JP6931280B2 - A method for producing a composition for forming a porous film, a separator, an electrochemical element, and an electrode composite. - Google Patents

Description

In the present invention, a composition for forming a porous film, a separator formed by using the composition for forming a porous film, an electrochemical element provided with the above-mentioned separator, and an electrode composite using the above-mentioned porous film are used. Regarding the manufacturing method of the body.

Conventionally, various porous membranes have been used for applications such as filters. Further, in recent years, the porous membrane has been increasingly applied to separator applications for secondary batteries such as lithium batteries.

As the porous membrane used as a separator, for example, a porous membrane containing a fiber material in the form of a fiber aggregate formed so as to be fixed to an electrode has been proposed (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2015-191871

The porous membrane having a function as a separator described in Patent Document 1 is produced by using a slurry containing water and fibers such as cellulose. However, it is difficult to disperse fibers such as cellulose in a slurry containing water in a good and uniform manner. If the dispersed state of fibers such as cellulose is non-uniform, the film thickness of the porous film formed by using the slurry is often not sufficiently uniform. If the film thickness of the porous film is not uniform, problems such as the formation of lithium dendrite are likely to occur due to the bias of the electric field, and it is difficult to obtain a high-performance electrochemical element.

The present invention has been made in view of the above problems, and is porous capable of forming a porous film that contains insulating fibers that are well and uniformly dispersed and can be used as a separator that provides an electrochemical element having excellent performance. It is an object of the present invention to provide a film-forming composition, a separator formed from the above-mentioned composition, an electrochemical element provided with the above-mentioned separator, and a method for producing an electrode composite using the above-mentioned composition.

The present inventors can solve the above-mentioned problems by using a composition for forming a porous film containing a hydrophobically modified insulating fiber (A), a binder resin (B), and a solvent (S). The present invention has been completed. Specifically, the present invention provides the following.

The first aspect of the present invention is a composition for forming a porous film, which contains a hydrophobically modified insulating fiber (A), a binder resin (B), and a solvent (S).

A second aspect of the present invention is a separator formed from the composition according to the first aspect.

A third aspect of the present invention is an electrochemical device including the separator according to the second aspect.

A fourth aspect of the present invention is a method for producing an electrode composite, comprising a step of applying the composition according to the first aspect onto an electrode.

According to the present invention, a composition for forming a porous film containing insulating fibers that are well and uniformly dispersed and capable of forming a porous film that can be used as a separator that provides an electrochemical element having excellent performance, and the above-mentioned composition. It is possible to provide a separator formed from an object, an electrochemical element including the above-mentioned separator, and a method for producing an electrode composite using the above-mentioned composition.

<< Composition for forming a porous film >>
The composition for forming a porous film contains a hydrophobically modified insulating fiber (A), a binder resin (B), and a solvent (S).
When the solvent (S) was removed from the film made of the composition for forming a porous film, the insulating fibers (A) to which the binder resin (B) was attached were entangled to form between the insulating fibers (A). A porous film containing a large number of pores is formed.
Since the hydrophobically modified insulating fiber (A) is well and uniformly dispersed in the composition for forming a porous membrane, the insulating fiber (A) is well entangled in the porous membrane and is a homogeneous empty space. A porous membrane having pores can be formed.

When forming the porous film, the film composed of the composition for forming a porous film is preferably formed by applying the composition for forming a porous film on some substrate. That is, the composition for forming a porous film is preferably a coating type composition used for forming a porous film by a method including coating.
By coating, a coating film adjusted to a desired film thickness and having a uniform film thickness can be formed, and as a result, a porous film having a desired film thickness and a uniform film thickness can be formed.

Further, when the porous film is formed from the coating film formed by coating, the surface of the base material to which the composition for forming the porous film is applied may have irregularities. When the surface of the base material has irregularities, a coating film is formed on the surface of the base material according to the shape of the irregularities, and the solvent (S) is removed from the formed coating film to follow the surface shape of the base material. A porous film having a shape can be formed.

Further, since the porous film formed by using the above-mentioned composition for forming a porous film contains the hydrophobically modified insulating fiber (A), it is very compatible with an electrolytic solution containing dimethyl carbonate or the like. Therefore, when the porous membrane formed by using the composition for forming a porous membrane is used as a separator for an electrochemical element, the electrolytic solution is rapidly permeated.

Hereinafter, essential or arbitrary components contained in the composition for forming a porous film will be described.

<Insulating fiber (A)>
The insulating fiber (A) is not particularly limited as long as it is uniformly dispersed in the composition in a state of being subjected to a predetermined hydrophobic modification.
When the solvent (S) described later is removed from the coating film formed by using the composition in which the insulating fibers (A) are dispersed to form a porous film, the insulating fibers (A) are entangled in the film. By doing so, pores are formed between the insulating fibers (A).

The insulating fiber (A) is not particularly limited as long as it is made of an insulating material at least on its surface and is generally recognized as a fiber.
The insulating fiber (A) may be an organic fiber or an inorganic fiber. Organic fibers are preferable as the insulating fibers (A) because the fibers are flexible and easily entangled and have good insulating properties.
Preferable examples of the inorganic fiber include micro glass (small diameter glass fiber), rock wool and the like. Preferable examples of organic fibers include cellulose esters such as cellulose, carboxymethyl cellulose and cellulose acetate, cellulose fiber materials such as lignocellulose, neutral mucopolysaccharide fiber materials such as chitin and chitosan, and aliphatic nylons. And synthetic resin fiber materials made of polyamides such as aromatic nylon (aramid), polyolefins such as polyethylene and polypropylene, and resins such as vinylon, polyester, polyimide, polyamideimide, and polyvinylidene fluoride. For synthetic resin-based fiber materials, fine fibers of synthetic resin can be obtained by, for example, a method such as electrospinning.

