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

Abstract

The purpose of the present invention is to provide a composition capable of forming an electrochemical element functional layer that can provide excellent process adhesiveness and blocking resistance to electrochemical element members such as electrodes and separators and that enables electrochemical elements to exert excellent electrochemical properties. The composition for an electrochemical element functional layer according to the present invention is characterized by containing a particulate polymer and a binding material and is characterized in that the molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the particulate polymer is 1.0-3.0.

Description

[Technical Field]

[0001] The present invention relates to a composition for a functional layer of 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] For example, lithium-ion secondary batteries generally include battery components such as a positive electrode, a negative electrode, and a separator that separates the positive and negative electrodes to prevent short circuits between them. Here, the surfaces of the electrodes and / or separators may be provided with a porous membrane layer to improve heat resistance and strength, or an adhesive layer to improve adhesion between battery components (hereinafter, these may be collectively referred to as "functional layers"). Specifically, battery components include electrodes formed by forming a functional layer on an electrode substrate, which is formed by providing an electrode mixture layer on a current collector, and separators formed by forming a functional layer on a separator substrate. The functional layer is formed by applying a functional layer composition to the substrate and drying the applied functional layer composition.

[0004] Therefore, in recent years, improvements to functional layers have been actively pursued with the aim of further improving the performance of electrochemical devices such as lithium ion secondary batteries (for example, Patent Documents 1 and 2). Specifically, Patent Document 1 proposes a technique of incorporating a particulate polymer with specific composition and properties into a non-aqueous secondary battery functional layer composition. It has been reported that incorporating such a particulate polymer into a functional layer composition can increase the adhesiveness of the resulting functional layer and improve battery performance. Patent Document 2 proposes a technique of incorporating a particulate polymer with specific properties and inorganic particles into a composition for a porous membrane for a non-aqueous secondary battery. It has been reported that by incorporating such a particulate polymer and inorganic particles with specific properties into a composition for a porous membrane for a non-aqueous secondary battery, the heat shrinkage resistance of the resulting porous membrane (functional layer) can be improved, thereby improving battery performance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 034093 [Patent Document 2] International Publication No. 2018 / 034094 Summary of the Invention [Problem to be solved by the invention]

[0006] In the manufacturing process of electrochemical devices such as lithium-ion secondary batteries, electrochemical device components before immersion in an electrolyte solution are stacked together using a roll press or the like, and then cut to a desired size as needed or transported as a stack. During the cutting or transport, the stacked electrochemical device components may become misaligned, resulting in defects and reduced productivity. Therefore, electrochemical device components are required to have the ability to bond together electrochemical device components during the manufacturing process of the electrochemical device (process adhesion).

[0007] On the other hand, in the manufacturing process of electrochemical devices such as lithium-ion secondary batteries, it is common to store and transport long electrochemical device components as they are wound up. However, when electrochemical device components having functional layers are stored or transported in a wound state, adjacent electrochemical device components may adhere to each other via the functional layer, i.e., blocking may occur, resulting in defects and reduced productivity. Therefore, electrochemical device components having functional layers are required to ensure the above-mentioned process adhesion while also having the ability to suppress blocking during storage, transportation, and the manufacturing process (blocking resistance).

[0008] However, the functional layers according to the above-mentioned prior art leave room for improvement in terms of achieving high levels of both process adhesion and blocking resistance between electrochemical element components of electrochemical elements such as lithium ion secondary batteries. Furthermore, electrochemical elements manufactured using such functional layers leave room for improvement in their electrochemical properties (internal resistance and cycle characteristics). Therefore, an object of the present invention is to provide a technology relating to a functional layer for an electrochemical element that can impart excellent process adhesion and blocking resistance to electrochemical element components such as electrodes and separators, and that can enable the electrochemical element to exhibit excellent electrochemical properties. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems, and have found that by using a particulate polymer having predetermined properties in combination with a binder, a composition for forming a functional layer for an electrochemical device can be obtained that can form a functional layer for an electrochemical device that can impart excellent process adhesion and blocking resistance to electrochemical device components such as electrodes and separators, and that the electrochemical properties (particularly internal resistance properties and cycle properties) of an electrochemical device including a functional layer formed using the functional layer composition can be improved, thereby completing the present invention.

[0010] That is, the present invention aims to advantageously solve the above-mentioned problems. The composition for electrochemical device functional layers of the present invention is characterized by comprising a particulate polymer and a binder, and the molecular weight distribution of the particulate polymer (weight average molecular weight (Mw) / number average molecular weight (Mn)) is 1.0 or more and 3.0 or less. Thus, by incorporating a particulate polymer and a binder having a molecular weight distribution within a predetermined range into the composition for electrochemical device functional layers, a composition for electrochemical device functional layers can be obtained that can form functional layers for electrochemical devices that can impart excellent process adhesion and blocking resistance to electrochemical device components such as electrodes and separators. Furthermore, the electrochemical properties (internal resistance and cycle characteristics) of electrochemical devices equipped with functional layers formed using the composition for electrochemical device functional layers can be improved. In the present invention, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the particulate polymer can be measured by the method described in the examples.

[0011] In the composition for an electrochemical device functional layer of the present invention, the particulate polymer preferably has a dithioester structure. If the particulate polymer has a dithioester structure, the process adhesion and blocking resistance of the electrochemical device member including the obtained functional layer can be further improved.

[0012] In the composition for an electrochemical device functional layer of the present invention, the particulate polymer preferably has a glass transition temperature of 25° C. or higher and 90° C. or lower. If the particulate polymer has a glass transition temperature of 25° C. or higher and 90° C. or lower, the electrochemical device member provided with the resulting functional layer can have good both process adhesion and blocking resistance. In the present invention, the glass transition temperature of the particulate polymer can be measured by the method described in the examples.

[0013] In the composition for an electrochemical element functional layer of the present invention, the particulate polymer preferably contains a (meth)acrylic acid ester monomer unit. If the particulate polymer contains a (meth)acrylic acid ester monomer unit, the process adhesion of the resulting electrochemical element member including the functional layer can be further improved. In the present invention, the phrase "containing a monomer unit" means that "a polymer obtained using the monomer contains a structural unit derived from the monomer."

[0014] In the composition for an electrochemical element functional layer of the present invention, the binder preferably comprises a polymer containing a (meth)acrylic acid ester monomer unit. If the binder comprises a polymer containing a (meth)acrylic acid ester monomer unit, the process adhesion of the resulting electrochemical element member including the functional layer can be further improved.

[0015] The composition for an electrochemical device functional layer of the present invention preferably further contains non-conductive heat-resistant particles. If the composition for an electrochemical device functional layer further contains non-conductive heat-resistant particles, heat resistance can be imparted to the resulting functional layer.

[0016] In the composition for an electrochemical device functional layer of the present invention, the non-conductive heat-resistant particles preferably include inorganic particles. If the non-conductive heat-resistant particles include inorganic particles, the heat resistance of the resulting functional layer can be further improved.

[0017] In the composition for an electrochemical device functional layer of the present invention, the inorganic particles preferably contain at least one selected from the group consisting of alumina, boehmite, barium sulfate, and magnesium hydroxide. If the inorganic particles contain at least one selected from the group consisting of alumina, boehmite, barium sulfate, and magnesium hydroxide, the heat resistance of the resulting functional layer can be further improved.

[0018] 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 for electrochemical devices formed on the substrate, the functional layer for electrochemical devices being formed using any of the compositions for electrochemical device functional layers described above. This makes it possible to provide a laminate for electrochemical devices comprising a functional layer for electrochemical devices that can impart excellent process adhesion and blocking resistance to electrochemical device components such as electrodes and separators and that can enable the electrochemical device to exhibit excellent electrochemical properties.

[0019] Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and provides an electrochemical device comprising the above-mentioned laminate for an electrochemical device. In this way, by providing an electrochemical device with the laminate for an electrochemical device of the present invention, it is possible to provide an electrochemical device that can exhibit excellent electrochemical properties. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a composition for an electrochemical element functional layer that can impart excellent process adhesion and blocking resistance to electrochemical element components such as electrodes and separators, and can form a functional layer for an electrochemical element that can enable the electrochemical element to exhibit excellent electrochemical properties. Furthermore, according to the present invention, it is possible to provide a laminate for an electrochemical element that is capable of imparting excellent process adhesion and blocking resistance to electrochemical element components such as electrodes and separators, and that is equipped with a functional layer for an electrochemical element that can enable the electrochemical element to exhibit excellent electrochemical properties. Furthermore, according to the present invention, an electrochemical device capable of exhibiting excellent electrochemical properties can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described in detail. Here, the composition for an electrochemical device functional layer of the present invention is used as a material for producing a functional layer for an electrochemical device. The laminate for an electrochemical device of the present invention is produced using the composition for an electrochemical device functional layer of the present invention and can be used, for example, as an electrochemical device member. The electrochemical device of the present invention includes at least the laminate for an electrochemical device of the present invention as an electrochemical device member.

[0022] (Composition for electrochemical device functional layer) The composition for an electrochemical device functional layer of the present invention (hereinafter also simply referred to as "functional layer composition") contains a particulate polymer and a binder, and optionally contains other components.

[0023] <Particulate polymer> The particulate polymer contained in the functional layer composition of the present invention must have a molecular weight distribution (the weight-average molecular weight (Mw) of the particulate polymer divided by the number-average molecular weight (Mn) of the particulate polymer) of 1.0 to 3.0. By keeping the molecular weight distribution within the above range, the electrochemical device member including the obtained functional layer has excellent process adhesion and blocking resistance. Furthermore, the electrochemical device including the functional layer exhibits excellent battery chemical properties. From the viewpoint of further improving the process adhesion and blocking resistance of an electrochemical element component having a functional layer, and further improving the electrochemical properties of an electrochemical element having the functional layer, the molecular weight distribution of the particulate polymer is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.3 or less.

