Functional layer for electrochemical element and method for manufacturing same, separator with functional layer for electrochemical element and method for manufacturing same, and electrochemical element and method for manufacturing same

Abstract

A functional layer for electrochemical elements according to the present invention contains inorganic particles and a particulate polymer, and is characterized in that: the functional layer has particle fall-off parts; the area ratio of the particle fall-off parts in the total area of the particulate polymer and the particle fall-off parts is from 0.1% to 40.0% when the surface of the functional layer for electrochemical elements is viewed in plan; and the volume average particle diameter of the particulate polymer is larger than the thickness of an inorganic particle layer that contains the inorganic particles.

Description

[Technical Field]

[0001] The present invention relates to a functional layer for an electrochemical device and a method for producing the same, a separator with a functional layer for an electrochemical device and a method for producing the same, and an electrochemical device and a method for producing the same. [Background technology]

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

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

[0004] In recent years, further improvements in separators have been investigated with the aim of further improving the performance of lithium ion secondary batteries. Specifically, for example, Patent Document 1 proposes a separator in which a heat-resistant layer containing non-conductive particles and a binder is formed on a separator substrate, and an adhesive layer containing a predetermined particulate polymer is further provided on the heat-resistant layer. Patent Document 1 also reports that the use of a separator having an adhesive layer on the heat-resistant layer can improve the adhesion between the separator and electrodes and the battery characteristics of the secondary battery. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2013 / 151144 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the conventional separator having a heat-resistant layer and an adhesive layer requires sequential formation of the heat-resistant layer on the separator substrate and the adhesive layer on the heat-resistant layer, resulting in a complicated manufacturing process.

[0007] To address this problem, it is conceivable that the separator manufacturing process could be simplified and productivity could be increased by forming a single layer (such a layer will be referred to as a "functional layer" hereinafter) on the separator substrate, instead of the heat-resistant layer and adhesive layer that are provided separately.

[0008] Therefore, the present inventors have focused on the fact that by using a composition containing a component that contributes to heat resistance and a component that contributes to adhesion, it is possible to simultaneously exhibit heat resistance and adhesion in the resulting functional layer. However, through investigations by the present inventors, it has become clear that functional layers formed using a composition that simply mixes a component that contributes to heat resistance and a component that contributes to adhesion have insufficient adhesion between components during the manufacturing process of an electrochemical device (hereinafter also referred to as "process adhesion"). Furthermore, electrochemical devices manufactured using such functional layers have room for improvement in terms of exhibiting excellent cycle characteristics.

[0009] Therefore, an object of the present invention is to provide a technology relating to a functional layer for an electrochemical element that has excellent process adhesion and can enable the electrochemical element to exhibit excellent cycle characteristics. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to achieve the above object, and have found that a functional layer containing inorganic particles and a particulate polymer, having particle-shed portions, in which, in a plan view, the ratio of the area of ​​the particle-shed portions to the total area of ​​the particulate polymer and the particle-shed portions is within a predetermined range, and the volume-average particle diameter of the particulate polymer is larger than the thickness of an inorganic particle layer containing inorganic particles, can provide excellent process adhesion and enable an electrochemical element to exhibit excellent cycle characteristics, thereby completing the present invention.

[0011] The present invention has an object to advantageously solve the above-mentioned problems, and provides a functional layer for electrochemical devices comprising inorganic particles and a particulate polymer, the functional layer having particle shed portions, the area of ​​the particle shed portions accounting for a total area of ​​the particulate polymer and the particle shed portions being 0.1% to 40.0% in a plan view of the surface of the functional layer for electrochemical devices, and the volume average particle diameter of the particulate polymer being greater than the thickness of the inorganic particle layer containing the inorganic particles. Thus, a functional layer for electrochemical devices (hereinafter sometimes simply referred to as "functional layer") comprising inorganic particles and a particulate polymer, the particle shed portions, the area of ​​the particle shed portions accounting for a total area of ​​the particulate polymer and the particle shed portions being within a predetermined range in a plan view, and the volume average particle diameter of the particulate polymer being greater than the thickness of the inorganic particle layer, can provide excellent process adhesion and excellent cycle characteristics for an electrochemical device. In the present invention, the "ratio of the area of ​​particle-shedding portions to the total area of ​​the particulate polymer and particle-shedding portions when the surface of the functional layer is viewed in plan," the "volume average particle diameter" of the particulate polymer in the functional layer, and the "thickness of the inorganic particle layer" can be measured by the methods described in the examples of this specification.

[0012] Here, in the functional layer for electrochemical devices of the present invention, the particulate polymer preferably has a volume average particle diameter of 1.0 μm or more and 10.0 μm or less. When the volume average particle diameter of the particulate polymer is within the above-mentioned range, the process adhesiveness of the functional layer can be further improved. Furthermore, when the volume average particle diameter of the particulate polymer is within the above-mentioned range, the heat resistance of the functional layer can be improved, and the injectability of an electrolyte solution (hereinafter, sometimes referred to as "electrolyte injectability of an electrochemical device") when an electrochemical device is manufactured using a battery component including the functional layer can be improved.

[0013] Furthermore, in the functional layer for electrochemical devices of the present invention, the particle size distribution of the particulate polymer is preferably 1.5 or less. If the particle size distribution of the particulate polymer is equal to or less than the above-mentioned predetermined value, the storage characteristics of the electrochemical device can be improved. In the present invention, the "particle size distribution" of the particulate polymer in the functional layer can be measured by the method described in the examples of this specification.

[0014] In addition, in the functional layer for electrochemical devices of the present invention, the ratio of the volume average particle diameter of the particulate polymer to the thickness of the inorganic particle layer (volume average particle diameter of particulate polymer / thickness of inorganic particle layer) is preferably 1.1 or more and 10.0 or less. When the ratio of the volume average particle diameter of the particulate polymer to the thickness of the inorganic particle layer (volume average particle diameter of particulate polymer / thickness of inorganic particle layer) is within the above-mentioned range, the process adhesion of the functional layer can be further improved. Furthermore, when the ratio of the volume average particle diameter of the particulate polymer to the thickness of the inorganic particle layer (volume average particle diameter of particulate polymer / thickness of inorganic particle layer) is within the above-mentioned range, the heat resistance of the functional layer can be improved and the electrolyte injection properties of the electrochemical device can be enhanced.

[0015] Furthermore, in the functional layer for an electrochemical device of the present invention, the particulate polymer preferably satisfies the following 1) or 2). 1) The glass transition temperature of the particulate polymer is 10°C or higher and 90°C or lower. 2) The melting point of the particulate polymer is 50°C or higher When the glass transition temperature of the particulate polymer is within the above-mentioned range, the blocking of the functional layer can be suppressed while ensuring good adhesion of the functional layer. Furthermore, when the melting point of the particulate polymer is 50°C or higher, good adhesion of the functional layer can be ensured even when the particulate polymer contains a crystalline polymer. In the present invention, the "glass transition temperature" and "melting point" of the particulate polymer can be measured by the method described in the examples of this specification.

[0016] Furthermore, in the functional layer for electrochemical devices of the present invention, when the surface of the functional layer for electrochemical devices is viewed in plan, the ratio of the total area of ​​the particulate polymer and the particle-shedded portions per unit area of ​​the functional layer for electrochemical devices is preferably 10% or less. When the ratio of the total area of ​​the particulate polymer and the particle-shedded portions per unit area of ​​the functional layer when the surface of the functional layer is viewed in plan is the above-mentioned predetermined value or less, the heat resistance of the functional layer can be improved. In the present invention, "the ratio of the total area of ​​particulate polymer and particle shed portions per unit area of ​​the functional layer when the surface of the functional layer is viewed in a plane" can be measured by the method described in the examples of this specification.

[0017] Furthermore, in the functional layer for electrochemical devices of the present invention, the particulate polymer preferably contains an aromatic vinyl monomer unit, which improves the elasticity of the particulate polymer and increases the strength of the functional layer.

[0018] In the functional layer for an electrochemical device of the present invention, the particulate polymer may contain a fluorine atom-containing monomer unit.

[0019] The present invention aims to advantageously solve the above-mentioned problems, and provides a separator with a functional layer for an electrochemical element, which comprises any one of the functional layers for an electrochemical element described above on a separator substrate, thereby providing a separator with a functional layer that has excellent process adhesion and can enable an electrochemical element to exhibit excellent cycle characteristics.

[0020] The present invention also aims to advantageously solve the above-mentioned problems, and provides an electrochemical device comprising the above-mentioned separator with a functional layer for an electrochemical device. By including the separator with a functional layer for an electrochemical device of the present invention, an electrochemical device capable of exhibiting excellent cycle characteristics can be provided.

[0021] Furthermore, the present invention has an object to advantageously solve the above-mentioned problems, and the method for producing a functional layer for an electrochemical element of the present invention includes the steps of: forming a coating of a composition for a functional layer for an electrochemical element, the composition including inorganic particles and a particulate polymer, on a substrate; drying the coating to form a pre-functional layer; and applying a pressure of 1 N / mm 2 More than 20N / mm 2 and a step of applying tension as follows: According to the method for producing a functional layer for an electrochemical device of the present invention, it is possible to produce a functional layer for an electrochemical device that has excellent process adhesion and is capable of causing the electrochemical device to exhibit excellent cycle characteristics.

[0022] In the method for producing a functional layer for an electrochemical device of the present invention, the particulate polymer preferably has a volume average particle diameter of 1.0 μm or more and 10.0 μm or less. When the volume average particle diameter of the particulate polymer is within the above-mentioned range, the process adhesion of the produced functional layer can be further improved, and the cycle characteristics of the electrochemical device can be further improved. Furthermore, when the volume average particle diameter of the particulate polymer is within the above-mentioned range, the heat resistance of the produced functional layer can be improved, and the electrolyte injection properties of the electrochemical device can be improved. In the present invention, the "volume average particle diameter" of the particulate polymer in the composition for electrochemical element functional layers (hereinafter sometimes simply referred to as "composition for functional layers") can be measured by the method described in the examples of this specification.

[0023] Furthermore, in the method for producing a functional layer for an electrochemical device of the present invention, it is preferable that the particle size distribution of the particulate polymer is 1.5 or less. If the particle size distribution of the particulate polymer is the above-mentioned predetermined value or less, the process adhesion of the produced functional layer for an electrochemical device can be further improved, and the cycle characteristics of the electrochemical device can be further improved. Furthermore, if the particle size distribution of the particulate polymer is the above-mentioned predetermined value or less, the electrolyte injection properties of the electrochemical device can be improved. Furthermore, if the particle size distribution of the particulate polymer is the above-mentioned predetermined value or less, the storage characteristics of the electrochemical device can be improved. In the present invention, the "particle size distribution" of the particulate polymer in the composition for the functional layer can be measured by the method described in the examples of this specification.

[0024] In the method for producing a functional layer for an electrochemical device of the present invention, the particulate polymer preferably satisfies the following 3) or 4). 3) The glass transition temperature of the particulate polymer is 10°C or higher and 90°C or lower. 4) The melting point of the particulate polymer is 50°C or higher When the glass transition temperature of the particulate polymer is within the above-mentioned range, the functional layer to be produced can be prevented from blocking while ensuring good adhesion. Furthermore, when the melting point of the particulate polymer is 50°C or higher, the functional layer to be produced can be ensured to have good adhesion even when the particulate polymer contains a crystalline polymer.

[0025] Furthermore, in the method for producing a functional layer for an electrochemical device of the present invention, it is preferable that the volume ratio of the inorganic particles to the particulate polymer in the composition for a functional layer for an electrochemical device (inorganic particles / particulate polymer) is 55 / 45 or more and 95 / 5 or less. If the volume ratio of the inorganic particles to the particulate polymer in the composition for a functional layer (inorganic particles / particulate polymer) is within the above-mentioned range, a good balance between the heat resistance and process adhesion of the produced functional layer can be maintained.

[0026] In the method for producing a functional layer for an electrochemical device of the present invention, the particulate polymer preferably contains an aromatic vinyl monomer unit, which improves the elasticity of the particulate polymer and increases the strength of the produced functional layer.

[0027] Furthermore, in the method for producing a functional layer for an electrochemical device of the present invention, the particulate polymer may contain a fluorine atom-containing monomer unit.