Among the above-mentioned insulating fibers (A), fibers having a preferable size can be easily prepared and obtained, and fibers that are well dispersed in the solvent (S) can be easily obtained by the treatment of hydrophobic modification. Cellulose esters such as carboxymethyl cellulose and cellulose acetate, cellulosic fiber materials such as lignocellulose, and neutral mucopolysaccharide fiber materials such as chitin and chitosan are preferable, the above cellulosic fiber materials are more preferable, and cellulose is particularly preferable. preferable.

The hydrophobizing modification is not particularly limited as long as it is a modification treatment capable of improving the hydrophobicity of the surface of the insulating fiber (A). Specifically, the hydrophobic modification is a treatment in which a hydrophobic functional group such as a hydrocarbon group, a halogenated hydrocarbon group, and an organosiloxane structure and a chemical structure are present on the surface of the insulating fiber (A). ..

The treatment for allowing a hydrophobic functional group or chemical structure to exist on the surface of the insulating fiber (A) may be, for example, a treatment for coating at least a part of the surface of the insulating fiber (A) with a denaturing agent. The treatment may be a treatment in which the modifying agent is attached to the surface of the insulating fiber (A), or a treatment in which the modifying agent is chemically bonded to the surface of the insulating fiber (A).

（式（ａ１）中、Ｒ^ａ１、Ｒ^ａ２、及びＲ^ａ２は、それぞれ独立に炭素原子数１〜３の炭化水素基を示し、Ｘ⁻はアニオン性の原子又は基を表す。）
で表される化合物が挙げられる。 Preferable specific examples of the hydrophobization modification treatment include surface modification with a compound having at least one selected from the group consisting of a cardo structure, an acetyl group, a methyl group, and a bisphenol structure. These hydrophobization modification treatments may include a combination of a plurality of surface modifications.
Further, a cationizing agent having a methyl group, an acetyl group or the like as well as a reactive group such as an epoxy group can be suitably used for the hydrophobic modification treatment of the insulating fiber (A). A suitable example of such a cationizing agent is the following formula (a1):

(In the formula (a1), Ra ¹ , Ra ² , and Ra ² each independently represent a hydrocarbon group having 1 to 3 carbon atoms, and X ⁻ represents an anionic atom or group.)
Examples thereof include compounds represented by.

Wherein ^(a1), the hydrocarbon group having 1 to 3 carbon atoms for R ^{a1, R a2,} and ^{R a2,} methyl group, ethyl group, n- propyl group, and isopropyl group. The methyl group and the ethyl group are preferable, and the methyl group is more preferable, as ^{Ra 1} , Ra ² , and Ra ² from the viewpoint of the reactivity of the cationizing agent and the availability.

X ⁻ represents an anionic atom or group which is a counterion of the quaternary ammonium cation moiety in the formula (a1). Examples of X ⁻ include inorganic anions such as halide ions and organic anions such as alkyl sulfate ions and fatty acid ions. A halide ion and an alkyl sulfate ion having 1 to 3 carbon atoms are preferable, and a halide ion is more preferable, because the cationizing agent is easily available and the insulating fiber (A) is easily modified.
Specific examples of the halide ion include fluoride ion, chloride ion, bromide ion, and iodide ion, and chloride ion and bromide ion are selected from the viewpoint of chemical stability of the cationizing agent and availability. Chloride ions are preferred, and chloride ions are more preferred.

Specific examples of suitable cationizing agents include glycidyltrimethylammonium chloride, glycidyltrimethylammonium bromide, glycidyltrimethylammonium methylsulfate, glycidyltriethylammonium chloride, glycidyltriethylammonium bromide, glycidyltriethylammoniummethylsulfate, glycidyltripropylammonium chloride, glycidyl. Examples thereof include tripropylammonium bromide and glycidyltripropylammonium methyl sulfate.

Among these hydrophobization modification treatments, since the insulating fiber (A) is more easily dispersed in the composition for forming a porous film, surface modification with a compound having a cardo structure and a compound having a bisphenol structure are used. Surface modification is preferable, and surface modification with a compound having a cardo structure is more preferable.

Hereinafter, the hydrophobization modification treatment using a compound having a cardo structure will be described.
The compound having a cardo structure is not particularly limited as long as it is a compound generally recognized as a compound having a cardo structure.
As the compound having a cardo structure, a compound having a 9,9-bisarylfluorene skeleton (sometimes simply referred to as a compound having a fluorene skeleton) is preferable.
By mixing the insulating fiber (A) with the compound having a cardo structure and then recovering the fiber, the hydrophobically modified insulating fiber (A) can be obtained.

As described above, a compound having a fluorene skeleton is preferably used as the compound having a cardo structure.
The compound having a fluorene skeleton is not particularly limited as long as it has a 9,9-bisarylfluorene skeleton (for example, 9,9-bisphenylfluorene skeleton, 9,9-bisnaphthylfluorene skeleton).
Usually, 9,9-bis (aminoaryl) fluorene (eg, 9,9-bis (4-aminophenyl) fluorene, etc.), 9,9-bis (carboxyaryl) fluorene (eg, 9,9-bis (carboxyl)). A compound having a fluorene skeleton having a functional group (for example, an amino group, a carboxyl group, a hydroxyl group, an epoxy group, etc.) such as phenyl) fluorene), 9,9-bis (hydroxyaryl) fluorene, etc. can be preferably used.

A preferable example of the compound having a fluorene skeleton is a compound represented by the following formula (1).

In formula (1), ring Z represents an aromatic hydrocarbon ring. R ¹ indicates a substituent. X represents a heteroatom-containing functional group. R ² represents an alkylene group. R ³ indicates a substituent. k represents an integer from 0 to 4. m indicates an integer of 0 or more. n represents an integer of 1 or more. p indicates an integer of 0 or more.

