JP7071310B2 - Slurry for separators for power storage devices and separators using them - Google Patents

Description

The present invention relates to a slurry for coating a substrate to obtain a separator, and a separator for a power storage device provided with a thermoplastic polymer layer obtained by using the slurry.

Conventionally, the development of power storage devices represented by lithium ion secondary batteries has been actively carried out. Usually, the power storage device is provided with a separator having a base material between the positive electrode and the negative electrode. The separator has a function of preventing direct contact between the positive electrode and the negative electrode and allowing ions to permeate through the electrolytic solution held in the microporous.

The separator has the characteristic of quickly stopping the battery reaction when abnormally heated (fuse characteristic), and the ability to maintain the shape even at high temperatures and prevent the dangerous situation where the positive and negative electrodes directly react (short characteristic). Performance related to safety is required. Further, for the purpose of increasing the capacity of the power storage device, a technique is used in which a wound body in which a laminated body of an electrode and a separator is wound is hot-pressed to reduce the volume of the wound body. In order to fix the electrode and the 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 arranged on the substrate to form a separator, and the separator and the electrode are formed. A technique for improving the adhesiveness with the material is also used.

As the slurry for producing the thermoplastic polymer layer, a water-soluble polymer or a water-insoluble particulate polymer is used, and among them, the water-insoluble particulate polymer obtained by emulsion polymerization is preferable. It is used. As such a slurry, for example, the slurry described in Patent Documents 1 and 2 is known. In addition, the slurry described in Patent Document 3 is also known.

International Publication No. 2017/169848 International Publication No. 2016/123404 International Publication No. 2014/017651

However, in Patent Documents 1 and 2, the slurry coated on the microporous polyolefin membrane has not been studied, and in Patent Document 3, the viewpoint of suppressing the generation of bubbles in the slurry has not been studied. Therefore, in Patent Documents 1 to 3, when the surface tension of the slurry is higher than that of the base material, the wettability is poor and cissing occurs, so that a large number of defects (pins) are formed in the thermoplastic polymer layer obtained on the base material. Holes) may occur. Further, since the slurry for producing the thermoplastic polymer layer is easily foamed, when the thermoplastic polymer layer is formed using the slurry, a large number of defects (pinholes) are formed in the thermoplastic polymer layer due to the bubbles in the slurry. May occur. In recent years, it has been desired to be able to suppress the occurrence of pinholes and repellents more satisfactorily than expected in the prior art including Patent Documents 1 to 3.

Therefore, an object of the present invention is to provide a slurry for a separator which is excellent in coatability on a base material and can satisfactorily suppress the generation of pinholes and cissing. Another object of the present invention is to provide a separator for a power storage device, which has a thermoplastic polymer layer in which the generation of pinholes and cissing is well suppressed and can improve the electrical characteristics of a power storage device represented by a secondary battery. And.

The present inventors have studied to solve the above-mentioned problems, and have found that the above-mentioned problems can be solved by using a slurry for a separator having the following constitution, and have completed the present invention. That is, the present invention is as follows.
[1]
A slurry used for coating a substrate containing a microporous polyolefin membrane.
It contains a thermoplastic polymer containing a particulate polymer and an acetylene-based surfactant.
A separator slurry containing 0.001 part by mass or more and 10 parts by mass or less of the acetylene-based surfactant when the thermoplastic polymer is 100 parts by mass.
[2]
The slurry for a separator according to [1], wherein the slurry contains the acetylene-based surfactant in a proportion of 0.01 parts by mass or more and 5 parts by mass or less when the thermoplastic polymer is 100 parts by mass.
[3]
The separator according to [1] or [2], wherein the slurry contains the acetylene-based surfactant in a proportion of 0.1 parts by mass or more and 3 parts by mass or less when the thermoplastic polymer is 100 parts by mass. slurry.
[4]
The separator slurry according to any one of [1] to [3], wherein the slurry has a viscosity of less than 3500 mPa · s.
[5]
The separator slurry according to any one of [1] to [4], wherein the slurry has a viscosity of less than 350 mPa · s.
[6]
The slurry for a separator according to any one of [1] to [5], wherein the thermoplastic polymer contains a copolymer composed of a unit of a (meth) acrylic acid ester monomer.
[7]
The thermoplastic polymer has at least two glass transition temperatures and
At least one of the glass transition temperatures is present in the region below 20 ° C.
The separator slurry according to any one of [1] to [6], wherein at least one of the glass transition temperatures is present in a region of 20 ° C. or higher.
[8]
Item 2. The separator according to any one of [1] to [7], wherein the slurry contains an inorganic filler in a proportion of 0.001 part by mass or more and less than 1 part by mass when the thermoplastic polymer is 100 parts by mass. Slurry for.
[9]
It has a substrate containing a microporous polyolefin membrane and a thermoplastic polymer layer that covers at least a portion of at least one surface of the substrate.
A separator for a power storage device containing 0.001 part by mass or more and 10 parts by mass or less of an acetylene-based surfactant when the amount of the thermoplastic polymer in the thermoplastic polymer layer is 100 parts by mass.
[10]
The storage device according to [9], wherein the thermoplastic polymer layer contains the acetylene-based surfactant in a proportion of 0.01 parts by mass or more and 5 parts by mass or less when the thermoplastic polymer is 100 parts by mass. Separator.
[11]
[9] or [10], wherein the thermoplastic polymer layer contains the acetylene-based surfactant in a proportion of 0.1 parts by mass or more and 3 parts by mass or less when the thermoplastic polymer is 100 parts by mass. Separator for power storage devices.
[12]
[9] to [11], wherein the area ratio of the base material covered with the thermoplastic polymer layer is 95% or less with respect to the total area of 100% of the surface on which the thermoplastic polymer layer is arranged. The separator for a power storage device according to any one of the above items.
[13]
Any of claims 9 to 12, wherein the area ratio of the base material covered with the thermoplastic polymer layer is 80% or less with respect to the total area of 100% of the surface on which the thermoplastic polymer layer is arranged. The separator for a power storage device according to item 1.
[14]
The separator for a power storage device according to any one of [9] to [13], wherein the thermoplastic polymer contains a copolymer composed of a unit of a (meth) acrylic acid ester monomer.
[15]
The thermoplastic polymer has at least two glass transition temperatures and
At least one of the glass transition temperatures is present in the region below 20 ° C.
The separator for a power storage device according to any one of [9] to [14], wherein at least one of the glass transition temperatures is present in a region of 20 ° C. or higher.
[16]
Item 6. The separator for the storage device described.

According to the present invention, it is possible to reduce the surface tension on the surface to be coated while suppressing the foaming of the slurry, and therefore, the coating property on the substrate is excellent, and the generation of pinholes and cissing is satisfactorily suppressed. It is possible to provide a slurry for a separator which can be used. Further, according to the present invention, it is possible to provide a separator for a power storage device in which the generation of pinholes and cissing is satisfactorily suppressed.

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

<Slurry for separator>
(Particulate polymer)
The separator slurry according to the present embodiment (hereinafter, also simply referred to as “slurry”) is used for producing a separator for a power storage device (hereinafter, also simply referred to as “separator”) according to the present embodiment. The slurry contains a thermoplastic polymer, and the thermoplastic polymer contains a particulate polymer. Since the thermoplastic polymer contains the particulate polymer, it is possible to achieve both excellent adhesive strength to the electrode and ion permeability. In the present specification.

Specific examples of the particulate polymer (for example, a water-insoluble particulate polymer) include an acrylic polymer, a conjugated diene polymer, a polyvinyl alcohol resin, and a fluororesin. Above all, an acrylic polymer is preferable from the viewpoint of more effectively and surely exerting the action and effect of the present invention. Further, an acrylic polymer and a fluororesin are preferable from the viewpoint of withstand voltage, and a conjugated diene polymer is also preferable from the viewpoint of easy compatibility with an electrode. Further, from the viewpoint of more effectively and surely exerting the action and effect of the present invention, it is preferable that the particulate polymer contains a particulate copolymer.

The particulate polymer is preferably used in combination of two or more different types from each other. That is, it is preferable that the slurry contains two or more kinds of thermoplastic polymers different from each other.
By preparing the thermoplastic polymer layer using a slurry containing two or more kinds of thermoplastic polymers different from each other, the thermoplastic polymer layer contains two or more kinds of thermoplastic polymers different from each other.

The thermoplastic polymer contains a particulate polymer in an amount of preferably 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 thereof. The thermoplastic polymer layer may contain a polymer other than the particulate polymer to the extent that the effect of the present invention is not impaired.

The conjugated diene-based 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-chlor-1,3-butadiene, and substituted linear conjugated. Examples thereof include pentadiene, substitution, and side chain conjugated hexadiene, which may be used alone or in combination of two or more. Of these, 1,3-butadiene is particularly preferable. Further, the conjugated diene-based polymer may contain a (meth) acrylic compound or another monomer described later as a monomer unit. Examples of such monomers include styrene-butadiene copolymers and hydrides thereof, acrylonitrile-butadiene copolymers and hydrides thereof, acrylonitrile-butadiene-styrene copolymers thereof, and hydrides thereof. Be done.

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

The acrylic polymer is a polymer having a (meth) acrylic compound as a monomer unit, that is, a polymerization unit. The (meth) acrylic compound refers to at least one selected from the group consisting of (meth) acrylic acid and (meth) acrylic acid ester. Examples of such a compound include a compound represented by the following formula.
CH ₂ = CR ^Y1 -COO-R ^Y2
In the formula, ^RY1 represents a hydrogen atom or a methyl group, and ^RY2 represents a hydrogen atom or a monovalent hydrocarbon group. When ^RY2 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 hetero atom include a halogen atom and an oxygen atom.
The (meth) acrylic compound may be used alone or in combination of two or more. Examples of such (meth) acrylic compounds include (meth) acrylic acid, chain alkyl (meth) acrylate, cycloalkyl (meth) acrylate, (meth) acrylate having a hydroxyl group, and phenyl group-containing (meth) acrylate. Can be mentioned.

As a chain alkyl group which is a kind of ^RY2 , specifically, a chain alkyl group having 1 to 3 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group; n-butyl. Examples thereof include a group, an isobutyl group, a t-butyl group, an n-hexyl group, a 2-ethylhexyl group; and a chain alkyl group having 4 or more carbon atoms such as a lauryl group. Moreover, as an aryl group which is one kind of ^RY2 , for example, a phenyl group can be mentioned. Specific examples of the (meth) acrylic acid ester monomer having ^RY2 include, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, and n-hexyl. Chains such as acrylates, 2-ethylhexyl acrylates, lauryl acrylates, methyl methacrylates, ethyl methacrylates, propyl methacrylates, isopropyl methacrylates, butyl methacrylates, isobutyl methacrylates, t-butyl methacrylates, n-hexyl methacrylates, 2-ethylhexyl methacrylates, and lauryl methacrylates. Examples thereof include (meth) acrylates having a lylic alkyl group; and (meth) acrylates having an aromatic ring such as phenyl (meth) acrylates and benzyl (meth) acrylates.

Above all, from the viewpoint of improving the adhesiveness of the separator to the electrode (electrode active material), a monomer having a chain alkyl group having 4 or more carbon atoms, more specifically, a chain having ^RY2 having 4 or more carbon atoms. A (meth) acrylic acid ester monomer which is a state alkyl group is preferable. More specifically, at least one selected from the group consisting of butyl acrylate, butyl methacrylate, and 2-ethylhexyl acrylate is preferable. 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 7 is preferable. These (meth) acrylic acid ester monomers are used alone or in combination of two or more.

The (meth) acrylic acid ester monomer may contain a monomer having a cycloalkyl group as ^RY2 in place of or in addition to the monomer having a chain alkyl group having 4 or more carbon atoms. preferable. This also further improves the adhesiveness of the separator to the electrode. More specific examples of the monomer having such a cycloalkyl group include cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and adamantyl (meth) acrylate. The number of carbon atoms constituting the alicyclic of the cycloalkyl group is preferably 4 to 8, more preferably 6 to 7, and particularly preferably 6. Further, the cycloalkyl group may or may not have a substituent. Examples of the substituent include a methyl group and a t-butyl group. Among them, at least one selected from the group consisting of cyclohexyl acrylate and cyclohexyl methacrylate is preferable in that the polymerization stability at the time of preparing the acrylic polymer is good. These may be used alone or in combination of two or more.

The acrylic polymer preferably contains, as the (meth) acrylic acid ester monomer, a crosslinkable monomer in place of or in addition to the above, preferably in addition to the above. Examples of the crosslinkable monomer include a monomer having two or more radically polymerizable double bonds, a monomer having a functional group that gives 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. Examples thereof include dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These may be used alone or in combination of two or more. Above all, from the same viewpoint as above, at least one of trimethylolpropane triacrylate or trimethylolpropane trimethacrylate is preferable.

