JP7438673B2 - Water dispersion slurry for coating separators for power storage devices, and separators for power storage devices using the same - Google Patents

Description

The present invention relates to a slurry for obtaining a separator by coating a base material, and a separator for power storage devices comprising a thermoplastic polymer layer obtained using the slurry.

BACKGROUND ART Conventionally, power storage devices such as lithium ion secondary batteries have been actively developed. Usually, in an electricity storage device, a separator having a base material is provided between a positive electrode and a negative electrode. The separator has the function of preventing direct contact between the positive electrode and the negative electrode and allowing ions to permeate through the electrolyte held in the micropores.

The separator has the property of quickly stopping the battery reaction in the event of abnormal heating (fuse property), and the property of maintaining its shape even at high temperatures to prevent a dangerous situation where the positive and negative electrodes directly react (short-circuit property). Performance related to safety is required. Furthermore, for the purpose of increasing the capacity of power storage devices, a technique is used in which the volume of the wound body is reduced by hot pressing the wound body in which the laminated body of electrodes and separators is wound. In order to fix the electrode and separator after pressing and maintain the volume at the time of pressing, a thermoplastic polymer layer that exhibits an adhesive function under predetermined conditions is placed on the base material to form the separator, and the separator and electrode are bonded together. Techniques are also being used to improve adhesion.

As the slurry for producing the thermoplastic polymer layer, a water-soluble polymer or a water-insoluble particulate polymer is used, and among them, a water-insoluble particulate polymer obtained by emulsion polymerization is preferably used. It is used. As such slurries, for example, the slurries described in Patent Documents 1 to 3 are known. In addition, the slurry described in Patent Document 4 is also known.

International Publication No. 2018/043192 International Publication No. 2016/123404 Japanese Patent Application Publication No. 2014-229406 International Publication No. 2014/017651

However, if the surface tension of the slurry is higher than that of the base material, poor wettability may result in repellency, which may result in a large number of defects (pinholes) in the thermoplastic polymer layer obtained on the base material. In addition, since the slurry for making the thermoplastic polymer layer is prone to foaming, if the slurry is used to form the thermoplastic polymer layer, the bubbles in the slurry will cause numerous defects (pinholes) in the thermoplastic polymer layer. may occur. In recent years, it has been desired to be able to better suppress the occurrence of pinholes and cissing than expected with the conventional techniques including Patent Documents 1 to 4.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a slurry for a separator that has excellent coatability on a surface to be coated and can satisfactorily suppress the occurrence of pinholes and repellency. Another object of the present invention is to provide a separator for power storage devices, which is equipped with a thermoplastic polymer layer in which the occurrence of pinholes and cissing is well suppressed, and which can improve the electrical characteristics of power storage devices such as secondary batteries. shall be.

The present inventors have conducted studies to solve the above problems, and have found that the above problems can be solved by using a separator slurry having the following configuration, and have completed the present invention. That is, the present invention is as follows.
[1]
A slurry used for coating a substrate containing a polyolefin microporous membrane, the slurry comprising:
A thermoplastic polymer containing a particulate polymer and an antifoaming agent containing an inorganic filler,
A slurry for a separator, comprising the inorganic filler in a proportion of 0.001 parts by mass or more and less than 1 part by mass when the thermoplastic polymer is 100 parts by mass.
[2]
The slurry for a separator according to [1], wherein the slurry contains the inorganic filler in a proportion of 0.01 parts by mass or more and less than 0.1 parts by mass, based on 100 parts by mass of the thermoplastic polymer.
[3]
The slurry for a separator according to [1] or [2], wherein the slurry has a viscosity of less than 3500 mPa·s.
[4]
The slurry for a separator according to any one of [1] to [3], wherein the slurry has a viscosity of less than 350 mPa·s.
[5]
The slurry for a separator according to any one of [1] to [4], wherein the thermoplastic polymer contains a copolymer consisting of units of (meth)acrylic acid ester monomer.
[6]
the thermoplastic polymer has at least two glass transition temperatures;
At least one of the glass transition temperatures exists in a region below 20°C,
The slurry for a separator according to any one of [1] to [5], wherein at least one of the glass transition temperatures exists in a region of 20° C. or higher.
[7]
The slurry for a separator according to any one of [1] to [6], wherein the inorganic filler is a hydrophobic silica particle.
[8]
The slurry for a separator according to any one of [1] to [7], wherein the slurry has a defoaming time of less than 50 seconds as measured by a diffuser stone method.
[9]
The slurry for a separator according to any one of [1] to [8], wherein the slurry has a surface tension of less than 45 mN/m at a surface life of 10 ms.
[10]
A base material comprising a microporous polyolefin membrane, and a thermoplastic polymer layer covering at least a portion of at least one surface of the base material,
A separator for an electricity storage device, comprising an inorganic filler in a proportion of 0.001 parts by mass or more and less than 1 part by mass, when the thermoplastic polymer in the thermoplastic polymer layer is 100 parts by mass.
[11]
The separator for an electricity storage device according to [10], wherein the thermoplastic polymer layer contains an inorganic filler in a proportion of 0.01 parts by mass or more and less than 0.1 parts by mass, based on 100 parts by mass of the thermoplastic polymer.
[12]
According to [10] or [11], the area ratio of the base material covered by the thermoplastic polymer layer is 95% or less with respect to 100% of the total surface area on which the thermoplastic polymer layer is arranged. Separators for energy storage devices.
[13]
[10] to [12], wherein the area ratio of the base material covered by the thermoplastic polymer layer is 80% or less with respect to 100% of the total area of the surface on which the thermoplastic polymer layer is arranged. A separator for an electricity storage device according to any one of the items.
[14]
The separator for an electricity storage device according to any one of [10] to [13], wherein the thermoplastic polymer includes a copolymer consisting of units of (meth)acrylic acid ester monomer.
[15]
the thermoplastic polymer has at least two glass transition temperatures;
At least one of the glass transition temperatures exists in a region below 20°C,
The separator for an electricity storage device according to any one of [10] to [14], wherein at least one of the glass transition temperatures exists in a region of 20° C. or higher.
[16]
The separator for an electricity storage device according to any one of [10] to [15], wherein the inorganic filler is a hydrophobic silica filler.

According to the present invention, it is possible to reduce the surface tension of the slurry to the surface to be coated while suppressing foaming, and therefore, it has excellent coating properties on the base material, and the occurrence of pinholes and cissing can be suppressed well. It is possible to provide a slurry for a separator that can be used. Further, according to the present invention, it is possible to provide a separator for a power storage device in which the occurrence of pinholes and cissing is well suppressed.

Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "this embodiment") will be described in detail. The present invention can be modified in various ways without departing from the gist thereof.
In this specification, "(meth)acrylic" means "acrylic" and its corresponding "methacrylic", and "(meth)acrylate" means "acrylate" and its corresponding "methacrylate". do.
Further, in this specification, "above" and "formed on a surface" do not mean that the positional relationship of each member is limited to "directly above". For example, the expressions "thermoplastic polymer layer formed on a substrate" and "thermoplastic polymer layer formed on the surface of the substrate" refer to any layer between the substrate and the thermoplastic polymer layer. (A layer having a heat-resistant function, for example, an inorganic filler porous layer) is not excluded. Furthermore, the term "ethylenically unsaturated monomer" as used herein means a monomer having one or more ethylenically unsaturated bonds in the molecule. Furthermore, the term "~" in this specification, unless otherwise specified, means that the numerical values listed at both ends thereof are included as an upper limit value and a lower limit value.

<Slurry for separator>
(Particulate polymer)
The separator slurry (hereinafter also simply referred to as "slurry") according to this embodiment is used to produce the separator for electricity storage devices (hereinafter also simply referred to as "separator") according to this embodiment. The slurry includes a thermoplastic polymer, and the thermoplastic polymer includes a particulate polymer. When the thermoplastic polymer contains a particulate polymer, it is possible to achieve both excellent adhesion to the electrode and ion permeability.

Specific examples of particulate polymers (for example, water-insoluble particulate polymers) include acrylic polymers, conjugated diene polymers, polyvinyl alcohol resins, and fluororesins. Among these, acrylic polymers are preferred from the viewpoint of more effectively and reliably achieving the effects of the present invention. Further, acrylic polymers and fluororesins are also preferred from the viewpoint of voltage resistance, and conjugated diene polymers are also preferred from the viewpoint of ease of compatibility with electrodes. Furthermore, from the viewpoint of achieving the effects of the present invention more effectively and reliably, it is preferable that the particulate polymer contains a particulate copolymer.

It is preferable that two or more different particulate polymers are used in combination. That is, the slurry preferably contains two or more different thermoplastic polymers.
Note that by producing the thermoplastic polymer layer using a slurry containing two or more different thermoplastic polymers, the thermoplastic polymer layer contains two or more different thermoplastic polymers.

The thermoplastic polymer preferably contains particulate polymer in an amount of 60% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 98% by mass or more, based on the total amount. The thermoplastic polymer layer may contain a polymer other than the particulate polymer to an extent that does not impair the effects of the present invention.

A conjugated diene polymer is a polymer having a conjugated diene compound as a monomer unit. Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated Examples include pentadienes, substituted hexadienes, and side chain conjugated hexadienes, and these may be used alone or in combination of two or more. Among these, 1,3-butadiene is particularly preferred. Further, the conjugated diene polymer may contain a (meth)acrylic compound or other monomers described below as a monomer unit. Examples of such monomers include styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride. It will be done.

Examples of the polyvinyl alcohol resin include polyvinyl alcohol, polyvinyl acetate, and the like. Examples of the fluororesin include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer. Examples include ethylene copolymers.

An acrylic polymer is a polymer having a (meth)acrylic compound as a monomer unit, that is, a polymerized unit. The (meth)acrylic compound refers to at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylic ester. Examples of such compounds include compounds represented by the following formulas.
CH ₂ =CR ^Y1 -COO-R ^Y2
In the formula, R ^Y1 represents a hydrogen atom or a methyl group, and R ^Y2 represents a hydrogen atom or a monovalent hydrocarbon group. When R ^Y2 is a monovalent hydrocarbon group, it may have a substituent and may have a heteroatom in the chain. Examples of the monovalent hydrocarbon group include a chain alkyl group, which may be linear or branched, a cycloalkyl group, and an aryl group. Examples of the substituent include a hydroxyl group and a phenyl group, and examples of the heteroatom include a halogen atom and an oxygen atom. The (meth)acrylic compounds may be used alone or in combination of two or more. Such (meth)acrylic compounds include (meth)acrylic acid, chain alkyl (meth)acrylate, cycloalkyl (meth)acrylate, (meth)acrylate having a hydroxyl group, and (meth)acrylate containing a phenyl group. can be mentioned.

Specifically, the chain alkyl group which is one type of R ^Y2 includes a chain alkyl group having 1 to 3 carbon atoms such as methyl group, ethyl group, n-propyl group, and isopropyl group; n-butyl Examples include chain alkyl groups having 4 or more carbon atoms, such as isobutyl group, t-butyl group, n-hexyl group, 2-ethylhexyl group; and lauryl group. In addition, examples of the aryl group that is one type of R ^Y2 include a phenyl group. Specific examples of such (meth)acrylic acid ester monomers having R ^Y2 include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl Chains such as acrylates, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate Examples include (meth)acrylates having an alkyl group; and (meth)acrylates having an aromatic ring such as phenyl (meth)acrylate and benzyl (meth)acrylate.

Among these, from the viewpoint of improving the adhesion of the separator to the electrode (electrode active material), monomers having a chain alkyl group having 4 or more carbon atoms, more specifically, R ^Y2 is a chain having 4 or more carbon atoms. A (meth)acrylic acid ester monomer having an alkyl group is preferred. More specifically, at least one selected from the group consisting of butyl acrylate, butyl methacrylate, and 2-ethylhexyl acrylate is preferred. Note that the upper limit of the number of carbon atoms in the chain alkyl group having 4 or more carbon atoms may be, for example, 14, but is preferably 7. These (meth)acrylic acid ester monomers may be used alone or in combination of two or more.

The (meth)acrylic acid ester monomer may also include a monomer having a cycloalkyl group as R ^Y2 instead of or in addition to a monomer having a chain alkyl group having 4 or more carbon atoms. preferable. This also further improves the adhesion of the separator to the electrodes. More specific examples of monomers having such a cycloalkyl group include cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and adamantyl (meth)acrylate. The number of carbon atoms constituting the alicyclic ring of the cycloalkyl group is preferably 4 to 8, more preferably 6 to 7, and particularly preferably 6. Furthermore, the cycloalkyl group may or may not have a substituent. Examples of the substituent include a methyl group and a t-butyl group. Among these, at least one selected from the group consisting of cyclohexyl acrylate and cyclohexyl methacrylate is preferred in terms of good polymerization stability during preparation of the acrylic polymer. These may be used alone or in combination of two or more.

The acrylic polymer preferably contains a crosslinkable monomer as the (meth)acrylic ester monomer instead of or in addition to the above, preferably in addition to the above. Examples of crosslinkable monomers include monomers having two or more radically polymerizable double bonds, monomers having functional groups that provide a self-crosslinking structure during or after polymerization, and the like. . These may be used alone or in combination of two or more.

Examples of the monomer having two or more radically polymerizable double bonds include divinylbenzene and polyfunctional (meth)acrylate. The polyfunctional (meth)acrylate may be at least one selected from the group consisting of bifunctional (meth)acrylate, trifunctional (meth)acrylate, and tetrafunctional (meth)acrylate. Specifically, for example, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol Dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These may be used alone or in combination of two or more. Among them, from the same viewpoint as above, at least one of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate is preferred.

Examples of the monomer having a functional group that provides a self-crosslinking structure during or after polymerization include a monomer having an epoxy group, a monomer having a methylol group, a monomer having an alkoxymethyl group, and a monomer having a hydrolyzable group. Examples include monomers having a silyl group. As the monomer having an epoxy group, an ethylenically unsaturated monomer having an alkoxymethyl group is preferable, and specifically, for example, glycidyl (meth)acrylate, 2,3-epoxycyclohexyl (meth)acrylate, 3, Examples include 4-epoxycyclohexyl (meth)acrylate and allyl glycidyl ether.

Examples of the monomer having a methylol group include N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide. The monomer having an alkoxymethyl group is preferably an ethylenically unsaturated monomer having an alkoxymethyl group, and specifically, for example, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide. , and N-butoxymethyl methacrylamide. Examples of monomers having a hydrolyzable silyl group include vinylsilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyl. Triethoxysilane is mentioned. These may be used alone or in combination of two or more.

The acrylic polymer may further contain monomers other than those mentioned above as monomer units in order to improve various qualities and physical properties. Examples of such monomers include monomers having a carboxyl group (excluding (meth)acrylic acid), monomers having an amide group, monomers having a cyano group, and monomers having a hydroxyl group. and aromatic vinyl monomers (excluding divinylbenzene). Furthermore, various vinyl monomers having functional groups such as sulfonic acid groups or phosphoric acid groups, as well as vinyl acetate, vinyl propionate, vinyl versatate, vinyl pyrrolidone, methyl vinyl ketone, butadiene, ethylene, propylene, chloride Vinyl and vinylidene chloride are also used if necessary. These may be used alone or in combination of two or more. Furthermore, such other monomers may belong to two or more of the above-mentioned monomers at the same time.

Examples of monomers having an amide group include (meth)acrylamide. As the monomer having a cyano group, an ethylenically unsaturated monomer having a cyano group is preferable, and a specific example thereof includes (meth)acrylonitrile. Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth)acrylate.