[0028] The present invention aims to advantageously solve the above-mentioned problems, and the method for manufacturing a separator with a functional layer for electrochemical devices of the present invention is characterized by forming a functional layer for electrochemical devices on a separator substrate using any of the above-mentioned methods for manufacturing a functional layer for electrochemical devices. According to the method for manufacturing a separator with a functional layer for electrochemical devices of the present invention, it is possible to manufacture a separator having a functional layer for electrochemical devices that has excellent process adhesion and that can enable the electrochemical device to exhibit excellent cycle characteristics.

[0029] The present invention also aims to advantageously solve the above-mentioned problems, and provides a method for producing an electrochemical element, which is characterized by using a separator with a functional layer for an electrochemical element obtained by the above-mentioned method for producing a separator with a functional layer for an electrochemical element. The method for producing an electrochemical element of the present invention makes it possible to produce an electrochemical element that exhibits excellent cycle characteristics. [Effects of the Invention]

[0030] According to the present invention, it is possible to provide a functional layer for an electrochemical device that has excellent process adhesion and allows the electrochemical device to exhibit excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide a separator with a functional layer for an electrochemical element, which has excellent process adhesion and is provided with a functional layer for an electrochemical element that can enable the electrochemical element to exhibit excellent cycle characteristics. Furthermore, according to the present invention, an electrochemical device capable of exhibiting excellent cycle characteristics can be provided. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a functional layer for an electrochemical device according to the present invention. [Figure 2] FIG. 2 is a schematic plan view showing an example of the configuration of the functional layer for electrochemical devices according to the present invention, when the surface of the functional layer for electrochemical devices is viewed in plan view. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, embodiments of the present invention will be described in detail. The functional layer for an electrochemical device of the present invention can be used to bond components of an electrochemical device together. The separator with a functional layer for an electrochemical device of the present invention can be produced using the functional layer for an electrochemical device of the present invention. The electrochemical device of the present invention is an electrochemical device that includes at least the separator with a functional layer for an electrochemical device of the present invention. The functional layer for an electrochemical device of the present invention can be preferably produced using the method for producing a functional layer for an electrochemical device of the present invention. The separator with a functional layer for an electrochemical device of the present invention can be preferably produced using the method for producing a separator with a functional layer for an electrochemical device of the present invention. Furthermore, the electrochemical device of the present invention can be preferably produced using the method for producing an electrochemical device of the present invention.

[0033] (functional layer for electrochemical elements) The functional layer of the present invention includes inorganic particles and a particulate polymer. The functional layer of the present invention has particle-shedding portions, and is characterized in that, in a planar view of the surface of the functional layer, the ratio of the area of ​​the particle-shedding portions to the total area of ​​the particulate polymer and the particle-shedding portions is within a predetermined range, and the volume-average particle diameter of the particulate polymer is larger than the thickness of the inorganic particle layer containing the inorganic particles. The functional layer of the present invention has excellent process adhesion and can enable an electrochemical device to exhibit excellent cycle characteristics. Furthermore, the functional layer of the present invention formed on a substrate such as a separator substrate can be suitably used as a single layer that simultaneously exhibits the function of a heat-resistant layer that enhances the heat resistance of the substrate and the function of an adhesive layer that firmly bonds components together. The functional layer of the present invention may optionally further contain other components in addition to the inorganic particles and particulate polymer described above.

[0034] Fig. 1 is a schematic cross-sectional view showing an example of a functional layer for an electrochemical element according to the present invention. As shown in Fig. 1, the functional layer 1 contains inorganic particles 11 and a particulate polymer 12. In the functional layer 1, a plurality of inorganic particles 11 are stacked in the thickness direction of the functional layer 1 to form an inorganic particle layer 13. The particulate polymer 12 is embedded in the inorganic particle layer 13. That is, a portion of the particulate polymer 12 is embedded in the inorganic particle layer 13, and the portion of the particulate polymer 12 that is not embedded in the inorganic particle layer 13 protrudes from the surface of the inorganic particle layer 13.

[0035] <Inorganic particles> The inorganic particles contained in the functional layer are a material that can impart heat resistance to the functional layer. Here, 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 oxide (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 and montmorillonite. Among these, aluminum oxide, boehmite, titanium oxide, and barium sulfate are preferred, with aluminum oxide being more preferred. Furthermore, these inorganic particles may be subjected to element substitution, surface treatment, solid solution formation, etc., as necessary. These inorganic particles may be used alone or in combination of two or more kinds in any ratio.

[0036] <<Volume average particle size of inorganic particles>> The volume average particle diameter (D50) of the inorganic 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 inorganic particles is equal to or greater than the above-mentioned lower limit, the inorganic particles are densely packed in the functional layer. This prevents a decrease in ionic conductivity in the functional layer, thereby further improving the electrochemical characteristics (particularly, output characteristics) of the electrochemical device. Furthermore, when the volume average particle diameter of the inorganic particles is equal to or less than the above-mentioned upper limit, the functional layer can exhibit excellent heat resistance even when the thickness of the inorganic particle layer is reduced, thereby increasing the capacity of the electrochemical device. The volume average particle size (D50) of the inorganic particles can be measured by the method described in the examples of this specification.

[0037] <<Inorganic particle layer>> In the functional layer of the present invention, an inorganic particle layer containing inorganic particles is formed. In the functional layer, the inorganic particle layer is usually formed by a plurality of inorganic particles overlapping each other in the thickness direction of the functional layer. The inorganic particle layer may further contain other components in addition to the inorganic particles. Examples of other components that the inorganic particle layer may contain include other components that may be contained in the functional layer, which will be described later.

[0038] [Thickness of inorganic particle layer] The thickness of the inorganic 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. When the thickness of the inorganic 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, when the thickness of the inorganic particle layer is equal to or less than the above upper limit, a decrease in the energy density of an electrochemical device including the functional layer can be suppressed. Furthermore, when the thickness of the inorganic 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 inorganic particle layer can be adjusted, for example, by the content ratio of inorganic particles in the functional layer composition used in the coating formation step of the functional layer manufacturing method described below, and the thickness of the coating to be formed.

[0039] <Particulate polymer> The particulate polymer contained in the functional layer must have a volume average particle diameter larger than the thickness of the inorganic particle layer. By making the volume average particle diameter of the particulate polymer in the functional layer larger than the thickness of the inorganic particle layer, the functional layer can exhibit good process adhesion. Here, the particulate polymer contained in the functional layer is not particularly limited as long as it is particulate. Furthermore, after bonding the members together via the functional layer, the particulate polymer may be in a particulate shape or any other shape. Furthermore, the particulate polymer may be a crystalline high molecular weight polymer, a non-crystalline high molecular weight polymer, or a mixture thereof. In the functional layer, the particulate polymer is usually embedded in the inorganic particle layer.

[0040] <<Volume average particle size of particulate polymer>> The particulate polymer in the functional layer preferably has a volume average particle diameter of 1.0 μm or more, more preferably 2.5 μm or more, and even more 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.

[0041] 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 inorganic particles on the thickness direction surface of the functional layer, thereby enabling the functional layer to exhibit even better process adhesion. Furthermore, when a component having the functional layer is bonded to another component, a gap is secured between the inorganic particle layer and the other component in the thickness direction of the functional layer. Then, 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 lower limit or more is not clear, but is presumed as follows. That is, in order to improve heat resistance, the proportion of inorganic particles in the functional layer needs to be high. Then, it is thought that the particulate polymer protrudes from the inorganic particles on the thickness direction surface of the functional layer, which apparently increases the proportion of inorganic particles in the inorganic particle layer, thereby improving heat resistance.

[0042] 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.

[0043] The volume average particle diameter 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. Metal hydroxides will be described in detail later. The volume average particle diameter of the particulate polymer in the functional layer can also be adjusted, for example, by the tension applied to the substrate when transporting the substrate on a roll in the production method of the functional layer described later.

[0044] <<Ratio of volume average particle size of particulate polymer to thickness of inorganic 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 inorganic particle layer (volume average particle diameter of the particulate polymer / thickness of the inorganic 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.

[0045] When the ratio of the volume average particle diameter of the particulate polymer in the functional layer to the thickness of the inorganic particle layer is equal to or greater than the above-mentioned lower limit, the particulate polymer is more likely to protrude from the inorganic particles on the surface of the functional layer in the thickness direction, thereby enabling the functional layer to exhibit even better process adhesion. Furthermore, when a component having a functional layer is bonded to another component, a gap is secured between the inorganic particle layer and the other component in the thickness direction of the functional layer. Then, the electrolyte is injected through this gap, improving the electrolyte injection properties of the electrochemical element. Furthermore, when the ratio of the volume average particle diameter of the particulate polymer in the functional layer to the thickness of the inorganic particle layer is equal to or greater than the above-mentioned lower limit, the heat resistance of the functional layer is improved.

[0046] 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 inorganic 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.

[0047] <<Particle size distribution of particulate polymer>> The particle size distribution of the particulate polymer in the functional layer is preferably 1.10 or more, more preferably 1.18 or more, and preferably 1.50 or less, more preferably 1.40 or less. If the particle size distribution of the particulate polymer is above the lower limit, a functional layer can be formed that can follow the expansion and contraction of an electrode, particularly a negative electrode. On the other hand, if the particle size distribution of the particulate polymer is below the upper limit, when components are bonded together via the functional layer, the variation in the distance between the components is small, thereby suppressing gas accumulation and improving the storage characteristics of the electrochemical device. The particle size distribution of the particulate polymer in the functional layer can be adjusted, for example, by the stirring and classification conditions when the particulate polymer used in producing the functional layer is prepared by suspension polymerization. The particle size distribution of the particulate polymer in the functional layer can also be adjusted, for example, by the tension applied to the substrate when the substrate is transported on a roll in the production method of the functional layer described below.

[0048] <<Glass transition temperature of particulate polymers>> The glass transition temperature (Tg) of the particulate polymer is preferably 10°C or higher, more preferably 20°C or higher, even more preferably 30°C or higher, and preferably 90°C or lower, more preferably 80°C or lower. If the glass transition temperature of the particulate polymer is above the above lower limit, it is possible to prevent adjacent components from sticking together (blocking) via the functional layer during storage and transportation of a component having a functional layer, as well as during the manufacturing process of an electrochemical device. That is, if the glass transition temperature of the particulate polymer is above the above lower limit, it is possible to improve the blocking resistance of the functional layer. On the other hand, if the glass transition temperature of the particulate polymer is below the above upper limit, it is possible to obtain good adhesion of the functional layer even when components are pressed together via the functional layer to be bonded.

[0049] <<Melting point of particulate polymer>> Furthermore, the melting point (Tm) of the particulate polymer is preferably 50° C. or higher, more preferably 100° C. or higher. When the melting point of the particulate polymer is equal to or higher than the lower limit, good adhesion of the functional layer can be ensured even when the particulate polymer contains a crystalline polymer. When the particulate polymer has both a glass transition temperature and a melting point, the melting point of the particulate polymer is preferably equal to or higher than the above lower limit in order to further improve the adhesiveness of the functional layer.

[0050] <<Electrolyte swelling degree of particulate polymer>> Furthermore, the electrolyte swelling degree of the particulate polymer is preferably 1.0 times or more, more preferably 1.2 times or more, even more preferably 1.3 times or more, and preferably 15 times or less, more preferably 10 times or less, and even more preferably 3 times or less. If the electrolyte swelling degree of the particulate polymer is above the above lower limit, the adhesive strength of the functional layer in the electrolyte can be strengthened. On the other hand, if the electrolyte swelling degree of the particulate polymer is below the above upper limit, the resistance of the functional layer in the electrolyte can be reduced, thereby improving the electrochemical properties of an electrochemical element including a functional layer. Furthermore, if the electrolyte swelling degree of the particulate polymer is below the above upper limit, the electrolyte injection property of the electrochemical element can be improved. In the present invention, the "electrolyte swelling degree" of the particulate polymer can be measured by the method described in the examples of this specification.

[0051] <<Composition of particulate polymer>> The composition of the particulate polymer 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 binder when forming a functional layer can be used.

[0052] Examples of the monomer units constituting the particulate polymer include aromatic vinyl monomer units, (meth)acrylic acid ester monomer units, fluorine atom-containing monomer units, etc. The particulate polymer may contain one type of these monomer units alone, or may contain two or more types in any ratio. In the present invention, "(meth)acrylic" means acrylic and / or methacrylic. Furthermore, in the present invention, when a polymer "contains a monomer unit," it means that the polymer obtained using the monomer contains repeating units derived from the monomer.

