WO2014050707A1

WO2014050707A1 - Method for producing porous membrane separator for lithium ion secondary batteries, and method for producing laminate for lithium ion secondary batteries

Info

Publication number: WO2014050707A1
Application number: PCT/JP2013/075362
Authority: WO
Inventors: 裕次郎豊田
Original assignee: 日本ゼオン株式会社
Priority date: 2012-09-28
Filing date: 2013-09-19
Publication date: 2014-04-03
Also published as: JP6119759B2; CN104364938A; KR102090111B1; KR20150063020A; CN104364938B; JPWO2014050707A1

Abstract

A method for producing a porous membrane separator for lithium ion secondary batteries, which comprises: a step wherein a slurry composition for porous membranes, which contains non-conductive particles, a water-soluble polymer compound, water and at least one low-molecular-weight compound that is selected from the group consisting of ammonia and amine compounds, is applied onto at least one surface of a separator base and dried thereon, thereby obtaining a porous membrane; and a step wherein a slurry composition for adhesive layers, which contains a particulate polymer having a glass transition temperature of from 10°C to 110°C (inclusive) and water, is applied onto the porous membrane and dried thereon, thereby obtaining an adhesive layer.

Description

Method for producing porous membrane separator for lithium ion secondary battery, and method for producing laminate for lithium ion secondary battery

The present invention relates to a method for producing a porous membrane separator for a lithium ion secondary battery and a method for producing a laminate for a lithium ion secondary battery.

Among the batteries in practical use, lithium ion secondary batteries exhibit a high energy density, and are often used especially for small electronics. In addition to small-sized applications, development for automobiles is also expected. Such a lithium ion secondary battery generally includes a positive electrode and a negative electrode, a separator, and a non-aqueous electrolyte.

When the battery is activated, it generally generates heat. As a result, the separator made of a stretched resin such as a stretched polyethylene resin is also heated. In general, a separator made of stretched resin tends to shrink even at a temperature of 150 ° C. or less, and easily causes a short circuit of the battery. In order to solve such problems, a separator having a porous film containing non-conductive particles such as an inorganic filler (hereinafter sometimes referred to as a “porous film separator” as appropriate) has been proposed (patent). Reference 1). Usually, the porous film is unlikely to shrink due to heat, so in a battery using the porous film separator, the risk of short circuit is greatly reduced, and a significant improvement in safety is expected. Moreover, since the porous film has pores, the electrolytic solution can penetrate into the porous film, and the battery reaction is not inhibited by the porous film.

Also, it has been proposed to provide an adhesive layer on the porous film (Patent Document 2). When an adhesive layer is provided on the porous film, the adhesion between the porous film and the electrode can be improved. For this reason, since the porous membrane can be stably fixed to the electrode, for example, shrinkage due to heat of the porous membrane can be further suppressed, and safety can be further improved.

Also, techniques such as Patent Documents 3 and 4 are known.

International Publication No. 2009/096528 Japanese Patent No. 4806735 Japanese Patent No. 4657019 JP 2010-9940 A

The porous film can be produced, for example, by applying a slurry composition containing non-conductive particles and a solvent, and if necessary, an optional component on a separator substrate, and drying the solvent.
The adhesive layer can be prepared, for example, by applying a slurry composition containing a polymer and a solvent, and if necessary, an optional component on the porous film and drying the solvent.

Conventionally, an organic solvent has been generally used as a solvent for a slurry composition for producing a porous film and an adhesive layer. However, in the production method using an organic solvent, there are problems that it is necessary to recycle the organic solvent or to ensure safety by using the organic solvent. Therefore, in recent years, a production method using an aqueous slurry composition containing water as a solvent has been studied.

However, when both the porous film and the adhesive layer are produced with an aqueous slurry composition, the porous film may be dissolved by the slurry composition for the adhesive layer. Specifically, the porous film formed by applying and drying an aqueous slurry composition contains a water-soluble component. Therefore, when an aqueous slurry composition is applied on the porous film in order to form an adhesive layer, water-soluble components of the porous film are dissolved in the solvent contained in the applied slurry composition, and as a result, the porous film is formed. It was sometimes melted. When the porous film is melted, the adhesion between the porous film and the adhesive layer is lowered, so that the adhesion of the porous film separator to the electrode also tends to be lowered. Therefore, it has been desired to develop a production method in which the porous film and the adhesive layer can be produced using an aqueous slurry composition, and the porous film is not easily dissolved in the slurry composition for the adhesive layer.

In general, the separator has a sheet-like shape. Moreover, these sheet-like separators are usually transported or stored in a state of being wound up in a roll shape. However, when blocking occurs in the separator, the separators that are overlapped with each other in a roll shape are fixed to each other, and handling properties may be impaired. Here, generally, a porous membrane separator having better adhesion to electrodes tends to cause blocking. Therefore, in a porous membrane separator provided with an adhesive layer, blocking is particularly likely to occur. Therefore, development of a method for producing a porous membrane separator excellent in both adhesiveness and blocking resistance has also been desired.

The present invention was devised in view of the above problems, and is a method for producing a porous membrane separator for a lithium ion secondary battery provided with a porous membrane and an adhesive layer, using an aqueous slurry composition containing water. A production method for producing a porous membrane separator capable of producing a porous membrane and an adhesive layer, wherein the porous membrane is not easily dissolved in the slurry composition for the adhesive layer, and excellent in both adhesion to an electrode and blocking resistance. The purpose is to provide.
Moreover, an object of this invention is to provide the manufacturing method of the laminated body for lithium ion secondary batteries provided with the porous membrane separator manufactured with the manufacturing method of the porous membrane separator of this invention.

As a result of intensive studies to solve the above problems, the present inventor has obtained a porous film containing non-conductive particles, a water-soluble polymer compound, water, and at least one low-molecular compound selected from the group consisting of ammonia and an amine compound. Applying the slurry composition for at least one side of the separator substrate and drying to obtain a porous film; and the slurry composition for an adhesive layer containing a particulate polymer having a glass transition temperature in a predetermined range and water. The manufacturing method including the steps of applying onto the film and drying to obtain the adhesive layer, while suppressing the porous film from being dissolved by the slurry composition for the adhesive layer, was excellent in both adhesion and blocking resistance The inventors have found that a porous membrane separator can be produced, and completed the present invention.
That is, the present invention is as follows.

[1] A slurry composition for a porous membrane containing at least one kind of low-molecular compound selected from the group consisting of non-conductive particles, water-soluble polymer compound, water, and ammonia and an amine compound is used as at least one surface of a separator substrate. Applying to and drying to obtain a porous film, and
A lithium ion secondary comprising a step of applying a slurry composition for an adhesive layer containing a particulate polymer having a glass transition temperature of 10 ° C. or higher and 110 ° C. or lower and water on the porous film and drying to obtain an adhesive layer. A method for producing a porous membrane separator for a battery.
[2] The method for producing a porous membrane separator according to [1], wherein the water-soluble polymer compound has an acidic group.
[3] The method for producing a porous membrane separator according to [2], wherein the acidic group is a carboxyl group.
[4] The method for producing a porous membrane separator according to any one of [1] to [3], wherein the concentration of the low molecular compound in the porous membrane is 1000 ppm or less per unit weight of the porous membrane.
[5] The method for producing a porous membrane separator according to any one of [1] to [4], wherein the low molecular compound is ammonia.
[6] The water-soluble polymer compound is at least one selected from the group consisting of carboxymethylcellulose and a maleimide-maleic acid copolymer containing a structural unit represented by the following formula (I): ]-[5] The manufacturing method of the separator as described in any one of [5].

(In the formula (I), R ¹ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a phenyl group, a phenyl group substituted with an alkyl group having 1 to 6 carbon atoms, (It is at least one selected from the group consisting of a phenyl group substituted with an alkyloxy group having 1 to 6 carbon atoms, a phenyl group substituted with a halogen atom, and a hydroxyphenyl group.)
[7] Manufacture of a laminate for a lithium ion secondary battery, comprising pressure bonding the electrode and the porous membrane separator manufactured by the manufacturing method according to any one of [1] to [6] Method.

According to the method for producing a porous membrane separator of the present invention, a porous membrane separator for a lithium ion secondary battery having a porous membrane and an adhesive layer can be produced. Moreover, a porous film and an adhesive layer can be produced using a slurry composition containing water, and the porous film is hardly dissolved in the slurry composition for the adhesive layer. Furthermore, according to the production method of the present invention, a porous membrane separator excellent in both adhesion to electrodes and blocking resistance can be obtained.
Moreover, according to the manufacturing method of the laminated body for lithium ion secondary batteries of this invention, the laminated body for lithium ion secondary batteries provided with the porous membrane separator manufactured with the manufacturing method of the porous membrane separator of this invention is obtained. .

Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the following embodiments and exemplifications, and may be arbitrarily modified and implemented without departing from the scope of the claims of the present invention and its equivalent scope.

In the following description, (meth) acrylic acid means acrylic acid and methacrylic acid. Moreover, (meth) acrylate means an acrylate and a methacrylate. Furthermore, (meth) acrylonitrile means acrylonitrile and methacrylonitrile.

Furthermore, that a certain substance is water-soluble means that an insoluble content is less than 0.5% by weight when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C. On the other hand, that a certain substance is water-insoluble means that an insoluble content is 90% by weight or more when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C.

[1. Method for producing porous membrane separator]
The method for producing a porous membrane separator of the present invention comprises a step of applying a slurry composition for a porous membrane to at least one surface of a separator substrate and drying to obtain a porous membrane; and a slurry composition for an adhesive layer on the porous membrane. The process includes applying and drying to obtain an adhesive layer. In the manufacturing method of the porous membrane separator of this invention, the thing containing water is used as said slurry composition for porous films, and the slurry composition for contact bonding layers.

[1.1. Step of obtaining a porous film]
In the step of obtaining the porous film, the slurry composition for porous film is applied to at least one surface of the separator substrate and dried to obtain the porous film. A porous film formed using a conventional slurry composition containing water as a solvent is generally easily soluble in water. However, the porous film formed using the slurry composition for porous films according to the present invention is hardly soluble in water. Therefore, even if the slurry composition for adhesive layers containing water is applied on the porous film, the porous film is hardly dissolved.

[1.1.1. Separator substrate]
As the separator base material, any member that can prevent short-circuiting of electrodes without interfering with charge / discharge of the battery in the lithium ion secondary battery can be used. As the separator substrate, for example, a porous substrate having fine pores can be used. Usually, a porous substrate made of an organic material (that is, an organic separator) is used as the separator substrate. Specific examples of the separator base material include microporous membranes and nonwoven fabrics containing polyolefin resins such as polyethylene and polypropylene, aromatic polyamide resins, and the like.

The thickness of the separator substrate is usually 0.5 μm or more, preferably 1 μm or more, and usually 40 μm or less, preferably 30 μm or less, more preferably 10 μm or less. Within this range, the resistance due to the separator substrate in the battery is reduced, and the workability during battery production is excellent.

[1.1.2. Slurry composition for porous film]
The slurry composition for a porous membrane comprises at least one low-molecular compound selected from the group consisting of non-conductive particles, water-soluble polymer compound, water, and ammonia and an amine compound (hereinafter referred to as “low-molecular compound X” as appropriate). May be called.) Moreover, it is preferable that the slurry composition for porous films contains a binder.

[1.1.2.1. Non-conductive particles]
As the non-conductive particles, inorganic particles or organic particles may be used.

Inorganic particles are excellent in dispersion stability in a solvent, hardly settled in the slurry composition for porous membranes, and can usually maintain a uniform slurry state for a long time. In addition, when inorganic particles are used, the heat resistance of the porous film can usually be increased. As the material for the non-conductive particles, an electrochemically stable material is preferable. From this point of view, preferable examples of inorganic materials for non-conductive particles include aluminum oxide (alumina), aluminum oxide hydrate (boehmite (AlOOH), gibbsite (Al (OH) ₃ ), silicon oxide, Oxide particles such as magnesium oxide (magnesia), magnesium hydroxide, calcium oxide, titanium oxide (titania), BaTiO ₃ , ZrO, alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; silicon, diamond Covalent crystal particles such as barium sulfate, calcium fluoride, barium fluoride, etc. Insoluble ion crystal particles such as talc, montmorillonite clay fine particles, etc. Among these, stability in electrolyte From the viewpoint of potential stability, oxide particles are preferable, and in particular, water absorption is low. Titanium oxide, aluminum oxide, aluminum oxide hydrate, magnesium oxide and magnesium hydroxide are more preferred from the viewpoint of excellent heat resistance (for example, resistance to high temperature of 180 ° C. or higher), and aluminum oxide, aluminum oxide hydrate, oxidation Magnesium and magnesium hydroxide are more preferred, and aluminum oxide is particularly preferred.

Polymer particles are usually used as the organic particles. The organic particles can control the affinity for water by adjusting the type and amount of the functional group on the surface of the organic particles, and thus can control the amount of water contained in the porous film. Organic particles are excellent in that they usually have less metal ion elution. Preferable examples of the organic material for the non-conductive particles include various polymers such as polystyrene, polyethylene, polyimide, melamine resin, and phenol resin. The polymer forming the particles may be a mixture, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, a crosslinked product, or the like. The organic particles may be formed by a mixture of two or more kinds of polymers.

When organic particles are used as non-conductive particles, the glass transition temperature may not be present, but when the organic material forming the organic particles has a glass transition temperature, the glass transition temperature is usually 150 ° C. or higher, preferably Is 200 ° C or higher, more preferably 250 ° C or higher, and usually 400 ° C or lower.

Non-conductive particles may be subjected to, for example, element substitution, surface treatment, solid solution, and the like as necessary. Further, the non-conductive particles may include one kind of the above materials alone in one particle, or may contain two or more kinds in combination at an arbitrary ratio. . Further, the non-conductive particles may be used in combination of two or more kinds of particles formed of different materials.