Examples of aromatic vinyl monomers include styrene, vinyltoluene, and α-methylstyrene. Preferably it is styrene.

The proportion of the acrylic polymer having a (meth)acrylic compound as a monomer unit, that is, a polymerization unit, is preferably 5% by mass or more and 95% by mass or less based on 100% by mass of the acrylic polymer. The lower limit is more preferably 15% by mass, still more preferably 20% by mass, particularly preferably 30% by mass. It is preferable that the content of monomer units is 5% by mass or more from the viewpoint of binding to the base material and oxidation resistance. On the other hand, a more preferred upper limit is 92% by mass, an even more preferred upper limit is 80% by mass, and an especially preferred upper limit is 60% by mass. It is preferable that the monomer content is 95% by mass or less because adhesiveness to the base material improves.

When the acrylic polymer has linear alkyl (meth)acrylate or cycloalkyl (meth)acrylate as a monomer unit, the total content ratio thereof is preferably 100% by mass based on 100% by mass of the acrylic polymer. , 3% by mass or more and 92% by mass or less, more preferably 10% by mass or more and 90% by mass or less, still more preferably 15% by mass or more and 75% by mass or less, particularly preferably 25% by mass or more and 55% by mass or less. The content ratio of these monomers is preferably 3% by mass or more in terms of improving oxidation resistance, and the content ratio of 92% by mass or less is preferred since binding with the base material is improved.

When the acrylic polymer has (meth)acrylic acid as a monomer unit, its content is preferably 0.1% by mass or more and 5% by mass or less based on 100% by mass of the acrylic polymer. . When the content of the above monomer is 0.1% by mass or more, the separator tends to have improved cushioning properties in a swollen state, and when it is 5% by mass or less, polymerization stability tends to be good. be.

When the acrylic polymer has a crosslinkable monomer as a monomer unit, the content of the crosslinkable monomer in the acrylic polymer is preferably 0.0% based on 100% by mass of the acrylic polymer. The content is 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 5% by mass or less, and even more preferably 0.1% by mass or more and 3% by mass or less. When the content of the monomer is 0.01% by mass or more, electrolyte resistance is further improved, and when it is 10% by mass or less, deterioration in cushioning properties in a swollen state can be further suppressed.

As the acrylic polymer, one of the following embodiments is preferred. The following copolymer content ratios are all values based on 100% by mass of the copolymer.
(1) A copolymer having a (meth)acrylic acid ester as a monomer unit (excluding the copolymer in (2) and the copolymer in (3) below). Preferably, (meth)acrylic acid is 5% by mass or less (more preferably 0.1% by mass or more and 5% by mass or less) and (meth)acrylic acid ester monomer is 3% by mass or more and 92% by mass or less (more preferably 10% by mass or more and 90% by mass or less, more preferably 15% by mass or more and 75% by mass or less, particularly preferably 25% by mass or more and 55% by mass or less), a monomer having an amide group, and a monomer having a cyano group. and at least 15% by mass (more preferably 10% by mass or less) of at least one selected from the group consisting of a monomer having a hydroxyl group, and 10% by mass or less (more preferably 0.01% by mass or less) of a crosslinkable monomer. % by mass or more and 5% by mass or less, more preferably 0.1% by mass or more and 3% by mass or less);
(2) A copolymer having an aromatic vinyl monomer and a (meth)acrylic acid ester monomer as monomer units. Preferably, the aromatic vinyl monomer is 5% by mass or more and 95% by mass or less (more preferably 10% by mass or more and 92% by mass or less, even more preferably 25% by mass or more and 80% by mass or less, particularly preferably 40% by mass or more and 60% by mass or less). (mass% or less), (meth)acrylic acid 5% by mass or less (more preferably 0.1 mass% or more and 5 mass% or less), (meth)acrylic acid ester monomer 5 mass% or more and 95 mass% or less ( (more preferably 15% by mass or more and 85% by mass or less, still more preferably 20% by mass or more and 80% by mass or less, particularly preferably 30% by mass or more and 75% by mass or less), a monomer having an amide group, and a cyano group. 10% by mass or less (more preferably 5% by mass or less) of at least one selected from the group consisting of a monomer and a monomer having a hydroxyl group, and 10% by mass or less (more preferably 5% by mass or less) of a crosslinkable monomer. 0.01% by mass or more and 5% by mass or less, more preferably 0.1% by mass or more and 3% by mass or less); and (3) a monomer having a cyano group and a (meth)acrylic acid ester. A copolymer having a monomer as a monomer unit. Preferably, 1% by mass or more and 95% by mass or less of a monomer having a cyano group (more preferably 5% by mass or more and 90% by mass or less, even more preferably 50% by mass or more and 85% by mass or less) and (meth)acrylic acid. 5% by mass or less (preferably 0.1% by mass or more and 5% by mass or less), and (meth)acrylic acid ester monomer 1% by mass or more and 95% by mass or less (more preferably 5% by mass or more and 85% by mass or less, more preferably 10% by mass or more and 50% by mass or less), and at least one type selected from the group consisting of a monomer having an amide group, a monomer having a cyano group, and a monomer having a hydroxyl group. % or less (more preferably 5% by mass or less) and 10% by mass or less of the crosslinkable monomer (more preferably 0.01% by mass or more and 5% by mass or less, still more preferably 0.1% by mass or more and 3% by mass or less) ) and copolymers of.

In the above copolymer (2), it is preferable to have a hydrocarbon ester of (meth)acrylic acid as the (meth)acrylic acid ester monomer. In this case, the copolymerization ratio of the hydrocarbon ester of (meth)acrylic acid is preferably 0.1% by mass or more and 5% by mass or less. Further, when the copolymer (2) above contains a monomer having an amide group, the copolymerization ratio thereof is preferably 0.1% by mass or more and 5% by mass or less. Furthermore, when the above copolymer (2) has a monomer having a hydroxyl group, the copolymerization ratio thereof is preferably 0.1% by mass or more and 5% by mass or less.

The copolymer of (3) above may contain at least one selected from the group consisting of chain alkyl (meth)acrylate and cycloalkyl (meth)acrylate as the (meth)acrylic ester monomer. preferable. As the chain alkyl (meth)acrylate, a (meth)acrylic acid ester having a chain alkyl group having 6 or more carbon atoms is preferable. The copolymerization ratio of chain alkyl (meth)acrylate in the copolymer (3) is preferably 1% by mass or more and 95% by mass or less, more preferably 3% by mass or more and 90% by mass or less, and even more preferably 5% by mass. The content is 85% by mass or less. The upper limit of this copolymerization ratio may be 60% by mass, particularly 40% by mass or 30% by mass, particularly preferably 20% by mass. The copolymerization ratio of cyclohexyl alkyl (meth)acrylate in the copolymer (3) is preferably 1% by mass or more and 95% by mass or less, more preferably 3% by mass or more and 90% by mass or less, even more preferably 5% by mass or more. It is 85% by mass or less. The upper limit of this copolymerization ratio may be 60% by mass, particularly 50% by mass, particularly preferably 40% by mass. Further, when the copolymer (3) above has a monomer having an amide group, the copolymerization ratio thereof is preferably 0.1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 10% by mass. % or less. Furthermore, when the above copolymer (3) has a monomer having a hydroxyl group, the copolymerization ratio thereof is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 10% by mass. % or less.

A surfactant is a compound having at least one hydrophilic group and one or more lipophilic group in one molecule. As the surfactant, polyether surfactants are preferred. The surfactant here is added as a raw material when polymerizing the particulate polymer, and is also referred to as a surfactant added after the polymerization reaction (hereinafter also referred to as "post-added surfactant"). is different. The surfactant will be described later.
Further, the radical polymerization initiator is one that initiates addition polymerization of monomers by radical decomposition using heat or a reducing substance. The radical polymerization initiator will be described later.

Among the forms of thermoplastic polymers, monomers are preferred from the viewpoint of improving the adhesion between separators and electrodes, high-temperature storage characteristics, and cycle characteristics of power storage devices, and achieving thinner adhesives between electrodes and separators. Preferred is an acrylic copolymer latex formed from an emulsion containing an emulsifier, an emulsifier, an initiator, and water.

From the viewpoint of adhesion to electrodes and ion permeability, the glass transition temperature (Tg) of the particulate polymer is preferably -50°C or higher, more preferably -30°C or higher, and 20°C or higher. It is more preferable that the temperature is above 40° C., and even more preferable that it is 40° C. or above. Further, the glass transition temperature of the particulate polymer is preferably 100°C or lower. The glass transition temperature refers to the midpoint glass transition temperature described in JIS K7121, and is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, for a straight line that is the same distance in the vertical axis direction from a straight line that extends the baseline on the low temperature side of the DSC curve toward the high temperature side, and a straight line that extends the baseline on the high temperature side of the DSC curve toward the low temperature side, The temperature at the point where the curve of the stepwise change portion of the glass transition intersects can be employed as the glass transition temperature. More specifically, it may be determined according to the method described in Examples. Furthermore, "glass transition" refers to a change in heat flow on the endothermic side due to a change in the state of a polymer, which is a test piece, in DSC. Such a change in heat flow rate is observed as a step-like change in the DSC curve. A "step-like change" refers to a portion of the DSC curve where the curve leaves the previous baseline on the low-temperature side and transitions to a new baseline on the high-temperature side. Note that a combination of a step-like change and a peak is also included in the step-like change. In addition, in the step-like changing portion, when the upper side is the heat generation side, it can also be expressed as a point where an upwardly convex curve changes to a downwardly convex curve. A "peak" refers to a portion of a DSC curve from when the curve departs from the baseline on the low temperature side until it returns to the same baseline again. "Baseline" refers to a DSC curve in a temperature range in which no transition or reaction occurs in the test piece.

The glass transition temperature Tg of the particulate polymer depends, for example, on the type of monomer used when producing the particulate polymer and, if the particulate polymer is a copolymer, the blending ratio of each monomer. By changing it, you can adjust it as appropriate. That is, for each monomer used in the production of a particulate polymer, the generally indicated Tg of the homopolymer (as described in the "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the Tg of the monomer are determined. The glass transition temperature can be roughly estimated from the blending ratio. For example, a copolymer copolymerized with a high proportion of monomers such as methyl methacrylate, acrylonitrile, and methacrylic acid to give a homopolymer with a Tg of about 100°C has a high Tg of about -50°C. The Tg of a copolymer obtained by copolymerizing a high proportion of monomers such as n-butyl acrylate and 2-ethylhexyl acrylate to give a homopolymer with a Tg of .
Further, the Tg of the copolymer can also be approximately estimated using the FOX equation expressed by the following mathematical formula (1).
1/Tg=W ₁ /Tg ₁ +W ₂ /Tg ₂ +...+W _i /Tg _i +...W _n /Tg _n (1)
where Tg (K) is the Tg of the copolymer, Tg _i (K) is the Tg of the homopolymer of monomer i, and W _i is the mass fraction of each monomer. .
However, as the glass transition temperature Tg of the particulate polymer in this embodiment, a value measured by the method using the above-mentioned DSC is adopted.

From the viewpoints of wettability to the base material, adhesiveness between the base material and the thermoplastic polymer layer, and adhesion to the electrode, the thermoplastic polymer layer must contain a polymer with a glass transition temperature of less than 40°C. is preferred. The glass transition temperature of the polymer having a glass transition temperature of less than 40°C is preferably -100°C or higher, more preferably -50°C or higher, even more preferably -40°C or higher from the viewpoint of ion permeability, and the glass transition temperature of the polymer is preferably -100°C or higher, more preferably -50°C or higher, and still more preferably -40°C or higher, and the glass transition temperature of the polymer is lower than 40°C. From the viewpoint of binding with the plastic polymer layer, the temperature is preferably less than 20°C, more preferably less than 15°C, and even more preferably less than -10°C.

Preferably, the particulate polymer has at least two glass transition temperatures. That is, it is preferable that the thermoplastic polymer layer contains two or more types of thermoplastic polymers having mutually different glass transition temperatures. Examples of methods for making the particulate polymer have at least two glass transition temperatures include a method of blending two or more types of particulate polymers, and a method of using a particulate polymer having a core-shell structure. A core-shell structure is a structure that has a center part and an outer shell part that covers the center part, and is a polymer in the form of a double structure in which the types or compositions of the polymers constituting each part are different from each other. . In particular, in the polymer blend and core-shell structure, the glass transition temperature of the entire particulate polymer can be controlled by combining a polymer with a high glass transition temperature and a polymer with a low glass transition temperature. Moreover, multiple functions can be imparted to the entire particulate polymer.

For example, when blending two or more kinds of particulate polymers, in particular, one or more kinds of polymers exist in a region with a glass transition temperature of 20°C or higher, and one or more kinds of polymers exist in a region with a glass transition temperature of less than 20°C. By blending with the above polymer, it is possible to achieve both stickiness resistance and applicability to the substrate even better. The mixing ratio of each polymer in the case of blending is 0.1:99 as a ratio of a polymer existing in a region with a glass transition temperature of 20° C. or higher to a polymer existing in a region having a glass transition temperature of less than 20° C. The ratio is preferably in the range of .9 to 99.9:0.1, more preferably 5:95 to 95:5, even more preferably 50:50 to 95:5, particularly preferably 60: The ratio is 40 to 90:10.

When using a particulate polymer with a core-shell structure, the adhesion and compatibility of the thermoplastic polymer layer to other members (e.g., base material) can be adjusted by selecting the type of polymer for the outer shell. . Furthermore, by selecting the type of polymer in the central portion, it is possible to improve the adhesion to the electrode after hot pressing, for example. Alternatively, it is also possible to control the viscoelasticity of the thermoplastic polymer layer by combining a polymer with high viscosity and a polymer with high elasticity.

The glass transition temperature of the outer shell of the thermoplastic polymer having a core-shell structure is preferably less than 20°C, more preferably 15°C or less, and even more preferably -30°C or more and 15°C or less. Further, the glass transition temperature of the central portion (core) of the thermoplastic polymer having a core-shell structure is preferably 20°C or higher, more preferably 20°C or higher and 100°C or lower, and even more preferably 50°C or higher and 100°C or lower.

The arithmetic mean particle size of the particulate polymer is preferably 10 nm or more, more preferably 100 nm or more, still more preferably 200 nm or more. Further, the arithmetic mean particle diameter of the particulate polymer is preferably 1000 nm or less, more preferably 800 nm or less, still more preferably 700 nm or less. By setting this arithmetic mean particle size to 10 nm or more, the ion permeability of the separator can be maintained higher. Therefore, in this case, it is preferable from the viewpoint of improving the adhesiveness between the electrode and the separator, and the cycle characteristics and rate characteristics of the electricity storage device. Further, it is preferable to set the arithmetic mean particle size to 1000 nm or less from the viewpoint of ensuring dispersion stability when a thermoplastic polymer layer containing a particulate polymer is formed from an aqueous dispersion. This is preferable from the viewpoint of being able to flexibly control the thickness of the polymer layer. From these viewpoints, it is particularly preferable that the arithmetic mean particle diameter of the particulate polymer is 200 nm or more and 1000 nm or less.

The thermoplastic polymer layer can also contain two or more particulate polymers each having a different arithmetic mean particle size. For example, it is preferable to use a combination of a particulate polymer having an arithmetic mean particle size of 10 nm or more and 300 nm or less and a particulate polymer having an arithmetic mean particle size of more than 100 nm and 2000 nm or less.

