can be used. However, from the viewpoint of eliminating the need for a transfer operation and improving production efficiency, it is preferable to produce the laminate through a step of supplying a functional layer composition onto a substrate (supplying step) and a step of drying the functional layer composition supplied onto the substrate (drying step).

[0105] <<Supply process>> In the supplying step, the functional layer composition of the present invention is supplied onto a substrate to form a coating of the functional layer composition on the substrate. The method for supplying the functional layer composition onto the substrate is not particularly limited, and the functional layer composition may be applied to the surface of the substrate, or the substrate may be immersed in the functional layer composition. Furthermore, it is preferable to apply the functional layer composition to the surface of the substrate, as this makes it easier to control the thickness of the functional layer to be produced. The method for applying the composition for the functional layer to the surface of the substrate is not particularly limited, and examples thereof include the doctor blade method, reverse roll method, direct roll method, gravure coating method, bar coating method, extrusion method, and brush coating method. In the supplying step, a coating of the composition for a functional layer may be formed on only one surface of the substrate, or a coating of the composition for a functional layer may be formed on both surfaces of the substrate.

[0106] <<Drying process>> In the drying step, the coating of the functional layer composition formed on the substrate in the supplying step is dried to remove the dispersion medium, thereby forming a functional layer. The method for drying the coating of the composition for functional layer is not particularly limited and any known method can be used, such as drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams, etc. The drying conditions are not particularly limited, but the drying temperature is preferably 50 to 150°C, and the drying time is preferably 1 to 30 minutes.

[0107] In addition, when manufacturing the laminate of the present invention, a supplying process and a drying process may be performed on one side of the substrate to form a functional layer, and then a supplying process and a drying process may be performed on the other side of the substrate to form a functional layer.

[0108] (electrochemical element) The electrochemical element of the present invention comprises an electrode and a separator, and is characterized in that at least one of the electrode and the separator comprises the laminate of the present invention described above. The electrochemical element of the present invention has excellent electrochemical properties because it uses the laminate of the present invention described above as at least one of the element components of the electrode and the separator.

[0109] The electrochemical device of the present invention is not particularly limited, and may be, for example, a lithium ion secondary battery, an electric double layer capacitor, or a lithium ion capacitor, and is preferably a lithium ion secondary battery.

[0110] Hereinafter, a lithium ion secondary battery will be taken as an example of the electrochemical element of the present invention, and a case where the above-described laminate of the present invention is used as a separator of the lithium ion secondary battery will be described, but the electrochemical element of the present invention is not limited thereto.

[0111] <Positive and negative electrodes> As the positive electrode and negative electrode, electrodes made of the known electrode substrates (positive electrode substrate and negative electrode substrate) described above in the section "Substrate" can be used.

[0112] <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.

[0113] 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), methyl ethyl carbonate (ethyl methyl carbonate (EMC)), and vinylene carbonate; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; and the like are suitably used.

[0114] A mixture of these solvents may also be used. Among them, carbonates are preferred because of their high dielectric constant and wide stable potential range. Generally, the lower the viscosity of the solvent used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted by the type of solvent. The concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate. Known additives may also be added to the electrolytic solution.

[0115] <Method of manufacturing an electrochemical element> The method for producing the electrochemical element of the present invention is not particularly limited. For example, the lithium ion secondary battery, which is an example of the electrochemical element of the present invention described above, can be produced by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the stack as necessary, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. At least one of the element components among the positive electrode, negative electrode, and separator is the laminate of the present invention. Furthermore, the battery container may contain an expanded metal, a fuse, an overcurrent prevention element such as a PTC element, a lead plate, or the like, as necessary, to prevent pressure buildup within the battery and overcharging and discharging. The shape of the battery may be any shape, such as a coin type, button type, sheet type, cylindrical type, rectangular type, or flat type. [Example]

[0116] 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. Furthermore, in a polymer produced by copolymerizing multiple types of monomers, the proportion of structural units formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of that certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified.

[0117] In the examples and comparative examples, the measurement and evaluation of various attributes were carried out as follows.

[0118] <Glass transition temperature> The particulate polymers (Polymer A and Polymer B) and binders prepared in the Examples and Comparative Examples were used as measurement samples. 10 mg of the sample was weighed into an aluminum pan and measured using a differential scanning calorimetry (DSC) analyzer (SII NanoTechnology, Inc., "EXSTAR DSC6220") under the conditions specified in JIS Z 8703. The measurement temperature range was -100°C to 200°C, and the heating rate was 10°C / min. The DSC curve was obtained under the conditions specified in JIS Z 8703. The glass transition temperature (°C) was determined by the intersection of the baseline just before the endothermic peak of the DSC curve, where the differential signal (DDSC) was 0.05 mW / min / mg or greater, and the tangent to the DSC curve at the first inflection point after the endothermic peak. The measurement samples of polymer A and polymer B constituting the particulate polymer were prepared as follows: Aqueous dispersions containing each polymer, which served as measurement samples, were prepared using the monomers and various additives used in forming polymer A and polymer B under the same polymerization conditions as those for polymer A and polymer B. The prepared aqueous dispersions were then dried to obtain measurement samples.

[0119] <Volume average particle size of particulate polymer and particulate B as heat-resistant particulate> The particulate polymers and organic fine particles serving as heat-resistant fine particles prepared in the examples and comparative examples were used as measurement samples. A 0.1 g equivalent amount of the measurement sample was weighed and placed in a beaker, and 0.1 mL of an alkylbenzene sulfonic acid aqueous solution (Fujifilm Corporation, "Drywell") was added as a dispersant. 10-30 mL of a diluent (Beckman Coulter, Inc., "Isoton II") was then added to the beaker, and the mixture was dispersed for 3 minutes using a 20 W (Watt) ultrasonic disperser. The volume-average particle diameter of the measurement sample was then measured using a particle size analyzer (Beckman Coulter, Inc., "Multisizer") under the following conditions: aperture diameter: 20 μm, medium: Isoton II, and particle count: 100,000. The volume-average particle diameter was defined as the particle diameter D50 at which the cumulative volume calculated from the smallest diameter side in the particle size distribution (volume-based) measured by the particle size analyzer reached 50%.

