Composition for functional layer of electrochemical element, laminate for electrochemical element, and electrochemical element

Abstract

The purpose of the present invention is to provide a composition for a functional layer of an electrochemical element, said composition being capable of forming a functional layer for an electrochemical element, said functional layer having excellent normal-temperature adhesiveness and being capable of reducing the internal resistance of the electrochemical element. This composition for a functional layer of an electrochemical element contains a particulate polymer A. The particulate polymer A has a volume average particle diameter of from 0.75 [mu] m to 17.5 [mu] m (inclusive), an elution amount of the particulate polymer A into tetrahydrofuran of from 0.05% by mass to 60% by mass (inclusive), and a storage modulus at 25 DEG C of 35 MPa or less.

Description

Technical Field

[0001] This invention relates to compositions for functional layers of electrochemical elements, laminates for electrochemical elements, and electrochemical elements. Background Technology

[0002] Electrochemical components such as lithium-ion secondary batteries and electric double-layer capacitors are characterized by their small size, light weight, high energy density, and ability to be repeatedly charged and discharged, and are used in a wide range of applications. Moreover, electrochemical components typically consist of a positive electrode, a negative electrode, and spacers that separate the positive and negative electrodes to prevent short circuits between them.

[0003] Here, in electrochemical elements such as lithium-ion secondary batteries, components are used that have porous film layers for improving heat resistance and strength, adhesive layers for bonding battery components together, etc. (hereinafter, these are collectively referred to as "functional layers for electrochemical elements", sometimes simply "functional layers"). Specifically, electrodes formed by further forming functional layers on electrode substrates formed by providing electrode composite material layers on current collectors, or spacers formed by forming functional layers on spacer substrates, are used as battery components.

[0004] Furthermore, in recent years, with the aim of further improving the performance of electrochemical components such as lithium-ion secondary batteries, research is being conducted on further improving the composition for the functional layer of electrochemical components (hereinafter, sometimes simply referred to as "composition for the functional layer") used to form the functional layer (see Patent Documents 1-3).

[0005] Prior technology documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Publication No. 2023-523279;

[0008] Patent Document 2: Japanese Patent Publication No. 2023-515152;

[0009] Patent document 3: Japanese Patent Application Publication No. 2016-183209. Summary of the Invention

[0010] The problem the invention aims to solve

[0011] From the viewpoint of improving the productivity of electrochemical devices, the functional layer preferably exhibits high adhesion strength at room temperature (i.e., excellent adhesion at room temperature). Furthermore, from the viewpoint of improving electrochemical characteristics, the electrochemical device with the functional layer preferably has low internal resistance.

[0012] However, there is room for improvement in the existing functional layer compositions described above in terms of achieving a good balance between room temperature adhesion of the functional layer and reducing the internal resistance of the electrochemical element.

[0013] Therefore, the object of the present invention is to provide a composition for an electrochemical element functional layer that can form a functional layer for an electrochemical element with excellent room temperature adhesion and can reduce the internal resistance of the electrochemical element.

[0014] Furthermore, the present invention aims to provide a laminate for electrochemical elements that can reduce the internal resistance of electrochemical elements.

[0015] Furthermore, the present invention aims to provide an electrochemical element with low internal resistance.

[0016] Solution for solving the problem

[0017] The inventors conducted in-depth research to solve the above-mentioned problems. Then, the inventors made a new discovery that if a functional layer composition containing particulate polymers that meet specified conditions regarding volume average particle size, the amount of tetrahydrofuran dissolved during film formation, and the storage modulus at 25°C, the above-mentioned problems can be solved, thus completing the present invention.

[0018] That is, the object of the present invention is to advantageously solve the above-mentioned problems, and according to the present invention, the following [1] to

[11] electrochemical element functional layer composition, the following

[12] electrochemical element laminate and the following

[13] electrochemical element are provided.

[0019] [1] A composition for a functional layer of an electrochemical element, comprising particulate polymer A,

[0020] The volume average particle size of the above-mentioned particulate polymer A is 0.75 μm or more and 17.5 μm or less.

[0021] The leaching amount of the above-mentioned particulate polymer A to tetrahydrofuran is more than 0.05% by mass and less than 60% by mass.

[0022] The storage modulus of the above-mentioned particulate polymer A at 25°C is below 35 MPa.

[0023] In this way, a functional layer composition for a particulate polymer A, wherein the volume average particle size and the amount of tetrahydrofuran (THF leaching) are within the above-mentioned ranges and the storage modulus at 25°C is below the above-mentioned value, can be well fabricated to produce a functional layer with excellent room-temperature adhesion. Furthermore, based on this functional layer, the internal resistance of electrochemical devices can be reduced.

[0024] Furthermore, in this invention, "volume average particle size" refers to "the particle size (D50) that constitutes 50% of the cumulative volume calculated from the smallest diameter side in a particle size distribution (volume standard) determined by laser diffraction," and can be measured using the methods described in the embodiments of this specification.

[0025] Furthermore, in this invention, the "THF dissolution amount" and "storage modulus at 25°C" of the particulate polymer A can be determined using the methods described in the examples of this specification.

[0026] [2] According to the composition for the functional layer of the electrochemical element described in [1] above, wherein the number average molecular weight of the tetrahydrofuran leaching component of the particulate polymer A is 500 or more and 500,000 or less.

[0027] If the number-average molecular weight of the tetrahydrofuran (THF) leaching component of the particulate polymer A is within the above range, the room temperature adhesion of the functional layer can be further improved, and the internal resistance of the electrochemical element can be further reduced.

[0028] Furthermore, in this invention, the "number-average molecular weight of the THF dissolution components" can be determined using the methods described in the examples of this specification.

[0029] [3] The composition for the functional layer of the electrochemical element according to [1] or [2] above, wherein the glass transition temperature of the particulate polymer A is -50°C or higher and 95°C or lower.

[0030] If the glass transition temperature of the particulate polymer A is within the above range, it is possible to improve the room temperature adhesion while improving the anti-blocking properties of the functional layer.

[0031] Furthermore, in this invention, the glass transition temperature of the particulate polymer A can be determined using the methods described in the examples of this specification.

[0032] [4] The composition for the functional layer of an electrochemical element according to any one of [1] to [3] above, wherein the electrolyte swelling degree of the particulate polymer A is 100% or more and 500% or less.

[0033] If the electrolyte swelling degree of the particulate polymer A is within the above range, the room temperature adhesion of the functional layer can be further improved, and the internal resistance of the electrochemical element can be further reduced.

[0034] Furthermore, in this invention, the "electrolyte swelling degree" of the particulate polymer A can be measured using the method described in the examples of this specification.

[0035] [5] The composition for the functional layer of an electrochemical element according to any one of [1] to [4] above, wherein the composition for the functional layer of an electrochemical element further comprises a dispersion medium containing water, and the pH is 3.0 or more and 12.0 or less.

[0036] If the pH of the composition for the functional layer is within the above range, the dispersibility of the composition for the functional layer can be improved, and the room temperature adhesion of the functional layer can be further improved.

[0037] Furthermore, in this invention, the “pH” of the composition for the functional layer refers to the pH measured at a temperature of 25°C, which can be measured using the method described in the examples of this specification.

[0038] [6] The composition for the functional layer of an electrochemical element according to any one of [1] to [5] above, wherein the composition for the functional layer of an electrochemical element further comprises a particulate polymer B different from the particulate polymer A and a dispersant, wherein the mass ratio of the particulate polymer A to the particulate polymer B (particulate polymer A / particulate polymer B) is 1 / 99 or more and 99 / 1 or less.

[0039] According to the functional layer composition that also includes particulate polymer B and a dispersant, and the mass ratio of particulate polymer A to particulate polymer B is within the above range, the room temperature adhesion of the functional layer can be further improved, and the internal resistance of the electrochemical element can be further reduced.

[0040] [7] The composition for the functional layer of an electrochemical element according to any one of [1] to [6] above, wherein the particulate polymer A contains aromatic vinyl monomer units in a proportion of 10% by mass or more.

[0041] If the proportion of aromatic vinyl monomer units in the particulate polymer A is above the above value, the room temperature adhesion can be further improved while improving the anti-blocking property of the functional layer.

[0042] Furthermore, in this invention, the term "monomer unit" in a polymer refers to "a repeating unit derived from that monomer contained in a polymer obtained using that monomer." Additionally, the proportion of monomer units in the polymer can be determined using... 1 The measurements were performed using nuclear magnetic resonance (NMR) methods such as H-NMR.

[0043] [8] The composition for the functional layer of an electrochemical element according to any one of [1] to [7] above, wherein the particulate polymer A contains crosslinking monomer units in a proportion of 0.01% by mass or more and 50% by mass or less.

[0044] If the proportion of crosslinked monomer units in the particulate polymer A is within the above range, the room temperature adhesion of the functional layer can be further improved, and the internal resistance of the electrochemical element can be further reduced.

[0045] [9] The composition for the functional layer of an electrochemical element according to any one of [1] to [8] above, wherein the particulate polymer A has a core-shell structure.

[0046] If the particulate polymer A has a core-shell structure, it can improve the room temperature adhesion while enhancing the anti-blocking properties of the functional layer.

[0047]

[10] The composition for the functional layer of the electrochemical element according to [9] above, wherein the mass ratio (core / shell) of the core portion to the shell portion of the core-shell structure is 0.1 / 99.9 or more and 99.9 / 0.1 or less.

[0048] If the particulate polymer A has a core-shell structure with a core-to-shell mass ratio within the above range, it is possible to improve the room temperature adhesion while improving the anti-adhesion of the functional layer.

[0049]

[11] The composition for the functional layer of an electrochemical element according to any one of [1] to

[10] above, wherein the composition for the functional layer of an electrochemical element further contains non-conductive heat-resistant particles.

[0050] The composition for the functional layer, which also contains non-conductive heat-resistant particles, can improve the heat resistance of the functional layer.

[0051]

[12] A laminate for an electrochemical element having a substrate and an electrochemical element functional layer formed on the substrate, wherein the electrochemical element functional layer is formed using the composition for an electrochemical element functional layer described in any one of [1] to

[11] .

[0052] An electrochemical element laminate (hereinafter sometimes simply referred to as "laminate") having a functional layer formed using any of the above-mentioned functional layer compositions can reduce the internal resistance of the electrochemical element.

[0053]

[13] An electrochemical element having the electrochemical element laminate described above

[12] .

[0054] The internal resistance of electrochemical elements with the above-mentioned stacked structure is reduced.

[0055] Invention Effects

[0056] According to the present invention, a composition for an electrochemical element functional layer is provided that can form a functional layer for an electrochemical element with excellent room temperature adhesion and reduced internal resistance of the electrochemical element.

[0057] Furthermore, according to the present invention, it is possible to provide a laminate for electrochemical elements that can reduce the internal resistance of electrochemical elements.

[0058] Furthermore, according to the present invention, it is possible to provide an electrochemical element with low internal resistance. Detailed Implementation

[0059] The embodiments of the present invention will now be described in detail.

[0060] Here, the functional layer composition of the present invention can be used as a material when forming the functional layer of the laminate of the present invention. Furthermore, the laminate of the present invention is characterized by having a functional layer formed using the functional layer composition of the present invention. In addition, the electrochemical element of the present invention has the laminate of the present invention. Furthermore, the functional layer formed using the functional layer composition of the present invention provides adhesive ability for bonding electrochemical element components together, but may also further have the function of improving the heat resistance and strength of electrochemical element components such as spacers and electrodes.

[0061] (Composition for functional layers of electrochemical components)

[0062] The functional layer composition of the present invention comprises particulate polymer A, and optionally also contains particulate polymer B, a dispersion medium, a dispersant, non-conductive heat-resistant particles, and other components.