Examples of the shape of the nonconductive particles include a spherical shape, an elliptical spherical shape, a polygonal shape, a tetrapod (registered trademark) shape, a plate shape, and a scale shape. Among these, from the viewpoint of increasing the porosity of the porous membrane and suppressing the decrease in ionic conductivity due to the porous membrane separator, a tetrapod (registered trademark) shape, a plate shape, and a scale shape are preferable.

The volume average particle diameter D50 of the nonconductive particles is usually 0.1 μm or more, preferably 0.2 μm or more, and usually 5 μm or less, preferably 2 μm or less, more preferably 1 μm or less. By using such non-conductive particles having a volume average particle diameter D50, a uniform porous film can be obtained even if the thickness of the porous film is thin, so that the capacity of the battery can be increased. Here, the volume average particle diameter D50 represents the particle diameter at which the cumulative volume calculated from the small diameter side becomes 50% in the particle diameter distribution measured by the laser diffraction method.

The BET specific surface area of the non-conductive particles is, for example, preferably 0.9 m ² / g or more, more preferably 1.5 m ² / g or more. Further, from the viewpoint of suppressing aggregation of non-conductive particles and optimizing the fluidity of the slurry composition for a porous membrane, the BET specific surface area is preferably not too large, for example, 150 m ² / g or less. .

[1.1.2.2. Water-soluble polymer compound]
The water-soluble polymer compound has a function of binding nonconductive particles to each other in the porous film. Therefore, the strength of the porous membrane can be increased by including the water-soluble polymer compound. It is also possible to prevent the nonconductive particles from falling off the porous film.
The water-soluble polymer compound has a function of binding non-conductive particles and the separator base material in the porous membrane separator. Therefore, the binding property between the porous membrane and the separator base material can be enhanced by including the water-soluble polymer compound in the porous membrane.
Furthermore, the water-soluble polymer compound can usually function as a viscosity modifier in the slurry composition for a porous membrane. Therefore, the application | coating property of the slurry composition for porous films can be improved because the slurry composition for porous films contains a water-soluble polymer compound.

The water-soluble polymer compound preferably has an acidic group. Since an acidic group has the effect | action which improves the hydrophilic property of a water-soluble polymer compound, the water-soluble polymer compound which has an acidic group can improve water solubility. In addition, the acidic group usually has an effect of enhancing the binding property of the water-soluble polymer compound to the non-conductive particles and the binding property of the porous membrane to the separator substrate in the porous membrane separator.

Examples of the acidic group possessed by the water-soluble polymer compound include a carboxyl group, a sulfo group, a phosphate group, and a hydroxyl group, and among them, a carboxyl group is preferable. Here, an acidic group may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Examples of water-soluble polymer compounds include maleimide-maleic acid copolymers containing a structural unit (a) represented by the following formula (I). By using this maleimide-maleic acid copolymer, a porous membrane separator having excellent heat shrinkage resistance can be realized, so that the safety of the lithium ion secondary battery can be improved. In addition, since a porous film with a small amount of moisture can be formed, decomposition of the electrolytic solution due to residual moisture can be suppressed. Therefore, since the expansion of the lithium ion secondary battery due to the decomposition of the electrolytic solution can be suppressed, the cycle characteristics of the lithium ion secondary battery can be improved.

In the formula (I), R ¹ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a phenyl group, a phenyl group substituted with an alkyl group having 1 to 6 carbon atoms, It represents at least one selected from the group consisting of a phenyl group substituted with an alkyloxy group having 1 to 6 carbon atoms, a phenyl group substituted with a halogen atom, and a hydroxyphenyl group.

The structural unit (a) represented by the formula (I) represents a maleimide unit of a maleimide-maleic acid copolymer. The structural unit (a) represented by the formula (I) can be derived from, for example, maleimides represented by the following formula (I-1).

In the formula (I-1), R ² is a phenyl substituted by a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a phenyl group, or an alkyl group having 1 to 6 carbon atoms. And at least one selected from the group consisting of a group, a phenyl group substituted with an alkyloxy group having 1 to 6 carbon atoms, a phenyl group substituted with a halogen atom, and a hydroxyphenyl group.

Specific examples of maleimides represented by the formula (I-1) include maleimide; N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-butylmaleimide, N-pentylmaleimide, N-hexylmaleimide; N-phenylmaleimide; N- (2-methylphenyl) maleimide, N- (3-methylphenyl) maleimide, N- (4-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N- (3- Ethylphenyl) maleimide, N- (2-N-propylphenyl) maleimide, N- (2-i-propylphenyl) maleimide, N- (2-N-butylphenyl) maleimide, N- (2,6-dimethylphenyl) ) Maleimide, N- (2,4,6-trimethylphenyl) maleimide, N- (2,6-diethylphenyl) Nyl) maleimide, N- (2,4,6-triethylphenyl) maleimide, N- (2-methoxyphenyl) maleimide, N- (2,6-dimethoxyphenyl) maleimide, N- (2-bromophenyl) maleimide, Examples thereof include N- (2-chlorophenyl) maleimide, N- (2,6-dibromophenyl) maleimide; N- (4-hydroxyphenyl) maleimide and the like. Among these, maleimide is preferable from the viewpoint of reactivity to non-conductive particles. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

The structural unit (a) represented by the formula (I) can also be obtained, for example, by imidizing the structural unit (b) represented by the formula (II) described later.

The maleimide-maleic acid copolymer containing the structural unit (a) represented by the formula (I) contains a maleic acid unit in addition to the maleimide unit. Therefore, the maleimide-maleic acid copolymer including the structural unit (a) represented by the formula (I) includes the structural unit (b) represented by the following formula (II).

In the formula (II), X represents a maleic acid unit. Here, the maleic acid unit represents a structural unit having a structure formed by polymerizing maleic acid. Moreover, the maleic acid unit represented by X may be partially neutralized with ions other than hydrogen ions, may be partially anhydrous, or may be partially esterified.

The structural unit (b) represented by the formula (II) can be derived from, for example, maleic acids represented by the following formula (II-1) or maleic anhydride represented by the formula (II-2).

In the formula (II-1), R ³ and R ⁴ are at least one selected from the group consisting of a hydrogen atom, an alkyl group, an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an alkyl ammonium ion, and an alkanol ammonium ion. Represents. Here, the alkylammonium ion refers to a cation obtained by adding one hydrogen atom to the nitrogen atom of alkylamine. The alkanol ammonium ion refers to a cation obtained by adding one hydrogen atom to the nitrogen atom of alkanolamine. At this time, R ³ and R ⁴ may be the same or different. When R ³ or R ⁴ is an alkyl group, formula (II-1) represents a maleate ester. When R ³ or R ⁴ is an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an alkyl ammonium ion, or an alkanol ammonium ion, the formula (II-1) represents a maleate.

Specific examples of maleic acids represented by the formula (II-1) include maleic acid esters and maleic acid salts.
Examples of maleic acid esters include monomethyl maleate, dimethyl maleate, monoethyl maleate, diethyl maleate, monopropyl maleate, dipropyl maleate and the like.
Examples of maleates include alkali metal salts of maleic acid such as monolithium maleate, dilithium maleate, monosodium maleate, disodium maleate, monopotassium maleate, dipotassium maleate; calcium maleate, maleic acid Alkaline earth metal salts of maleic acid such as magnesium; ammonium salts of maleic acid such as monoammonium maleate and diammonium maleate; monomethylammonium maleate, bismonomethylammonium maleate, monodimethylammonium maleate, bisdimethylmaleate Alkylamine salts of maleic acid such as ammonium; 2-hydroxyethylammonium maleate, bis-2-hydroxyethylammonium maleate, di (2-hydroxymaleate) And the like; chill) ammonium, alkanol amine salts of maleic acid, such as Bisuji maleate (2-hydroxyethyl) ammonium.
Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Furthermore, the maleimide-maleic acid copolymer containing the structural unit (a) represented by the formula (I) is a structural unit represented by the structural unit (a) and the formula (II) represented by the formula (I). In addition to (b), it is preferable to further contain a structural unit (c) represented by the formula (III). The maleimide-maleic acid copolymer containing the structural unit (a) represented by the formula (I) has the structural unit (c) represented by the formula (III), thereby reducing the water content in the porous membrane. Therefore, the cycle characteristics of the lithium ion secondary battery can be improved.

In the formula (III), Y represents a hydrocarbon group having 2 to 12 carbon atoms. The valence of this hydrocarbon group is usually divalent.

The structural unit (c) represented by the formula (III) includes, for example, ethylene, 1-butene, isobutene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, isobutylene, diisobutylene, It can be derived from hydrocarbon compounds such as 1-nonene, 1-decene, 1-dodecene and other olefinic hydrocarbons; styrene, α-methylstyrene and other aromatic hydrocarbons. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

In the maleimide-maleic acid copolymer containing the structural unit (a) represented by the formula (I), when the amount of all the structural units is 100 mol%, the structural unit (a) represented by the formula (I) Is preferably 5 mol% or more, more preferably 10 mol% or more, particularly preferably 15 mol% or more, preferably 75 mol% or less, more preferably 60 mol% or less, particularly preferably 45 mol%. % Or less. By setting the content ratio of the structural unit (a) in the maleimide-maleic acid copolymer to be equal to or higher than the lower limit of the above range, the heat shrinkage resistance of the porous film can be effectively enhanced. Further, the binding property between the non-conductive particles and the water-soluble polymer compound can be improved. Furthermore, by making the amount not more than the upper limit of the above range, the swelling property of the water-soluble polymer compound with respect to the electrolytic solution in the lithium ion secondary battery can be reduced, so that the cycle characteristics of the lithium ion secondary battery are improved. be able to.

In the maleimide-maleic acid copolymer containing the structural unit (a) represented by the formula (I), when the total amount of the structural units is 100 mol%, the structural unit (b) represented by the formula (II) Is preferably 5 mol% or more, more preferably 10 mol% or more, particularly preferably 15 mol% or more, preferably 75 mol% or less, more preferably 60 mol% or less, particularly preferably 45 mol%. % Or less. By setting the content ratio of the structural unit (b) in the maleimide-maleic acid copolymer to be equal to or higher than the lower limit of the above range, the water content of the porous film can be effectively reduced. Can be suppressed. For this reason, expansion of the lithium ion secondary battery due to decomposition of the electrolytic solution can be suppressed, and cycle characteristics can be improved. In addition, by setting it to the upper limit value or less, the heat resistance of the maleimide-maleic acid copolymer can be improved, and the heat shrinkage resistance of the porous film can be effectively enhanced.

In the maleimide-maleic acid copolymer containing the structural unit (a) represented by the formula (I), when the total amount of the structural units is 100 mol%, the structural unit (c) represented by the formula (III) Is preferably 5 mol% or more, more preferably 10 mol% or more, particularly preferably 15 mol% or more, preferably 75 mol% or less, more preferably 60 mol% or less, particularly preferably 45 mol%. % Or less. By setting the content ratio of the structural unit (c) in the maleimide-maleic acid copolymer to be equal to or higher than the lower limit of the above range, the heat resistance of the maleimide-maleic acid copolymer can be effectively enhanced. Therefore, it is possible to improve the heat shrinkage resistance of the porous membrane separator. Moreover, by setting it as the upper limit value or less, the moisture content in the porous film can be further reduced, and the cycle characteristics of the secondary battery can be improved.

Examples of the method for producing a maleimide-maleic acid copolymer containing the structural unit (a) represented by the formula (I) include the following production method A and production method B.
Production Method A: A method of polymerizing maleimides represented by the formula (I-1) and maleic acids represented by the formula (II-1) or maleic anhydride represented by the formula (II-2).
Production method B: a structural unit formed by polymerizing maleic acid represented by formula (II-1) or maleic anhydride represented by (II-2) and then polymerizing the maleic acid or maleic anhydride. A method in which a part is maleamically oxidized with a compound having the group R ² in formula (I-1), and a part thereof is cyclized and dehydrated (imidized).

As the polymerization method in production method A, a known polymerization method may be employed. Among these, a solution polymerization method is preferable because polymerization in a homogeneous system is preferable. Examples of the solvent used in the solution polymerization method include methanol, isopropyl alcohol, isobutyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, butyl acetate, ethyl lactate, tetrahydrofuran, dioxane, butyl cellosolve, dimethylformamide, dimethyl sulfoxide. , Benzene, ethylbenzene, toluene, xylene, cyclohexane, ethylcyclohexane, acetonitrile and the like. These solvents may be used alone or in combination of two or more at any ratio. These solvents may be used after dehydration.

The amount of the solvent used is usually 600 parts by weight or less, preferably 400 parts by weight or less with respect to 100 parts by weight of the maleimide-maleic acid copolymer to be produced. Thereby, a maleimide-maleic acid copolymer having a high molecular weight can be obtained. The lower limit is not particularly limited as long as a solution can be formed.

In the production method A, polymerization is usually carried out by charging a polymerization raw material into a reaction vessel. In the polymerization, it is desirable to exclude dissolved oxygen from the reaction system in advance, for example, by vacuum degassing or nitrogen replacement. The polymerization temperature is preferably −50 ° C. or higher, more preferably 50 ° C. or higher, preferably 200 ° C. or lower, more preferably 150 ° C. or lower in terms of efficiently proceeding the reaction. The polymerization time is preferably 1 hour or longer, preferably 100 hours or shorter, more preferably 50 hours or shorter. By setting the polymerization temperature and the polymerization time in the above ranges, the ease of polymerization control and productivity can be effectively increased.

In the production method B, examples of the compound having the group R ² in the formula (I-1) include ammonia; and primary amines having the group R ² such as aminophenol and normal butylamine. These compounds may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

As production method B, as a production method using a polymer containing units obtained by polymerizing maleic anhydride, for example, a copolymer of a hydrocarbon group having 2 to 12 carbon atoms and maleic anhydride is used. Examples thereof include Production Method B-1 and Production Method B-2.