[0024] Here, when the molecular weight distribution (Mw / Mn) of the particulate polymer is 1.0 or more and 3.0 or less, the electrochemical element component having the resulting functional layer can be imparted with excellent process adhesion and blocking resistance, and the electrochemical element having the functional layer can exhibit excellent battery chemical properties. Although the reason for this is not entirely clear, it is presumed to be as follows. Specifically, when the molecular weight distribution (Mw / Mn) of the particulate polymer is 1.0 or more and 3.0 or less, the molecular mass of the particulate polymer contains fewer low-molecular-weight components, which are adhesive components, and thus the electrochemical device component having a functional layer is less likely to block. Furthermore, when the amount of low-molecular-weight components is small, the particulate polymer is less likely to dissolve in the electrolytic solution in the electrochemical device. This suppresses the formation of a coating by the dissolved particulate polymer, and thus suppresses an increase in the internal resistance of the electrochemical device. Furthermore, when the molecular weight distribution (Mw / Mn) of the particulate polymer is 1.0 or more and 3.0 or less, the molecular mass of the particulate polymer contains fewer high-molecular-weight components, which are resistant to softening upon heating, and thus the electrochemical device component having a functional layer exhibits adhesiveness and improves process adhesiveness. Furthermore, when the amount of high-molecular-weight components is small, the electrochemical device component maintains its adhesive strength in the electrolytic solution, improving gas release and reducing the likelihood of precipitation of ionic conductors such as lithium ions. This suppresses a decrease in the electrochemical properties of the electrochemical device. For these reasons, it is presumed that it is possible to achieve high levels of both process adhesion and blocking resistance, and also to improve the electrochemical properties of the electrochemical element.

[0025] The molecular weight distribution (Mw / Mn) of the particulate polymer can be suitably controlled, for example, by adding a chain transfer agent described later when preparing the particulate polymer. Specifically, the molecular weight distribution of the particulate polymer can be controlled by appropriately adjusting the type, amount and / or number of times of addition of the chain transfer agent when preparing the particulate polymer.

[0026] <<Weight average molecular weight (Mw) of particulate polymer>> The weight average molecular weight (Mw) of the particulate polymer is preferably 20,000 or more, more preferably 50,000 or more, even more preferably 80,000 or more, even more preferably 100,000 or more, and preferably 500,000 or less, more preferably 300,000 or less, even more preferably 200,000 or less. When the weight-average molecular weight of the particulate polymer is equal to or greater than the lower limit, the blocking resistance of the resulting electrochemical device components, such as separators and electrodes, having a functional layer is further improved. When the weight-average molecular weight of the particulate polymer is equal to or less than the upper limit, the process adhesion of the resulting electrochemical device components, such as separators and electrodes, having a functional layer is further improved. The weight average molecular weight of the particulate polymer can be obtained as a value converted into standard polystyrene by gel permeation chromatography (GPC).

[0027] <<Glass transition temperature (Tg) of particulate polymer>> The glass transition temperature (Tg) of the particulate polymer is preferably 25°C or higher, more preferably 30°C or higher, and even more preferably 35°C or higher. It is also preferably lower than the glass transition temperature of organic particles serving as non-conductive heat-resistant particles, which will be described later, and is more preferably 90°C or lower, and even more preferably 80°C or lower. When the glass transition temperature of the particulate polymer is equal to or higher than the lower limit, blocking of the resulting electrochemical element member having a functional layer can be further suppressed. On the other hand, when the glass transition temperature of the particulate polymer is 90°C or lower, the process adhesion of the resulting electrochemical element member having a functional layer can be further improved.

[0028] <<Volume average particle size of particulate polymer>> The volume average particle diameter of the particulate polymer in the composition for the functional layer is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1.0 μm or more, particularly preferably 2.5 μm or more, and most preferably 5.0 μm or more, and is preferably 10.0 μm or less, more preferably 9.0 μm or less, and even more preferably 8.0 μm or less. If the volume average particle diameter of the particulate polymer is equal to or greater than the lower limit, when the functional layer composition contains the non-conductive heat-resistant particles described below, the particulate polymer is more likely to protrude from the surface of the layer of non-conductive heat-resistant particles in the resulting functional layer. Therefore, the electrochemical element member having the functional layer can exhibit superior process adhesion. Furthermore, if the volume average particle diameter of the particulate polymer is equal to or less than the upper limit, the particulate polymer particles are less likely to fall off from the layer of non-conductive heat-resistant particles, and the decrease in process adhesion can be further suppressed. In the present invention, the volume average particle size of the particulate polymer can be measured by the method described in the Examples.

[0029] <<Composition of particulate polymer>> The composition of the particulate polymer contained in the composition for a functional layer of the present invention is not particularly limited as long as the desired effects of the present invention can be obtained. Therefore, as the particulate polymer, for example, a known polymer that can be used as a particulate polymer when producing a functional layer for an electrochemical device can be used.

[0030] Examples of the monomer units constituting the particulate polymer include (meth)acrylic acid ester monomer units and aromatic vinyl monomer units. The particulate polymer may contain one type of these monomer units alone or two or more types in any ratio, but preferably contains at least a (meth)acrylic acid ester monomer unit. In the present invention, "(meth)acrylic" means acrylic and / or methacrylic.

[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, and n-butyl acrylate is more 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 the particulate polymer is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 65% ​​by mass or less, more preferably 60% by mass or less, when the total repeating units of the particulate polymer are taken as 100% by mass. If the content of (meth)acrylic acid ester monomer units is equal to or less than the upper limit, the blocking resistance of the electrochemical element member having the obtained functional layer can be improved. On the other hand, if the content of (meth)acrylic acid ester monomer units is equal to or greater than the lower limit, the adhesion between the functional layer and the substrate can be improved. In the present invention, the "content ratio of each monomer unit" is1 It can be measured using nuclear magnetic resonance (NMR) techniques such as H-NMR.

[0033] [Aromatic vinyl monomer unit] When the particulate polymer contains an aromatic vinyl monomer unit, the elasticity of the particulate polymer is improved, and the strength of the functional layer can be increased. Here, examples of aromatic vinyl monomers capable of forming aromatic vinyl monomer units include, but are not limited to, styrene, α-methylstyrene, styrenesulfonic acid, butoxystyrene, vinylnaphthalene, etc., and among these, styrene is preferred. These aromatic vinyl monomers may be used singly or in combination of two or more kinds in any ratio.

[0034] The content of aromatic vinyl monomer units in the particulate polymer is preferably 30% by mass or more, more preferably 60% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, when the total amount of monomer units in the particulate polymer is 100% by mass. If the content of aromatic vinyl monomer units is equal to or greater than the lower limit, the elasticity of the particulate polymer is improved, the strength of the resulting functional layer is ensured, and the adhesion of the functional layer to the substrate can be improved. On the other hand, if the content of aromatic vinyl monomer units is equal to or less than the upper limit, the flexibility of the particulate polymer is increased, and the adhesion of the functional layer to the substrate can be improved.

[0035] [Other monomer units] The particulate polymer may contain other monomer units in addition to the (meth)acrylic acid ester monomer units and the aromatic vinyl monomer units. The other monomer units are not particularly limited, but examples thereof include acid group-containing monomer units, crosslinkable monomer units, and nitrile group monomer units, which will be described later in the section on "binder."

[0036] The content of the other monomer units in the particulate polymer is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less. When the content of the other monomer units is 10% by mass or less, the stability of the functional layer composition used to form the functional layer can be prevented from decreasing.

[0037] [Dithioester structure] The particulate polymer preferably contains a dithioester structure. If the particulate polymer has a dithioester structure, the process adhesion and blocking resistance of the electrochemical device member having the obtained functional layer can be further improved. The dithioester structure can be suitably imparted by adding a dithioester compound as a chain transfer agent, which will be described later, to the polymerization system during preparation of the particulate polymer. The particulate polymer may have the dithioester structure in the molecule and / or at the molecular terminal. Here, the term "dithioester structure" refers to a chemical structure having a thiocarbonylthio group (-C(=S)-S-). The "dithioester structure" can be introduced by using a compound having a dithioester structure and a free radical leaving group as a chain transfer agent.

[0038] The content of the dithioester structure in the particulate polymer is not particularly limited, but is preferably 0.004% by mass or less relative to 100% by mass of the particulate polymer. The content of the dithioester structure in the particulate polymer can be measured by infrared spectroscopy (IR) such as FT-IR.

[0039] <<Preparation of particulate polymers>> 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.

[0040] The polymerization method is not particularly limited, and any method such as a suspension polymerization method, an emulsion polymerization aggregation method, a pulverization method, or a dissolution suspension method can be used. Among them, from the viewpoint of efficiently preparing a particulate polymer, the suspension polymerization method and the emulsion polymerization aggregation method are preferred, and the suspension polymerization method is more preferred. Furthermore, as the polymerization reaction, any reaction such as radical polymerization or living radical polymerization can be used, but from the viewpoint of well controlling the molecular weight distribution of the particulate polymer using a chain transfer agent, living radical polymerization is preferred.

[0041] Therefore, when preparing the particulate polymer, it is preferable that the polymerization system contains a chain transfer agent. By adding the chain transfer agent to the polymerization system, the molecular weight distribution of the obtained particulate polymer can be well controlled. Here, the chain transfer agent is not particularly limited, and known chain transfer agents used in the preparation of conventional particulate polymers can be used. However, from the viewpoint of imparting the above-mentioned dithioester structure to the obtained particulate polymer, it is preferable to use a dithioester compound (dithioester derivative) having a thiocarbonylthio group (-C(=S)-S-) in the molecule. Examples of dithioester compounds that can impart the above-mentioned dithioester structure to the particulate polymer include dithioesters, dithiobenzoates, dithiocarbamates, trithiocarbonates, and xanthates. Specific examples of such dithioester compounds that can be used in the present invention include dithioester compounds represented by the following structural formula: [ka] [ka] These chain transfer agents can be used alone or in combination of two or more in any ratio.

[0042] The amount of the chain transfer agent used is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.5 parts by mass or more, and particularly preferably 1.0 parts by mass or more, per 100 parts by mass of the total monomers in the monomer composition. It is also preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less, even more preferably 3.0 parts by mass or less, and particularly preferably 2.0 parts by mass or less. When the amount of the chain transfer agent used is equal to or greater than the above-mentioned lower limit, the molecular weight distribution of the resulting particulate polymer can be well controlled. When the amount of the chain transfer agent used is equal to or less than the above-mentioned upper limit, the proportion of low molecular weight molecules in the molecular mass of the resulting particulate polymer can be kept low, which can further improve the blocking resistance of the electrochemical device member having the resulting functional layer, and can further suppress deterioration of the electrochemical properties of the electrochemical device.

[0043] The chain transfer agent may be added to the polymerization system all at once or in two or more divided portions, but is preferably added all at once from the viewpoint of narrowing the molecular weight distribution of the resulting particulate polymer, because adding the chain transfer agent in divided portions increases the amount of low molecular weight compounds produced, which tends to broaden the molecular weight distribution.

[0044] [Other compounding agents] Further, the monomer composition used in preparing the particulate polymer may contain other additives such as 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.

[0045] Here, as an example, a method for preparing a particulate polymer by suspension polymerization will be described.