Particulate polymers (eg, acrylic polymers) can be produced by known polymerization methods, except for using the monomers described above. As the polymerization method, for example, an appropriate method such as solution polymerization, emulsion polymerization, bulk polymerization, etc. can be adopted. In particular, emulsion polymerization is preferred for the purpose of obtaining a particle-shaped dispersion.
As for the emulsion polymerization method, known methods can be used. For example, in a dispersion system consisting of the above-mentioned monomers, a surfactant, a radical polymerization initiator, and other additive components used as necessary in an aqueous medium as basic composition components, A polymer is obtained by polymerizing a monomer composition. During polymerization, the composition of the monomer composition to be supplied is kept constant during the entire polymerization process, or it is changed sequentially or continuously during the polymerization process to prevent morphological changes in the composition of the particles of the resulting resin dispersion. Various methods can be used as needed, such as a method of giving. When the polymer is obtained by emulsion polymerization, it may be in the form of an aqueous dispersion (latex) containing water and particulate polymer dispersed in the water, for example.

Examples of surfactants (surfactants added as raw materials when polymerizing particulate polymers) include polyether surfactants; non-reactive alkyl sulfate esters, polyoxyethylene alkyl ether sulfate esters, etc. salt, alkylbenzene sulfonate, alkylnaphthalene sulfonate, alkyl sulfosuccinate, alkyldiphenyl ether disulfonate, naphthalene sulfonic acid formalin condensate, polyoxyethylene polycyclic phenyl ether sulfate salt, polyoxyethylene distyrenated phenyl ether Anionic surfactants such as sulfate ester salts, fatty acid salts, alkyl phosphates, and polyoxyethylene alkylphenyl ether sulfate salts; and non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene Polycyclic phenyl ether, polyoxyethylene distyrenated phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkyl alkanol Examples include nonionic surfactants such as amides and polyoxyethylene alkylphenyl ethers. In addition to these, so-called reactive surfactants in which an ethylenic double bond is introduced into the chemical structural formula of a surfactant having a hydrophilic group and a lipophilic group may also be used.

Examples of anionic surfactants among reactive surfactants include ethylenically unsaturated monomers having a sulfonic acid group, a sulfonate group, or a sulfuric acid ester group, and salts thereof; A compound having a group (ammonium sulfonate group or alkali metal sulfonate group) that is an ammonium salt or an alkali metal salt thereof is preferable. Specifically, for example, alkylaryl sulfosuccinates (for example, Eleminol (trademark) JS-20 manufactured by Sanyo Chemical Co., Ltd., Latemul (trademark, hereinafter the same) manufactured by Kao Corporation) S-120, S-180A, S- 180), polyoxyethylene alkyl propenyl phenyl ether sulfate ester salt (for example, Aqualon (trademark, hereinafter the same) HS-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), α-[1-[ (allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfate ester salt (for example, ADEKA RISORP (trademark, hereinafter the same) SE-10N manufactured by ADEKA Co., Ltd.), ammonium =α-sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene (for example, Aqualon KH-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), styrene sulfonate (for example, Tosoh Organic Chemical Co., Ltd.) ), α-[2-[(allyloxy)-1-(alkyloxymethyl)ethyl]-ω-polyoxyethylene sulfate salt (for example, Adekarya manufactured by ADEKA Co., Ltd.), α-[2-[(allyloxy)-1-(alkyloxymethyl)ethyl]-ω-polyoxyethylene sulfate salt Soap SR-10), and polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether sulfate ester salts (for example, Latemul PD-104 manufactured by Kao Corporation). .

In addition, examples of nonionic surfactants among the reactive surfactants include α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxypolyoxyethylene (for example, ADEKA Co., Ltd.'s Adekaria Soap NE-20, NE-30, NE-40), polyoxyethylene alkyl propenyl phenyl ether (for example, Daiichi Kogyo Seiyaku Co., Ltd.'s Aqualon RN-10, RN-20, RN-30, RN-50), α-[2-[(allyloxy)-1-(alkyloxymethyl)ethyl]-ω-hydroxypolyoxyethylene (for example, Adekaria Soap ER manufactured by ADEKA Co., Ltd. -10), and polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether (for example, Latemul PD-420 manufactured by Kao Corporation). The surfactant is preferably used in a range of 0.1 parts by mass to 5 parts by mass based on 100 parts by mass of the monomer composition. The surfactants may be used alone or in combination of two or more.

The surfactant can be added as a raw material when polymerizing the particulate polymer, or it can also be added after the polymerization reaction. By adding a surfactant after the polymerization reaction, the surface energy of the thermoplastic polymer layer formed on the surface of the base material can be adjusted. By adjusting the surface energy of the thermoplastic polymer layer, it is possible to adjust the contact angle of the separator surface on which the thermoplastic polymer is formed. Post-adding a surfactant is preferable from the viewpoint that the surface energy of the thermoplastic polymer layer can be adjusted without being affected by the conditions of the polymerization reaction. Post-addition of the surfactant causes a large amount of free surfactant to be present in the slurry, and it is thought that when the slurry is dried, a large amount of the surfactant is present on the outermost surface of the binder. As a result, the surface energy of the thermoplastic polymer layer can be adjusted with a smaller amount than in the case of adding it as a raw material for polymerization reaction.
The surfactant added after the polymerization reaction of particulate polymers can be the same as the surfactant added during the polymerization reaction, but since the polymerization reaction has already been completed by the time of post-addition, the reactive surface It is preferred to use surfactants that are not active agents. Of these, the foaming of the slurry can be easily suppressed, the dispersion effect increases as it is added, and it is easy to ensure dispersibility, and a small amount has the effect of greatly changing the surface tension of the base material. , polyether surfactants, or anionic surfactants are preferred.
The surfactant to be added later is preferably used in a range of 0.05 parts by mass to 20 parts by mass based on 100 parts by mass of the monomer composition.
When the amount is 0.05 parts by mass or more, sufficient surface energy adjustment is possible, and when it is 20 parts by mass or less, surface energy can be adjusted without inhibiting the adhesive force of the thermoplastic polymer layer with the electrode. .

As the radical polymerization initiator, both inorganic initiators and organic initiators can be used. As the radical polymerization initiator, a water-soluble or oil-soluble polymerization initiator can be used. Examples of water-soluble polymerization initiators include peroxodisulfates, peroxides, water-soluble azobis compounds, and peroxide-reducing agent redox systems. Examples of peroxodisulfates include potassium peroxodisulfate (KPS), sodium peroxodisulfate (NPS), and ammonium peroxodisulfate (APS), and examples of peroxides include hydrogen peroxide, t- Examples of water-soluble azobis compounds include butyl hydroperoxide, t-butyl peroxymaleic acid, succinic acid peroxide, and benzoyl peroxide. , 2-azobis(2-amidinopropane) dichloride, and 4,4-azobis(4-cyanopentanoic acid). One or more reducing agents such as sodium sulfoxylate formaldehyde, sodium bisulfite, sodium thiosulfate, sodium hydroxymethanesulfinate, L-ascorbic acid, and its salts, cuprous salts, and ferrous salts. A combination of these can be mentioned.

The radical polymerization initiator can be used preferably in an amount of 0.05 parts by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the monomer composition. The radical polymerization initiators may be used alone or in combination of two or more.

In addition, a monomer containing an ethylenically unsaturated monomer (P) having a polyalkylene glycol group, an ethylenically unsaturated monomer (A) having a cycloalkyl group, and another monomer (B) When emulsion polymerizing the body composition to form a dispersion in which polymer particles are dispersed in a solvent (water), the solid content of the obtained dispersion should be 30% by mass or more and 70% by mass or less. preferable. The pH of the dispersion is preferably adjusted to a range of 5 to 12 in order to maintain long-term dispersion stability. For adjusting the pH, it is preferable to use amines such as ammonia, sodium hydroxide, potassium hydroxide, and dimethylaminoethanol, and it is more preferable to adjust the pH with ammonia (water) or sodium hydroxide.

The aqueous dispersion includes particles (polymer particles) dispersed in water of a polymer obtained by polymerizing a monomer composition containing the above-mentioned specific monomer. In addition to water and the polymer, the aqueous dispersion may contain a solvent such as methanol, ethanol, isopropyl alcohol, a dispersant, a lubricant, a thickener, a bactericide, and the like. Since the thermoplastic polymer layer can be easily formed by coating, it is preferable to form a particulate polymer by emulsion polymerization and use the resulting particulate polymer emulsion as a water-based latex.

(Inorganic filler (inorganic particles))
In this embodiment, the inorganic filler used as an antifoaming agent is preferably a hydrophobic silica filler. Hydrophobic silica filler is preferred because it has excellent slurry defoaming ability.
The primary particle size of the inorganic filler is preferably 0.1 nm or more, more preferably 1.0 nm or more. Further, the primary particle diameter of the inorganic filler is preferably 1000 nm or less, more preferably 500 nm or less, and still more preferably 100 nm or less. By setting the average primary particle size of the inorganic filler to 100 nm or less, antifoaming properties can be exhibited without inhibiting the adhesive force of the thermoplastic polymer layer.

The proportion of the inorganic filler is 0.001 part by mass or more and less than 1 part by mass when the thermoplastic polymer is 100 parts by mass. By controlling the proportion of the inorganic filler to less than 1 part by mass, it is possible to maintain good adhesive force between the thermoplastic polymer layer and the electrode. On the other hand, when the proportion of the inorganic filler is 0.001 parts by mass or more, the inorganic filler can exhibit good antifoaming properties.
Therefore, when the slurry contains an inorganic filler in a proportion of 0.001 parts by mass or more and 1 part by mass or less when the thermoplastic polymer is 100 parts by mass, foaming of the slurry can be suppressed and the surface tension against the surface to be coated can be reduced. Therefore, it is possible to excellently coat the base material and suppress the occurrence of pinholes and repellency. The resulting thermoplastic polymer layer can maintain good adhesion to the electrode.
From the same viewpoint as above, the content ratio of the inorganic filler is preferably 0.01 part by mass or more and 0.1 part by mass or less.
If the above-mentioned slurry is used, a separator containing an inorganic filler in a proportion of 0.001 parts by mass or more and 1 part by mass or less when the thermoplastic polymer in the thermoplastic polymer layer is 100 parts by mass can be obtained. The resulting separator includes a thermoplastic polymer layer in which the occurrence of pinholes and cissing is well suppressed, so by including such a separator, it is possible to improve the electrical characteristics of power storage devices such as secondary batteries. be able to.

Other components that can be added together with the inorganic filler after the polymerization reaction include, for the purpose of enhancing the antifoaming effect, oil-based antifoaming agents such as castor oil, sesame oil, linseed oil, and animal and vegetable oils; stearic acid, oleic acid, Fatty acid antifoaming agents such as palmitic acid; Fatty acid ester antifoaming agents such as isoamyl stearate, distearyl succinate, ethylene glycol distearate, butyl stearate; Polyoxyalkylene monohydric alcohol, di-t-amyl Alcohol-based antifoaming agents such as phenoxyethanol, 3-heptanol, and 2-ethylhexanol; Ether-based antifoaming agents such as 3-heptyl cellosolve, nonyl cellosolve, 3-heptyl carbitol, and polyalkylene glycol; Tributyl phosphate, tris (buethyl) Phosphate-based antifoaming agents such as phosphate; Amine-based antifoaming agents such as diamylamine; Amide-based antifoaming agents such as polyalkyleneamide and acylate polyamine; Sulfuric acid ester-based antifoaming agents such as sodium lauryl sulfate; Dimethyl poly It may contain a polysiloxane antifoaming agent such as siloxane; mineral oil such as paraffinic mineral oil, naphthenic mineral oil such as cyclopentene, cyclohexane, fuchterite, and oleanane. Among these, mineral oil is preferred because it has excellent antifoaming properties.

（式中、Ｒ５～Ｒ８は、互いに独立して、炭素数１～１０のアルキル基を表し、ｎ、及びｍは、互いに独立して０以上の整数を表すが、ｎ＋ｍ＝０～４０である）
で表されるアセチレングリコールのエトキシル化体を含む界面活性剤（アセチレン系界面活性剤）を用いることが好ましい。炭素数１～１０のアルキル基の具体例としては、直鎖状、分岐鎖状、環状のいずれでもよく、例えば、メチル基、エチル基、ｎ－プロピル基、イソプロピル基、ｎ－ブチル基、ｓｅｃ－ブチル基、ｔｅｒｔ－ブチル基、ｎ－ペンチル基、ｎ－ヘキシル基、ｎ－ヘプチル基、ｎ－オクチル基、ｎ－ノニル基、ｎ－デシル基等が挙げられる。 (post-added surfactant)
A specific example of the surfactant (post-added surfactant) used in this embodiment is the following formula (A):

(In the formula, R5 to R8 each independently represent an alkyl group having 1 to 10 carbon atoms, and n and m independently represent an integer of 0 or more, and n+m=0 to 40. )
It is preferable to use a surfactant containing an ethoxylated acetylene glycol represented by (acetylene surfactant). Specific examples of the alkyl group having 1 to 10 carbon atoms may be linear, branched, or cyclic, such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec -butyl group, tert-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group and the like.

Specific examples of acetylene glycol represented by formula (A) include 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 5,8-dimethyl-6-dodecyne-5,8 -diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 4,7-dimethyl-5-decyne-4,7-diol, 2,3,6,7-tetramethyl -4-octyne-3,6-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,4,7,9 - Ethoxylated product of tetramethyl-5-decyne-4,7-diol (number of moles of ethylene oxide added: 1.3), 2,4,7,9-tetramethyl-5-decyne-4,7-diol Ethoxylated product (number of moles of ethylene oxide added: 4), ethoxylated product of 3,6-dimethyl-4-octyne-3,6-diol (number of moles of ethylene oxide added: 4), 2,5,8,11- Ethoxylated product of tetramethyl-6-dodecyne-5,8-diol (number of moles of ethylene oxide added: 6) Ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol ( Number of moles of ethylene oxide added: 10), ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (number of moles of ethylene oxide added: 30), 3,6-dimethyl-4 Examples include ethoxylated products of -octyne-3,6-diol (number of moles of ethylene oxide added: 20), and these may be used alone or in combination of two or more.

Acetylene surfactants can also be obtained as commercial products, such as Olfine SPC (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 80% by mass, light yellow liquid), Olfine AF-103 (manufactured by Nissin Chemical Industry Co., Ltd., light brown liquid), Olfin AF-104 (manufactured by Nissin Chemical Industry Co., Ltd., light brown liquid), Olfin SK-14 (manufactured by Nissin Chemical Industry Co., Ltd.) , short yellow viscous liquid), Olfin AK-02 (manufactured by Nissin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfin AF-201F (manufactured by Nissin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfin D-10PG (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 50% by mass, pale yellow liquid), Olfin E-1004 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100% by mass, pale yellow liquid), Olfin E-1010 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100% by mass, pale yellow liquid), Olfin E-1020 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100% by mass, pale yellow liquid), Olfine E-1030W (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 75% by mass, pale yellow liquid), Surfynol 420 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100% by mass, pale yellow viscous), Surfy Nol 440 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100% by mass, pale yellow viscous body), Surfynol 104E (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 50% by mass, pale yellow viscous body) etc.

As the post-added surfactant, a polyether surfactant and/or a silicone surfactant can also be used instead of or together with the acetylene surfactant.
Typical examples of polyether surfactants include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene dodecyl ether, and polyoxyethylene. Examples include nonylphenyl ether, polyoxyethylene octylphenyl ether, and polyoxyethylene/polyoxypropylene block copolymer. Among these, polyethylene glycol is particularly preferred. Note that these surfactants may be used alone or in combination of two or more.

Polyether surfactants can also be obtained as commercial products, and examples of such commercial products include E-D052, E-D054, and E-F010 (manufactured by San Nopco Co., Ltd.).