[0120] <Acid value of polymer A> The acid value of Polymer A was measured in accordance with JIS K 0070, which is a standard method for analyzing fats and oils established by the Japanese Industrial Standards Committee (JICS).

[0121] <Weight-average molecular weight of polymer A> 0.1 g of polymer A was weighed out as a measurement sample in the same manner as when measuring the glass transition temperature, and placed in a 100 mL glass sample bottle. Then, 49.9 g of tetrahydrofuran (THF) was added. Next, a stirrer tip was added, and the mixture was stirred at room temperature for 1 hour using a magnetic stirrer. The mixture was then filtered through a 0.2 μm PTFE filter to obtain a THF solution of polymer A. Finally, 100 μL of each THF solution was injected into a GPC measurement device and subjected to GPC measurement. The weight-average molecular weight (Mw) was calculated from the obtained GPC elution curve using a calibration curve based on commercially available monodisperse standard polystyrene. (GPC measurement conditions) GPC: HLC-8220 (Tosoh Corporation) Column: Two TSK-GEL MULTIPORE HXL-M columns connected together (Tosoh Corporation) Eluent:THF Flow rate: 1.0mL / min Temperature: 40℃

[0122] <Volume average particle size of binder> The volume-average particle diameter of the binder prepared in the examples was measured by laser diffraction. Specifically, an aqueous dispersion containing the prepared binder (adjusted to a solids concentration of 0.1% by mass) was used as a sample. The particle size distribution (volume basis) measured using a laser diffraction particle size distribution analyzer (manufactured by Beckman Coulter, Inc., "LS-230") was used. The particle diameter D50 at which the cumulative volume calculated from the smallest diameter side reached 50% was defined as the volume-average particle diameter.

[0123] <Thickness of heat-resistant fine particle layer> The cross section of the separator with the functional layer was observed using a field emission scanning electron microscope (FE-SEM), and the thickness of the heat-resistant particle layer was calculated from the obtained image. The thickness of the heat-resistant particle layer was defined as the vertical distance from the surface of the separator on the side where the functional layer was formed to the heat-resistant particle forming the surface of the functional layer. When organic particle was contained in addition to inorganic particle, as in Examples 14 to 27 and Comparative Example 7, the thickness of the heat-resistant particle layer was calculated as the vertical distance to the inorganic particle forming the surface of the functional layer.

[0124] <Ratio of volume average particle size of heat-resistant fine particles to volume average particle size of particulate polymer> The volume average particle diameter of the heat-resistant fine particles used in the examples and comparative examples was divided by the volume average particle diameter of the particulate polymer measured above to calculate the ratio (%). The volume average particle diameter of the alumina used as the heat-resistant fine particles in the examples and comparative examples was the volume average particle diameter D50 obtained based on the particle size distribution measured using a particle size distribution measuring device (manufactured by Microtrac, "MT3300") according to the laser diffraction / scattering method.

[0125] <Slurry stability: Settling> The functional layer compositions (slurry compositions) prepared in the Examples and Comparative Examples were poured into 1 cm diameter test tubes to a height of 5 cm, and five of each were used as test samples. The test samples were placed vertically on a table. The condition of the test samples was observed for three days and evaluated according to the following criteria. The absence of two-phase separation indicated excellent sedimentation. A: No separation into two phases was observed even after 3 days. B: Separation into two phases is observed after 1 to 3 days. C: Two-phase separation is observed after 3 hours to 1 day. D: Separation into two phases occurs within 3 hours.

[0126] <Process Adhesion> The positive electrode and separator with functional layer prepared in the examples and comparative examples were each cut to a width of 10 mm and a length of 50 mm, and the positive electrode and separator with functional layer were stacked and pressed using a roll press under conditions of a temperature of 60°C, a load of 10 kN / m, and a press speed of 30 m / min to obtain an integrated product in which the positive electrode and separator with functional layer were integrated. The resulting integrated product was placed with the current collector side of the positive electrode facing downwards, and cellophane tape was attached to the surface of the positive electrode. The cellophane tape used conformed to JIS Z1522. The cellophane tape was fixed to a horizontal test table. One end of the separator with the functional layer was then pulled vertically upward at a pulling rate of 50 mm / min, and the stress when peeled off was measured. The negative electrodes prepared in the examples and comparative examples were also subjected to the same operations as in the case of using the positive electrodes, and the stress was measured. The above-mentioned stress measurement was performed three times for each of the integrated positive electrode and separator with functional layer, and the integrated negative electrode and separator with functional layer, for a total of six times, and the average stress value was calculated. The obtained average value was used as the peel strength (N / m). The calculated peel strength was then used to evaluate the process adhesion between the electrode and the separator with a functional layer according to the following criteria: The higher the peel strength, the higher the process adhesion (the adhesion between battery components during the battery manufacturing process). A: Peel strength is 3N / m or more B: Peel strength is 2N / m or more and less than 3N / m C: Peel strength is 1N / m or more and less than 2N / m D: Peel strength is less than 1N / m

[0127] <Blocking resistance of functional layer> Two test pieces measuring 4 cm wide x 4 cm long were cut from the separators with functional layers prepared in the Examples and Comparative Examples. The two test pieces were stacked with the functional layers facing each other and pressed for 2 minutes at 40°C and a load of 8 kN using a flat press to obtain a pressed body. One end of the pressed body was fixed, and the other end was pulled vertically upward at a tensile speed of 50 mm / min. The stress measured when peeled was used to measure the blocking strength. The blocking strength was evaluated according to the following criteria. A lower blocking strength indicates that the functional layer effectively suppresses blocking, i.e., the functional layer has high blocking resistance. A: Less than 4N / m B: 4N / m or more and less than 6N / m C: 6N / m or more

[0128] <Heat shrinkage resistance of functional layer> The separators with functional layers prepared in the examples and comparative examples were cut into squares measuring 12 cm wide x 12 cm long, and a square with sides of 10 cm was drawn inside each of the resulting squares to prepare test pieces. The test pieces were then placed in a thermostatic chamber at 150°C and left for 1 hour. 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 thermal shrinkage rate and evaluated according to the following criteria. A smaller thermal shrinkage rate indicates better heat shrinkage resistance for the separator with a functional layer. A: Heat shrinkage rate is less than 3% B: Heat shrinkage rate is 3% or more and less than 5% C: Heat shrinkage rate is 5% or more and less than 10% D: Heat shrinkage rate is 10% or more