[0063] Here, the functional layer composition of the present invention is characterized in that the volume average particle size and THF dissolution amount of the particulate polymer A are within a specified range, and the storage modulus of the particulate polymer A at 25°C is below a specified value.

[0064] In addition, the functional layer compositions of the present invention generally do not contain electrode active materials.

[0065] Furthermore, since the functional layer composition of the present invention contains particulate polymer A that satisfies the above-described properties, using the functional layer composition of the present invention enables the functional layer to exhibit excellent room-temperature adhesion while reducing the internal resistance of the electrochemical element. The reason for obtaining the above effects by using the functional layer composition of the present invention is not yet clear, but it is speculated as follows.

[0066] First, the particulate polymer A contained in the functional layer composition of the present invention has a relatively large volume average particle size of 0.75 μm or more and 17.5 μm or less. Therefore, on the thickness direction surface of the functional layer formed using the functional layer composition of the present invention, the particulate polymer A protrudes relative to materials other than the particulate polymer A, making it easier to contact the electrochemical element component, thereby improving the adhesion of the functional layer. Furthermore, since the storage modulus of the particulate polymer A at 25°C is 35 MPa or less, and the THF dissolution of the particulate polymer A is 0.05% by mass or more, the particulate polymer A is easily deformable at room temperature on the contact surface with the electrochemical element component in contact with the functional layer formed using the functional layer composition of the present invention, thus exhibiting good room temperature adhesion.

[0067] Furthermore, by reducing the THF leaching amount of particulate polymer A to below 60% by mass, the amount of particulate polymer A leached into the electrolyte is decreased, which can suppress the increase in internal resistance of the electrochemical element caused by the leached particulate polymer A adsorbing on the surface of the electrode active material or clogging the pores of the spacer. Moreover, as described above, since the volume average particle size of particulate polymer A is relatively large, the pores of the spacer are less likely to be clogged by the particulate polymer A dissolved in the electrolyte, thus suppressing the increase in internal resistance of the electrochemical element.

[0068] Based on the above reasons, it can be considered that if the functional layer composition of the present invention is used, the room temperature adhesion of the functional layer can be improved, and the internal resistance of the electrochemical element can be reduced.

[0069] <Particulate Polymer A>

[0070] The particulate polymer A serves to enable the functional layer formed by the composition of the functional layer to exhibit excellent adhesive properties. Here, "particulate polymer" refers to a polymer that can be dispersed in an aqueous medium such as water, and exists in a particulate form in the aqueous medium. Furthermore, the particulate polymer A is generally not water-soluble.

[0071] Furthermore, in this invention, "non-water-soluble" means that when 0.5g of the polymer is dissolved in 100g of water at a temperature of 25°C, the insoluble component is 90% or more by mass.

[0072] The composition of the particulate polymer A is not particularly limited as long as it meets the above-mentioned conditions for volume average particle size, THF dissolution rate, and storage modulus. Preferably, the particulate polymer A contains at least crosslinking monomer units, and more preferably contains aromatic vinyl monomer units and crosslinking monomer units. Additionally, the particulate polymer A may contain monomer units other than aromatic vinyl monomer units and crosslinking monomer units (hereinafter referred to as "other monomer units").

[0073] <<Aromatic Vinyl Monomer Units>>

[0074] Examples of aromatic vinyl monomers capable of forming aromatic vinyl monomer units include styrene, α-methylstyrene, p-tert-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. These can be used alone or in combination of two or more. Among these, styrene is preferred.

[0075] Furthermore, taking all monomer units in the particulate polymer A as 100% by mass, the proportion of aromatic vinyl monomer units in the particulate polymer A is preferably 10% by mass or more, more preferably 11.5% by mass or more, even more preferably 13% by mass or more, and preferably 99% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 60% by mass or less. If the proportion of aromatic vinyl monomer units in the particulate polymer A is above or below the above-mentioned lower limit, the glass transition temperature of the particulate polymer A increases, which can improve the anti-blocking properties of the functional layer. In addition, if the proportion of aromatic vinyl monomer units in the particulate polymer A is below the above-mentioned upper limit, the room temperature adhesion of the functional layer can be further improved.

[0076] <<Crosslinked monomer unit>>

[0077] Examples of crosslinking monomers capable of forming crosslinking monomer units include: crosslinking monomers having thermally crosslinking crosslinking groups and having one olefinic double bond per molecule; and crosslinking monomers having two or more olefinic double bonds per molecule.

[0078] Examples of thermally crosslinkable crosslinking groups include epoxy groups, N-hydroxymethylamide groups, oxetyl butyl groups, oxazoline groups, and combinations thereof. Among these, epoxy groups are preferred.

[0079] Furthermore, examples of crosslinking monomers having an epoxy group as a thermally crosslinking group and possessing an olefinic double bond include: unsaturated glycidyl ethers such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and o-allyl phenyl glycidyl ether; and monoepoxides of dienes or polyenes such as butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, and 1,2-epoxy-5,9-cyclododecadiene. Compounds; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, and 1,2-epoxy-9-decene; and glycidyl esters of unsaturated carboxylic acids such as glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl 4-heptenoic acid, glycidyl sorbate, glycidyl linoleic acid, glycidyl 4-methyl-3-pentenoic acid, glycidyl 3-cyclohexene carboxylic acid, and glycidyl 4-methyl-3-cyclohexene carboxylic acid.

[0080] Furthermore, examples of crosslinking monomers having an N-hydroxymethyl amide group as a thermally crosslinking crosslinking group and having an olefinic double bond include N-hydroxymethyl (meth)acrylamide and other (meth)acrylamides having a hydroxymethyl group.

[0081] In addition, in this invention, "(meth)acrylamide" refers to acrylamide and / or methacrylamide.

[0082] Furthermore, examples of crosslinking monomers having an oxetyl group as a thermally crosslinking crosslinking group and having an olefinic double bond include: 3-((meth)acryloyloxymethyl)oxetane, 3-((meth)acryloyloxymethyl)-2-trifluoromethyloxetane, 3-((meth)acryloyloxymethyl)-2-phenyloxetane, 2-((meth)acryloyloxymethyl)oxetane, and 2-((meth)acryloyloxymethyl)-4-trifluoromethyloxetane.

[0083] Furthermore, examples of crosslinking monomers having an oxazoline group as a thermally crosslinking group and having an olefinic double bond include: 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0084] Furthermore, examples of crosslinkable monomers having two or more olefinic double bonds per molecule include: butadiene, isoprene, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipropylene glycol diallyl ether, polyethylene glycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallylpropoxyethane, trimethylolpropane-diallyl ether, allyl or vinyl ethers of polyfunctional alcohols other than those mentioned above, triallylamine, methylenebisacrylamide, and divinylbenzene.

[0085] In addition, in this invention, "(meth)acrylate" refers to acrylate and / or methacrylate.

[0086] The aforementioned crosslinking monomers can be used alone or in combination of two or more. Among these, ethylene glycol dimethacrylate and glycidyl methacrylate are preferred.

[0087] With all monomer units in the particulate polymer A as 100% by mass, the proportion of crosslinked monomer units in the particulate polymer A is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.5% by mass or more, particularly preferably 1% by mass or more, preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 15% by mass or less, and particularly preferably 12% by mass or less. If the proportion of crosslinked monomer units in the particulate polymer A is above or below the above lower limit, the dissolution of the particulate polymer A into the electrolyte can be suppressed, and the internal resistance of the electrochemical element can be further reduced. Furthermore, if the proportion of crosslinked monomer units in the particulate polymer A is below the above upper limit, the room temperature adhesion of the functional layer can be further improved.

[0088] <<Other Monomer Units>>

[0089] Other monomer units include, for example, (meth)acrylate monomer units. Furthermore, the particulate polymer A preferably contains (meth)acrylate monomer units as other monomer units.

[0090] Examples of (meth)acrylate monomers capable of forming (meth)acrylate monomer units include: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, and other alkyl acrylates; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, and other alkyl methacrylates; etc. These can be used alone or in combination of two or more in any ratio. Among these, n-butyl acrylate and 2-ethylhexyl acrylate are preferred as (meth)acrylate monomers.

[0091] With all monomer units in the particulate polymer A as 100% by mass, the proportion of (meth)acrylate monomer units in the particulate polymer A is preferably 1% by mass or more, more preferably 10% by mass or more, further preferably 20% by mass or more, particularly preferably 29% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, and further preferably 85% by mass or less. If the proportion of (meth)acrylate monomer units in the particulate polymer A is above or below the above-mentioned lower limit, the room temperature adhesion of the functional layer can be further improved. Furthermore, if the proportion of (meth)acrylate monomer units in the particulate polymer A is below or below the above-mentioned upper limit, the anti-blocking property of the functional layer can be improved.

[0092] Furthermore, the particulate polymer A can be a particle formed from a single polymer (single polymer particle) or a particle formed from two or more polymers (composite polymer particle). A composite polymer particle is a heterogeneous structure in which different polymer portions exist within the particle. Here, a heterogeneous structure refers to a single particle formed by the physical or chemical bonding of two or more different polymers, rather than a particle composed of a single-phase structure formed from a single polymer such as a block polymer. Specific examples of heterogeneous structures include: a core-shell structure where the core and at least a portion of the shell covering the outer surface of the core are formed from different polymers, resulting in spherical particles; a side-by-side structure where two or more polymers are arranged side-by-side; and so on. Moreover, from the viewpoint of improving both the anti-adhesion properties of the functional layer and room-temperature adhesion, the particulate polymer A preferably has a core-shell structure.

[0093] Core-shell structure

[0094] Here, in the particulate polymer A having a core-shell structure, the shell portion can cover the entire outer surface of the core portion, or it can partially cover the outer surface of the core portion. Furthermore, even if the outer surface of the core portion appears to be completely covered by the shell portion, if a hole is formed connecting the inside and outside of the shell portion, then the shell portion is a shell portion that partially covers the outer surface of the core portion. Therefore, for example, a particulate polymer A having a shell portion with a fine hole connecting from the outer surface of the shell portion (i.e., the circumferential surface of the particulate polymer A) to the outer surface of the core portion is equivalent to a particulate polymer A where the shell portion partially covers the outer surface of the core portion.

[0095] Furthermore, the particulate polymer A with a core-shell structure may have any constituent elements other than the core and shell described above, provided that it does not significantly impair the intended effect. Specifically, for example, the particulate polymer A may have a portion inside the core formed of a polymer different from the core. As a specific example, the seed particles used in manufacturing the core using seed polymerization may remain inside the core. However, from the viewpoint of significantly achieving the intended effect, the particulate polymer A preferably has only a core and a shell.

[0096] [Nuclear Section]

[0097] The polymer in the core is not particularly limited in the type of monomer units it contains, but aromatic vinyl monomer units and crosslinking monomer units are preferred examples. Furthermore, the polymer in the core may contain only one type of monomer unit or may contain multiple types.

[0098] -Aromatic vinyl monomer unit-

[0099] Aromatic vinyl monomers, which are aromatic vinyl monomer units in polymers capable of forming the core, can include monomers identical to those described above. These can be used individually or in combination. Among these, styrene is preferred.

[0100] With all monomer units contained in the polymer of the core portion as 100% by mass, the proportion of aromatic vinyl monomer units contained in the polymer of the core portion is preferably 1% by mass or more, more preferably 2% by mass or more, further preferably 3% by mass or more, particularly preferably 4% by mass or more, preferably 99% by mass or less, more preferably 90% by mass or less, further preferably 75% by mass or less, and particularly preferably 60% by mass or less. If the proportion of aromatic vinyl monomer units in the polymer of the core portion is above the above-mentioned lower limit, the glass transition temperature of the polymer of the core portion increases, which can improve the anti-blocking property of the functional layer. Furthermore, if the proportion of aromatic vinyl monomer units in the polymer of the core portion is below the above-mentioned upper limit, the room temperature adhesion of the functional layer can be further improved.