Production method B-1: A copolymer of a hydrocarbon group having 2 to 12 carbon atoms and maleic anhydride and an aminophenol are usually reacted in an organic solvent such as dimethylformaldehyde at a reaction temperature of usually 40 ° C. or higher and 150 ° C. or lower. The reaction is allowed for 20 hours. Thereby, a part of the maleic anhydride unit is changed to an N- (hydroxyphenyl) malemic acid unit. Here, the maleic anhydride unit represents a structural unit having a structure formed by polymerizing maleic anhydride. The N- (hydroxyphenyl) maleamic acid unit represents a structural unit having a structure formed by polymerizing N- (hydroxyphenyl) malemic acid units. Thereafter, an azeotropic solvent is mixed in order to further remove the water generated by the cyclization dehydration, and the cyclization dehydration reaction is usually carried out at a reaction temperature of 80 ° C. or more and 200 ° C. or less for usually 1 hour to 20 hours. An acid copolymer is obtained.

Production method B-2: A copolymer of a hydrocarbon group having 2 to 12 carbon atoms and maleic anhydride, and aminophenol are usually 80 ° C. or higher and 200 ° C. in an organic solvent such as dimethylformaldehyde in the presence of an azeotropic solvent. The reaction is usually carried out at the following reaction temperature for 1 to 20 hours. Thereby, a part of the maleic anhydride unit is subjected to cyclization dehydration through the N- (hydroxyphenyl) malemic acid unit to obtain a maleimide-maleic acid copolymer.

Specific examples of the copolymer of a hydrocarbon group having 2 to 12 carbon atoms and maleic anhydride described in the above production method B-1 and production method B-2 include a copolymer of isobutylene and maleic anhydride (hereinafter, referred to as “copolymer of maleic anhydride”). As appropriate, it may be referred to as “isobutylene-maleic anhydride copolymer”).

In any of the above production methods B-1 and B-2, water may be removed without using an azeotropic solvent during the cyclization dehydration reaction. For example, water can be removed at a temperature of 100 ° C. or higher and 200 ° C. or lower. Further, the dehydration reaction can be effectively performed by the circulation of nitrogen gas.

Examples of the azeotropic solvent used for removing water generated in the cyclization dehydration reaction include benzene, toluene, xylene and the like. One of these may be used alone, or two or more of these may be used in combination at any ratio.
In the cyclization dehydration reaction, 1 mol of water is generated from 1 mol of N- (hydroxyphenyl) malemic acid unit generated by the reaction of maleic anhydride unit and aminophenol in the isobutylene-maleic anhydride copolymer. The amount of the azeotropic solvent used may be an amount sufficient to azeotropically remove the generated water.

When the reaction of a hydrocarbon group having 2 to 12 carbon atoms, a maleic anhydride copolymer and aminophenol is carried out in two stages as in the above production method B-1, the reaction of the first stage reaction The temperature is usually 40 ° C. or higher, preferably 50 ° C. or higher, and is usually 150 ° C. or lower, preferably 100 ° C. or lower. The reaction temperature of the second stage reaction is usually 80 ° C. or higher, preferably 100 ° C. or higher, and is usually 200 ° C. or lower, preferably 150 ° C. or lower. Here, the reaction in the first stage is to produce a copolymer of N- (hydroxyphenyl) malemic acid by reaction of a copolymer of a hydrocarbon group having 2 to 12 carbon atoms with maleic anhydride and aminophenol. Means a reaction to The second-stage reaction means a reaction in which a copolymer of N- (hydroxyphenyl) malemic acid is cyclized and dehydrated.

Further, as in the above production method B-2, the reaction of a hydrocarbon group having 2 to 12 carbon atoms, a maleic anhydride copolymer and aminophenol is carried out in one step in the presence of an azeotropic solvent for dehydration. When carried out, the reaction temperature is usually 80 ° C. or higher, preferably 100 ° C. or higher, and is usually 200 ° C. or lower, preferably 150 ° C. or lower.

In the above production method B-1 and production method B-2, the reaction time of the copolymer of a hydrocarbon group having 2 to 12 carbon atoms and maleic anhydride and aminophenol is the reaction temperature, the amount of aminophenol used, and the purpose. It depends on the reaction rate. Here, examples of the reaction rate include a modification rate of maleic anhydride units to N- (hydroxyphenyl) maleimide units in the isobutylene-maleic anhydride copolymer. In general, in the production method B-1, both the first stage reaction and the second stage reaction can be performed for 1 hour to 20 hours. In addition, the reaction time in production method B-2 can be 1 to 20 hours.

In the production method described above, the content of the structural unit (a) represented by the formula (I) in the target maleimide-maleic acid copolymer is controlled by, for example, using the amount of aminophenol used, the reaction temperature, and the reaction time. It can be easily done by adjusting.

After completion of the reaction, the maleimide-maleic acid copolymer is easily recovered from the reaction solution by, for example, precipitating the maleimide-maleic acid copolymer using an inert solvent such as water and ethers. sell.

The maleimide-maleic acid copolymer obtained as described above can be made soluble in water by, for example, hydrolysis or neutralization of maleic acid units in the maleimide-maleic acid copolymer. . Specific examples include (1) a method in which maleic anhydride units in a maleimide-maleic acid copolymer are hydrolyzed at a high temperature (80 ° C. or more and 100 ° C. or less); (2) a malein in the maleimide-maleic acid copolymer; The method of neutralizing an acid unit with a neutralizing agent is mentioned. In the method (1), it is preferable to mix a neutralizing agent during the hydrolysis. In the method (2), the temperature at which the neutralizing agent is mixed is not particularly limited, and may be, for example, room temperature.

Examples of the neutralizing agent include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide, magnesium hydroxide, and barium hydroxide; Hydroxides such as hydroxides of metals belonging to Group IIIA in the long periodic table such as aluminum hydroxide; Alkali metal carbonates such as sodium carbonate and potassium carbonate; Alkaline earth metal carbonates such as magnesium carbonate And carbonates of organic amines. Examples of the organic amine include alkyl amines such as ethylamine, diethylamine, and propylamine; alcohol amines such as monomethanolamine, monoethanolamine, and monopropanolamine; ammonia such as ammonia. Among these, those capable of generating sodium ions, lithium ions, and ammonium ions are preferable because they have a high effect of solubilization in water. Moreover, a neutralizing agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Other examples of water-soluble polymer compounds include: carboxymethylcellulose, carboxymethylethylcellulose, methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose and other cellulose derivatives; poly (meth) acrylic acid polymers Etc. Examples of the water-soluble polymer compound include salts such as ammonium salts and alkali metal salts. Among these, a salt of carboxymethyl cellulose is preferable, and an ammonium salt of carboxymethyl cellulose is particularly preferable.

A commercially available ammonium salt of carboxymethyl cellulose can be used. In addition, ammonia used for neutralization may remain in the commercially available ammonium salt of carboxymethyl cellulose. In this case, the remaining ammonia is treated as the low molecular compound X.

The degree of etherification of the cellulose derivative is preferably 0.5 or more, preferably 2 or less, more preferably 1.5 or less. Here, the degree of etherification is a value representing how many hydroxyl groups contained per 3 glucose units of cellulose are etherified on average. By making the degree of etherification within the above range, the slurry composition has high stability, and it is possible to make it difficult for sedimentation and aggregation of solids to occur. Furthermore, the coating property and fluidity | liquidity of a coating material improve by using a cellulose derivative.
Among the water-soluble polymer compounds described above, a maleimide-maleic acid copolymer containing carboxymethylcellulose and the structural unit (a) represented by the formula (I) is preferable.
Moreover, a water-soluble high molecular compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The weight average molecular weight of the water-soluble polymer compound is preferably 1000 or more, more preferably 1500 or more, particularly preferably 2000 or more, preferably 500,000 or less, more preferably 250,000 or less, and particularly preferably 150,000 or less. In particular, the weight average molecular weight of the maleimide-maleic acid copolymer containing the structural unit (a) represented by the formula (I) is preferably 50,000 or more and 100,000 or less. By setting the weight average molecular weight of the water-soluble polymer compound to the lower limit of the above range or more, the strength of the water-soluble polymer compound can be increased and a stable porous film can be formed. Durability such as storage characteristics can be improved. Moreover, since the water-soluble polymer compound can be softened by setting it to the upper limit value or less of the above range, for example, the binding property of the porous film to the separator substrate can be improved. Here, the weight average molecular weight of the water-soluble polymer compound is a value in terms of polystyrene by GPC (gel permeation chromatography) and by gel permeation chromatography (GPC) using N, N-dimethylformamide (DMF) as a developing solution. Can be measured as

The amount of the water-soluble polymer compound is usually 0.1% by weight or more and usually 30% by weight or less as the amount in the porous membrane. Among these, when inorganic particles are used as the non-conductive particles, the amount is preferably 10% by weight or less, more preferably 5% by weight or less. When organic particles are used as the non-conductive particles, the amount is preferably 3% by weight or more, and preferably 10% by weight or less. The amount of the water-soluble polymer compound is preferably 0.01 parts by weight or more, more preferably 0.1 parts by weight or more, particularly preferably 0.5 parts by weight or more with respect to 100 parts by weight of the non-conductive particles. It is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and particularly preferably 10 parts by weight or less. By setting the amount of the water-soluble polymer compound to be equal to or higher than the lower limit of the above range, it is possible to improve the strength and binding property of the porous film and the applicability of the slurry composition for porous film. Moreover, since both the intensity | strength and porosity of a porous membrane can be made high by setting it as an upper limit or less, both the short circuit resistance by a porous membrane separator and the battery characteristic of a lithium ion secondary battery can be made favorable.

[1.1.2.3. Low molecular weight compound]
The slurry composition for a porous film has at least one low molecular compound X selected from the group consisting of ammonia and an amine compound. Since the low molecular compound X is usually vaporized when the film of the slurry composition for porous film is dried, it hardly remains in the porous film. However, it is considered that the removal of the low molecular weight compound X during the above-described drying causes some action, improves the water resistance of the porous film, and makes the porous film difficult to dissolve in water.

Examples of the low molecular weight compound X include ammonia; secondary amines such as dimethylamine, diethylamine, and dibutylamine; tertiary amines such as trimethylamine, triethylamine, tributylamine, and cazabicyclononene. Of these, ammonia is preferable. One of these may be used alone, or two or more of these may be used in combination at any ratio.

The molecular weight of the low molecular compound X is preferably 17 or more, preferably less than 1000, more preferably 200 or less, and particularly preferably 150 or less. By setting the molecular weight of the low molecular compound X below the upper limit of the above range, the low molecular compound X can be stably vaporized and removed from the porous film when the film of the slurry composition for porous film is dried. .

The boiling point of the low molecular compound X is usually 100 ° C. or lower, preferably 90 ° C. or lower, more preferably 80 ° C. or lower. When the boiling point is so low, the low molecular weight compound X can be stably vaporized and removed from the porous membrane when the membrane of the slurry composition for porous membrane is dried. The lower limit is not limited, but is usually −33 ° C. or higher.

In the slurry composition for a porous membrane, the amount of the low molecular compound X is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, particularly preferably 100 parts by weight of the water-soluble polymer compound. It is 0.1 parts by weight or more, preferably 50 parts by weight or less, more preferably 40 parts by weight or less, and particularly preferably 30 parts by weight or less. When the amount of the low molecular compound X is not less than the lower limit of the above range, the water-soluble polymer compound can be neutralized and dissolved. Moreover, when it becomes below the upper limit of the said range, when drying the film | membrane of the slurry composition for porous films, the low molecular compound X can be vaporized stably.

[1.1.2.4. water]
The amount of water in the slurry composition for porous membranes is such that the viscosity of the slurry composition for porous membranes is in a range suitable for coating depending on the types of non-conductive particles, water-soluble polymer compound and low-molecular compound X. It is preferable to adjust. Specifically, the solid content concentration of the non-conductive particles, the water-soluble polymer compound and the low-molecular compound X, and the binder and optional components used as necessary is preferably 20% by weight or more. More preferably, water is used in an amount of 30% by weight or more, preferably 60% by weight or less, more preferably 50% by weight or less.

[1.1.2.5. binder]
It is preferable that the slurry composition for porous films contains a binder. By including the binder, the binding property of the porous membrane is improved, and the strength against mechanical force applied to the porous membrane separator during handling such as winding and transportation can be improved.

As the binder, various polymer components can be used. Examples include styrene / butadiene copolymer (SBR), acrylonitrile / butadiene copolymer (NBR), hydrogenated SBR, hydrogenated NBR, styrene-isoprene-styrene block copolymer (SIS), acrylic polymer, and the like. . Among them, an acrylic polymer is preferable as the binder, and a copolymer of a (meth) acrylic acid ester monomer and a (meth) acrylonitrile monomer is particularly preferable.

Examples of (meth) acrylic acid ester monomers include compounds represented by CH ₂ ═CR ⁵ —COOR ⁶ . Here, R ⁵ represents a hydrogen atom or a methyl group, and R ⁶ represents an alkyl group or a cycloalkyl group.
Examples of (meth) acrylate monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, acrylic N-amyl acid, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, hexyl acrylate, nonyl acrylate, lauryl acrylate, acrylic Acrylates such as stearyl acid and benzyl acrylate; methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-amyl methacrylate, Acrylic acid isoamyl methacrylate n- hexyl, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate, and methacrylate and the like such as benzyl methacrylate. Among these, acrylate is preferable, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferable in that the strength of the porous film can be improved. Moreover, these monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The (meth) acrylonitrile monomer and the (meth) acrylonitrile monomer unit may be used alone or in combination of two or more at any ratio.