[0046] [Preparation of particulate polymers by suspension polymerization] (1) Preparation of Monomer Composition First, the monomers constituting the desired particulate polymer, and a chain transfer agent and / or other compounding agents added as needed, are mixed to prepare a monomer composition. (2) Droplet formation Next, the monomer composition is dispersed in water, a polymerization initiator is added, and then droplets of the monomer composition are formed. Here, the method for forming the droplets is not particularly limited, and for example, the droplets can be formed by shearing and stirring an aqueous medium containing the monomer composition using a disperser such as an emulsifying disperser.

[0047] In this case, examples of the polymerization initiator to be used include oil-soluble polymerization initiators such as t-butylperoxy-2-ethylhexanoate and azobisisobutyronitrile. The polymerization initiator may be added after the monomer composition is dispersed in water and before droplets are formed, or may be added to the monomer composition before it is dispersed in water.

[0048] From the viewpoint of stabilizing the formed droplets of the monomer composition in water, it is preferable to form the droplets of the monomer composition by adding a dispersion stabilizer to the water. In this case, the dispersion stabilizer may be, for example, a metal hydroxide such as magnesium hydroxide, or sodium dodecylbenzenesulfonate.

[0049] (3) Polymerization After forming droplets of the monomer composition, the water containing the formed droplets is heated to initiate polymerization, thereby forming a particulate polymer in the water. At this time, 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. When the chain transfer agent is added in portions, the second and subsequent additions are carried out during the polymerization reaction (during the heat treatment).

[0050] (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.

[0051] <Binding material> The binder contained in the functional layer composition is used to prevent components such as the particulate polymer from falling off from the functional layer.

[0052] <<Binder composition>> The composition of the binder is not particularly limited, and examples thereof include known polymers that are water-insoluble and dispersible in a dispersion medium such as water. Among these, conjugated diene polymers and acrylic polymers are preferred, and acrylic polymers are more preferred. The acrylic polymer refers to a polymer containing a (meth)acrylic acid ester monomer unit. 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.

[0053] 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. These binders may be used singly or in combination of two or more kinds in any ratio.

[0054] 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 (meth)acrylic acid ester monomer unit, and an acid group-containing monomer unit, a nitrile group-containing monomer unit, and a crosslinkable monomer unit, which will be described below.

[0055] [Acid group-containing monomer unit] Examples of acid group-containing monomers that can form acid 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.

[0056] 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, and 3-allyloxy-2-hydroxypropanesulfonic acid. 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 acid group-containing monomers may be used alone or in combination of two or more kinds in any ratio.

[0057] [Nitrile group-containing monomer unit] Examples of nitrile group-containing monomers capable of forming nitrile group-containing monomer units include α,β-ethylenically unsaturated nitrile monomers. Specifically, the α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, and examples thereof include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. These nitrile group-containing monomers may be used alone or in combination of two or more kinds in any ratio.

[0058] [Crosslinkable monomer unit] The crosslinkable monomer unit is a monomer unit that can form a crosslinked structure during or after polymerization by heating or irradiation with energy rays. 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. Among these, allyl methacrylate, ethylene glycol dimethacrylate, and allyl glycidyl ether are preferred. These crosslinkable monomers may be used singly or in combination of two or more kinds in any ratio.

[0059] [Content ratio of each monomer unit] The content 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, when the total repeating units in the acrylic polymer is taken as 100% by mass. By making the content of (meth)acrylic acid ester monomer units equal to or greater than the lower limit of the above range, the process adhesion and wet adhesion of the functional layer can be further improved. Furthermore, by making the content equal to or less than the upper limit, the electrochemical properties of an electrochemical device including the functional layer can be further improved.

[0060] The content 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, when the total amount of repeating units in the acrylic polymer is taken as 100% by mass. By making the content of the acid group-containing monomer units equal to or greater than the lower limit, the dispersibility of the binder 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 content of the acid group-containing monomer units equal to or less than the 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.

[0061] The content of the nitrile group-containing monomer units in the acrylic polymer is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 30% by mass or less, and more preferably 20% by mass or less, when the total amount of repeating units in the acrylic polymer is taken as 100% by mass. If the content of the nitrile group-containing monomer units is equal to or greater than the lower limit, the binding strength of the acrylic polymer can be improved, and the process adhesion and wet adhesion of the functional layer can be further enhanced. On the other hand, if the content of the nitrile group-containing monomer units is equal to or less than the upper limit, the flexibility of the acrylic polymer can be increased.

[0062] The content of the 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, when the amount of all monomer units in the acrylic polymer is taken as 100% by mass. By making the content of the crosslinkable monomer units equal to or greater than the above-mentioned lower limit, the electrochemical properties of an electrochemical device including a functional layer can be further improved. Furthermore, by making the content of the crosslinkable monomer units equal to or less than the above-mentioned upper limit, the process adhesion and wet adhesion of the functional layer can be further improved.

[0063] [Other monomer units] Furthermore, the acrylic polymer may contain other monomer units. Examples of other monomers that can form other monomer units that can be contained in the acrylic polymer include aliphatic conjugated diene monomers such as 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-butadiene; aromatic vinyl monomers described in the section "Composition of Particulate Polymer," olefin monomers such as ethylene and propylene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether; vinyl ketone monomers such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; and heterocycle-containing vinyl compound monomers such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole. These other monomers may be used singly or in any combination of two or more at any ratio. The content of the other monomer units in the acrylic polymer may be adjusted as appropriate.

[0064] <<Binding material structure>> The structure of the binder in the composition for the functional layer may be the same as or different from the structure of the binder in the functional layer. For example, the structure of the binder in the composition for the functional layer may be particulate or non-particulate. The structure of the binder in the functional layer is not particularly limited, but is usually non-particulate.

[0065] <<Volume average particle size of binder>> When the binder is present in particulate form in the functional layer composition, the volume average particle diameter of the binder is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.15 μm or more, and is preferably 0.5 μm or less, more preferably 0.4 μm or less, and even more preferably 0.3 μm or less. If the volume average particle diameter of the binder is equal to or greater than the lower limit, the dispersibility of the binder in the functional layer can be improved. If the volume average particle diameter is equal to or less than the upper limit, the particulate polymer can be more effectively bound in the functional layer. In the present invention, the volume average particle size of the binder can be measured by the method described in the examples.

[0066] <<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, and even more preferably -80°C or higher. It is also preferably lower than the glass transition temperature of the particulate polymer, more preferably 30°C or lower, even more preferably 20°C or lower, and particularly preferably 15°C or lower. If the glass transition temperature of the binder is above the lower limit, the adhesiveness and strength of the binder can be increased. If the glass transition temperature of the binder is 30°C or lower, the particulate polymer can be fixed to the substrate without heating, allowing the functional layer to be well formed on the substrate. In the present invention, the glass transition temperature of the binder can be measured by the method described in the examples.

[0067] <<Binder content>> The content of the binder in the composition for the functional layer 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 particulate polymer. If the content of the binder is equal to or greater than the above-mentioned lower limit, the particulate polymer can be sufficiently prevented from falling off the functional layer, and the process adhesion and wet adhesion of the functional layer can be sufficiently improved. On the other hand, if the content of the binder is equal to or less than the above-mentioned upper limit, a decrease in the ionic conductivity of the functional layer can be suppressed, and a decrease in the electrochemical properties of the electrochemical element can be suppressed.

[0068] 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.

[0069] 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.

[0070] <Other ingredients> The composition for a functional layer of the present invention may further contain other components in addition to the particulate polymer and binder described above, such as a dispersion medium, non-conductive heat-resistant particles, a water-soluble polymer, and other additives.

[0071] <<Dispersion medium>> The dispersion medium that can be optionally contained in the functional layer composition of the present invention is capable of turning the functional layer composition into a slurry (hereinafter, the slurry functional layer composition may be referred to as a "slurry functional layer composition"). When forming a functional layer using the functional layer slurry composition, including a drying step, the dispersion medium volatilizes. As a result, a functional layer consisting of the solid content (dried matter) of the functional layer slurry composition is obtained.

[0072] As the dispersion medium, any medium can be used that can be volatilized during the formation of the functional layer, has low dissolving properties for components such as the particulate polymer, and can maintain the dispersion state of the components such as the particulate polymer. An aqueous medium is preferred as the dispersion medium. The aqueous medium is water or a mixture of water and a medium other than water. By using an aqueous medium as the dispersion medium, the environmental load can be reduced and the handling of the slurry composition for the functional layer can be made easier.

[0073] Examples of aqueous media that can be used in combination with water include cycloaliphatic hydrocarbon compounds such as cyclopentane and cyclohexane; aromatic hydrocarbon compounds such as toluene and xylene; ketone compounds such as ethyl methyl ketone and cyclohexanone; ester compounds such as ethyl acetate, butyl acetate, γ-butyrolactone, and ε-caprolactone; nitrile compounds such as acetonitrile and propionitrile; ether compounds such as tetrahydrofuran and ethylene glycol diethyl ether; alcohol compounds such as methanol, ethanol, isopropanol, ethylene glycol, and ethylene glycol monomethyl ether; and amide compounds such as N-methylpyrrolidone (NMP) and N,N-dimethylformamide. These may be used alone or in combination of two or more in any ratio. The amount of the medium other than water is preferably 5 parts by mass or less per 100 parts by mass of water.

[0074] The amount of the dispersion medium in the functional layer slurry composition is preferably set so that the solid content of the functional layer slurry composition falls within a desired range. The specific solid content of the functional layer slurry composition is preferably 10% by weight or more, more preferably 15% by weight or more, even more preferably 20% by weight or more, and preferably 80% by weight or less, more preferably 75% by weight or less, even more preferably 70% by weight or less, and particularly preferably 65% ​​by weight or less. By setting the solid content within the above range, the functional layer slurry composition can have properties suitable for the coating and drying processes.