[0101] -Crosslinked monomer unit-

[0102] As crosslinking monomers that form the crosslinking monomer unit in a polymer capable of forming the core, examples of crosslinking monomers include those identical to those described above. These can be used individually or in combination. Among these, ethylene glycol dimethacrylate and glycidyl methacrylate are preferred.

[0103] With all monomer units contained in the polymer of the core as 100% by mass, the proportion of crosslinkable monomer units contained in the polymer of the core is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, particularly preferably 1% by mass or more, preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 15% by mass or less. If the proportion of crosslinkable monomer units in the polymer of the core is above or below the above-mentioned lower limit, the dissolution of particulate polymer A into the electrolyte can be suppressed, and the internal resistance of the electrochemical element can be further reduced. Furthermore, if the proportion of crosslinkable monomer units in the polymer of the core is below the above-mentioned upper limit, the room temperature adhesion of the functional layer can be further improved.

[0104] -Other monomer units-

[0105] The polymer that forms the core may contain monomer units other than aromatic vinyl monomer units and crosslinking monomer units (other monomer units), without particular limitation; for example, (meth)acrylate monomer units can be cited.

[0106] As (meth)acrylate monomers that can form the core of a polymer, examples of (meth)acrylate monomers include those identical to those described above. These can be used individually or in combination. Among these, n-butyl acrylate and 2-ethylhexyl acrylate are preferred.

[0107] With all monomer units contained in the polymer of the core portion as 100% by mass, the proportion of (meth)acrylate monomer units contained in the polymer of the core portion is preferably 1% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, particularly preferably 30% by mass or more, preferably 99% by mass or less, more preferably 97% by mass or less, and even more preferably 95% by mass or less. If the proportion of (meth)acrylate monomer units contained in the polymer of the core portion is above or below the above-mentioned lower limit, the room temperature adhesion of the functional layer can be further improved. Furthermore, if the proportion of (meth)acrylate monomer units contained in the polymer of the core portion is below or below the above-mentioned upper limit, the anti-blocking property of the functional layer can be improved.

[0108] [Shell]

[0109] The polymer in the shell is not particularly limited in the type of monomer units it contains, but aromatic vinyl monomer units are preferred. Furthermore, the polymer in the shell may contain only one type of monomer unit or multiple types.

[0110] -Aromatic vinyl monomer unit-

[0111] Aromatic vinyl monomers, which are aromatic vinyl monomer units in polymers capable of forming shells, can include monomers identical to those described above. These can be used individually or in combination. Among these, styrene is preferred.

[0112] With all monomer units contained in the polymer of the shell portion as 100% by mass, the proportion of aromatic vinyl monomer units contained in the polymer of the shell portion is preferably 30% by mass or more, more preferably 50% by mass or more, further preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass (i.e., the polymer of the shell portion contains only aromatic vinyl monomer units). If the proportion of aromatic vinyl monomer units in the polymer of the shell portion is above the above-mentioned lower limit, the glass transition temperature of the polymer of the shell portion increases, which can improve the anti-adhesion of the functional layer.

[0113] -Other monomer units-

[0114] The polymer that forms the shell can contain monomer units other than aromatic vinyl monomer units (other monomer units), and examples include the crosslinking monomer units and (meth)acrylate monomer units mentioned above.

[0115] Furthermore, when the particulate polymer A has a core-shell structure, the mass ratio of the core to the shell (core / shell) is preferably 0.1 / 99.9 or more, more preferably 1 / 99 or more, even more preferably 10 / 90 or more, particularly preferably 50 / 50 or more, preferably 99.9 / 0.1 or less, more preferably 99 / 1 or less, and even more preferably 95 / 5 or less. If the mass ratio of the core to the shell is above the aforementioned lower limit, the room temperature adhesion of the functional layer can be further improved. In addition, if the mass ratio of the core to the shell is below the aforementioned upper limit, the anti-adhesion of the functional layer can be improved.

[0116] Properties of Particulate Polymer A

[0117] [Volume Average Particle Size]

[0118] Here, the volume average particle size of the particulate polymer A used in this invention needs to be 0.75 μm or more and 17.5 μm or less. Preferably, the volume average particle size of the particulate polymer A is 1 μm or more, more preferably 1.5 μm or more, even more preferably 2.5 μm or more, particularly preferably 3 μm or more, preferably 15 μm or less, more preferably 12 μm or less, and even more preferably 10 μm or less. If the volume average particle size of the particulate polymer A is 0.75 μm or more, the room temperature adhesion of the functional layer can be improved, while the internal resistance of the electrochemical element can be reduced. On the other hand, if the volume average particle size of the particulate polymer A is 17.5 μm or less, the anti-adhesion property of the functional layer can be improved.

[0119] In addition, the volume average particle size of the particulate polymer A can be adjusted by changing the type and amount of metal hydroxide used in the preparation of the particulate polymer A, as well as the preparation method and conditions of the particulate polymer A.

[0120] [THF dissolution rate]

[0121] The THF leaching amount of the particulate polymer A needs to be 0.05% by mass or more and 60% by mass or less. Preferably, the THF leaching amount is 0.1% by mass or more, more preferably 0.5% by mass or more, further preferably 1% by mass or more, even more preferably 5% by mass or more, particularly preferably 10% by mass or more, preferably 50% by mass or less, more preferably 47% by mass or less, and even more preferably 45% by mass or less. If the THF leaching amount of the particulate polymer A is 0.05% by mass or more, the room temperature adhesion of the functional layer can be improved. Furthermore, if the THF leaching amount of the particulate polymer A is 60% by mass or less, the dissolution of the particulate polymer A into the electrolyte can be suppressed, thereby reducing the internal resistance of the electrochemical element.

[0122] Furthermore, the THF leaching amount of particulate polymer A can be adjusted by changing, for example, the type and / or amount of crosslinking monomers used to prepare particulate polymer A. Specifically, increasing the amount of crosslinking monomers used to prepare particulate polymer A reduces the THF leaching amount, while decreasing the amount of crosslinking monomers used increases the THF leaching amount.

[0123] [Energy Storage Modulus]

[0124] The storage modulus of the particulate polymer A at 25°C needs to be below 35 MPa, preferably below 30 MPa, more preferably below 20 MPa, further preferably below 10 MPa, particularly preferably below 5 MPa, more preferably above 0.05 MPa, and more preferably above 0.1 MPa. If the storage modulus of the particulate polymer A at 25°C is below 35 MPa, the room-temperature adhesion of the functional layer can be improved. Furthermore, if the storage modulus of the particulate polymer A at 25°C is above 0.05 MPa, the anti-adhesion of the functional layer can be improved, and the internal resistance of the electrochemical element can be further reduced.

[0125] In addition, the storage modulus of the particulate polymer A can be adjusted by changing, for example, the type and / or amount of monomers used to prepare the particulate polymer A.

[0126] [Number-average molecular weight of THF dissolved components]

[0127] The number-average molecular weight of the THF leaching component of the particulate polymer A is preferably 500 or more, more preferably 750 or more, further preferably 1000 or more, even more preferably 2500 or more, particularly preferably 5000 or more, preferably 500,000 or less, more preferably 400,000 or less, further preferably 300,000 or less, and particularly preferably 200,000 or less. If the number-average molecular weight of the THF leaching component of the particulate polymer A is above the lower limit mentioned above, the dissolution of the particulate polymer A into the electrolyte can be suppressed, and the room-temperature adhesion of the functional layer can be further improved. Furthermore, if the number-average molecular weight of the THF leaching component of the particulate polymer A is below the upper limit mentioned above, the increase in electrolyte viscosity can be suppressed, and the internal resistance of the electrochemical element can be further reduced.

[0128] Furthermore, the number-average molecular weight of the THF leaching components of particulate polymer A can be adjusted by changing, for example, the preparation method and preparation conditions of particulate polymer A.

[0129] Glass transition temperature

[0130] The glass transition temperature of the particulate polymer A is preferably -50°C or higher, more preferably -45°C or higher, even more preferably -40°C or higher, preferably 95°C or lower, more preferably 80°C or lower, even more preferably 60°C or lower, even more preferably 40°C or lower, and particularly preferably 25°C or lower. If the glass transition temperature of the particulate polymer A is above the aforementioned lower limit, the anti-blocking property of the functional layer can be improved. Furthermore, if the glass transition temperature of the particulate polymer A is below the aforementioned upper limit, the room temperature adhesion of the functional layer can be further improved.

[0131] In addition, the glass transition temperature of the particulate polymer A can be adjusted by changing, for example, the type and / or amount of monomer used to prepare the particulate polymer A.

[0132] [Electrolyte swelling degree]

[0133] The electrolyte swelling degree of the particulate polymer A is preferably 100% or more, more preferably 125% or more, even more preferably 150% or more, preferably 500% or less, more preferably 400% or less, even more preferably 300% or less, and particularly preferably 210% or less. If the electrolyte swelling degree of the particulate polymer A is above the above-mentioned lower limit, the room temperature adhesion of the functional layer can be further improved. Furthermore, if the electrolyte swelling degree of the particulate polymer A is below the above-mentioned upper limit, the internal resistance of the electrochemical element can be further reduced.

[0134] Furthermore, the electrolyte swelling degree of the particulate polymer A can be adjusted by changing, for example, the type and / or amount of crosslinking monomers used to prepare the particulate polymer A. Specifically, by increasing the amount of crosslinking monomers used to prepare the particulate polymer A, the electrolyte swelling degree decreases; by decreasing the amount of crosslinking monomers used, the electrolyte swelling degree increases.

[0135] <<Preparation of Particulate Polymer A>>

[0136] Particulate polymer A can be prepared by polymerizing a monomer composition containing the above-described monomers in an aqueous solvent, such as water. Here, the proportions of each monomer in the monomer composition are generally the same as the proportions of each monomer unit in particulate polymer A.

[0137] Furthermore, the polymerization method is not particularly limited, and any method such as suspension polymerization, emulsion polymerization, or pulverization can be used. Among these, suspension polymerization and emulsion polymerization are preferred, with suspension polymerization being more preferred. In addition, any reaction such as free radical polymerization or living free radical polymerization can also be used as the polymerization reaction.

[0138] Furthermore, in the monomer composition used to prepare granular polymer A, chain transfer agents, polymerization regulators, polymerization retarders, reactive fluidizing agents, fillers, flame retardants, antioxidants, colorants, and other compounding agents can be added in any amount.

[0139] Here, as an example, the preparation method of a core-shell structured particulate polymer A using suspension polymerization will be described.

[0140] [Preparation of particulate polymer A using suspension polymerization]

[0141] (1) Preparation of monomer composition for core formation

[0142] First, a monomer composition for core formation is prepared by mixing monomers of the polymer constituting the core and other complexing agents added as needed.

[0143] (2) Formation of droplets

[0144] Next, the monomer composition for core formation is dispersed in water, and a polymerization initiator is added to form droplets of the monomer composition for core formation. The method for forming the droplets is not particularly limited; for example, a disperser such as an emulsifying disperser can be used to shear and stir the water containing the monomer composition to form the droplets.

[0145] Examples of polymerization initiators include oil-soluble polymerization initiators such as tert-butyl peroxide-2-ethylhexanoate and azobisisobutyronitrile. The polymerization initiator can be added after the monomer composition is dispersed in water but before droplet formation, or it can be added to the monomer composition before it is dispersed in water.

[0146] Furthermore, from the viewpoint of stabilizing the droplets of the formed monomer composition in water, it is preferable to add a dispersant stabilizer to water to form the droplets of the monomer composition. At this time, metal hydroxides such as magnesium hydroxide, sodium dodecylbenzenesulfonate, etc., can be used as dispersant stabilizers. Here, the dispersant stabilizer can be added, for example, in the form of a colloidal dispersion formed by dispersing the dispersant stabilizer in water.