[0129] <Cycle characteristics of secondary batteries> The lithium ion secondary batteries fabricated in the examples and comparative examples were left standing at 25°C for 5 hours. Next, they were charged to a cell voltage of 3.65V at a constant current of 0.2C at 25°C, and then aged for 12 hours at 60°C. Then, they were discharged to a cell voltage of 3.00V at a constant current of 0.2C at 25°C. Then, they were subjected to CC-CV charging (upper limit cell voltage 4.20V) at a constant current of 0.2C, and CC discharging to 3.00V at a constant current of 0.2C. This charging and discharging at 0.2C was repeated three times. Thereafter, 100 cycles of charge and discharge were performed at a temperature of 25°C, a cell voltage of 4.20-3.00V, and a charge and discharge rate of 1.0 C. The discharge capacity of the first cycle was defined as X1, and the discharge capacity of the 100th cycle as X2. Then, the discharge capacity X1 and the discharge capacity X2 were used to calculate the capacity retention rate ΔC′=(X2 / X1)×100(%), and the capacity retention rate was evaluated according to the following criteria: A larger value of the capacity retention rate ΔC′ indicates that the secondary battery has better cycle characteristics. A: Capacity retention rate ΔC' is 93% or more B: Capacity retention rate ΔC' is 90% or more and less than 93% C: Capacity retention rate ΔC' is less than 90%

[0130] <Rechargeable battery output characteristics (rate characteristics)> The lithium ion secondary batteries fabricated in the examples and comparative examples were charged to 4.3 V at a constant current / constant voltage (CCCV) in an atmosphere at 25°C to prepare cells. The prepared cells were discharged to 3.0 V at constant currents of 0.2 C and 1.5 C to determine the electric capacity. The discharge capacity retention rate, expressed as the ratio of the electric capacities [= (electric capacity at 1.5 C / electric capacity at 0.2 C) × 100 (%)], was then calculated. This measurement was performed on five lithium ion secondary battery cells. The average value of the discharge capacity retention rate for each cell was then calculated and evaluated according to the following criteria. A higher average value of the discharge capacity retention rate indicates that the secondary battery has better output characteristics. A: The average discharge capacity retention rate is 90% or more B: The average discharge capacity retention rate is 85% or more and less than 90% C: The average discharge capacity retention rate is less than 85%

[0131] Example 1 <Preparation of particulate polymer> [Preparation of Polymer (A)] 200 parts of toluene were added to a reaction vessel, and the atmosphere inside the reaction vessel was thoroughly purged with nitrogen while stirring the toluene. The temperature was then raised to 90°C. A mixed solution of 97 parts of methyl methacrylate as (meth)acrylic acid ester monomer units, 2.6 parts of n-butyl acrylate, 0.4 parts of acrylic acid as acidic group-containing monomer units, and 3 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O) as a polymerization initiator was then added dropwise to the reaction vessel over 2 hours. The mixture was then maintained under toluene reflux for 10 hours to complete the polymerization, after which the solvent was distilled off under reduced pressure. The copolymer thus obtained was designated Polymer (A). [Preparation of Monomer Composition (B)] A monomer composition (B) was prepared by mixing 75 parts of styrene as an aromatic vinyl monomer, 24.5 parts of 2-ethylhexyl acrylate as a (meth)acrylic acid ester monomer, and 0.5 parts of ethylene glycol dimethacrylate as a crosslinkable monomer.

[0132] [Preparation of metal hydroxides] A colloidal dispersion (A) containing magnesium hydroxide as the metal hydroxide was prepared by gradually adding, with stirring, an aqueous solution (A2) prepared by dissolving 5.6 parts of sodium hydroxide in 50 parts of ion-exchanged water to an aqueous solution (A1) prepared by dissolving 8 parts of magnesium chloride in 200 parts of ion-exchanged water.

[0133] [Suspension polymerization method] A particulate polymer was prepared by suspension polymerization. Specifically, the polymer (A) and monomer composition (B) obtained as described above were added to the colloidal dispersion (A) containing magnesium hydroxide, and after further stirring, 2.0 parts of t-butylperoxy-2-ethylhexanoate (NOF Corporation, "Perbutyl (registered trademark) O") was added as a polymerization initiator to obtain a mixed solution. The blending ratio of the polymer (A) to the monomer composition (B) was such that the ratio of polymer (A) in the resulting particulate polymer was as shown in Table 1. The resulting mixed solution was subjected to high-shear stirring at 15,000 rpm for 1 minute using an in-line emulsifying disperser (Pacific Machinery Works, "Cavitron") to form mixed droplets of the polymer (A) and the monomer composition (B) in the colloidal dispersion (A) containing magnesium hydroxide.

[0134] The colloidal dispersion (A) containing magnesium hydroxide and in which droplets of the monomer composition were formed was placed in a reactor, heated to 90°C, and subjected to a polymerization reaction for 5 hours to obtain an aqueous dispersion containing a particulate polymer.

[0135] Further, while stirring the aqueous dispersion containing the particulate polymer, sulfuric acid was added dropwise at room temperature (25°C) and acid washing was carried out until the pH became 6.5 or less. Next, filtration and separation were carried out, and 500 parts of ion-exchanged water was added to the obtained solid matter to re-slurry it, and water washing treatment (washing, filtration and dehydration) was carried out several times. Then, filtration and separation were carried out, and the obtained solid matter was placed in a container of a dryer and dried at 40°C for 48 hours to obtain a dried particulate polymer.

[0136] <Preparation of aqueous dispersion containing binder (α)> 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, "EMAL (registered trademark) 2F") as an emulsifier, and 0.5 parts of ammonium persulfate as a polymerization initiator were supplied, the gas phase was replaced with nitrogen gas, and the temperature was raised to 60°C. Meanwhile, in another container, 50 parts of ion-exchanged water, 0.5 parts of sodium dodecylbenzenesulfonate as a dispersion stabilizer, 94 parts of n-butyl acrylate as a (meth)acrylic acid ester monomer, 2 parts of methacrylic acid as an acid group-containing monomer, and 2 parts of acrylonitrile as a nitrile group-containing monomer, as well as 1 part of allyl methacrylate and 1 part of allyl glycidyl ether as crosslinkable monomers were mixed to prepare a monomer composition (α). The obtained monomer composition (α) was continuously added to the above-mentioned reactor equipped with a stirrer over 4 hours to carry out polymerization. During the addition, the reaction was carried out at 60°C. After the addition was completed, the mixture was stirred at 70°C for an additional 3 hours, and then the reaction was terminated, yielding an aqueous dispersion containing a particulate binder (α) as an acrylic polymer. The obtained particulate binder (α) had a volume average particle diameter of 0.25 μm and a glass transition temperature of -40°C.