Examples of the monomer having a functional group that gives a self-crosslinking structure during or after the polymerization include a monomer having an epoxy group, a monomer having a methylol group, a monomer having an alkoxymethyl group, and hydrolysis. Examples thereof include a monomer having a sex 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 thereof include 4-epoxide cyclohexyl (meth) acrylate and allyl glycidyl ether.

Examples of the monomer having a methylol group include N-methylolacrylamide, N-methylolmethacrylamide, dimethylolacrylamide, and dimethylolmethacrylamide. As the monomer having an alkoxymethyl group, an ethylenically unsaturated monomer having an alkoxymethyl group is preferable, and specifically, for example, N-methoxymethylacrylamide, N-methoxymethylmethacrylate, and N-butoxymethylacrylamide. , And N-butoxymethylmethacrylamide. Examples of the monomer having a hydrolyzable silyl group include vinylsilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyl. Triethoxysilane can be mentioned. These may be used alone or in combination of two or more.

The acrylic polymer may further have a monomer other than the above as a monomer unit in order to improve various qualities and physical properties. Examples of such a monomer include a monomer having a carboxyl group (excluding (meth) acrylic acid), a monomer having an amide group, a monomer having a cyano group, and a hydroxyl group. Examples thereof include a monomer having and an aromatic vinyl monomer (excluding divinylbenzene). Further, various vinyl-based monomers having a functional group such as a sulfonic acid group or a phosphoric acid group, and vinyl acetate, vinyl propionate, vinyl versatic acid, vinylpyrrolidone, methylvinyl ketone, butadiene, ethylene, propylene, chloride. Vinyl and vinylidene chloride are also used as needed. These may be used alone or in combination of two or more. Further, such other monomers may belong to two or more of the above-mentioned monomers at the same time.

Examples of the monomer 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 specific examples thereof include (meth) acrylonitrile. Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate.

Examples of the aromatic vinyl monomer include styrene, vinyltoluene, and α-methylstyrene. Styrene is preferable.

The ratio of the acrylic polymer having the (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 with respect to 100% by mass of the acrylic polymer. The lower limit is more preferably 15% by mass, still more preferably 20% by mass, and particularly preferably 30% by mass. When the content ratio of the monomer unit is 5% by mass or more, it is preferable in terms of binding property to the substrate and oxidation resistance. On the other hand, a more preferable upper limit value is 92% by mass, a further preferable upper limit value is 80% by mass, and a particularly preferable upper limit value is 60% by mass. When the content ratio of the monomer is 95% by mass or less, the adhesiveness to the substrate is improved, which is preferable.

When the acrylic polymer has chain alkyl (meth) acrylate or cycloalkyl (meth) acrylate as a monomer unit, the total content ratio thereof is preferably 100% by mass of the acrylic polymer. It 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, further preferably 15% by mass or more and 75% by mass or less, and particularly preferably 25% by mass or more and 55% by mass or less. When the content ratio of these monomers is 3% by mass or more, it is preferable from the viewpoint of improving the oxidation resistance, and when it is 92% by mass or less, the binding property to the substrate is improved, which is preferable.

When the acrylic polymer has (meth) acrylic acid as a monomer unit, the content ratio thereof is preferably 0.1% by mass or more and 5% by mass or less with respect to 100% by mass of the acrylic polymer. .. When the content ratio of the above-mentioned monomer is 0.1% by mass or more, the separator tends to improve the cushioning property in the swollen state, and when it is 5% by mass or less, the polymerization stability tends to be good. be.

When the acrylic polymer has a crosslinkable monomer as a monomer unit, the content ratio of the crosslinkable monomer in the acrylic polymer is preferably 0. With respect to 100% by mass of the acrylic polymer. It is 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 further preferably 0.1% by mass or more and 3% by mass or less. When the content ratio of the monomer is 0.01% by mass or more, the electrolytic solution resistance is further improved, and when it is 10% by mass or less, the deterioration of the cushioning property in the swollen state can be further suppressed.

As the acrylic polymer, any of the following aspects is preferable. The content ratios of the following copolymers are all values based on 100% by mass of the copolymer.
(1) A copolymer having a (meth) acrylic acid ester as a monomer unit (however, the copolymer of (2) and the copolymer of (3) below are excluded). 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 one selected from the group consisting of monomers having a hydroxyl group, 15% by mass or less (more preferably 10% by mass or less), and 10% by mass or less of the crosslinkable monomer (more preferably 0.01). A copolymer of% 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 a monomer unit. 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, still more preferably 25% by mass or more and 80% by mass or less, and particularly preferably 40% by mass or more and 60% by mass. (Mass% or less), (meth) acrylic acid 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 5% by mass or more and 95% by mass or less (more preferably). It has a monomer having an amide group and a cyano group, more preferably 15% by mass or more and 85% by mass or less, further preferably 20% by mass or more and 80% by mass or less, and particularly preferably 30% by mass or more and 75% by mass or less. At least one selected from the group consisting of a monomer and a monomer having a hydroxyl group is 10% by mass or less (more preferably 5% by mass or less) and a crosslinkable monomer 10% by mass or less (more preferably). A copolymer of 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, the monomer having a cyano group is 1% by mass or more and 95% by mass or less (more preferably 5% by mass or more and 90% by mass or less, still 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 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, 10% by mass. % 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 a copolymer of.

In the above-mentioned copolymer (2), it is preferable to have a (meth) acrylic acid hydrocarbon ester as the (meth) acrylic acid ester monomer. In this case, the copolymerization ratio of the (meth) acrylic acid hydrocarbon ester is preferably 0.1% by mass or more and 5% by mass or less. When the copolymer of (2) above has a monomer having an amide group, the copolymerization ratio thereof is preferably 0.1% by mass or more and 5% by mass or less. Further, when the copolymer of the above (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) acrylates and cycloalkyl (meth) acrylates as the (meth) acrylic acid 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 the chain alkyl (meth) acrylate in the copolymer of (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 further preferably 5% by mass. It is 85% by mass or less. The upper limit of the copolymerization ratio may be 60% by mass, particularly 40% by mass or 30% by mass, and particularly preferably 20% by mass. The copolymerization ratio of cyclohexylalkyl (meth) acrylate in the copolymer of (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 further preferably 5% by mass or more. It is 85% by mass or less. The upper limit of the copolymerization ratio may be 60% by mass, particularly 50% by mass, and particularly preferably 40% by mass. When the copolymer of (3) above has a monomer having an amide group, the copolymerization ratio 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. Further, when the copolymer of the above (3) has a monomer having a hydroxyl group, the copolymerization ratio 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.

Surfactants are compounds having at least one hydrophilic group and one or more lipophilic groups in one molecule. As the surfactant, a polyether surfactant is preferable. The surfactant here is added as a raw material when the particulate polymer is polymerized, and is different from the post-added surfactant added after the polymerization reaction. The surfactant will be described later.
The radical polymerization initiator is one that radically decomposes with a heat or a reducing substance to initiate addition polymerization of the monomer. The radical polymerization initiator will be described later.

Among the forms of thermoplastic polymers, monomers are used from the viewpoint of improving the adhesiveness between the separator and the electrode, the high temperature storage property of the power storage device, and the cycle property, and achieving the thinning of the adhesive between the electrode and the separator. Acrylic copolymer latex formed from an emulsion containing an emulsifier, an initiator and water is preferred.

The glass transition temperature (Tg) of the particulate polymer is preferably −50 ° C. or higher, more preferably −30 ° C. or higher, still more preferably 20 ° C. or higher, from the viewpoint of adhesion to the electrode and ion permeability. It is also preferably 40 ° C. or higher. 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 the DSC curve obtained by differential scanning calorimetry (DSC). Specifically, for a straight line in which the baseline on the low temperature side of the DSC curve is extended to the high temperature side and a straight line in which the baseline on the high temperature side in the DSC curve is extended to the low temperature side at equal distances in the vertical axis direction. The temperature at the point where the curve of the change portion on the stage of the glass transition intersects can be adopted as the glass transition temperature. More specifically, it may be determined according to the method described in the examples. Further, "glass transition" refers to a DSC in which a change in heat flow rate due to a change in the state of a polymer as a test piece occurs on the endothermic side. Such changes in heat flow are observed as the shape of stepped changes in the DSC curve. The “step change” refers to the portion of the DSC curve until the curve departs from the previous baseline on the low temperature side and shifts to a new baseline on the high temperature side. In addition, the combination of the step-like change and the peak is also included in the step-like change. Further, in the stepped change portion, when the upper side is the heat generating side, it can be expressed as a point where the upwardly convex curve changes to the downwardly convex curve. “Peak” refers to the portion of the DSC curve from when the curve leaves the baseline on the cold side until it returns to the same baseline again. "Baseline" refers to the DSC curve in the temperature range where no transition or reaction occurs on the test piece.

The glass transition temperature Tg of the particulate polymer is, for example, the type of monomer used when producing the particulate polymer, and the compounding ratio of each monomer when the particulate polymer is a copolymer. By changing it, it can be adjusted as appropriate. That is, for each monomer used in the production of the particulate polymer, the Tg of the homopolymer generally shown (eg, described in the "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the monomer. The approximate glass transition temperature can be estimated from the compounding ratio. For example, a copolymer obtained by copolymerizing a monomer such as methylmethacrylate, acrylicnitrile, and methacrylic acid which gives a homopolymer of Tg at about 100 ° C. at a high ratio increases the Tg of about -50 ° C. The Tg of a copolymer obtained by copolymerizing a monomer such as n-butylacryllate and 2-ethylhexylacryllate, which give a homopolymer of Tg, at a high ratio is low.
Further, the Tg of the copolymer can be roughly estimated by the formula of FOX represented by the following formula (1).
1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ + ... + _{Wi / Tg i +} ... W _n / Tg _n (1)
Here, in the formula, Tg (K) is the Tg of the copolymer, Tg _i (K) is the Tg of the homopolymer of the monomer i, and Wi _i is the mass fraction of each monomer. ..
However, as the glass transition temperature Tg of the particulate polymer in this embodiment, the value measured by the method using the DSC is adopted.

From the viewpoint of wettability to the substrate, adhesion between the substrate and the thermoplastic polymer layer, and adhesion to the electrode, the thermoplastic polymer layer contains a polymer having a glass transition temperature of less than 40 ° C. Is preferable. 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, still more preferably −40 ° C. or higher, and the substrate and heat. From the viewpoint of binding to the plastic polymer layer, the temperature is preferably less than 20 ° C, more preferably less than 15 ° C, still more preferably less than −10 ° C.

The particulate polymer preferably has at least two glass transition temperatures. That is, it is preferable that the thermoplastic polymer layer contains two or more kinds of thermoplastic polymers having different glass transition temperatures. Examples of the method for allowing the particulate polymer to have at least two glass transition temperatures include a method of blending two or more kinds of particulate polymers and a method of using a particulate polymer having a core-shell structure. The core-shell structure is a structure having a central portion and an outer shell portion that covers the central portion, and is a polymer in the form of a double structure in which the types or compositions of the polymers constituting the respective portions are different from each other. .. In particular, in the polymer blend and the core-shell structure, the glass transition temperature of the entire particulate polymer can be controlled by combining a polymer having a high glass transition temperature and a polymer having a low glass transition temperature. In addition, a plurality of functions can be imparted to the entire particulate polymer.

For example, when two or more kinds of particulate polymers are blended, one or more polymers having a glass transition temperature of 20 ° C. or higher and one or more polymers having a glass transition temperature of less than 20 ° C. are particularly present. By blending with the polymer of No. 1, it is possible to achieve both stickiness resistance and applicability to a base material more satisfactorily. The mixing ratio of each polymer when blended is 0.1:99 as the ratio of the polymer presenting in the region where the glass transition temperature is 20 ° C or higher to the polymer existing in the region where the glass transition temperature is lower than 20 ° C. It is preferably in the range of 9.9 to 99.9: 0.1, more preferably 5:95 to 95: 5, still more preferably 50:50 to 95: 5, and particularly preferably 60 :. It is 40 to 90:10.

When a particulate polymer having a core-shell structure is used, the adhesiveness and compatibility with other members (for example, a base material) of the thermoplastic polymer layer can be adjusted by selecting the type of polymer in the outer shell portion. .. Further, by selecting the type of polymer in the central portion, for example, the adhesiveness to the electrode after hot pressing can be enhanced. Alternatively, it is also possible to control the viscoelasticity of the thermoplastic polymer layer by combining a highly viscous polymer and a highly elastic polymer.