[0147] (3) Aggregation

[0148] Then, after forming droplets of the monomer composition for core formation, the water containing the formed droplets is heated to initiate polymerization, thereby forming particulate polymers constituting the core in water. Furthermore, by polymerizing the monomers forming the shell in the presence of these particulate polymers constituting the core, particulate polymer A having the aforementioned core-shell structure can be obtained. Alternatively, the polymerization of the monomers forming the shell can be carried out, for example, by centrifuging the particulate polymer constituting the core to precipitate, redispersing the resulting wet filter cake in water, adding a polymerization initiator and the monomers for forming the shell, and then heating. Moreover, examples of water-soluble thermal free radical polymerization initiators used at this time include 2,2'-azobis(2-methylpropanediamine) dihydrochloride.

[0149] <Particulate Polymer B>

[0150] The functional layer composition of the present invention may optionally contain particulate polymer B, which functions as an adhesive material and is typically formed from a polymer with adhesive properties. By including particulate polymer B in the functional layer composition, the room temperature adhesion of the functional layer can be further improved. Moreover, the particulate polymer B is a different component from the particulate polymer A described above, and is preferably non-water-soluble.

[0151] Here, the particulate polymer B is not particularly limited as long as it is different from the particulate polymer A described above, is non-water-soluble, and can be dispersed in a dispersion medium such as water. For example, conjugated diene polymers and acrylic polymers can be used. Moreover, among these, acrylic polymers are preferred. Furthermore, the particulate polymer B differs from the particulate polymer A in at least one aspect of volume average particle size, dissolution to THF, and storage modulus at 25°C. That is, the particulate polymer B does not satisfy at least one of the above-mentioned physical properties (volume average particle size, dissolution to THF, and storage modulus at 25°C) that the particulate polymer A needs to satisfy.

[0152] Furthermore, conjugated diene polymers refer to polymers containing conjugated diene monomer units. Moreover, specific examples of conjugated diene polymers are not particularly limited, but can include: styrene-butadiene copolymers (SBR) and other copolymers containing aromatic vinyl monomer units and aliphatic conjugated diene monomer units; butadiene rubber (BR); nitrile rubber (NBR) (a copolymer containing acrylonitrile units and butadiene units); and their hydrides.

[0153] In addition, acrylic polymers refer to polymers that contain (meth)acrylate monomer units.

[0154] In addition, these can be used individually or in combination of two or more in any ratio.

[0155] Furthermore, there are no particular limitations on the acrylic polymers that can be preferably used as particulate polymer B, and examples include polymers containing the crosslinking monomer units and (meth)acrylate monomer units described above, as well as the acidic monomer units described below.

[0156] Examples of monomers containing acidic groups that can form monomer units containing acidic groups include, for example, monomers containing carboxyl groups, monomers containing sulfonic acid groups, and monomers containing phosphate groups.

[0157] Examples of monomers containing a carboxyl group include monocarboxylic acids and dicarboxylic acids. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.

[0158] Examples of monomers containing sulfonic acid groups include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, ethyl (meth)acrylic acid-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid.

[0159] Additionally, in this specification, "(methyl)allyl" refers to allyl and / or methylallyl.

[0160] Examples of monomers containing a phosphate group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl(meth)acryloyloxyethyl phosphate.

[0161] Additionally, in this specification, "(meth)acryloyl" refers to acryloyl and / or methacryloyl.

[0162] The aforementioned acid-containing monomers can be used alone or in combination of two or more in any ratio. Furthermore, among these, monomers containing acid groups are preferably those with carboxyl groups, more preferably acrylic acid or methacrylic acid, and even more preferably methacrylic acid.

[0163] Furthermore, the proportion of (meth)acrylate 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, preferably 98% by mass or less, more preferably 97% by mass or less, and even more preferably 96% by mass or less. If the proportion of (meth)acrylate monomer units in the acrylic polymer is above the above-mentioned lower limit, the room temperature adhesion of the functional layer can be further improved. In addition, if the proportion of (meth)acrylate monomer units in the acrylic polymer is below the above-mentioned upper limit, the anti-blocking property of the functional layer can be improved.

[0164] The proportion of acid-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, preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. If the proportion of acid-containing monomer units in the acrylic polymer is above the lower limit mentioned above, the dispersibility of the particulate polymer B in the functional layer composition and in the functional layer can be improved, and the room-temperature adhesion of the functional layer can be further improved. Furthermore, if the proportion of acid-containing monomer units in the acrylic polymer is below the upper limit mentioned above, the residual moisture content of the functional layer can be reduced, and the anti-blocking property of the functional layer can be improved.

[0165] The proportion of crosslinking monomer units in the acrylic polymer is preferably 0.1% by mass or more, more preferably 1% by mass or more, more preferably 3% by mass or less, and more preferably 2.5% by mass or less. If the proportion of crosslinking monomer units in the acrylic polymer is above the lower limit mentioned above, the anti-blocking property of the functional layer can be improved. Furthermore, if the proportion of crosslinking monomer units in the acrylic polymer is below the upper limit mentioned above, the room temperature adhesion of the functional layer can be further improved.

[0166] Acrylic polymers can contain monomer units other than (meth)acrylate monomer units, monomer units containing acidic groups, and crosslinking monomer units (other monomer units). Furthermore, other monomers that can form other monomer units that can be contained in acrylic polymers 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 aforementioned aromatic vinyl monomers; nitrile monomers such as acrylonitrile and methacrylonitrile; olefin monomers such as ethylene and propylene; halogen-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 isopropylene vinyl ketone; and monomers containing heterocyclic vinyl compounds such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazolium. Among the other monomers, nitrile-containing monomers are preferred, and acrylonitrile is more preferred.

[0167] In addition, these other monomers can be used alone or in combination of two or more in any ratio. Furthermore, the proportion of other monomer units in the acrylic polymer can be adjusted appropriately.

[0168] <<Properties of Particulate Polymer B>>

[0169] Glass transition temperature

[0170] The glass transition temperature (Tg) of the particulate polymer B is preferably -100°C or higher, more preferably -90°C or higher, even more preferably -80°C or higher, preferably below 30°C, more preferably below 20°C, and even more preferably below 15°C.

[0171] If the glass transition temperature of the particulate polymer B is above the aforementioned lower limit, the room-temperature adhesion of the functional layer can be further improved. Furthermore, the anti-blocking properties of the functional layer can be improved. On the other hand, if the glass transition temperature of the particulate polymer B is below the aforementioned upper limit, the flexibility of the functional layer can be improved.

[0172] [Volume Average Particle Size]

[0173] The volume average particle size of the particulate polymer B is preferably 0.05 μm or more, more preferably 0.1 μm or more, more preferably less than 0.75 μm, and even more preferably less than 0.5 μm. If the volume average particle size of the particulate polymer B is 0.05 μm or more, the dispersibility of the particulate polymer B can be improved. Furthermore, if the volume average particle size of the particulate polymer B is less than 0.75 μm, the adhesiveness of the particulate polymer B can be improved.

[0174] Furthermore, the volume average particle size of the particulate polymer B can be measured in the same manner as that of the particulate polymer A.

[0175] When the functional layer composition includes particulate polymer B, the mass ratio of particulate polymer A to particulate polymer B in the functional layer composition (particulate polymer A / particulate polymer B) is preferably 1 / 99 or more, more preferably 5 / 95 or more, further preferably 10 / 90 or more, particularly preferably 50 / 50 or more, preferably 99 / 1 or less, more preferably 95 / 5 or less, and further preferably 90 / 10 or less. If the mass ratio of particulate polymer A to particulate polymer B is above the above lower limit, the room temperature adhesion of the functional layer can be further improved. Furthermore, if the mass ratio of particulate polymer A to particulate polymer B is below the above upper limit, the internal resistance of the electrochemical element can be further reduced.

[0176] When the functional layer composition further comprises the non-conductive heat-resistant particles described later, the content of the particulate polymer B in the functional layer composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.5 parts by mass or more, particularly preferably 3 parts by mass or more, 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. If the content of the particulate polymer B is above the above-mentioned lower limit, the room temperature adhesion of the functional layer can be further improved. On the other hand, if the content of the particulate polymer B is below the above-mentioned upper limit, the internal resistance of the electrochemical element can be further reduced.

[0177] <<Preparation of Particulate Polymer B>>

[0178] Furthermore, the particulate polymer B 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 proportion of each monomer in the monomer composition is generally the same as the proportion of each monomer unit in the particulate polymer B.

[0179] Furthermore, there are no particular limitations on the polymerization method and polymerization reaction; for example, the polymerization methods and polymerization reactions listed in the polymerization methods for the particulate polymer A described above can be used.

[0180] <Dispersion Medium>

[0181] The functional layer composition of the present invention typically includes a dispersion medium. Examples of dispersion media include water, and organic solvents such as esters, ketones, and alcohols. These can be used individually or in combination of two or more. Among these, water is preferred. That is, the functional layer composition of the present invention is preferably a slurry composition formed by dispersing the aforementioned particulate polymer A and other components in a dispersion medium containing water. Furthermore, with a total dispersion medium volume of 100%, the proportion of water in the dispersion medium is preferably 50% by volume or more, more preferably 70% by volume or more, further preferably 90% by volume or more, even more preferably 99% by volume or more, and particularly preferably 100% by volume (i.e., the functional layer composition contains only water as a dispersion medium).

[0182] <Dispersant>

[0183] The functional layer composition of the present invention preferably further comprises a dispersant. If the functional layer composition further comprises a dispersant, the room temperature adhesion of the functional layer can be further improved.

[0184] Examples of preferred dispersants include polycarboxylic acids such as polyacrylic acid, polymethacrylic acid, and alginate. Polycarboxylic acids can also form salts with alkali metals, ammonia, etc. Among these, polyacrylic acid and its salts are preferred. Furthermore, a single dispersant can be used, or two or more can be used in any ratio.

[0185] When the functional layer composition contains a dispersant, the amount of dispersant in the functional layer composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, relative to 100 parts by mass of particulate polymer A. If the amount of dispersant in the functional layer composition is above or below the above-mentioned lower limit, the uneven presence of particulate polymer A and particulate polymer B in the functional layer can be suppressed, and the room temperature adhesion of the functional layer can be further improved. Furthermore, if the amount of dispersant in the functional layer composition is below or below the above-mentioned upper limit, the internal resistance of the electrochemical element can be further reduced.

[0186] <Non-conductive heat-resistant particles>

[0187] The functional layer composition of the present invention preferably further comprises non-conductive heat-resistant particles (hereinafter also referred to as "heat-resistant particles"). If the functional layer composition further comprises heat-resistant particles, the heat resistance of the functional layer can be improved.

[0188] In this specification, "non-conductive heat-resistant particles" refers to non-conductive microparticles with a heat resistance temperature of 200°C or higher. In addition, "heat resistance temperature" refers to the temperature at which no substantial physical changes such as thermal deformation occur.

[0189] As heat-resistant particles, there are no particular restrictions as long as they are microparticles with a heat resistance temperature above 200℃, electrochemical stability, and electrical insulation, but inorganic particles are preferred.

[0190] Inorganic particles have a relatively high specific gravity. Therefore, when forming a functional layer, such as by coating a functional layer containing inorganic particles onto a substrate, the particulate polymer A is more likely to protrude from the inorganic particles on the surface of the functional layer in the thickness direction. As a result, the room temperature adhesion of the functional layer can be further improved.