The silicone surfactant may be linear, branched, or cyclic, as long as it contains at least a silicone chain, and may contain either a hydrophobic group or a hydrophilic group. Specific examples of the hydrophobic group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, n-hexyl group, n- Examples include alkyl groups such as heptyl group, n-octyl group, n-nonyl group, and n-decyl group; cyclic alkyl groups such as cyclohexyl group; and aromatic hydrocarbon groups such as phenyl group. Specific examples of hydrophilic groups include amino groups, thiol groups, hydroxyl groups, alkoxy groups, carboxylic acids, sulfonic acids, phosphoric acids, nitric acids, and their organic and inorganic salts, ester groups, aldehyde groups, glycerol groups, heterogeneous Examples include ring groups.
Typical examples of silicone surfactants include dimethyl silicone, methylphenyl silicone, chlorophenyl silicone, alkyl-modified silicone, fluorine-modified silicone, amino-modified silicone, alcohol-modified silicone, phenol-modified silicone, carboxy-modified silicone, epoxy-modified silicone, and fatty acid. Examples include ester-modified silicone, polyether-modified silicone, and the like.

Silicone surfactants can also be obtained as commercial products, such as BYK-300, BYK-301, BYK-302, BYK-306, BYK-307, BYK-310, BYK-313, BYK-320BYK-333, BYK-341, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349 (all product names, manufactured by BYK Chemie Japan Co., Ltd.), KM-80 , KF-3
51A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF- 6011, KF-6012, KF-6015, KF-6017 (the above product names, manufactured by Shin-Etsu Chemical Co., Ltd.), SH-28PA, SH8400, SH-190, SF-8428 (the above product names, Toray Dow Corning ( Polyflow KL-245, Polyflow KL-270, Polyflow KL-100 (manufactured by Kyoeisha Chemical Co., Ltd.), Silface SAG002, Silface SAG005, Silface SAG0085 (product names, Nissin) (manufactured by Kagaku Kogyo Co., Ltd.), etc.

<Viscosity modifier>
The slurry may also include a viscosity modifier. By including the viscosity modifier, the viscosity of the slurry can be adjusted to a desired range, thereby improving the dispersibility of particles and the coatability of the slurry. As the viscosity modifier, it is preferable to use water-soluble polysaccharides. Examples of polysaccharides include natural polymer compounds, cellulose semi-synthetic polymer compounds, and the like. Note that the viscosity modifiers may be used alone or in combination of two or more in any ratio.

Examples of natural polymer compounds include polysaccharides and proteins derived from plants or animals. Further, natural polymer compounds that have been subjected to fermentation treatment using microorganisms or the like or heat treatment can also be exemplified. These natural polymer compounds can be classified as plant-based natural polymer compounds, animal-based natural polymer compounds, microbial-based natural polymer compounds, and the like.

Examples of plant-based natural polymer compounds include gum arabic, gum tragacanth, galactan, guar gum, carob gum, gum karaya, carrageenan, pectin, cannan, quince seed (quince), alkecolloid (gassou extract), starch (rice, corn, potato, (derived from wheat, etc.), glycyrrhizin, etc. Further, examples of animal-based natural polymer compounds include collagen, casein, albumin, gelatin, and the like. Furthermore, examples of microbial natural polymer compounds include xanthan gum, dextran, succinoglucan, bullulan, and the like.

Cellulose semisynthetic polymer compounds can be classified into nonionic, anionic, and cationic.

Nonionic cellulose semi-synthetic polymer compounds include, for example, alkyl celluloses such as methyl cellulose, methyl ethyl cellulose, ethyl cellulose, and microcrystalline cellulose; hydroxyethyl cellulose, hydroxybutyl methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose. Examples include hydroxyalkyl celluloses such as stearoxy ether, carboxymethyl hydroxyethyl cellulose, alkyl hydroxy ethyl cellulose, and nonoxynyl hydroxy ethyl cellulose.

Examples of the anionic cellulose semi-synthetic polymer compound include alkyl celluloses obtained by substituting the above-mentioned nonionic cellulose semi-synthetic polymer compounds with various derivative groups, their sodium salts, and ammonium salts. Specific examples include sodium cellulose sulfate, methylcellulose, methylethylcellulose, ethylcellulose, carboxymethylcellulose (CMC), and salts thereof.

Examples of cationic cellulose semisynthetic polymer compounds include low nitrogen hydroxyethylcellulose dimethyldiallylammonium chloride (polyquaternium-4), O-[2-hydroxy-3-(trimethylammonio)propyl]hydroxyethylcellulose chloride (polyquaternium-10), ), O-[2-hydroxy-3-(lauryldimethylammonio)propyl]hydroxyethylcellulose chloride (polyquaternium-24), and the like.

Among these, cellulose semisynthetic polymer compounds, their sodium salts, and their ammonium salts are preferred because they can have cationic, anionic, or amphoteric properties. Further, among these, anionic cellulose semi-synthetic polymer compounds are particularly preferred from the viewpoint of dispersibility of non-conductive fine particles.

Further, the degree of etherification of the cellulose semi-synthetic polymer compound is preferably 0.5 or more, more preferably 0.6 or more, preferably 1.0 or less, and more preferably 0.8 or less. Here, the degree of etherification refers to the degree of substitution of hydroxyl groups (3) per anhydroglucose unit in cellulose with substituents such as carboxymethyl groups. The degree of etherification can theoretically take values from 0 to 3. When the degree of etherification is within the above range, the cellulose semi-synthetic polymer compound adsorbs on the surface of the non-conductive fine particles and is also compatible with water, so it has excellent dispersibility and converts the non-conductive fine particles into primary particles. It can be finely dispersed up to the level.

<Various characteristics regarding slurry for separators>
(solid content)
Generally, the solid content concentration of the slurry may be arbitrarily set within a range in which the slurry has a viscosity that does not impair workability when producing a porous membrane. Specifically, the solid content concentration of the slurry can be usually adjusted to 3 to 50% by mass.

(defoaming time)
The defoaming time of the slurry can be measured by the diffuser stone method, specifically the method described in the Examples. Since the slurry according to the present embodiment has excellent defoaming properties, the defoaming time is shorter than that of the comparative example, as confirmed in the Examples column.

(surface tension)
The dynamic surface tension of the slurry at a surface life of 10 ms is preferably 60 mN/m or less, more preferably 50 mN/m or less, even more preferably 45 mN/m or less. By setting the dynamic surface tension at a surface life of 10 ms to 60 mN/m or less, it is possible to provide a slurry that can satisfactorily suppress the occurrence of cissing.

(viscosity)
The viscosity of the slurry is preferably less than 3500 mPa·s, more preferably less than 350 mPa·s, even more preferably 100 mPa·s or less. Further, it is preferably 20 mPa·s or more. When the viscosity is within such a range, coating properties are excellent and a uniform coating layer can be provided.

<Separator for electricity storage devices>
The separator according to this embodiment includes a base material and a thermoplastic polymer layer formed on at least one surface (one surface) of the base material. Both an embodiment in which a thermoplastic polymer layer is formed on only one side of the separator and an embodiment in which a thermoplastic polymer layer is formed on both sides of the separator are within the scope of the present invention.

[Base material]
The base material itself may be one that has been conventionally used as a separator. The base material is preferably a porous membrane, and more preferably a porous membrane with fine pores that has no electronic conductivity, ion conductivity, and high resistance to organic solvents. Such porous membranes include, for example, resins as main components such as polyolefins (e.g., polyethylene, polypropylene, polybutene, and polyvinyl chloride), mixtures thereof, or copolymers of monomers thereof. Examples include microporous membranes. These may be used alone or in combination of two or more. Note that the concept of "substrate" in this specification includes not only the polyolefin microporous membrane itself but also one having an inorganic coating layer.

In order to reduce the thickness of the separator, increase the active material ratio in the power storage device, and ultimately increase the capacity per volume, a microporous polyolefin membrane containing polyolefin resin as the main component was used as the base material. It is preferable to use When a microporous polyolefin membrane undergoes a step of applying a coating liquid onto the membrane, it has excellent coatability with a coating liquid, and is therefore advantageous in making the thickness of the separator thinner.
Note that "containing polyolefin resin as a main component" means containing it in an amount exceeding 50% by mass based on the total mass of the base material. The content of the polyolefin resin is preferably 75% by mass or more, more preferably 85% by mass or more, still more preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably from the viewpoint of shutdown performance etc. may be 98% by mass or more and 100% by mass.

The base material has a polyolefin resin as a main component, but may also contain resins other than the polyolefin resin (other resins) to the extent that the effects of the present invention are not impaired. Examples of other resins include resins such as polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene.

The polyolefin resin may be a polyolefin resin that can be used in conventional extrusion, injection, inflation, blow molding, and the like. Examples of polyolefin resins include homopolymers containing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers, and two or more of these monomers. copolymers, and multistage polymers. These homopolymers, copolymers, and multistage polymers may be used alone or in combination of two or more.

Typical examples of polyolefin resins include polyethylene, polypropylene, and polybutene, and more specifically, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra-high molecular weight polyethylene, and isotactic polyethylene. Atactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene, and ethylene propylene rubber. These may be used alone or in combination of two or more. As the polyolefin resin, polyethylenes such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene are preferable from the viewpoint of shutdown characteristics in which pores are closed by thermal melting. In particular, high-density polyethylene is preferred because it has a low melting point and high strength, and polyethylene whose density measured according to JIS K 7112 is 0.93 g/cm ³ or more is more preferred. The polymerization catalyst used in producing these polyethylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts.

In order to improve the heat resistance of the base material, the microporous polyolefin membrane more preferably contains polypropylene and a polyolefin resin other than polypropylene. Here, the three-dimensional structure of polypropylene may be, for example, any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. Examples of polyolefin resins other than polypropylene include homopolymers containing ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers, and monomers thereof. Mention may be made of copolymers of two or more types and multistage polymers, specific examples of which are those already explained above. The polymerization catalyst used when producing polypropylene is not particularly limited, and examples include Ziegler-Natta catalysts and metallocene catalysts.

The content ratio of polypropylene (polypropylene/polyolefin) to the total amount of polyolefin in the microporous polyolefin membrane is preferably 1 to 35% by mass, more preferably 3 to 20% by mass from the viewpoint of achieving both heat resistance and good shutdown function. , more preferably 4 to 10% by mass. From the same viewpoint, the content ratio of olefin resin other than polypropylene, for example polyethylene (olefin resin other than polypropylene/polyolefin) to the total amount of polyolefin in the microporous polyolefin membrane is preferably 65 to 99% by mass, more preferably is 80 to 97% by weight, more preferably 90 to 96% by weight.
Examples of polyolefin resins other than polyethylene and polypropylene include polybutene and ethylene-propylene random copolymers.

The viscosity average molecular weight of the polyolefin resin constituting the microporous polyolefin membrane is preferably from 30,000 to 12 million, more preferably from 50,000 to less than 2 million, and still more preferably from 100,000 to less than 1 million. It is preferable that the viscosity average molecular weight is 30,000 or more because the melt tension during melt molding increases, resulting in better moldability, and the entanglement of polymers tends to further increase strength. On the other hand, when the viscosity average molecular weight is 12 million or less, uniform melt-kneading becomes easy and sheet formability, particularly thickness stability, tends to be excellent, which is preferable. Furthermore, it is preferable that the viscosity average molecular weight is less than 1 million, because the pores tend to be easily blocked when the temperature rises, and a better shutdown function tends to be obtained. Instead of using a polyolefin with a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin with a viscosity average molecular weight of 2 million and a polyolefin with a viscosity average molecular weight of 270,000, the viscosity average molecular weight of which is less than 1 million, is used. Good too. Note that the viscosity average molecular weight (Mv) is measured by the method described in Examples.

The base material can contain optional additives. Such additives include, for example, polymers other than polyolefins; inorganic fillers; phenol-based, phosphorus-based, and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers. agents; antistatic agents; antifogging agents; and coloring pigments. The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, based on 100 parts by mass of the polyolefin resin in the base material. .

The porosity of the base material is preferably greater than 20%, more preferably greater than 35%, and even more preferably greater than 40%. On the other hand, the porosity thereof is preferably 90% or less, more preferably 80% or less. It is preferable to set the porosity to 20% or more from the viewpoint of ensuring the permeability of the separator more effectively and reliably. On the other hand, it is preferable to set the porosity to 90% or less from the viewpoint of ensuring puncture strength more effectively and reliably. Porosity is measured by the method described in Examples. Here, for example, in the case of a microporous polyolefin membrane made of polyethylene, calculations can be made assuming that the membrane density is 0.95 (g/cm ³ ). The porosity can be adjusted by changing the stretching ratio of the microporous polyolefin membrane.

The air permeability of the base material is preferably 10 sec/100 cm ³ or more, more preferably 50 sec/100 cm ³ or more, and preferably 1000 sec/100 cm ³ or less, more preferably 500 sec/100 cm ³ or less. It is preferable that the air permeability is 10 sec/100 cm ³ or more from the viewpoint of suppressing self-discharge of the electricity storage device. On the other hand, it is preferable that the air permeability be 1000 sec/100 cm ³ or less from the viewpoint of obtaining good charge/discharge characteristics. Air permeability is air permeability resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and/or stretching ratio of the base material.

The average pore diameter of the base material is preferably 0.15 μm or less, more preferably 0.1 μm or less, and preferably 0.01 μm or more. Setting the average pore diameter to 0.15 μm or less is preferable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing capacity reduction. The average pore diameter can be adjusted by changing the stretching ratio when manufacturing the base material.

The puncture strength of the base material is preferably 200 gf/20 μm or more, more preferably 300 gf/20 μm or more, even more preferably 400 gf/20 μm or more, and preferably 2000 gf/20 μm or less, more preferably 1000 gf/20 μm or less. The puncture strength of 200 gf/20 μm or more is intended to suppress membrane rupture due to fallen active materials when the separator is wound together with the electrodes, and to suppress concerns about short circuits caused by expansion and contraction of the electrodes during charging and discharging. It is also preferable from the viewpoint of On the other hand, it is preferable that the puncture strength is 2000 gf/20 μm or less from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. Puncture strength is measured according to the method described in Examples. The puncture strength can be adjusted by adjusting the stretching ratio and/or stretching temperature of the base material.

The thickness of the base material is preferably 2 μm or more, more preferably 5 μm or more, and preferably 100 μm or less, more preferably 60 μm or less, and still more preferably 50 μm or less. It is preferable that the film thickness be 2 μm or more from the viewpoint of improving mechanical strength. On the other hand, setting the film thickness to 100 μm or less is preferable because the volume occupied by the separator in the electricity storage device decreases, which tends to be advantageous in terms of increasing the capacity of the electricity storage device.

[Thermoplastic polymer layer]
The thermoplastic polymer layer contains a thermoplastic polymer. The thermoplastic polymer layer may be placed on the entire surface of the base material, or may be placed on a part of the surface of the base material. More preferably, the thermoplastic polymer layer is disposed only on a portion of the surface of the base material so that the resulting electricity storage device exhibits high ion permeability.

It is envisaged that the thermoplastic polymer layer will be bonded directly to the electrode. At least one thermoplastic polymer layer included in the separator is arranged to be directly bonded to the electrode, for example, such that at least a portion of the base material and the electrode are bonded via the thermoplastic polymer layer. is preferred.