The glass transition temperature of the outer shell portion (shell) of the thermoplastic polymer having a core-shell structure is preferably less than 20 ° C, more preferably 15 ° C or lower, still more preferably −30 ° C or higher and 15 ° C or lower. 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 further 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, and further preferably 200 nm or more. The arithmetic average particle size of the particulate polymer is preferably 1000 nm or less, more preferably 800 nm or less, and further preferably 700 nm or less. By setting the 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, the cycle characteristics of the power storage device, and the rate characteristics. Further, it is preferable that the arithmetic mean particle size is 1000 nm or less from the viewpoint of ensuring the dispersion stability when the thermoplastic polymer layer containing the particulate polymer is formed from the aqueous dispersion, and the thermoplasticity is also preferable. It is preferable from the viewpoint that the thickness of the polymer layer can be flexibly controlled. From these viewpoints, it is particularly preferable that the arithmetic average particle size of the particulate polymer is 200 nm or more and 1000 nm or less.

Two or more particulate polymers, each with a different arithmetic mean particle size, can also be contained in the thermoplastic polymer layer. For example, it is preferable to use a combination of a particulate polymer having an arithmetic average particle size of 10 nm or more and 300 nm or less and a particulate polymer having an arithmetic average particle size of more than 100 nm and 2000 nm or less.

The particulate polymer (for example, an acrylic polymer) can be produced by a known polymerization method other than using the monomer described above. As the polymerization method, for example, an appropriate method such as solution polymerization, emulsion polymerization, bulk polymerization or the like can be adopted. In particular, an emulsion polymerization method is preferable for the purpose of obtaining a dispersion having a particle shape.
As for the method of emulsion polymerization, a known method can be used. For example, in a dispersion system containing the above-mentioned monomers, surfactants, radical polymerization initiators, and other additive components used as necessary as basic composition components in an aqueous medium, a simple component of each monomer is used. A polymer is obtained by polymerizing the monomer composition. In the case of polymerization, a method of making the composition of the supplied monomer composition constant in the entire polymerization process, and a morphological change in the composition of the particles of the resin dispersion produced by sequentially or continuously changing the composition in the polymerization process. Various methods such as a method of giving can be used as needed. When the polymer is obtained by emulsion polymerization, it may be in the form of an aqueous dispersion (latex) containing, for example, water and a particulate polymer dispersed in the water.

Examples of the surfactant (the surfactant added as a raw material when the particulate polymer is polymerized) include polyether-based surfactants; non-reactive alkyl sulfate esters and polyoxyethylene alkyl ether sulfate esters. Salts, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkylsulfosuccinates, alkyldiphenyl ether disulfonates, naphthalene sulfonic acid formarin condensates, polyoxyethylene polycyclic phenyl ether sulfates, polyoxyethylene distyrene phenyl ethers Anionic surfactants such as sulfate esters, fatty acid salts, alkyl phosphates, and polyoxyethylene alkylphenyl ether sulfates; as well as non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene. Polycyclic phenyl ether, polyoxyethylene distyrene 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 Nonionic surfactants such as amides and polyoxyethylene alkyl phenyl ethers can be mentioned. In addition to these, a so-called reactive surfactant in which an ethylenic double bond is introduced into the chemical structural formula of the surfactant having a hydrophilic group and an oil base oil group may be used.

Examples of the anionic surfactant among the reactive surfactants include sulfonic acid groups, sulfonate groups or sulfate ester groups, and ethylenically unsaturated monomers having salts thereof, and examples thereof include sulfonic acid groups or sulfonic acid groups. It is preferable that the compound has a group (ammonium sulfonate group or alkali metal sulfonate group) which is the ammonium salt or the alkali metal salt. Specifically, for example, alkylallyl sulfosuccinate (for example, Eleminor (trademark) JS-20 manufactured by Sanyo Chemical Industries, Ltd., Latemul (trademark; the same applies hereinafter) manufactured by Kao Corporation) S-120, S-180A, S- 180 is mentioned), polyoxyethylene alkylpropenylphenyl ether sulfate ester salt (for example, Aqualon (trademark; the same applies hereinafter) HS-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), α- [1- [. (Allyloxy) Methyl] -2- (Nonylphenoxy) Ethyl] -ω-Polyoxyethylene sulfate ester salt (for example, Adecaria soap manufactured by ADEKA Co., Ltd. (trademark; the same applies hereinafter) SE-10N), ammonium. = Α-sulfonato-ω-1- (allyloxymethyl) alkyloxypolyoxyethylene (for example, Aqualon KH-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), styrene sulfonate (for example, Toso Organic Chemicals Co., Ltd.) Spinomer ™ NaSS manufactured by the company can be mentioned.), Α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, Adecaria manufactured by ADEKA Co., Ltd.) Soap SR-10) and sulfate ester salts of polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether (eg, Latemul PD-104 manufactured by Kao Corporation). ..

Examples of the nonionic surfactant among the reactive surfactants include α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene (for example, Adecaria soap NE-20, NE-30, NE-40 manufactured by ADEKA Co., Ltd.), polyoxyethylene alkylpropenylphenyl ether (for example, Aqualon RN-10, RN-20 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), RN-30, RN-50, etc.), α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-hydroxypolyoxyethylene (for example, Adecaria Soap ER manufactured by ADEKA Co., Ltd.) -10), and polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether (for example, Latemul PD-420 manufactured by Kao Co., Ltd.). The surfactant is preferably used in an amount of 0.1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the monomer composition. The surfactant may be used alone or in combination of two or more.

As the radical polymerization initiator, either an inorganic initiator or an organic initiator can be used. As the radical polymerization initiator, a water-soluble or oil-soluble polymerization initiator can be used. Examples of the water-soluble polymerization initiator include peroxodisulfuric acid salts, peroxides, water-soluble azobis compounds, and redox systems of peroxide-reducing agents. Examples of the peroxodisulfate include potassium peroxodisulfate (KPS), sodium peroxodisulfate (NPS), and ammonium peroxodisulfate (APS), and examples of the peroxide include hydrogen peroxide and t-. Examples thereof include butylhydroperoxide, t-butylperoxymaleic acid, succinic acid peroxide, and benzoyl peroxide, and examples of the water-soluble azobis compound include 2,2-azobis (N-hydroxyethylisobutylamide) and 2. , 2-azobis (2-amidinopropane) hydrogen dichloride, and 4,4-azobis (4-cyanopentanoic acid). Examples of the redox system of the peroxide-reducing agent include the above-mentioned peroxide. One or more of reducing agents such as sodium sulfooxylate formaldehyde, sodium hydrogen sulfite, sodium thiosulfate, sodium hydroxymethanesulfuric acid, L-ascorbic acid, and salts thereof, ferrous salts, and ferrous salts. Can be mentioned as a combination of.

The radical polymerization initiator can be preferably used 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 initiator may be used alone or in combination of two or more.

A single amount 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 the body composition is emulsion-polymerized to form a dispersion in which the polymer particles are dispersed in a solvent (water), the solid content of the obtained dispersion is preferably 30% by mass or more and 70% by mass or less. .. The pH of the dispersion is preferably adjusted to the 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 contains a polymer obtained by polymerizing a monomer composition containing the above-mentioned specific monomer as particles (polymer particles) dispersed in water. 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 bactericidal agent, 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 to use the obtained particulate polymer emulsion as an aqueous latex.

(Acetylene-based surfactant)
In the present embodiment, unlike adding a surfactant as a raw material for polymerizing a particulate polymer, the surfactant is post-added after the polymerization reaction. As the post-added surfactant, an acetylene-based surfactant is used. Since the acetylene surfactant is a relatively small molecule, it has a great effect of lowering the dynamic surface tension, and it is possible to form a coating layer in which the generation of cissing is well suppressed. On the other hand, since the hydrophobicity per molecule is high, it has the effect of promoting the coalescence of bubbles and suppressing foaming.
The slurry contains 0.001 part by mass or more and 10 parts by mass or less of the acetylene-based surfactant when the thermoplastic polymer is 100 parts by mass. By selecting an acetylene-based surfactant as the post-added surfactant and setting the content ratio to 0.001 part by mass or more, the surface energy of the thermoplastic polymer layer formed on the surface of the substrate can be adjusted. can. 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. By adding an acetylene-based surfactant afterwards, the surface energy of the thermoplastic polymer layer can be adjusted without being affected by the conditions of the polymerization reaction. Further, by adding an acetylene-based surfactant afterwards, a large amount of free surfactant is present in the slurry, and it is considered that a large amount of the surfactant is present on the outermost surface of the binder when the slurry is dried. .. As a result, the surface energy of the thermoplastic polymer layer can be adjusted with a smaller amount as compared with the method of adding it as a raw material for the polymerization reaction.
Therefore, the content ratio of the acetylene-based surfactant can be reduced to 10 parts by mass or less, and the content ratio of the thermoplastic polymer can be secured. In addition, by setting the content ratio of the acetylene-based surfactant to 10 parts by mass or less, the surface energy can be adjusted without impairing the adhesive force of the thermoplastic polymer layer with the electrode.

Therefore, when the thermoplastic polymer is 100 parts by mass, the slurry contains 0.001 part by mass or more and 10 parts by mass or less of the acetylene-based surfactant, thereby suppressing foaming of the slurry and the surface to be coated. Therefore, it is possible to reduce the surface tension with respect to the substrate, and therefore, it is possible to excellently coat the substrate and to satisfactorily suppress the generation of pinholes and cissing. From the same viewpoint as above, the content ratio of the acetylene-based surfactant is preferably 0.01 parts by mass or more and 5 parts by mass or less, and more preferably 0.1 parts by mass or more and 3 parts by mass or less.
Then, by using the above slurry, a separator containing 0.001 part by mass or more and 10 parts by mass or less of the acetylene-based surfactant can be obtained when the thermoplastic polymer in the thermoplastic polymer layer is 100 parts by mass. Since the obtained separator has a thermoplastic polymer layer in which pinholes and cissing are well suppressed, the provision of such a separator aims to improve the electrical characteristics of a power storage device represented by a secondary battery. be able to.

After the polymerization reaction of the particulate polymer, other surfactants (other post-added surfactants) may be post-added in addition to the acetylene-based surfactant. As the other post-added surfactant, the same surfactant as that added at the time of the polymerization reaction can be used, but since the polymerization reaction has already been completed at the time of the post-addition, the surfactant is not a reactive surfactant. It is preferable to use. Of these, from the viewpoint that it is easy to suppress foaming of the slurry, the dispersal effect increases as the addition is added, it is easy to secure dispersibility, and there is an effect that the surface tension of the base material is greatly changed with a small amount. Polyether-based surfactants or anionic surfactants are preferable.

（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。 Specific examples of the acetylene-based surfactant used as the defoaming agent in the present embodiment include the following formula (A):

(In the formula, R5 to R8 represent alkyl groups having 1 to 10 carbon atoms independently of each other, and n and m represent integers of 0 or more independently of each other, but n + m = 0 to 40. )
It is preferable to use a surfactant (acetylene-based surfactant) containing an ethoxylated form of acetylene glycol represented by. Specific examples of the alkyl group having 1 to 10 carbon atoms may be linear, branched or cyclic, and for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group and 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 can be mentioned.

Specific examples of the acetylene glycol represented by the formula (A) include 2,5,8,11-tetramethyl-6-decyne-5,8-diol and 5,8-dimethyl-6-dodecyne-5,8. -Glycol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 4,7-dimethyl-5-decyne-4,7-diol, 2,3,6,7-tetramethyl -4-octin-3,6-diol, 3,6-dimethyl-4-octin-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,4,7,9 -Tetramethyl-5-decyne-4,7-diol ethoxylated form (number of moles added with ethylene oxide: 1.3), 2,4,7,9-tetramethyl-5-decyne-4,7-diol Glycolized product (number of moles added with ethylene oxide: 4), ethoxylated product of 3,6-dimethyl-4-octine-3,6-diol (number of moles added with ethylene oxide: 4), 2,5,8,11- Ethanolylated form of tetramethyl-6-dodecyne-5,8-diol (number of moles added with ethylene oxide: 6) ethoxylated form of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (the number of moles added) Number of moles added with ethylene oxide: 10), ethoxylated form of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (number of moles added with ethylene oxide: 30), 3,6-dimethyl-4 -An ethoxylated form of octin-3,6-diol (number of moles added with ethylene oxide: 20) and the like can be mentioned, and these may be used alone or in combination of two or more.