[0137] <Preparation of Slurry Composition> To 100 parts of alumina ("AKP30" manufactured by Sumitomo Chemical Co., Ltd., volume average particle diameter: 0.3 μm) as heat-resistant fine particles (fine particles A; inorganic fine particles), 0.5 parts of polyacrylic acid as a dispersant was added, and 5 parts of an aqueous dispersion containing a binder (α) in terms of solid content and 1.5 parts of carboxymethyl cellulose as a thickener were added. Ion-exchanged water was added so that the solid content concentration became 55%, and the mixture was mixed using a ball mill to obtain a pre-mixing slurry. To 100 parts of the particulate polymer, 0.2 parts of sodium dodecylbenzenesulfonate ("Neopelex G-15" manufactured by Kao Chemical Corporation) was added as a surfactant, and the mixture was mixed to a solids concentration of 40%, and the resulting mixture was added to the pre-mixing slurry obtained as described above. Further, ion-exchanged water was added to a solids concentration of 40%, to obtain a slurry composition (composition for functional layer) in which the mixing ratio of heat-resistant fine particles (alumina) to particulate polymer was as shown in Table 1. The slurry stability of the obtained composition for functional layer (slurry composition) was evaluated as described above. The results are shown in Table 1.

[0138] <Fabrication of separator with functional layer> A polyethylene microporous membrane (thickness: 12 μm) was prepared as a separator substrate. The slurry composition obtained as described above was applied to one side of this separator substrate using a bar coater method. Next, the separator substrate coated with the slurry composition was dried at 50°C for 1 minute to form a functional layer. The same operation was performed on the other side of the separator substrate, producing a separator with a functional layer provided on each side of the separator substrate. The thickness of the heat-resistant fine particle layer in each functional layer was 2.0 μm.

[0139] <Preparation of positive electrode> A mixture of 100 parts of LiCoO2 (volume average particle diameter: 12 μm) as a positive electrode active material, 2 parts of acetylene black (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, 2 parts of polyvinylidene fluoride (#7208, manufactured by Kureha Corporation) as a binder for the positive electrode composite layer in terms of solid content, and N-methylpyrrolidone as a solvent was mixed to a total solid content of 70%. These components were mixed using a planetary mixer to prepare a positive electrode slurry composition. The positive electrode slurry composition was applied to a 20 μm-thick aluminum foil current collector using a comma coater so that the dried film thickness was approximately 150 μm, and then dried. This drying was performed by transporting the aluminum foil at a speed of 0.5 m / min through an oven at 60°C for 2 minutes. The aluminum foil was then heat-treated at 120°C for 2 minutes to obtain a pre-pressed positive electrode blank. This pre-pressed positive electrode blank was rolled using a roll press to obtain a pre-pressed positive electrode having a positive electrode composite layer (thickness: 60 μm).

[0140] <Preparation of negative electrode> A 5 MPa pressure vessel equipped with a stirrer was charged with 33 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 63.5 parts of styrene, 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. When the polymerization conversion reached 96%, the reaction was stopped by cooling, yielding a mixture containing a binder (SBR) for the negative electrode composite layer. A 5% aqueous sodium hydroxide solution was added to the mixture containing the binder for the negative electrode composite layer, adjusting the pH to 8, and then the unreacted monomer was removed by heated vacuum distillation. The mixture was then cooled to below 30 °C to obtain an aqueous dispersion containing the desired binder for the negative electrode composite layer. 80 parts of artificial graphite (volume average particle diameter: 15.6 μm) as the negative electrode active material (1) and 16 parts of silicon-based active material SiOx (volume average particle diameter: 4.9 μm) as the negative electrode active material (2) were blended, and 2.5 parts of a 2% aqueous solution of carboxymethylcellulose sodium salt (manufactured by Nippon Paper Industries Co., Ltd., "MAC350HC") as a viscosity modifier, in terms of solid content, and ion-exchanged water were mixed to adjust the solid content to 68%, and then further mixed at 25 ° C. for 60 minutes. The solid content was further adjusted to 62% with ion-exchanged water, and then further mixed at 25 ° C. for 15 minutes to obtain a mixed solution. 1.5 parts of the aqueous dispersion containing the above-mentioned binder for the negative electrode composite layer, in terms of solid content, and ion-exchanged water were added to this mixed solution, and the final solid content was adjusted to 52%, and then further mixed for 10 minutes to obtain a mixed solution. This mixed solution was degassed under reduced pressure to obtain a negative electrode slurry composition with good fluidity. The negative electrode slurry composition was applied to a 20 μm-thick copper foil current collector using a comma coater so that the dried film thickness was approximately 150 μm, and then dried. This drying was performed by transporting the copper foil at a speed of 0.5 m / min through an oven at 60°C for 2 minutes. The copper foil was then heat-treated at 120°C for 2 minutes to obtain a pre-pressed negative electrode blank. This pre-pressed negative electrode blank was rolled using a roll press to obtain a pre-pressed negative electrode having a negative electrode composite layer (thickness: 80 μm).

[0141] The separator with the functional layer, the positive electrode, and the negative electrode obtained as described above were used to evaluate the process adhesion, the blocking resistance of the functional layer, and the heat resistance of the functional layer. The results are shown in Table 1.