The coating amount of the thermoplastic polymer layer on the base material, that is, the amount of the thermoplastic polymer layer formed (disposed amount) per area of one surface of the base material is 0.03 g/m ² or more in terms of solid content. It is preferably 0.05 g/m ² or more, and more preferably 0.05 g/m 2 or more. Further, the coating amount is preferably 2.0 g/m ² or less, more preferably 1.5 g/m ² or less. Setting the coating amount to 0.03 g/m ² or more improves the adhesive force between the thermoplastic polymer layer and the electrode in the resulting separator, realizes more uniform charging and discharging, and improves device characteristics (for example, battery This is preferable in that it improves the cycle characteristics (cycle characteristics). On the other hand, it is preferable that the coating amount be 2.0 g/m ² or less from the viewpoint of further suppressing a decrease in ion permeability.

The ratio of the surface on which the thermoplastic polymer layer is present to the total area of the surface on which the thermoplastic polymer layer is arranged in the base material, that is, the ratio of the area covered by the thermoplastic polymer layer to the base material is preferably 95%. Below, it is more preferably 80% or less, still more preferably 50% or less, particularly preferably 35% or less, and most preferably 30% or less. Moreover, this coverage area ratio is preferably 5% or more, more preferably 10% or more. Setting this coverage area ratio to 50% or less means that when only the separator is wound, the exposed part of the surface of the base material (the part where no thermoplastic polymer layer is present) and the part covered with another base material or another thermoplastic polymer It is preferable to increase the contact area with the layer from the viewpoint of ensuring blocking resistance. It is also preferable from the viewpoint of further suppressing blockage of the pores of the base material by the particulate polymer and further improving the permeability of the separator. On the other hand, it is preferable to make the coverage area ratio 5% or more from the viewpoint of further improving the adhesion to the electrode. The coverage area ratio is measured by observing the surface of the obtained separator on which the thermoplastic polymer layer is formed using a SEM, and in detail, it is measured according to the method described in Examples.
For example, in the separator manufacturing method described below, the coverage area ratio is determined by the type of particulate polymer in the coating liquid applied to the surface of the base material, the concentration of the polymer, the amount of the coating liquid applied, the coating method, and the coating area ratio. It can be adjusted by changing the conditions. However, the method of adjusting the coating area is not limited to these methods.

When the thermoplastic polymer layer is placed only on a part of the surface of the base material, the existing form (pattern) of the thermoplastic polymer may be a state in which the thermoplastic polymer exists irregularly over the entire surface of the base material, or a fixed pattern. A state that exists periodically with a certain frequency is preferred. When the thermoplastic polymer periodically exists in a certain pattern with a certain frequency, examples of the arrangement pattern include dots, stripes, lattice, stripes, hexagonal, etc., and combinations thereof. Among these, a dot shape is preferable from the viewpoint of achieving the effects of the present invention more effectively and reliably and from the viewpoint of productivity. When the arrangement pattern is in the form of dots, the dot diameter is preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more. Further, the dot diameter is preferably 1 mm or less, more preferably 500 μm or less. When the dot diameter is 50 μm or more, the flow of ions in the electrolyte becomes even better, and the permeability is further improved. When the dot diameter is 1 mm or less, the separator can be more uniformly bonded to the electrode, and the in-plane current density can be made more uniform. Furthermore, by providing a portion not coated with thermoplastic polymer in the dot-like arrangement pattern, the in-plane current density can be made even more uniform.

When the thermoplastic polymer layer is partially arranged, it is desirable that the coverage area ratio be uniform within a certain area range. Specifically, it is preferable that the rate of change in the coverage area ratio expressed by the following formula is within ±50% in an observation field of view of 10 mm x 10 mm or more when the surface of the separator is observed with an SEM.
(Change rate of coverage area ratio (%)) = (C1-C2)/C1×100
Here, C1 indicates the coverage area ratio in an arbitrary observation visual field range of 10 mm x 10 mm or more, and C2 indicates the coverage area ratio in the other observation visual field range of 10 mm x 10 mm or more.

The thickness of the thermoplastic polymer layer is preferably 0.01 μm or more, more preferably 0.1 μm or more per surface of the base material. Moreover, the thickness is preferably 5.0 μm or less, more preferably 3.0 μm or less, and even more preferably 2.0 μm or less per surface of the base material. Setting the thickness to 0.01 μm or more is preferable in terms of uniformly developing adhesive force between the electrode and the base material, and as a result, device characteristics can be improved. Further, it is preferable that the thickness be 5.0 μm or less in order to suppress a decrease in ion permeability. The thickness of the thermoplastic polymer layer can be adjusted, for example, by changing the type of particulate polymer in the coating solution applied to the substrate, the concentration of the polymer, the coating amount of the coating solution, the coating method, and the coating conditions. can do. However, this thickness adjustment method is not limited to these.

[Any layer]
Embodiments that include an optional layer, such as an inorganic filler porous layer, between the substrate and the thermoplastic polymer layer are also within the scope of the present invention. The inorganic filler porous layer contains an inorganic filler and has a plurality of pores. In this column, an embodiment including an inorganic filler porous layer between the base material and the thermoplastic polymer layer will be assumed, and such an inorganic filler porous layer will be explained. Layers can be omitted.

(Inorganic filler)
As the inorganic filler, it is possible to use one that has a melting point of 200° C. or higher, has high electrical insulation properties, and is electrochemically stable within the usage range of power storage devices such as lithium ion secondary batteries.

Examples of inorganic fillers include inorganic oxides (oxide ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; silicon nitride, titanium nitride, and boron nitride. Inorganic nitrides (nitride ceramics); silicon carbide, calcium carbonate, magnesium sulfate, barium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyro Ceramics such as phyllite, montmorillonite, sericite, mica, amethyte, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers may be mentioned. These may be used alone or in combination of two or more.

The average particle diameter D50 of the inorganic filler is, for example, 0.01 μm or more, 0.2 μm or more, and further 0.5 μm or more. Moreover, the average particle diameter D50 is 4.0 μm or less, 3.5 μm or less, and further less than 1.0 μm. Examples of methods for adjusting the particle size and distribution of the inorganic filler include a method of reducing the particle size by pulverizing the inorganic filler using an appropriate pulverizer such as a ball mill, bead mill, jet mill, or the like.
The particle size distribution of the inorganic filler can be such that there is one peak in a graph of frequency versus particle size. However, a trapezoidal chart with two peaks or no peaks may be used.

The arithmetic mean particle size of the particulate polymer may be larger than the average pore size of the inorganic filler porous layer. For example, the arithmetic mean particle size of the particulate polymer is, for example, 1.2 times or more, 1.5 times or more, or even 1.8 times or more, with respect to the average pore size of the inorganic filler porous layer, and 6. It is 0 times or less, further 3.0 times or less. The average pore diameter of the inorganic filler porous layer is a quantitative definition of the gap between the inorganic filler and the inorganic filler, the inorganic filler and the binder, or the gap between the binders in the inorganic filler porous layer. Further, the content of the particulate polymer contained in the inorganic filler porous layer is, for example, 20 volume % or less, 15 volume % or less, 10 volume % or less, or even 5 volume % or less with respect to the total amount of the inorganic filler porous layer. % or less.

When measuring the average pore diameter of the inorganic filler porous layer, the cross section of the separator is preferably observed in a region of the separator cross section that is not involved in ion conduction. The average pore diameter of the inorganic filler porous layer may be measured, for example, on a separator that has just been manufactured and has not yet been incorporated into an electricity storage device. Alternatively, if the separator has been incorporated into a power storage device, measure the so-called "ears" of the separator (regions near the outer edge of the separator that are not involved in ion conduction). Good too.
The average pore diameter of the inorganic filler porous layer is, for example, 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, and further 0.2 μm or more. Further, the average pore diameter is 5 μm or less, 3 μm or less, 0.7 μm or less, and further 0.5 μm or less.

The average pore diameter of the inorganic filler porous layer is an index representing the size of voids formed between inorganic fillers bound together by a resin binder, preferably in the inorganic filler porous layer formed on at least one side of the base material. be. The average pore diameter of the inorganic filler porous layer is determined by the method of forming the inorganic filler porous layer, so for example, the properties of the inorganic filler used, the properties of the slurry for the inorganic filler porous layer for forming the inorganic filler porous layer, and the inorganic filler porosity. It can be adjusted by the formation method used when forming the layer.

Examples of the shape of the inorganic filler include a plate, a scale, a needle, a column, a sphere, a polyhedron, and a block. You may use multiple types of inorganic fillers having these shapes in combination.
The content ratio of the inorganic filler in the inorganic filler porous layer is, for example, 20 mass% or more and less than 100 mass%, 30 mass% or more and 80 mass% or less, 35 mass% or more and 70 mass%, based on the total amount of the inorganic filler porous layer. Below, it is 40 mass % or more and 60 mass % or less.

(resin binder)
The type of resin of the resin binder contained in the inorganic filler porous layer is one that is insoluble in the electrolyte of a power storage device such as a lithium ion secondary battery, and one that is used in a power storage device such as a lithium ion secondary battery. Electrochemically stable resins within a range can be used. As the resin of the resin binder, in addition to the resin binder (A) contained in the inorganic filler porous layer and the particulate polymer (B) contained in the thermoplastic polymer layer, the particulate polymer contained in the thermoplastic polymer layer A binding binder (C) may be used that binds (B) to the substrate or to the inorganic filler porous layer. The resin binder (A) and binding binder (C) are usually not in the form of particles in the separator. On the other hand, the particulate polymer (B) is in the form of particles in the separator, and the particulate polymer (B) can contain a different type of resin from the resin binder (A) and the binding binder (C).

Specific examples of such resins include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers; Fluororubbers such as ethylene-tetrafluoroethylene copolymers; styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, acrylonitrile-butadiene-styrene copolymers and their hydrides Rubbers such as , methacrylic acid ester-acrylic ester copolymer, styrene-acrylic ester copolymer, acrylonitrile-acrylic ester copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate; ethyl cellulose, methyl cellulose, hydroxy Cellulose derivatives such as ethyl cellulose and carboxymethyl cellulose; and resins with a melting point and/or glass transition temperature of 180°C or higher, such as polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester. can be mentioned. These may be used alone or in combination of two or more.

The resin binder can include, for example, a resin latex binder. As the resin latex binder, for example, a copolymer of an unsaturated carboxylic acid monomer and another monomer copolymerizable with these monomers can be used. Here, examples of aliphatic conjugated diene monomers include butadiene and isoprene, examples of unsaturated carboxylic acid monomers include (meth)acrylic acid, and examples of other monomers include , for example, styrene. Although there are no particular limitations on the method of polymerizing such a copolymer, emulsion polymerization is preferred. The emulsion polymerization method is not particularly limited, and known methods can be used. The method of adding monomers and other components is not particularly limited, and any of a batch addition method, a divided addition method, and a continuous addition method can be adopted, and the polymerization method includes one-stage polymerization, Either two-stage polymerization or multi-stage polymerization of three or more stages can be employed.

Specific examples of the resin binder include the following 1) to 7).
1) Polyolefin: For example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof;
2) Conjugated diene polymer: For example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride;
3) Acrylic polymers: for example, methacrylic ester-acrylic ester copolymers, styrene-acrylic ester copolymers, and acrylonitrile-acrylic ester copolymers;
4) Polyvinyl alcohol resin: for example, polyvinyl alcohol and polyvinyl acetate;
5) Fluorine-containing resin: for example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer;
6) Cellulose derivatives: for example, ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; and 7) Resins with a melting point and/or glass transition temperature of 180°C or higher, or polymers without a melting point but with a decomposition temperature of 200°C or higher: For example, polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

When the resin binder is a resin latex binder, its average particle diameter (D50) is, for example, 50 to 500 nm, 60 to 460 nm, or even 80 to 250 nm. The average particle size of the resin binder can be controlled by, for example, adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material input order, pH, etc.
The content ratio of the resin binder in the inorganic filler porous layer is, for example, more than 0 mass% and 80 mass% or less, 1 mass% or more and 20 mass% or less, 2 mass% or more and 10 mass% or less, based on the total amount of the inorganic filler porous layer. % or less, more preferably 3% by mass or more and 5% by mass or less.
The content of the particulate polymer contained in the inorganic filler porous layer is, for example, less than 5% by volume, less than 3% by volume, and even less than 2% by volume of the content of the particulate polymer contained in the separator. It can be done.

The thickness of the inorganic filler porous layer can be, for example, 10.0 μm or less, and further 6.0 μm or less. Further, the thickness of the inorganic filler porous layer can be, for example, 0.5 μm or more. The layer density of the inorganic filler porous layer should be, for example, 0.5 g/(m ² ·μm) or more and 3.0 g/(m ² ·μm) or less, and more preferably 0.7 to 2.0 cm ³ . I can do it.

(Various characteristics related to separators)
From the viewpoint of improving safety during a collision test, the separator preferably has a heat shrinkage rate in TD at 120°C of less than 15.0%, more preferably 0% or more and 10% or less, and even more preferably is 0% or more and 5.0% or less. Here, when the thermal contraction rate at TD is less than 15.0%, when heat is generated due to a short circuit during a collision test, the occurrence of short circuits at locations other than those to which external force is applied is more effectively suppressed. This makes it possible to more reliably prevent a rise in the temperature of the entire battery, as well as smoke and ignition that may occur as a result. The heat shrinkage rate of the separator can be adjusted by appropriately combining the stretching operation and heat treatment of the base material described above.

The air permeability of the separator is preferably 10 sec/100 cm ³ or more and 10000 sec/100 cm ³ or less, more preferably 10 sec/100 cm ³ or more and 1000 sec/100 cm ³ or less, and still more preferably 50 sec/100 cm ³ or more and 500 sec/100 cm ³ or less. As a result, when the separator is applied to an electricity storage device, it exhibits good and high ion permeability. This air permeability, like the air permeability of the base material, is the air permeation resistance measured in accordance with JIS P-8117.

<Separator manufacturing method>
[Method for manufacturing base material]
The base material can be manufactured by any known manufacturing method. For example, the polyolefin microporous membrane contained in the base material can be manufactured by either a wet porosization method or a dry porosization method. You may. An example of a wet porosification method is, for example, a method in which a resin composition and a plasticizer are melt-kneaded, formed into a sheet, optionally stretched, and then made porous by extracting the plasticizer; A method in which a polyolefin resin composition containing a resin as a main component is melt-kneaded and extruded at a high draw ratio, and then made porous by exfoliating the polyolefin crystal interface by heat treatment and stretching; A method in which the polyolefin is melt-kneaded and formed into a sheet, and then the interface between the polyolefin and the inorganic filler is peeled off by stretching to make it porous; and after the polyolefin resin composition is dissolved, it is immersed in a poor solvent for polyolefin to solidify the polyolefin. An example of this method is to make the material porous by simultaneously removing the solvent.

Hereinafter, as an example of a method for manufacturing a polyolefin microporous membrane, a method will be described in which a polyolefin resin composition and a plasticizer are melt-kneaded, molded into a sheet shape, and then the plasticizer is extracted. First, a polyolefin resin composition and a plasticizer are melt-kneaded. As a melt-kneading method, for example, a polyolefin resin and other additives as necessary are put into a resin kneading device such as an extruder, a kneader, a laboplast mill, a kneading roll, or a Banbury mixer, and the resin components are heated and melted. An example of this method is to introduce a plasticizer in an arbitrary ratio and knead the mixture. At this time, it is preferable that the polyolefin resin, other additives, and plasticizer be pre-kneaded in a predetermined ratio using a Henschel mixer or the like before being introduced into the resin kneading device. More preferably, only a part of the plasticizer is added during preliminary kneading, and the remaining plasticizer is kneaded while being side-fed to the resin kneading device.