[0191] Here, the preferred inorganic particle material is one that is stable in the operating environment of the electrochemical element and is electrochemically stable. Examples include: oxide particles such as alumina, alumina hydrate (boehmite (AlOOH)), gibbsite (Al(OH)3), silicon dioxide, magnesium oxide, magnesium hydroxide, calcium oxide, titanium dioxide, barium titanate (BaTiO3), zirconium oxide (ZrO2), and alumina-silica composite oxides; nitride particles such as aluminum nitride and boron nitride; covalently bonded grains such as silicon and diamond; sparingly soluble ionic grains such as barium sulfate, calcium fluoride, and barium fluoride; and clay particles such as talc and montmorillonite. Among these, alumina, alumina hydrate (boehmite), magnesium hydroxide, and barium sulfate are more preferred, with alumina being the most preferred. Furthermore, these particles can be subjected to elemental substitution, surface treatment, solid solution formation, etc., as needed.

[0192] In addition, these inorganic particles can be used alone or in combination of two or more in any ratio.

[0193] <<Volume Average Particle Size of Heat-Resistant Granules>>

[0194] The volume average particle size (D50) of the heat-resistant particles is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.25 μm or more, preferably 1.5 μm or less, more preferably 1.0 μm or less, and even more preferably 0.8 μm or less. If the volume average particle size of the heat-resistant particles is above the lower limit mentioned above, the heat-resistant particles are densely packed in the functional layer. Therefore, the reduction in ionic conductivity in the functional layer can be further suppressed, and the electrochemical characteristics (especially output characteristics) of the electrochemical element can be improved. On the other hand, if the volume average particle size of the heat-resistant particles is below the upper limit mentioned above, the functional layer can still exhibit excellent heat resistance even when the functional layer is thinned, thus improving the capacity of the electrochemical element.

[0195] In addition, the volume average particle size of the heat-resistant particles can be determined by laser diffraction.

[0196] <<Mixing ratio of heat-resistant granules to particulate polymer A>>

[0197] The mixing ratio of heat-resistant particles to particulate polymer A in the composition for the functional layer is preferably 40 / 60 or more by mass ratio (heat-resistant particles / particulate polymer A), more preferably 50 / 50 or more, even more preferably 60 / 40 or more, preferably 99 / 1 or less, more preferably 90 / 10 or less, and even more preferably 80 / 20 or less.

[0198] If the mass ratio of heat-resistant particles to particulate polymer A is within the above range, the balance between the heat resistance and room temperature adhesion of the functional layer becomes better.

[0199] <Other Ingredients>

[0200] In addition to the particulate polymer A, particulate polymer B, dispersion medium, dispersant, and heat-resistant particles described above, the functional layer composition of the present invention may also contain any other components. These other components are not particularly limited as long as they do not affect the electrochemical reaction in the electrochemical element, and examples include: thickeners such as carboxymethyl cellulose and hydroxypropyl methyl cellulose; wetting agents; dispersing stabilizers such as sodium dodecylbenzene sulfonate; and other known additives. These other components may be used alone or in combination of two or more.

[0201] <Properties of the composition for functional layers>

[0202] < <ph>>

[0203] When the functional layer composition of the present invention contains water as a dispersion medium, the pH of the functional layer composition is preferably 3.0 or higher, more preferably 4.0 or higher, even more preferably 5.0 or higher, preferably 12.0 or lower, more preferably 10.0 or lower, and even more preferably 9.0 or lower. If the pH of the functional layer composition is above or below the above lower limit, the room temperature adhesion of the functional layer can be further improved. Furthermore, if the pH of the functional layer composition is below the above upper limit, the hydrolysis of thickeners such as carboxymethyl cellulose can be suppressed, and the dispersibility of the functional layer composition can be improved.

[0204] In addition, the pH of the composition for the functional layer can be adjusted by adding known acidic or basic compounds.

[0205] <Preparation method of composition for functional layer>

[0206] The preparation method of the functional layer composition is not particularly limited. For example, it can be prepared by mixing the above-mentioned particulate polymer A, and particulate polymer B, dispersion medium, dispersant, heat-resistant particles, and other components as needed. Alternatively, when preparing particulate polymer A and particulate polymer B by polymerizing the monomer composition in an aqueous solvent, particulate polymer A and particulate polymer B can be directly mixed with other components in an aqueous dispersion state. Furthermore, when mixing particulate polymer A and particulate polymer B in an aqueous dispersion state, water in the aqueous dispersion can also be used as the dispersion medium.

[0207] Here, there are no particular limitations on the mixing method of the above-mentioned components, but in order to efficiently disperse the components, it is preferable to use a disperser as the mixing device. Moreover, the disperser is preferably a device capable of uniformly dispersing and mixing the above-mentioned components. Examples of dispersers include: ball mills, sand mills, pigment dispersers, grinding mills, ultrasonic dispersers, homogenizers, planetary mixers, etc.

[0208] (Laminated assembly for electrochemical components)

[0209] The laminate of the present invention has a substrate and a functional layer formed on the substrate, the functional layer being formed using the functional layer composition of the present invention. The laminate of the present invention, having a functional layer formed using the above-described functional layer composition, can reduce the internal resistance of electrochemical devices.

[0210] <Substrate>

[0211] There are no particular limitations on the substrate. For example, when the functional layer is used as part of a spacer, a spacer substrate can be used as the substrate. Furthermore, when the functional layer is used as part of an electrode, an electrode substrate formed by forming an electrode composite layer on a current collector can be used as the substrate. There are no particular limitations on the use of the laminate obtained by forming a functional layer on a substrate using a functional layer composition. For example, the functional layer can be formed on a spacer substrate and used directly as an electrochemical element component such as a spacer, or the functional layer can be formed on an electrode substrate and used directly as an electrode.

[0212] <<Spacer Substrate>>

[0213] There are no particular limitations on the spacer substrate used to form the functional layer, and spacer substrates such as those described in Japanese Patent Application Publication No. 2012-204303 can be used. Among these, a microporous membrane formed of a polyolefin-based resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred from the perspective of reducing the overall film thickness of the spacer, thereby increasing the ratio of electrode active material in the electrochemical element and increasing the capacity per unit volume. Furthermore, the spacer substrate may include any layer other than the functional layer that performs the intended function in a portion thereof.

[0214] <<Electrode Substrate>>

[0215] There are no particular limitations on the electrode substrate (positive electrode substrate and negative electrode substrate), and an electrode substrate on which an electrode composite material layer is formed on the current collector can be cited as an example. Here, the current collector, the electrode active materials (positive electrode active material and negative electrode active material) in the electrode composite material layer, the binder materials for the electrode composite material layer (binder for the positive electrode composite material layer and binder for the negative electrode composite material layer), and the method for forming the electrode composite material layer on the current collector can all be known, such as those described in Japanese Patent Application Publication No. 2013-145763. Furthermore, the electrode substrate may include, in a portion thereof, any layer having a desired function other than a functional layer.

[0216] <Functional Layer>

[0217] The functional layer can be formed on the above-mentioned substrate using the functional layer composition of the present invention. Here, the functional layer at least comprises the above-mentioned particulate polymer A, and optionally comprises particulate polymer B, a dispersant, heat-resistant particles, and other components. Furthermore, the components included in the functional layer are the same as those included in the above-mentioned functional layer composition, and the preferred proportions of these components are the same as the preferred proportions of the components in the functional layer composition.

[0218] <<Methods for Forming Functional Layers>>

[0219] There are no particular limitations on the method of forming a functional layer on a substrate using a functional layer composition, and examples include:

[0220] 1) A method of coating the surface of the above-mentioned substrate with a composition for a functional layer and then drying it;

[0221] 2) A method for drying the substrate after impregnating it with the composition for the functional layer;

[0222] 3) A method of applying the functional layer composition onto a release substrate, drying it to form a functional layer, and transferring the obtained functional layer onto the surface of the substrate.

[0223] In addition, the functional layer can be formed on only one side of the substrate or on both sides of the substrate.

[0224] Here, there are no particular limitations on the release substrate, and any known release substrate can be used.

[0225] Among these, the method described in 1) above is preferred because it allows for easy control of the thickness of the functional layer. Moreover, the method described in 1) above may include, for example, a process of applying the functional layer to a substrate using a composition (coating process); and a process of drying the functional layer applied to the substrate using a composition to form a functional layer (functional layer forming process).

[0226] [Coating Process]

[0227] In the coating process, there are no particular limitations on the method of applying the functional layer composition to the substrate, and examples include: doctor blade method, reverse roller method, direct roller method, gravure printing method, extrusion method, brush coating method, etc.

[0228] [Functional layer formation process]

[0229] In the functional layer formation process, the method for using the composition of the functional layer on the drying substrate is not particularly limited, and known methods can be used, such as drying using warm air, hot air, or low-humidity air; vacuum drying; and drying methods using irradiation with infrared rays, electron beams, etc. The drying conditions are not particularly limited, but the drying temperature is preferably 50°C or higher and 150°C or lower, and the drying time is preferably 1 minute or higher and 30 minutes or lower.

[0230] Here, the functional layer composition of the present invention can be a first functional layer composition containing particulate polymer A and not containing heat-resistant particles, or it can be a second functional layer composition containing heat-resistant particles in addition to particulate polymer A. Furthermore, when a functional layer is formed on a substrate using the first functional layer composition, an adhesive layer serving as the functional layer can be obtained. Moreover, when a functional layer is formed on a substrate using the second functional layer composition, a single layer can be obtained that simultaneously exhibits the function of a heat-resistant layer that improves the heat resistance of the substrate and the function of an adhesive layer that firmly bonds components together.

[0231] Moreover, the laminate having a functional layer formed using a composition for a second functional layer can be manufactured in less time and with less labor compared to existing substrates having a heat-resistant layer and an adhesive layer, thus resulting in higher productivity.

[0232] <<Thickness of Functional Layer>>

[0233] The thickness of the functional layer formed using the composition for the electrochemical element functional layer of the present invention is preferably 0.5 μm or more, and preferably 5 μm or less. If the thickness of the functional layer is above the lower limit mentioned above, the room temperature adhesion of the functional layer can be further improved. Furthermore, if the thickness of the functional layer is below the upper limit mentioned above, the anti-blocking property of the functional layer can be improved.

[0234] (Electrochemical element)

[0235] The electrochemical element of the present invention has electrodes and spacers, characterized in that it has at least one of the above-described laminates of the present invention as electrodes and spacers. Because the electrochemical element of the present invention uses the above-described laminates of the present invention as element components for at least any one of electrodes and spacers, it has low internal resistance.

[0236] Furthermore, the electrochemical element of the present invention is not particularly limited, and examples include lithium-ion secondary batteries, double-layer capacitors and lithium-ion capacitors, with lithium-ion secondary batteries being preferred.

[0237] Here, a lithium-ion secondary battery will be given as an example of an electrochemical element of the present invention, and the case in which the stack of the present invention described above is used as a spacer in the lithium-ion secondary battery will be explained, but the electrochemical element of the present invention is not limited thereto.

[0238] Positive and negative electrodes

[0239] As the positive and negative electrodes, electrodes made of the known electrode substrates (positive electrode substrate and negative electrode substrate) described above in the "Substrate" section can be used.

[0240] Electrolyte

[0241] As an electrolyte, an organic electrolyte in which the supporting electrolyte is dissolved in an organic solvent is typically used. As the supporting electrolyte, lithium salts can be used, for example, in lithium-ion secondary batteries. Examples of lithium salts include: LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. LiPF6, LiClO4, and CF3SO3Li are particularly preferred because they are readily soluble in solvents and exhibit high dissociation. Furthermore, a single electrolyte can be used, or two or more can be used in combination. Generally, there is a tendency for higher dissociation degrees of supporting electrolytes to result in higher lithium-ion conductivity; therefore, the lithium-ion conductivity can be adjusted according to the type of supporting electrolyte.