In the formula (1), examples of the aromatic hydrocarbon ring represented by ring Z include a benzene ring and a condensed polycyclic hydrocarbon ring (for example, a condensed bicyclic hydrocarbon ring (for example, inden, naphthalene and the like). 2 to 4 rings such as C _8- C ₂₀ fused bicyclic hydrocarbon rings, preferably C _10- C ₁₆ condensed bicyclic hydrocarbon rings, condensed tricyclic hydrocarbon rings (eg, anthracene, phenanthrene, etc.) (Fused ring type hydrocarbon ring) and the like.
As the ring Z, a benzene ring or a naphthalene ring is preferable.
The substitution position of the ring Z to be substituted at the 9-position of fluorene is not particularly limited. For example, when the ring Z is a naphthalene ring, the group corresponding to the ring Z substituted at the 9-position of fluorene may be a 1-naphthyl group, a 2-naphthyl group, or the like.

In the formula (1) ^{, examples of the substituent represented by the group R 1} include a cyano group, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.) and a hydrocarbon group (for example, an alkyl group and an aryl group (phenyl). C _6- C ₁₀ aryl groups such as groups), etc.) and the like can be mentioned. If there are groups R ¹ on the fluorene ring, typically, group R ¹ is a halogen atom, a cyano group or an alkyl group (particularly an alkyl group).
Examples of the alkyl group, methyl group, ethyl group, n- propyl group, an isopropyl group, n- butyl group, _C 1 -C ₆ alkyl _(eg, C 1 -C ₄ alkyl group such as a tert- butyl group, especially methyl Group) and the like.

When k is 2 or more, the plurality of groups R ¹ may be the same or different from each other. Furthermore, the radicals R ¹ to be substituted with two benzene rings constituting the fluorene (or fluorene skeleton) may be the same or may be different.
Further, the bonding position of the group R ¹ for benzene rings constituting the fluorene (substitution position) is not particularly limited. The preferred number of substitutions k is 0 or 1, especially 0. In the two benzene rings constituting fluorene, the number of substitutions k may be the same or different from each other.

In the formula (1), examples of the heteroatom-containing functional group include a functional group having at least one selected from oxygen, sulfur and nitrogen atoms.
The number of heteroatoms contained in such a functional group is not particularly limited, but is usually 1 to 3, preferably 1 or 2.
Examples of the functional group include an oxygen atom-containing functional group such as a hydroxyl group, an epoxy-containing group (glycidyloxy group, etc.) and a carboxy group; a sulfur atom-containing functional group such as a mercapto group; an amino group or an N-mono-substituted amino group. (e.g., methylamino group, N- monoalkylamino group (N- mono _C 1 -C ₄ alkylamino groups such as ethylamino group, etc.), N- mono-hydroxyalkyl amino groups such as hydroxyethylamino group (N- mono- Examples thereof include a nitrogen atom-containing functional group such as hydroxy C _1- C _{4 alkylamino group), etc.).}
Preferred groups X include a hydroxy group, a mercapto group, an epoxy-containing group (glycidyloxy group and the like), an amino group, an N-mono-substituted amino group and the like, and a hydroxy group is particularly preferable.
In addition, X may be the same or different group in different Z, and may be the same or different group in the same ring Z.

In the formula (1), the alkylene group represented by the ^{group R 2 is not particularly limited.} The alkylene group represented by group ^{R 2,} for _example, C 2 _{-C 10} alkylene group (e.g., ethylene group, trimethylene group, a propylene group, butane-1,2-diyl group, _C 2 -C such hexylene ₆ mentioned alkylene group) and the _like, C 2 -C ₄ alkylene group (in particular, an ethylene group, _C 2 -C ₃ alkylene group) is preferable and propylene group, or may be a particularly ethylene group.
The group R ² may be the same or different alkylene groups (that is, when m is plural, R ² may be the same or different). That is, when m is 2 or more, the polyalkoxy (polyoxyalkylene) group [-(OR ² ) _m- ] may be composed of the same oxyalkylene group, and a plurality of oxyalkylene groups (for example, oxy). It may be composed of an ethylene group and an oxypropylene group, etc.).
Generally, R ² may be the same alkylene group in the same benzene ring.

The number (additional moles) m of the oxyalkylene group (OR ² ) can be selected from the range of, for example, about 0 to 15 (for example, 1 to 10), and is preferably 0 to 8 (for example, 0 to 7). May be 0 to 6, more preferably 0 to 5 (for example, 0 to 3), and particularly 1.
Further, m may be different in two rings Z, or may be different in the same ring Z.
For example, in the same ring Z, it may have a group −X in which m is 0 and a group − [(OR ² ) _m −X] in which m is 1 or more. In the formula (1), the ^{number of substitutions n of the group − [(OR 2} ) _m −X] depends on the type of the ring Z, but is, for example, 1 to 6, preferably 1 to 4, and more preferably 1. It may be ~ 3, especially 1-2.