[0075] <<Non-conductive heat-resistant particles>> The non-conductive heat-resistant particles that may be optionally contained in the functional layer composition of the present invention are materials that can impart heat resistance to the resulting functional layer. If the functional layer composition contains non-conductive heat-resistant particles, the resulting functional layer can combine the adhesiveness of the particulate polymer with the heat resistance of the non-conductive heat-resistant particles, which is preferable. The non-conductive heat-resistant particles can be inorganic particles and / or organic particles. In particular, it is preferable that the non-conductive heat-resistant particles contain inorganic particles. If the functional layer composition contains inorganic particles, the heat resistance of the resulting functional layer can be further improved. The inorganic particle material is preferably stable in the environment in which the electrochemical device is used and is electrochemically stable. From this perspective, preferred inorganic particle materials include oxide particles such as aluminum oxide (alumina), aluminum oxide hydrate (boehmite (AlOOH)), gibbsite (Al(OH)), silicon oxide, magnesium hydroxide (magnesia), magnesium hydroxide, calcium oxide, titanium oxide (titania), barium titanate (BaTiO), 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 particles such as talc, montmorillonite, kaolin, and calcined kaolin. Among these, the inorganic particles preferably contain one selected from the group consisting of alumina, boehmite, barium sulfate, and magnesium hydroxide, and more preferably contain alumina. Furthermore, these inorganic particles may be subjected to element substitution, surface treatment, solid solution formation, etc., as required. These inorganic particles may be used alone or in combination of two or more kinds in any ratio. The organic particle material is preferably stable in the environment in which the electrochemical device is used and is electrochemically stable. From this perspective, preferred materials for the organic particles include those containing polyfunctional ethylenically unsaturated monomer units. As the polyfunctional ethylenically unsaturated monomer capable of forming the polyfunctional ethylenically unsaturated monomer unit, a monomer having two or more ethylenically unsaturated bonds per molecule (excluding conjugated diene monomers such as 1,3-butadiene) can be used.

[0076] Here, examples of the polyfunctional ethylenically unsaturated monomer include polyfunctional (meth)acrylic acid ester monomers such as allyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate; Polyfunctional aromatic vinyl monomers such as divinylbenzene and diisopropenylbenzene; Examples of such an ester include dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane diallyl ether, allyl or vinyl ethers of polyfunctional alcohols other than those mentioned above, triallylamine, methylenebisacrylamide, etc. Among these, from the viewpoint of further improving the heat shrinkage resistance of the functional layer, polyfunctional (meth)acrylic acid ester monomers and polyfunctional aromatic vinyl monomers are preferred, polyfunctional (meth)acrylic acid ester monomers are more preferred, and ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate are even more preferred. The content of the polyfunctional monomer units in the organic particles is preferably 50% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more, and is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 83% by mass or less, assuming that the total repeating units of the polymer constituting the organic particles is 100% by mass. These organic particles may be used alone or in combination of two or more kinds at any ratio. Furthermore, organic particles and inorganic particles may be used in combination at any ratio. In addition, from the viewpoint of imparting heat resistance, the glass transition temperature (Tg) of the organic particles is preferably higher than 200° C. The glass transition temperature of the organic particles can be measured by differential scanning calorimetry (DSC) described in the examples, similar to the glass transition temperatures of the above-mentioned particulate polymer and binder.

[0077] [Volume average particle size of non-conductive heat-resistant particles] The volume average particle diameter (D50) of the non-conductive heat-resistant particles is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.3 μm or more, and preferably 1 μm or less, more preferably 0.9 μm or less, and even more preferably 0.8 μm or less. When the volume average particle diameter of the non-conductive heat-resistant particles is equal to or greater than the above-mentioned lower limit, it is possible to satisfactorily achieve both dense packing of the non-conductive heat-resistant particles in the functional layer and improved output characteristics of the resulting electrochemical device. Furthermore, when the volume average particle diameter of the non-conductive heat-resistant particles is equal to or less than the above-mentioned upper limit, it is possible to ensure that the functional layer exhibits excellent heat resistance even when the thickness of the non-conductive heat-resistant particle layer described below is reduced, thereby increasing the capacity of the electrochemical device. The volume average particle size (D50) of the non-conductive heat-resistant particles can be measured by the method described in the examples of this specification.

[0078] [Volume ratio of non-conductive heat-resistant particles to particulate polymer] The volume ratio of the non-conductive heat-resistant particles to the particulate polymer (non-conductive heat-resistant particles / particulate polymer) in the composition for the functional layer is preferably 55 / 45 or more, more preferably 60 / 40 or more, even more preferably 65 / 35 or more, preferably 95 / 5 or less, more preferably 80 / 20 or less, even more preferably 75 / 25 or less, and particularly preferably 70 / 30 or less. If the volume ratio of the non-conductive heat-resistant particles to the particulate polymer in the composition for the functional layer is equal to or greater than the lower limit, the heat resistance of the functional layer produced can be improved. On the other hand, if the volume ratio of the non-conductive heat-resistant particles to the particulate polymer in the composition for the functional layer is equal to or less than the upper limit, the process adhesion of the functional layer produced can be further improved.

[0079] [Mass ratio of non-conductive heat-resistant particles to particulate polymer] Furthermore, the mass ratio of the non-conductive heat-resistant particles to the particulate polymer (non-conductive heat-resistant particles / particulate polymer) in the composition for the functional layer is preferably 49 / 51 or more, more preferably 58 / 42 or more, even more preferably 64 / 36 or more, and preferably 99 / 1 or less, more preferably 94 / 6 or less, and even more preferably 91 / 9 or less. If the mass ratio of the non-conductive heat-resistant particles to the particulate polymer in the composition for the functional layer is equal to or greater than the lower limit, the heat resistance of the functional layer produced can be improved. On the other hand, if the mass ratio of the non-conductive heat-resistant particles to the particulate polymer in the composition for the functional layer is equal to or less than the upper limit, the process adhesion of the functional layer produced can be further improved.

[0080] <<Water-soluble polymer>> The water-soluble polymer that can be optionally contained in the functional layer composition of the present invention is a water-soluble polymer used to well disperse components such as a particulate polymer and a binder in the functional layer. If the functional layer composition contains a water-soluble polymer, the components such as the particulate polymer and the binder are well dispersed in the resulting functional layer, so that the functional layer can exhibit even better process adhesion. In the present invention, a polymer being "water-soluble" means that when 0.5 g of the polymer is dissolved in 100 g of water at 25°C, the insoluble content is less than 1.0 mass %.

[0081] As the water-soluble polymer that can be contained in the composition for the functional layer, it is preferable to use polyacrylic acid from the viewpoint of dispersing the particulate polymer and the binder in the functional layer more satisfactorily.

[0082] The content of the water-soluble polymer in the functional layer composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.3 parts by mass or more, and preferably 1 part by mass or less, more preferably 0.9 parts by mass or less, and even more preferably 0.8 parts by mass or less, per 100 parts by mass of the particulate polymer. If the content of the water-soluble polymer is above the above-mentioned lower limit, the particulate polymer and the binder can be more effectively dispersed in the functional layer, thereby further improving the process adhesion of the electrochemical element member including the functional layer. On the other hand, if the content of the water-soluble polymer is below the above-mentioned upper limit, a decrease in the ionic conductivity of the functional layer can be suppressed, and a decrease in the electrochemical properties of the electrochemical element can be suppressed.

[0083] <<Other additives>> Other additives that may be optionally contained in the functional layer composition include thickeners and dispersants. Examples of the thickener include carboxymethyl cellulose. Examples of the dispersant include sodium dodecylbenzenesulfonate. The amount of these additives used in the composition for the functional layer can be appropriately set within a range that provides the desired effects of the present invention.

[0084] <Preparation of Functional Layer Composition> Although the method for preparing the functional layer composition of the present invention is not particularly limited, typically, a particulate polymer, a binder, water as a dispersion medium, and optional components (non-conductive heat-resistant particles, water-soluble polymer, and / or other additives) are mixed together to prepare a functional layer slurry composition. Although the mixing method is not particularly limited, a disperser is typically used as a mixing device to efficiently disperse each component. The dispersing machine is preferably a machine capable of uniformly dispersing and mixing the above components. Examples include a ball mill, a sand mill, a pigment dispersing machine, a crusher, an ultrasonic dispersing machine, a homogenizer, a planetary mixer, etc. In addition, from the viewpoint of being able to apply a high dispersion shear, high-dispersing machines such as a bead mill, a roll mill, and a Filmix are also suitable.

[0085] (Laminate for electrochemical devices) A functional layer for an electrochemical device (hereinafter also simply referred to as "functional layer") can be obtained by forming the functional layer composition described above on a suitable substrate. By forming the functional layer on the substrate in this manner, a laminate for an electrochemical device (hereinafter also simply referred to as "laminate") of the present invention can be obtained. The functional layer formed on the substrate can impart excellent process adhesion and blocking resistance to the electrochemical device components. This can also enable the electrochemical device to exhibit excellent electrochemical properties (internal resistance properties and cycle properties).

[0086] <Functional layer for electrochemical devices> The functional layer for electrochemical devices contains a particulate polymer and a binder, and optionally contains non-conductive heat-resistant particles, a water-soluble polymer, etc. Note that the particulate polymer, binder, non-conductive heat-resistant particles, water-soluble polymer, etc. may be those described above in the section "Composition for electrochemical device functional layer." The particulate polymer contained in the functional layer is not particularly limited as long as it is in particulate form. Furthermore, after bonding the members together via the functional layer, the particulate polymer may be in a particle shape or any other shape.

[0087] The thickness of the functional layer is preferably 0.01 μm or more, more preferably 0.1 μm or more, even more preferably 0.5 μm or more, and is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 6 μm or less. When the thickness of the functional layer is at least the lower limit of the above range, the strength of the functional layer can be sufficiently ensured, and when the thickness is at most the upper limit of the above range, the ion diffusibility of the functional layer can be ensured, and the low-temperature output characteristics of the electrochemical device can be further improved.

[0088] The functional layer is not particularly limited and may be used as an adhesive layer that does not contain non-conductive heat-resistant particles, or may be used as an adhesive layer that contains non-conductive heat-resistant particles, but is preferably used as an adhesive layer that contains non-conductive heat-resistant particles, because, as described above, the inclusion of non-conductive heat-resistant particles can impart heat resistance to the functional layer, and the functional layer can function as both an adhesive layer and a heat-resistant layer in one layer. Here, when the functional layer contains non-conductive heat-resistant particles, the area in the functional layer where the non-conductive heat-resistant particles are present is referred to as the non-conductive heat-resistant particle layer. That is, for example, when the non-conductive heat-resistant particles are present only in a portion of the thickness direction of the functional layer (for example, when the particle diameter of the particulate polymer contained in the functional layer is larger than the area where the non-conductive heat-resistant particles are present), the thickness of the non-conductive heat-resistant particle layer will be smaller than the thickness of the functional layer. On the other hand, when the non-conductive heat-resistant particles are present throughout the entire thickness of the functional layer, the thickness of the functional layer and the thickness of the non-conductive heat-resistant particle layer will be equal.