The polymerization ratio of the (meth) acrylic acid ester monomer to the (meth) acrylonitrile monomer ((meth) acrylonitrile monomer / (meth) acrylic acid ester monomer) is preferably 1/99 or more. Preferably it is 5/95 or more, preferably 30/70 or less, more preferably 25/75 or less. By making the polymerization ratio of the (meth) acrylic acid ester monomer and the (meth) acrylonitrile monomer equal to or higher than the lower limit of the above range, the swellability of the binder with respect to the electrolytic solution is suppressed, and the ionic conductivity is lowered. Can be prevented. Moreover, the intensity | strength of a binder can be made high and the intensity | strength of a porous membrane separator can be made high by setting it as an upper limit or less.

In addition, the copolymer of the (meth) acrylic acid ester monomer and the (meth) acrylonitrile monomer may include a (meth) acrylic acid ester monomer and a (meth) acrylonitrile monomer, if necessary. Further, copolymerization components other than those may be further copolymerized. Examples of the structural unit corresponding to these copolymer components include a structural unit having a structure formed by polymerizing a vinyl monomer having an acidic group, a crosslinkable monomer unit, and the like.

Examples of the vinyl monomer having an acidic group include a monomer having a —COOH group (carboxyl group; also referred to as “carboxylic acid group”), a monomer having an —OH group (hydroxyl group), and —SO _3. A monomer having an H group (sulfo group; also referred to as “sulfonic acid group”), a monomer having a —PO ₃ H ₂ group, a —PO (OH) (OR) group (R represents a hydrocarbon group) ) And a monomer having a lower polyoxyalkylene group. Moreover, the acid anhydride which produces | generates a carboxylic acid group by a hydrolysis can be used similarly.

Examples of the monomer having a carboxylic acid group include monocarboxylic acids, dicarboxylic acids, dicarboxylic acid anhydrides, and derivatives thereof. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, and isocrotonic acid. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, and methylmaleic acid. Examples of the acid anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride and the like.

Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol, 5-hexen-1-ol; 2-hydroxyethyl acrylate, acrylic acid Alkanol esters of ethylenically unsaturated carboxylic acids such as -2-hydroxypropyl and methacrylic acid-2-hydroxyethyl; general formula CH ₂ ═CR ⁷ —COO— (C _n H _2n O) _m —H (m is 2 An integer of 1 to 9, n is an integer of 2 to 4, R ⁷ represents hydrogen or a methyl group) and esters of (meth) acrylic acid and 2-hydroxyethyl-2 ′-( Dicarboxylic acids such as (meth) acryloyloxyphthalate and 2-hydroxyethyl-2 '-(meth) acryloyloxysuccinate Mono (meth) acrylic esters of droxy esters; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; (meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether Mono (meth) allyl ethers of alkylene glycols such as (meth) allyl-3-hydroxypropyl ether; polyoxyalkylene glycols (meth) such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether Monoallyl ethers; glycerol mono (meth) allyl ether, (meth) allyl-2-chloro-3-hydroxypropyl ether, (meth) allyl-2-hydroxy-3-chloropropyl ether (Poly) alkylene glycol halogen and hydroxy substituted mono (meth) allyl ethers; poly (phenol) mono (meth) allyl ethers of polyphenols such as eugenol and isoeugenol and their halogen substituted products; (meth) allyl-2- And (meth) allyl thioethers of alkylene glycols such as hydroxyethyl thioether and (meth) allyl-2-hydroxypropyl thioether.

Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2-acrylamide-2. -Methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid and the like.

Examples of a monomer having a —PO ₃ H ₂ group and / or —PO (OH) (OR) group (R represents a hydrocarbon group) include, for example, 2- (meth) acryloyloxyethyl phosphate, phosphorus Examples include methyl-2- (meth) acryloyloxyethyl acid, and ethyl (meth) acryloyloxyethyl phosphate.

Examples of the monomer having a lower polyoxyalkylene group include poly (alkylene oxide) such as poly (ethylene oxide).

Among these, the vinyl monomer having an acidic group is a single monomer having a carboxylic acid group because of excellent adhesion to an organic separator and efficient capture of transition metal ions eluted from a positive electrode active material. Preferred are monocarboxylic acids having 5 or less carbon atoms having carboxylic acid groups such as acrylic acid and methacrylic acid, and dicarboxylic acids having 5 or less carbon atoms having two carboxylic acid groups such as maleic acid and itaconic acid. Is preferred. Furthermore, acrylic acid, methacrylic acid, and itaconic acid are preferable from the viewpoint that the prepared slurry composition has high storage stability.

In the copolymer of the (meth) acrylic acid ester monomer and the (meth) acrylonitrile monomer, the content ratio of the structural unit having a structure formed by polymerizing a vinyl monomer having an acidic group is The content is preferably 1.0% by weight or more, more preferably 1.5% by weight or more, preferably 3.0% by weight or less, more preferably 2.5% by weight or less.

The crosslinkable monomer unit is a structural unit obtained by polymerizing a crosslinkable monomer. The crosslinkable monomer is a monomer that can form a crosslinked structure during or after polymerization by heating or energy ray irradiation. As an example of the crosslinkable monomer, a monomer having thermal crosslinkability can be usually mentioned. More specifically, a monofunctional crosslinkable monomer having a thermally crosslinkable crosslinkable group and one olefinic double bond per molecule; a polyfunctional monomer having two or more olefinic double bonds per molecule. A functional crosslinkable monomer is mentioned.

Examples of thermally crosslinkable groups include epoxy groups, N-methylolamide groups, oxetanyl groups, oxazoline groups, and combinations thereof. Among these, an epoxy group is more preferable in terms of easy adjustment of crosslinking and crosslinking density.

Examples of the crosslinkable monomer having an epoxy group as a thermally crosslinkable group and having an olefinic double bond include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl. Unsaturated glycidyl ethers such as ether; butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene Monoepoxides of dienes or polyenes such as; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; and glycidyl acrylate, glycidyl methacrylate, Glycidyl crotonate, Unsaturated carboxylic acids such as glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid Examples include glycidyl esters of acids.

Examples of the crosslinkable monomer having an N-methylolamide group as a thermally crosslinkable group and having an olefinic double bond have a methylol group such as N-methylol (meth) acrylamide (meta ) Acrylamides.

Examples of the crosslinkable monomer having an oxetanyl group as a thermally crosslinkable group and having an olefinic double bond include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) Acryloyloxymethyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, and 2-((meth) acryloyloxymethyl) ) -4-Trifluoromethyloxetane.

Examples of the crosslinkable monomer having an oxazoline group as a heat crosslinkable group and having an olefinic double bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2- Oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

Examples of crosslinkable monomers having two or more olefinic double bonds per molecule include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, and triethylene glycol di (meth). Acrylate, tetraethylene glycol di (meth) acrylate, trimethylolpropane-tri (meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane Diallyl ethers, allyl or vinyl ethers of other polyfunctional alcohols, triallylamine, methylenebisacrylamide, and divinylbenzene It is.

Among these, as the crosslinkable monomer, ethylene dimethacrylate, allyl glycidyl ether, and glycidyl methacrylate are particularly preferable.
Moreover, a crosslinking | crosslinked monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The content ratio of the crosslinkable monomer unit in the copolymer of the (meth) acrylic acid ester monomer and the (meth) acrylonitrile monomer is preferably 0.1% by weight or more, preferably 10%. % By weight or less, more preferably 5% by weight or less. By making the content rate of a crosslinkable monomer unit into the said range, the deformation | transformation of a heat-resistant layer by the elution to the electrolyte solution of a polymer can be suppressed, and the cycling characteristics of a secondary battery can be improved.

The binder may be used alone or in combination of two or more at any ratio.

The weight average molecular weight of the polymer forming the binder is preferably 10,000 or more, more preferably 20,000 or more, preferably 1,000,000 or less, more preferably 500,000 or less. When the weight average molecular weight of the polymer forming the binder is in the above range, the strength of the porous membrane separator and the dispersibility of the nonconductive particles are easily improved.

The glass transition temperature of the binder is preferably −60 ° C. or higher, more preferably −55 ° C. or higher, particularly preferably −50 ° C. or higher, usually 20 ° C. or lower, preferably 15 ° C. or lower, more preferably 5 ° C. or lower. is there. By making the glass transition temperature of a binder more than the lower limit of the said range, the intensity | strength of a binder can be raised and the intensity | strength of a porous film can be improved. Moreover, the softness | flexibility of a porous membrane separator can be made high by setting it as an upper limit or less.

Further, it is preferable to use a particulate binder as the binder. By using a particulate binder, the binder can be bound to the non-conductive particles by points rather than surfaces. For this reason, the space | gap between nonelectroconductive particles can be enlarged and the porosity of a porous film can be made high. In this case, the binder is usually water-insoluble polymer particles.

When the binder is particulate, the volume average particle diameter D50 of the particulate binder is preferably 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, more preferably 400 nm or less. When the volume average particle diameter D50 of the particulate binder is in the above range, the strength and flexibility of the obtained porous membrane separator can be improved.

The amount of the binder in the slurry composition for a porous membrane is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, particularly preferably 0.5 parts by weight with respect to 100 parts by weight of the non-conductive particles. The amount is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and particularly preferably 10 parts by weight or less. By setting the amount of the binder to be equal to or higher than the lower limit of the above range, the binding property between the separator substrate and the porous film can be increased. Moreover, the fall of the ion conductivity by a porous membrane separator can be prevented by making it into an upper limit or less.

The method for producing the binder is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method may be used. Among these, the emulsion polymerization method and the suspension polymerization method are preferable because they can be polymerized in water and used as they are as a material for the slurry composition for porous membranes. Moreover, when manufacturing a binder, it is preferable to include a dispersing agent in the reaction system. As the dispersant, those used in usual synthesis can be used. The amount of the dispersant can be arbitrarily set, and is usually about 0.01 to 10 parts by weight with respect to 100 parts by weight of the total amount of monomers. By using a dispersing agent, sedimentation and aggregation of solid content in the slurry can be suppressed.

[1.1.2.6. Other ingredients]
The slurry composition for porous films may contain arbitrary components other than what was mentioned above as needed. As such components, those that do not affect the battery reaction can be used. Examples of these components include isothiazoline compounds, chelate compounds, pyrithione compounds, dispersants, leveling agents, antioxidants, thickeners, antifoaming agents, and surfactants. Moreover, the electrolyte solution additive which has functions, such as electrolytic solution decomposition suppression, is also mentioned. Moreover, these components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[1.1.2.7. State and production method of slurry composition for porous membrane]
The slurry composition for a porous membrane is usually fluid. In the slurry composition for a porous membrane, the nonconductive particles are dispersed in water, and the water-soluble polymer compound and the low-molecular compound X are dissolved in water. In the slurry composition for porous membranes, a part of the water-soluble polymer compound is usually free in water, but another part is adsorbed on the surface of the non-conductive particle, thereby causing non-conductive particles. Is covered with a stable layer of a water-soluble polymer compound, and the dispersibility of non-conductive particles in water is improved. For this reason, the slurry composition for porous films has good coating properties when applied to the separator substrate. Moreover, when the slurry composition for porous films contains a binder, the binder may be dissolved in water or dispersed. When a particulate binder is used as the binder, the binder is usually dispersed in water.

The slurry composition for a porous membrane is obtained by mixing non-conductive particles, a water-soluble polymer compound, water, a low-molecular compound X, and a binder and optional components as necessary. Mixing may be performed by supplying the above components all at once to a mixer. Moreover, you may divide and mix in multiple steps in arbitrary orders. Further, when the water-soluble polymer compound has an acidic group, the water-soluble polymer compound may form a salt with the low-molecular compound X in some cases. In that case, if a porous slurry composition containing a water-soluble polymer compound and a low molecular compound X is obtained as a result, instead of mixing the water-soluble polymer compound and the low molecular compound X separately, A salt of the water-soluble polymer compound and the low-molecular compound X may be mixed.

As the mixer, for example, a ball mill, sand mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, Hobart mixer, or the like may be used.

[1.1.3. Application]
After preparing the slurry composition for porous membranes, the slurry composition for porous membranes is applied onto the separator substrate. Thereby, the film | membrane of the slurry composition for porous films is formed on a separator base material.
There is no restriction | limiting in the application | coating method of the slurry composition for porous films. Examples of the coating method include a doctor blade method, a dipping method, a die coating method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.
The application amount of the slurry composition for a porous film is usually within a range where a porous film having a desired thickness can be obtained.

[1.1.4. Dry]
After forming the film | membrane of the slurry composition for porous films on a separator base material, the film | membrane is dried. By drying, water is removed from the membrane of the slurry composition for porous membrane, and a porous membrane is obtained. Further, during drying, most of the low molecular weight compound X is vaporized and removed from the membrane of the porous membrane slurry composition. Thereby, the water resistance of the porous film is remarkably improved, and the porous film is hardly dissolved in water.

Examples of the drying method include drying with warm air, hot air, low-humidity air, and the like, vacuum drying, drying with irradiation of energy rays such as infrared rays, far infrared rays, and electron beams.

The temperature during drying is preferably 40 ° C. or higher, more preferably 45 ° C. or higher, particularly preferably 50 ° C. or higher, preferably 90 ° C. or lower, more preferably 80 ° C. or lower, particularly preferably 70 ° C. or lower. . By setting the drying temperature to be equal to or higher than the lower limit of the above range, moisture and low molecular weight compound X from the slurry composition for porous membrane can be efficiently removed. Moreover, the shrinkage | contraction by the heat | fever of a separator base material can be suppressed by making it below an upper limit, and can be applied.

The drying time is preferably 5 seconds or more, more preferably 10 seconds or more, particularly preferably 15 seconds or more, preferably 3 minutes or less, more preferably 2 minutes or less, and particularly preferably 1 minute or less. By setting the drying time to be equal to or more than the lower limit of the above range, water can be sufficiently removed from the porous film, so that the output characteristics of the battery can be improved. Moreover, manufacturing efficiency can be improved by setting it as an upper limit or less.