The acetylene-based surfactant can also be obtained as a commercial product, and such commercial products include, for example, Orfin SPC (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 80% by mass, pale yellow liquid), Orfin. AF-103 (manufactured by Nisshin Chemical Industry Co., Ltd., light brown liquid), Orfin AF-104 (manufactured by Nisshin Chemical Industry Co., Ltd., light brown liquid), Orfin SK-14 (manufactured by Nisshin Chemical Industry Co., Ltd.) , Short yellow viscous liquid), Orfin AK-02 (manufactured by Nisshin Chemical Industry Co., Ltd., short yellow viscous liquid), Orfin AF-201F (manufactured by Nisshin Chemical Industry Co., Ltd., short yellow viscous liquid), Orfin D-10PG (manufactured by Nisshin Chemical Industry Co., Ltd., active ingredient 50% by mass, pale yellow liquid), Orfin E-1004 (manufactured by Nisshin Chemical Industry Co., Ltd., active ingredient 100% by mass, pale yellow liquid), Orfin E-1010 (manufactured by Nisshin Chemical Industry Co., Ltd., active ingredient 100% by mass, pale yellow liquid), Orfin E-1020 (manufactured by Nisshin Chemical Industry Co., Ltd., active ingredient 100% by mass, pale yellow liquid), Orfin E-1030W (manufactured by Nisshin Chemical Industry Co., Ltd., active ingredient 75% by mass, pale yellow liquid), Surfinol 420 (manufactured by Nisshin Chemical Industry Co., Ltd., active ingredient 100% by mass, pale yellow viscous body), Surfactant Knoll 440 (manufactured by Nisshin Chemical Industry Co., Ltd., active ingredient 100% by mass, pale yellow viscous body), Surfinol 104E (manufactured by Nisshin Chemical Industry Co., Ltd., active ingredient 50% by mass, pale yellow viscous body) And so on.

It is desirable that the acetylene-based surfactant contains an inorganic filler (inorganic particles) as a defoaming component. Among the inorganic fillers, the hydrophobic silica filler is particularly desirable. The primary particle size of the inorganic filler is preferably 0.1 nm or more, more preferably 1.0 nm. The primary particle size of the inorganic filler is preferably 1000 nm or less, more preferably 500 nm or less, still more preferably 100 nm or less. By setting the average primary particle size of the inorganic filler to 100 nm or less, defoaming property can be exhibited without impairing the adhesive force of the thermoplastic polymer layer.

The ratio of the inorganic filler in the slurry is preferably 0.001 part by mass or more and less than 1 part by mass when the thermoplastic polymer is 100 parts by mass. By setting the ratio of the inorganic filler to less than 1 part by mass, the adhesive force of the thermoplastic polymer layer with the electrode can be kept good. On the other hand, when the ratio of the inorganic filler is less than 0.001 part by mass, it is difficult for the inorganic filler to exhibit good defoaming property.

As other components (components added after the polymerization reaction), for the purpose of enhancing the defoaming effect, for example, oil-based defoaming agents such as castor oil, sesame oil, flaxseed oil, animal and vegetable oil; stearic acid, oleic acid, palmitin. Fatty acid defoamers such as acids; fatty acid ester defoamers such as isoamyl stearate, distearyl succinate, ethylene glycol distearate, butyl stearate; polyoxyalkylene monohydric alcohol, di-t-amylphenoxyethanol , 3-Heptanol, 2-ethylhexanol and other alcohol-based defoamers; 3-heptyl cellosolve, nonyl cellosolve, 3-heptyl carbitol, polyalkylene glycol and other ether-based defoamers; tributyl phosphate, tris (bushiethyl) phosphate Phosphoric acid ester-based defoaming agent such as; Amin-based defoaming agent such as diamilamine; Amid-based defoaming agent such as polyalkyleneamide and acylate polyamine; Sulfate-based defoaming agent such as lauryl sulfate ester sodium; Dimethylpolysiloxane Etc. Polysiloxane defoaming agent; may contain mineral oil such as paraffin mineral oil, cyclopentene, cyclohexane, phichterite, oleanan and the like naphthenic mineral oil. Of these, mineral oil is preferable because it has excellent defoaming properties.

<Viscosity adjuster>
The slurry may contain a viscosity modifier. By including the viscosity adjusting agent, the viscosity of the slurry can be set in a desired range to improve the dispersibility of the particles and the coatability of the slurry. As the viscosity modifier, it is preferable to use a water-soluble polysaccharide. Examples of the polysaccharide include natural polymer compounds and cellulose semi-synthetic polymer compounds. The viscosity adjusting agent may be used alone or in combination of two or more at any ratio.

Examples of the natural polymer compound include polysaccharides derived from plants or animals, proteins and the like. Further, in some cases, a natural polymer compound that has been fermented with a microorganism or the like or treated with heat can 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 Arabic gum, tragacanto gum, galactan, guagam, carob gum, karaya gum, carrageenan, pectin, cannan, quince seed (quince), alke colloid (gasso extract), starch (rice, corn, potato), and so on. (Derived from wheat and the like), glycyrrhizin and the like. Examples of animal-based natural polymer compounds include collagen, casein, albumin, gelatin and the like. Further, examples of the microbial natural polymer compound include xanthan gum, dextran, succinoglucan, and burran.

Cellulose semi-synthetic polymer compounds can be classified into nonionic, anionic, and cationic.

Examples of the nonionic cellulose semi-synthetic polymer compound include alkyl celluloses such as methyl cellulose, methyl ethyl cellulose, ethyl cellulose, and microcrystallin cellulose; hydroxyethyl cellulose, hydroxybutyl methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose. Hydroxyalkyl celluloses such as stearoxy ether, carboxymethyl hydroxyethyl cellulose, alkyl hydroxyethyl cellulose, nonoxynyl hydroxyethyl cellulose; and the like.

Examples of the anionic cellulose semi-synthetic polymer compound include alkyl cellulose in which the above-mentioned nonionic cellulose semi-synthetic polymer compound is substituted with various inducing groups, a sodium salt thereof, an ammonium salt and the like. Specific examples include sodium cellulose sulfate, methyl cellulose, methyl ethyl cellulose, ethyl cellulose, carboxymethyl cellulose (CMC), salts thereof and the like.

Examples of the cationic cellulose semi-synthetic polymer compound include low nitrogen hydroxyethyl cellulose dimethyldiallyl ammonium chloride (polyquaternium-4) and O- [2-hydroxy-3- (trimethylammonio) propyl] hydroxyethyl cellulose (polyquaternium-10) chloride. ), O- [2-Hydroxy-3- (lauryldimethylammonio) propyl] hydroxyethyl cellulose (polyquaternium-24) and the like.

Among them, a cellulose semisynthetic polymer compound, a sodium salt thereof, and an ammonium salt thereof are preferable because they can have cationic, anionic and amphoteric properties. Further, among them, an anionic cellulose semisynthetic polymer compound is particularly preferable from the viewpoint of dispersibility of the non-conductive fine particles.

The degree of etherification of the cellulose semisynthetic 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 anhydrous glucose unit in cellulose with a substituent such as a carboxymethyl group. The degree of etherification can theoretically take a value of 0 to 3. When the degree of etherification is within the above range, the cellulose semi-synthetic polymer compound is adsorbed on the surface of the non-conductive fine particles, and compatibility with water is also observed, so that the dispersibility is excellent and the non-conductive fine particles are the primary particles. Can be finely dispersed to the level.

<Various characteristics related to slurry>
(Solid content)
The solid content concentration of the slurry may be arbitrarily set as long as the slurry has a viscosity within a range that does not impair workability when the thermoplastic polymer layer is produced. Specifically, the solid content concentration of the slurry can be usually adjusted to 3 to 50% by mass.

(surface tension)
The dynamic surface tension when the surface life of the slurry is 10 ms is preferably 60 mN / m or less, more preferably 50 mN / m or less, still more preferably 45 mN / m or less. If the dynamic surface tension at a surface life of 10 ms is 60 mN / m or less, it is possible to provide a slurry capable of satisfactorily suppressing the generation of cissing.

(viscosity)
The viscosity of the slurry is preferably less than 3500 mPa · s, more preferably less than 350 mPa · s, and 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, the coatability is excellent and a uniform coat layer can be provided.

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

[Base material]
The base material itself may be one that has been conventionally used as a separator. As the base material, a porous membrane is preferable, and in addition, a porous membrane having a fine pore size, which has no electron conductivity and ionic conductivity and has high resistance to an organic solvent, is more preferable. Such a porous film contains, for example, a resin such as a polyolefin-based (for example, polyethylene, polypropylene, polybutene, and polyvinyl chloride) and a mixture thereof or a copolymer of their monomers as a main component. Examples include microporous membranes. These may be used alone or in combination of two or more. The concept of "base material" in the present specification includes not only the polyolefin microporous film itself but also those having an inorganic coating layer.

From the viewpoint of making the film thickness of the separator thinner, increasing the ratio of active substances in the power storage device, and increasing the capacity per volume, the base material is a microporous polyolefin membrane containing a polyolefin-based resin as the main component. Use. The microporous polyolefin membrane is advantageous in reducing the thickness of the separator because it is excellent in the coatability of the coating liquid when the coating liquid is applied onto the film.
The term "containing the polyolefin resin as the main component" means that the polyolefin resin is contained in an amount of more than 50% by mass with respect to the total mass of the base material. From the viewpoint of shutdown performance and the like, 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. It may be 98% by mass or more and 100% by mass.

The base material may contain a resin other than the polyolefin resin (other resin) as long as the effect of the present invention is not impaired, while the main component is the polyolefin resin. Examples of other resins include resins such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene.

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

Representative examples of polyolefin resins include, for example, polyethylene, polypropylene, and polybutene, more specifically low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultrahigh molecular weight polyethylene, isotac. Included are tick polypropylene, atactic polypropylene, ethylene-propylene random copolymers, polyethylene, and polyethylene propylene rubber. These may be used alone or in combination of two or more. As the polyolefin resin, polyethylene 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 shut-down characteristics in which the pores are closed by thermal melting. In particular, high-density polyethylene is preferable because of its low melting point and high strength, and polyethylene having a density of 0.93 g / cm ³ or more measured according to JIS K 7112 is more preferable. Examples of the polymerization catalyst used in the production of these polyethylenes include Ziegler-Natta-based catalysts, Philips-based catalysts, and metallocene-based catalysts.

In order to improve the heat resistance of the base material, it is more preferable that the polyolefin microporous film 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 the polyolefin resin other than polypropylene include homopolymers having ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like as monomers, and their monomers. Examples thereof include two or more kinds of copolymers and multi-stage polymers, and specific examples thereof include those already described. Examples of the polymerization catalyst used in producing polypropylene include Ziegler-Natta-based catalysts and metallocene-based catalysts.

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

The viscosity average molecular weight of the polyolefin resin constituting the polyolefin microporous film is preferably 30,000 or more and 12 million or less, more preferably 50,000 or more and less than 2 million, and further preferably 100,000 or more and less than 1 million. When the viscosity average molecular weight is 30,000 or more, the melt tension at the time of melt molding becomes large and the moldability becomes better, and the polymer tends to be entangled with each other to have higher strength, which is preferable. On the other hand, when the viscosity average molecular weight is 12 million or less, it becomes easy to uniformly melt and knead, and the formability of the sheet, particularly the thickness stability tends to be excellent, which is preferable. Further, when the viscosity average molecular weight is less than 1,000,000, the pores are easily closed when the temperature rises, and a better shutdown function tends to be obtained, which is preferable. Instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000 and having a viscosity average molecular weight of less than 1 million is used. May be good. The viscosity average molecular weight (Mv) is measured by the method described in Examples.

The substrate can contain any additive. Such additives include, for example, polymers other than polyolefins; inorganic fillers; phenolic, phosphorus, and sulfur antioxidants; metal soaps such as calcium stearate, zinc stearate; UV absorbers; light stable. Agents; antistatic agents; antifogging agents; as well as colored pigments and the like. The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin in the base material. ..

The porosity of the substrate is preferably 20% or more, more preferably 35% or more, still more preferably greater than 40%. On the other hand, the porosity is preferably 90% or less, more preferably 80% or less. It is preferable that the porosity is 20% or more from the viewpoint of more effectively and surely ensuring the permeability of the separator. On the other hand, setting the porosity to 90% or less is preferable from the viewpoint of more effectively and surely ensuring the puncture strength. Porosity is measured by the method described in the examples.
Here, in the case of a microporous polyolefin membrane made of polyethylene, the calculation can be performed on the assumption that the membrane density is 0.95 (g / cm ³ ). The porosity can be adjusted by changing the draw 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, preferably 1000 sec / 100 cm ³ or less, and 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 power storage device. On the other hand, it is preferable that the air permeability is 1000 sec / 100 cm ³ or less from the viewpoint of obtaining good charge / discharge characteristics. The air permeability is the air permeability resistance measured according to JIS P-8117. The air permeability can be adjusted by changing the stretching temperature of the base material and / or the stretching ratio.