[0053] [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.

[0054] 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. In the present invention, the "content ratio of each monomer unit" is 1 It can be measured using nuclear magnetic resonance (NMR) techniques such as H-NMR.

[0055] [(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 2-ethylhexyl 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.

[0056] The content of the (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 the (meth)acrylic acid ester monomer units is equal to or greater than the lower limit, the glass transition temperature of the particulate polymer is prevented from excessively decreasing, and the blocking resistance of the resulting functional layer can be improved. On the other hand, if the content of the (meth)acrylic acid ester monomer units is equal to or less than the upper limit, the adhesion between the functional layer and the substrate can be improved.

[0057] [Crosslinkable monomer unit] Furthermore, the particulate polymer may contain, in addition to the above-mentioned monomer units, a crosslinkable monomer unit. Here, the crosslinkable monomer unit is a monomer that can form a crosslinked structure during or after polymerization by heating or irradiation with energy rays.

[0058] 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 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, ethylene glycol dimethacrylate is preferred. These crosslinkable monomers may be used singly or in combination of two or more kinds in any ratio.

[0059] The content of the crosslinkable monomer unit in the particulate polymer is preferably 0.02% by mass or more, preferably 2% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1% by mass or less, when the amount of all the monomer units in the particulate polymer is taken as 100% by mass. If the content of the crosslinkable monomer unit is within the above range, the elution of the particulate polymer into the electrolyte can be sufficiently suppressed.

[0060] [Other monomer units] The particulate polymer may contain other monomer units in addition to the aromatic vinyl monomer units, the (meth)acrylic acid ester monomer units, and the crosslinkable monomer units. The other monomer units are not particularly limited, but examples thereof include nitrile group-containing monomer units and acid group-containing monomer units described in the "Binder" section below.

[0061] [Nitrile group-containing monomer unit] Here, 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.

[0062] The content of the nitrile group-containing monomer units in the particulate polymer is preferably 3% by mass or more, more preferably 4% by mass or more, even more preferably 6% by mass or more, and preferably 30% by mass or less, more preferably 27% by mass or less, and even more preferably 25% by mass or less, when the total repeating units in the particulate 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 particulate polymer can be improved, and the peel strength of the functional layer can be increased. 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 particulate polymer can be increased.

[0063] The content of other monomer units in the particulate polymer is preferably 0% by mass or more, preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less. If the content of other monomer units is 10% by mass or less, it is possible to prevent the stability of the functional layer composition used to form the functional layer from decreasing.

[0064] [Fluorine atom-containing monomer unit] The particulate polymer may also contain a fluorine atom-containing monomer unit. Examples of fluorine atom-containing monomers that can form the fluorine atom-containing monomer unit are not particularly limited, and include, for example, vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, vinyl trifluoride chloride, vinyl fluoride, and perfluoroalkyl vinyl ether. Among these, vinylidene fluoride is preferred. These fluorine atom-containing monomers may be used alone or in combination of two or more kinds in any ratio.

[0065] Here, when the particulate polymer contains a fluorine atom-containing monomer unit, from the viewpoint of ensuring better adhesion of the functional layer, the particulate polymer is preferably a fluorine atom-containing polymer using vinylidene fluoride as the fluorine atom-containing monomer. Among them, the fluorine atom-containing polymer is preferably a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and another fluorine atom-containing monomer copolymerizable therewith, or a copolymer of vinylidene fluoride and another fluorine atom-containing monomer copolymerizable therewith and a monomer copolymerizable therewith. Among the fluorine atom-containing polymers, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polyvinyl fluoride, and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer are preferred.

[0066] <<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.

[0067] The polymerization method is not particularly limited, and any of methods such as suspension polymerization, emulsion polymerization aggregation, and pulverization can be used. Among them, from the viewpoint of efficiently preparing a particulate polymer, suspension polymerization and emulsion polymerization aggregation are preferred, and suspension polymerization is more preferred. Furthermore, any of reactions such as radical polymerization and living radical polymerization can be used as the polymerization reaction.

[0068] [Other compounding agents] Further, the monomer composition used in preparing the particulate polymer may contain other additives such as a chain transfer agent, a polymerization regulator, a polymerization reaction retarder, a reactive fluidizing agent, a filler, a flame retardant, an antioxidant, and a colorant in any blending amount.

[0069] Here, as an example, a method for preparing a particulate polymer by suspension polymerization will be described.

[0070] [Preparation of particulate polymers by suspension polymerization] (1) Preparation of Monomer Composition First, the monomers constituting the desired particulate polymer and other compounding ingredients 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.

[0071] In this case, examples of the polymerization initiator to be used include oil-soluble polymerization initiators such as t-butylperoxy-2-ethylhexanoate, azobisisobutyronitrile, etc. 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.

[0072] 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.

[0073] (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.

[0074] (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.

[0075] <Particle falling part> The functional layer of the present invention has particle-shedding portions. Here, the particle-shedding portions are recesses (depressions) formed on the surface of the inorganic particle layer. By having the particle-shedding portions in the functional layer, the electrolyte in the electrochemical device accumulates in the particle-shedding portions, thereby improving the electrolyte retention capacity of the functional layer and allowing the electrochemical device to exhibit excellent cycle characteristics.

[0076] The particle-dropped portion is usually formed by the dropout of particulate polymers embedded in the inorganic particle layer, but may also be formed by the dropout of inorganic particles constituting the inorganic particle layer.

[0077] 2 is a schematic plan view showing an example of the configuration of a functional layer for electrochemical devices according to the present invention, when the surface of the functional layer for electrochemical devices is viewed in plan view. As shown in FIG. 2, the functional layer 1 includes an inorganic particle layer 13 containing inorganic particles and a particulate polymer 12. The functional layer 1 also has a particle-shedding portion 14.

[0078] <<Proportion of the area of ​​particle shed areas to the total area of ​​particulate polymer and particle shed areas>> Here, when the surface of the functional layer is viewed from above, the ratio of the area of ​​the particle-shedded portions to the total area of ​​the particulate polymer and the particle-shedded portions must be 0.1% or more, preferably 0.5% or more, more preferably 1.5% or more, and even more preferably 5.0% or more, and must be 40.0% or less, preferably 30.0% or less, and more preferably 15.0% or less. When the ratio of the area of ​​the particle-shedded portions to the total area of ​​the particulate polymer and the particle-shedded portions is above the above-mentioned lower limit, the electrolyte retention of the functional layer can be improved, thereby improving the cycle characteristics of the electrochemical device. On the other hand, when the ratio of the area of ​​the particle-shedded portions to the total area of ​​the particulate polymer and the particle-shedded portions is below the above-mentioned upper limit, an appropriate amount of particulate polymer remains in the functional layer, thereby improving the process adhesion of the functional layer. Furthermore, if the ratio of the area of ​​the particle-shed portions to the total area of ​​the particulate polymer and the particle-shed portions is equal to or less than the above upper limit, a sufficient amount of particulate polymer remains in the functional layer, and the particulate polymer in the functional layer can protect the separator during pressing in the manufacture of the electrochemical device. Therefore, the separator is not excessively crushed, thereby improving the cycle characteristics of the electrochemical device. Furthermore, a sufficient amount of particulate polymer remains in the functional layer, ensuring a gap between the inorganic particle layer and other components. Then, the electrolyte is injected through this gap, improving the electrolyte injection properties of the electrochemical device. When the surface of the functional layer is viewed in plan, the ratio of the area of ​​the particle-shedding portions to the total area of ​​the particulate polymer and the particle-shedding portions can be adjusted, for example, by the volume average particle size and particle size distribution of the particulate polymer in the functional layer composition used in the coating formation process of the functional layer manufacturing method described below, and the tension applied during the particle-shedding process.

[0079] <<Proportion of the total area of ​​particulate polymer and particle shed areas per unit area of ​​the functional layer>> Furthermore, when the surface of the functional layer is viewed in plan, the ratio of the total area of ​​the particulate polymer and particle-shedding portions per unit area of ​​the functional layer is preferably 10% or less, more preferably 7% or less, preferably 1% or more, and more preferably 4% or more. If the ratio of the total area of ​​the particulate polymer and particle-shedding portions per unit area of ​​the functional layer is below the above-mentioned upper limit, the heat resistance of the functional layer can be improved. On the other hand, if the ratio of the total area of ​​the particulate polymer and particle-shedding portions per unit area of ​​the functional layer is above the above-mentioned lower limit, the process adhesion of the functional layer can be further improved. When the surface of the functional layer is viewed in plan, the proportion of the total area of ​​the particulate polymer and particle shed portions per unit area of ​​the functional layer can be adjusted, for example, by the volume average particle diameter of the particulate polymer in the functional layer composition used in the coating formation process of the functional layer manufacturing method described below, and the volume ratio of the inorganic particles to the particulate polymer.

[0080] <Other ingredients> The functional layer of the present invention may further contain other components in addition to the inorganic particles and particulate polymer described above. Note that the other components are usually contained in the inorganic particle layer described above. As other components, for example, a binder and a water-soluble polymer can be used.

[0081] <<Binding material>> The binder that may be optionally contained in the functional layer is used to prevent components contained in the functional layer, such as the particulate polymer, from falling off from the functional layer.

[0082] [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, such as binder resins such as thermoplastic elastomers. As the thermoplastic elastomer, conjugated diene polymers and acrylic polymers are preferred, and acrylic polymers are more preferred. In the present invention, the 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.

[0083] 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. Moreover, the acrylic polymer refers to a polymer containing a (meth)acrylic acid ester monomer unit. These binders may be used alone or in combination of two or more kinds in any ratio.

[0084] The acrylic polymer that can be preferably used as the binder is not particularly limited, and examples thereof include a monomer containing the above-mentioned (meth)acrylic acid ester monomer unit, a crosslinkable monomer unit, and an acid group-containing monomer unit described below.

[0085] Here, 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.

[0086] 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.

[0087] The proportion of (meth)acrylic acid ester monomer units in the acrylic polymer is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 58% by mass or more, and preferably 98% by mass or less, more preferably 97% by mass or less, even more preferably 96% by mass or less. By making the proportion of (meth)acrylic acid ester monomer units equal to or greater than the lower limit of the above range, the peel strength of the functional layer can be further increased. On the other hand, by making it equal to or less than the upper limit, the electrochemical properties of an electrochemical device including the functional layer can be further improved.

[0088] The proportion of crosslinkable monomer units in the acrylic polymer is preferably 0.1% by mass or more, more preferably 1.0% by mass or more, and preferably 3.0% by mass or less, more preferably 2.5% by mass or less. By making the proportion of crosslinkable monomer units equal to or greater than the above limit, the electrochemical properties of an electrochemical device including a functional layer can be further improved. By making the proportion of crosslinkable monomer units equal to or less than the above upper limit, the peel strength of the functional layer can be further increased.

[0089] The proportion of the acid group-containing monomer units in the acrylic polymer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. By making the proportion of the acid group-containing monomer units equal to or greater than the above-mentioned lower limit, the dispersibility of the binder in the functional layer can be improved, and the electrochemical properties of an electrochemical device including the functional layer can be sufficiently improved. Furthermore, by making the proportion of the acid group-containing monomer units equal to or less than the above-mentioned upper limit, the amount of residual moisture in the functional layer can be reduced, and the electrochemical properties of an electrochemical device can be sufficiently improved.

[0090] 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; the aromatic vinyl monomers and nitrile group-containing monomers described in the section "Composition of Particulate Polymer," and 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. Among these, the other monomer is preferably acrylonitrile. 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.

[0091] [Binder structure] The structure of the binder in the functional layer is not particularly limited, but is usually non-particulate. The structure of the binder in the functional layer composition used in the manufacturing method of the functional layer described later 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 functional layer composition may be particulate or non-particulate.

[0092] [Glass transition temperature of binder] The glass transition temperature (Tg) of the binder is preferably -100°C or higher, more preferably -90°C or higher, even more preferably -80°C or higher, and preferably less than 30°C, more preferably 20°C or lower, and even more preferably 15°C or lower. If the glass transition temperature of the binder is above the lower limit, the adhesiveness and strength of the binder can be increased. On the other hand, if the glass transition temperature of the binder is below the upper limit or below the upper limit, the flexibility of the functional layer can be further increased.