Further, in the formula (1) ^{, examples of the substituent represented by the group R 3} _{include C 1} − such as an alkyl group (for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group and an n-butyl group). C ₁₂ alkyl group, preferably C _1- C ₈ alkyl group, more preferably C _1- C ₆ alkyl group, etc., cycloalkyl group (C _5- C ₁₀ cycloalkyl group such as cyclohexyl group, preferably C) ₅ -C ₈ cycloalkyl group, more preferably a _C 5 -C ₆ cycloalkyl group), an aryl group (e.g., phenyl group, tolyl group, xylyl group, _C 6 _{-C 14} aryl group such as a naphthyl group, preferably A _{group in which a C 6-} C ₁₀ aryl group, more preferably a C _6- C ₈ aryl group, etc.) and an aralkyl group (a C _6- C ₁₀ aryl group _{such as a benzyl group and a phenethyl group are bonded to a C 1-} C ₄ alkyl group). _{(Et.) and other hydrocarbon groups; C 1-} C ₁₂ alkoxy groups such as alkoxy groups (methoxy group, ethoxy group, propoxy group, butoxy group, etc.), preferably C _1- C ₈ alkoxy groups, more preferably C _1- C ₆ alkoxy group, etc.), _C 5 _{-C 10} cycloalkyl group such as a cycloalkoxy group (hexyloxy group cyclohexylene, etc.), _C 6 _{-C 10} aryloxy group such as an aryloxy group (phenoxy group), aralkyloxy group (e.g. , _C 6 _{-C 10} aryl group _C 1 -C ₄ such groups attached to an alkyl group) such group -OR ⁴ in (wherein such a benzyloxy group, ^{R 4} is a hydrocarbon group (the above exemplified hydrocarbon shows a group));. an alkylthio group (methylthio group, ethylthio group, propylthio group, butylthio _C 1 _{-C 20} alkylthio group such as, preferably _C 1 -C ₈ alkylthio group, more preferably a _C 1 -C ₆ alkylthio group), _C 5 _{-C 10} cycloalkylthio group such as a cycloalkylthio group (cyclohexylthio group cyclohexylene, etc.), _C 6 _{-C 10} arylthio group such as an arylthio group (thiophenoxy group), aralkylthio group (e.g., benzylthio Group C _6- C ₁₀ aryl group such as group bonded to _{C 1-} C ₄ ^{alkylthio group Group-SR 4} (in the formula, R ⁴ is the same as above); acyl group (C such as acetyl group) ₁ -C ₆ acyl group); an alkoxycarbonyl group (binding to _C 1 -C ₄ alkoxy carbonyl group such as methoxycarbonyl group Combined groups, etc.); Halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, iodine atoms, etc.); nitro groups; cyano groups; mercapto groups; carboxy groups; amino groups; carbamoyl groups; substituted amino groups (eg, dimethylamino groups) dialkylamino group, etc.) and the like; sulfonyl groups; these substituents substituents mutually bonded (e.g., an alkoxyaryl group (eg, C ₁ -C ₄ alkoxy group is C ₆ -C ₁₀ aryl group such as methoxyphenyl group attached group), alkoxycarbonyl aryl group (e.g., methoxycarbonyl phenyl group, and groups in which C ₁ -C ₄ alkoxy group is bonded to C ₆ -C ₁₀ aryl group through a carbonyl group such as ethoxycarbonyl phenyl group) ) Etc. can be mentioned.

Of these, typically, the group R ³ is a hydrocarbon group, -OR ⁴ (in the formula, R ⁴ is a hydrocarbon group), -SR ⁴ (in the formula, R ⁴ is the same as above). ), An acyl group, an alkoxycarbonyl group, a halogen atom, a nitro group, a cyano group, a substituted amino group and the like.

Preferred groups R ³ include hydrocarbon groups (eg, alkyl groups (eg, C _1- C ₆ alkyl groups), cycloalkyl groups (eg, C _5- C ₈ cycloalkyl groups), aryl groups (eg, C _6). -C ₁₀ aryl group), an aralkyl group (for example, a group in which C _6- C ₈ aryl is _{bonded to a C 1-} C ₂ alkyl group, etc.), an alkoxy group (for example, a C _1- C ₄ alkoxy group, etc.) and the like.
In particular, ^{R 3} is an alkyl group _(C 1 -C ₄ alkyl group (especially methyl), etc.), an aryl group _(e.g., C 6 _{-C 10} aryl group (especially phenyl group)) is preferably such.

The number of substitutions p is preferably 0 to 8, more preferably 0 to 4 (for example, 0 to 3), and even more preferably 0 to 2.
In different rings Z, the substitution numbers p may be the same or different from each other, and may usually be the same. Further, in the same ring Z, if p is plural (2 or more), groups R ³ may be different from each other, may be identical. Further, in the two rings Z, groups R ³ may be the same or different.

In the formula (1), the value of n + p may be, for example, 1 to 6, preferably 1 to 4, and more preferably about 1 to 3, although it depends on the type of ring Z.

As a typical example of the compound represented by the formula (1), ring Z is a benzene ring or a naphthalene ring, X is a hydroxyl group, a mercapto group, a carboxyl group, a glycidyloxy group or an amino group (particularly a hydroxyl group). R ² is C2-6 alkylene group (particularly _C 2 -C ₄ alkylene group), m is 0-10 (e.g., 0~6), n is include compounds is 1-3.

Preferable specific examples of the compound represented by the formula (1) include 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis (3,4-dihydroxyphenyl) fluorene and the like. 9-bis (hydroxyphenyl) fluorene; 9,9-bis (4-hydroxy-3-methylphenyl) fluorene, 9,9-bis (4-hydroxy-3,5-dimethylphenyl) fluorene, etc. 9,9- Bis (hydroxy-alkylphenyl) fluorene; 9,9-bis (hydroxy-arylphenyl) fluorene such as 9,9-bis (4-hydroxy-3-phenylphenyl) fluorene; 9,9-bis [4- (2) -Hydroxyethoxy) phenyl] fluorene, 9,9-bis [3,4-di (2-hydroxyethoxy) phenyl] fluorene and other 9,9-bis [(hydroxyalkoxy) phenyl] fluorene; 9,9-bis [ 9,9-bis [(hydroxyalkoxy)] such as 4- (2-hydroxyethoxy) -3-methylphenyl] fluorene and 9,9-bis [4- (2-hydroxyethoxy) -3,5-dimethylphenyl] fluorene. ) -Alkylphenyl] fluorene; 9,9-bis [(hydroxyalkoxy) -arylphenyl] fluorene such as 9,9-bis [4- (2-hydroxyethoxy) -3-phenylphenyl] fluorene; Correspondingly, compounds in which ring Z is replaced with a naphthalene ring, for example, 9,9-bis (hydroxynaphthyl) fluorene such as 9,9-bis (6-hydroxy-2-naphthyl) fluorene, 9,9-bis [6 -(2-Hydroxyethoxy) -2-naphthyl] fluorene and the like 9,9-bis [(hydroxyalkoxy) naphthyl] fluorene and the like in formula (1) where X is a hydroxyl group; A compound in which X is substituted with a mercapto group, a carboxyl group, a glycidyl group or an amino group is included.