The average pore size of the substrate is preferably 0.15 μm or less, more preferably 0.1 μm or less, and preferably 0.01 μm or more. It is preferable that the average pore diameter is 0.15 μm or less from the viewpoint of suppressing the self-discharge of the power storage device and suppressing the capacity decrease. The average pore size can be adjusted by changing the draw 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, further preferably 400 gf / 20 μm or more, preferably 2000 gf / 20 μm or less, and more preferably 1000 gf / 20 μm or less. The puncture strength of 200 gf / 20 μm or more suppresses the viewpoint of suppressing film breakage due to the active material that has fallen off when the separator is wound together with the electrode, and suppresses the concern of short circuit due to expansion and contraction of the electrode due to charging and discharging. It is also preferable from the viewpoint of On the other hand, the puncture strength of 2000 gf / 20 μm or less is preferable from the viewpoint of reducing the width shrinkage due to the relaxation of orientation during heating. The puncture strength is measured according to the method described in the examples. The puncture strength can be adjusted by adjusting the draw ratio and / or the draw temperature of the base material.

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

[Thermoplastic polymer layer]
The thermoplastic polymer layer contains a thermoplastic polymer. The thermoplastic polymer layer may be arranged on the entire surface or a part of the surface of the substrate. It is more preferred that the thermoplastic polymer layer be placed only on a portion of the surface of the substrate so that the resulting energy storage device exhibits high ion permeability.

The thermoplastic polymer layer is expected to adhere directly to the electrodes. The at least one thermoplastic polymer layer provided in the separator is arranged so as to be directly bonded to the electrode, for example, at least a part of the substrate and the electrode are bonded via the thermoplastic polymer layer. Is preferable.

The amount of the thermoplastic polymer layer applied to the substrate, that is, the amount of the thermoplastic polymer layer formed (arranged) per area of one surface of the substrate 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. The coating amount is preferably 2.0 g / m ² or less, and more preferably 1.5 g / m ² or less. When the coating amount is 0.03 g / m ² or more, the adhesive force between the thermoplastic polymer layer and the electrode is improved in the obtained separator, more uniform charge and discharge is realized, and the device characteristics (for example, a battery) are achieved. It is preferable in terms of improving the cycle characteristics of the above. On the other hand, it is preferable that the coating amount is 2.0 g / m ² or less from the viewpoint of further suppressing the 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 substrate, that is, the ratio of the covering area of the thermoplastic polymer layer to the substrate is preferably 95%. Below, it is more preferably 80% or less, further preferably 50% or less, particularly preferably 35% or less, and most preferably 30% or less. The coverage area ratio is preferably 5% or more, more preferably 10% or more. This coverage ratio of 50% or less means that when only the separator is wound, the exposed portion of the surface of the substrate (the portion where the thermoplastic polymer layer does not exist) and another substrate or another thermoplastic polymer are used. It is preferable from the viewpoint of ensuring blocking resistance by increasing the contact area with the layer. It is also preferable from the viewpoint of further suppressing the blockage of the pores of the base material due to the particulate polymer and further improving the permeability of the separator. On the other hand, it is preferable that the covering area ratio is 5% or more from the viewpoint of further improving the adhesiveness to the electrode. The coverage area ratio is measured by observing the surface on which the thermoplastic polymer layer is formed in the obtained separator by SEM, and in detail, it is measured according to the method described in Examples.
The coverage area ratio is, for example, in the method for producing a separator described later, the type of particulate polymer in the coating liquid to be applied to the surface of the base material or the concentration of the polymer, the coating amount of the coating liquid, the coating method, and the coating. It can be adjusted by changing the conditions. However, the method of adjusting the coated area is not limited to them.

When the thermoplastic polymer layer is arranged only on a part of the surface of the base material, the existence form (pattern) of the thermoplastic polymer is a state in which the thermoplastic polymer is irregularly present over the entire surface of the base material, or a constant pattern. A state that exists periodically at a certain frequency is preferable. If the thermoplastic polymer is present periodically at a certain frequency, the arrangement pattern may include, for example, dots, stripes, lattices, stripes, hexagonal patterns, etc., and combinations thereof. Above all, the dot shape is preferable from the viewpoint of more effectively and surely exerting the action and effect of the present invention and from the viewpoint of productivity. When the arrangement pattern is dot-shaped, the dot diameter is preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more. 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 electrolytic solution is further improved and the permeability is further improved. When the dot diameter is 1 mm or less, the separator can be more uniformly adhered to the electrode, and the in-plane current density can be further made uniform. Further, by providing a portion in which the thermoplastic polymer is not applied in the dot-shaped arrangement pattern, the in-plane current density can be further made uniform.

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

The thickness of the thermoplastic polymer layer is preferably 0.01 μm or more, and more preferably 0.1 μm or more per surface of the substrate. The thickness thereof is preferably 5.0 μm or less, more preferably 3.0 μm or less, and further preferably 2.0 μm or less per surface of the substrate. It is preferable that the thickness is 0.01 μm or more in that the adhesive force between the electrode and the base material is uniformly exhibited, and as a result, the device characteristics can be improved. Further, it is preferable that the thickness is 5.0 μm or less in terms of suppressing a decrease in ion permeability. The thickness of the thermoplastic polymer layer is adjusted, for example, by changing the type of particulate polymer in the coating liquid to be applied to the substrate, the concentration of the polymer, the coating amount of the coating liquid, the coating method, and the coating conditions. can do. However, this method of adjusting the thickness is not limited to them.

[Any layer]
Also included within the scope of the invention is an embodiment comprising any layer between the substrate and the thermoplastic polymer layer, eg, an inorganic filler porous layer. The inorganic filler porous layer contains an inorganic filler and has a plurality of pores. In this column, it is assumed that an inorganic filler porous layer is included between the base material and the thermoplastic polymer layer, and the inorganic filler porous layer will be described. However, in the present invention, any arbitrary filler porous layer such as the inorganic filler porous layer will be described. Layers can be omitted.

(Inorganic filler)
As the inorganic filler, one having a melting point of 200 ° C. or higher, having high electrical insulation, and being electrochemically stable within the range of use of a power storage device such as a lithium ion secondary battery can be used.

Examples of the inorganic filler include inorganic oxides (oxide-based ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, itria, zinc oxide, and iron oxide; silicon nitride, titanium nitride, and boron nitride. Inorganic Nitride (Nitride Ceramics); Silicon Carbide, Calcium Carbonate, Magnesium Sulfate, Barium Sulfate, Aluminum Sulfate, Aluminum Hydroxide, Aluminum Oxide Oxide, Potassium Titanium, Tarku, Kaolinite, Decite, Nacrite, Halloysite, Pyro Ceramics such as phyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous soil, and silica sand; and glass fiber. These may be used alone or in combination of two or more.

The average particle size 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. The average particle size D50 is 4.0 μm or less, 3.5 μm or less, and further less than 1.0 μm. Examples of the method for adjusting the particle size of the inorganic filler and its distribution include a method of pulverizing the inorganic filler using an appropriate pulverizing device such as a ball mill, a bead mill, or a jet mill to reduce the particle size.
The particle size distribution of the inorganic filler can be such that the peak is one in the graph of the frequency with respect to the particle size. However, the chart may have a trapezoidal shape with two peaks or no peaks.

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, and further 1.8 times or more the average pore size of the inorganic filler porous layer. It is 0 times or less, and further 3.0 times or less. The average pore size 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 binder and the binder in the inorganic filler porous layer. The content of the particulate polymer contained in the porous inorganic filler layer is, for example, 20% by volume or less, 15% by volume or less, 10% by volume or less, and further 5 volumes with respect to the total amount of the porous inorganic filler layer. % Or less.

When measuring the average pore size of the inorganic filler porous layer, it is preferable to observe the cross section of the separator in the region of the cross section of the separator that is not involved in ionic conduction. The average pore size of the inorganic filler porous layer may be measured, for example, for a separator that has just been manufactured and has not yet been incorporated into the power storage device. Alternatively, after the separator is incorporated into the power storage device, the so-called "ear" portion of the separator (the region near the outer edge of the separator and not involved in ion conduction) is measured. May be good.
The average pore size 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. 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 size of the inorganic filler porous layer is an index showing the size of the void portion formed between the inorganic fillers bonded by the resin binder in the inorganic filler porous layer formed on at least one surface of the base material. be. Since the average pore size of the inorganic filler porous layer is determined by the method for forming the inorganic filler porous layer, 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 porous layer. It can be adjusted by the forming method when forming the layer.

Examples of the shape of the inorganic filler include a plate shape, a scale shape, a needle shape, a columnar shape, a spherical shape, a polyhedral shape, and a lump shape (block shape). A plurality of types of inorganic fillers having these shapes may be used in combination.
The content ratio of the inorganic filler in the inorganic filler porous layer is, for example, 20% by mass or more and less than 100% by mass, 30% by mass or more and 80% by mass or less, and 35% by mass or more and 70% by mass with respect to the total amount of the inorganic filler porous layer. Hereinafter, it is further 40% by mass or more and 60% by mass or less.

(Resin binder)
As the type of resin of the resin binder contained in the inorganic filler porous layer, the use of a power storage device such as a lithium ion secondary battery which is insoluble in the electrolytic solution of the power storage device such as a lithium ion secondary battery. An electrochemically stable resin can be used in the range. 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 is contained in the thermoplastic polymer layer. A binding binder (C) that binds (B) to the base material or the porous layer of the inorganic filler may be used. The resin binder (A) and the binder 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 resin of a different type from the resin binder (A) and the binder binder (C).

Specific examples of such resins include, for example, polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and Fluoro-containing rubber such as ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride , Methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, rubbers such as polyvinyl acetate; ethyl cellulose, methyl cellulose, hydroxy Cellulous derivatives such as ethyl cellulose and carboxymethyl cellulose; and resins having a melting point and / or a 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 the unsaturated carboxylic acid monomer can be used. Here, examples of the aliphatic conjugated diene-based monomer include butadiene and isoprene, examples of the unsaturated carboxylic acid monomer include (meth) acrylic acid, and examples of the other monomer include (meth) acrylic acid. , For example, styrene. Emulsion polymerization is preferable as a method for polymerizing such a copolymer. As a method of emulsion polymerization, a known method can be used. As for the method of adding the monomer and other components, any of a batch addition method, a split addition method, and a continuous addition method can be adopted, and the polymerization method is one-step polymerization, two-step polymerization, or three or more steps. Any of the multi-step polymerizations can be adopted.

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) Conjugate diene-based polymer: For example, a styrene-butadiene copolymer and a hydride thereof, an acrylonitrile-butadiene copolymer and a hydride thereof, an acrylonitrile-butadiene-styrene copolymer and a hydride thereof;
3) Acrylic polymers: For example, methacrylic acid ester-acrylic acid ester copolymers, styrene-acrylic acid ester copolymers, and acrylonitrile-acrylic acid ester copolymers;
4) Polyvinyl alcohol-based resin: For example, polyvinyl alcohol and polyvinyl acetate;
5) Fluororesin: For example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer;
6) Cellulose derivatives: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and 7) resin with melting point and / or glass transition temperature of 180 ° C or higher or polymer having no melting point but decomposition temperature of 200 ° C or higher: For example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

When the resin binder is a resin latex binder, its average particle size (D50) is, for example, 50 to 500 nm, 60 to 460 nm, and further 80 to 250 nm. The average particle size of the resin binder can be controlled by adjusting, for example, the polymerization time, the polymerization temperature, the raw material composition ratio, the raw material charging order, the pH, and the like.
The content ratio of the resin binder in the inorganic filler porous layer is, for example, more than 0% by mass and 80% by mass or less, 1% by mass or more and 20% by mass or less, and 2% by mass or more and 10% by mass with respect to the total amount of the inorganic filler porous layer. % Or less, further 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 further less than 2% by volume of the content of the particulate polymer contained in the separator. Can be.

The thickness of the inorganic filler porous layer can be, for example, 10.0 μm or less, further 6.0 μm or less. Further, the thickness of the inorganic filler porous layer can be set to, 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 further 0.7 to 2.0 cm ³ . Can be done.

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

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, still more preferably 50 sec / 100 cm ³ or more and 500 sec / 100 cm ³ or less, and particularly preferably. Is 50 sec / 100 cm ³ or more and 300 sec / 100 cm ³ or less. This means that when the separator is applied to a power storage device, it exhibits good high ion permeability. This air permeability is the air permeability resistance measured in accordance with JIS P-8117, like the air permeability of the base material.