[0093] [Binder content] The content of the binder in 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 inorganic particles. 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 peel strength of the functional layer can be sufficiently increased. On the other hand, if the content of the binder is equal to or less than the 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.

[0094] 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.

[0095] 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.

[0096] <<Water-soluble polymer>> The water-soluble polymer that can be optionally contained in the functional layer is a water-soluble polymer used to disperse components such as inorganic particles and particulate polymers well in the functional layer. If the functional layer contains a water-soluble polymer, components such as inorganic particles and particulate polymers are dispersed well, improving heat resistance and enabling the layer to 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 %.

[0097] As the water-soluble polymer that can be contained in the functional layer, it is preferable to use polyacrylic acid from the viewpoint of dispersing the inorganic particles and the particulate polymer in the functional layer more satisfactorily.

[0098] The content of the water-soluble polymer in the functional layer is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.3 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 inorganic particles. If the content of the water-soluble polymer is above the above-mentioned lower limit, the inorganic particles and the particulate polymer can be more effectively dispersed in the functional layer, thereby further improving the heat resistance of the functional layer and further enhancing the process adhesion of 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.

[0099] <<Other additives>> The functional layer of the present invention may further contain, as other components, additives other than the binder and the water-soluble polymer. Additives that may be optionally included in the functional layer include thickeners and dispersants. Here, for example, carboxymethyl cellulose can be used as the thickener, and for example, sodium dodecylbenzenesulfonate can be used as the dispersant. 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.

[0100] (Method of manufacturing a functional layer for an electrochemical element) The method for producing a functional layer for an electrochemical device of the present invention is characterized by comprising the steps of: forming a coating of a composition for a functional layer for an electrochemical device, the composition including inorganic particles and a particulate polymer, on a substrate (coating formation step); drying the coating to form a pre-functional layer (drying step); and applying tension within a predetermined range to the substrate on which the pre-functional layer has been formed (particle detachment step). According to the method for producing a functional layer for an electrochemical device of the present invention, a functional layer for an electrochemical device that has excellent process adhesion and can provide an electrochemical device with excellent cycle characteristics can be produced. The method for producing a functional layer for an electrochemical device of the present invention may include other steps in addition to the above-mentioned film-forming step, drying step, and particle-shedding step.

[0101] The method for producing a functional layer for an electrochemical device of the present invention can produce the functional layer for an electrochemical device of the present invention described above. That is, the method for producing a functional layer for an electrochemical device of the present invention can produce a functional layer that contains inorganic particles and a particulate polymer, has particle-shedding portions, and in which, in a plan view, the ratio of the area of ​​the particle-shedding portions to the total area of ​​the particulate polymer and the particle-shedding portions is within the above-mentioned predetermined range, and the volume average particle diameter of the particulate polymer is larger than the thickness of the inorganic particle layer containing the inorganic particles. The functional layer for an electrochemical device of the present invention can also be produced by a method other than the method for producing a functional layer for an electrochemical device of the present invention.

[0102] <Film formation process> In the coating formation step, a coating of the functional layer composition is formed on the substrate.

[0103] <<Composition for functional layer>> The functional layer composition used in the coating formation step contains at least inorganic particles and a particulate polymer, and typically contains inorganic particles, a particulate polymer, water as a dispersion medium, and other optional components.

[0104] [Inorganic particles] As the inorganic particles contained in the composition for functional layer, the inorganic particles described above in the section "Functional layer for electrochemical device" can be used.

[0105] [Particulate polymer] The glass transition temperature, melting point, and electrolyte swelling degree of the particulate polymer contained in the composition for functional layer can be in the same range as the glass transition temperature, melting point, and electrolyte swelling degree of the particulate polymer described above in the section "Functional layer for electrochemical element." The composition of the particulate polymer contained in the composition for functional layer may be the same as the particulate polymer described above in the section "Functional layer for electrochemical device."

[0106] The volume average particle diameter of the particulate polymer contained in the composition for the functional layer is preferably 1.0 μm or more, more preferably 2.5 μm or more, and even more 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.

[0107] If the volume average particle diameter of the particulate polymer in the functional layer composition is equal to or greater than the lower limit, the particulate polymer will be more likely to protrude from the inorganic particles on the thickness direction surface of the functional layer to be produced, thereby enabling the functional layer to exhibit even better process adhesion. Furthermore, when a component including the functional layer to be produced is bonded to another component, a gap is secured between the inorganic particle layer and the other component in the thickness direction of the functional layer. Then, the electrolyte is injected through this gap, improving the electrolyte injection properties of the electrochemical device. Furthermore, if the volume average particle diameter of the particulate polymer in the functional layer composition is equal to or greater than the lower limit, the heat resistance of the functional layer to be produced is improved. Furthermore, if the volume average particle diameter of the particulate polymer in the functional layer composition is equal to or greater than the lower limit, the particulate polymer will appropriately detach in the particle detachment step described below, forming particle-detached portions in the inorganic particle layer. This further enhances the electrolyte retention of the functional layer to enable the electrochemical device to exhibit even better cycle characteristics.

[0108] On the other hand, if the volume average particle diameter of the particulate polymer in the functional layer composition is equal to or less than the above upper limit, the particulate polymer does not fall off excessively during the particle shedding process described below, for example, when the separator is transported on a roll, allowing the particulate polymer to remain sufficiently in the functional layer to be produced. This further improves the process adhesion of the functional layer for an electrochemical device to be produced. Furthermore, the particulate polymer remaining in the functional layer can protect the separator during pressing during the production of the electrochemical device. Therefore, the separator is not excessively crushed, thereby improving the cycle characteristics of the electrochemical device. Furthermore, by allowing the particulate polymer to remain sufficiently in the functional layer to be produced, a gap is secured between the inorganic particle layer and other components. The electrolyte is then injected through this gap, thereby improving the electrolyte injection properties of the electrochemical device. Furthermore, if the volume average particle diameter of the particulate polymer in the composition for 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 produced will be large, and the number of adhesion points when bonding a component having the functional layer to another component will increase, thereby further improving the process adhesion of the functional layer.

[0109] The volume average particle size of the particulate polymer in the composition for the functional layer can be adjusted by the type and amount of the metal hydroxide used in preparing the particulate polymer.

[0110] The particle size distribution of the particulate polymer in the composition for the functional layer is preferably 1.10 or more, more preferably 1.20 or more, and preferably 1.50 or less, more preferably 1.40 or less.

[0111] If the particle size distribution of the particulate polymer in the composition for a functional layer is equal to or greater than the lower limit, the particle sizes of the particulate polymer vary appropriately, so that particulate polymers with larger particle sizes fall off and particle-shedding portions are appropriately formed. Therefore, the electrolyte retention of the produced functional layer is improved, and the cycle characteristics of the electrochemical device can be further improved. Furthermore, if the particle size distribution of the particulate polymer is equal to or greater than the lower limit, a functional layer can be formed that can follow the expansion and contraction of the electrode, particularly the negative electrode.

[0112] On the other hand, if the particle size distribution of the particulate polymer in the functional layer composition is equal to or less than the above upper limit, the particle size variation of the particulate polymer is small, and there is little particulate polymer with a large particle size that can fall off during the particle shedding process described below, for example, when the separator is transported on a roll. This allows the particulate polymer to remain sufficiently in the functional layer produced. This further improves the process adhesion of the functional layer for electrochemical devices produced. Furthermore, the particulate polymer remaining in the functional layer can protect the separator during pressing during the production of electrochemical devices. Therefore, the separator is not excessively crushed, thereby improving the cycle characteristics of the electrochemical device. Furthermore, by allowing the particulate polymer to remain sufficiently in the functional layer produced, gaps are secured between the inorganic particle layer and other components. The electrolyte is then injected through these gaps, thereby improving the electrolyte injection properties of the electrochemical device. Furthermore, if the particle size distribution of the particulate polymer in the composition for the functional layer is below the above upper limit, when components are bonded together via the produced functional layer, the variation in the distance between the components is small, thereby preventing gas accumulation and improving the storage characteristics of the electrochemical element.

[0113] The particle size distribution of the particulate polymer in the composition for the functional layer can be adjusted, for example, by the stirring and classification conditions when preparing the particulate polymer by suspension polymerization.

[0114] Here, the volume average particle size and particle size distribution of the particulate polymer in the functional layer composition may differ from those of the particulate polymer in the produced functional layer. This is thought to be because, among the particulate polymers contained in the functional layer composition, particles with larger particle sizes tend to fall off more easily during the separator transport in the particle falling-off step described below, and as a result, the volume average particle size and particle size distribution of the particulate polymer remaining in the functional layer may become smaller.

[0115] The particulate polymer contained in the composition for a functional layer can be prepared by the same method as the method for preparing the particulate polymer described above in the section "Functional layer for electrochemical device."

[0116] [Volume ratio of inorganic particles to particulate polymer] The volume ratio of inorganic particles to particulate polymer (inorganic particles / particulate polymer) in the composition for 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 inorganic particles to particulate polymer in the composition for functional layer is equal to or greater than the above-mentioned lower limit, the heat resistance of the produced functional layer can be improved. On the other hand, if the volume ratio of inorganic particles to particulate polymer in the composition for functional layer is equal to or less than the above-mentioned upper limit, the process adhesion of the produced functional layer can be further improved.

[0117] [Mass ratio of inorganic particles to particulate polymer] Furthermore, the mass ratio of inorganic particles to particulate polymer (inorganic particles / particulate polymer) in the composition for 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 inorganic particles to particulate polymer in the composition for functional layer is equal to or greater than the above-mentioned lower limit, the heat resistance of the produced functional layer can be improved. On the other hand, if the mass ratio of inorganic particles to particulate polymer in the composition for functional layer is equal to or less than the above-mentioned upper limit, the process adhesion of the produced functional layer can be further improved.

[0118] [Other ingredients] In addition, as components other than the inorganic particles and particulate polymers that may be contained in the composition for functional layers, the other components (binders, water-soluble polymers, etc.) described above in the section "Functional layer for electrochemical elements" can be used, and the type and content thereof can be the same as those described in the same section.

[0119] [Method for preparing composition for functional layer] The method for preparing the composition for the functional layer is not particularly limited, and can be prepared, for example, by mixing the above-mentioned inorganic particles, a particulate polymer, water as a dispersion medium, and other components (such as a binder and a water-soluble polymer) used as needed. When the particulate polymer or binder is prepared by polymerizing a monomer composition in an aqueous solvent, the particulate polymer or binder may be mixed with other components as is in the form of an aqueous dispersion. When the particulate polymer or binder is mixed in the form of an aqueous dispersion, the water in the aqueous dispersion may be used as the dispersion medium.

[0120] Here, the method for mixing the above-mentioned components is not particularly limited, but in order to efficiently disperse each component, it is preferable to use a disperser as a mixing device. The disperser is preferably a device that can uniformly disperse and mix the above-mentioned components. Examples of dispersers include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer.

[0121] <<Base material>> The substrate used in the coating formation process is not particularly limited, but it is preferable to use a separator substrate. It should be noted that a release substrate other than the separator substrate can also be used as the substrate. However, when a separator with a functional layer is produced, if a release substrate is used, it is necessary to transfer the functional layer formed on the release substrate to the separator substrate after the particle detachment process described below. On the other hand, if a separator substrate is used as the substrate, the above-mentioned transfer process is not necessary, and therefore a separator with a functional layer can be produced efficiently. The separator substrate will be described in detail later. The substrate used in the method for producing a functional layer of the present invention may have stretchability.

[0122] <<Coating formation method>> The method for forming the coating of the functional layer composition on the substrate is not particularly limited, and the functional layer composition may be applied to the surface of the substrate, or the substrate may be immersed in the functional layer composition. Furthermore, it is preferable to apply the functional layer composition to the surface of the substrate, since this makes it easier to control the thickness of the functional layer (inorganic particle layer) to be produced. The method for applying the composition for the functional layer to the surface of the substrate is not particularly limited, and examples thereof include the doctor blade method, reverse roll method, direct roll method, gravure coating method, bar coating method, extrusion method, and brush coating method. In the coating formation step, a coating of the composition for a functional layer may be formed on only one surface of the substrate, or a coating of the composition for a functional layer may be formed on both surfaces of the substrate.