As the plasticizer, a nonvolatile solvent capable of forming a homogeneous solution at a temperature equal to or higher than the melting point of the polyolefin can be used. Specific examples of such nonvolatile solvents include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. Among them, liquid paraffin is preferred.

The ratio of the polyolefin resin composition to the plasticizer may be within a range that allows them to be uniformly melt-kneaded and molded into a sheet. For example, the mass fraction of the plasticizer in a composition consisting of a polyolefin resin composition and a plasticizer is preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 70% by mass or less. Setting the mass fraction of the plasticizer within this range is preferable from the viewpoint of achieving both melt tension during melt molding and formability of a uniform and fine pore structure.

Next, the melt-kneaded product obtained by heating, melting and kneading as described above is formed into a sheet shape. As a method for producing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet-like form through a T-die, etc., and cooled to a temperature sufficiently lower than the crystallization temperature of the resin component by contacting with a heat conductor. An example of this method is to solidify the material. Thermal conductors used for cooling and solidification include metals, water, air, and plasticizers themselves, but metal rolls are preferred because of their high heat conduction efficiency. In this case, if the molten mixture is sandwiched between the rolls when it is brought into contact with the metal rolls, the heat conduction efficiency will be further increased, the sheet will be oriented, the film strength will be increased, and the surface smoothness of the sheet will also be improved. Therefore, it is more preferable. The die lip interval when extruding into a sheet form from a T-die is preferably 400 μm or more and 3000 μm or less, more preferably 500 μm or more and 2500 μm or less.

It is preferred that the sheet-like molded product thus obtained is then stretched. As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used. Biaxial stretching is preferred from the viewpoint of the strength of the resulting base material. When a sheet-like molded product is stretched biaxially at a high magnification, the molecules are oriented in the plane direction, and the porous base material finally obtained becomes difficult to tear and has high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferred from the viewpoint of improving puncture strength, uniformity of stretching, and shutdown properties.

The stretching ratio is preferably in the range of 20 times or more and 100 times or less in area magnification, and more preferably in the range of 25 times or more and 50 times or less. The stretching ratio in each axial direction is preferably in the range of 4 times or more and 10 times or less in MD, 4 times or more and 10 times or less in TD, 5 times or more and 8 times or less in MD, and 5 times or more and 8 times or less in TD. It is more preferable that it is in the range of . Setting the stretching ratio within this range is preferable because more sufficient strength can be imparted, film breakage in the stretching process can be prevented, and high productivity can be obtained.
Note that MD means, for example, the machine direction when continuously molding the base material, and TD means the direction that crosses the MD at an angle of 90°.

The sheet-like molded product obtained as described above may be further rolled. Rolling can be carried out, for example, by a pressing method using a double belt press machine or the like. By rolling, the orientation of the surface layer portion of the sheet-like molded product can be increased. The rolling surface magnification is preferably greater than 1 time and not more than 3 times, more preferably greater than 1 time and not more than 2 times. By setting the rolling ratio in this range, the membrane strength of the porous base material finally obtained is increased, and a more uniform porous structure in the thickness direction of the membrane can be formed, which is preferable.

Next, the plasticizer is removed from the sheet-like molded body to obtain a porous base material. As a method for removing the plasticizer, for example, a method of immersing the sheet-like molded body in an extraction solvent to extract the plasticizer, and thoroughly drying the molded body is exemplified. The method for extracting the plasticizer may be either a batch method or a continuous method. In order to suppress shrinkage of the porous substrate, it is preferable to restrain the ends of the sheet-like molded body during the series of steps of dipping and drying. Further, the amount of plasticizer remaining in the porous base material is preferably less than 1% by mass.

As the extraction solvent, it is preferable to use one that is a poor solvent for the polyolefin resin, a good solvent for the plasticizer, and has a boiling point lower than the melting point of the polyolefin resin. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; hydrofluoroethers and hydrofluorocarbons; Non-chlorinated halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. Note that these extraction solvents may be recovered and reused by operations such as distillation.

In order to suppress shrinkage of the porous base material, heat treatment such as heat setting or thermal relaxation may be performed after the stretching step or after the formation of the porous base material. The porous base material may be subjected to post-treatments such as hydrophilization treatment using a surfactant or the like, crosslinking treatment using ionizing radiation or the like.

An example of a dry porosification method, which is different from a wet porosification method, will be given. First, a film is produced by directly stretching and oriented after melt-kneading in an extruder without using a solvent, and then an annealing process, a cold stretching process, and a hot stretching process are performed in order to produce a base material. In the dry porosification method, a method in which a molten resin is stretched and oriented from an extruder through a T-die, an inflation method, etc. can be used, and the method is not particularly limited.

[Method of arranging thermoplastic polymer layer]
A thermoplastic polymer layer is disposed on at least one side (one surface) of the substrate. When an inorganic filler porous layer is arranged on the surface of the base material, a thermoplastic polymer layer is arranged on all or part of the surface of the inorganic filler porous layer, or no inorganic filler porous layer is formed. A thermoplastic polymer layer is placed on the substrate surface. Examples of the method for arranging the thermoplastic polymer layer include a method of applying a coating liquid containing a particulate polymer to an inorganic filler porous layer or a base material.

As the coating liquid, a dispersion in which a particulate polymer is dispersed in a solvent that does not dissolve the polymer can be preferably used. Particularly preferably, the particulate polymer is synthesized by emulsion polymerization, and the emulsion obtained by the emulsion polymerization can be used as it is as a coating liquid.

The method of applying the coating solution containing the particulate polymer onto the substrate may be any method as long as it can achieve the desired coating pattern, coating thickness, and coating area. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast Examples include coater method, die coater method, screen printing method, spray coating method, and inkjet coating method. Among these, the gravure coater method or the spray coating method is preferable from the viewpoint that the degree of freedom in the coating shape of the particulate polymer is high and a preferable area ratio can be easily obtained.

The medium for the coating solution is preferably water or a mixed solvent consisting of water and a water-soluble organic medium. Examples of the water-soluble organic medium include ethanol, methanol, and the like. Among them, water is preferred. When applying the coating liquid to the base material, if the coating liquid penetrates into the inside of the base material, the particulate polymer containing the polymer will block the surface and inside of the pores of the base material, reducing permeability. It becomes easier to decrease. In this regard, when water is used as a solvent or dispersion medium for the coating solution, it becomes difficult for the coating solution to enter the inside of the substrate, and the particulate polymer containing the polymer is mainly present on the outer surface of the substrate. This is preferable because the reduction in permeability can be more effectively suppressed. Furthermore, examples of solvents or dispersion media that can be used in combination with water include ethanol and methanol.

The method for removing the solvent from the coating film after coating may be any method as long as it does not adversely affect the base material and the thermoplastic polymer layer. For example, methods include drying at a temperature below the melting point of the base material while fixing it, drying under reduced pressure at low temperatures, and simultaneously solidifying the particulate polymer into particles by immersing it in a poor solvent for the particulate polymer. Examples include a method of extracting a solvent.

[Method for forming inorganic filler porous layer]
When an inorganic filler porous layer is disposed on at least one side of the base material, the inorganic filler porous layer can be formed by a known method. For example, a method may be used in which a coating liquid containing an inorganic filler and, if necessary, a resin binder is applied to the base material. A raw material containing an inorganic filler and a resin binder and a raw material for a base material containing a resin may be laminated and extruded by a coextrusion method, or the base material and the inorganic filler porous layer (membrane) may be separately produced and then extruded. They may be pasted together.

The solvent for the coating solution is preferably one that can uniformly and stably disperse or dissolve the inorganic filler and, if necessary, the resin binder, such as N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide. , water, ethanol, toluene, hot xylene, methylene chloride, and hexane.

Various additives such as a dispersant such as a surfactant; a thickener; a wetting agent; an antifoaming agent; a PH adjuster containing an acid or an alkali may be added to the coating liquid.

Examples of methods for dispersing or dissolving the inorganic filler and optionally the resin binder in the medium of the coating solution include ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloid mills, attritors, roll mills, and high-speed impeller dispersion. , a disperser, a homogenizer, a high-speed impact mill, an ultrasonic dispersion, and mechanical stirring using a stirring blade.

Examples of methods for applying the coating liquid to the base material include gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, and blade coater method. Examples include coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, and spray coating method.

The method for removing the solvent from the coating film after coating may be any method as long as it does not adversely affect the substrate. For example, methods include drying the base material at a temperature below the melting point of the material constituting the base material while fixing it, drying at a low temperature under reduced pressure, and immersing the resin binder in a poor solvent to solidify the resin binder while simultaneously removing the solvent. One example is the extraction method. Further, a portion of the solvent may remain as long as it does not significantly affect the device characteristics.

<Electricity storage device>
A power storage device including a separator may be the same as a known power storage device except for the power storage device separator. Examples of power storage devices include batteries such as non-aqueous electrolyte secondary batteries, capacitors, and capacitors. Among these, batteries are preferred, non-aqueous electrolyte secondary batteries are more preferred, and lithium ion secondary batteries are even more preferred, from the viewpoint of more effectively obtaining the benefits of the effects of the present invention. Since the separator of this embodiment is included, the power storage device has excellent device characteristics such as power storage performance. In addition, lithium ion secondary batteries have excellent battery characteristics.

The electrode used to measure the peel strength with the electrode may be either a positive electrode or a negative electrode, but in order to properly understand the effect of the separator, it is appropriate to use the positive electrode. In particular, when the electricity storage device is a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector is used, and the positive electrode active material layer is a separator. It is appropriate to stack the thermoplastic polymer layer so as to face the surface on which the thermoplastic polymer layer is formed and to perform the measurement after hot pressing as described above.

When manufacturing a lithium ion secondary battery using a separator, there are no limitations on the positive electrode, negative electrode, and non-aqueous electrolyte, and known ones can be used for each.
As the positive electrode, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector can be suitably used. Examples of the positive electrode current collector include aluminum foil. Examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel-type LiMnO ₄ , and olivine-type LiFePO ₄ . The positive electrode active material layer may appropriately contain a binder, a conductive material, etc. in addition to the positive electrode active material.

As the negative electrode, a negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector can be suitably used. Examples of the negative electrode current collector include copper foil. Examples of negative electrode active materials include carbon materials such as graphite, non-graphitizable carbon materials, easily graphitizable carbon materials, and composite carbon bodies, as well as silicon, tin, metallic lithium, and various alloy materials.

As the non-aqueous electrolyte, an electrolyte in which an electrolyte is dissolved in an organic solvent can be used. Examples of organic solvents include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

<Method for manufacturing electricity storage device>
Examples of the method for manufacturing a power storage device using a separator include the following method. First, a vertically elongated separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m) is manufactured. Next, the layers are laminated in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator and wound into a circular or flat spiral shape to obtain a wound body. It can be manufactured by housing the wound body in a device can (for example, a battery can) and further injecting an electrolyte. Alternatively, the electrode and the separator may be folded to form a wound body, which is then placed in a device container (for example, an aluminum film), and an electrolyte solution may be poured into the device container.

At this time, the wound body can be pressed. Specifically, a separator, a current collector, and an electrode having an active material layer formed on at least one side of the current collector are stacked such that the former thermoplastic polymer layer and active material layer face each other. An example of a method of pressing together can be given.

The pressing temperature is preferably, for example, 20° C. or higher as a temperature at which adhesiveness can be effectively developed. Further, in order to suppress clogging of holes or thermal shrinkage in the separator due to heat pressing, the pressing temperature is preferably lower than the melting point of the material contained in the base material, and more preferably 120° C. or lower. The press pressure is preferably 20 MPa or less from the viewpoint of suppressing clogging of holes in the separator. The pressing time may be 1 second or less when using a roll press, or may be surface pressing for several hours, but is preferably 2 hours or less from the viewpoint of productivity. By using the separator for an electricity storage device of this embodiment and going through the above manufacturing process, pressback can be suppressed when a wound body consisting of an electrode and a separator is press-molded. Therefore, it is possible to suppress a decrease in yield in the device assembly process and shorten the production process time, which is preferable.

The electricity storage device manufactured as described above, especially the lithium ion secondary battery, has high adhesiveness and has a separator with reduced ionic resistance, so it has excellent battery characteristics (rate characteristics) and long-term continuous operation. Excellent operating durability (cycle characteristics). In addition, it is an object of the present invention to provide a separator for power storage devices that is equipped with a thermoplastic polymer layer in which the occurrence of pinholes and cissing is well suppressed, and that can improve the electrical characteristics of power storage devices such as secondary batteries. I can do it.

The physical property evaluation described in this Example section was performed according to the following method.

(1) Viscosity average molecular weight Mv
In accordance with ASTM-D4020, the intrinsic viscosity [η] at 135°C in a decalin solvent was determined. Using this [η] value, the viscosity average molecular weight Mv was calculated from the relationship of the following formula.
In the case of polyethylene: [η] = 0.00068 x Mv ^0.67
In the case of polypropylene: [η] = 1.10 x Mv ^0.80

(2) Thickness of base material (μm)
Cut a 10 cm x 10 cm square sample from the base material, select 9 points (3 points x 3 points) in a grid pattern, and measure the sample at room temperature 23 ± 2 using a micro-thickness meter (Toyo Seiki Seisakusho Co., Ltd., type KBM). Thickness was measured at °C. The average value of the obtained measured values at nine locations was calculated as the thickness of the base material.

(3) Porosity of base material (%)
A 10 cm x 10 cm square sample was cut from the base material, and its volume (cm ³ ) and mass (g) were determined. Using these values and assuming the density of the base material to be 0.95 (g/cm ³ ), the porosity was determined from the following formula.
Porosity (%) = (1-mass/volume/0.95) x 100

(4) Air permeability of base material (sec/100cm ³ )
The air permeability of the base material was determined by measuring the air permeability with a Gurley air permeability meter G-B2 (model name) manufactured by Toyo Seiki Co., Ltd. in accordance with JIS P-8117. If the thermoplastic polymer layer is present on only one side of the substrate, the needle can be inserted from the side where the thermoplastic polymer layer is present.

(5) Puncture strength of base material (gf)
Using a handy compression tester KES-G5 (model name) manufactured by Kato Tech, the substrate was fixed with a sample holder having an opening diameter of 11.3 mm. Next, a puncture test was performed on the central part of the fixed base material using a needle with a tip radius of curvature of 0.5 mm at a puncture speed of 2 mm/sec in an atmosphere of 25°C to determine the maximum puncture load. was measured. The value obtained by converting the maximum puncture load per 20 μm thickness was defined as the puncture strength (gf/20 μm). If the thermoplastic polymer is present on only one side of the substrate, the needle can be inserted from the side where the thermoplastic polymer layer is present.