The compounds having a cardo structure represented by the compounds having a fluorene skeleton described above may be used alone or in combination of two or more.

As the compound represented by the formula (1), a commercially available product may be used. For example, fluorenones and phenols are mixed in the presence of an acid catalyst (sulfuric acid, hydrochloric acid, etc.) and thiols (mercaptocarboxylic acid, etc.). It may be synthesized by a conventional method such as a reaction method.

The compound having the cardo structure described above is mixed with the unmodified insulating fiber (A).
The (mixing ratio) of the insulating fiber (A) and the compound having a cardo structure is, for example, 99/1 to 1/99 (for example, a mass ratio) as a compound having an insulating fiber (A) / cardo structure (mass ratio). 95/5 to 5/95), preferably 93/7 to 7/93 (eg, 90/10 to 10/90), more preferably 85/15 to 5/95 (eg, 80/20 to 6/94). ), In particular, it may be about 75/25 to 5/95 (for example, 70/30 to 7/93), and usually about 70/30 to 10/90.

Mixing may be carried out in the presence of a solvent, if desired.
The mixing conditions can be selected according to the properties of the compound having a cardo structure (for example, whether it is liquid or solid), the pressure at the time of mixing, and the like. Usually, the mixing may be carried out under heating (or under heating). The heating temperature is, for example, 100 to 300 ° C. (for example, 120 to 250 ° C.), preferably 150 to 300 ° C. (for example, 160 to 300 ° C.), and more preferably 165 to 270 ° C. (for example, 165 to 250 ° C.). In particular, it may be about 170 to 250 ° C.
The heating and mixing can be carried out in an atmosphere of an inert gas or in air under reduced pressure, normal pressure or pressure (for example, under a pressure of about 0.05 to 15 MPa).
The mixing is preferably carried out under the condition that the compound having a cardo structure is in a liquid state.

The mixing time or heating time (heating mixing time) can be selected according to the mixing temperature (or reaction temperature) and the like, and is, for example, 10 minutes or more (for example, 20 minutes to 24 hours), preferably 30 minutes or more (for example, 40). It may be about minutes to 12 hours).
The mixing device may be a continuous mixing device or a batch type mixing device. For example, when mixing is performed using an extruder, it is preferable because the mixing can be performed while unraveling the insulating fiber (A).

The method for separating the hydrophobically modified insulating fiber (A) from the mixture obtained by the methods described above is not particularly limited. For example, the obtained mixture is washed with a suitable solvent (for example, a solvent capable of dissolving a compound having a cardo structure), a liquid phase in which a part of the compound having a cardo structure is dissolved is separated, and then the cardo structure is formed. The insulating fiber (A) hydrophobized with the compound having is separated from the mixture.
The content of the compound having a cardo structure in the hydrophobically modified insulating fiber (A) is preferably 0.01 to 10% by mass with respect to the mass of the hydrophobically modified insulating fiber (A).

The type of solvent is not particularly limited as long as it can dissolve a compound having a cardo structure. Specific examples of the solvent include hydrocarbons (for example, aliphatic hydrocarbons such as pentane and hexane; alicyclic hydrocarbons such as cyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene) and halogen-based solvents (for example). , Methylene chloride, chloroform, halogenated hydrocarbons such as carbon tetrachloride, etc.), alcohols (eg, methanol, ethanol, isopropanol, etc.), ethers (eg, diethyl ether, chain ethers such as diisopropyl ether; dioxane, Cyclic ethers such as tetrahydrofuran), ketones (eg, dialkyl ketones such as acetone, methyl ethyl ketone, isobutyl methyl ketone), cellosolves (eg, methyl cellosolve, ethyl cellosolve, etc.), carbitols (methyl carbitol, etc.), esters (For example, acetates such as methyl acetate, ethyl acetate, butyl acetate, etc.), amides (dimethylformamide, etc.), sulfoxides (dimethylsulfoxide, etc.), nitriles (acetritale, benzonitrile, etc.) and the like. These solvents can be used alone or as a mixed solvent.

Among these solvents, alcohols (particularly methanol), cyclic ethers (particularly 1,4-dioxane), nitriles and the like are preferable. Moreover, the solvent may be a mixed solvent with water.

The hydrophobized and modified insulating fiber (A) recovered as described above is preferably defibrated. However, since the insulating fiber (A) can be defibrated at the time of preparing the composition for forming a porous film, the defibration treatment is not necessarily performed immediately after the recovery of the hydrophobically modified insulating fiber (A). Need to do Yes. The defibration treatment is preferably carried out in the presence of a dispersion medium.

The defibration method (defibration treatment) of the hydrophobized insulating fiber (A) is not particularly limited, but for example, a mechanical treatment (for example, a homogenizer, a mill (bead mill, ball mill, etc.), a mixer, a grinder, etc. Defibering treatment using a dispersed medium such as a paint shaker), ultrasonic treatment, etc. can be mentioned. The defibration treatment may be performed alone or in combination of two or more.

The hydrophobizing modification using a compound having a bisphenol structure can be carried out in the same manner as the hydrophobizing modification using a compound having a cardo structure.
The compound having a bisphenol structure is not particularly limited as long as it is a compound other than the compound having a cardo structure and is generally recognized as a bisphenol.