[0089] [Thickness of non-conductive heat-resistant particle layer] The thickness of the non-conductive heat-resistant particle 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 non-conductive heat-resistant particle layer is equal to or greater than the above lower limit, the heat resistance of the functional layer can be improved. On the other hand, if the thickness of the non-conductive heat-resistant particle layer is equal to or less than the above upper limit, a decrease in the energy density of an electrochemical element including the functional layer can be suppressed. Furthermore, if the thickness of the non-conductive heat-resistant particle layer is equal to or less than the above upper limit, the process adhesion of the functional layer can be improved. The thickness of the non-conductive heat-resistant particle layer can be measured, for example, by observing the cross section of the laminate using a field emission scanning electron microscope (FE-SEM) or the like and from the obtained SEM image. Here, the thickness of the non-conductive heat-resistant particle layer is defined as the distance from the surface of the substrate on which the functional layer is formed to the non-conductive heat-resistant particle that is farthest in the vertical direction. The thickness of the non-conductive heat-resistant particle layer can be adjusted, for example, by the content ratio of the non-conductive heat-resistant particles in the functional layer composition used in the method for forming a laminate for electrochemical devices described below, and the thickness of the coating film to be formed.

[0090] When the functional layer includes a non-conductive heat-resistant particle layer, the particulate polymer contained in the functional layer preferably has a volume average particle diameter larger than the thickness of the non-conductive heat-resistant particle layer, thereby allowing the functional layer to exhibit good process adhesion. In the functional layer, the particulate polymer is usually at least partially embedded in the non-conductive heat-resistant particle layer. The non-conductive heat-resistant particle layer may further contain other components in addition to the non-conductive heat-resistant particles. Note that the other components are usually contained in the non-conductive heat-resistant particle layer. Examples of other components that the non-conductive heat-resistant particle layer may contain include the above-mentioned binder and water-soluble polymer.

[0091] <<Volume average particle size of particulate polymer>> Here, the particulate polymer in the functional layer preferably has a volume average particle diameter of 0.1 μm or more, more preferably 1.0 μm or more, even more preferably 2.5 μm or more, and particularly preferably 5.0 μm or more, and preferably 10.0 μm or less, more preferably 9.0 μm or less, and even more preferably 8.0 μm or less.

[0092] If the volume average particle diameter of the particulate polymer in the functional layer is equal to or greater than the lower limit, the particulate polymer is more likely to protrude from the non-conductive heat-resistant particles on the thickness-direction surface of the functional layer, thereby enabling the functional layer to exhibit even better process adhesiveness. Furthermore, when a component having a functional layer is bonded to another component, a gap is secured between the non-conductive heat-resistant particle layer and the other component in the thickness direction of the functional layer. Furthermore, since the electrolyte is injected through this gap, the electrolyte injection properties of the electrochemical element are improved. Furthermore, if the volume average particle diameter of the particulate polymer in the functional layer is equal to or greater than the lower limit, the heat resistance of the functional layer is improved. Here, the reason why the heat resistance of the functional layer is improved by setting the volume average particle diameter of the particulate polymer in the functional layer to the above-mentioned lower limit or more is not clear, but is presumed as follows. That is, in order to improve heat resistance, the proportion of non-conductive heat-resistant particles in the functional layer needs to be high. Then, it is thought that the particulate polymer protrudes from the non-conductive heat-resistant particles on the thickness direction surface of the functional layer, which apparently increases the proportion of non-conductive heat-resistant particles in the non-conductive heat-resistant particle layer, thereby improving heat resistance.

[0093] On the other hand, if the volume average particle diameter of the particulate polymer in the functional layer is below the above upper limit, the number of particles relative to the volume of the particulate polymer in the functional layer increases, and the number of bonding points increases when bonding a component having the functional layer to another component, thereby further improving the process adhesion of the functional layer.

[0094] The volume average particle size of the particulate polymer in the functional layer can be adjusted, for example, by the type and amount of metal hydroxide used when preparing the particulate polymer used in producing the functional layer. The volume average particle size of the particulate polymer in the functional layer can be measured by the method described in the Examples.

[0095] <<Ratio of volume average particle size of particulate polymer to thickness of non-conductive heat-resistant particle layer>> In addition, the ratio of the volume average particle diameter of the particulate polymer in the functional layer to the thickness of the non-conductive heat-resistant particle layer (volume average particle diameter of the particulate polymer / thickness of the non-conductive heat-resistant particle layer) is preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.6 or more, and is preferably 10.0 or less, more preferably 5.0 or less, even more preferably 3.5 or less.

[0096] When the ratio of the volume average particle diameter of the particulate polymer in the functional layer to the thickness of the non-conductive heat-resistant particle layer is equal to or greater than the lower limit, the particulate polymer is more likely to protrude from the non-conductive heat-resistant particles on the thickness-wise surface of the functional layer, thereby enabling the functional layer to exhibit even better process adhesiveness. Furthermore, when a component having a functional layer is bonded to another component, a gap is secured between the non-conductive heat-resistant particle layer and the other component in the thickness direction of the functional layer. Furthermore, since the electrolyte is injected through this gap, the electrolyte injection properties of the electrochemical element are improved. Furthermore, when the ratio of the volume average particle diameter of the particulate polymer in the functional layer to the thickness of the non-conductive heat-resistant particle layer is equal to or greater than the lower limit, the heat resistance of the functional layer is improved.

[0097] On the other hand, if the ratio of the volume average particle diameter of the particulate polymer in the functional layer to the thickness of the non-conductive heat-resistant particle layer is not more than the above upper limit, the number of particles relative to the volume of the particulate polymer in the functional layer increases, and the number of bonding points increases when bonding a component having the functional layer to another component, thereby further improving the process adhesion of the functional layer.

[0098] <<Other additives>> The functional layer may further contain, as other components, additives other than the non-conductive heat-resistant particles and the water-soluble polymer. Additives that can be optionally contained in the functional layer include those described in the section [Composition for electrochemical device functional layer]. The amount of these additives used in the functional layer can be appropriately set within a range that provides the desired effects of the present invention.

[0099] <Base material> The type of substrate on which the functional layer is formed is not particularly limited. For example, when the functional layer is used as a component constituting part of the separator, a separator substrate can be used as the substrate. Also, when the functional layer is used as a component constituting part of the electrode, an electrode substrate formed by forming an electrode mixture layer on a current collector can be used as the substrate. Furthermore, there are no particular limitations on the use of the laminate obtained by forming a functional layer on a substrate using a functional layer composition. For example, the functional layer may be formed on a separator substrate or the like and used as an electrochemical element component such as a separator, or the functional layer may be formed on an electrode substrate and used as an electrode, or the functional layer formed on a release substrate may be peeled off from the release substrate and attached to another substrate to be used as an electrochemical element component. However, from the viewpoint of improving the manufacturing efficiency of the electrochemical element member by omitting the step of peeling off the release substrate from the functional layer, it is preferable to use a separator substrate or an electrode substrate as the substrate and use the laminate as is as the electrochemical element member. The functional layer formed on the separator substrate or the electrode substrate contains the above-mentioned particulate polymer and binder, and therefore can impart excellent process adhesion and blocking resistance to the electrochemical element member and can improve the electrochemical characteristics of the electrochemical element.

[0100] <<Separator substrate>> The separator substrate for forming the functional layer is not particularly limited, and can be, for example, one described in JP 2012-204303 A. Among these, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it can reduce the overall separator thickness, thereby increasing the proportion of electrode active material in the electrochemical device and increasing the capacity per volume.

[0101] <<Electrode base material>> The electrode substrates (positive electrode substrate and negative electrode substrate) on which the functional layers are formed 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 components in the electrode mixture layer (e.g., electrode active materials (positive electrode active materials, negative electrode active materials) and electrode mixture layer binders (positive electrode mixture layer binders, negative electrode mixture layer binders)), and the method for forming the electrode mixture layer on the current collector can be known. Specifically, for example, the method described in JP 2013-145763 A can be used.

[0102] [Release base material] The release substrate on which the functional layer is formed is not particularly limited, and any known release substrate can be used.

[0103] <<Other layers>> The laminate of the present invention may further include one or more layers on the substrate other than the functional layer described above that exhibit the desired function. For example, the laminate may include a heat-resistant layer containing non-conductive heat-resistant particles and a binder between the substrate and the functional layer. This allows the laminate to be imparted with heat resistance even when the functional layer is used as an adhesive layer that does not contain non-conductive heat-resistant particles. The non-conductive heat-resistant particles and binder used in the heat-resistant layer may be those described above. The thickness of the heat-resistant layer is not particularly limited as long as it can provide sufficient heat resistance, but is preferably 0.1 μm or more, more preferably 0.2 μm or more, and is preferably 20 μm or less, more preferably 15 μm or less. By setting the thickness of the heat-resistant layer within the above range, it is possible to suppress a decrease in ionic conductivity and the heat-resistant layer has sufficient binding properties. The method for producing the heat-resistant layer is not particularly limited, and the heat-resistant layer can be formed, for example, by applying a slurry for the heat-resistant layer containing non-conductive heat-resistant particles, a binder, and a dispersion medium such as water onto a substrate and drying the resulting coating film. Alternatively, the heat-resistant layer may be formed on the above-mentioned release substrate, and then peeled off from the release material and attached to the substrate. The other layers such as the heat-resistant layer may be provided on one surface or both surfaces of the substrate.

[0104] <<Method for forming laminate for electrochemical device>> The laminate for an electrochemical device can be formed, for example, by forming a functional layer on an electrode substrate or a separator substrate by the following method. 1) A method in which the functional layer composition is applied to the surface of a separator substrate or an electrode substrate (in the case of an electrode substrate, the surface on the electrode mixture layer side; the same applies hereinafter) and then dried; 2) A method in which a separator substrate or an electrode substrate is immersed in a composition for a functional layer and then dried; 3) A method in which a functional layer composition is applied to a release substrate, dried to produce a functional layer, and the resulting functional layer is transferred to the surface of a separator substrate or electrode substrate. Among these, method 1) is particularly preferred because it allows for easy control of the film thickness of the functional layer. Specifically, method 1) includes a step of applying a functional layer composition to a separator substrate or an electrode substrate (application step), and a step of drying the functional layer composition applied to the separator substrate or the electrode substrate to form a functional layer (drying step). The functional layer may be formed on only one side of the substrate, or on both sides of the substrate.

[0105] In the coating step, the method for coating the functional layer composition onto the separator substrate or electrode substrate is not particularly limited, and examples thereof include spray coating, doctor blade coating, reverse roll coating, direct roll coating, gravure coating, extrusion coating, brush coating, etc. Among these, gravure coating and spray coating are preferred in terms of forming a thinner functional layer. In the drying step, the method for drying the functional layer composition on the substrate 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 30 to 80°C, and the drying time is preferably 30 seconds to 10 minutes.

[0106] <Electrochemical element> The electrochemical device of the present invention is characterized by comprising the above-described laminate for an electrochemical device of the present invention. Since the electrochemical device of the present invention comprises the above-described laminate for an electrochemical device of the present invention, it can exhibit excellent electrochemical properties.