(6) Rate characteristics a. Preparation of positive electrode As a positive electrode active material, 90.4% by mass of nickel, manganese, cobalt composite oxide (NMC) (Ni:Mn:Co=1:1:1 (element ratio), density 4.70 g/cm ³ ), 1.6% by mass of graphite powder (KS6) (density 2.26 g/cm ³ , number average particle diameter 6.5 μm) and acetylene black powder (AB) (density 1.95 g/cm ³ , number average particle size 6.5 μm) as conductive additives. 3.8% by mass of polyvinylidene fluoride (PVdF) (density 1.75g/cm 3 ) as a binder, and 4.2% by mass of polyvinylidene fluoride (PVdF) (density 1.75g/cm ³ ) as a binder. ) to prepare a slurry. This slurry was applied using a die coater to one side of an aluminum foil with a thickness of 20 μm, which will serve as the positive electrode current collector. After drying at 130°C for 3 minutes, the positive electrode was formed by compression molding using a roll press machine. Created. The amount of positive electrode active material applied at this time was 109 g/m ² .

b. Preparation of Negative Electrode As negative electrode active materials, 87.6% by mass of graphite powder A (density 2.23 g/cm ³ , number average particle size 12.7 μm) and graphite powder B (density 2.27 g/cm ³ , number average particle size) were used as negative electrode active materials. 9.7% by mass of ammonium salt of carboxymethylcellulose (diameter 6.5 μm) as a binder, 1.4% by mass (in terms of solid content) (solid content concentration 1.83% by mass aqueous solution), and 1.7% by mass of diene rubber latex. % (in terms of solid content) (solid content concentration 40% by mass aqueous solution) was dispersed in purified water to prepare a slurry. This slurry was coated on one side of a 12 μm thick copper foil serving as a negative electrode current collector using a die coater, dried at 120° C. for 3 minutes, and then compression molded using a roll press to produce a negative electrode. The amount of negative electrode active material applied at this time was 5.2 g/m ² .

c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte is prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1:2 (volume ratio) to a concentration of 1.0 mol/L. Prepared.

d. Battery Assembly The multilayer porous membrane or base material was cut out into a circle with a diameter of 24 mm, and the positive electrode and negative electrode were each cut into a circle with a diameter of 16 mm. The negative electrode, the multilayer porous membrane or base material, and the positive electrode were stacked in this order so that the active material surfaces of the positive electrode and negative electrode faced each other, and the mixture was housed in a stainless steel container with a lid. The container and the lid were insulated, and the container was in contact with the copper foil serving as the negative electrode, and the lid was in contact with the aluminum foil serving as the positive electrode. A battery was assembled by injecting 0.4 ml of non-aqueous electrolyte into this container and sealing it.

e. Evaluation of rate characteristics d. After charging the simple battery assembled at 25°C with a current value of 3 mA (approximately 0.5 C) to a battery voltage of 4.2 V, the current value is started to be reduced from 3 mA while maintaining 4.2 V. The first charge after the battery was made was carried out for a total of about 6 hours. Thereafter, the battery was discharged to a voltage of 3.0 V at a current value of 3 mA.
Next, at 25°C, charge the battery to a voltage of 4.2V with a current value of 6mA (approximately 1.0C), and then start reducing the current value from 6mA while maintaining 4.2V. Charged for hours. Thereafter, the discharge capacity when the battery was discharged to a battery voltage of 3.0 V at a current value of 6 mA was defined as 1C discharge capacity (mAh).
Next, at 25°C, charge the battery to a voltage of 4.2V with a current value of 6mA (approximately 1.0C), and then start reducing the current value from 6mA while maintaining 4.2V. Charged for hours. Thereafter, the discharge capacity when the battery was discharged to a battery voltage of 3.0 V at a current value of 12 mA (approximately 2.0 C) was defined as 2C discharge capacity (mAh). Then, the ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was taken as the rate characteristic.
Rate characteristics (%) = (2C discharge capacity/1C discharge capacity) x 100
Evaluation criteria for rate characteristics (%) 〇 (Good): Rate characteristics are more than 85% △ (Acceptable): Rate characteristics are more than 80% and less than 85% × (Poor): Rate characteristics are less than 80%

(7) Average particle size (D50) and particle size distribution of inorganic filler The average particle size and particle size distribution of the inorganic filler were measured using a particle size measuring device (manufactured by Nikkiso Co., Ltd., product name "Microtrac UPA150"). The measurement conditions were a loading index of 0.20 and a measurement time of 300 seconds, and the value of the 50% particle diameter (D50) in the obtained data was described as the average particle diameter.

(8) Thickness of inorganic filler porous layer (μm)
The difference between the thickness of the base material obtained by the method described in the "Thickness of the base material" section above and the thickness of the multilayer porous membrane obtained by the method described in the "Thickness of the multilayer porous membrane" section described below. Calculated.

(9) Thickness of multilayer porous membrane of base material and inorganic filler porous layer (μm)
The measurement target was a multilayer porous membrane, and the measurement was performed using the same method as described in the "Thickness of base material" section above.

(10) 130°C heat shrinkage rate (%) of multilayer porous film of base material and inorganic filler porous layer
A sample of the multilayer porous membrane cut into 100 mm in TD and 100 mm in MD was left standing in an oven at 130° C. for 1 hour. At this time, the sample was sandwiched between two sheets of paper so that the hot air did not directly hit the sample. After the sample was taken out of the oven and cooled, its length (mm) was measured, and the heat shrinkage rate of MD was calculated using the following formula.
MD heat shrinkage rate (%) = 100 - length in MD after heating (mm)

(11) Rate characteristics of a multilayer porous membrane consisting of a base material and an inorganic filler porous layer A battery was assembled using the multilayer porous membrane, and the rate characteristics were measured using the same method as described in the "Evaluation of rate characteristics" section above.

(12) Glass transition temperature of thermoplastic polymer (℃)
An appropriate amount of an aqueous dispersion containing a thermoplastic polymer (solid content = 38 to 42% by mass, pH = 9.0) was placed in an aluminum dish and allowed to stand at room temperature for 24 hours to obtain a dry film. Approximately 17 mg of the dried film was filled into an aluminum container for measurement, and a DSC curve and a DSC curve in a nitrogen atmosphere were obtained using a DSC measuring device (manufactured by Shimadzu Corporation, model name: "DSC6220"). The measurement conditions were as follows.
1st stage heating program: Start at 30°C, raise the temperature at a rate of 10°C per minute. After reaching 110°C, maintain for 5 minutes.
Second stage temperature reduction program: The temperature is lowered from 110℃ at a rate of 10℃ per minute. After reaching -50°C, maintain for 5 minutes.
Third stage heating program: Raise the temperature from -50°C to 130°C at a rate of 10°C per minute. DSC and DDSC data were acquired during this third stage of temperature rise.
The glass transition temperature was determined for the obtained DSC curve according to the method described in JIS-K7121. Specifically, for a straight line that is the same distance in the vertical axis direction from a straight line that extends the baseline on the low temperature side of the DSC curve toward the high temperature side, and a straight line that extends the baseline on the high temperature side of the DSC curve toward the low temperature side, The temperature at the point where the curve of the stepwise change portion of the glass transition intersects was defined as the glass transition temperature (Tg).

(13) Average particle size of particulate polymer (D50)
The average particle diameter (D50) of the particulate polymer was measured using a particle diameter measuring device (manufactured by Nikkiso Co., Ltd., product name "Microtrac UPA150"). The measurement conditions were a loading index of 0.20 and a measurement time of 300 seconds, and the value of the 50% particle diameter (D50) in the obtained data was described as the average particle diameter.

(14) Solid Content Approximately 1 g of the thermoplastic polymer water dispersion was accurately weighed on an aluminum plate, and the mass of the water dispersion weighed at this time was defined as (a)g. It was dried in a hot air dryer at 130° C. for 1 hour, and the dry mass of the thermoplastic polymer after drying was defined as (b) g. The solid content was calculated using the following formula.
Solid content = ((b)/(a)) x 100 [%]

(15) Viscosity The viscosity of each water-dispersed slurry was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., product name "TV-22").

(16) Coverage area ratio (%) of thermoplastic polymer layer
The coverage area ratio of the thermoplastic polymer layer was measured using a scanning electron microscope (SEM) (model: S-4800, manufactured by HITACHI). A sample separator was deposited with osmium and observed under conditions of an acceleration voltage of 1.0 kV and a magnification of 50 times, and the surface coverage was calculated from the following formula. Note that the region where the porous structure on the surface of the base material was not visible in the SEM image was defined as the thermoplastic polymer layer region.
Covering area ratio (%) of thermoplastic polymer layer = {Area of thermoplastic polymer layer / (Area including pores of base material + Area of thermoplastic polymer layer)} x 100
The coverage area ratio in each sample was determined by performing the above measurement three times and using the arithmetic average value.

(17) Defoaming time (diffuser stone method)
50 mL of the slurry was placed in a plastic cup with an inner diameter of 78 mm and a volume of 500 mL, and air was pumped in from an air stone (Air Pump Silent Air SA-200S, As One Corporation) at a flow rate of 2.0 L/min to foam the slurry for 300 seconds. Thereafter, the time required for all the foam to defoam was visually measured, and this time was defined as the defoaming time of the slurry.

(18) Surface tension Dynamic surface tension was measured using a bubble pressure dynamic surface tension meter (BP100, KRUSS GmbH). Thereafter, the surface tension at a surface life of 10 ms was defined as the dynamic surface tension of the slurry.

(19) Wettability Using a contact angle meter (CA-V) (model name) manufactured by Kyowa Interface Science Co., Ltd., 2 μl of each slurry was dropped onto the surface of a clean base material, and the contact angle was measured after 40 seconds had elapsed. For the contact angle of water, the average value measured three times each in MD and TD was used. Further, this measurement method was applied to both the front and back surfaces of the separator, and the larger value of either one was used to evaluate the wettability based on the following criteria.
◎ (Very good): Contact angle is less than 40 degrees.
○ (Good): Contact angle is 40 degrees or more and less than 60 degrees.
Δ (slightly poor): Contact angle is 60 degrees or more and less than 80 degrees.
× (Poor): Contact angle is 80 degrees or more.

(20) Adhesion between the base material and the thermoplastic polymer layer A matte roll with 100 lines (manufactured by Otec Co., Ltd., Ra = 3.1 μm) was installed at a holding angle of 45°, and the separator after coating was It was transported at a speed of 20 m/min. After that, the separator was continuously conveyed for a total of 1 minute, and the surface of the matte roll was observed, and the adhesiveness between the base material and the thermoplastic polymer layer was evaluated based on the following criteria.
◎ (Very good): Powder derived from the thermoplastic polymer layer adheres to less than 10% of the surface of the matte roll. ○ (Good): Powder derived from the thermoplastic polymer layer adheres to 10% or more and less than 30% of the surface of the matte roll. Adhesion △ (slightly poor): Powder derived from the thermoplastic polymer layer adheres to 30% or more and less than 50% of the surface of the matte roll × (poor): Powder derived from the thermoplastic polymer layer adheres to 50% or more of the surface of the matte roll. adhesion

(21) Adhesion to electrodes The separators obtained in Examples and Comparative Examples and the positive electrode as an adherend (manufactured by Enertech, positive electrode material: LiCoO ₂ , conductive aid: acetylene black, binder: PVdF, LiCoO ₂ /acetylene black/PVdF (mass ratio) = 95/2/3, L/W: 36 mg/cm ² on both sides, density: 3.9 g/cm ³ , thickness of Al current collector: 15 μm, positive electrode after pressing (thickness: 107 μm) is cut into a rectangular shape with a width of 15 mm and a length of 60 mm, and stacked so that the thermoplastic polymer layer of the separator and the positive electrode active material face each other to obtain a laminate. The bodies were pressed under the following conditions. Furthermore, the room temperature at the time of evaluation was 23° C., and the humidity was 30%.
Press pressure: 1MPa
Temperature: 100℃
Press time: 5 seconds

After pressing, the laminate was peeled off at a peeling speed of 50 mm/min by fixing the electrodes and gripping and pulling the separator using force gauges ZP-5N and MX2-500N (product names) manufactured by Imada Co., Ltd. A 90° peel test was conducted to measure the peel strength. At this time, the average value of the peel strength in the peel test over a length of 40 mm conducted under the above conditions was adopted as the peel strength, and the adhesiveness with the electrode was evaluated according to the following criteria.
○ (Good): Peel strength is 5 N/m or more.
Δ (slightly poor): Peel strength is 3 N/m or more and less than 5 N/m.
× (Poor): Peel strength is less than 3 N/m.

Regarding the above "adhesion to electrode" test, Table 1 shows the test results when a polyolefin microporous membrane was used in place of the above separator, and Table 2 shows the test results when a polyolefin microporous membrane was used in place of the above separator. The test results when using a multilayer porous membrane are shown. As can be seen from Tables 1 and 2, a microporous polyolefin membrane or a multilayer porous membrane alone, that is, without a thermoplastic polymer layer, does not exhibit good adhesion to the electrode.

[Production Example 1-1] (Production of microporous polyolefin membrane B1)
Mv is 700,000 and 45 parts by mass of homopolymer high-density polyethylene, Mv is 300,000 and 45 parts by mass of homopolymer high-density polyethylene, and Mv is 400,000 and homopolymer polypropylene and Mv is 15. 10 parts by mass of a homopolymer and polypropylene (mass ratio = 4:3) were dry blended using a tumbler blender. 1 part by mass of tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane as an antioxidant was added to 99 parts by mass of the obtained polyolefin mixture, and the mixture was again blended in a tumbler blender. A mixture was obtained by dry blending. The resulting mixture was fed to a twin-screw extruder by a feeder under a nitrogen atmosphere. Additionally, liquid paraffin (kinematic viscosity at 37.78°C: 7.59×10 ⁻⁵ m ² /s) was injected into the extruder cylinder using a plunger pump. The operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin in 100 parts by mass of the total extruded mixture was 65 parts by mass, that is, the proportion of the resin composition was 35 parts by mass.

Next, they were melt-kneaded in a twin-screw extruder while heating to 230°C, and the obtained melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 80°C, and the extrudate was A sheet-like molded product was obtained by molding (casting) in contact with a cooling roll and cooling and solidifying. This sheet was stretched using a simultaneous biaxial stretching machine at a magnification of 7 x 6.4 times at a temperature of 112°C, then immersed in methylene chloride to extract and remove liquid paraffin, dried, and then stretched using a tenter stretching machine at a temperature of 112°C. It was stretched 2 times in the transverse direction at 130°C. Thereafter, this stretched sheet was relaxed by about 10% in the width direction and heat treated to obtain a polyolefin microporous membrane B1 as a base material.

The physical properties of the obtained microporous polyolefin membrane B1 were measured by the method described above. Further, the obtained microporous polyolefin membrane was used as a separator and evaluated by the above method. The results obtained are shown in Table 1.

[Production Example 1-2] (Production of microporous polyolefin membrane B2)
Separator manufactured by Celgard, H1609 (model name); A uniaxially stretched membrane produced by a dry method was used as polyolefin microporous membrane B2, and evaluated in the same manner as in Production Example 1-1. The results obtained are shown in Table 1.

[Manufacture example 2-1]
As an inorganic filler, 47.7 parts by mass of block-shaped aluminum hydroxide oxide and 0.48 parts by mass of polycarboxylic acid ammonium salt are uniformly dispersed in 47.7 parts by mass of water, and subjected to bead mill treatment to form an inorganic filler. Crushing was performed so that the average particle size of the filler (aluminum hydroxide oxide) was as shown in Table 2. At this time, there was one peak in the particle size distribution chart. Thereafter, an aqueous solution to which 0.10 parts by mass of a thickener and 4.1 parts by mass (as solid content) of acrylic latex (average particle size (D50): 300 μm) were added was subjected to corona treatment at a discharge amount of 1.0 kV. It was coated on the surface of the polyolefin microporous membrane B1 using a gravure coater at a line speed of 30 m/min. The applied membrane was dried at 40°C for 10 seconds and then at 70°C for 10 seconds or more to remove water, and a 4 μm thick inorganic filler porous layer (layer density: 1.5 g/(m A multilayer porous membrane B1-1 having a total thickness of 15 μm and having a total thickness of ² μm) was obtained. The obtained multilayer porous membrane was evaluated as described above. The results obtained are shown in Table 2.