Preferable examples of compounds having a bisphenol structure are 4,4'-biphenol, 2,2-bis (4-hydroxyphenyl) propane (bisphenol A), 1,1-bis (4-hydroxyphenyl) -1-. Phenylethane (bisphenol AP), 2,2-bis (4-hydroxyphenyl) hexafluoropropane (bisphenol AF), 2,2-bis (4-hydroxyphenyl) butane (bisphenol B), bis (4-hydroxyphenyl) Diphenylmethane (bisphenol BP), 2,2-bis (3-methyl-4-hydroxyphenyl) propane (bisphenol C), 1,1-bis (4-hydroxyphenyl) ethane (bisphenol E), bis (4-hydroxyphenyl) ) Methan (bisphenol F), 2,2-bis (4-hydroxy-3-isopropylphenyl) propane (bisphenol G), 1,3-bis (2- (4-hydroxyphenyl) -2-propyl) benzene (bisphenol) M), bis (4-hydroxyphenyl) sulfone (bisphenol S), 1,4-bis (2- (4-hydroxyphenyl) -2-propyl) benzene (bisphenol P), 5,5'-(1-methyl Ethiliden) -bis [1,1'-(bisphenol) -2-ol] propane (bisphenol PH), 1,1-bis (4-hydroxyphenyl) cyclohexane (bisphenol Z) and the like can be mentioned.

When the surface of the insulating fiber (A) is coated with a denaturing agent having an acetyl group or a methyl group, or when a denaturing agent is attached to the surface of the insulating fiber (A) for hydrophobic modification, the acetyl group or A portion of the denaturing agent having a methyl group other than the acetyl group or the methyl group may be attached to the surface of the insulating fiber (A).
Such hydrophobizing modification is carried out in the same manner as hydrophobizing modification using a compound having a cardo structure using a modifying agent having an acetyl group or a methyl group.

Further, the surface of the insulating fiber (A) can be surface-modified with an acetyl group or a methyl group to perform hydrophobic modification. The surface modification method using an acetyl group or a methyl group is not particularly limited as long as it can introduce an acetyl group or a methyl group into the surface of the insulating fiber (A).
When a modifier having an acetyl group or a methyl group is chemically bonded to the surface of the insulating fiber (A) to perform hydrophobic modification, the acetyl group or the methyl group is the insulating fiber (the insulating fiber (A) via a linking group. It suffices to bond to the surface of A), and the acetyl group or methyl group need not be directly chemically bonded to the surface of the insulating fiber (A).
Since a high denaturing effect can be obtained by using a small amount of denaturing agent, it is preferable to chemically bond an acetyl group or a methyl group directly to the surface of the insulating fiber (A) for hydrophobizing modification. ..

Examples of the method for surface-modifying the insulating fiber (A) with an acetyl group or a methyl group include acetylating agents such as acetyl chloride, acetyl bromide, and acetic anhydride, methyl bromide, methyl iodide, and dimethyl sulfate. Examples thereof include a method in which a methylating agent such as dimethyl carbonate, methyl trifluoromethanesulfonate, methyl fluorosulfonate, methyllithium, and methylmagnesium bromide is reacted with the surface of the insulating fiber (A) according to a well-known method.

Further, when the surface of the insulating fiber (A) is modified by using a cationizing agent having a methyl group, an acetyl group or the like together with a reactive group such as an epoxy group, for example, it is insulated from an organic solvent solution of the cationizing agent. It may be brought into contact with the sex fiber (A). At this time, the cationizing agent may be reacted with the insulating fiber (A) on the surface by heating to 40 to 80 ° C., preferably about 60 ° C.
Even if the cationizing agent is reacted on the surface of the insulating fiber (A) by applying impact, shearing force, pressure, etc. to the cationizing agent and the insulating fiber (A) by mechanical force. good. Devices that apply mechanical force include high-pressure compression roll mills, roll rotation mills, ring rollers, roller race mills, ball race mills, rolling ball mills, vibrating ball mills, vibrating rod mills, vibrating tube mills, planetary ball mills, centrifugal fluidization mills, etc. Examples thereof include a tower type crusher, a stirring tank type mill, a distribution tank type mill, an annual type mill, a high-speed centrifugal roller mill, an ong mill, a mortar, and a stone mill.
The treatment temperature when the treatment is performed by mechanical force is not particularly limited, but for example, it is preferably -20 to 200 ° C, more preferably -10 to 100 ° C, particularly preferably 0 to 80 ° C, and most preferably 10 to 60 ° C. .. The processing time for performing the treatment by mechanical force is usually preferably 0.01 to 20 hours, more preferably 0.05 to 10 hours, and particularly preferably 0.1 to 5 hours.

The content of the hydrophobically modified insulating fiber (A) in the composition for forming a porous film is preferably 0.1 to 10% by mass, and 0.5 to 5% by mass, based on the total mass of the composition. The mass% is more preferable, and 0.5 to 2% by mass is particularly preferable.
When a hydrophobically modified insulating fiber (A) is used in such an amount, the insulating fiber (A) is closely entangled, the electrolytic solution is rapidly permeated, and ions such as lithium ions are good. It is possible to form a porous film preferably used as a separator, which can be moved to.
Further, by satisfactorily dispersing the insulating fibers (A) in the composition for forming a porous film, it is possible to form a porous film having a narrow distribution of opening diameters and a uniform film thickness. Therefore, the porous membrane formed by using the composition for forming a porous membrane is also suitably used as a filter for filtering a liquid or gas.

<Binder resin (B)>
The composition for forming a porous film contains a binder resin (B). By containing the binder resin (B), the composition for forming a porous film has a film-forming property that can easily form a porous film.
The binder resin (B) is not particularly limited as long as it is a resin soluble in the solvent (S). Further, the binder resin (B) is usually an insulating resin.

Preferable specific examples of the binder resin (B) include polyvinylidene fluoride, hexafluoropropylene, vinylidene polyvinylidene-hexafluoropropylene, vinylidene fluoride-trichloroethylene, styrene butadiene rubber, carboxylmethylcellulose, polymethylmethacrylate, and polybutylacrylate. Polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-vinylacetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, Examples thereof include purulan, carboxylmethylcellulose, acrylonitrile-styrene-butadiene copolymer, and polyimide resin.
One of these binder resins (B) may be used alone, or two or more thereof may be used in combination.