[0123] <Drying process> In the drying step, the coating of the functional layer composition is dried to form a pre-functional layer. The method for drying the coating of the composition for functional layer is not particularly limited and any known method can be used, such as drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams, etc. The drying conditions are not particularly limited, but the drying temperature is preferably 50 to 150°C, and the drying time is preferably 1 to 30 minutes.

[0124] The formed pre-functional layer contains at least inorganic particles and a particulate polymer. An inorganic particle layer containing inorganic particles is formed in the pre-functional layer. In the pre-functional layer, a plurality of inorganic particles are typically stacked in the thickness direction of the functional layer to form the inorganic particle layer. The particulate polymer is typically embedded in the inorganic particle layer.

[0125] <Particle shedding process> In the particle detachment step, tension within a predetermined range is applied to the substrate on which the pre-functional layer has been formed, thereby obtaining a functional layer formed on the substrate. Here, by applying tension to the substrate on which the pre-functional layer is formed, a portion of the particulate polymer embedded in the inorganic particle layer in the pre-functional layer can be shed, thereby forming a particle-shed portion. Then, by adjusting the tension applied to the substrate within a predetermined range, when the surface of the manufactured functional layer is viewed in plan, the ratio of the area of ​​the particle-shed portion to the total area of ​​the particulate polymer and the area of ​​the particle-shed portion in the inorganic particle layer can be easily kept within the predetermined range described above, for example, in the section "Functional layer for electrochemical devices." In the particle-shedding process, the tension applied to the substrate on which the pre-functional layer is formed is assumed to be tension in the in-plane direction of the substrate. For example, in the particle-shedding process, tension can be applied in the longitudinal direction of the substrate on which the pre-functional layer is formed.

[0126] Here, the tension applied to the substrate on which the pre-functional layer was formed was 1 N / mm 2 It must be at least 1.5N / mm 2 It is preferable that the resistance is 2N / mm or more. 2More preferably, it is 2.5N / mm 2 More preferably, it is 4N / mm 2 More preferably, it is 20 N / mm 2 It must be less than 16N / mm 2 Preferably, it is 12 N / mm or less. 2 More preferably, it is 8N / mm or less. 2 More preferably, it is 7N / mm 2 It is even more preferred that:

[0127] When the tension applied to the substrate on which the pre-functional layer is formed is equal to or greater than the above-mentioned lower limit, the particulate polymer can be detached from the inorganic particle layer, sufficiently forming a particle-detached portion, thereby improving the electrolyte retention of the resulting functional layer and allowing the electrochemical device to exhibit excellent cycle characteristics. Furthermore, when the tension applied to the substrate on which the pre-functional layer is formed is equal to or greater than the above-mentioned lower limit, particulate polymers with extremely large particle diameters can be detached, thereby reducing the variation in particle diameter of the particulate polymers remaining in the resulting functional layer. Therefore, when components are bonded together via the functional layer, the variation in the distance between the components is small, thereby suppressing gas accumulation and improving the storage characteristics of the electrochemical device.

[0128] On the other hand, when the tension applied to the substrate on which the pre-functional layer is formed is equal to or less than the above upper limit, the particulate polymer does not fall off excessively from the inorganic particle layer, allowing a suitable amount of the particulate polymer to remain in the functional layer to be produced. This can improve the process adhesion of the functional layer for an electrochemical device to be produced. Furthermore, the particulate polymer remaining in the functional layer can protect the separator during pressing in the production of the electrochemical device. This prevents the separator from being excessively crushed, improving the cycle characteristics of the electrochemical device. Furthermore, by leaving a sufficient amount of the particulate polymer in the functional layer to be produced, a gap is secured between the inorganic particle layer and other components. The electrolyte is then injected through this gap, thereby improving the electrolyte injection properties of the electrochemical device.

[0129] In the method for producing a functional layer of the present invention, the above-described coating process, drying process, and particle detachment process can be continuously performed using a roll-to-roll system while transporting the substrate. Specifically, first, the substrate wound around a substrate roll is unwound, and a functional layer composition is applied to the surface of the substrate using a coating method such as gravure coating to form a coating of the functional layer composition (coating process). Next, while transporting the substrate with the coating formed, the coating is dried to form a pre-functional layer (drying process). The resulting substrate with the pre-functional layer formed thereon is then transported and wound around a recovery roll for recovery in roll form. When the method for producing a functional layer is performed using the roll-to-roll system, tension is applied to the substrate to transport it. Specifically, tension within the above-mentioned predetermined range is applied to the substrate with the pre-functional layer formed thereon. This allows a portion of the particulate polymer embedded in the inorganic particle layer in the pre-functional layer to be detached, forming a particle-detached portion. Therefore, the above-described transport can be performed as a particle-detachment process. The substrate on which the functional layer has been formed can then be collected onto the collection roll. In addition, in the above-mentioned transport, the substrate may be transported on a roll such as a transport roll. When the substrate is transported on a roll, the pre-functional layer formed on the substrate may contact the transport roll during transport, or may be bent along the shape of the transport roll together with the substrate. When the pre-functional layer formed on the substrate contacts the transport roll and / or is bent along the shape of the transport roll while being subjected to tension within the above-mentioned predetermined range, a portion of the particulate polymer embedded in the inorganic particle layer in the pre-functional layer may fall off, forming a particle-dropped portion.

[0130] In the functional layer produced by the method of the present invention, the volume average particle diameter of the particulate polymer is larger than the thickness of the inorganic particle layer containing inorganic particles. By having the volume average particle diameter of the particulate polymer in the produced functional layer larger than the thickness of the inorganic particle layer, the functional layer can exhibit excellent process adhesion. The volume average particle diameter of the particulate polymer in the functional layer and the thickness of the inorganic particle layer can be appropriately adjusted so that the volume average particle diameter of the particulate polymer in the functional layer is larger than the thickness of the inorganic particle layer. Note that the volume average particle diameter of the particulate polymer in the functional layer and the thickness of the inorganic particle layer can be adjusted by the methods described above in the section "Functional layer for electrochemical devices."

[0131] In the method for manufacturing a functional layer for an electrochemical device of the present invention, after the above-mentioned coating process, drying process, and particle detachment process are performed on one surface (front surface) of the substrate to form a functional layer, the coating process, drying process, and particle detachment process may be performed on the other surface (rear surface) of the substrate to form a functional layer. Here, the conditions for the above steps performed on the front surface of the substrate may be the same as or different from the conditions for the above steps performed on the rear surface of the substrate.

[0132] (Separator with functional layer for electrochemical elements) The separator with a functional layer for an electrochemical element of the present invention (hereinafter also referred to simply as "separator with a functional layer") is characterized by having the above-described functional layer for an electrochemical element of the present invention on a separator substrate. Therefore, the separator with a functional layer of the present invention has excellent process adhesion and is equipped with a functional layer that can enable the electrochemical element to exhibit excellent cycle characteristics.

[0133] The separator with a functional layer of the present invention may have the functional layer of the present invention on only one side of the separator substrate, or may have the functional layer of the present invention on both sides of the separator substrate. Also, the separator with a functional layer of the present invention may have a functional layer other than the functional layer of the present invention.

[0134] The separator substrate is not particularly limited, and may 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, as it allows the overall thickness of the separator with a functional layer to be thin, thereby increasing the proportion of electrode active material in the electrochemical device and increasing the capacity per volume.

[0135] (Method for manufacturing separator with functional layer for electrochemical element) The method for manufacturing a separator with a functional layer for an electrochemical device of the present invention is characterized by forming a functional layer for an electrochemical device on a separator substrate using the method for manufacturing a functional layer for an electrochemical device of the present invention described above. The method for manufacturing a separator with a functional layer of the present invention makes it possible to manufacture a separator having a functional layer that has excellent process adhesion and that can enable an electrochemical device to exhibit excellent cycle characteristics. Furthermore, the method for manufacturing a separator with a functional layer of the present invention makes it possible to manufacture the separator with a functional layer of the present invention described above.

[0136] Furthermore, separators with functional layers manufactured by the manufacturing method of separators with functional layers of the present invention can be produced in fewer steps and in less time than substrates that have a heat-resistant layer and adhesive layer separately, and therefore have high productivity.

[0137] The method for producing a separator with a functional layer of the present invention can be carried out, for example, by using a separator substrate as the substrate in the method for producing a functional layer of the present invention described above. As the separator substrate used in the method for producing a separator with a functional layer of the present invention, the separator substrate described above in the section "Separator with a functional layer for electrochemical devices" can be used.

[0138] (electrochemical element) The electrochemical element of the present invention is characterized by including the separator with a functional layer for an electrochemical element of the present invention described above. Because the electrochemical element of the present invention includes the separator with a functional layer for an electrochemical element of the present invention described above, it can exhibit excellent cycle characteristics.

[0139] 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.

[0140] 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 according to the present invention includes the separator with a functional layer of the present invention described above. More specifically, the lithium ion secondary battery includes a positive electrode, a negative electrode, the separator with a functional layer of the present invention, and an electrolyte solution.

[0141] In the lithium-ion secondary battery according to the present invention, the functional layer of the separator firmly bonds the positive electrode and separator substrate, and / or the negative electrode and separator substrate, in the electrolyte. This prevents the distance between the electrodes from increasing with repeated charge and discharge, resulting in good battery characteristics, such as cycle characteristics. In addition, in this lithium-ion secondary battery, the functional layer of the separator improves the heat resistance of the separator substrate. Furthermore, in the lithium-ion secondary battery according to the present invention, particle-shedding portions are formed in the functional layer of the separator, allowing the electrolyte to be well retained, resulting in good cycle characteristics.

[0142] 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.

[0143] <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.

[0144] <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.

[0145] 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.

[0146] 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.

[0147] (Method of manufacturing an electrochemical element) The method for producing an electrochemical element of the present invention is characterized by using a separator with a functional layer for an electrochemical element obtained by the method for producing a separator with a functional layer for an electrochemical element of the present invention described above.The method for producing an electrochemical element of the present invention makes it possible to produce an electrochemical element that can exhibit excellent cycle characteristics.Furthermore, the method for producing an electrochemical element of the present invention makes it possible to produce the electrochemical element of the present invention described above. Furthermore, according to the method for producing an electrochemical element of the present invention, the time required to produce the separator can be shortened, and electrochemical elements can be produced with high productivity, compared to when a separator having a heat-resistant layer and an adhesive layer is produced and used separately.

[0148] When a lithium ion secondary battery is manufactured using the method for manufacturing an electrochemical element of the present invention, for example, the positive electrode and negative electrode described in the "Electrochemical Element" section are stacked with a separator with a functional layer interposed therebetween, and the resulting stack is then rolled, folded, or otherwise inserted into a battery container, after which an electrolyte solution is poured into the battery container and sealed to produce a lithium ion secondary battery. The separator with a functional layer obtained by the method for manufacturing a separator with a functional layer of the present invention described above is used as the separator with a functional layer. Here, the battery container may optionally contain an expanded metal, a fuse, an overcurrent protection 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 any other suitable shape. [Example]

[0149] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. Furthermore, in a polymer produced by copolymerizing multiple types of monomers, the proportion of structural units formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of that certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified.

[0150] In the examples and comparative examples, the glass transition temperature, melting point, volume average particle size, particle size distribution, degree of swelling in electrolyte, the ratio of the total area of ​​the particulate polymer and particle shed portions per unit area of ​​the functional layer when viewed in plan, the ratio of the area of ​​particle shed portions to the total area of ​​the particulate polymer and particle shed portions, the thickness of the inorganic particle layer, the ratio of the volume average particle size of the particulate polymer in the functional layer to the thickness of the inorganic particle layer, and the volume ratio and mass ratio of the inorganic particles to the particulate polymer were measured by the following methods. In addition, the process adhesion of the functional layer, the heat resistance of the functional layer, the electrolyte injection property of the secondary battery, the cycle characteristics of the secondary battery, and the storage characteristics of the secondary battery were evaluated by the following methods.

[0151] <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.

[0152] <Melting point> The melting point (Tm) of the particulate polymer prepared in Example 13 was measured as follows. First, the particulate polymer was melted by heating, and the melted polymer was rapidly cooled with dry ice, thereby obtaining an amorphous polymer. Next, the melting point (Tm) of the amorphous polymer was measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min (heating mode) using the test sample.