[0107] The electrochemical device of the present invention is not particularly limited, and may be, for example, a lithium ion secondary battery or an electric double layer capacitor, and is preferably a lithium ion secondary battery.

[0108] Hereinafter, a lithium ion secondary battery will be described as an example of the electrochemical element of the present invention. The lithium ion secondary battery of the present invention includes the above-described laminate for electrochemical elements of the present invention. More specifically, the lithium ion secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, and at least one of the positive electrode, the negative electrode, and the separator is made of the above-described laminate for electrochemical elements of the present invention. In the lithium ion battery of the present invention, the positive electrode and the separator, and / or the negative electrode and the separator, are firmly bonded together via a functional layer in the electrolyte. Therefore, the lithium ion secondary battery has excellent battery characteristics such as internal resistance characteristics and cycle characteristics.

[0109] As the positive electrode, negative electrode, and electrolyte solution described above, known positive electrodes, negative electrodes, and electrolyte solutions used in lithium ion secondary batteries can be used.

[0110] <Positive and negative electrodes> Specifically, the electrodes (positive and negative electrodes) can be electrodes in which an electrode mixture layer is formed on a current collector. The current collector can be made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum. Among these, a current collector made of copper is preferably used as the current collector for the negative electrode. Furthermore, a current collector made of aluminum is preferably used as the current collector for the positive electrode. Furthermore, a layer containing an electrode active material and a binder can be used as the electrode mixture layer.

[0111] <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.

[0112] 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.

[0113] 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.

[0114] <Method of manufacturing an electrochemical element> The electrochemical device of the present invention can be produced using the above-mentioned laminate for an electrochemical device of the present invention. Specifically, for example, when manufacturing a lithium ion secondary battery, a positive electrode and a negative electrode are stacked with a separator interposed therebetween, and the stack is then rolled, folded, or otherwise placed in a battery container as needed. An electrolyte solution is then poured into the battery container and sealed, thereby producing a lithium ion secondary battery. At least one of the positive electrode, negative electrode, and separator is manufactured using the above-described laminate for electrochemical devices of the present invention. Here, the battery container may optionally contain an expanded metal, a fuse, an overcurrent prevention element such as a PTC element, or a lead plate to prevent pressure buildup within the battery and overcharging and discharging. The shape of the battery may be, for example, a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, or the like. [Example]

[0115] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. Various measurements and evaluations in the examples and comparative examples were carried out according to the following methods. 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.

[0116] In the examples and comparative examples, the weight-average molecular weight (Mw), number-average molecular weight (Mn), glass transition temperature, volume-average particle size, volume ratio of non-conductive heat-resistant particles to particulate polymer, and thickness of the non-conductive heat-resistant particle layer were measured by the following methods. In the examples and comparative examples, the process adhesion, wet adhesion, and blocking resistance of the functional layer (battery component), as well as the internal resistance characteristics and cycle characteristics of the secondary battery, were evaluated by the following methods.

[0117] <Weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of particulate polymer> A portion of the particulate polymer prepared in each of the examples and comparative examples was collected, and the weight average molecular weight (Mw) and number average molecular weight (Mn) were measured using gel permeation chromatography (GPC), and the molecular weight distribution (Mw / Mn) was calculated. Specifically, the particulate polymer was adjusted to a solids concentration of 0.2% and passed through a 0.2 μm filter. The resulting solution was analyzed in a gel permeation chromatograph (Tosoh Corporation, HLC-8220) using one Tosoh "TSK guard column α" and two Tosoh "TSKgel Super HZM-M" columns connected in series, with tetrahydrofuran as the solvent at a flow rate of 1.0 mL / min. The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the particulate polymer were determined in terms of standard polystyrene. The molecular weight distribution (Mw / Mn) was then calculated.

[0118] <Glass transition temperature of particulate polymer and binder> The particulate polymers 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 500°C, with a heating rate of 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.

[0119] <Volume average particle size of particulate polymer prepared by suspension polymerization> The particulate polymers prepared in Examples 1 to 11 and Comparative Example 1 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 to 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 size of the measurement sample was then determined 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.

[0120] <Volume average particle size of particulate polymer and binder prepared by emulsion polymerization method> The volume-average particle diameters of the particulate polymers produced in Example 12 and Comparative Example 2, and the binders prepared in Examples 1 to 12 and Comparative Examples 1 and 2, were measured by laser diffraction. Specifically, an aqueous dispersion (adjusted to a solids concentration of 0.1% by mass) containing the prepared particulate polymer or binder particles was used as a sample. The particle diameter D50 at which the cumulative volume calculated from the smallest diameter reached 50% in the particle diameter distribution (volume basis) measured using a laser diffraction particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name "LS-13 320") was taken as the volume-average particle diameter.

[0121] <Volume average particle size of particulate polymer in functional layer> The surfaces of the functional layers of the separators with functional layers prepared in the examples and comparative examples were observed under magnification for each particulate polymer using a field emission scanning electron microscope (FE-SEM, JEOL Ltd., "JSM-7800 Prime", detector: BED-C, acceleration voltage: 5 kV, magnification: 5000 to 10000 times). 200 particulate polymers were observed. The observed images of the particulate polymer were binarized to determine the area of ​​the particulate polymer within the field of view. Specifically, image analysis software (Mitani Corporation, "WinROOF") was used, with the emphasis conditions set to "brightness: -30" and "contrast: +70," the filter set to 7 × 7, and two thresholds set to binarization (threshold 38). The surface of the functional layer was then viewed in plan for each of the 200 SEM images obtained, and the area of ​​the particulate polymer was determined. The particulate polymer was assumed to be a perfect sphere, and the diameter of the particulate polymer was calculated from the obtained area of ​​the particulate polymer. The volume was calculated from the diameters of the 200 particulate polymers, assuming the particulate polymers to be perfect spheres. The total volume of all particulate polymers was set to 100%, and the amount of particulate polymer present in each particle size range was expressed as a percentage. The particle size at which the amount of particulate polymer reached 50% was defined as the volume-average particle size of the particulate polymer in the functional layer.

[0122] <Volume average particle size of non-conductive heat-resistant particles> The volume average particle diameter of the non-conductive heat-resistant particles used in the examples and comparative examples was determined as the particle diameter (D50) at which the cumulative volume calculated from the smallest diameter side becomes 50% in the particle diameter distribution (volume basis) measured by a laser diffraction method.

[0123] <Volume ratio of non-conductive heat-resistant particles to particulate polymer> The volume ratio of the non-conductive heat-resistant particles to the particulate polymer (non-conductive heat-resistant particles / particulate polymer) was calculated from the amounts of the non-conductive heat-resistant particles and the particulate polymer charged when the slurry composition was prepared.

[0124] <Thickness of non-conductive heat-resistant 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 non-conductive heat-resistant particle layer was calculated from the obtained image. The thickness of the non-conductive 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 surface of the non-conductive heat-resistant particles that form the surface of the functional layer.

[0125] <Process Adhesion> The positive electrode, negative electrode, and separator with functional layer produced in the examples and comparative examples were each cut into a width of 10 mm and a length of 50 mm. The positive electrode and the separator with functional layer were stacked so that the surface of the positive electrode facing the positive electrode composite layer faced the separator, and pressed at a press speed of 30 m / min using a roll press with a temperature of 70°C and a load of 5 kN / m to obtain a test piece. The test piece was placed with the positive electrode current collector side facing downward, and cellophane tape was attached to the surface of the electrode. The cellophane tape used was that specified in JIS Z1522. The cellophane tape was fixed to a horizontal test table. One end of the separator substrate was then pulled vertically upward at a pulling rate of 50 mm / min, and the stress when peeled off was measured. Furthermore, for the test pieces of the negative electrode and the separator with the functional layer, stress was measured three times in total in the same manner as in the case of using the positive electrode. The average stress value obtained from the six measurements using the positive and negative electrodes was calculated as the peel strength P1 (N / m), and the process adhesion between the electrode and the separator with the functional layer was evaluated according to the following criteria: The higher the peel strength, the better the process adhesion of the functional layer. A: Peel strength P1 is 8N / m or more B: Peel strength P1 is 5N / m or more and less than 8N / m C: Peel strength P1 is 3N / m or more and less than 5N / m D: Peel strength P1 is less than 3N / m

[0126] <Wet adhesion> The functional layer compositions obtained in the Examples and Comparative Examples were applied to the surface of a separator substrate, and the functional layer compositions on the separator substrate were dried at 50°C for 10 minutes to form a functional layer (thickness: 2 μm). This separator with the functional layer was used as the separator for evaluation. The separator with the functional layer was cut into a 10 mm x 100 mm strip. The separator was then placed against the surface of the negative electrode (negative electrode composite layer side) prepared in the Examples and Comparative Examples, and then hot-pressed at a temperature of 85°C and a pressure of 0.5 MPa for 6 minutes to produce a laminate comprising a negative electrode and a separator with the functional layer. This laminate was used as a test specimen. The test piece was placed in a laminated packaging material together with approximately 400 μL of electrolyte. After one hour, the test piece was pressed together with the laminated packaging material at 40°C under a pressure of 0.5 MPa for 15 minutes. After pressing, the test piece was kept at 40°C for one day. The electrolyte used was a mixed solvent of EC, DEC, and vinylene carbonate (VC) (EC / DEC / VC (volume ratio at 25°C) = 68.5 / 30 / 1.5) with LiPF6 dissolved as a supporting electrolyte at a concentration of 1 mol / L. The test specimen was then removed, and the electrolyte solution adhering to the surface was wiped off. Next, the test specimen was placed with the negative electrode current collector side facing downwards, and cellophane tape was applied to the negative electrode current collector side. The cellophane tape used was specified in JIS Z1522. The cellophane tape was fixed to a horizontal test bench. One end of the separator substrate was then pulled vertically upward at a pulling rate of 50 mm / min to measure the stress when peeled. This measurement was performed three times, and the average stress value was calculated as the peel strength P2 (N / m) and evaluated according to the following criteria. The evaluation results are shown in Table 1. A higher peel strength P2 indicates better adhesion (wet adhesion) of the functional layer after immersion in the electrolyte, indicating strong adhesion between the electrode and the separator with the functional layer even in the electrolyte. A: Peel strength P2 is 5.0 N / m or more B: Peel strength P2 is 3.0 N / m or more and less than 5.0 N / m C: Peel strength P2 is 1.0 N / m or more and less than 3.0 N / m D: Peel strength P2 is less than 1.0 N / m