<Manufacturing method of separator>
[Manufacturing method of base material]
As a method for producing a base material, a known production method can be adopted. For example, as a method for producing a polyolefin microporous film contained in a base material, either a wet porosity method or a dry perforation method is adopted. You may. Examples of the wet porosity method include, for example, a method of melt-kneading a polyolefin resin composition and a plasticizing agent to form a sheet, stretching the resin composition in some cases, and then extracting the plasticizing agent to make the polyolefin. A method of melt-kneading a polyolefin resin composition containing a resin as a main component, extruding it at a high draw ratio, and then exfoliating the polyolefin crystal interface by heat treatment and stretching to make it porous; A method of melt-kneading, forming on a sheet, and then stretching to exfoliate the interface between the polyolefin and the inorganic filler to make the polyolefin porous; and after dissolving the polyolefin resin composition, the polyolefin is immersed in a poor solvent for the polyolefin to solidify the polyolefin. At the same time, a method of making the porous by removing the solvent can be mentioned.

Hereinafter, as an example of a method for producing a microporous polyolefin film, a method of melting and kneading a polyolefin resin composition and a plasticizer to form a sheet and then extracting the plasticizer will be described. First, the polyolefin resin composition and the plasticizer are melt-kneaded. As a melt-kneading method, for example, a polyolefin resin and, if necessary, other additives are put into a resin kneading device such as an extruder, a kneader, a lab plast mill, a kneading roll, and a Banbury mixer to heat and melt the resin components. However, there is a method of introducing a plasticizer at an arbitrary ratio and kneading. At this time, it is preferable to pre-knead the polyolefin resin, other additives, and the plasticizer at a predetermined ratio using a Henschel mixer or the like before putting them into the resin kneading apparatus. More preferably, in the pre-kneading, only a part of the plasticizer is added, and the remaining plasticizer is kneaded while side-feeding the resin kneader.

As the plasticizer, a non-volatile solvent capable of forming a uniform solution above the melting point of the polyolefin can be used. Specific examples of such non-volatile solvents include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such as oleyl alcohol and stearyl alcohol. Of these, liquid paraffin is preferred.

The ratio of the polyolefin resin composition to the plasticizer may be as long as it can be uniformly melt-kneaded and formed into a sheet. For example, the mass fraction of the plasticizer in the composition composed of the polyolefin resin composition and the plasticizer is preferably 30% by mass or more and 80% by mass or less, and more preferably 40% by mass or more and 70% by mass or less. By setting the mass fraction of the plasticizer in this range, it is preferable from the viewpoint of achieving both the melt tension at the time of melt molding and the formability of a uniform and fine pore structure.

Next, the melt-kneaded product obtained by heating and melting and kneading as described above is formed into a sheet. As a method for producing a sheet-shaped molded body, for example, the melt-kneaded product is extruded into a sheet-like shape via a T-die or the like, brought into contact with a heat conductor, and cooled to a temperature sufficiently lower than the crystallization temperature of the resin component. There is a method of solidifying. Examples of the heat conductor used for cooling solidification include metal, water, air, and the plasticizer itself, but metal rolls are preferable because of their high heat conduction efficiency. In this case, if the melt-kneaded material is sandwiched between the rolls when they are brought into contact with the metal rolls, the efficiency of heat conduction is further increased, the sheet is oriented to increase the film strength, and the surface smoothness of the sheet is also improved. Therefore, it is more preferable. The die lip interval when extruded into a sheet from the T die is preferably 400 μm or more and 3000 μm or less, and more preferably 500 μm or more and 2500 μm or less.

It is preferable that the sheet-shaped molded product thus obtained is then stretched. As the stretching treatment, either uniaxial stretching or biaxial stretching can be preferably used. Biaxial stretching is preferable from the viewpoint of the strength of the obtained base material and the like. When the sheet-shaped molded product is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, the finally obtained base material becomes difficult to tear, and the sheet-shaped molded product 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 preferable from the viewpoint of improving puncture strength, stretching uniformity, and shutdown property.

The draw ratio is preferably in the range of 20 times or more and 100 times or less in terms of surface magnification, and more preferably in the range of 25 times or more and 50 times or less. The draw ratio in each axial direction is preferably in the range of 4 times or more and 10 times or less for MD, 4 times or more and 10 times or less for TD, 5 times or more and 8 times or less for MD, and 5 times or more and 8 times or less for TD. It is more preferable that the range is. By setting the draw ratio to a ratio in this range, more sufficient strength can be imparted, film breakage in the drawing step can be prevented, and high productivity can be obtained, which is preferable.
The MD means, for example, the mechanical direction when continuously molding the base material, and the TD means the direction across the MD at an angle of 90 °.

The obtained sheet-shaped molded product may be further rolled. Rolling can be carried out by, for example, a pressing method using a double belt press machine or the like. Rolling can increase the orientation of the surface layer portion of the sheet-shaped molded product in particular. The rolled surface magnification is preferably greater than 1x and 3x or less, and more preferably greater than 1x and 2x or less. By setting the rolling ratio in this range, the film strength of the finally obtained base material is increased, and a uniform porous structure can be formed depending on the thickness direction of the film, which is preferable.

Then, the plasticizer is removed from the sheet-shaped molded product to obtain a base material. Examples of the method for removing the plasticizer include a method in which a sheet-shaped molded product is immersed in an extraction solvent to extract the plasticizer and sufficiently dried. The method for extracting the plasticizer may be either a batch method or a continuous method. In order to suppress the shrinkage of the base material, it is preferable to restrain the end portion of the sheet-shaped molded product during a series of dipping and drying steps. Further, the residual amount of the plasticizer in the substrate is preferably less than 1% by mass.

As the extraction solvent, it is preferable to use a solvent that is poor with respect to the polyolefin resin, is a good solvent with respect to the plasticizer, and has a boiling point lower than the melting point of the polyolefin resin. Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; hydrofluoroethers, hydrofluorocarbons and the like. Examples thereof include non-chlorine halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by an operation such as distillation.

In order to suppress the shrinkage of the base material, heat treatment such as heat fixing or heat relaxation may be performed after the stretching step or after the formation of the base material. The base material may be subjected to post-treatment such as hydrophilization treatment with a surfactant or the like, cross-linking treatment with ionizing radiation or the like.

An example of a dry-type porous method, which is different from the wet-type porous method, will be given. First, a film that is directly stretch-oriented after melt-kneading in an extruder without using a solvent is produced, and then a substrate is produced through an annealing step, a cold stretching step, and a heat stretching step in this order. In the dry porosity method, a method of stretching and orienting a molten resin from an extruder via a T-die, an inflation method, and the like can be used, and the method is not particularly limited.

[Arrangement method of thermoplastic polymer layer]
A thermoplastic polymer layer is placed on at least one side (one surface) of the substrate. When the inorganic filler porous layer is arranged on the surface of the substrate, the thermoplastic polymer layer is arranged on all or part of the surface of the inorganic filler porous layer, or the inorganic filler porous layer is not formed. A thermoplastic polymer layer is placed on the surface of the substrate. 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 the 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 liquid containing the particulate polymer on the substrate may be any method as long as it can realize a desired coating pattern, coating film 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 thereof include a coater method, a die coater method, a screen printing method, a spray coating method, and an inkjet coating method. Of 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.

As the medium of the coating liquid, water or a mixed solvent composed of water and a water-soluble organic medium is preferable. Examples of the water-soluble organic medium include ethanol, methanol and the like. Of these, water is preferable. When the coating liquid is applied to the base material, if the coating liquid penetrates into the inside of the base material, the particulate polymer containing the polymer closes the surface and the inside of the pores of the base material and becomes permeable. It tends to decrease. In this respect, when water is used as the solvent or dispersion medium of the coating liquid, it becomes difficult for the coating liquid to enter the inside of the base material, and the particulate polymer containing the polymer is mainly present on the outer surface of the base material. Since it becomes easy, it is preferable because the decrease in permeability can be suppressed more effectively. Examples of the solvent or dispersion medium 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 substrate and the thermoplastic polymer layer. For example, a method of fixing the substrate and drying it at a temperature below its melting point, a method of drying under reduced pressure at a low temperature, or a method of immersing the substrate in a poor solvent for the particulate polymer to coagulate the particulate polymer into particles at the same time. Examples thereof include a method of extracting a solvent.

[Method of forming a porous layer of inorganic filler]
When the inorganic filler porous layer is arranged on at least one surface of the base material, it can be formed by a known method as a method for forming the inorganic filler porous layer. For example, a method of applying a coating liquid containing an inorganic filler and, if necessary, a resin binder to the base material can be mentioned. The raw material containing the inorganic filler and the resin binder and the raw material of the base material may be laminated and extruded by a coextrusion method, or the base material and the inorganic filler porous layer (membrane) may be individually prepared and then pasted. You may match.

The solvent of the coating liquid is preferably one capable of uniformly and stably dispersing or dissolving the inorganic filler and, if necessary, the resin binder, for example, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide. , Water, ethanol, toluene, thermoxylene, methylene chloride, and hexane.

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

As a method of dispersing or dissolving the inorganic filler and the resin binder in the medium of the coating liquid, for example, a ball mill, a bead mill, a planetary ball mill, a vibration ball mill, a sand mill, a colloid mill, an attritor, a roll mill, and a high-speed impeller dispersion. , Disperser, homogenizer, high-speed impact mill, ultrasonic dispersion, and mechanical stirring with stirring blades and the like.

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

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

<Power storage device>
The power storage device provided with the separator may be the same as that known, except that the power storage device includes the separator for the power storage device. Examples of the power storage device include a battery such as a non-aqueous electrolyte secondary battery, a capacitor, and a capacitor. Among them, a battery is preferable, a non-aqueous electrolyte secondary battery is more preferable, and a lithium ion secondary battery is further preferable, from the viewpoint of more effectively obtaining the benefits of the action and effect of the present invention. Since the separator of the present embodiment is provided, the power storage device is excellent in device characteristics such as power storage performance. Further, the lithium ion secondary battery has excellent battery characteristics.

The electrode used for measuring the peel strength from the electrode may be either a positive electrode or a negative electrode, but it is appropriate to use a positive electrode in order to appropriately grasp the effect of the separator. In particular, when the power storage device is a lithium ion secondary battery, the 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, and the positive electrode active material layer is a separator. It is appropriate to superimpose them so as to face the forming surface of the thermoplastic polymer layer and heat-press them before measurement.

When a lithium ion secondary battery is manufactured using a separator, the positive electrode, the negative electrode, and the non-aqueous electrolytic solution are not limited, and known ones can be used.
As the positive electrode, a positive electrode formed by forming a positive electrode active material layer containing a positive electrode active material on a positive electrode current collector can be preferably 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 . In addition to the positive electrode active material, the positive electrode active material layer may appropriately contain a binder, a conductive material, or the like.

As the negative electrode, a negative electrode having a negative electrode active material layer containing a negative electrode active material formed on the negative electrode current collector can be preferably used. Examples of the negative electrode current collector include copper foil. Examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbon, easily graphitized carbon, and composite carbons; and silicon, tin, metallic lithium, and various alloy materials.

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

<Manufacturing method of power storage device>
As a method for manufacturing a power storage device using a separator, for example, the following method can be exemplified. 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 positive electrode-separator-negative electrode-separator or the negative electrode-separator-positive electrode-separator are laminated in this order and wound in a circular or flat spiral shape to obtain a wound body. The wound body can be manufactured by storing it in a device can (for example, a battery can) and further injecting an electrolytic solution. Alternatively, the electrode and the separator may be folded into a wound body, which may be produced by putting it in a device container (for example, an aluminum film) and injecting an electrolytic solution.

At this time, the wound body can be pressed. Specifically, the separator and the current collector and the electrode having the active material layer formed on at least one surface of the current collector are laminated so that the former thermoplastic polymer layer and the active material layer face each other. A method of pressing together can be exemplified.

The press temperature is preferably, for example, 20 ° C. or higher as a temperature at which adhesiveness can be effectively exhibited. Further, the press temperature is preferably lower than the melting point of the material contained in the base material, and more preferably 120 ° C. or lower, in terms of suppressing clogging or heat shrinkage of holes in the separator by hot pressing. The press pressure is preferably 20 MPa or less from the viewpoint of suppressing clogging of the holes in the separator. The press time may be 1 second or less when a roll press is used, or may be a surface press for several hours, but 2 hours or less is preferable from the viewpoint of productivity. By using the separator for a power storage device of the present embodiment and undergoing the above manufacturing process, it is possible to suppress pressback when a wound body composed 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 power storage device manufactured as described above, particularly a lithium ion secondary battery, has a separator having high adhesiveness and reduced ion resistance, and therefore has excellent battery characteristics (rate characteristics) and long-term continuity. Excellent operation resistance (cycle characteristics). In addition, to provide a separator for a power storage device that can improve the electrical characteristics of a power storage device typified by a secondary battery because it includes a thermoplastic polymer layer in which the generation of pinholes and cissing is well suppressed. Can be done.