Among the above, polyvinylidene fluoride and styrene-butadiene rubber are preferable as the binder resin (B).
Here, there is a preferable combination of the binder resin (B) and the solvent (S) described later. For example, when the binder resin (B) is polyvinylidene fluoride, the solvent (S) is preferably a nitrogen-containing polar organic solvent such as N-methyl-2-pyrrolidone. When the binder resin (B) is styrene-butadiene rubber, the solvent (S) is preferably a water-containing solvent.

The content of the binder resin (B) in the composition for forming a porous film is preferably 0.01 to 20% by mass, preferably 0.05, based on 100 parts by mass of the hydrophobically modified insulating fiber (A). 10% by mass is more preferable, and 0.05 to 5% by mass is particularly preferable. When the binder resin (B) in such an amount is used, the film-forming property of the composition for forming a porous film is good, and the film-forming property is good.

<Fine particles (C)>
The composition for forming a porous film has been conventionally used in the production of a separator for an electrochemical device, for example, and may contain various fine particles (C) that are insoluble in a solvent (S). The fine particles (C) may be inorganic fine particles or organic fine particles. Since the composition for forming a porous film contains fine particles (C), it is easy to form a porous film having excellent mechanical strength and dimensional stability by using the composition for forming a porous film.

Preferable specific examples of the inorganic fine particles include inorganic oxide fine particles such as iron oxide, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), titania (TIO ₂ ), BaTIO ₃ , and lithium ion conductive ceramics (LLTO). Inorganic nitride fine particles such as aluminum nitride and silicon nitride; sparingly soluble ionic crystal fine particles such as calcium fluoride, barium fluoride and barium sulfate; covalently bonded crystal fine particles such as silicon and diamond; clay fine particles such as montmorillonite; etc. Can be mentioned.

The inorganic oxide fine particles may be natural minerals such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, and mica, or may be artificial substances.
Further, it is also possible to use fine particles in which the surface of the fine particles of the conductive material is coated with an insulating material (for example, the above-mentioned inorganic oxide or organic polymer material). Examples of the conductive material include metals; _{conductive oxides such as SnO 2} and indium tin oxide (ITO); carbonaceous materials such as carbon black and graphite.

The material of the organic fine particles is preferably a resin material because it is poorly soluble in the solvent (S) and the fine particles can be easily produced. Preferable specific examples of the organic fine particles include aromatic polyamide resin fine particles, polyimide resin fine particles, liquid crystal polyester resin fine particles, acrylic fine particles, olefin fine particles and the like.

The particle size of the fine particles (C) is not particularly limited as long as the object of the present invention is not impaired. The particle size of the fine particles (C) is preferably 0.1 to 200 μm as the volume average particle size. The volume average particle size of the fine particles (C) can be measured using a laser diffraction type particle size distribution measuring device.

The content of the fine particles (C) in the composition for forming a porous film is preferably 0.01 to 20% by mass, preferably 0.05 to 20% by mass, based on 100 parts by mass of the hydrophobized insulating fiber (A). 10% by mass is more preferable, and 0.05 to 5% by mass is particularly preferable. When fine particles (C) in such an amount are used, it is easy to form a porous film having particularly excellent mechanical strength and dimensional stability by using the composition for forming a porous film.

<Solvent (S)>
The solvent (S) is not particularly limited as long as it is a solvent that does not dissolve the insulating fiber (A) or remove the hydrophobic structure introduced by the hydrophobic modification from the surface of the insulating fiber.
The solvent (S) may be used in combination of two or more.
The solvent (S) may contain water as long as the object of the present invention is not impaired. When the solvent (S) contains water, the dispersibility of the insulating fiber (A) and the fact that water does not easily remain in the separator when the porous film is used as the separator are used in the composition for forming the porous film. The water content is preferably 50% by mass or less, more preferably 30% by mass or less, further preferably 10% by mass or less, particularly preferably 5% by mass or less, and most preferably 1% by mass or less.

The solvent (S) is glycol, glycol alkyl ether, glycol alkyl ether acetate, chain or cyclic ester, chain or cyclic ketone, solvent having a carbon-carbon double bond, ether other than the above, number of carbon atoms other than the above. It is preferably at least one selected from the group consisting of 7 or less alcohols, amine-based solvents, and aprotonic polar solvents other than the above. When these solvents (S) are used, the hydrophobically modified insulating fibers (A) can be easily dispersed uniformly in the composition for forming a porous film without agglutination or precipitation.

Glycol is an aliphatic diol. Glycols may contain ether bonds in their structure. Glycols containing ether bonds are described as glycols rather than ethers in the specification and claims of the present application.
Preferable examples of glycols include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol (DPG), triethylene glycol, tripropylene glycol and the like.

The glycol alkyl ether is the above-mentioned glycol monoalkyl ether or dialkyl ether. The glycol alkyl ethers, preferably C ₁ -C ₆ alkyl ethers of glycols, more preferably C ₁ -C ₄ alkyl ethers of glycol, ethyl ether of methyl ether or glycol glycol are particularly preferred.
Examples of glycol alkyl ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono n-propyl ether, propylene glycol monomethyl ether (PGME), propylene glycol monoethyl ether, propylene glycol mono n-propyl ether, and diethylene glycol monomethyl ether. , Diethylene glycol monoethyl ether, diethylene glycol monon-propyl ether, dipropylene glycol monomethyl ether (MFDG), dipropylene glycol monoethyl ether, dipropylene glycol monon-propyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether , Triethylene glycol mono-n-propyl ether, tripropylene glycol monomethyl ether (MFTG), tripropylene glycol monoethyl ether, tripropylene glycol mono n-propyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol din-propyl Ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol din-propyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol din-propyl ether, dipropylene glycol dimethyl ether (DMM), dipropylene glycol diethyl ether, dipropylene glycol Examples thereof include din-propyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol din-propyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, and tripropylene glycol din-propyl ether.