[1.1.5. Other operations]
In the step of obtaining the porous film, any operation other than those described above may be performed. For example, the porous film may be subjected to pressure treatment by a pressing method such as a mold press and a roll press. By performing the pressure treatment, the binding property between the separator substrate and the porous film can be improved. However, if the pressure treatment is excessively performed, the porosity of the porous film may be impaired. Therefore, it is preferable to appropriately control the pressure and the pressure time. Moreover, it is preferable to dry in vacuum drying or a dry room for residual moisture removal. Heat treatment is also preferred, whereby the thermally crosslinkable group in the binder is crosslinked, and the binding force is further improved.

[1.1.6. Porous membrane]
By passing through the process mentioned above, a porous film is formed on a separator base material. This porous film contains non-conductive particles and a water-soluble polymer compound, and, if necessary, a binder and optional components. The amounts of the non-conductive particles, the water-soluble polymer compound and the binder are usually the same as the amounts contained in the porous membrane slurry composition.

Since the voids between the non-conductive particles form pores in the porous film, the porous film has a porous structure. For this reason, since the porous film has liquid permeability, the movement of ions is not hindered by the porous film. Therefore, in the lithium ion secondary battery, the porous film does not inhibit the battery reaction. In addition, since the non-conductive particles do not have conductivity, the porous film can exhibit insulation. Furthermore, since the rigidity of the porous film can be increased by including non-conductive particles, the rigidity of the porous film separator can be increased, and a short circuit can be stably prevented.

This porous film is excellent in water resistance and hardly dissolves in water. That is, the water-soluble polymer compound contained in the porous film is difficult to elute into water. Therefore, the porous film has a high binding property with respect to the separator substrate.
Moreover, since water is removed by drying, the porous film has a low water content. Therefore, since generation of gas due to water can be suppressed, a decrease in discharge capacity due to charge / discharge can be suppressed. For this reason, it is possible to improve the cycle characteristics of a lithium ion secondary battery.

Further, since the low molecular compound X is removed from the slurry composition for the porous membrane during drying, the concentration of the low molecular compound X remaining in the porous membrane is small. Specifically, the concentration of the low molecular compound X in the porous membrane is usually 1000 ppm or less, preferably 500 ppm or less, more preferably 200 ppm or less per weight of the porous membrane. The lower limit is ideally 0 ppm, but is usually 1 ppm or more.

The thickness of the porous membrane is preferably 0.1 μm or more, more preferably 0.2 μm or more, particularly preferably 0.3 μm or more, preferably 20 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. By setting the thickness of the porous film to be equal to or more than the lower limit of the above range, the heat resistance of the porous film can be increased. Moreover, the fall of the ionic conductivity by a porous film can be suppressed by setting it as an upper limit or less.

[1.2. Step of obtaining an adhesive layer]
In the step of obtaining the adhesive layer, the adhesive layer slurry composition is applied onto the porous film and dried to obtain the adhesive layer. At this time, since the porous film has high water resistance, the porous film is hardly dissolved even when the slurry composition for adhesive layer containing water is applied.

[1.2.1. Slurry composition for adhesive layer]
The slurry composition for an adhesive layer contains a particulate polymer and water. Moreover, the slurry composition for adhesive layers may contain the binder.

[1.2.1.1. Particulate polymer]
The particulate polymer usually has a glass transition temperature of 10 ° C. or higher, preferably 30 ° C. or higher, more preferably 40 ° C. or higher, and usually 110 ° C. or lower, preferably 100 ° C. or lower, more preferably 90 ° C. or lower. A particulate polymer is used. When the glass transition temperature of the particulate polymer is equal to or higher than the lower limit of the above range, the softening of the particulate polymer can be suppressed during storage, transportation and handling of the porous membrane separator, and blocking can be prevented. Moreover, the heat resistance of a contact bonding layer improves by using a particulate polymer with a high glass transition temperature. Therefore, even if the battery becomes high temperature when the lithium ion secondary battery is used, peeling of the porous membrane separator can be prevented, and the safety of the battery can be improved. Moreover, when it is below the upper limit, the particulate polymer can be easily softened by heat when the porous membrane separator is bonded to the electrode. In addition, the adhesive layer can be heat-sealed at a low temperature without damaging the elements constituting the battery such as the separator substrate. Therefore, the porous membrane separator and the electrode can be easily bonded by hot pressing.

As the particulate polymer, various polymers having a glass transition temperature in the above range can be used.
Among them, as the particulate polymer, a polymer containing a structural unit having a structure formed by polymerizing an acrylate monomer (hereinafter sometimes referred to as “acrylate ester monomer unit” as appropriate). Is preferred.
Examples of the acrylate monomer include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl. Examples include acrylic acid alkyl esters such as acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate. These may use only 1 type and may use it combining 2 or more types by arbitrary ratios.

The ratio of the acrylate monomer in the total amount of the monomer of the particulate polymer is usually 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more, and usually 95% by weight or less. Preferably it is 90 weight% or less, More preferably, it is 85 weight% or less. By setting the ratio of the acrylate monomer to be equal to or higher than the lower limit of the above range, the binding property between the adhesive layer and the porous film can be enhanced. Moreover, the ionic conductivity of a porous membrane separator can be made high by suppressing the swelling property with respect to the electrolyte solution of an adhesive layer by setting it as an upper limit or less. Here, the ratio of the acrylate monomer in the total amount of the monomer of the particulate polymer usually coincides with the ratio of the acrylate monomer unit in the particulate polymer.

Further, the particulate polymer may be referred to as a structural unit having a structure formed by polymerizing an ethylenically unsaturated carboxylic acid monomer (hereinafter, referred to as “ethylenically unsaturated carboxylic acid monomer unit” as appropriate). ) Is preferred.
Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acid, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof. Examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid and the like. Examples of the ethylenically unsaturated dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like. Examples of the acid anhydride of the ethylenically unsaturated dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride and the like. Among these, ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferable. This is because the dispersibility of the particulate polymer in water can be further improved. These may use only 1 type and may use it combining 2 or more types by arbitrary ratios.

The ratio of the ethylenically unsaturated carboxylic acid monomer in the total amount of the monomer of the particulate polymer is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more. In general, it is 95% by weight or less, preferably 90% by weight or less, more preferably 85% by weight or less. By making the ratio of the ethylenically unsaturated carboxylic acid monomer equal to or higher than the lower limit of the above range, the blocking resistance of the porous membrane separator can be enhanced. Moreover, the adhesive strength of a porous membrane separator and an electrode can be raised by setting it as below an upper limit. Here, the ratio of the ethylenically unsaturated carboxylic acid monomer in the total amount of the monomer of the particulate polymer usually coincides with the ratio of the ethylenically unsaturated carboxylic acid monomer unit in the particulate polymer.

Further, as the particulate polymer, a polymer containing a structural unit having a structure formed by polymerizing an aromatic vinyl monomer (hereinafter sometimes referred to as “aromatic vinyl monomer unit” as appropriate). Is preferred.
Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene. Of these, styrene is preferred. One of these may be used alone, or two or more of these may be used in combination at any ratio.

The ratio of the aromatic vinyl monomer to the total amount of the monomer of the particulate polymer is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more, usually 95%. % By weight or less, preferably 90% by weight or less, more preferably 85% by weight or less. By making the ratio of the aromatic vinyl monomer equal to or higher than the lower limit of the above range, the blocking resistance of the porous membrane separator can be enhanced. Moreover, the adhesive strength of a porous membrane separator and an electrode can be raised by setting it as below an upper limit. Here, the ratio of the aromatic vinyl monomer in the total amount of the monomer of the particulate polymer usually coincides with the ratio of the aromatic vinyl monomer unit in the particulate polymer.

The particulate polymer includes a structural unit having a structure formed by polymerizing a (meth) acrylonitrile monomer (hereinafter sometimes referred to as “(meth) acrylonitrile monomer unit” as appropriate). Polymers are preferred.
Examples of the (meth) acrylonitrile monomer include acrylonitrile and methacrylonitrile. As the (meth) acrylonitrile monomer, only acrylonitrile may be used, methacrylonitrile alone may be used, or both acrylonitrile and methacrylonitrile may be used in combination at any ratio.

The ratio of the (meth) acrylonitrile monomer in the total amount of the monomer of the particulate polymer is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more. It is 95 weight% or less, Preferably it is 90 weight% or less, More preferably, it is 85 weight% or less. By setting the ratio of the (meth) acrylonitrile monomer to the lower limit value or more of the above range, the adhesive strength between the porous membrane separator and the electrode can be increased. Moreover, the binding property of a contact bonding layer and a porous film can be improved by setting it as an upper limit or less. Here, the ratio of the (meth) acrylonitrile monomer in the total amount of the monomer of the particulate polymer usually coincides with the ratio of the (meth) acrylonitrile monomer unit in the particulate polymer.

Moreover, it is preferable to use what has a crosslinkable group as a particulate polymer. Therefore, it is preferable to use a crosslinkable monomer as the monomer of the particulate polymer. Here, the crosslinkable monomer represents a monomer capable of forming a crosslinked structure during or after polymerization by heating.
Examples of the crosslinkable monomer include a monomer having thermal crosslinkability. More specifically, for example, a monofunctional monomer having a thermally crosslinkable crosslinkable group and one olefinic double bond per molecule; a polyfunctional monomer having two or more olefinic double bonds per molecule; A functional monomer is mentioned.

Among these examples, ethylene dimethacrylate, allyl glycidyl ether, and glycidyl methacrylate are particularly preferable as the crosslinkable monomer.
Moreover, a crosslinking | crosslinked monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The ratio of the crosslinkable monomer in the total amount of the monomer of the particulate polymer is usually 0.01% by weight or more, preferably 0.05% by weight or more, usually 5% by weight or less, preferably 3% by weight. Hereinafter, it is more preferably 2% by weight or less. By setting the ratio of the crosslinkable monomer to the lower limit value or more of the above range, the strength of the porous film can be increased. In addition, swelling of the porous membrane due to the electrolytic solution can be suppressed. Moreover, the softness | flexibility of a porous film can be made high by setting it as an upper limit or less. Here, the ratio of the crosslinkable monomer in the total amount of the monomer of the particulate polymer usually coincides with the ratio of the crosslinkable monomer unit in the particulate polymer.

The volume average particle diameter D50 of the particulate polymer is preferably 10 nm or more, more preferably 50 nm or more, particularly preferably 100 nm or more, preferably 1000 nm or less, more preferably 800 nm or less, and particularly preferably 500 nm or less. Since the volume average particle diameter D50 of the particulate polymer is not less than the lower limit of the above range, it is possible to suppress an increase in the particle filling rate in the porous film, and thus the ionic conductivity in the porous film is reduced. Can be suppressed, and excellent cycle characteristics can be realized. Moreover, since it becomes easy to control the dispersion state of a slurry because it is below an upper limit, manufacture of the porous film of uniform predetermined thickness becomes easy.

[1.2.1.2. binder]
The slurry composition for adhesive layers may contain a binder. By including the binder, the binding property of the adhesive layer to the porous film can be enhanced.

As the binder, for example, the same binder as described in the section of the slurry composition for porous film can be used. However, the particulate polymer whose glass transition temperature falls within the temperature range described in the section of the particulate polymer is handled not as a binder but as a particulate polymer.

The amount of the binder in the slurry composition for the adhesive layer is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, and particularly preferably 1 part by weight or more with respect to 100 parts by weight of the particulate polymer. Yes, preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and particularly preferably 10 parts by weight or less. By setting the amount of the binder to be equal to or more than the lower limit of the above range, the binding force between the particulate polymers can be improved, and the separation of the particulate polymers can be prevented. Moreover, it can suppress that the ionic conductivity of an contact bonding layer falls by setting it as an upper limit or less, and can implement | achieve the outstanding cycling characteristics.

[1.2.1.3. water]
The amount of water in the slurry composition for the adhesive layer should be adjusted so that the viscosity of the slurry composition for the adhesive layer is in a range suitable for coating depending on the type of the particulate polymer and the binder used as necessary. Is preferred. Specifically, the solid content of the particulate polymer and the binder and optional components used as necessary is preferably 10% by weight or more, more preferably 20% by weight or more, and preferably Is used in an amount of 60% by weight or less, more preferably 50% by weight or less.

[1.2.1.4. Other ingredients]
The slurry composition for adhesive layers may contain arbitrary components other than what was mentioned above as needed. As such components, those that do not affect the battery reaction can be used. Examples of these components include water-soluble polymers for adjusting viscosity and preventing sedimentation, and wetting agents for improving wettability to organic separators. Moreover, these components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[1.2.1.5. State and production method of slurry composition for adhesive layer]
The slurry composition for an adhesive layer is usually fluid. In the slurry composition for an adhesive layer, the particulate polymer is dispersed in water. Further, the binder may be dispersed in water or dissolved. When a particulate binder is used as the binder, the binder is usually dispersed in water.

The method for producing the slurry composition for the adhesive layer is not particularly limited. Usually, it is obtained by mixing the above-mentioned particulate polymer and water, and a binder and optional components used as necessary. There is no particular limitation on the mixing order. There is no particular limitation on the mixing method.

[1.2.2. Application]
After preparing the slurry composition for adhesive layers, the slurry composition for adhesive layers is apply | coated on a porous film. Thereby, the film | membrane of the slurry composition for contact bonding layers is formed on a porous film.
There is no restriction | limiting in the application method of the slurry composition for contact bonding layers. Examples of the coating method include a doctor blade method, a dipping method, a die coating method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.
The application amount of the slurry composition for the adhesive layer is usually in a range where an adhesive layer having a desired thickness can be obtained.

[1.2.3. Dry]
After forming the film | membrane of the slurry composition for contact bonding layers on a porous film, the film | membrane is dried. By drying, water is removed from the film | membrane of the slurry composition for contact bonding layers, and an contact bonding layer is obtained.