[0242] As for organic solvents used in electrolytes, there are no particular limitations as long as they can dissolve the supporting electrolyte. For example, in lithium-ion secondary batteries, preferred solvents include: dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butyl carbonate (BC), ethyl methyl carbonate (ethyl methyl carbonate (EMC)), vinylene carbonate, and other carbonates; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; etc. Mixtures of these solvents can also be used.

[0243] Carbonates are particularly preferred due to their high dielectric constant and wide stable potential range. Generally, lower solvent viscosity tends to result in higher lithium-ion conductivity; therefore, the lithium-ion conductivity can be adjusted according to the type of solvent. Furthermore, the concentration of the electrolyte in the electrolyte solution can be appropriately adjusted. In addition, known additives can be added to the electrolyte solution.

[0244] <Methods for Manufacturing Electrochemical Components>

[0245] The method for manufacturing the electrochemical element of the present invention is not particularly limited. For example, a lithium-ion secondary battery, which is an example of the electrochemical element of the present invention described above, can be manufactured by overlapping the positive and negative electrodes with a spacer in between, and then, as needed, winding, folding, or placing them into a battery container, injecting electrolyte into the battery container, and sealing it. Furthermore, at least one of the positive electrode, negative electrode, and spacer can be used as the laminate of the present invention. In addition, as needed, overcurrent protection elements such as porous metal mesh, fuses, PTC elements, and conductive plates can be placed in the battery container to prevent pressure rise and overcharging / discharging inside the battery. The shape of the battery can be any of, for example, coin-shaped, button-shaped, sheet-shaped, cylindrical, square, or flat.

[0246] Example

[0247] The present invention will now be specifically described based on embodiments, but the present invention is not limited to these embodiments. Furthermore, in the following description, unless otherwise specified, "%" and "parts" refer to quantities based on mass.

[0248] Furthermore, unless otherwise stated, in a polymer made by polymerizing multiple monomers, the proportion of a monomer unit formed by polymerizing a particular monomer in the polymer is generally consistent with the proportion (feed ratio) of that particular monomer in all the monomers used in the polymerization of the polymer.

[0249] In the examples and comparative examples, the determination and evaluation of various physical properties were carried out as follows.

[0250] <Volume average particle size of granular polymer A>

[0251] The aqueous dispersion containing particulate polymer A prepared in the examples and comparative examples was taken into a beaker with a solid content of 0.1 g, and 0.1 mL of an aqueous solution of alkylbenzene sulfonic acid (manufactured by Fujifilm Corporation, product name "DRIWEL") was added. 10–30 mL of diluent (manufactured by Beckman Coulter, product name "ISOTON II") was further added to the beaker, and the mixture was dispersed for 3 minutes using a 20 W ultrasonic disperser to obtain the test sample. Then, using a particle size analyzer (manufactured by Beckman Coulter, product name "Multisizer"), under the conditions of pore size: 20 μm, medium: ISOTON II, and number of test particles: 100,000, the particle size distribution (volume basis) of the test sample was obtained. In the obtained particle size distribution, the particle size at which the cumulative volume from the smallest particle size side becomes 50% (D50) was used as the volume average particle size.

[0252] Glass transition temperature

[0253] The aqueous dispersion containing particulate polymer A prepared in the examples and comparative examples was dried and solidified, and the resulting powdered sample was used as the test sample. 10 mg of the test sample was weighed in an aluminum pan, and the measurement was performed using a differential scanning calorimetry (DSC) apparatus (manufactured by SII NanoTechnology Co., Ltd., product name "EXSTAR DSC6220") within the measurement temperature range of -100°C to 500°C, at a heating rate of 10°C / min, under the conditions specified in JIS Z 8703, to obtain a differential scanning calorimetry (DSC) curve. An empty aluminum pan was used as a control. During this heating process, the intersection of the baseline of the DSC curve just before the endothermic peak appears (when the differential signal (DDSC) is 0.05 mW / min / mg or higher) and the tangent line of the DSC curve at the first inflection point after the endothermic peak was used as the glass transition temperature (°C).

[0254] <Energy Storage Modulus>

[0255] The aqueous dispersions containing particulate polymer A prepared in the examples and comparative examples were weighed to a volume with a solid content of 0.48 g and a bottom area of ​​5.3 cm². 2 The sample was air-dried in an aluminum cup. After air-drying, a film with a thickness of 70–80 μm was obtained, formed from particulate polymer A. The obtained film was punched into a 12 mm diameter piece and used as the test sample. Alternatively, for the sample that did not form a film after air-drying and became powder, approximately 0.1 g of the air-dried powder was weighed in a 12 mm diameter tablet forming machine and formed into a tablet (12 mm diameter × 75 μm thickness) by applying 9 kN of pressure for 10 seconds. This tablet was used as the test sample. Then, a viscoelasticity measuring device (Anton Paar, product name "MCR302") was used as the dynamic viscoelasticity measuring device, and the storage modulus (MPa) was measured at a parallel plate (diameter 8 mm), strain 0.01%, frequency 1 Hz, and temperature of 25°C.

[0256] <Electrolyte swelling degree>

[0257] The aqueous dispersions containing granular polymer A prepared in the examples and comparative examples were dropped into a polytetrafluoroethylene petri dish such that the solid content was 1.0 g, and dried at 25 °C for 48 hours to produce a film. Additionally, for granular polymer A with a glass transition temperature of 25 °C or higher, a film was produced by pressing 0.2 ± 0.05 g of the dried specimen at a temperature of 200 °C and a pressure of 5 MPa for 2 minutes. The produced film was cut into 1.5 mm square film pieces, and 0.2 ± 0.05 g was accurately weighed. The mass of the accurately weighed film piece was designated as W0. Next, the accurately weighed film piece was immersed in 50 mL of an electrolyte solution at 60 °C for 72 hours. Then, the film piece was taken out from the electrolyte solution, the electrolyte solution on the surface of the film piece was wiped off, and its mass (the mass of the film piece after the immersion test) W1 was measured. Using the measured weights W0 and W1, the electrolyte swelling degree S (%) was calculated in the form of S = (W1 / W0) × 100. Additionally, as the electrolyte solution, an electrolyte solution was used in which 2 vol% (solvent ratio) of vinylene carbonate was added to a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (weight mixing ratio: EC / EMC = 3 / 7), and LiPF6 was dissolved at a concentration of 1 mol / L as a supporting electrolyte.

[0258] <THF dissolution amount>

[0259] The aqueous dispersions containing granular polymer A prepared in the examples and comparative examples were dropped into a petri dish such that the solid content was 1.5 g, and dried in an environment of 23 - 27 °C for 24 hours, and then further dried at 110 °C for 1 hour to produce a film. Additionally, for granular polymer A with a glass transition temperature of 25 °C or higher, a film was produced by pressing 0.2 ± 0.05 g of the dried specimen at a temperature of 200 °C and a pressure of 5 MPa for 2 minutes. The produced film was cut into 2.0 - 3.0 mm square film pieces, and 0.2 ± 0.05 g was accurately weighed. The mass of the accurately weighed film piece was designated as W2. Next, the accurately weighed film piece was immersed in 80 mL of tetrahydrofuran (THF) at 25 °C for 24 hours. Then, the film piece was taken out from the THF, and the taken-out film piece was vacuum dried at 105 °C for 3 hours, and its mass (the mass of the insoluble component) W3 was measured. Then, the THF dissolution amount (%) was calculated according to the following formula.

[0260] THF dissolution amount (%) = (W2 - W3) / W2 × 100

[0261] <Number-average molecular weight of THF-soluble component>

[0262] In the above determination of "THF dissolution," the THF after impregnation of the membrane was recovered and dried. The resin obtained after drying was recovered, and 2 mg of the recovered resin was dissolved in 5 g of THF. Then, 0.2 g of cyclohexane was added, and the resulting substance was used as the test sample. The number-average molecular weight of the THF dissolution component of the particulate polymer A was then determined by gel permeation chromatography (GPC). The GPC determination conditions are as follows. A calibration curve was prepared using standard polystyrene (TSKgel (registered trademark) standard Polystyrene), and the number-average molecular weight was determined.

[0263] Device name: HLC-8320 (manufactured by Tosoh Corporation);

[0264] Chromatographic columns: TSKgel SuperH2000 (inner diameter 6mm, length 150mm, pore size 2nm), TSKgel SuperH4000 (inner diameter 6mm, length 150mm, pore size 20nm), TSKgel SuperH5000 (inner diameter 6mm, length 150mm, pore size 65nm) (all manufactured by Tosoh Corporation);

[0265] Detector: HLC-8320 differential refractometer (manufactured by Tosoh Corporation).

[0266] <ph>

[0267] The pH of the functional layer compositions prepared in the examples and comparative examples at 25°C was determined using a benchtop pH meter (manufactured by Horiba Manufacturing Co., Ltd., product name "LAQUA-PH-SE").

[0268] <Anti-adhesion>

[0269] A polyethylene microporous membrane (thickness: 12 μm) was prepared as the spacer substrate. The functional layer composition prepared in the examples and comparative examples was applied to one side of the spacer substrate using a bar coating method. Next, the spacer substrate coated with the functional layer composition was dried at 50°C for 10 minutes to produce a spacer (laminated structure) with a functional layer having a thickness of 2.0 μm on one side of the spacer substrate. This spacer with the functional layer was used as an evaluation spacer. The evaluation spacer was cut into two strips of 10 mm × 50 mm. The two strips were overlapped so that the functional layers faced each other to obtain a pre-pressing test piece. The pre-pressing test piece was placed in laminated packaging material and, together with the packaging material, heated and pressed for 5 minutes using a flatbed press at a temperature of 40°C and a load of 6.0 MPa. The pressed test piece was removed from the packaging material, and transparent tape was attached to one side of the test piece. The transparent tape specified in JIS Z1522 was used. Furthermore, the transparent tape was pre-fixed on a horizontal test table. Then, one end of the spacer was stretched vertically upwards at a tensile speed of 50 mm / min, and the stress during peeling was measured. This measurement was performed three times, and the average value was taken as the peel strength P1 (N / m), which was then evaluated according to the following criteria. A smaller peel strength P1 indicates better anti-adhesion properties.

[0270] A: The spacer detached before the peel strength test;

[0271] B: Peel strength P1 is less than 0.2 N / m;

[0272] C: Peel strength P1 is greater than 0.2 N / m and less than 0.5 N / m;

[0273] D: Peel strength P1 is above 0.5 N / m.

[0274] <Standard temperature adhesion>

[0275] A polyethylene microporous membrane (thickness: 12 μm) was prepared as the spacer substrate. The functional layer composition prepared in the examples and comparative examples was applied to one side of the spacer substrate using a bar coating method. Next, the spacer substrate coated with the functional layer composition was dried at 50°C for 10 minutes to produce a spacer (laminated structure) with a functional layer having a thickness of 2.0 μm on one side of the spacer substrate. This spacer with the functional layer was used as an evaluation spacer. The evaluation spacer was cut into strips of 10 mm × 50 mm. The surface of the negative electrode (negative electrode composite layer side) prepared in the examples and comparative examples was attached to the surface of the functional layer of the cut evaluation spacer to obtain a pre-pressing test piece. The pre-pressing test piece was placed in laminated packaging material, and together with the packaging material, it was heated and pressed for 1 minute using a flatbed press at a temperature of 25°C and a load of 1.0 MPa. The pressed test piece was removed from the packaging material, and transparent tape was attached to the surface of the negative electrode current collector side of the test piece with the current collector side of the negative electrode facing down. At this point, the transparent tape specified in JIS Z1522 is used. Furthermore, the transparent tape is pre-fixed on a horizontal test bench. Then, one end of the spacer is stretched vertically upwards at a tensile speed of 50 mm / min, and the stress during peeling is measured. The same measurement is performed three times, and the average value is taken as the peel strength P2, which is evaluated according to the following criteria. A higher peel strength P2 indicates better adhesion at room temperature.