[0142] <Fabrication of lithium-ion secondary batteries> The pressed positive electrode prepared as described above was cut into a 49 cm x 5 cm rectangle and placed with the surface of the positive electrode composite layer facing up. The separator with functional layer, cut to 120 cm x 5.5 cm, was placed on top of the positive electrode composite layer so that the positive electrode was located on one side of the separator with functional layer in the longitudinal direction. Furthermore, the pressed negative electrode prepared as described above was cut into a 50 cm x 5.2 cm rectangle and placed on the separator with functional layer so that the surface of the negative electrode composite layer faced the separator with functional layer and the negative electrode was located on the other side of the separator with functional layer in the longitudinal direction. The resulting laminate was then wound using a winding machine to obtain a wound body. This wound body was pressed at 70°C and 1 MPa to form a flat body, which was then wrapped in an aluminum packaging exterior as the battery exterior, and an electrolyte solution [solvent: ethylene carbonate / diethyl carbonate / vinylene carbonate (volume ratio) = 68.5 / 30 / 1.5, electrolyte: LiPF6 with a concentration of 1M)] was injected so that no air remained. The opening of the aluminum packaging exterior was then heat-sealed at a temperature of 150°C to produce a wound-type lithium-ion secondary battery with a capacity of 800 mAh. The cycle characteristics and output characteristics of the obtained lithium ion secondary battery were evaluated, and the results are shown in Table 1.

[0143] (Examples 2 and 3) The same operations, measurements, and evaluations as in Example 1 were carried out, except that the amount of magnesium hydroxide used as a dispersion stabilizer in preparing the particulate polymer was changed so that the volume average particle diameter of the particulate polymer would be as shown in Table 1. The results are shown in Table 1.

[0144] Example 4 The same operations, measurements, and evaluations as in Example 1 were carried out to prepare Polymer A, except that the types and amounts of the monomers to be blended were changed so that the composition of the resulting copolymer would be as shown in Table 1. The results are shown in Table 1.

[0145] Example 5 When preparing polymer A, the same operations, measurements, and evaluations as in Example 1 were carried out, except that the types and amounts of the monomers to be mixed and the amount of the polymerization initiator were changed so that the composition and weight-average molecular weight of the resulting copolymer would be as shown in Table 1. The results are shown in Table 1.

[0146] Example 6 The same operations, measurements, and evaluations as in Example 1 were carried out to prepare Polymer A, except that the types and amounts of the monomers to be blended were changed so that the composition and glass transition temperature of the resulting copolymer would be as shown in Table 1. The results are shown in Table 1.

[0147] (Examples 7 to 8) The same operations, measurements, and evaluations as in Example 1 were carried out, except that the blending ratio of the polymer (A) and the monomer composition (B) during suspension polymerization to prepare the particulate polymer was changed so that the ratio of the polymer (A) and the polymer (B) in the obtained particulate polymer was as shown in Table 1. The results are shown in Table 1.

[0148] Example 9 The same operations, measurements, and evaluations as in Example 1 were carried out, except that alumina (manufactured by Kojundo Chemical Laboratory Co., Ltd., "AL011PB") having a volume average particle diameter of 1 μm was used as the heat-resistant fine particles (fine particles A; inorganic fine particles) when preparing the composition for the functional layer. The results are shown in Table 2.

[0149] Example 10 The same operations, measurements, and evaluations were carried out as in Example 1, except that alumina (manufactured by Sumitomo Chemical Co., Ltd., "AKP-3000") with a volume average particle diameter of 0.7 μm was used as the heat-resistant fine particles (fine particles A; inorganic fine particles) when preparing the composition for the functional layer. The results are shown in Table 2.

[0150] Example 11 The same operations, measurements, and evaluations as in Example 1 were carried out, except that alumina (manufactured by Sumitomo Chemical Co., Ltd., "AKP-50") with a volume average particle size of 0.2 μm was used as the heat-resistant fine particles (fine particles A; inorganic fine particles) when preparing the composition for the functional layer. The results are shown in Table 2.

[0151] (Examples 12 to 13) The same operations, measurements, and evaluations as in Example 1 were carried out, except that in preparing the composition for the functional layer, the amounts of heat-resistant fine particles (fine particles A; inorganic fine particles) and the particulate polymer were changed so that the mixing ratio was as shown in Table 2. The results are shown in Table 2.

[0152] Example 14 In preparing the composition for the functional layer, when a mixed liquid containing a particulate polymer and a surfactant was added to a pre-mixing slurry containing fine particles A (inorganic fine particles) as heat-resistant fine particles, fine particles B (organic fine particles) prepared as described below were blended. The blending ratio was such that the ratio of fine particles B to the particulate polymer was as shown in Table 2. Other than this, the same operations, measurements, and evaluations as in Example 1 were carried out. The results are shown in Table 2.

[0153] <Preparation of organic fine particles> [Preparation of Monomer Composition (C)] A monomer composition (C) was prepared by mixing 50 parts of styrene as an aromatic vinyl monomer and 50 parts of ethylene glycol dimethacrylate as a crosslinkable monomer.

[0154] [Preparation of metal hydroxides] A colloidal dispersion (A) containing magnesium hydroxide as the metal hydroxide was prepared by gradually adding, with stirring, an aqueous solution (A2) prepared by dissolving 5.6 parts of sodium hydroxide in 50 parts of ion-exchanged water to an aqueous solution (A1) prepared by dissolving 8 parts of magnesium chloride in 200 parts of ion-exchanged water.

[0155] [Suspension polymerization method] Organic microparticles were prepared by suspension polymerization. Specifically, the monomer composition (C) obtained as described above was added to the colloidal dispersion (A) containing magnesium hydroxide, and after further stirring, 2.0 parts of t-butylperoxy-2-ethylhexanoate (NOF Corp., "Perbutyl (registered trademark) O") was added as a polymerization initiator to obtain a mixed solution. The resulting mixed solution was subjected to high-shear stirring at 15,000 rpm for 1 minute using an in-line emulsifying disperser (Pacific Machinery Works, "Cavitron") to form droplets of the monomer composition (C) in the colloidal dispersion (A) containing magnesium hydroxide.

[0156] The colloidal dispersion (A) containing magnesium hydroxide in which droplets of the monomer composition (C) had been formed was placed in a reactor, heated to 90°C, and subjected to a polymerization reaction for 5 hours to obtain an aqueous dispersion containing organic fine particles.

[0157] Further, while stirring the aqueous dispersion containing the particulate polymer, sulfuric acid was added dropwise at room temperature (25°C) and acid washing was performed until the pH reached 6.5 or less. Next, filtration and separation were performed, and 500 parts of ion-exchanged water was added to the obtained solid matter to re-slurry it, and the water washing treatment (washing, filtration, and dehydration) was repeated several times. Then, filtration and separation were performed, and the obtained solid matter was placed in a container of a dryer and dried at 40°C for 48 hours to obtain dried organic microparticles. The volume average particle diameter of the obtained organic microparticles was evaluated as described above. The results are shown in Table 2.