[0127] <Blocking resistance> 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 and pressed at 20°C and 5 MPa for 2 minutes 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 to separate the two. The stress measured was used as 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., has higher blocking resistance. A: Blocking strength is less than 1N / m B: Blocking strength is 1N / m or more and less than 3N / m C: Blocking strength is 3N / m or more and less than 5N / m D: Blocking strength is 5N / m or more

[0128] <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 4.40V) at a constant current of 0.2C, and CC discharging to 3.00V at a constant current of 0.2C. This charge / discharge cycle at 0.2C was repeated three times. Thereafter, 100 cycles of charge and discharge were performed at a temperature of 10°C, a cell voltage of 4.40-3.00V, 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 90% or more B: Capacity retention rate ΔC' is 85% or more and less than 90% C: Capacity retention rate ΔC' is 80% or more and less than 85%

[0129] <Internal resistance characteristics of secondary batteries> The lithium ion secondary batteries fabricated in the examples and comparative examples were charged to 50% of SOC (State of Charge) at 1C (C is a value expressed as rated capacity (mA) / 1h (hours)) under 10°C conditions, and then charged for 15 seconds and discharged for 15 seconds at 0.5C, 1.0C, 1.5C, and 2.0C, centered around 50% SOC. The battery voltage after 10 seconds in each case (on the charge side and the discharge side) was plotted against the current value, and the slope was divided by the area of ​​the positive electrode of the fabricated lithium ion secondary battery to obtain the IV resistance (Ω cm 2 ) (IV resistance during charging and IV resistance during discharging). The obtained IV resistance value (Ω cm 2 ) were evaluated according to the following criteria. The smaller the value of IV resistance, the lower the internal resistance (lower the DC resistance) and the better the internal resistance characteristics. A: IV resistance is 22 Ω·cm 2 below B: IV resistance is 22 Ω·cm 2 Super 25Ω cm 2 below C: IV resistance is 25 Ω·cm 2 Super 28Ω cm 2 below D: IV resistance is 28 Ω·cm 2 super

[0130] Example 1 <Preparation of particulate polymer> [Preparation of Monomer Composition (A)] A monomer composition (A) was prepared by mixing 70 parts of styrene as an aromatic vinyl monomer and 30 parts of butyl acrylate as a (meth)acrylic acid ester monomer.

[0131] [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 8.0 parts of magnesium chloride in 200 parts of ion-exchanged water.

[0132] [Suspension polymerization method] A particulate polymer was prepared by suspension polymerization. Specifically, the monomer composition (A) 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 Corporation, "Perbutyl O") as a polymerization initiator and 2.0 parts of chain transfer agent (A) (S,S-dibenzyl trithiocarbonate, Fujifilm Wako Pure Chemical Industries, Ltd., 043-33983) were added 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 in the colloidal dispersion (A) containing magnesium hydroxide.

[0133] 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.

[0134] 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. Note that, as a result of measuring the obtained particulate polymer by FT-IR, it was confirmed that the particulate polymer contained a dithioester structure. The weight average molecular weight, number average molecular weight, glass transition temperature, and volume average particle size of the resulting particulate polymer were measured. The results are shown in Table 1.

[0135] <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 binder (α) had a volume average particle diameter of 0.25 μm and a glass transition temperature of -40°C.

[0136] <Preparation of Slurry Composition (Functional Layer Composition)> To 100 parts of alumina (manufactured by Sumitomo Chemical Co., Ltd., "AKP3000", volume average particle diameter: 0.7 μm) as inorganic particles, 0.5 parts of polyacrylic acid as a water-soluble polymer was added, and ion-exchanged water was added so that the solid concentration became 55 wt.%, 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 Co., Ltd.) was added as a dispersant. Furthermore, 6 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 mixed to 100 parts of the particulate polymer so that the solid content concentration was 40 wt.%, and the resulting mixture was added to the pre-mixing slurry obtained as described above. Further, ion-exchanged water was added to 40 wt.% of the solid content to obtain a slurry composition (composition for functional layer). The volume ratio of the inorganic particles (alumina) to the particulate polymer (inorganic particles / particulate polymer) in the slurry composition was 70 / 30.

[0137] <Production of separator (laminate) with functional layer> A polyethylene microporous membrane (thickness: 12 μm) was prepared as a separator substrate. The functional layer composition (slurry composition) was applied to one side of the prepared separator substrate using a bar coater method. The coating was dried at 50°C. The same operation as above was then performed on the other side of the separator substrate to produce a separator with a functional layer (a laminate for electrochemical devices) having a functional layer on each side of the separator substrate. The volume average particle diameter of the particulate polymer in the functional layer of the obtained laminate was 6.0 μm. The thickness of the non-conductive heat-resistant particle layer contained in the functional layer of the obtained laminate was 2.0 μm.

[0138] <Preparation of positive electrode> A mixture of 100 parts of LiCoO2 (volume average particle diameter: 12 μm) as the positive electrode active material, 2 parts of acetylene black (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) as the conductive material, 2 parts of polyvinylidene fluoride (#7208, manufactured by Kureha Corporation) as the binder for the positive electrode composite layer in terms of solid content, and N-methylpyrrolidone as the 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 10 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).

[0139] <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. 96 parts of artificial graphite (volume average particle diameter: 15.6 μm) as the negative electrode active material, 1.0 part (solids equivalent) of a 2% aqueous solution of carboxymethylcellulose sodium salt (manufactured by Nippon Paper Industries Co., Ltd., "MAC350HC") as a viscosity modifier, and ion-exchanged water were mixed to adjust the solids concentration to 68%, and then further mixed at 25°C for 60 minutes. The solids concentration 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 (solids equivalent) of the aqueous dispersion containing the binder for the negative electrode composite layer and ion-exchanged water were added to this mixed solution, and the final solids concentration 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 6 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-press negative electrode blank. This pre-press negative electrode blank was rolled using a roll press to obtain a pre-press negative electrode having a negative electrode composite layer (thickness: 80 μm).

[0140] The separator with the functional layer, positive electrode, and negative electrode obtained as described above were used to evaluate process adhesion, adhesion after wetting with an electrolyte (wet adhesion), and blocking resistance. The results are shown in Table 1.

[0141] <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 functional layer-equipped separator, cut to 120 cm x 5.5 cm, was placed on top of the positive electrode composite layer so that the positive electrode was positioned on one side of the functional layer-equipped separator 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 functional layer-equipped separator so that the surface of the negative electrode composite layer faced the functional layer-equipped separator and the negative electrode was positioned on the other side of the functional layer-equipped separator in the longitudinal direction. The functional layer-equipped separator was then positioned so that the front surface of the functional layer-equipped separator faced the positive electrode and the back surface of the functional layer-equipped separator faced the negative electrode. The resulting laminate was then wound using a winding machine to obtain a wound body. This wound body was pressed at 50°C and 1 MPa to form a flat body, 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 concentration 1 mol)] 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 internal resistance characteristics of the resulting lithium-ion secondary battery were evaluated. The results are shown in Table 1.

[0142] Example 2 A particulate polymer, a binder (α), a slurry composition, a separator with a functional layer, a positive electrode, and a negative electrode were prepared in the same manner as in Example 1, except that the particulate polymer was prepared by the following suspension polymerization method, and a lithium ion secondary battery was obtained. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1. [Suspension polymerization method] The monomer composition (A) produced in Example 1 was added to the colloidal dispersion (A) containing magnesium hydroxide produced in Example 1, and after further stirring, 2.0 parts of t-butylperoxy-2-ethylhexanoate (NOF Corporation, "Perbutyl O") as a polymerization initiator and 1.0 part of chain transfer agent (A) were added to obtain a mixed solution. The resulting mixed solution was stirred at 15,000 rpm for 1 minute using an in-line emulsifying disperser (Pacific Machinery Works, "Cavitron") under high shear to form droplets of the monomer composition (A) in the colloidal dispersion (A) containing magnesium hydroxide.

[0143] The colloidal dispersion (A) containing magnesium hydroxide and droplets of the monomer composition (A) was placed in a reactor and heated to 90°C. 10 minutes after the temperature was raised, 1.0 part of chain transfer agent (A) was added to the reactor. A polymerization reaction was then carried out for 5 hours to obtain an aqueous dispersion containing a particulate polymer. The obtained particulate polymer was analyzed by FT-IR and was confirmed to contain a dithioester structure.

[0144] Example 3 A particulate polymer, a binder (α), a slurry composition, a separator with a functional layer, a positive electrode, and a negative electrode were prepared in the same manner as in Example 1, except that the particulate polymer was prepared by the following suspension polymerization method, and a lithium ion secondary battery was obtained. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0145] [Suspension polymerization method] The monomer composition (A) produced in Example 1 was added to the colloidal dispersion (A) containing magnesium hydroxide produced in Example 1, and after further stirring, 2.0 parts of t-butylperoxy-2-ethylhexanoate (NOF Corporation, "Perbutyl O") as a polymerization initiator and 0.66 parts of chain transfer agent (A) were added to obtain a mixed solution. The resulting mixed solution was stirred at high shear for 1 minute using an in-line emulsifying disperser (Pacific Machinery Works, Ltd., "Cavitron") at a rotation speed of 15,000 rpm to form droplets of the monomer composition (A) in the colloidal dispersion (A) containing magnesium hydroxide.

[0146] The colloidal dispersion (A) containing magnesium hydroxide and droplets of the monomer composition (A) was placed in a reactor and heated to 90°C. 10 minutes after the temperature was raised, 0.66 parts of chain transfer agent (A) was added to the reactor. After another 10 minutes, 0.66 parts of chain transfer agent (A) was added to the reactor. A polymerization reaction was then carried out for 5 hours to obtain an aqueous dispersion containing a particulate polymer. FT-IR analysis of the obtained particulate polymer confirmed that the particulate polymer contained a dithioester structure.

[0147] Example 4 A particulate polymer, a binder (α), a slurry composition, a separator with a functional layer, a positive electrode, and a negative electrode were produced in the same manner as in Example 1, except that a chain transfer agent (B) (methyl 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoate, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 356-40753) was used instead of the chain transfer agent (A) in the preparation of the particulate polymer, and a lithium ion secondary battery was obtained. Then, various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1. The obtained particulate polymer was measured by FT-IR, and it was confirmed that the particulate polymer contained a dithioester structure.

[0148] Example 5 A particulate polymer, a binder (α), a slurry composition, a separator with a functional layer, a positive electrode, and a negative electrode were produced in the same manner as in Example 1, except that in the preparation of the particulate polymer, a chain transfer agent (C) (4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl)pentanoic acid, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 036-24643) was used instead of the chain transfer agent (A). A lithium ion secondary battery was obtained. Then, various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1. The obtained particulate polymer was measured by FT-IR, and it was confirmed that the particulate polymer contained a dithioester structure.