[0153] <Volume Average Particle Diameter and Particle Diameter Distribution of Particulate Polymer in Functional Layer Composition> The dried particulate polymers prepared in the Examples and Comparative Examples were used as measurement samples. A 0.1 g sample equivalent was weighed and placed in a beaker. 0.1 mL of an alkylbenzene sulfonic acid aqueous solution (Fujifilm Corporation, Drywell) was added as a dispersant. 10–30 mL of diluent (Beckman Coulter, Isoton II) was then added to the beaker and dispersed for 3 minutes using a 20 W (Watt) ultrasonic disperser. The volume-average particle diameter (Dv) of the measurement sample was then determined using a particle size analyzer (Beckman Coulter, Multisizer) under the following conditions: aperture diameter: 20 μm, medium: Isoton II, and particle count: 100,000. This was used as the volume-average particle diameter of the particulate polymer in the functional layer composition. The number-average particle diameter (Dn) of the measurement sample was also measured, and the particle size distribution (Dv / Dn) of the particulate polymer in the functional layer composition was calculated.

[0154] <Volume average particle size of binder> The volume-average particle diameter of the binder prepared in the examples was measured by laser diffraction. Specifically, an aqueous dispersion containing the prepared binder (adjusted to a solids concentration of 0.1% by mass) was used as a sample. The particle size distribution (volume basis) measured using a laser diffraction particle size distribution analyzer (manufactured by Beckman Coulter, Inc., "LS-230") was used. The particle diameter D50 at which the cumulative volume calculated from the smallest diameter side reached 50% was defined as the volume-average particle diameter.

[0155] <Volume average particle size of inorganic particles> In the particle size distribution (volume basis) measured by laser diffraction, the particle size (D50) at which the cumulative volume calculated from the smallest diameter side becomes 50% was defined as the volume-average particle size of the inorganic particles.

[0156] <Electrolyte swelling rate> The aqueous dispersions containing the particulate polymers prepared in the Examples and Comparative Examples were placed in polytetrafluoroethylene petri dishes and dried at 25°C for 48 hours to prepare powders. Approximately 0.2 g of the obtained powder was pressed at 200°C and 5 MPa for 2 minutes to obtain a film. The obtained film was then cut into 1 cm squares to obtain test pieces. The mass W0 of this test piece was measured. The above test piece was immersed in an electrolyte solution for 72 hours at 60° C. Thereafter, the test piece was taken out of the electrolyte solution, the electrolyte solution on the surface of the test piece was wiped off, and the mass W1 of the test piece after the immersion test was measured. Using the measured masses W0 and W1, the degree of swelling in the electrolyte solution S (times) was calculated as S=W1 / W0. The electrolyte used was a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and vinylene carbonate (VC) (volume ratio: EC / DEC / VC = 68.5 / 30 / 1.5) with LiPF6 dissolved as a supporting electrolyte at a concentration of 1 mol / L.

[0157] <Volume average particle size and particle size distribution 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. 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 diameter (Dv) of the particulate polymer in the functional layer. Next, the total diameter of the particulate polymers obtained from 200 SEM images was divided by the number of particulate polymers (200) to obtain the average diameter of the particulate polymers, which was designated as the number-average particle diameter (Dn).Then, based on the volume-average particle diameter (Dv) and number-average particle diameter (Dn) values ​​obtained above, the particle size distribution (Dv / Dn) of the particulate polymers in the functional layer was calculated.

[0158] <The ratio of the total area of ​​the particulate polymer and particle shed portions to the unit area of ​​the functional layer when the functional layer is viewed in plan, and the ratio of the area of ​​the particle shed portions to the total area of ​​the particulate polymer and particle shed portions> The surface of the functional layer of the separator with functional layer prepared in the examples and comparative examples was observed using a field emission scanning electron microscope (FE-SEM, JEOL Ltd., "JSM-7800 Prime", detector: BED-C, acceleration voltage: 5kV, magnification: 500x) in a field of view of 186 μm vertically and 248 μm horizontally, with five fields of view on each of the front and back of the separator with functional layer. The 10 observed fields were then binarized to determine the area ratios of particulate polymer and particle shed areas within the field of view. Specifically, image analysis software (Mitani Corporation, "WinROOF") was used to perform binarization with the emphasis conditions set to "brightness: -30" and "contrast: +70," a filter set to 7 × 7, and two threshold values ​​set to 38. The average of the 10 SEM images was then used to determine the percentage of the total area of ​​particulate polymer and particle shed areas per unit area of ​​the functional layer surface when viewed in plan view. Furthermore, the same image analysis software (Mitani Corporation, "WinROOF") was used to perform binarization with the emphasis conditions set to "brightness: +30" and "contrast: +70," a filter set to 7 × 7, and two threshold values ​​set to 38. The percentage of the area of ​​particle shed areas per unit area of ​​the functional layer surface, S2 (%), was determined. Then, from the obtained S1 and S2 values, the ratio (100×S2 / S1) (%) of the area of ​​the particle shed portions to the total area of ​​the particulate polymer and particle shed portions when the functional layer was viewed in a plane was calculated.

[0159] <Thickness of inorganic particle layer> The cross section of the separator with the functional layer was observed using the field emission scanning electron microscope (FE-SEM) and the thickness of the inorganic particle layer was calculated from the SEM image, which was defined as the distance from the surface of the separator substrate on which the functional layer was formed to the most distant inorganic particle in the vertical direction.

[0160] <Ratio of Volume Average Particle Diameter of Particulate Polymer in Functional Layer to Thickness of Inorganic Particle Layer> Based on the volume average particle diameter of the particulate polymer in the functional layer obtained as described above and the thickness of the inorganic particle layer, the ratio of the volume average particle diameter of the particulate polymer in the functional layer to the thickness of the inorganic particle layer (volume average particle diameter of the particulate polymer / thickness of the inorganic particle layer) was calculated.

[0161] <Volume Ratio and Mass Ratio of Inorganic Particles to Particulate Polymer> The volume ratio (inorganic particles / particulate polymer) and mass ratio (inorganic particles / particulate polymer) of the inorganic particles (alumina) to the particulate polymer were calculated from the amounts of inorganic particles (alumina) and particulate polymer charged when preparing the slurry composition. The density of alumina was 4 g / cm. 3 It was calculated as:

[0162] <Process Adhesion> The positive electrode, negative electrode, and separator with functional layer prepared in the examples and comparative examples were each cut into a 10 mm wide x 50 mm long piece, and the positive electrode and separator with functional layer were stacked and pressed using a roll press at a temperature of 70°C, a load of 8 kN / m, and a press speed of 30 m / min to obtain an integrated product in which the positive electrode and separator with functional layer were integrated. The surfaces of the positive electrode and separator with functional layer were stacked facing each other. The resulting integrated product was placed with the current collector side of the positive electrode facing downwards, and cellophane tape was attached to the surface of the electrode. The cellophane tape used conformed to JIS Z1522. The cellophane tape was fixed to a horizontal test table. One end of the separator with the functional layer was then pulled vertically upward at a pulling rate of 50 mm / min, and the stress when peeled off was measured. The negative electrodes prepared in the examples and comparative examples were also subjected to the same procedure as in the case of using the positive electrodes, and the stress was measured. The negative electrodes and the rear surfaces of the separators with functional layers were stacked so as to face each other. The above-mentioned stress measurement was performed six times in total, three times for each of the integrated positive electrode and separator with functional layer, and the integrated negative electrode and separator with functional layer, and the average stress was calculated. The average value obtained was used as the peel strength (N / m). The calculated peel strength was then used to evaluate the process adhesion between the electrode and the separator with the functional layer according to the following criteria: A higher peel strength indicates that the functional layer has better process adhesion (adhesion between battery components via the functional layer during the secondary battery manufacturing process). A: Peel strength 3N / m or more B: Peel strength 2N / m or more and less than 3N / m C: Peel strength less than 2N / m

[0163] <Heat resistance of functional layer> The separators with functional layers prepared in the examples and comparative examples were cut into squares measuring 12 cm wide and 12 cm long, and a square with sides of 10 cm was drawn inside each square to prepare a test piece. The test piece was then placed in a thermostatic chamber at 150°C and left for 1 hour. The change in the area of ​​the square drawn inside (= {(area of ​​square before leaving - area of ​​square after leaving) / area of ​​square before leaving} × 100%) was calculated as the thermal shrinkage rate and evaluated according to the following criteria. A smaller thermal shrinkage rate indicates better heat resistance of the separator with functional layers. A: Heat shrinkage rate is less than 3% B: Heat shrinkage rate is 3% or more and less than 5% C: Heat shrinkage rate is 5% or more

[0164] <Electrolyte injection performance> An electrolyte solution was injected into the lithium ion secondary batteries produced in the Examples and Comparative Examples before injection of the electrolyte solution. The pressure inside the lithium ion secondary batteries was then reduced to -100 kPa and maintained in this state for 1 minute. Heat sealing was then performed. After 10 minutes, the electrode (positive electrode) was disassembled, and the state of impregnation of the electrolyte solution in the electrode was visually confirmed. Evaluation was then performed according to the following criteria. The larger the portion of the electrode impregnated with the electrolyte solution, the higher the electrolyte injectability of the lithium ion secondary battery. A: The electrolyte is impregnated on all surfaces of the electrode. B: The part of the electrode that is not impregnated with electrolyte is 1 cm 2 Less than 100% of the surface is impregnated (except for all surfaces). C: The part of the electrode that is not impregnated with electrolyte is 1 cm 2 More than

[0165] <Rechargeable battery cycle characteristics (100 cycles)> After injecting the electrolyte, 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 at 25°C and a constant current of 0.2C to a cell voltage of 3.65V, and then aged at 60°C for 12 hours. Then, they were discharged at 25°C and a constant current of 0.2C to a cell voltage of 3.00V. Then, they were subjected to CC-CV charging at a constant current of 0.2C (upper limit cell voltage 4.20V), and CC discharging at a constant current of 0.2C to 3.00V. This charge / discharge cycle at 0.2C was repeated three times. Thereafter, 100 cycles of charge and discharge were performed at a temperature of 25°C, a cell voltage of 4.20-3.00V, and a charge and discharge rate of 1.0 C. The discharge capacity of the first cycle was defined as X1, and the discharge capacity of the 100th cycle as X2. Then, the discharge capacity X1 and the discharge capacity X2 were used to calculate the capacity retention rate ΔC' = (X2 / X1) × 100 (%) and evaluated according to the following criteria. A larger value of the capacity retention rate ΔC' indicates that the secondary battery has better cycle characteristics at 100 cycles. The reason why the secondary battery has excellent cycle characteristics at 100 cycles is presumed to be because the functional layer of the secondary battery can retain the electrolyte well. A: Capacity retention rate ΔC' is 93% or more B: Capacity retention rate ΔC' is 90% or more and less than 93% C: Capacity retention rate ΔC' is 87% or more and less than 90%

[0166] <Rechargeable battery cycle characteristics (300 cycles)> After injecting the electrolyte, 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 at 25°C and a constant current of 0.2C to a cell voltage of 3.65V, and then aged at 60°C for 12 hours. Then, they were discharged at 25°C and a constant current of 0.2C to a cell voltage of 3.00V. Then, they were subjected to CC-CV charging at a constant current of 0.2C (upper limit cell voltage 4.20V), and CC discharging at a constant current of 0.2C to 3.00V. This charge / discharge cycle at 0.2C was repeated three times. Thereafter, 300 cycles of charge and discharge were performed at a cell voltage of 4.20-3.00 V and a charge and discharge rate of 1.0 C in an environment of 25°C. The discharge capacity of the first cycle was defined as X1, and the discharge capacity of the 100th cycle was defined as X3. Then, the capacity retention rate ΔC' = (X3 / X1) × 100 (%) was calculated using the discharge capacities X1 and X3, and evaluated according to the following criteria. A larger value of the capacity retention rate ΔC' indicates that the secondary battery has better cycle characteristics at 300 cycles. The reason why the secondary battery has excellent cycle characteristics at 300 cycles is presumably because the separator is protected by the particulate polymer in the functional layer during pressing in the production of the secondary battery, preventing the separator from being excessively crushed. 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 less than 85%

[0167] <Storage characteristics of secondary batteries> The secondary batteries prepared in the examples and comparative examples were left standing for 24 hours, then charged to 4.4 V at a charge / discharge rate of 0.1 C and discharged to 3.0 V to measure the initial capacity C0. Furthermore, the batteries were charged to 4.4 V at a charge / discharge rate of 0.1 C in a 25°C environment. After leaving the batteries standing for 7 days in a 60°C environment, they were discharged to 3.0 V at a discharge rate of 0.1 C to measure the remaining capacity C1. The remaining capacity ratio, expressed as ΔC = C1 / C0 × 100 (%), was calculated from the obtained C0 and C1 values. A higher remaining capacity ratio indicates that the secondary battery can maintain good battery performance (i.e., has excellent storage characteristics) even when stored at high potential and under high temperature conditions. A: 80% or more B: 75% or more but less than 80% C: Less than 75%

[0168] Example 1 <Preparation of Particulate Polymer (A)> [Preparation of Monomer Composition (A)] A monomer composition (A) was prepared by mixing 81.9 parts of styrene as an aromatic vinyl monomer, 18 parts of 2-ethylhexyl acrylate as a (meth)acrylic acid ester monomer, and 0.1 parts of ethylene glycol dimethacrylate as a crosslinkable monomer.