The temperature during drying is preferably 40 ° C or higher, more preferably 45 ° C or higher, particularly preferably 50 ° C or higher, preferably 80 ° C or lower, more preferably 75 ° C or lower, particularly preferably 70 ° C or lower. . By making the drying temperature equal to or higher than the lower limit of the above range, moisture from the slurry composition for the adhesive layer can be efficiently removed. Moreover, the shrinkage | contraction by the heat | fever of a separator base material can be suppressed by making it below an upper limit, and can be applied.

The drying time is preferably 5 seconds or more, more preferably 10 seconds or more, particularly preferably 15 seconds or more, preferably 3 minutes or less, more preferably 2 minutes or less, and particularly preferably 1 minute or less. By making drying time more than the minimum of the said range, the water | moisture content from the slurry composition for contact bonding layers can fully be removed. Moreover, the shrinkage | contraction by the heat | fever of a separator base material can be suppressed by setting it as an upper limit or less.

[1.2.4. Other operations]
In the step of obtaining the adhesive layer, any operation other than those described above may be performed. For example, in order to remove residual moisture, a drying process may be performed in vacuum drying or a dry room, or a heat treatment may be performed.

[1.2.5. Adhesive layer]
By passing through the process mentioned above, an adhesion layer is formed on a porous membrane and a porous membrane separator is obtained. This adhesive layer contains a particulate polymer and, if necessary, a binder and optional components. The amount of the particulate polymer and the binder is usually the same as the amount contained in the adhesive layer slurry composition.

Since the voids between the particulate polymers form pores in the adhesive layer, the adhesive layer has a porous structure. For this reason, since the adhesive layer has liquid permeability, the movement of ions is not hindered by the adhesive layer. Therefore, in the lithium ion secondary battery, the battery reaction is not inhibited by the adhesive layer. In addition, since the particulate polymer does not have conductivity, the adhesive layer can exhibit insulation.

In such an adhesive layer, the particulate polymer can be softened by heating. Therefore, the adhesive layer can be favorably adhered to other members such as an electrode by performing pressure adhesion while heating. Therefore, the porous membrane separator provided with the adhesive layer can be adhered to the electrode with high adhesive strength. Moreover, since the particulate polymer has a high glass transition temperature, the adhesive layer has high heat resistance. Therefore, even when the temperature of the lithium ion secondary battery becomes high due to charging / discharging, the porous membrane separator is difficult to peel off from the electrode. Therefore, short circuit can be prevented more stably, and safety can be improved.

The thickness of the adhesive layer is preferably 0.1 μm or more, more preferably 0.2 μm or more, particularly preferably 0.3 μm or more, preferably 8.0 μm or less, more preferably 5.0 μm or less, particularly preferably 3 0.0 μm or less. By setting the thickness of the adhesive layer to be equal to or more than the lower limit of the above range, the adhesion strength between the porous membrane separator and the electrode can be increased. Moreover, the ion conductivity of a porous membrane separator can be made high by setting it as an upper limit or less.

[1.3. Other processes]
In the method for producing a porous membrane separator of the present invention, steps other than those described above may be performed as long as a desired porous membrane separator is obtained. For example, in order to remove residual moisture, a drying process may be performed in vacuum drying or a dry room, or a heat treatment may be performed.

[2. Porous membrane separator]
The porous membrane separator produced by the method for producing a porous membrane separator of the present invention comprises a separator substrate, a porous membrane, and an adhesive layer in this order. Since the electrolytic solution can permeate into these separator base material, porous membrane and adhesive layer, the porous membrane separator does not adversely affect the battery characteristics. Moreover, since the porous film is difficult to dissolve into the slurry composition for the adhesive layer, the strength and binding property of the porous film are good. Therefore, since the adhesive strength of the porous membrane separator to the electrode can be increased, the safety of the lithium ion secondary battery can be improved. Furthermore, the particulate polymer contained in the adhesive layer is difficult to soften in the normal use environment of the porous membrane separator. Therefore, the porous membrane separator has excellent blocking resistance.

The porous membrane separator may include components other than the separator substrate, the porous membrane, and the adhesive layer.
In addition, the porous film and the adhesive layer may be provided on only one side of the separator substrate or on both sides.

[3. Manufacturing method of laminate]
The manufacturing method of the laminated body for lithium ion secondary batteries of this invention includes pressure-bonding an electrode and the porous membrane separator manufactured with the manufacturing method of the porous membrane separator of this invention.

[3.1. electrode]
The electrode usually includes a current collector and an electrode active material layer provided on the current collector.

[3.1.1. Current collector]
As the current collector, a material having electrical conductivity and electrochemical durability can be used. Among these, metal materials such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum are preferable from the viewpoint of heat resistance. Among them, aluminum is particularly preferable for the positive electrode, and copper is particularly preferable for the negative electrode.

The shape of the current collector is not particularly limited, but for example, a sheet shape having a thickness of 0.001 mm to 0.5 mm is preferable.
In order to increase the adhesive strength with the electrode active material layer, the current collector is preferably used after roughening in advance. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, for example, an abrasive cloth paper to which abrasive particles are fixed, a grindstone, an emery buff, a wire brush provided with a steel wire, or the like can be used.
Further, an intermediate layer may be formed on the current collector surface in order to increase the adhesive strength and conductivity with the electrode active material layer.

[3.1.2. Electrode active material layer]
The electrode active material layer includes an electrode active material. In the following description, among the electrode active materials, the electrode active material for the positive electrode may be referred to as “positive electrode active material”, and the electrode active material for the negative electrode may be referred to as “negative electrode active material”.

As the electrode active material, a material capable of reversibly inserting and releasing lithium ions by applying a potential in an electrolytic solution can be used. As the electrode active material, an inorganic compound or an organic compound may be used.

The positive electrode active material is roughly classified into those made of inorganic compounds and those made of organic compounds. Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Examples of the transition metal include Fe, Co, Ni, and Mn. Specific examples of inorganic compounds used for the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO _{4, and} other lithium-containing composite metal oxides; TiS ₂ , TiS ₃ , non- Transition metal sulfides such as crystalline MoS ₂ ; transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O _13, etc. Can be mentioned. On the other hand, examples of the positive electrode active material made of an organic compound include conductive polymers such as polyacetylene and poly-p-phenylene.

Furthermore, you may use the positive electrode active material which consists of a composite material which combined the inorganic compound and the organic compound.
Alternatively, for example, a composite material covered with a carbon material may be produced by reducing and firing an iron-based oxide in the presence of a carbon source material, and the composite material may be used as a positive electrode active material. Iron-based oxides tend to have poor electrical conductivity, but can be used as a high-performance positive electrode active material by using a composite material as described above.
Furthermore, you may use as a positive electrode active material what carried out the element substitution of the said compound partially.
These positive electrode active materials may be used alone or in combination of two or more at any ratio.

The particle size of the positive electrode active material is appropriately selected in consideration of other constituent elements of the battery. From the viewpoint of improving battery characteristics such as load characteristics and cycle characteristics, the volume average particle diameter D50 of the positive electrode active material is usually 0.1 μm or more, preferably 1 μm or more, and usually 50 μm or less, preferably 20 μm or less. When the volume average particle diameter D50 of the positive electrode active material is within this range, a battery having a large charge / discharge capacity can be obtained, and handling in producing the slurry composition for an active material layer and the electrode is easy.

Examples of the negative electrode active material include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, and pitch-based carbon fibers; and conductive polymers such as polyacene. Further, metals such as silicon, tin, zinc, manganese, iron and nickel, and alloys thereof; oxides of the metals or alloys; sulfates of the metals or alloys; Further, metallic lithium; lithium alloys such as Li—Al, Li—Bi—Cd, and Li—Sn—Cd; lithium transition metal nitride; silicon and the like may be used. Further, an electrode active material having a conductive material attached to the surface by a mechanical modification method may be used. These negative electrode active materials may be used alone or in combination of two or more at any ratio.

The particle size of the negative electrode active material is appropriately selected in consideration of other constituent elements of the battery. From the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics, the volume average particle diameter D50 of the negative electrode active material is usually 1 μm or more, preferably 15 μm or more, and usually 50 μm or less, preferably 30 μm or less. .

The electrode active material layer preferably contains a binder in addition to the electrode active material. By including the binder, the binding property of the electrode active material layer in the electrode is improved, and the strength against the mechanical force is increased in the process of winding the electrode. In addition, since the electrode active material layer in the electrode is difficult to be detached, the risk of a short circuit due to the desorbed material is reduced.

As the binder for the electrode active material layer, various polymer components can be used. For example, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives, and the like may be used. Moreover, you may use the binder similar to what was demonstrated by the term of the porous film of the porous film separator or the contact bonding layer. Moreover, a binder may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

The amount of the binder in the electrode active material layer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, and particularly preferably 0.5 parts by weight or more with respect to 100 parts by weight of the electrode active material. The amount is preferably 5 parts by weight or less, more preferably 4 parts by weight or less, and particularly preferably 3 parts by weight or less. When the amount of the binder is within the above range, it is possible to prevent the electrode active material from dropping from the electrode without inhibiting the battery reaction.

The electrode active material layer may contain any component other than the electrode active material and the binder as long as the effects of the present invention are not significantly impaired. Examples thereof include a conductive material and a reinforcing material. In addition, arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Examples of the conductive material include conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube; carbon powder such as graphite; fiber and foil of various metals; . By using a conductive material, electrical contact between electrode active materials can be improved, and discharge characteristics can be improved particularly when used in a lithium secondary battery.

As the reinforcing material, for example, various inorganic and organic spherical, plate, rod or fiber fillers can be used.

The amount of the conductive material and the reinforcing material used is usually 0 part by weight or more, preferably 1 part by weight or more, and usually 20 parts by weight or less, preferably 10 parts by weight or less, with respect to 100 parts by weight of the electrode active material. is there.

The thickness of the electrode active material layer for both the positive electrode and the negative electrode is usually 5 μm or more, preferably 10 μm or more, and usually 300 μm or less, preferably 250 μm or less.

The method for producing the electrode active material layer is not particularly limited. The electrode active material layer can be produced, for example, by applying a slurry containing an electrode active material and a solvent, and, if necessary, a binder and optional components on a current collector and drying it. As the solvent, either water or an organic solvent can be used.

[3.2. Pressure bonding]
A laminate for a lithium secondary battery is obtained by pressure-bonding the electrode and the porous membrane separator. When the electrode includes an electrode active material layer, the electrode and the porous membrane separator are usually stacked and bonded so that the electrode active material layer of the electrode and the adhesive layer of the porous membrane separator face each other.

The magnitude of the pressure applied during bonding is usually 0.01 MPa or more, preferably 0.05 MPa or more, more preferably 0.1 MPa or more, and usually 2 MPa or less, preferably 1.5 MPa or less, more preferably 1 MPa or less. It is. By making the magnitude of the pressure equal to or greater than the lower limit of the above range, the electrode plate and the adhesive layer can be sufficiently bonded. Moreover, the film breakage of a porous membrane separator can be prevented at the time of adhesion | attachment by setting it as below an upper limit.

Also, the porous membrane separator is usually heated at the time of bonding. The specific temperature at this time is usually not lower than the glass transition temperature of the particulate polymer contained in the adhesive layer of the porous membrane separator, preferably 40 ° C. or higher, more preferably 50 ° C. or higher, particularly preferably 60 ° C. In addition, the temperature is preferably 100 ° C. or lower, more preferably 95 ° C. or lower, and particularly preferably 90 ° C. or lower. By setting the temperature to be equal to or higher than the lower limit of the above range, the electrode and the porous membrane separator can be firmly bonded. Moreover, deterioration by the heat | fever of the element which comprises a battery can be prevented by setting it as below an upper limit.

The time for applying pressure and heat as described above is preferably 0.5 seconds or more, more preferably 1 second or more, particularly preferably 2 seconds or more, preferably 30 seconds or less, more preferably 20 seconds or less, particularly Preferably it is 10 seconds or less. By setting the time for applying pressure and heat to be equal to or greater than the lower limit of the above range, the electrode and the porous membrane separator can be firmly bonded. Moreover, the film breakage of a porous membrane separator can be prevented at the time of adhesion | attachment by setting it as below an upper limit.

By performing pressure bonding as described above, a laminate for a lithium ion secondary battery including an electrode and a porous membrane separator is obtained. At this time, the electrode may be adhered to only one surface of the porous membrane separator, or the electrode may be adhered to both surfaces. For example, when using a porous membrane separator provided with a porous membrane and an adhesive layer on both sides of the separator substrate, a laminate for a lithium ion secondary battery comprising a positive electrode, a porous membrane separator, and a negative electrode in this order can be produced.

[3.3. Other processing]
In the manufacturing method of the laminated body for lithium ion secondary batteries of this invention, in addition to the process mentioned above, you may perform an arbitrary process further.
For example, after winding or laminating an electrode and a separator, the electrode and the separator may be embedded, embedded in a laminate film, injected with an electrolytic solution, sealed, and then pressed together with the cell to adhere to the electrode and the separator.

[4. Lithium ion secondary battery]
A lithium ion secondary battery can be manufactured by using the porous membrane separator or the laminate for a lithium ion secondary battery obtained by the manufacturing method described above. This lithium ion secondary battery includes a positive electrode, a porous membrane separator, and a negative electrode in this order, and further includes an electrolytic solution. This lithium ion secondary battery has high adhesiveness between the porous membrane separator and the electrode, and usually has high safety because the porous membrane separator has high heat resistance.

As a porous membrane separator, what was manufactured by the manufacturing method mentioned above is used.
Moreover, as an electrode, what was demonstrated in the term of the manufacturing method of the laminated body for lithium ion secondary batteries can be used, for example.