[0276] A: Peel strength P2 is above 2.0 N / m;

[0277] B: Peel strength P2 is greater than 0.5 N / m and less than 2.0 N / m;

[0278] C: Peel strength P2 is less than 0.5 N / m;

[0279] D: The spacer detached before the peel strength test.

[0280] <Internal resistance>

[0281] The lithium-ion secondary batteries prepared in the examples and comparative examples were left to stand at 25°C for 5 hours after electrolyte injection. Then, they were charged to a cell voltage of 3.65V using a constant current method at 25°C and 0.2C (C is a value expressed as rated capacity (mA) / 1h (hour)). Afterward, they were aged at 60°C for 12 hours. Then, they were discharged to a cell voltage of 3.00V using a constant current method at 25°C and 0.2C. Next, they were subjected to CC-CV charging (upper limit cell voltage 4.20V) using a constant current method at 0.2C, and CC discharging to 3.00V using a constant current method at 0.2C. This 0.2C charge-discharge cycle was repeated three times.

[0282] Then, at 25°C, the battery was charged at 1C to 50% of its State of Charge (SOC). Using 50% SOC as the center, it was charged and discharged for 15 seconds at 0.5C, 1.0C, 1.5C, and 2.0C respectively. The battery voltage was plotted against the current after 0.1 seconds for each case (charging and discharging sides), and the slope was used as the IV resistance (Ω) to calculate both the IV resistance during charging and discharging. The obtained IV resistance value (Ω) was evaluated according to the following criteria: a smaller IV resistance value indicates a smaller internal resistance and a lower DC resistance.

[0283] A: IV resistance is below 5Ω;

[0284] B: IV resistance is greater than 5Ω and less than 6Ω;

[0285] C: IV resistance is greater than 6Ω and less than 7.5Ω;

[0286] D: IV resistance is greater than 7.5Ω.

[0287] (Example 1)

[0288] <Preparation of an aqueous dispersion containing particulate polymer A>

[0289] [Preparation of Monomer Compositions]

[0290] A monomer composition was prepared by mixing 20.6 parts of styrene as an aromatic vinyl monomer, 0.5 parts of ethylene glycol dimethacrylate as a crosslinking monomer, 10.0 parts of glycidyl methacrylate, and 58.9 parts of 2-ethylhexyl acrylate as a (meth)acrylate monomer.

[0291] [Preparation of colloidal dispersions]

[0292] A colloidal dispersion containing magnesium hydroxide as a metal hydroxide was prepared by dissolving 10.0 parts of magnesium chloride in 200 parts of ion-exchanged water in an aqueous solution, and then slowly adding an aqueous solution containing 7.0 parts of sodium hydroxide in 50 parts of ion-exchanged water while stirring.

[0293] [The formation of the core]

[0294] Particulate polymer A was prepared by suspension polymerization. Specifically, the monomer composition was added to the colloidal dispersion containing magnesium hydroxide, and after further stirring, 2.0 parts of tert-butyl peroxide-2-ethylhexanoate (manufactured by Nippon Oil Co., Ltd., product name "PERBUTYL O") as a polymerization initiator were added to obtain a mixture. Using an inline emulsifying disperser (manufactured by Pacific Machinery Co., Ltd., product name "Cavitron"), the resulting mixture was stirred at a high shear speed of 12,000 rpm for 1 minute to form droplets of the monomer composition in the colloidal dispersion containing magnesium hydroxide. The colloidal dispersion containing magnesium hydroxide with droplets of the monomer composition formed was placed in a reactor, heated to 90°C, and subjected to polymerization for 5 hours to obtain an aqueous dispersion containing particulate polymer constituting the core.

[0295] [Formation of the shell]

[0296] 0.5 parts of hydroxypropyl methylcellulose were dissolved in 420 parts of ion-exchanged water at room temperature to prepare an aqueous solution of hydroxypropyl methylcellulose. The aqueous dispersion of the particulate polymer containing the core structure obtained by suspension polymerization was centrifuged (10,000 rpm, 10 minutes, 25°C), and the wet filter cake of the precipitated polymer was recovered. The solid component of the obtained wet filter cake was added in an amount of 15.5 parts to the above aqueous solution of hydroxypropyl methylcellulose, and the mixture was stirred at room temperature for 30 minutes to redisperse it. 0.15 parts of 2,2'-azobis(2-methylpropanediamine) dihydrochloride as a polymerization initiator and 1.72 parts of styrene as an aromatic vinyl monomer (wet filter cake / styrene (mass ratio) = 90 / 10) were added to the redispersed dispersion, and the mixture was heated to 70°C and subjected to polymerization for 6 hours to obtain an aqueous dispersion containing particulate polymer A with a core-shell structure.

[0297] Using an aqueous dispersion containing particulate polymer A, the volume average particle size, glass transition temperature, storage modulus, electrolyte swelling degree, THF dissolution amount, and number-average molecular weight of the THF dissolution component were determined. The results are shown in Table 1.

[0298] <Preparation of an aqueous dispersion containing particulate polymer B>

[0299] 70 parts of ion-exchanged water, 0.15 parts of sodium lauryl sulfate (manufactured by Kao Chemical Co., Ltd., product name "EMAL (registered trademark) 2F") as emulsifier, and 0.5 parts of ammonium persulfate as polymerization initiator were supplied to a reactor equipped with a stirrer. The gas phase was replaced with nitrogen and the temperature was raised to 60°C.

[0300] On the other hand, in another container, a monomer composition is prepared by mixing 50 parts of deionized water, 0.5 parts of sodium dodecylbenzenesulfonate as a dispersion stabilizer, 94 parts of n-butyl acrylate as a (meth)acrylate monomer, 2 parts of methacrylic acid as an acidic monomer, 2 parts of acrylonitrile as a nitrile monomer, and 1 part of allyl methacrylate and 1 part of allyl glycidyl ether as crosslinking monomers.

[0301] The obtained monomer composition was continuously added to the reactor equipped with a stirrer over a period of 4 hours for polymerization. The reaction was carried out at 60°C during the addition process. After the addition was completed, the mixture was further stirred at 70°C for 3 hours, after which the reaction was terminated, yielding an aqueous dispersion containing particulate polymer B. The obtained particulate polymer B had a volume average particle size of 0.25 μm and a glass transition temperature of -40°C.

[0302] <Preparation of Compositions for Functional Layers>

[0303] 70 parts of alumina (manufactured by Sumitomo Chemical Co., Ltd., product name "AKP3000", volume average particle size: 0.7 μm) as heat-resistant particles were mixed with 0.5 parts of sodium polyacrylate as a dispersant, and deionized water was added to make the solid content concentration 55%. The mixture was then mixed using a ball mill to obtain a pre-mixing slurry.

[0304] Furthermore, an aqueous dispersion containing particulate polymer A (based on solids content) of 20 parts, an aqueous dispersion containing particulate polymer B (based on solids content) of 5 parts, 1.5 parts of carboxymethyl cellulose as a thickener, and 0.2 parts of sodium dodecylbenzenesulfonate (manufactured by Kao Chemical Co., Ltd., "Neopelex G-15") as a dispersion stabilizer were mixed, and the resulting mixture (particulate polymer A / particulate polymer B (mass ratio) = 80 / 20) was added to the above-mentioned pre-mixing slurry. Then, deionized water was added to bring the solids content concentration to 40%, and the pH was adjusted to 7.0 using a 3% sodium hydroxide aqueous solution to obtain a composition for the functional layer.

[0305] Using the composition for the functional layer, spacers (laminated structures) with functional layers on one side of a spacer substrate were fabricated, and their anti-blocking properties and room temperature adhesion were evaluated. The results are shown in Table 1.

[0306] Fabrication of spacers (laminated structures) with functional layers

[0307] A polyethylene microporous membrane (thickness: 12 μm) was prepared as the spacer substrate. The functional layer composition obtained above was coated onto one side of the spacer substrate using a bar coating method. Next, the spacer substrate coated with the functional layer composition was dried at 50°C for 10 minutes to form a functional layer. The same operation was performed on the other side of the spacer substrate to fabricate a spacer (laminated structure) with functional layers having a thickness of 2.0 μm on each side of the spacer substrate.

[0308] <The Making of the Positive Electrode>

[0309] A slurry composition for the positive electrode was prepared by mixing 100 parts of LiCoO2 (volume average particle size: 12 μm) as the positive electrode active material, 2 parts of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., "HS-100") as the conductive material, 2 parts of polyvinylidene fluoride (manufactured by Kureha Co., Ltd., "#7208") as the binder material for the positive electrode composite layer, and N-methylpyrrolidone as the solvent, to a total solids concentration of 70%. These components were mixed using a planetary mixer.

[0310] The above-mentioned positive electrode slurry composition was applied to a 20 μm thick aluminum foil (serving as a current collector) using a comma coating machine to achieve a dried film thickness of approximately 150 μm, and then dried. This drying was performed by conveying the aluminum foil at 0.5 m / min in an oven at 60°C for 2 minutes. Then, it was heat-treated at 120°C for 2 minutes to obtain the positive electrode raw material before pressing. This raw material was then calendered using a roll press to obtain a positive electrode with a positive electrode composite layer (thickness: 60 μm).

[0311] <Making the Negative Electrode>

[0312] 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 deionized water, and 0.5 parts of potassium persulfate as a polymerization initiator were added to a 5 MPa pressure vessel equipped with a stirrer. After thorough stirring, the mixture was heated to 50°C to initiate polymerization. The reaction was terminated by cooling when the polymerization conversion reached 96%, yielding a mixture containing a binder material for the negative electrode composite layer (SBR). A 5% sodium hydroxide aqueous solution was added to this mixture to adjust the pH to 8, and unreacted monomers were removed by heated vacuum distillation. The mixture was then cooled to below 30°C to obtain the desired aqueous dispersion containing the binder material for the negative electrode composite layer.

[0313] 80 parts of artificial graphite (volume average particle size: 15.6 μm) as negative electrode active material (1), 16 parts of silicon-based active material SiOx (volume average particle size: 4.9 μm) as negative electrode active material (2), 2.5 parts of sodium carboxymethyl cellulose (manufactured by Nippon Paper Corporation, "MAC350HC") as a viscosity modifier (based on solids equivalent) in a 2% aqueous solution, and deionized water were mixed to adjust the solids concentration to 68%, and then further mixed at 25°C for 60 minutes. The solids concentration was further adjusted to 62% with deionized water, and then further mixed at 25°C for 15 minutes to obtain a mixture. 1.5 parts of the above-mentioned aqueous dispersion containing the binder material for the negative electrode composite layer (based on solids equivalent) and deionized water were added to this mixture to adjust the final solids concentration to 52%, and then further mixed for 10 minutes to obtain a mixture. The mixture was degassed under reduced pressure to obtain a slurry composition for a negative electrode with good flowability.

[0314] The above-mentioned negative electrode slurry composition was applied to a 20 μm thick copper foil (serving as the current collector) using a comma coating machine to achieve a dried film thickness of approximately 150 μm, and then dried. This drying was performed by conveying the copper foil at 0.5 m / min in an oven at 60°C for 2 minutes. Then, it was heat-treated at 120°C for 2 minutes to obtain the negative electrode raw material before pressing. This raw material was then calendered using a roll press to obtain a negative electrode with a negative electrode composite layer (thickness: 80 μm).