[0158] Example 15 In preparing the composition for the functional layer, fine particles B (organic fine particles) prepared as described below were blended in addition to fine particles A (inorganic fine particles) as heat-resistant fine particles. The blending ratio was such that the addition ratio of fine particles B to the particulate polymer was as shown in Table 2. Except for this, the same operations, measurements, and evaluations as in Example 14 were carried out. The results are shown in Table 2.

[0159] <Preparation of organic fine particles> [Preparation of Monomer Composition (C)] A monomer composition (C) was prepared by mixing 50 parts of methyl methacrylate as a (meth)acrylic acid ester monomer and 50 parts of ethylene glycol dimethacrylate as a crosslinkable monomer. [Preparation of metal hydroxides] In the same manner as in Example 14, a colloidal dispersion (A) containing magnesium hydroxide was prepared. [Suspension polymerization method] Organic fine particles were prepared by the same suspension polymerization method as in Example 14.

[0160] Example 16 In preparing the composition for the functional layer, fine particles B (organic fine particles) prepared as described below were blended in addition to fine particles A (inorganic fine particles) as heat-resistant fine particles. The blending ratio was such that the addition ratio of fine particles B to the particulate polymer was as shown in Table 2. Except for this, the same operations, measurements, and evaluations as in Example 14 were carried out. The results are shown in Table 2.

[0161] <Preparation of organic fine particles> [Preparation of Monomer Composition (C)] A monomer composition (C) was prepared by mixing 50 parts of styrene as an aromatic vinyl monomer and 50 parts of divinylbenzene as a crosslinkable monomer. [Preparation of metal hydroxides] In the same manner as in Example 14, a colloidal dispersion (A) containing magnesium hydroxide was prepared. [Suspension polymerization method] Organic fine particles were prepared by the same suspension polymerization method as in Example 14.

[0162] Example 17 In preparing the composition for the functional layer, fine particles B (organic fine particles) prepared as described below were blended in addition to fine particles A (inorganic fine particles) as heat-resistant fine particles. The blending ratio was such that the addition ratio of fine particles B to the particulate polymer was as shown in Table 2. Except for this, the same operations, measurements, and evaluations as in Example 14 were carried out. The results are shown in Table 2.

[0163] <Preparation of organic fine particles> [Preparation of Monomer Composition (C)] A monomer composition (C) was prepared by mixing 25 parts of styrene as an aromatic vinyl monomer and 75 parts of ethylene glycol dimethacrylate as a crosslinkable monomer. [Preparation of metal hydroxides] In the same manner as in Example 14, a colloidal dispersion (A) containing magnesium hydroxide was prepared. [Suspension polymerization method] Organic fine particles were prepared by the same suspension polymerization method as in Example 14.

[0164] Example 18 In preparing the composition for the functional layer, fine particles B (organic fine particles) prepared as described below were blended in addition to fine particles A (inorganic fine particles) as heat-resistant fine particles. The blending ratio was such that the addition ratio of fine particles B to the particulate polymer was as shown in Table 2. Except for this, the same operations, measurements, and evaluations as in Example 14 were carried out. The results are shown in Table 2.

[0165] <Preparation of organic fine particles> [Preparation of Monomer Composition (C)] A monomer composition (C) was prepared by mixing 5 parts of styrene as an aromatic vinyl monomer and 95 parts of ethylene glycol dimethacrylate as a crosslinkable monomer. [Preparation of metal hydroxides] In the same manner as in Example 14, a colloidal dispersion (A) containing magnesium hydroxide was prepared. [Suspension polymerization method] Organic fine particles were prepared by the same suspension polymerization method as in Example 14.

[0166] Example 19 The composition for the functional layer was prepared by the same operations, measurements, and evaluations as in Example 14, except that a particulate polymer (volume average particle diameter: 8 μm) prepared in the same manner as in Example 3 and organic fine particles (fine particles B) prepared as heat-resistant fine particles as described below were used. The results are shown in Table 3.

[0167] <Preparation of organic fine particles> [Preparation of Monomer Composition (C)] A monomer composition (C) was prepared by mixing 50 parts of styrene as an aromatic vinyl monomer and 50 parts of ethylene glycol dimethacrylate as a crosslinkable monomer. [Preparation of metal hydroxides] In the same manner as in Example 14, a colloidal dispersion (A) containing magnesium hydroxide was prepared. [Suspension polymerization method] Organic microparticles were prepared by the same suspension polymerization method as in Example 14, except that the amount of magnesium hydroxide used as a dispersion stabilizer during the preparation of the organic microparticles was changed so that the volume average particle diameter of the resulting organic microparticles would be 8 μm.

[0168] Example 20 The composition for the functional layer was prepared by the same procedures, measurements, and evaluations as in Example 14, except that fine particles B (organic fine particles) prepared as described below were blended in addition to fine particles A (inorganic fine particles) as heat-resistant fine particles. The results are shown in Table 3.

[0169] <Preparation of organic fine particles> [Preparation of Monomer Composition (C)] A monomer composition (C) was prepared by mixing 50 parts of styrene as an aromatic vinyl monomer and 50 parts of ethylene glycol dimethacrylate as a crosslinkable monomer. [Preparation of metal hydroxides] In the same manner as in Example 14, a colloidal dispersion (A) containing magnesium hydroxide was prepared. [Suspension polymerization method] Organic microparticles were prepared by the same suspension polymerization method as in Example 14, except that the amount of magnesium hydroxide used as a dispersion stabilizer during the preparation of the organic microparticles was changed so that the volume average particle diameter of the resulting organic microparticles would be 5 μm.

[0170] Example 21 In preparing the composition for the functional layer, the same operations, measurements, and evaluations as in Example 14 were carried out, except that in addition to the fine particles A (inorganic fine particles) as heat-resistant fine particles, fine particles B (organic fine particles) prepared in the same manner as in Example 19 were blended. The results are shown in Table 3.