As the electrolytic solution, for example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and other lithium salts. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used. One of these may be used alone, or two or more of these may be used in combination at any ratio.

The amount of the supporting electrolyte is usually 1% by weight or more, preferably 5% by weight or more, and usually 30% by weight or less, preferably 20% by weight or less with respect to the electrolytic solution. By keeping the amount of the supporting electrolyte within this range, the ionic conductivity can be increased, and the charging characteristics and discharging characteristics of the lithium ion secondary battery can be improved.

As the solvent used in the electrolytic solution, a solvent capable of dissolving the supporting electrolyte can be used. Examples of the solvent include alkyl carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), methyl ethyl carbonate (MEC); Esters such as butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferred because high ion conductivity is easily obtained and the use temperature range is wide. A solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

In addition, an additive may be included in the electrolytic solution as necessary. As the additive, for example, carbonate compounds such as vinylene carbonate (VC) are preferable. An additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Examples of the electrolytic solution other than the above include a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolytic solution; an inorganic solid electrolyte such as lithium sulfide, LiI, and Li ₃ N; Can do.

As a method for producing a lithium ion secondary battery, for example, an electrode, a porous membrane separator, and a laminated body for a lithium ion secondary battery are appropriately combined as necessary, and are rolled, folded, or the like according to the battery shape. Examples of the method include putting the battery in a battery container, injecting an electrolyte into the battery container, and sealing. In addition, if necessary, an overcurrent prevention element such as a fuse or a PTC element, a lead plate, an expanded metal, or the like may be inserted to prevent overcharging / discharging or an increase in pressure inside the battery. The shape of the battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.
In the following description, “%” and “part” representing amounts are based on weight unless otherwise specified. In addition, the operations described below were performed under normal temperature and normal pressure conditions unless otherwise specified.

[Evaluation methods]
[Resolution rate of water-soluble polymer compound film in water]
In Examples 1 to 4, 6 to 9, 11 and 12, and Comparative Examples 1 to 3, aqueous solutions containing carboxymethyl cellulose ammonium salt and ammonia are prepared. As this aqueous solution, what contains carboxymethylcellulose ammonium salt and ammonia in the ratio similar to the slurry composition for porous films which concerns on each Example and a comparative example is used.
In Examples 5 and 10, an aqueous solution containing the water-soluble polymer compound and the low-molecular compound X used in each Example in the same ratio as the porous membrane slurry composition according to each Example is prepared.

The prepared aqueous solution is applied onto a copper foil having a thickness of 20 μm so that the thickness after drying is 2 μm and dried at 120 ° C. for 10 minutes to form a film of a water-soluble polymer compound. Thereby, a copper foil having a film of a water-soluble polymer compound on the surface is obtained. This copper foil is cut into 1 × 1 cm ² and used as a test piece. The weight M1 of this test piece is measured.

Further, a copper foil in which a film of a water-soluble polymer compound is not formed is cut out with the same size as the above test piece, and its weight M0 is measured.

Further, the test piece is immersed in 25 ° C. ion exchange water for 1 hour. Thereafter, the test piece is taken out from the ion exchange water and dried at 120 ° C. for 10 minutes. After drying, the weight M2 of the test piece is measured.

From the measured weights M0, M1, and M2, the re-dissolution rate ΔM is calculated by the following equation. It shows that it is excellent in form maintenance property, so that re-dissolution rate (DELTA) M is small.
ΔM = (M1-M2) / (M1-M0) × 100 (%)
A: Re-dissolution rate ΔM is less than 5% B: Re-dissolution rate ΔM is 5% or more and less than 10% C: Re-dissolution rate ΔM is 10% or more and less than 15% D: Re-dissolution rate ΔM is 15 % Or more

[Heat shrinkage]
A porous membrane separator is cut into a square having a width of 5 cm and a length of 5 cm to obtain a test piece. After putting a test piece into a 150 degreeC thermostat and leaving to stand for 1 hour, a square area change is calculated | required as a heat shrinkage rate. The smaller the heat shrinkage rate, the better the heat shrinkability of the porous membrane separator.
A: The heat shrinkage rate is less than 1%.
B: The heat shrinkage rate is 1% or more and less than 5%.
C: Thermal contraction rate is 5% or more and less than 10%.
D: Thermal contraction rate is 10% or more.

[Adhesiveness of adhesive layer in electrolyte]
A porous membrane separator is cut into a width of 5 cm and a length of 5 cm, and superimposed on a negative electrode having an electrode active material layer (width of 4 cm and length of 4 cm), and pressed under conditions of 90 ° C., 0.5 MPa, and 10 seconds. A laminate comprising a porous membrane separator and a negative electrode having an electrode active material layer is prepared. The prepared laminate is cut into a width of 10 mm to obtain a sample. This sample is immersed for 3 days at a temperature of 60 ° C. in the same electrolyte used for the production of the battery. Then, a sample is taken out from electrolyte solution and a porous membrane separator is peeled from a negative electrode in the moist state. The adhesiveness at this time is evaluated according to the following criteria. The larger the resistance when the porous membrane separator is peeled from the negative electrode active material, the higher the retention property of the adhesive strength of the adhesive layer in the electrolytic solution.

Moreover, the laminated body provided with the positive electrode which has a porous membrane separator and an electrode active material layer similarly to the laminated body provided with the said porous membrane separator and a negative electrode is prepared. This laminate is also evaluated for adhesiveness in the same manner as a laminate comprising a porous membrane separator and a negative electrode. Here, when the result of the adhesive evaluation between the porous membrane separator and the positive electrode is the same as the result of the adhesive evaluation between the porous membrane separator and the negative electrode, only the result of the adhesive evaluation between the porous membrane separator and the negative electrode Is described.
A: There is resistance when peeled (excellent adhesion).
B: There is almost no resistance when it peels (it is inferior to adhesiveness).
C: It has already peeled off when taken out from the electrolyte.

[Blocking resistance]
The porous membrane separator is cut into squares each having a width of 5 cm × a length of 5 cm and a width of 4 cm × a length of 4 cm to prepare a test piece. These two test pieces are overlapped. 24 samples, which were superposed but not pressurized (samples that were not pressed), and samples that were superposed at a temperature of 40 ° C. and a pressure of 10 g / cm ² (pressed samples) were each 24 Leave for hours. After standing for 24 hours, the sample was visually observed to confirm the adhesion state (blocking state) of the laminated porous membrane separator and evaluated according to the following criteria. Here, blocking refers to a phenomenon in which the laminated porous membrane separators adhere to each other.
A: The pressurized porous membrane separators do not block each other.
B: The pressurized porous membrane separator is blocked but peeled off.
C: Pressurized secondary battery separator blocks and does not peel off.
D: The porous membrane separators that are not pressurized block each other.

[Measurement method of residual concentration of low molecular compound X]
The quantitative determination of at least one low-molecular compound X selected from the group consisting of ammonia and amine compounds contained in the porous membrane was performed by the following purge & trap / gas chromatography (P & T / GC) method.
0.1 g of a porous membrane separator provided with a separator substrate, a porous membrane and an adhesive layer is placed in a purge vessel. While flowing helium gas as a carrier gas into the purge vessel at 50 ml / min, the temperature in the purge vessel is heated at a rate of 10 ° C./min. The temperature in the purge container, which was room temperature before heating, rises after the start of heating. When the temperature reaches 150 ° C, the temperature of 150 ° C is held for 30 minutes. Thereafter, the sample is heated to 200 ° C. at a rate of 10 ° C./min, and the generated volatile components are collected in a trap tube. After collection, the temperature of the purge vessel is returned to room temperature.

Next, the trap tube collecting the volatile components is heated from 130 ° C. to 280 ° C. at a rate of 50 ° C./min, and the volatile components are quantified using gas chromatography under the following conditions. Since the component that volatilizes when heated to a temperature of 150 ° C. or more and 200 ° C. or less is considered to be the low molecular compound X, the residual concentration of the low molecular compound X can be measured by quantifying the volatile component. .

The conditions for gas chromatography are as follows.
Measuring device: Agilent gas chromatograph 9890 (FID method)
Data processor: Shimadzu C-R7A Chromatopack Purge & Trap Sampler: Agilent TDS
Column: DB-5 manufactured by J & W (L = 30 m, ID = 0.32 mm, Film = 0.25 μm)
Column temperature: 50 ° C. (holding 2 minutes) to 270 ° C. (temperature increase 10 ° C./min)
Sample feeding temperature: 280 ° C
Detection temperature: 280 ° C
Carrier gas: Helium gas Flow rate: 1 ml / min

[Example 1]
(1.1. Production of meta (acrylic) polymer)
In a reactor equipped with a stirrer, 0.06 part of sodium dodecyl sulfate, 0.23 part of ammonium persulfate and 100 parts of ion-exchanged water were added and mixed to obtain a mixture A1. The mixture A1 was heated to 80 ° C.
On the other hand, in a separate container, 83.8 parts of butyl acrylate, 2.0 parts of methacrylic acid, 12.0 parts of acrylonitrile, 1.0 part of allyl glycidyl ether, 1.2 parts of N-methylol acrylamide, 0 sodium dodecyl sulfate 0.1 part and 100 parts of ion-exchanged water were mixed to prepare a dispersion of the monomer mixture B1.
The dispersion of the monomer mixture B1 was continuously added and polymerized in the mixture A1 over 4 hours. During the continuous addition of the dispersion of the monomer mixture B1, the reaction was carried out while maintaining the temperature of the reaction system at 80 ° C. After completion of the continuous addition, the reaction was further continued at 90 ° C. for 3 hours. This obtained the water dispersion containing the binder which consists of a (meth) acrylic polymer.

The obtained aqueous dispersion containing the binder was cooled to 25 ° C., and ammonia water was added thereto to adjust the pH to 7. Thereafter, steam was introduced to remove unreacted monomers. Immediately after that, while further adjusting the solid content concentration with ion-exchanged water, it is filtered through a 200 mesh (mesh size of about 77 μm) stainless steel wire mesh, and the binder is dispersed in water with an average particle size of 370 nm and a solid content concentration of 40%. A liquid was obtained.

(1.2. Production of slurry composition for porous membrane)
Alumina particles (“AKP-3000” manufactured by Sumitomo Chemical Co., Ltd., volume average particle diameter D50 = 0.45 μm, tetrapod (registered trademark) -like particles) were prepared as non-conductive particles.
As a viscosity modifier, carboxymethyl cellulose ammonium salt (“DN10L” manufactured by Daicel Finechem) was used. This carboxymethylcellulose ammonium salt was prepared in a state of an aqueous solution containing carboxymethylcellulose ammonium salt and ammonia. The viscosity of a 1% aqueous solution of this viscosity modifier was 10 mPa · s or more and 50 mPa · s or less.

100 parts of non-conductive particles, the aqueous solution of carboxymethyl cellulose ammonium salt as a viscosity modifier is 1.5 parts in total of carboxymethyl cellulose ammonium salt and ammonia, and the solid content concentration of ion-exchanged water is 40% by weight. Mixed and stirred. Further, 4 parts of an aqueous dispersion containing the (meth) acrylic polymer obtained in the step (1.1) as a binder was mixed with a solid content. Further, 0.2 part of a polyethylene glycol type surfactant (“SN wet 366” manufactured by San Nopco) was mixed to produce a slurry composition for a porous membrane.

Here, the carboxymethylcellulose ammonium salt used as a viscosity modifier is a neutralized salt of carboxymethylcellulose and ammonia. The slurry composition for a porous membrane produced using this carboxymethyl cellulose ammonium salt contains 1.4 parts of carboxymethyl cellulose ammonium salt which is a water-soluble polymer compound with respect to 100 parts of non-conductive particles, and has a high water solubility. 5 parts of ammonia which is a low molecular compound X is contained with respect to 100 parts of carboxymethylcellulose ammonium salt which is a molecular compound.
Using this carboxymethylcellulose ammonium salt, the re-dissolution rate of the water-soluble polymer compound film in water was measured in the manner described above.

(1.3. Production of particulate polymer)
In a 5 MPa pressure vessel equipped with a stirrer, 22.2 parts of butyl acrylate as a (meth) acrylate monomer, 2 parts of methacrylic acid as an ethylenically unsaturated carboxylic acid monomer, and styrene 75 as an aromatic vinyl monomer Part, 0.8 part of ethylene dimethacrylate as a crosslinkable monomer, 1 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator, Stir. Then, it heated to 60 degreeC and superposition | polymerization was started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain an aqueous dispersion containing a particulate polymer. The obtained particulate polymer had a volume average particle diameter D50 of 0.15 μm and a glass transition temperature of 76 ° C.

(1.4. Production of slurry composition for adhesive layer)
100 parts of the aqueous dispersion of the particulate polymer obtained in the step (1.3) in solid content and 4 parts of the (meth) acrylic polymer obtained in the step (1.1) as a binder in solid content. Mixed. Furthermore, ion-exchange water was mixed so that the solid content concentration was 20% to obtain a slurry composition for an adhesive layer.

(1.5. Production of porous membrane separator)
A separator substrate (thickness 16 μm) made of a polyethylene porous substrate was prepared. The said slurry composition for porous films was apply | coated to both surfaces of the prepared separator base material, and it was made to dry for 3 minutes at 50 degreeC. Thereby, a porous film having a thickness of 3 μm per layer was formed on the separator substrate.

Next, the adhesive layer slurry composition was applied on each porous film and dried at 50 ° C. for 1 minute to form an adhesive layer having a thickness of 0.5 μm per layer. Thereby, a porous membrane separator provided with an adhesive layer, a porous membrane, a separator substrate, a porous membrane, and an adhesive layer in this order was obtained. About the obtained porous membrane separator, heat shrinkability, the adhesiveness of the contact bonding layer in electrolyte solution, and blocking resistance were evaluated.