[0315] <Making of Lithium-ion Secondary Batteries>

[0316] An aluminum packaging material is prepared as the outer packaging for the battery. The positive electrode obtained above is cut into a 4×4cm square and arranged so that the surface of the current collector side contacts the aluminum packaging material. Then, the spacer with the functional layer obtained above is cut into a 4.4×4.4cm square and arranged on the surface of the positive electrode composite material layer of the positive electrode so that the functional layer of the spacer is opposite to the positive electrode. Then, the negative electrode obtained above is cut into a 4.2×4.2cm square and arranged on the spacer so that the surface of the negative electrode composite material layer is opposite to the spacer. Then, the obtained materials are wound by a winding machine to obtain a wound body. The wound body is pressed at 50°C and 1MPa to form a flat body, and then wrapped with the aluminum packaging material as the outer packaging for the battery. The electrolyte [solvent: a mixed solvent of ethylene carbonate / ethyl methyl carbonate (weight ratio) = 3 / 7, additive: ethylene carbonate containing 2% by volume (solvent ratio), supporting electrolyte: LiPF6 with a concentration of 1 mol / L] is injected in a way that leaves no air residue. Then, the opening of the aluminum packaging material is heat-sealed at a temperature of 150°C to produce a lithium-ion secondary battery.

[0317] The internal resistance of this lithium-ion secondary battery was evaluated. The results are shown in Table 1.

[0318] (Example 2)

[0319] In preparing the aqueous dispersion containing particulate polymer A, the amount of magnesium chloride was changed from 10.0 parts to 5.9 parts, and the amount of sodium hydroxide was changed from 7.0 parts to 4.1 parts. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0320] (Example 3)

[0321] In preparing the aqueous dispersion containing particulate polymer A, the amount of magnesium chloride was changed from 10.0 parts to 6.5 parts, and the amount of sodium hydroxide was changed from 7.0 parts to 4.6 parts. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0322] (Example 4)

[0323] In preparing the aqueous dispersion containing particulate polymer A, the amount of magnesium chloride was changed from 10.0 parts to 8.5 parts, and the amount of sodium hydroxide was changed from 7.0 parts to 6.0 parts. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0324] (Example 5)

[0325] In preparing the aqueous dispersion containing particulate polymer A, the amount of magnesium chloride was changed from 10.0 parts to 11.0 parts, and the amount of sodium hydroxide was changed from 7.0 parts to 7.7 parts. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0326] (Example 6)

[0327] In preparing the aqueous dispersion containing particulate polymer A, a 15% sodium dodecylbenzenesulfonate aqueous solution was used instead of the colloidal dispersion containing magnesium hydroxide as a metal hydroxide. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0328] (Examples 7-12 and 14-21)

[0329] In preparing the aqueous dispersion containing particulate polymer A, the amounts of each monomer added were changed as shown in Tables 1 and 2. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the functional layer composition, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0330] (Example 13)

[0331] In preparing the aqueous dispersion containing particulate polymer A, the amounts of each monomer added were changed as shown in Table 2, and 1 part of tert-dodecyl mercaptan was used as a chain transfer agent. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

[0332] (Example 22)

[0333] Using an aqueous dispersion containing particulate polymer A prepared as described below, an aqueous dispersion containing particulate polymer B, a composition for a functional layer, a spacer with a functional layer, a positive electrode, a negative electrode, and a lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. The evaluation was then performed in the same manner as in Example 1. The results are shown in Table 3.

[0334] <Preparation of an aqueous dispersion containing particulate polymer A>

[0335] A monomer composition was prepared by mixing 41 parts of styrene as an aromatic vinyl monomer, 1.2 parts of ethylene glycol dimethacrylate as a crosslinking monomer, 10 parts of glycidyl methacrylate, and 47.8 parts of 2-ethylhexyl acrylate as a (meth)acrylate monomer.

[0336] The above monomer composition was added to an aqueous solution containing 6.2 parts of polyvinyl alcohol with a degree of polymerization of 3000-4000 (based on solids content). After further stirring, 2.0 parts of tert-butyl peroxide-2-ethylhexanoate (manufactured by Nippon Oil Co., Ltd., "PERBUTYL O") as a polymerization initiator were added to obtain a mixture. The resulting mixture was stirred at a high shear speed of 12000 rpm for 1 minute using a pipeline emulsifying disperser (manufactured by Pacific Machinery Co., Ltd., "Cavitron") to form droplets of the monomer composition. The mixture containing the droplets of the above monomer composition was placed in a reactor, heated to 90°C, and subjected to a polymerization reaction for 5 hours to obtain an aqueous dispersion of granular polymer A containing individual polymer particles.

[0337] (Examples 23-25)

[0338] In preparing the aqueous dispersion containing particulate polymer A, the amounts of each monomer added were changed as shown in Table 3. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 22. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 3.

[0339] (Example 26)

[0340] In preparing the aqueous dispersion containing particulate polymer A, the amount of polyvinyl alcohol was changed from 6.2 parts to 7.8 parts. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 24. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 3.

[0341] (Example 27)

[0342] In preparing the aqueous dispersion containing particulate polymer A, the amount of polyvinyl alcohol was changed from 6.2 parts to 5.1 parts. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 24. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 3.

[0343] (Example 28)

[0344] In preparing the aqueous dispersion containing particulate polymer A, the amount of polyvinyl alcohol was changed from 6.2 parts to 2.4 parts. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 24. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 3.

[0345] (Comparative Examples 1-2)

[0346] In preparing the aqueous dispersion containing particulate polymer A, the amounts of each monomer added were changed as shown in Table 4. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 4.

[0347] (Comparative Example 3)

[0348] Using an aqueous dispersion containing particulate polymer A prepared as described below, an aqueous dispersion containing particulate polymer B, a composition for a functional layer, a spacer with a functional layer, a positive electrode, a negative electrode, and a lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. The evaluation was then performed in the same manner as in Example 1. The results are shown in Table 4.

[0349] <Preparation of an aqueous dispersion containing particulate polymer A>

[0350] In a flask, 20.6 parts of styrene as an aromatic vinyl monomer, 0.5 parts of ethylene glycol dimethacrylate and 10 parts of glycidyl methacrylate as a crosslinking monomer, 58.9 parts of 2-ethylhexyl acrylate as a (meth)acrylate monomer, 0.03 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of deionized water, and 0.5 parts of potassium persulfate as a polymerization initiator were added and stirred thoroughly. The mixture was then heated to 60°C to initiate polymerization. Polymerization was continued until a polymerization conversion of 96% was achieved, yielding an aqueous dispersion containing a particulate polymer forming the core. Next, the aqueous dispersion was heated to 70°C, and 10 parts of styrene were continuously added over 30 minutes to form the shell, continuing polymerization. At a polymerization conversion of 96%, the mixture was cooled to terminate the reaction, thereby obtaining an aqueous dispersion containing a particulate polymer A with a core-shell structure.

[0351] (Comparative Example 4)

[0352] In preparing the aqueous dispersion containing particulate polymer A, the amount of magnesium chloride was changed from 10.0 parts to 3.9 parts, and the amount of sodium hydroxide was changed from 7.0 parts to 2.7 parts. Otherwise, the aqueous dispersion containing particulate polymer A, the aqueous dispersion containing particulate polymer B, the composition for the functional layer, the spacer with the functional layer, the positive electrode, the negative electrode, and the lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 4.

[0353] Additionally, in Tables 1-4 shown below,

[0354] "ST" stands for styrene.

[0355] "EDMA" stands for ethylene glycol dimethacrylate.

[0356] "GMA" indicates glycidyl methacrylate.

[0357] "2EHA" indicates 2-ethylhexyl acrylate.

[0358] "BA" indicates n-butyl acrylate.

[0359] "TDM" stands for tert-dodecyl mercaptan.

[0360] [Table 1]

[0361]

[0362] [Table 2]

[0363]

[0364] [Table 3]

[0365]

[0366] [Table 4]

[0367]

[0368] As shown in Tables 1 to 4, in Examples 1 to 28, a functional layer composition using a particulate polymer A containing a volume average particle size and THF dissolution amount within a specified range and a storage modulus at 25°C below a specified value was obtained, resulting in a functional layer with high room temperature adhesion and a reduced internal resistance of the electrochemical element having the functional layer.

[0369] On the other hand, in Comparative Example 1, which used a functional layer composition containing particulate polymer A with a THF leaching amount outside the specified range, and in Comparative Example 4, which used a functional layer composition containing particulate polymer A with a volume average particle size outside the specified range, the internal resistance of the electrochemical element increased compared to Examples 1 to 28.

[0370] Furthermore, in Comparative Example 2, which used a composition for a functional layer containing a particulate polymer A with a storage modulus greater than a specified value, the room temperature adhesion of the functional layer decreased compared to Examples 1-28.

[0371] Furthermore, in Comparative Example 3, which used a functional layer composition containing particulate polymer A with a volume average particle size outside the specified range, the room temperature adhesion of the functional layer decreased compared to Examples 1-28, while the internal resistance of the electrochemical element increased.

[0372] Industrial availability

[0373] According to the present invention, a composition for an electrochemical element functional layer is provided that can form a functional layer for an electrochemical element with excellent room temperature adhesion and reduced internal resistance of the electrochemical element.

[0374] Furthermore, according to the present invention, it is possible to provide a laminate for electrochemical elements that can reduce the internal resistance of electrochemical elements.

[0375] Furthermore, according to the present invention, it is possible to provide an electrochemical element with low internal resistance.< / ph> < / ph>

Claims

1. A composition for a functional layer of an electrochemical element, comprising particulate polymer A, The volume average particle size of the particulate polymer A is greater than 0.75 μm and less than 17.5 μm. The leaching amount of the particulate polymer A to tetrahydrofuran is more than 0.05% by mass and less than 60% by mass. The particulate polymer A has a storage modulus of less than 35 MPa at 25°C.

2. The composition for the functional layer of an electrochemical element according to claim 1, wherein, The number-average molecular weight of the tetrahydrofuran leaching component of the particulate polymer A is above 500 and below 500,000.

3. The composition for the functional layer of an electrochemical element according to claim 1, wherein, The glass transition temperature of the particulate polymer A is above -50°C and below 95°C.

4. The composition for the functional layer of an electrochemical element according to claim 1, wherein, The electrolyte swelling degree of the granular polymer A is above 100% and below 500%.

5. The composition for the functional layer of an electrochemical element according to claim 1, wherein, The composition for the functional layer of the electrochemical element further comprises a dispersion medium containing water, and has a pH of 3.0 or higher and 12.0 or lower.

6. The composition for the functional layer of an electrochemical element according to claim 1, wherein, The composition for the functional layer of the electrochemical element further comprises a particulate polymer B, which is different from the particulate polymer A, and a dispersant, wherein the mass ratio of the particulate polymer A to the particulate polymer B (particulate polymer A / particulate polymer B) is 1 / 99 or more and 99 / 1 or less.

7. The composition for the functional layer of an electrochemical element according to claim 1, wherein, The particulate polymer A contains aromatic vinyl monomer units at a rate of 10% by mass or more.

8. The composition for the functional layer of an electrochemical element according to claim 1, wherein, The particulate polymer A contains crosslinking monomer units in a proportion of more than 0.01% by mass and less than 50% by mass.

9. The composition for the functional layer of an electrochemical element according to claim 1, wherein, The particulate polymer A has a core-shell structure.

10. The composition for the functional layer of an electrochemical element according to claim 9, wherein, The mass ratio (core / shell) of the core-shell structure is 0.1 / 99.9 or more and 99.9 / 0.1 or less.

11. The composition for the functional layer of an electrochemical element according to claim 1, wherein, The composition for the functional layer of the electrochemical element also includes non-conductive heat-resistant particles.

12. A laminate for an electrochemical element having a substrate and a functional layer for an electrochemical element formed on the substrate, the functional layer for an electrochemical element being formed using the composition for an electrochemical element functional layer according to any one of claims 1 to 11.

13. An electrochemical element having the electrochemical element laminate of claim 12.

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