[0171] (Examples 22 to 23) In preparing the composition for the functional layer, when a mixed liquid containing a particulate polymer and a surfactant was added to a pre-mixing slurry containing fine particles A (inorganic fine particles) as heat-resistant fine particles, fine particles B (organic fine particles) prepared in the same manner as in Example 14 were blended. The blending ratio was set so that the addition rate of fine particles B to the particulate polymer was as shown in Table 3. Other than this, the same operations, measurements, and evaluations as in Example 1 were carried out. The results are shown in Table 3.

[0172] (Examples 24 to 25) In preparing the particulate polymer, the composition of the monomer composition (B) was changed as shown in Table 3, and otherwise the particulate polymer was prepared in the same manner as in Example 1. Furthermore, in preparing the composition for the functional layer, when the mixed liquid containing the particulate polymer and the surfactant was added to the pre-mixing slurry containing the particulate A (inorganic particulate) as heat-resistant particulate, the particulate B (organic particulate) prepared in the same manner as in Example 14 was blended. The blending ratio was set so that the addition rate of the particulate B to the particulate polymer was as shown in Table 3. Except for this, the same operations, measurements, and evaluations as in Example 1 were carried out. The results are shown in Table 3.

[0173] Example 26 In preparing the slurry composition, a commercially available SBR binder (BM-451B manufactured by Zeon Corporation) was used as the binder. Otherwise, the same operations, measurements, and evaluations were carried out as in Example 14. The results are shown in Table 3.

[0174] Example 27 In preparing the slurry composition, a binder (β) prepared as follows was used as the binder. Other than that, the same operations, measurements, and evaluations were carried out as in Example 14. The results are shown in Table 3.

[0175] <Preparation of aqueous dispersion containing binder (β)> To a reactor equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 parts of polyoxyethylene lauryl ether (manufactured by Kao Chemical Corporation, "Emulgen (registered trademark) 120") as an emulsifier, and 0.5 parts of ammonium persulfate as a polymerization initiator were supplied, the gas phase was replaced with nitrogen gas, and the temperature was raised to 60°C. Meanwhile, in another container, 50 parts of ion-exchanged water, 0.5 parts of polyoxyethylene lauryl ether (manufactured by Kao Chemical Corporation, "Emulgen (registered trademark) 120") as an emulsifier, 70 parts of 2-ethylhexyl acrylate as a (meth)acrylic acid alkyl ester monomer, 25 parts of styrene as an aromatic vinyl monomer, 1.7 parts of allyl glycidyl ether and 0.3 parts of allyl methacrylate as crosslinkable monomers, and 3 parts of acrylic acid as an acid group-containing monomer were mixed to prepare a monomer composition (β). The obtained monomer composition (β) was continuously added to the above-mentioned reactor equipped with a stirrer over 4 hours to carry out polymerization. During the addition, the reaction was carried out at 70°C. After the addition was completed, the mixture was stirred at 80°C for an additional 3 hours, and then the reaction was terminated to obtain an aqueous dispersion containing particulate binder (β). Using the obtained aqueous dispersion containing binder (β), the volume average particle size and glass transition temperature of the binder (β) were measured. The volume average particle size of the binder (β) was 0.25 μm, and the glass transition temperature was -35°C.

[0176] (Comparative Example 1) Except for not adding heat-resistant fine particles when preparing the composition for the functional layer, the same operations, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 4.

[0177] (Comparative Example 2) The same operations, measurements, and evaluations as in Example 1 were carried out, except that a particulate polymer was not prepared and a composition for a functional layer containing no particulate polymer was obtained. The results are shown in Table 4.

[0178] (Comparative Example 3) The same operations, measurements, and evaluations as in Example 1 were carried out, except that a copolymer not containing polymer (A), prepared as described below, was used as the particulate polymer. The results are shown in Table 4. <Preparation of Particulate Polymer Not Containing Polymer A> The colloidal dispersion (A) containing magnesium hydroxide, in which droplets of the monomer composition (B) similar to that in Example 1 had been formed, was placed in a reactor, and the temperature was raised to 90°C to initiate polymerization. The polymerization was continued until the polymerization conversion rate reached 96%, thereby obtaining an aqueous dispersion containing a particulate polymer. When the conversion rate reached 96%, the reaction was stopped by cooling, and an aqueous dispersion containing a particulate polymer was obtained. The volume average particle size and glass transition temperature of the resulting particulate polymer were measured. The results are shown in Table 4.

[0179] Comparative Example 4 The same operations, measurements, and evaluations as in Example 1 were carried out, except that the copolymer prepared as described below was used as the particulate polymer. The results are shown in Table 4. <Preparation of particulate polymer> A particulate polymer was prepared in the same manner as in Example 1, except that a polymer not containing an acidic group-containing monomer unit (a polymer other than the polymer (A) and not containing an acidic group-containing monomer unit) prepared as follows was used instead of the polymer (A) prepared in Example 1. [Preparation of polymers free of acidic group-containing monomer units] 200 parts of toluene were added to a reaction vessel, and the atmosphere inside the reaction vessel was thoroughly replaced with nitrogen while stirring the toluene. The temperature was then raised to 90°C, and a mixed solution of 97.3 parts of methyl methacrylate, 2.7 parts of n-butyl acrylate, and 3 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O) was added dropwise to the reaction vessel over 2 hours. The mixture was then maintained under toluene reflux for 10 hours to complete the polymerization, and the solvent was then distilled off under reduced pressure. The copolymer thus obtained was used as polymer (A).

[0180] (Comparative Example 5) The same operations, measurements, and evaluations were carried out as in Example 1, except that a copolymer having a small volume average particle size prepared as described below was used as the particulate polymer. The results are shown in Table 4. <Preparation of particulate polymer> First, 24.5 parts of 2-ethylhexyl acrylate as a (meth)acrylic acid ester monomer, 74 parts of styrene as an aromatic vinyl monomer, 1 part of methacrylic acid as an acidic group-containing monomer, 0.5 parts of ethylene glycol dimethacrylate as a crosslinkable monomer, 1 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to 60 ° C. to initiate polymerization. Polymerization was continued until the polymerization conversion rate reached 96%, thereby obtaining an aqueous dispersion containing particulate polymer A. Next, when the polymerization conversion rate reached 96%, 97 parts of methyl methacrylate, 2.6 parts of n-butyl acrylate, and 0.4 parts of acrylic acid were added, and the mixture was heated to 70 ° C. to continue polymerization. When the conversion rate reached 96%, the mixture was cooled to stop the reaction, and an aqueous dispersion containing a particulate polymer was obtained.