(1.6. Production of positive electrode)
To 95 parts of lithium manganate having a spinel structure as the positive electrode active material, PVDF (polyvinylidene fluoride, manufactured by Kureha Co., Ltd., trade name: KF-1100) as a binder was added to 3 parts in terms of solid content, and Then, 2 parts of acetylene black and 20 parts of N-methylpyrrolidone were added and mixed with a planetary mixer to obtain a slurry composition for an active material layer for a positive electrode. This positive electrode active material layer slurry composition is applied to one side of an 18 μm thick aluminum foil, dried at 120 ° C. for 3 hours, and then roll-pressed to have an electrode active material layer with a total thickness of 100 μm. A positive electrode was obtained.

(1.7. Production of negative electrode)
98 parts of graphite having a particle size of 20 μm and a BET specific surface area of 4.2 m ² / g are mixed as the negative electrode active material, and 1 part of solid content equivalent of SBR (styrene-butadiene rubber, glass transition temperature: −10 ° C.) is mixed as the binder. Then, 1 part of carboxymethylcellulose was further mixed with this mixture, water was added as a solvent, and these were mixed with a planetary mixer to obtain a slurry composition for an active material layer for a negative electrode. This negative electrode active material layer slurry composition was applied to one side of a 18 μm thick copper foil, dried at 120 ° C. for 3 hours, and then roll-pressed to have an electrode active material layer with a total thickness of 60 μm. A negative electrode was obtained.

(1.8. Production of laminated body for secondary battery)
The positive electrode, the porous membrane separator, and the negative electrode were stacked. At this time, the positive electrode active material layer of the positive electrode and one adhesive layer of the porous membrane separator were in contact with each other, and the negative electrode active material layer of the negative electrode and the other adhesive layer of the porous membrane separator were in contact with each other. Thereafter, pressing was performed at a temperature of 80 ° C. and a pressure of 0.5 MPa for 10 seconds, and the positive electrode, the porous membrane separator, and the negative electrode were pressure bonded. This obtained the laminated body for secondary batteries provided with a positive electrode, a porous membrane separator, and a negative electrode.

(1.9. Manufacture of lithium ion secondary battery)
On the inner bottom surface of a stainless steel coin-type outer container provided with a polypropylene packing, the aforementioned secondary battery laminate having a negative electrode / secondary battery separator / positive electrode layer structure is installed, and these are placed in the container. Stored. Inject the electrolyte into the container so that no air remains, fix the outer container with a 0.2 mm thick stainless steel cap through a polypropylene packing, seal the battery can, and 20 mm in diameter. A full-cell lithium ion secondary battery (coin cell CR2032) having a thickness of about 3.2 mm was manufactured. As an electrolytic solution, LiPF ₆ is mixed at a concentration of 1 mol / liter in a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 1: 2 (volume ratio at 20 ° C.). The dissolved solution was used.

[Example 2]
In the step (1.2), boehmite particles (“APYRAL AOH 60” manufactured by Nabaltec, volume average particle diameter D50 = 0.9 μm, plate-like particles) were used instead of alumina particles as non-conductive particles. Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Example 3]
In the step (1.2), magnesium oxide particles (“PUREMAG FNM-G” manufactured by Tateho Chemical Co., Ltd., volume average particle diameter D50 = 0.5 μm, elliptical spherical particles and angles are used as non-conductive particles instead of alumina particles. A mixture of rounded polyhedral particles). Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Example 4]
(Manufacture of polymer particles)
In a reactor equipped with a stirrer, 0.06 part of sodium dodecyl sulfate, 0.23 part of ammonium persulfate, and 100 parts of ion-exchanged water were added and mixed to obtain a mixture A4. This mixture A4 was heated to 80 ° C.

On the other hand, in a separate container, 93.8 parts of butyl acrylate, 2.0 parts of methacrylic acid, 2.0 parts of acrylonitrile, 1.0 part of allyl glycidyl ether, 1.2 parts of N-methylol acrylamide, sodium dodecyl sulfate 0 0.1 part and 100 parts of ion-exchanged water were mixed to prepare a dispersion of the monomer mixture B4.

The dispersion of the monomer mixture B4 was continuously added and polymerized in the mixture A4 over 4 hours. During the continuous addition of the dispersion of the monomer mixture B4, the reaction was carried out while maintaining the temperature of the reaction system at 80 ° C. After completion of the continuous addition, the reaction was further continued at 90 ° C. for 3 hours. Thereby, an aqueous dispersion of seed polymer particles C4 having an average particle diameter of 370 nm was obtained.

Next, in a reactor equipped with a stirrer, 20 parts of the above-mentioned aqueous dispersion of seed polymer particles C4 on the basis of solid content (that is, based on the weight of seed polymer particles C4) and ethylene glycol dimethacrylate as a monomer (Kyoeisha) Chemical Co., Ltd. “Light Ester EG”) 100 parts, sodium dodecylbenzenesulfonate 1.0 part, t-butylperoxy-2-ethylhexanoate as a polymerization initiator (“Perbutyl O” manufactured by NOF Corporation) 4.0 parts and 200 parts of ion exchange water were added and stirred at 35 ° C. for 12 hours to completely absorb the monomer and the polymerization initiator in the seed polymer particles C4. This was then polymerized at 90 ° C. for 5 hours. Thereafter, steam was introduced to remove unreacted monomers and initiator decomposition products. As a result, an aqueous dispersion containing polymer particles as non-conductive particles having a volume average particle diameter D50 of 670 nm was obtained.

In the step (1.2), the polymer particles were used as non-conductive particles instead of alumina particles. Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Example 5]
(5.1. Production of maleimide-maleic acid copolymer)
In a reactor equipped with a stirrer, 100 parts of isobutylene-maleic anhydride copolymer (“Isoban-04” manufactured by Kuraray Co., Ltd.) was placed. Ammonia gas was blown into the reactor and the reaction was continued for about 1 hour while cooling with a water bath until the exotherm stopped. Subsequently, ammonia gas was injected while heating in an oil bath, and the temperature was raised to 200 ° C. while distilling off the generated water to perform imidization reaction. After completion of the reaction, the reaction product was taken out and dried by heating to obtain a maleimide-maleic acid copolymer. The composition of the obtained maleimide-maleic acid copolymer was 50 mol% of isobutylene units, 18 mol% of maleic anhydride units, 12 mol% of maleic acid units, and 20 mol% of maleimide units.
Also, 100 parts of the obtained maleimide-maleic acid copolymer and 540 parts of 25% strength aqueous ammonia were placed in a reactor equipped with a stirrer, and stirred at 90 ° C. for 5 hours, so that the solid concentration was An aqueous solution of 20% maleimide-maleic acid copolymer was obtained. The weight average molecular weight of the maleimide-maleic acid copolymer was 60000.

In the step (1.2), polymer particles produced in Example 4 were used as non-conductive particles instead of alumina particles.
In the step (1.2), 100 parts of the maleimide-maleic acid copolymer obtained in the step (5.1) was used instead of the aqueous solution of carboxymethyl cellulose ammonium salt. At this time, the maleimide-maleic acid copolymer was added in the form of an aqueous solution. The obtained slurry for porous membrane contains 15 parts of ammonia with respect to 100 parts of maleimide-maleic acid copolymer which is a water-soluble polymer compound.
Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Example 6]
In the step (1.3), the amount of butyl acrylate was changed to 52.2 parts, the amount of styrene was changed to 45 parts, and the glass transition temperature of the particulate polymer of the adhesive layer was adjusted to 15 ° C. did. Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Example 7]
In the step (1.3), the amount of butyl acrylate was changed to 27.2 parts, the amount of styrene was changed to 70 parts, and the glass transition temperature of the particulate polymer of the adhesive layer was adjusted to 35 ° C. did. Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Example 8]
In the step (1.3), the amount of butyl acrylate was changed to 7.2 parts, the amount of styrene was changed to 90 parts, and the glass transition temperature of the particulate polymer of the adhesive layer was adjusted to 93 ° C. did. Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Example 9]
In the said process (1.2), the quantity of the aqueous solution of carboxymethylcellulose ammonium salt was changed into 7 parts by the total amount of carboxymethylcellulose ammonium salt and ammonia. This aqueous solution of carboxymethyl cellulose ammonium salt contains 6.6 parts of carboxymethyl cellulose ammonium salt and 0.4 part of ammonia. Thereby, in the slurry composition for porous films, the amount of ammonia with respect to 100 parts of carboxymethylcellulose ammonium salt which is a water-soluble polymer compound was 5 parts.
Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Example 10]
An aqueous solution containing carboxymethylcellulose and 2-aminoethanol was prepared. In this aqueous solution, the amount of 2-aminoethanol with respect to 100 parts of carboxymethylcellulose was 18 parts. In this aqueous solution, carboxymethylcellulose and 2-aminoethanol react to form a neutralized salt of carboxymethylcellulose and 2-aminoethanol, which is a water-soluble polymer compound, and partially unreacted 2-aminoethanol is converted to Remains. The aqueous solution thus prepared was used in place of the aqueous solution of carboxymethyl cellulose ammonium salt in the step (1.2). The amount of the aqueous solution at this time was an amount containing 1.5 parts of carboxymethyl cellulose, neutralized salt of 2-aminoethanol and 0.1 part of 2-aminoethanol.
Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Example 11]
In the step (1.2), by adding an aqueous ammonia solution to the slurry composition for a porous membrane, the amount of ammonia that is the low molecular compound X is 10 parts with respect to 100 parts of the carboxymethyl cellulose ammonium salt that is the water-soluble polymer compound. I made it.
Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Example 12]
In the step (1.2), by adding an aqueous ammonia solution to the slurry composition for porous membrane, the amount of ammonia as the low molecular compound X with respect to 100 parts of the carboxymethyl cellulose ammonium salt as the water soluble polymer compound is 20 parts. I made it.
Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Comparative Example 1]
In the step (1.5), no adhesive layer was formed. Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Comparative Example 2]
In the step (1.3), the amount of butyl acrylate is changed to 4.2 parts, the amount of methacrylic acid is changed to 10 parts, the amount of styrene is changed to 85 parts, The glass transition temperature of the polymer was adjusted to 112 ° C. Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Comparative Example 3]
In step (1.3), 87.8 parts of ethyl acrylate was used instead of butyl acrylate, the amount of methacrylic acid was changed to 2 parts, 10 parts of acrylonitrile was used instead of styrene, and ethylene dimethacrylate The amount was changed to 0.2 part, and the glass transition temperature of the particulate polymer of the adhesive layer was adjusted to 5 ° C. Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Comparative Example 4]
In the step (1.2), an aqueous solution of carboxymethyl cellulose ammonium salt was not used.
Furthermore, in the said process (1.5), the thickness per layer of an adhesive layer was changed into 10 micrometers.
Except for the above, a porous membrane separator, a secondary battery laminate and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[Evaluation results]
The configurations of Examples and Comparative Examples are shown in Tables 1 to 4, and the results are shown in Tables 5 to 7. Here, the meanings of the abbreviations in the following table are as follows.
Amount relative to 100 parts of water-soluble polymer in the “low molecular compound” column: amount of low molecular compound X relative to 100 parts by weight of water-soluble polymer compound in slurry composition for porous membrane Binder composition: (meth) acrylonitrile monomer in binder Weight ratio of body unit / (meth) acrylic acid ester monomer unit Remaining amount of low molecular compound: Remaining amount of low molecular compound X in porous membrane Monomer I: Acrylic acid ester monomer Monomer II: Ethylene Unsaturated carboxylic acid monomer Monomer III: Aromatic vinyl monomer Monomer IV: (Meth) acrylonitrile monomer Monomer V: Crosslinker monomer CMC1: Carboxymethylcellulose ammonium salt CMC2: Carboxy Neutralized salt of methylcellulose and 2-aminoethanol ACL: Acrylic rubber BA: Butyl acrylate EA: Ethyl acrylate MAA: methacrylic acid ST: styrene EDMA: ethylene dimethacrylate isoban: maleimide-maleic acid copolymer

[Consideration]
As can be seen from the table, according to the present invention, using the slurry composition containing water, the porous film is hardly dissolved in the slurry composition for the adhesive layer, and both the adhesion to the electrode and the blocking resistance are improved. An excellent porous membrane separator can be produced.

Claims

A slurry composition for a porous film containing at least one kind of low-molecular compound selected from the group consisting of non-conductive particles, water-soluble polymer compounds, water, and ammonia and amine compounds is applied to at least one surface of a separator substrate. Drying to obtain a porous film, and
A lithium ion secondary comprising a step of applying a slurry composition for an adhesive layer containing a particulate polymer having a glass transition temperature of 10 ° C. or higher and 110 ° C. or lower and water on the porous film and drying to obtain an adhesive layer. A method for producing a porous membrane separator for a battery.
The method for producing a porous membrane separator according to claim 1, wherein the water-soluble polymer compound has an acidic group.
The method for producing a porous membrane separator according to claim 2, wherein the acidic group is a carboxyl group.
The method for producing a porous membrane separator according to any one of claims 1 to 3, wherein the concentration of the low molecular compound in the porous membrane is 1000 ppm or less per unit weight of the porous membrane.
The method for producing a porous membrane separator according to any one of claims 1 to 4, wherein the low-molecular compound is ammonia.
The water-soluble polymer compound is at least one selected from the group consisting of carboxymethylcellulose and a maleimide-maleic acid copolymer containing a structural unit represented by the following formula (I). The manufacturing method of the porous membrane separator as described in any one of these.

(In the formula (I), R 1 is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a phenyl group, a phenyl group substituted with an alkyl group having 1 to 6 carbon atoms, (It is at least one selected from the group consisting of a phenyl group substituted with an alkyloxy group having 1 to 6 carbon atoms, a phenyl group substituted with a halogen atom, and a hydroxyphenyl group.)
A method for producing a laminate for a lithium ion secondary battery, comprising pressure bonding an electrode and a porous membrane separator produced by the production method according to any one of claims 1 to 6.