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

(1) Viscosity average molecular weight Mv
The ultimate viscosity [η] at 135 ° C. in a decalin solvent was determined according to ASTM-D4020. Using this [η] value, the viscosity average molecular weight Mv was calculated from the relationship of the following mathematical formula.
For polyethylene: [η] = 0.00068 × Mv ^0.67
For polypropylene: [η] = 1.10 x Mv ^0.80

(2) Base material thickness (μm)
A 10 cm x 10 cm square sample is cut out from the base material, 9 points (3 points x 3 points) are selected in a grid pattern, and a room temperature 23 ± 2 is used using a microthickening instrument (Toyo Seiki Seisakusho Co., Ltd., type KBM). The thickness was measured at ° C. The average value of the obtained measured values at 9 points was calculated as the thickness of the base material.

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

(4) Air permeability of the base material (sec / 100 cm ³ )
The air permeability of the base material was defined as the air permeability resistance measured by the Garley type air permeability meter GB2 (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 pierced from the side where the thermoplastic polymer layer is present.

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

(6) Rate characteristics of the base material a. Preparation of positive electrode Nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ ) was used as the positive electrode active material in an amount of 90.4% by mass. As a conductive auxiliary agent, nickel powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) is 1.6% by mass, and acetylene black powder (AB) (density 1.95 g / cm ³ , number). An average particle size of 48 nm) was mixed at a ratio of 3.8% by mass, and polyvinylidene fluoride (PVdF) (density 1.75 g / cm ³ ) as a binder was mixed at a ratio of 4.2% by mass, and these were mixed with N-methylpyrrolidone (NMP). ) To prepare a slurry. This slurry is applied to one side of a 20 μm-thick aluminum foil that serves as a positive electrode current collector using a die coater, dried at 130 ° C. for 3 minutes, and then compression-molded using a roll press to obtain a positive electrode. Made. The amount of the positive electrode active material applied at this time was 109 g / m ² .

b. Preparation of negative electrode As negative electrode active material, graphite powder A (density 2.23 g / cm ³ , number average particle diameter 12.7 μm) was added to 87.6% by mass, and graphite powder B (density 2.27 g / cm ³ , number average particles). 9.7% by mass (diameter 6.5 μm), 1.4% by mass (solid content equivalent) of ammonium salt of carboxymethyl cellulose as a binder (solid content concentration 1.83% by mass aqueous solution), and 1.7% by mass of diene rubber-based latex. % (Solid content equivalent) (solid content concentration 40% by mass aqueous solution) was dispersed in purified water to prepare a slurry. A negative electrode was prepared by applying this slurry to one side of a copper foil having a thickness of 12 μm as a negative electrode current collector with a die coater, drying at 120 ° C. for 3 minutes, and then compression molding with a roll press machine. The amount of the negative electrode active material applied at this time was 5.2 g / m ² .

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

d. Battery assembly A multilayer porous membrane or base material was cut out into a circle of 24 mmφ, and a positive electrode and a negative electrode were cut out into a circle of 16 mmφ, respectively. The negative electrode, the multilayer porous membrane or the base material, and the positive electrode were stacked in this order so that the positive electrode and the active material surface of the negative electrode faced each other, and housed in a stainless metal container with a lid. The container and the lid were insulated, and the container was in contact with the copper foil of the negative electrode and the lid was in contact with the aluminum foil of the positive electrode. A battery was assembled by injecting 0.4 ml of a non-aqueous electrolytic solution into this container and sealing the container.

e. Evaluation of rate characteristics d. After charging the simple battery assembled in step 1 at 25 ° C with a current value of 3 mA (about 0.5 C) to a battery voltage of 4.2 V, the current value is started to be throttled from 3 mA so as to maintain 4.2 V. The first charge after the battery was made was carried out for a total of about 6 hours. After that, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, at 25 ° C., the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and then the current value is started to be throttled from 6 mA so as to maintain 4.2 V, for a total of about 3 Charged for hours. After that, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 6 mA was defined as 1 C discharge capacity (mAh).
Next, at 25 ° C., the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and then the current value is started to be throttled from 6 mA so as to maintain 4.2 V, for a total of about 3 Charged for hours. After that, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 12 mA (about 2.0 C) was defined as a 2 C discharge capacity (mAh). Then, the ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was used as the rate characteristic.
Rate characteristics (%) = (2C discharge capacity / 1C discharge capacity) x 100
Evaluation criteria for rate characteristics (%) 〇 (good): Rate characteristics are over 85% △ (possible): Rate characteristics are over 80% and 85% or less × (bad): Rate characteristics are over 80%

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

(8) Thickness of Inorganic Filler Porous Layer (μm)
The difference between the thickness of the base material obtained by the method described in the above "thickness of the base material" column and the thickness of the multilayer porous membrane obtained by the method described in the "thickness of the multilayer porous membrane" column described later. Calculated.

(9) Thickness (μm) of the multilayer porous membrane between the substrate and the inorganic filler porous layer
The measurement target was a multilayer porous membrane, and the measurement was performed by the same method as described in the above-mentioned "Base material thickness" column.

(10) 130 ° C. heat shrinkage rate (%) of the multilayer porous membrane of the base material and the inorganic filler porous layer.
A sample obtained by cutting the multilayer porous membrane to 100 mm in TD and 100 mm in MD was allowed to stand in an oven at 130 ° C. for 1 hour. At this time, the sample was sandwiched between two sheets of paper so that the warm air did not directly hit the sample. After taking out the sample from the oven and cooling it, the length (mm) was measured, and the heat shrinkage rate of MD was calculated by the following formula.
MD heat shrinkage rate (%) = 100-Length in MD after heating (mm)

(11) Rate Characteristics of Multilayer Porous Membrane of Substrate and Inorganic Filler Porous Layer A battery was assembled using the multilayer porous membrane, and the measurement was carried out by the same method as the method described in the above "evaluation of rate characteristics" column.

(12) Glass transition temperature (° C.) 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. About 17 mg of the dry film was filled in an aluminum container for measurement, and a DSC curve and a DSC curve under a nitrogen atmosphere were obtained with a DSC measuring device (manufactured by Shimadzu Corporation, model name "DSC6220"). The measurement conditions were as follows.
1st stage temperature rise program: Start at 30 ° C and raise the temperature at a rate of 10 ° C per minute. Maintained for 5 minutes after reaching 110 ° C.
Second stage temperature lowering program: The temperature is lowered from 110 ° C to 10 ° C per minute. Maintain for 5 minutes after reaching -50 ° C.
Third stage temperature rise program: The temperature rises from -50 ° C to 130 ° C at a rate of 10 ° C per minute. DSC and DDSC data are acquired when the temperature rises in the third stage.
For the obtained DSC curve, the glass transition temperature was determined by the method described in JIS-K7121. Specifically, for a straight line in which the baseline on the low temperature side of the DSC curve is extended to the high temperature side and a straight line in which the baseline on the high temperature side in the DSC curve is extended to the low temperature side at equal distances in the vertical axis direction. The temperature at the point where the curve of the change portion on the stage of the glass transition intersects was defined as the glass transition temperature (Tg).

(13) Average particle size of particulate polymer (D50)
The average particle size (D50) of the particulate polymer was 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 50% particle size (D50) in the obtained data was described as the average particle size.

(14) Solid content (%)
About 1 g of the aqueous dispersion of the thermoplastic polymer was precisely weighed on an aluminum dish, and the mass of the aqueous dispersion weighed at this time was taken 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 by the following formula.
Solid content = ((b) / (a)) x 100 [%]

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

(16) Cover area ratio (%) of the 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, Ltd.). The sample separator was vapor-deposited with osmium, observed under the conditions of an acceleration voltage of 1.0 kV and 50 times, and the surface coverage was calculated from the following formula. The region where the porous structure on the surface of the substrate cannot be seen in the SEM image was defined as the thermoplastic polymer layer region.
Cover area ratio (%) of the thermoplastic polymer layer = {area of the thermoplastic polymer layer / (area including the pore portion of the base material + area of the thermoplastic polymer layer)} × 100
The coverage ratio in each sample was measured three times and used as the arithmetic mean value.

(17) Liquid level after addition 100 ml of an aqueous dispersion of a thermoplastic polymer was placed in a 300 ml container and foamed by shaking by hand about 10 times. Then, the additive (post-added surfactant) was added in the amount shown in Table 5, and the state of the liquid surface 1 minute after the addition was observed.

(18) Repelling of coated surface The surface of the separator having an area of 0.5 m2 coated with the thermoplastic polymer layer was confirmed, and the repelling was determined based on the following criteria. The transfer portion means a concave portion of the coated plate.
None: (Covering area of thermoplastic polymer layer / Transfer area of coating roll) × 100 ≧ 100 (%)
Yes: (Covering area of thermoplastic polymer layer / Transfer area of coating roll) x 100 <100 (%)

(19) Wetness Using a contact angle meter (CA-V) (model name) manufactured by Kyowa Interface Science Co., Ltd., 2 μl of each slurry was dropped on a clean substrate surface, and the contact angle was measured after 40 seconds. For the contact angle of water, the average value measured three times for each of MD and TD was adopted. Moreover, this measurement method was carried out on both the front surface and the back surface of the separator, the larger value of either one was adopted, and the wettability was evaluated according to the following criteria.
◎ (Very good): The contact angle is less than 40 degrees.
◯ (good): The contact angle is 40 degrees or more and less than 60 degrees.
Δ (slightly defective): The contact angle is 60 degrees or more and less than 80 degrees.
X (defective): The contact angle is 80 degrees or more.

(20) Bonding property between the base material and the thermoplastic polymer layer A satin-finished roll (manufactured by Otec Co., Ltd., Ra = 3.1 μm) having a line line of 100 is installed so as to hold it at an angle of 45 °, and the separator after coating is placed. It was conveyed at a speed of 20 m / min. After that, the surface of the satin roll was observed after the separator was continuously conveyed for a total of 1 minute, and the bondability between the base material and the thermoplastic polymer layer was evaluated according to the following criteria.
◎ (Very good): The powder derived from the thermoplastic polymer layer adheres to less than 10% of the surface of the satin roll. ○ (Good): The powder derived from the thermoplastic polymer layer adheres to less than 10% and less than 30% of the surface of the satin roll. Adhesion △ (Slightly defective): The powder derived from the thermoplastic polymer layer adheres to 30% or more and less than 50% of the surface of the satin roll. × (Defective): The powder derived from the thermoplastic polymer layer adheres to 50% or more of the surface of the satin roll. Adhesion

(21) Adhesion to Electrodes The separator for power storage device 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 , Al current collector thickness: 15 μm, press After cutting the latter positive electrode thickness (thickness of 107 μm) into a rectangular shape with a width of 15 mm and a length of 60 mm, and superimposing the thermoplastic polymer layer of the separator and the positive electrode active material so as to face each other, a laminate was obtained. , The laminate was pressed under the following conditions. The room temperature at the time of evaluation was 23 ° C. and the humidity was 30%.
Press pressure: 1MPa
Temperature: 100 ° C
Press time: 5 seconds

For the laminated body after pressing, the electrode is fixed using the force gauge ZP-5N and MX2-500N (product name) manufactured by Imada Co., Ltd., and the peeling speed is 50 mm / min by the method of grasping and pulling the separator. A 90 ° peel test was performed and the peel strength was measured. At this time, the average value of the peel strength in the peel test for a length of 40 mm performed under the above conditions was adopted as the peel strength, and the adhesiveness with the electrode was evaluated according to the following criteria.
◯ (good): The peel strength is 5 N / m or more.
Δ (Slightly defective): The peel strength is 3 N / m or more and less than 5 N / m.
X (defective): The peel strength is less than 3 N / m.

Regarding the above-mentioned "adhesion to electrode" test, Table 1 shows the test results when a polyolefin microporous membrane was used instead of the above-mentioned separator, and Table 2 shows the test results in place of the above-mentioned separator. The test results when a multilayer porous membrane is used are shown. As can be seen from Tables 1 and 2, good adhesion to the electrode is not exhibited only by the polyolefin microporous membrane or the multilayer porous membrane, that is, when the thermoplastic polymer layer is not provided.

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

Then, they were melt-kneaded while being heated to 230 ° C. in a twin-screw extruder, and the obtained melt-kneaded product was extruded through a T-die onto a cooling roll controlled to a surface temperature of 80 ° C. to extrude the extruded product. A sheet-shaped molded product was obtained by contacting with a cooling roll and molding (casting) to cool and solidify. This sheet was stretched at a magnification of 7 × 6.4 times with a simultaneous biaxial stretching machine at a temperature of 112 ° C., then immersed in methylene chloride to extract and remove liquid paraffin, dried, and heated with a tenter stretching machine. It was stretched twice in the lateral direction at 130 ° C. Then, the stretched sheet was relaxed by about 10% in the width direction and heat-treated to obtain a polyolefin microporous film B1 as a base material.