[Production example 2-2]
A multilayer porous membrane B1-2 was obtained in the same manner as Production Example 2-1 except that aluminum oxide was used as the inorganic filler. This multilayer porous membrane was evaluated in the same manner as in Production Example 2-1. The results obtained are shown in Table 2.

[Production example 2-3]
A multilayer porous membrane B1-3 was obtained in the same manner as Production Example 2-1 except that aluminum hydroxide oxide of plate-like particles was used. This multilayer porous membrane was evaluated in the same manner as in Production Example 2-1. The results obtained are shown in Table 2.

[Production example 2-4]
A multilayer porous membrane B2-1 was obtained in the same manner as Production Example 2-1 except that the polyolefin microporous membrane B2 was used. This multilayer porous membrane was evaluated in the same manner as in Production Example 2-1. The results obtained are shown in Table 2.

<Synthesis of particulate polymer>
(Production Example A1) Synthesis of aqueous dispersion (denoted as "raw material polymer" in the table. The same applies hereinafter) A1 A reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer was charged with 70% of ion-exchanged water. 4 parts by mass, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd., indicated as "KH1025" in the table. The same applies hereinafter), and "Adecaria Soap SR1025" ( (registered trademark, manufactured by ADEKA Co., Ltd., 25% aqueous solution, indicated as "SR1025" in the table. The same applies hereinafter) was added, and the internal temperature of the reaction vessel was raised to 80°C. Thereafter, while maintaining the internal temperature of the container at 80° C., 7.5 parts by mass of ammonium persulfate (2% aqueous solution) (denoted as “APS (aq)” in the table, the same applies hereinafter) was added.

On the other hand, 38.5 parts by mass of methyl methacrylate, 19.6 parts by mass of n-butyl acrylate, 31.9 parts by mass of 2-ethylhexyl acrylate, 0.1 part by mass of methacrylic acid, 0.1 part by mass of acrylic acid, methacrylate 2 parts by mass of 2-hydroxyethyl acid, 5 parts by mass of acrylamide, 2.8 parts by mass of glycidyl methacrylate, 3 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), "Adecaria Soap"SR1025'' (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) 3 parts by mass, sodium p-styrene sulfonate 0.05 parts by mass, trimethylolpropane triacrylate (manufactured by Shin Nakamura Chemical Co., Ltd.) 0.7 parts by mass, A mixture of 0.3 parts by mass of γ-methacryloxypropyltrimethoxysilane, 7.5 parts by mass of ammonium persulfate (2% aqueous solution), and 52 parts by mass of ion-exchanged water was mixed for 5 minutes with a homomixer to form an emulsion. Created.
The obtained emulsion was dropped into the reaction vessel from the dropping tank. Dripping started 5 minutes after adding the aqueous ammonium persulfate solution to the reaction vessel, and the entire amount of the emulsion was added dropwise over 150 minutes. During the dropping of the emulsion, the internal temperature of the container was maintained at 80°C.

After the emulsion was added dropwise, the internal temperature of the reaction vessel was maintained at 80° C. for 90 minutes, and then cooled to room temperature to obtain an emulsion. The obtained emulsion was adjusted to pH=9.0 using an ammonium hydroxide aqueous solution (25% aqueous solution) to obtain an acrylic copolymer latex with a concentration of 40% by mass (raw material polymer A1). The obtained raw material polymer (aqueous dispersion) A1 was evaluated by the above method. The results obtained are shown in Table 3.

(Production Example A2) Synthesis of water dispersion A2 The same procedure as for raw material polymer (water dispersion) A1 was carried out, except that the compositions of the monomers and other raw materials were changed as shown in Table 3. A copolymer latex (raw material polymer A2) was obtained. The obtained raw material polymer (aqueous dispersion) A2 was evaluated by the above method. The results obtained are shown in Table 3.

The abbreviations of raw material names in Table 3 and Table 4 described later have the following meanings, respectively.
<Emulsifier>
KH1025: "Aqualon KH1025" registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% aqueous solution SR1025: "Adekaria Soap SR1025" registered trademark, manufactured by ADEKA Co., Ltd., 25% aqueous solution NaSS: Sodium p-styrene sulfonate <initiator ＞
APS (aq): ammonium persulfate (2% aqueous solution)
<Monomer>
((meth)acrylic acid monomer)
MAA: Methacrylic acid AA: Acrylic acid ((meth)acrylic acid ester)
MMA: Methyl methacrylate BA: n-butyl acrylate EHA: 2-ethylhexyl acrylate CHMA: cyclohexyl methacrylate (cyano group-containing monomer)
AN: Acrylonitrile (other functional group-containing monomers)
HEMA: 2-hydroxyethyl methacrylate AM: Acrylamide (crosslinkable monomer)
GMA: Glycidyl methacrylate A-TMPT: Trimethylolpropane triacrylate AcSi: γ-methacryloxypropyltrimethoxysilane

(Manufacturing example A2-1)
Aqueous dispersion A2-1 was synthesized by taking a portion of aqueous dispersion A2 obtained in Production Example A2 and performing multistage polymerization using this as a seed polymer. Specifically, first, 16 parts by mass of water dispersion A2 in terms of solid content and 0.5 parts by mass of Aqualon KH1025 (registered trademark) were placed in a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer. A mixture of 0.5 parts by mass, 0.5 parts by mass of Adekaria Soap SR1025 (registered trademark), and 70.4 parts by mass of ion-exchanged water was added, and the internal temperature of the reaction vessel was raised to 80°C. Thereafter, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) was added while maintaining the internal temperature of the container at 80°C. The above is the initial preparation.

On the other hand, 10 parts by mass of 2-ethylhexyl acrylate, 33 parts by mass of cyclohexyl methacrylate, 1 part by mass of methacrylic acid, 1 part by mass of acrylic acid, 55 parts by mass of acrylonitrile, 2 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution) , 1 part by mass of trimethylolpropane triacrylate, 0.5 parts by mass of γ-methacryloxypropyltrimethoxysilane, 7.5 parts by mass of ammonium persulfate (2% aqueous solution), and 52 parts by mass of ion-exchanged water in a homomixer. The mixture was mixed for 5 minutes to prepare an emulsion. The obtained emulsion was dropped into the reaction vessel from the dropping tank. Dripping started 5 minutes after adding the aqueous ammonium persulfate solution to the reaction vessel, and the entire amount of the emulsion was added dropwise over 150 minutes. During the dropping of the emulsion, the internal temperature of the container was maintained at 80°C.

After the emulsion was added dropwise, the internal temperature of the reaction vessel was maintained at 80° C. for 90 minutes, and then cooled to room temperature to obtain an emulsion. The resulting emulsion was adjusted to pH=9.0 using an ammonium hydroxide aqueous solution (25% aqueous solution) to obtain an acrylic copolymer latex with a concentration of 40% by mass (raw material polymer A2-1). The obtained raw material polymer A2-1 was evaluated by the above method.

(Manufacturing example A2-2)
Each copolymer latex was produced by multistage polymerization in the same manner as raw material polymer (aqueous dispersion) A1-1, except that the compositions of the seed polymer, monomer, and other raw materials were changed as shown in Table 3. I got it. Each of the obtained raw material polymers (aqueous dispersion) was evaluated by the above method.

[Example 1]
A coating liquid (solid content: 30% by mass) containing a thermoplastic polymer was prepared by uniformly dispersing water dispersion A2-2 and water dispersion A1 in water so that the solid content was 80:20. At this time, as the post-added surfactant C1-1, Olfine SK-14 (manufactured by Nissin Chemical Industry Co., Ltd.), which is an acetylene surfactant containing hydrophobic silica particles and mineral oil, is solidified against the coating liquid. A slurry for a separator was prepared by adding it to a proportion of 0.7% by mass.
Then, a coating liquid was applied to one side (side (A)) of the microporous polyolefin membrane B1-1 using a gravure coater. At this time, the ratio of the area covered by the thermoplastic polymer to the polyolefin microporous membrane was 20%. Thereafter, the coating liquid after coating was dried at 40° C. to remove water.
Furthermore, the coating liquid was similarly applied to the surface (surface (B)) opposite to the surface (A) of the microporous polyolefin membrane B1-1, and the same was dried again in the same manner as above. In this way, a separator was obtained in which thermoplastic polymer layers were formed on both sides of the polyolefin microporous membrane B1.

[Example 2]
Same as Example 1 except that the amount of Olfine SK-14 was 1.7% by mass based on the coating liquid, and the mixing ratio of the hydrophobic silica filler was as shown in Table 5. A slurry and a separator were prepared.

[Example 3]
Same as Example 1 except that Olfine SK-14 was added in an amount of 0.2% by mass based on the coating liquid, and the mixing ratio of the hydrophobic silica filler was as shown in Table 5. A slurry and a separator were prepared.

[Example 4]
Except that instead of Olfin SK-14, Olfin AF-103 (manufactured by Nissin Chemical Industry Co., Ltd.) as a post-added surfactant C1-2 was added to the coating solution at a concentration of 0.7% by mass. A slurry and a separator were prepared in the same manner as in Example 1.

[Example 5]
Instead of Olfine SK-14, Olfine AF-103 (manufactured by Nissin Chemical Industry Co., Ltd.) as a post-added surfactant C1-2 was added to the coating solution in an amount of 1.7% by mass, Further, a slurry and a separator were prepared in the same manner as in Example 1, except that the mixing ratio of the hydrophobic silica filler was changed as shown in Table 5.

[Example 6]
Instead of Olfine SK-14, E-F010 (manufactured by San Nopco Co., Ltd.) was added to the coating solution at a concentration of 1.7% by mass, and the mixing ratio of hydrophobic silica filler was as shown in Table 5. A slurry and a separator were produced in the same manner as in Example 1, except that

[Comparative example 1]
Slurry, A separator was also produced. Note that E-1004 is an acetylene surfactant and does not contain hydrophobic silica filler.

[Comparative example 2]
Slurry, A separator was also produced.

[Comparative example 3]
A slurry and a separator were prepared in the same manner as in Example 1, except that E-D052 (manufactured by San Nopco Co., Ltd.) was added to the coating solution in an amount of 1.7% by mass instead of Olfine SK-14. Created. Note that E-D052 is a polyether surfactant and does not contain hydrophobic silica filler.

[Comparative example 4]
A slurry and a separator were prepared in the same manner as in Example 1, except that BYK-349 (manufactured by BYK-Chemie Co., Ltd.) was added to the coating solution in an amount of 0.7% by mass instead of Olfine SK-14. Created. Note that BYK-349 is a silicone surfactant and does not contain hydrophobic silica filler.

[Comparative example 5]
A slurry and a separator were prepared in the same manner as in Example 1, except that BYK-349 (manufactured by BYK-Chemie Co., Ltd.) was added to the coating solution in an amount of 1.7% by mass instead of SK-14. did.

As can be seen from Table 5, all of Examples 1 to 6 have superior defoaming properties, can suppress the increase in dynamic surface tension of the slurry, and have better wettability of the base material than Comparative Examples 1 to 5. was also good. Furthermore, it was confirmed that all of Examples 1 to 6 had excellent binding properties between the base material and the thermoplastic polymer layer, and good adhesion to the electrodes.
Therefore, it was confirmed that Examples 1 to 6 provided a separator slurry that had excellent coatability on the substrate and was capable of satisfactorily suppressing the occurrence of pinholes and cissing. Furthermore, Examples 1 to 6 provide a separator for power storage devices that is equipped with a thermoplastic polymer layer that effectively suppresses the occurrence of pinholes and repelling, and also exhibits good adhesive function. confirmed.

Table 6 shows the results for a separator containing a thermoplastic polymer layer and a multilayer porous membrane prepared using the slurry shown in the example.

In addition, in Table 6, the thickness of the thermoplastic polymer layer is determined from the value obtained by the same method as described in the "Substrate thickness" column above, using the thermoplastic polymer layer as the measurement target. It was calculated by subtracting the thickness of the porous membrane.

Claims (15)

A thermoplastic polymer layer used for coating a substrate containing a microporous polyolefin membrane and formed on at least one surface of the substrate (provided that there is no arbitrary layer between the substrate and the thermoplastic polymer layer). a slurry for forming a slurry (without excluding embodiments comprising a layer) ,
A thermoplastic polymer containing a particulate polymer and an antifoaming agent containing an inorganic filler,
When the thermoplastic polymer is 100 parts by mass, the inorganic filler is contained in a proportion of 0.001 parts by mass or more and less than 1 part by mass,
A slurry for a separator, wherein the inorganic filler contained in the slurry is only the inorganic filler contained as the antifoaming agent . A separator slurry for use in the thermoplastic polymer layer of a separator comprising a base material containing a microporous polyolefin membrane and a thermoplastic polymer layer covering at least a portion of at least one surface of the base material,
The slurry for a separator according to claim 1, wherein the thermoplastic polymer layer is a layer containing an inorganic filler in a proportion of 0.001 parts by mass or more and less than 1 part by mass when the thermoplastic polymer is 100 parts by mass. The slurry for a separator according to claim 1 or 2, wherein the slurry has a viscosity of less than 3500 mPa·s. The slurry for a separator according to any one of claims 1 to 3, wherein the thermoplastic polymer contains a copolymer consisting of units of (meth)acrylic acid ester monomer. The thermoplastic polymer layer includes two or more thermoplastic polymers having mutually different glass transition temperatures,
At least one of the thermoplastic polymers has a glass transition temperature of less than 20°C,
The slurry for a separator according to any one of claims 1 to 4, wherein at least one of the thermoplastic polymers has a glass transition temperature in a range of 20°C or higher. The thermoplastic polymer layer includes two or more thermoplastic polymers having different glass transition temperatures,
At least one of the thermoplastic polymers has a glass transition temperature of less than 20°C,
The slurry for a separator according to any one of claims 1 to 5, wherein at least one of the thermoplastic polymers has a glass transition temperature in a range of 50°C or higher. The slurry for a separator according to any one of claims 1 to 6, wherein the inorganic filler is hydrophobic silica particles. The slurry for a separator according to any one of claims 1 to 7, wherein the slurry has a defoaming time measured by a diffuser stone method of less than 50 seconds. The slurry for a separator according to any one of claims 1 to 8, wherein the slurry has a surface tension of less than 45 mN/m at a surface life of 10 ms. A base material comprising a microporous polyolefin membrane, and a thermoplastic polymer layer covering at least a portion of at least one surface of the base material,
When the thermoplastic polymer in the thermoplastic polymer layer is 100 parts by mass, it contains an inorganic filler in a proportion of 0.001 parts by mass or more and less than 1 part by mass,
A separator for an electricity storage device, wherein the inorganic filler in the thermoplastic polymer layer is only the inorganic filler contained as an antifoaming agent . 11. The power storage device according to claim 10, wherein an area ratio of the base material covered with the thermoplastic polymer layer is 95% or less with respect to 100% of the total surface area on which the thermoplastic polymer layer is arranged. Separator. The separator for an electricity storage device according to claim 10 or 11, wherein the thermoplastic polymer includes a copolymer consisting of units of (meth)acrylic acid ester monomer. The thermoplastic polymer layer includes two or more thermoplastic polymers having different glass transition temperatures,
At least one of the thermoplastic polymers has a glass transition temperature of less than 20°C,
The separator for a power storage device according to any one of claims 10 to 12, wherein at least one of the thermoplastic polymers has a glass transition temperature in a region of 20° C. or higher. The separator for an electricity storage device according to any one of claims 10 to 13, wherein the inorganic filler is a hydrophobic silica filler. The separator for an electricity storage device according to any one of claims 10 to 14, comprising an inorganic filler porous layer at least in a portion between at least one surface of the base material and the thermoplastic polymer layer.