[0181] (Comparative Example 6) In preparing the slurry composition, a particulate polymer prepared in the same manner as in Comparative Example 5 was used, and instead of the inorganic fine particles (fine particles A) as heat-resistant fine particles, organic fine particles (fine particles B) prepared in the same manner as in Example 14 were blended. Except for these points, the same operations, measurements, and evaluations as in Example 1 were carried out. The results are shown in Table 4.

[0182] (Comparative Example 7) The slurry composition was prepared in the same manner as in Example 14, except that no particulate polymer was added. Except for this, the same operations, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 4.

[0183] In addition, in Tables 1 to 4, "AA" stands for acrylic acid, "MMA" indicates methyl methacrylate, "BA" indicates n-butyl acrylate; "ST" indicates styrene, "2EHA" indicates 2-ethylhexyl acrylate, "EDMA" refers to ethylene glycol dimethacrylate; "DVB" stands for divinylbenzene, "AN" indicates acrylonitrile, "AMA" indicates allyl methacrylate; "MAA" indicates methacrylic acid, "AGE" refers to allyl glycidyl ether.

[0184] [Table 1]

[0185] [Table 2]

[0186] [Table 3]

[0187] [Table 4]

[0188] Tables 1 to 4 show that the functional layers formed using the compositions for electrochemical element functional layers according to Examples 1 to 27, which contain polymer A containing (meth)acrylic acid ester monomer units and acidic group-containing monomer units, and polymer B, which is a polymer having a different composition from polymer A, and which also contain a particulate polymer having a volume average particle diameter of more than 1.0 μm and not more than 10.0 μm, a binder, and heat-resistant microparticles, have excellent process adhesion and blocking resistance. Furthermore, it can be seen that in Comparative Example 1, which lacks heat-resistant microparticles, Comparative Examples 2 and 7, which lack the specified particulate polymer, Comparative Examples 3 and 4, which contain a particulate polymer lacking polymer A satisfying the specified composition, and Comparative Examples 5 and 6, which contain a particulate polymer with a volume average particle diameter of less than 1.0 μm, the resulting functional layer was unable to achieve both good process adhesion and good blocking resistance. [Industrial Applicability]

[0189] According to the present invention, it is possible to provide a composition for an electrochemical device functional layer, which can provide a functional layer having both sufficiently high process adhesion and blocking resistance. Furthermore, according to the present invention, it is possible to provide a functional layer for an electrochemical device that has excellent process adhesion and blocking resistance, a laminate for an electrochemical device that includes such a functional layer for an electrochemical device, and an electrochemical device that includes such a laminate for an electrochemical device.

Claims

1. A composition for an electrochemical device functional layer, comprising a particulate polymer, a binder, and heat-resistant fine particles, the particulate polymer comprises polymer A and polymer B, The polymer A is a polymer containing a (meth)acrylic acid ester monomer unit and an acidic group-containing monomer unit, the polymer B is a polymer containing an aromatic vinyl monomer unit and having a composition different from that of the polymer A, The volume average particle diameter of the particulate polymer is more than 1.0 μm and not more than 10.0 μm. A composition for an electrochemical device functional layer.

2. 2. The composition for an electrochemical device functional layer according to claim 1, wherein the acidic group-containing monomer unit of the polymer A is a (meth)acrylic acid monomer unit.

3. 3. The composition for an electrochemical device functional layer according to claim 1, wherein the polymer A has a glass transition temperature of 60°C or higher and 85°C or lower.

4. 4. The composition for an electrochemical device functional layer according to claim 1, wherein the acid value of the polymer A is from 0.5 mg KOH / g to 7 mg KOH / g.

5. 5. The composition for an electrochemical device functional layer according to claim 1, wherein the weight average molecular weight of the polymer A is 5,000 or more and 100,000 or less.

6. The composition for an electrochemical device functional layer according to any one of claims 1 to 5, wherein the particulate polymer contains the polymer A in an amount of 0.1 mass% or more and 10 mass% or less based on the particulate polymer.

7. The composition for an electrochemical element functional layer according to any one of claims 1 to 6, wherein the heat-resistant fine particles are inorganic fine particles, and the volume average particle diameter of the inorganic fine particles is 2% to 25% of the volume average particle diameter of the particulate polymer.

8. The composition for an electrochemical element functional layer according to any one of claims 1 to 7, wherein the binder is a polymer containing a (meth)acrylic acid ester monomer unit and having a different composition from the polymer A and the polymer B.

9. A functional layer for an electrochemical device formed using the composition for an electrochemical device functional layer according to any one of claims 1 to 8.

10. the functional layer for an electrochemical device has a structure in which a part of the particulate polymer is embedded in a heat-resistant fine particle layer containing the heat-resistant fine particles, the ratio of the volume average particle diameter of the particulate polymer to the thickness of the heat-resistant fine particle layer is 1.0 or more and 5.0 or less; The functional layer for an electrochemical device according to claim 9 .

11. The composition for functional layers according to claim 7, further comprising organic fine particles as the heat-resistant fine particles, which have a volume average particle diameter of 50% to 150% of the volume average particle diameter of the particulate polymer, and which do not have a glass transition temperature or melting point in the range of 150°C or higher or 200°C or lower.

12. The composition for a functional layer according to claim 11, wherein the amount of the organic fine particles to be blended is 20 parts by mass or more and 1000 parts by mass or less based on the particulate polymer.

13. A functional layer for an electrochemical device formed using the composition for an electrochemical device functional layer according to claim 11 or 12.

14. the functional layer for an electrochemical element has a structure in which the particulate polymer and a portion of the organic fine particles serving as the heat-resistant fine particles are embedded in a heat-resistant fine particle layer containing the heat-resistant fine particles, the ratio of the volume average particle diameter of the particulate polymer to the thickness of the heat-resistant fine particle layer is 1.0 or more and 5.0 or less; The functional layer for an electrochemical device according to claim 13 .

15. A laminate for an electrochemical device, comprising a substrate and a functional layer for an electrochemical device formed on the substrate, wherein the functional layer for an electrochemical device is the functional layer for an electrochemical device according to any one of claims 9, 10, 13, and 14.

16. An electrochemical device comprising the laminate for an electrochemical device according to claim 15.

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