[0149] Example 6 A particulate polymer, a binder (α), a slurry composition, a separator with a functional layer, a positive electrode, and a negative electrode were produced in the same manner as in Example 1, except that 70 parts of methyl methacrylate and 30 parts of 2-ethylhexyl acrylate were used instead of 70 parts of styrene and 30 parts of butyl acrylate in the preparation of the particulate polymer, and a lithium ion secondary battery was obtained. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1. The obtained particulate polymer was measured by FT-IR, and it was confirmed that the particulate polymer contained a dithioester structure.

[0150] Example 7 A particulate polymer, binder (α), slurry composition, separator with functional layer, positive electrode, and negative electrode were produced in the same manner as in Example 1, except that in preparing the slurry composition, boehmite ("H43M" manufactured by Showa Denko K.K., volume average particle diameter: 0.8 μm) was used as the inorganic particles instead of alumina, and a lithium ion secondary battery was obtained. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0151] Example 8 In preparing the slurry composition, barium sulfate ("TS-2" manufactured by Takehara Chemical Co., Ltd., volume average particle diameter: 0.3 μm) was used instead of alumina as the inorganic particles. The particulate polymer, binder (α), slurry composition, separator with functional layer, positive electrode, and negative electrode were produced in the same manner as in Example 1, and a lithium ion secondary battery was obtained. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0152] Example 9 In preparing the slurry composition, a particulate polymer, a binder (α), a slurry composition, a separator with a functional layer, a positive electrode, and a negative electrode were produced in the same manner as in Example 1, except that magnesium hydroxide ("Magseeds X-6F" manufactured by Konoshima Chemical Co., Ltd., volume average particle diameter: 0.7 μm) was used instead of alumina as the inorganic particles, and a lithium ion secondary battery was obtained. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0153] Example 10 In preparing the slurry composition, except that the inorganic particles used as the non-conductive heat-resistant particles were replaced with organic particles prepared as follows, a particulate polymer, a binder (α), a slurry composition, a separator with a functional layer, a positive electrode, and a negative electrode were prepared in the same manner as in Example 1, and a lithium ion secondary battery was obtained. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0154] <Production of organic particle dispersion> (1) Preparation of Monomer Composition for Seed Particles In a reactor A equipped with a stirrer, 0.2 parts of sodium dodecyl sulfate, 0.30 parts of ammonium persulfate, and 180 parts of ion-exchanged water were mixed to form a mixture, and the mixture was heated to 65° C. Meanwhile, in a separate vessel, 80.0 parts of n-butyl acrylate as a monofunctional (meth)acrylic acid ester monomer, 10.0 parts of methacrylic acid as an acidic group-containing monomer, 10.0 parts of acrylonitrile as a nitrile group-containing monomer, 0.6 parts of sodium dodecyl sulfate, and 40 parts of ion-exchanged water were mixed to prepare a monomer composition for seed particles. This monomer composition for seed particles was continuously added to the above-mentioned reactor A over a period of 4 hours to carry out a polymerization reaction. The temperature inside the reactor was maintained at 65°C during the continuous addition of the monomer composition for seed particles. After the continuous addition was completed, the polymerization reaction was continued for an additional 3 hours at 80°C. This resulted in an aqueous dispersion of seed particles. The volume average particle diameter of the seed particles was measured using the same method as for measuring the volume average particle diameter of the particulate polymer and binder prepared by emulsion polymerization, and was found to be 120 nm. (2) Seeded polymerization of multifunctional monomers Next, 20 parts of the aqueous dispersion of the seed particles (based on solids content) (including 16 parts n-butyl acrylate units, 2 parts methacrylic acid units, and 2 parts acrylonitrile units), 80 parts ethylene glycol dimethacrylate (Kyoeisha Chemical Co., Ltd., product name "Light Ester EG") as a polyfunctional monomer, 0.8 parts sodium dodecylbenzenesulfonate, and 3.2 parts t-butylperoxy-2-ethylhexanoate (NOF Corporation, product name "Perbutyl O") as a polymerization initiator were added to a reactor equipped with a stirrer. 160 parts of ion-exchanged water was added, and the mixture was stirred at 35°C for 12 hours to completely absorb the polyfunctional monomer and polymerization initiator into the seed particles. The temperature inside the reactor was then maintained at 40°C, and ascorbic acid as a reducing agent was added dropwise over 1 hour. The polymerization reaction (seed polymerization) was then carried out for another 2 hours to obtain an organic particle dispersion in which organic particles were dispersed in water. The volume average particle diameter of the obtained organic particles was 200 nm, and the glass transition temperature was above 200° C. The volume average particle diameter and glass transition temperature of the organic particles were measured according to the same method as used to measure the volume average particle diameter of the particulate polymer and binder prepared by emulsion polymerization.

[0155] Example 11 A particulate polymer, a binder (α), a slurry composition, a separator with a functional layer, a positive electrode, and a negative electrode were prepared in the same manner as in Example 1, except that the amount of the polymerization initiator in the preparation of the particulate polymer was 0.25 parts, and a lithium ion secondary battery was obtained. Then, various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1. The obtained particulate polymer was measured by FT-IR, and it was confirmed that the particulate polymer contained a dithioester structure.

[0156] Example 12 A particulate polymer, binder (α), slurry composition, separator with functional layer (functional layer thickness: 1.0 μm), positive electrode, and negative electrode were produced in the same manner as in Example 1, except that the particulate polymer was prepared by the following emulsion polymerization method and the slurry composition (composition for functional layer) was prepared as follows, and a lithium ion secondary battery was obtained. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1. [Emulsion polymerization method] A reactor equipped with a stirrer was charged with 100 parts of the monomer composition (A) produced in Example 1, 1 part of the chain transfer agent (A), 0.3 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.3 parts of ammonium persulfate as a polymerization initiator, and after thorough stirring, the mixture was heated to 70°C to initiate polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to stop the reaction, and an aqueous dispersion containing a particulate polymer was obtained. The obtained particulate polymer was analyzed by FT-IR, and it was confirmed that the particulate polymer contained a dithioester structure.

[0157] <Preparation of Slurry Composition (Functional Layer Composition)> 65 parts (solid content equivalent) of the aqueous dispersion of the binder (α) was mixed in a stirring vessel with 1000 parts (solid content equivalent) of the aqueous dispersion of the particulate polymer prepared by the above emulsion polymerization method and 1 part of Emulgen 120 (manufactured by Kao) as a wetting agent to obtain a mixture. Ion-exchanged water was further added to the obtained mixture so that the solid content concentration was 10 mass %, to obtain a slurry composition (composition for functional layer).

[0158] (Comparative Example 1) In the preparation of the particulate polymer, except that no chain transfer agent was added, a particulate polymer, a binder (α), a slurry composition, a separator with a functional layer, a positive electrode, and a negative electrode were prepared in the same manner as in Example 1, and a lithium ion secondary battery was obtained. Then, various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0159] (Comparative Example 2) In the preparation of the particulate polymer, except that no chain transfer agent was added, a particulate polymer, a binder (α), a slurry composition, a separator with a functional layer, a positive electrode, and a negative electrode were prepared in the same manner as in Example 12, and a lithium ion secondary battery was obtained. Then, various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0160] In addition, in Table 1, "BA" indicates n-butyl acrylate; "ST" indicates styrene, "2EHA" indicates 2-ethylhexyl acrylate, "MMA" indicates methyl methacrylate, "MAA" indicates methacrylic acid, "AN" indicates acrylonitrile, "AMA" indicates allyl methacrylate; "AGE" refers to allyl glycidyl ether.

[0161] [Table 1]

[0162] The results in Table 1 show that Examples 1 to 12, in which the molecular weight distribution (Mw / Mn) of the particulate polymer is in the range of 1.0 to 3.0, have excellent process adhesion and blocking resistance, and the electrochemical properties of the electrochemical element are also excellent. In contrast, Comparative Example 1, in which the molecular weight distribution (Mw / Mn) of the particulate polymer exceeds 3.0, has good process adhesion but poor blocking resistance and internal resistance. Furthermore, Comparative Example 2, in which the molecular weight distribution (Mw / Mn) of the particulate polymer exceeds 3.0 and no non-conductive heat-resistant particles are blended, has good process adhesion but poorer blocking resistance, internal resistance, and cycle characteristics. [Industrial Applicability]

[0163] According to the present invention, it is possible to provide a composition for an electrochemical element functional layer that can impart excellent process adhesion and blocking resistance to electrochemical element components such as electrodes and separators, and can form a functional layer for an electrochemical element that can enable the electrochemical element to exhibit excellent electrochemical properties. Furthermore, according to the present invention, it is possible to provide a laminate for an electrochemical element that is capable of imparting excellent process adhesion and blocking resistance to electrochemical element components such as electrodes and separators, and that is equipped with a functional layer for an electrochemical element that can enable the electrochemical element to exhibit excellent electrochemical properties. Furthermore, according to the present invention, an electrochemical device capable of exhibiting excellent electrochemical properties can be provided.

Claims

1. A particulate polymer and a binder are included, the molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the particulate polymer is 1.0 or more and 3.0 or less; the binder has a glass transition temperature of −100° C. or higher and lower than the glass transition temperature of the particulate polymer; The composition for an electrochemical device functional layer, wherein the particulate polymer has a dithioester structure.

2. 2. The composition for an electrochemical device functional layer according to claim 1, wherein the particulate polymer has a glass transition temperature of 25°C or higher and 90°C or lower.

3. 3. The composition for an electrochemical device functional layer according to claim 1, wherein the particulate polymer contains a (meth)acrylic acid ester monomer unit.

4. 4. The composition for an electrochemical device functional layer according to claim 1, wherein the binder comprises a polymer containing a (meth)acrylic acid ester monomer unit.

5. The composition for an electrochemical device functional layer according to any one of claims 1 to 4, further comprising non-conductive heat-resistant particles.

6. The composition for an electrochemical device functional layer according to claim 5 , wherein the non-conductive heat-resistant particles include inorganic particles.

7. 7. The composition for an electrochemical device functional layer according to claim 6, wherein the inorganic particles contain at least one kind selected from the group consisting of alumina, boehmite, barium sulfate, and magnesium hydroxide.

8. A substrate and a functional layer for an electrochemical device formed on the substrate, 8. A laminate for an electrochemical device, wherein the functional layer for an electrochemical device is formed using the composition for an electrochemical device functional layer according to claim 1.

9. An electrochemical device comprising the laminate for an electrochemical device according to claim 8 .

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