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

[Production Example 1-2] (Production of Polyolefin Microporous Membrane B2)
Separator manufactured by Celgard Co., Ltd., H1609 (model name); the uniaxially stretched film by the dry method was a polyolefin microporous film B2, and the evaluation was carried out in the same manner as in Production Example 1-1. The results obtained are shown in Table 1.

[Manufacturing 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 were uniformly dispersed in 47.7 parts by mass of water, and bead milled to perform 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 only one peak in the particle size distribution chart. Then, an aqueous solution to which 0.10 part by mass of a thickener and 4.1 parts by mass (as a solid content amount) of acrylic latex (average particle size (D50): 300 μm) was added was corona-treated with a discharge amount of 1.0 kV. The surface of the latex microporous film B1 was coated with a gravure coater at a line speed of 30 m / min. Water was removed by drying the applied membrane at 40 ° C. for 10 seconds and then at 70 ° C. for 10 seconds or longer, and an inorganic filler porous layer having a thickness of 4 μm was placed on the polyolefin microporous membrane (layer density: 1.5 g / (m). A multilayer porous membrane B1-1 having a total thickness of 15 μm on which ^2. μm)) was formed was obtained. The obtained multilayer porous membrane was evaluated as described above. The results obtained are shown in Table 2.

[Manufacturing Example 2-2]
A multilayer porous film B1-2 was obtained in the same manner as in 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.

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

[Manufacturing Example 2-4]
A multilayer porous membrane B2-1 was obtained in the same manner as in 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) Aqueous dispersion (referred to as “raw material polymer” in the table. The same shall apply hereinafter.) Synthetic of A1 In a reaction vessel equipped with a stirrer, a reflux cooler, a dropping tank, and a thermometer, ion-exchanged water 70. 4 parts by mass, "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd., indicated as "KH1025" in the table. The same shall apply hereinafter), 0.5 parts by mass, and "Adecaria Soap SR1025" ( A registered trademark, manufactured by ADEKA Co., Ltd., 25% aqueous solution, described as "SR1025" in the table. The same shall apply hereinafter.) 0.5 parts by mass was charged, and the internal temperature of the reaction vessel was raised to 80 ° C. Then, while maintaining the container internal temperature of 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 methacrylate, 0.1 part by mass of acrylate, and methacryl. 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, 0.05 parts by mass of sodium p-styrene sulfonate, trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Industry 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 prepare an emulsion. Made.
The obtained emulsion was dropped from the dropping tank into the reaction vessel. The dropping was started 5 minutes after the ammonium persulfate aqueous solution was added to the reaction vessel, and the entire amount of the emulsion was dropped over 150 minutes. During the dropping of the emulsion, the temperature inside the container was maintained at 80 ° C.

After the completion of dropping the emulsion, the temperature inside 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 aqueous ammonium hydroxide solution (25% aqueous solution) to obtain an acrylic copolymer latex having 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 aqueous dispersion A2 The composition of the monomer and other raw materials is the same as that of the raw material polymer (aqueous dispersion) A1 except that the compositions are changed as shown in Table 3. Copolymer latex (raw material polymer A2) was obtained respectively. The obtained raw material polymers (aqueous dispersion) A2 were each evaluated by the above methods. The results obtained are shown in Table 3.

The abbreviations of the raw material names in Table 3 and Table 4 described later have the following meanings, respectively.
<Emulsifier>
KH1025: "Aqualon KH1025" registered trademark, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., 25% aqueous solution SR1025: "Adecaria Soap SR1025" registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution NaSS: sodium p-styrene sulfonate <initiator ＞
APS (aq): Ammonium persulfate (2% aqueous solution)
<Monomer>
((Meta) 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)
An aqueous dispersion A2-1 was synthesized by taking a part of the aqueous dispersion A2 obtained in Production Example A2 and performing multi-stage polymerization using this as a seed polymer. Specifically, first, in a reaction vessel equipped with a stirrer, a reflux cooler, a dropping tank, and a thermometer, 16 parts by mass of the aqueous dispersion A2 in terms of solid content, 0.5 mass of Aqualon KH1025 (registered trademark). A mixture of 0.5 parts by mass of Adecaria Soap SR1025 (registered trademark) and 70.4 parts by mass of ion-exchanged water was added to raise the temperature inside the reaction vessel to 80 ° C. Then, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) was added while maintaining the container internal temperature of 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 "Aqualon KH1025" (registered trademark, 25% aqueous solution) 2.0% by mass. A mixture of 1.0 part by mass of trimethylolpropane triacrylate, 0.5 part 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. , The mixture was mixed with a homomixer for 5 minutes to prepare an emulsion. The obtained emulsion was dropped from the dropping tank into the reaction vessel. The dropping was started 5 minutes after the ammonium persulfate aqueous solution was added to the reaction vessel, and the entire amount of the emulsion was dropped over 150 minutes. During the dropping of the emulsion, the temperature inside the container was maintained at 80 ° C.

After the completion of dropping the emulsion, the temperature inside 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 aqueous ammonium hydroxide solution (25% aqueous solution) to obtain an acrylic copolymer latex having 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 is subjected to multi-stage polymerization in the same manner as the raw material polymer (aqueous dispersion) A1-1, except that the compositions of the seed polymer, the monomer, and the other raw materials are changed as shown in Table 3, respectively. Got The obtained raw material polymers (aqueous dispersions) were evaluated by the above methods.

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

[Example 2]
A separator was prepared in the same manner as in Example 1 except that the slurry of Example 1 was applied to the polyolefin microporous membrane B2-1 instead of the polyolefin microporous membrane B1-1.
[Example 3]
A slurry and a separator were prepared in the same manner as in Example 1 except that the amount of Orfin SK-14 added was 1.7% by mass with respect to the coating liquid.

[Example 4]
Instead of Orfin SK-14, Orfin AF-103 (manufactured by Nisshin Kagaku Kogyo Co., Ltd.) as a post-added surfactant C1-2 was added so as to be 0.7% by mass with respect to the coating liquid. Made a slurry and a separator in the same manner as in Example 1.

[Example 5]
Instead of Orfin SK-14, Orfin AF-103 (manufactured by Nisshin Kagaku Kogyo Co., Ltd.) as a post-added surfactant C1-2 was added so as to be 1.7% by mass with respect to the coating liquid. Made a slurry and a separator in the same manner as in Example 1.

[Example 6]
Instead of Orfin SK-14, Orfin E-1004 (manufactured by Nisshin Kagaku Kogyo Co., Ltd.) as a post-added surfactant C1-3 was added so as to be 0.7% by mass with respect to the coating liquid. Made a slurry and a separator in the same manner as in Example 1. Orfin E-1004 is an acetylene-based surfactant, but unlike Orfin SK-14, it does not contain a hydrophobic silica filler (hydrophobic silica particles).

[Example 7]
Instead of Orfin SK-14, Orfin E-1004 (manufactured by Nisshin Kagaku Kogyo Co., Ltd.) as a post-added surfactant C1-3 was added so as to be 1.7% by mass with respect to the coating liquid. Made a slurry and a separator in the same manner as in Example 1.

[Comparative Example 1]
Examples except that E-D052 (manufactured by San Nopco Ltd.) as a post-added surfactant C2-1 was added in place of Orfin SK-14 so as to be 2.7% by mass with respect to the coating liquid. A slurry and a separator were prepared in the same manner as in 1. E-D052 is a polyether-based surfactant and does not contain a hydrophobic silica filler.

[Comparative Example 2]
Examples except that BYK-349 (manufactured by BIC Chemie Co., Ltd.) as a post-added surfactant C3-1 was added in place of Orfin SK-14 so as to be 0.8% by mass with respect to the coating liquid. A slurry and a separator were prepared in the same manner as in 1. BYK-349 is a silicone-based surfactant and does not contain a hydrophobic silica filler.

[Comparative Example 3]
Examples except that BYK-349 (manufactured by BIC Chemie Co., Ltd.) as a post-added surfactant C3-1 was added in place of Orfin SK-14 so as to be 1.7% by mass with respect to the coating liquid. A slurry and a separator were prepared in the same manner as in 1.

As can be seen from Table 5, all of Examples 1 to 7 have excellent defoaming properties, no repelling of the coated surface is observed, and the wettability of the base material is also good as compared with Comparative Examples 1 to 3. there were. Further, it was confirmed that in each of Examples 1 to 7, the bondability between the base material and the thermoplastic polymer layer was excellent, and the adhesiveness to the electrode was also good.
Therefore, it was confirmed by Examples 1 to 7 that a slurry for a separator, which has excellent coatability on a base material and can satisfactorily suppress the generation of pinholes and cissing, is provided. In addition, Examples 1 to 7 also provide separators for power storage devices provided with a thermoplastic polymer layer in which the generation of pinholes and cissing is satisfactorily suppressed and the adhesive function is also satisfactorily exhibited. confirmed.

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

In Table 6, the thickness of the thermoplastic polymer layer is based on the value obtained by the same method as the method described in the above-mentioned "thickness of base material" column, with the measurement target being the thermoplastic polymer layer. It was calculated by subtracting the thickness of the porous membrane.

Claims (16)

A slurry used for coating a substrate containing a microporous polyolefin membrane.
It contains a thermoplastic polymer containing a particulate polymer and an acetylene-based surfactant.
A separator slurry containing 0.001 part by mass or more and 10 parts by mass or less of the acetylene-based surfactant when the thermoplastic polymer is 100 parts by mass.
The slurry for a separator according to claim 1, wherein the slurry contains the acetylene-based surfactant in a proportion of 0.01 parts by mass or more and 5 parts by mass or less when the thermoplastic polymer is 100 parts by mass.
The slurry for a separator according to claim 1 or 2, wherein the slurry contains the acetylene-based surfactant in a proportion of 0.1 parts by mass or more and 3 parts by mass or less when the thermoplastic polymer is 100 parts by mass.
The separator slurry according to any one of claims 1 to 3, wherein the slurry has a viscosity of less than 3500 mPa · s.
The separator slurry according to any one of claims 1 to 4, wherein the slurry has a viscosity of less than 350 mPa · s.
The slurry for a separator according to any one of claims 1 to 5, wherein the thermoplastic polymer contains a copolymer composed of a unit of a (meth) acrylic acid ester monomer.
The thermoplastic polymer has at least two glass transition temperatures and
At least one of the glass transition temperatures is present in the region below 20 ° C.
The separator slurry according to any one of claims 1 to 6, wherein at least one of the glass transition temperatures is present in a region of 20 ° C. or higher.
The slurry for a separator according to any one of claims 1 to 7, wherein the slurry contains an inorganic filler in a proportion of 0.001 part by mass or more and less than 1 part by mass when the thermoplastic polymer is 100 parts by mass. ..
It has a substrate containing a microporous polyolefin membrane and a thermoplastic polymer layer that covers at least a portion of at least one surface of the substrate.
A separator for a power storage device containing 0.001 part by mass or more and 10 parts by mass or less of an acetylene-based surfactant when the amount of the thermoplastic polymer in the thermoplastic polymer layer is 100 parts by mass.
The storage device according to claim 9, wherein the thermoplastic polymer layer contains the acetylene-based surfactant in a proportion of 0.01 parts by mass or more and 5 parts by mass or less when the thermoplastic polymer is 100 parts by mass. Separator.
The storage capacity according to claim 9 or 10, wherein the thermoplastic polymer layer contains the acetylene-based surfactant in a proportion of 0.1 parts by mass or more and 3 parts by mass or less when the thermoplastic polymer is 100 parts by mass. Separator for devices.
Any of claims 9 to 11, wherein the area ratio of the base material covered with the thermoplastic polymer layer is 95% or less with respect to 100% of the total area of the surface on which the thermoplastic polymer layer is arranged. The separator for a power storage device according to item 1.
Any of claims 9 to 12, wherein the area ratio of the base material covered with the thermoplastic polymer layer is 80% or less with respect to the total area of 100% of the surface on which the thermoplastic polymer layer is arranged. The separator for a power storage device according to item 1.
The separator for a power storage device according to any one of claims 9 to 13, wherein the thermoplastic polymer contains a copolymer composed of a unit of a (meth) acrylic acid ester monomer.
The thermoplastic polymer has at least two glass transition temperatures and
At least one of the glass transition temperatures is present in the region below 20 ° C.
The separator for a power storage device according to any one of claims 9 to 14, wherein at least one of the glass transition temperatures is present in a region of 20 ° C. or higher.
The invention according to any one of claims 9 to 15, wherein the thermoplastic polymer layer contains an inorganic filler in a proportion of 0.001 part by mass or more and less than 1 part by mass when the thermoplastic polymer is 100 parts by mass. Separator for power storage devices.