[0169] [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.

[0170] [Suspension polymerization method] A particulate polymer (A) 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 Corp., "Perbutyl O") was added as a polymerization initiator to obtain a mixed solution. The resulting mixed solution was subjected to high-shear stirring at 15,000 rpm for 1 minute using an in-line emulsifying disperser (Pacific Machinery Works, "Cavitron") to form droplets of the monomer composition (A) in the colloidal dispersion (A) containing magnesium hydroxide.

[0171] The colloidal dispersion (A) containing magnesium hydroxide in which droplets of the monomer composition (A) 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 (A). The degree of swelling in an electrolyte solution was measured using the aqueous dispersion containing the particulate polymer (A). The results are shown in Table 1.

[0172] Further, while stirring the aqueous dispersion containing the particulate polymer (A), 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 separation was 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 separation was carried out, and the obtained solid matter was placed in a container of a dryer and dried at 40 ° C. for 48 hours, and dried particulate polymer (A) was obtained. The glass transition temperature, volume average particle size and particle size distribution of the obtained particulate polymer (A) were measured. The results are shown in Table 1.

[0173] <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.

[0174] <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%, and the mixture was mixed using a ball mill to obtain pre-mixing slurry 1. 100 parts of the particulate polymer (A) was mixed with 0.2 parts of sodium dodecylbenzenesulfonate (manufactured by Kao Chemical Corporation, "Neopelex G-15") as a dispersant and ion-exchanged water to a solids concentration of 40%, to obtain a pre-mixing slurry 2. Pre-mixing slurry 1 and pre-mixing slurry 2 were mixed so that the volume ratio of inorganic particles (alumina) to particulate polymer (A) in the slurry composition (inorganic particles / particulate polymer (A)) was 70 / 30, and then 4 parts of an aqueous dispersion containing a binder (α) in terms of solid content and 1.5 parts of carboxymethyl cellulose as a thickener were added to 100 parts of inorganic particles. Ion-exchanged water was then added to give a solid content of 40%, thereby obtaining a slurry composition (composition for functional layer). The mass ratio of the inorganic particles (alumina) to the particulate polymer (A) in the slurry composition (inorganic particles / particulate polymer (A)) was 90 / 10.

[0175] <Production of separator with functional layer (gravure coating method)> A polyethylene microporous membrane (thickness: 12 μm) was prepared as a separator substrate. The following steps were continuously performed using a roll-to-roll system: applying the above-mentioned slurry composition to one side of the separator substrate, drying the coating film (film) formed on the separator substrate, transporting the separator substrate with the pre-functional layer formed, and recovering it by winding it up on a recovery roll. The application of the slurry composition to one side of the separator substrate was performed using a gravure coating method. The coating film was dried at 50°C. The conveying speed of the separator substrate was set to 15 m / min. During the conveying of the separator substrate, a pressure of 4 N / mm was applied in the longitudinal direction of the separator substrate with the pre-functional layer formed. 2The same operation as above was then performed on the other side of the separator substrate to produce a separator with a functional layer, in which a functional layer with an inorganic particle layer thickness of 2.0 μm was provided on each side of the separator substrate. For ease of explanation, the side of the manufactured separator with functional layer on which the functional layer is formed first will be referred to as the "front side," and the other side on which the functional layer is formed later will be referred to as the "back side."

[0176] <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 20 μm-thick aluminum foil current collector using a comma coater so that the dried film thickness was approximately 150 μm, and then dried. This drying was performed by transporting the aluminum foil at a speed of 0.5 m / min through an oven at 60°C for 2 minutes. The aluminum foil was then heat-treated at 120°C for 2 minutes to obtain a pre-pressed positive electrode blank. This pre-pressed positive electrode blank was rolled using a roll press to obtain a pre-pressed positive electrode having a positive electrode composite layer (thickness: 60 μm).

[0177] <Preparation of negative electrode> A 5 MPa pressure vessel equipped with a stirrer was charged with 33 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 63.5 parts of styrene, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator. After thorough stirring, the mixture was heated to 50 °C to initiate polymerization. When the polymerization conversion reached 96%, the reaction was stopped by cooling, yielding a mixture containing a binder (SBR) for the negative electrode composite layer. A 5% aqueous sodium hydroxide solution was added to the mixture containing the binder for the negative electrode composite layer, adjusting the pH to 8, and then the unreacted monomer was removed by heated vacuum distillation. The mixture was then cooled to below 30 °C to obtain an aqueous dispersion containing the desired binder for the negative electrode composite layer. 80 parts of artificial graphite (volume average particle diameter: 15.6 μm) as the negative electrode active material (1) and 16 parts of silicon-based active material SiOx (volume average particle diameter: 4.9 μm) as the negative electrode active material (2) were blended, and 2.5 parts of a 2% aqueous solution of carboxymethylcellulose sodium salt (manufactured by Nippon Paper Industries Co., Ltd., "MAC350HC") as a viscosity modifier, in terms of solid content, and ion-exchanged water were mixed to adjust the solid content to 68%, and then further mixed at 25 ° C for 60 minutes. The solid content was further adjusted to 62% with ion-exchanged water, and then further mixed at 25 ° C for 15 minutes to obtain a mixed solution. 1.5 parts of the aqueous dispersion containing the above-mentioned binder for the negative electrode composite layer, in terms of solid content, and ion-exchanged water were added to this mixed solution, and the final solid content was adjusted to 52%, and then further mixed for 10 minutes to obtain a mixed solution. This mixed solution was degassed under reduced pressure to obtain a negative electrode slurry composition with good fluidity. The negative electrode slurry composition was applied to a 20 μm-thick copper foil current collector using a comma coater so that the dried film thickness was approximately 150 μm, and then dried. This drying was performed by transporting the copper foil at a speed of 0.5 m / min through an oven at 60°C for 2 minutes. The copper foil was then heat-treated at 120°C for 2 minutes to obtain a pre-pressed negative electrode blank. This pre-pressed negative electrode blank was rolled using a roll press to obtain a pre-pressed negative electrode having a negative electrode composite layer (thickness: 80 μm).

[0178] Using the separator with functional layer obtained as described above, the volume average particle size and particle size distribution of the particulate polymer in the functional layer, the ratio of the total area of ​​the particulate polymer and particle shed portions per unit area of ​​the functional layer when viewed in plan, the ratio of the area of ​​particle shed portions to the total area of ​​the particulate polymer and particle shed portions when viewed in plan, the thickness of the inorganic particle layer, and the ratio of the volume average particle size of the particulate polymer to the thickness of the inorganic particle layer were determined. In addition, the separator with functional layer, positive electrode, and negative electrode obtained as described above were used to evaluate the process adhesion and heat resistance of the functional layer. The results are shown in Table 1.

[0179] <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 around a wound body to obtain a wound body. This wound body was pressed at 70°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 obtained lithium ion secondary battery was used to evaluate the electrolyte injection property, cycle characteristics, and storage characteristics of the secondary battery. The results are shown in Table 1.

[0180] Example 2 In the production of the separator with a functional layer in Example 1, the tension applied during winding was 4 N / mm 2 to 7N / mm 2 Except for the above change, the particulate polymer (A), the binder (α), the slurry composition, the separator with the functional layer, the positive electrode, and the 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.

[0181] Example 3 In the production of the separator with a functional layer in Example 1, the tension applied during winding was 4 N / mm 2 to 1N / mm 2 Except for the above change, the particulate polymer (A), the binder (α), the slurry composition, the separator with the functional layer, the positive electrode, and the 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.

[0182] Example 4 In the production of the separator with a functional layer in Example 1, the tension applied during winding was 4 N / mm 2 to 2N / mm 2 Except for the above change, the particulate polymer (A), the binder (α), the slurry composition, the separator with the functional layer, the positive electrode, and the 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.

[0183] Example 5 In the production of the separator with a functional layer in Example 1, the tension applied during winding was 4 N / mm 2 to 10N / mm 2 Except for the above change, the particulate polymer (A), the binder (α), the slurry composition, the separator with the functional layer, the positive electrode, and the 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.

[0184] Example 6 In the production of the separator with a functional layer in Example 1, the tension applied during winding was 4 N / mm 2 to 20N / mm 2 Except for the above change, the particulate polymer (A), the binder (α), the slurry composition, the separator with the functional layer, the positive electrode, and the 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.

[0185] Example 7 In preparing the slurry composition of Example 1, except that the particulate polymer (B) prepared as follows was used instead of the particulate polymer (A), 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.

[0186] <Preparation of Particulate Polymer (B)> A particulate polymer (B) was prepared by the same procedure as in the preparation of the particulate polymer (A) in Example 1, except that a colloidal dispersion (B) containing magnesium hydroxide was used instead of the colloidal dispersion (A) containing magnesium hydroxide as a metal hydroxide. The colloidal dispersion (B) containing magnesium hydroxide was prepared by gradually adding, under stirring, an aqueous solution (B2) prepared by dissolving 7.0 parts of sodium hydroxide in 50 parts of ion-exchanged water to an aqueous solution (B1) prepared by dissolving 10.0 parts of magnesium chloride in 200 parts of ion-exchanged water.

[0187] Example 8 In the preparation of the slurry composition of Example 1, except that the particulate polymer (C) prepared as follows was used instead of the particulate polymer (A), 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.

[0188] <Preparation of Particulate Polymer (C)> A particulate polymer (C) was prepared by the same procedure as in the preparation of the particulate polymer (A) in Example 1, except that a colloidal dispersion (C) containing magnesium hydroxide was used instead of the colloidal dispersion (A) containing magnesium hydroxide as a metal hydroxide. The colloidal dispersion (C) containing magnesium hydroxide was prepared by gradually adding, under stirring, an aqueous solution (C2) prepared by dissolving 4.2 parts of sodium hydroxide in 50 parts of ion-exchanged water to an aqueous solution (C1) prepared by dissolving 6.0 parts of magnesium chloride in 200 parts of ion-exchanged water.

[0189] Example 9 In the preparation of the slurry composition of Example 1, except that the particulate polymer (D) prepared as follows was used instead of the particulate polymer (A), 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.

[0190] <Preparation of Particulate Polymer (D)> In carrying out the suspension polymerization method, the same operation as in the preparation of the particulate polymer (A) of Example 1 was carried out, except that the time for high shear stirring was changed from 1 minute to 10 seconds, to obtain a particulate polymer (D).

[0191] Example 10 In the preparation of the slurry composition of Example 1, except that the particulate polymer (E) prepared as follows was used instead of the particulate polymer (A), 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.

[0192] <Preparation of Particulate Polymer (E)> The particulate polymer (A) prepared in Example 1 was subjected to differentiation and coarse particle removal treatment using a classifier ("Alpine", manufactured by Hosokawa Micron Corporation) to obtain a particulate polymer (E).

[0193] Example 11 In preparing the slurry composition of Example 1, except that the volume ratio of the inorganic particles (alumina) to the particulate polymer (A) in the resulting slurry composition (inorganic particles / particulate polymer (A)) was changed from 70 / 30 to 80 / 20, the particulate polymer (A), binder (α), slurry composition, separator with functional layer, positive electrode, and 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.

[0194] Example 12 In preparing the slurry composition of Example 1, except that the volume ratio of the inorganic particles (alumina) to the particulate polymer (A) in the resulting slurry composition (inorganic particles / particulate polymer (A)) was changed from 70 / 30 to 55 / 45, the particulate polymer (A), binder (α), slurry composition, separator with functional layer, positive electrode, and 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.

[0195] Example 13 In the preparation of the slurry composition of Example 1, except that the particulate polymer (F) prepared as follows was used instead of the particulate polymer (A), 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, except that the melting point of the particulate polymer (F) was measured instead of the glass transition temperature. The results are shown in Table 1.

[0196] <Preparation of Particulate Polymer (F)> After thoroughly replacing the inside of a 1-L autoclave equipped with a stirrer with nitrogen, 400 g of deoxygenated pure water, 4 g of ammonium perfluorodecanoate as an emulsifier, and poval (polyvinyl alcohol) as a dispersion stabilizer were charged and the temperature was raised to 60 °C while stirring at 100 rpm. Next, a mixed gas consisting of 90 parts by weight of vinylidene fluoride (VDF) and 10 parts by weight of hexafluoropropylene (HFP) was charged until the internal pressure reached 3 MPa (gauge pressure). Diisopropyl peroxydicarbonate was then added as a polymerization initiator to initiate polymerization, and the reaction was continued for 3 hours. The reaction solution was cooled and stirring was stopped, and the unreacted monomer was released to terminate the reaction, yielding a latex of vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) as particulate polymer (F).

[0197] Example 14 In the preparation of the slurry composition of Example 1, except that the particulate polymer (G) prepared as follows was used instead of the particulate polymer (A), 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.

[0198] <Preparation of Particulate Polymer (G)> The same operation as that for preparing the particulate polymer (A) in Example 1 was carried out, except that the monomer composition (G) was used instead of the monomer composition (A), to prepare the particulate polymer (G). The monomer composition (G) was prepared by mixing 20.9 parts of n-butyl acrylate as a (meth)acrylic acid ester monomer, 20 parts of acrylonitrile as a nitrile group-containing monomer, 59 parts of methyl methacrylate as a (meth)acrylic acid ester monomer, and 0.1 parts of ethylene glycol dimethacrylate as a crosslinkable monomer.

[0199] (Comparative Example 1) In the production of the separator with a functional layer in Example 1, the tension applied during winding was 4 N / mm 2 from 25N / mm 2 Except for the above change, the particulate polymer (A), the binder (α), the slurry composition, the separator with the functional layer, the positive electrode, and the 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.

[0200] (Comparative Example 2) In preparing the slurry composition of Example 1, instead of the particulate polymer (A) prepared by suspension polymerization, a particulate polymer (H) prepared by seed polymerization as described below was used, and in preparing the separator with functional layer of Example 1, the slurry composition was applied to the separator substrate by bar coating as described below instead of gravure coating. The binder (α), slurry composition, separator with functional layer, positive electrode, and negative electrode were prepared in the same manner as in Example 1, and a lithium ion secondary battery was obtained. Various measurements and evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0201] <Preparation of Particulate Polymer (H)> A 5 MPa pressure vessel equipped with a stirrer was charged with a monomer composition (H1) containing 75 parts of styrene as an aromatic vinyl monomer, 20 parts of n-butyl acrylate as a (meth)acrylic acid alkyl ester monomer, 4 parts of methacrylic acid as an acid group-containing monomer, and 1 part of ethylene glycol dimethacrylate as a di(meth)acrylic acid ester monomer, 1.2 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator, and the mixture was thoroughly stirred and then heated to 60°C to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling, and seed particles (H S An aqueous dispersion containing 1) was obtained. Seed particles (H S To the aqueous dispersion containing 1), a monomer composition (H2) containing 75,000 parts of styrene as an aromatic vinyl monomer, 20,000 parts of n-butyl acrylate as a (meth)acrylic acid ester monomer, 4,000 parts of methacrylic acid as an acid group-containing monomer, and 1,000 parts of ethylene glycol dimethacrylate as a di(meth)acrylic acid ester monomer was further added, and after thorough stirring, the mixture was heated to 60°C to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain an aqueous dispersion containing a particulate polymer (H).

[0202] <Production of separator with functional layer (bar coating method)> A polyethylene microporous membrane (thickness: 12 μm) was prepared as a separator substrate. The slurry composition obtained as described above was applied to one side of this separator substrate using a bar coater. Next, the separator substrate to which the slurry composition had been applied was dried at 50°C for 1 minute to form a functional layer. The same operation was performed on the other side of the separator substrate, producing a separator with a functional layer, each of which had an inorganic particle layer 2.0 μm thick, on both sides of the separator substrate.

[0203] (Comparative Example 3) In the preparation of the slurry composition of Example 1, except that the particulate polymer (A) prepared by the suspension polymerization method was replaced with the particulate polymer (I) prepared by the emulsion polymerization method described below, the binder (α), slurry composition, separator with functional layer, positive electrode, and 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.

[0204] <Preparation of Particulate Polymer (I)> A 5 MPa pressure vessel equipped with a stirrer was charged with a monomer composition containing 77.9 parts of styrene as an aromatic vinyl monomer, 18 parts of 2-ethylhexyl acrylate as a (meth)acrylic acid alkyl ester monomer, 4 parts of methacrylic acid as an acid group-containing monomer, and 0.1 parts of ethylene glycol dimethacrylate as a di(meth)acrylic acid ester monomer, 1.2 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator, and after thorough stirring, the mixture was heated to 60 ° C. to initiate polymerization. When the polymerization conversion rate reached 99%, the mixture was cooled to stop the reaction, and an aqueous dispersion containing a particulate polymer (I) was obtained.

[0205] In addition, in Table 1, "ST" indicates styrene, "2EHA" indicates 2-ethylhexyl acrylate, "EDMA" refers to ethylene glycol dimethacrylate; "BA" indicates n-butyl acrylate; "PVdF" stands for vinylidene fluoride, "HFP" refers to hexafluoropropylene; "AN" indicates acrylonitrile, "MAA" indicates methacrylic acid, "MMA" indicates methyl methacrylate, "AGE" indicates allyl glycidyl ether, "AMA" refers to allyl methacrylate.

[0206] [Table 1]

[0207] Table 1 shows that the functional layers of Examples 1 to 14, which contain inorganic particles and a particulate polymer, have particle shed portions, and when viewed in a plane, the ratio of the area of ​​the particle shed portions to the total area of ​​the particulate polymer and the particle shed portions is within a specified range, and the volume average particle diameter of the particulate polymer is larger than the thickness of the inorganic particle layer containing the inorganic particles, have excellent process adhesion and can provide excellent cycle characteristics to electrical elements. In contrast, the functional layer of Comparative Example 1, in which the ratio of the area of ​​the particle shed portions to the total area of ​​the particulate polymer and the particle shed portions exceeds the specified range, is found to have poor process adhesion and to be unable to provide excellent cycle characteristics to the electrochemical element. Furthermore, it is clear that the functional layer of Comparative Example 2, which does not have particle-shedded portions, has excellent process adhesion, but is unable to provide excellent cycle characteristics to the electrochemical element. Furthermore, it can be seen that the functional layer of Comparative Example 3, which does not have particle shed portions and in which the volume average particle diameter of the particulate polymer is smaller than the thickness of the inorganic particle layer, has poor process adhesion and is unable to provide excellent cycle characteristics to the electrochemical element. [Industrial Applicability]

[0208] According to the present invention, it is possible to provide a functional layer for an electrochemical device that has excellent process adhesion and allows the electrochemical device to exhibit excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide a separator with a functional layer for an electrochemical element, which has excellent process adhesion and is provided with a functional layer for an electrochemical element that can enable the electrochemical element to exhibit excellent cycle characteristics. Furthermore, according to the present invention, an electrochemical device capable of exhibiting excellent cycle characteristics can be provided. [Explanation of symbols]

[0209] 1 Functional layer 11 Inorganic particles 12 Particle-like composites 13 Inorganic particle layer 14 Particle shedding section

Claims

1. A functional layer for an electrochemical element, comprising inorganic particles and a particulate polymer, and used for bonding components of an electrochemical element together, having a particle shed portion, when the surface of the functional layer for electrochemical devices is viewed from above, the ratio of the area of ​​the particle shed portions to the total area of ​​the particulate polymer and the particle shed portions is 0.1% or more and 40.0% or less; The functional layer for an electrochemical device, wherein the volume average particle diameter of the particulate polymer is larger than the thickness of the inorganic particle layer containing the inorganic particles.

2. 2. The functional layer for an electrochemical element according to claim 1, wherein the volume average particle diameter of the particulate polymer is 1.0 μm or more and 10.0 μm or less.

3. 3. The functional layer for an electrochemical device according to claim 1, wherein the particle size distribution of the particulate polymer is 1.5 or less.

4. The functional layer for electrochemical elements according to any one of claims 1 to 3, wherein the ratio of the volume average particle diameter of the particulate polymer to the thickness of the inorganic particle layer (volume average particle diameter of the particulate polymer / thickness of the inorganic particle layer) is 1.1 or more and 10.0 or less.

5. 5. The functional layer for an electrochemical device according to claim 1, wherein the particulate polymer satisfies the following 1) or 2): 1) The glass transition temperature of the particulate polymer is 10°C or higher and 90°C or lower. 2) The melting point of the particulate polymer is 50°C or higher

6. The functional layer for electrochemical devices according to any one of claims 1 to 5, wherein, when the surface of the functional layer for electrochemical devices is viewed in plan, the proportion of the total area of ​​the particulate polymer and the particle shed portions per unit area of ​​the functional layer for electrochemical devices is 10% or less.

7. 7. The functional layer for an electrochemical device according to claim 1, wherein the particulate polymer contains an aromatic vinyl monomer unit.

8. 7. The functional layer for an electrochemical device according to claim 1, wherein the particulate polymer contains a fluorine atom-containing monomer unit.

9. A separator with a functional layer for an electrochemical element, comprising the functional layer for an electrochemical element according to any one of claims 1 to 8 on a separator substrate.

10. An electrochemical element comprising a positive electrode, a negative electrode, and the separator with a functional layer for an electrochemical element according to claim 9, wherein the functional layer for an electrochemical element is adhered to at least one of the positive electrode and the negative electrode.

11. forming a coating of a composition for an electrochemical device functional layer, the composition including inorganic particles and a particulate polymer, on a substrate; drying the coating to form a pre-functional layer; 1 N / mm 2 20N / mm or more 2 The method for producing a functional layer for an electrochemical element according to any one of claims 1 to 8, comprising the step of: applying tension to the functional layer.

12. The method for producing a functional layer for an electrochemical element according to claim 11, wherein the particulate polymer has a volume average particle size of 1.0 μm or more and 10.0 μm or less.

13. The method for producing a functional layer for an electrochemical device according to claim 11 or 12, wherein the particle size distribution of the particulate polymer is 1.5 or less.

14. The method for producing a functional layer for an electrochemical element according to any one of claims 11 to 13, wherein the particulate polymer satisfies the following 3) or 4): 3) The glass transition temperature of the particulate polymer is 10°C or higher and 90°C or lower. 4) The melting point of the particulate polymer is 50°C or higher

15. The method for producing a functional layer for electrochemical elements according to any one of claims 11 to 14, wherein the volume ratio of the inorganic particles to the particulate polymer (inorganic particles / particulate polymer) in the composition for electrochemical element functional layers is 55 / 45 or more and 95 / 5 or less.

16. The method for producing a functional layer for an electrochemical element according to any one of claims 11 to 15, wherein the particulate polymer contains an aromatic vinyl monomer unit.

17. The method for producing a functional layer for an electrochemical device according to any one of claims 11 to 15, wherein the particulate polymer contains a fluorine atom-containing monomer unit.

18. A method for producing a separator with a functional layer for electrochemical devices, comprising forming a functional layer for electrochemical devices on a separator substrate using the method for producing a functional layer for electrochemical devices according to any one of claims 11 to 17.

19. A method for producing an electrochemical element, using a separator with a functional layer for an electrochemical element obtained by the method for producing a separator with a functional layer for an electrochemical element according to claim 18.

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