The glycol alkyl ether acetate is the monoalkyl ether acetate of the above glycol. The glycol alkyl ether acetates, preferably C ₁ -C ₆ monoalkyl ether acetate glycol, more preferably C ₁ -C ₄ monoalkyl ether acetate glycol, monoethyl ether acetate monomethyl ether acetate or glycol glycols, especially preferable.
Examples of glycol alkyl ether acetate include 3-methoxybutyl acetate (MA), ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono n-propyl ether acetate, propylene glycol monomethyl ether acetate (PGMEA), and propylene glycol mono. Ethyl ether acetate, propylene glycol mono n-propyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol mono n-propyl ether acetate, dipropylene glycol monomethyl ether acetate (DPMA), dipropylene glycol monoethyl ether acetate, Dipropylene glycol mono-n-propyl ether acetate, triethylene glycol monomethyl ether acetate, triethylene glycol monoethyl ether acetate, triethylene glycol mono n-propyl ether acetate, tripropylene glycol monomethyl ether acetate, tripropylene glycol monoethyl ether acetate, And tripropylene glycol mono-n-propyl ether acetate.

The chain or cyclic ester is a solvent containing an ester bond and is a compound that does not correspond to glycol alkyl ether acetate. The chain or cyclic ester may contain one or more selected from the group consisting of an ether bond, a keto group (ketone carbonyl group), and a hydroxyl group in its structure. For chain or cyclic esters having one or more selected from the group consisting of ether bonds, keto groups (ketone carbonyl groups), and hydroxyl groups, as far as the specification and patent claims of this application are concerned, ethers, ketones, or Notated as a chain or cyclic ester rather than an alcohol.
As chain or cyclic esters, methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, methylpentyl acetate, acetic acid Methylcyclohexyl, n-nonyl acetate, phenyl acetate, benzyl acetate, phenethyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, methyl acetoacetate, ethyl acetoacetate, ethylene Glycoldiacetate, propylene glycol diacetate, diethylene glycol diacetate, dipropylene glycol diacetate, dimethyl oxalate, diethyl oxalate, din-propyl oxalate, din-butyl oxalate, methyl lactate, ethyl lactate, n-lactate Propyl, isopropyl lactate, n-butyl lactate, dimethyl malonate, diethyl malonate, γ-butyrolactone (GBL), α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, γ-laurolactone, δ-valero Examples thereof include lactone and hexanolactone.

The chain or cyclic ketone may have an ether bond and / or a hydroxyl group in its structure. Chained or cyclic ketones having an ether bond and / or a hydroxyl group are described as chain or cyclic ketones rather than ethers or alcohols in the specification and claims of the present application.
Examples of the chain or cyclic ketone include acetone, methyl ethyl ketone, diethyl ketone, 2-pentanone, 2-hexanone, 3-hexanone, methyl isobutyl ketone, acetylacetone, cyclopentanone, cyclohexanone, and cycloheptanone.

A solvent having a carbon-carbon double bond has at least one selected from the group consisting of an ester bond, an ether bond, a keto group (ketone carbonyl group), a hydroxyl group, and an amino group in its structure. You may. The specification of the present application and a solvent having a carbon-carbon double bond having one or more selected from the group consisting of an ester bond, an ether bond, a keto group (ketone carbonyl group), a hydroxyl group, and an amino group. In the scope of the patent claim, it is described as a solvent having a carbon-carbon double bond, not as an ester, an ether, a ketone, an alcohol, or an amine-based solvent.
Examples of the solvent having a carbon-carbon double bond include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide and the like.

Ethers other than the above are solvents other than the above-mentioned glycol alkyl ethers, glycol alkyl ether acetates, chain or cyclic esters, chain or cyclic ketones, and solvents having a carbon-carbon double bond, and have an ether bond. It is a solvent. Ethers other than the above may have a hydroxyl group. Ethers other than the above having a hydroxyl group are described as ethers other than the above instead of alcohol in the specification of the present application and claims.
Examples of ethers other than the above include diethyl ether, din-propyl ether, diisopropyl ether, din-butyl ether, anisole, phenoxyethanol, tetrahydrofuran (THF), dioxane and the like.

Alcohols having 7 or less carbon atoms other than the above are the above-mentioned glycol alkyl ethers, glycol alkyl ether acetates, chain or cyclic esters, chain or cyclic ketones, solvents having carbon-carbon double bonds, and ethers other than the above. It is a solvent other than.
Other alcohols having 7 or less carbon atoms include methanol, ethanol, n-propanol, isopropanol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, n-pentyl alcohol, and n-hexyl alcohol. , Cyclohexyl alcohol, n-heptyl alcohol and the like.

The amine solvent is a solvent having an amino group which may be substituted with an organic group. The amine solvent may have one or more selected from the group consisting of an ester bond, an ether bond, a keto group (ketone carbonyl group), and a hydroxyl group in its structure. For amine-based solvents having one or more selected from the group consisting of ester bonds, ether bonds, keto groups (ketone carbonyl groups), and hydroxyl groups, as far as the specification and patent claims of this application are concerned, esters, ethers, Described as an amine-based solvent rather than a ketone or alcohol.
Examples of the amine-based solvent include triethylamine, monoethanolamine, diethanolamine, triethanolamine, aniline, N, N-dimethylaniline and the like.

Aprotonic polar solvents other than the above are glycols, glycol alkyl ethers, glycol alkyl ether acetates, chain or cyclic esters, chain or cyclic ketones, solvents with carbon-carbon double bonds, ethers other than the above, and other than the above. It is a solvent other than alcohol having 7 or less carbon atoms and amine-based solvent.
Examples of the aprotic polar solvent other than the above include N, N-dimethylformamide (DMF), N, N-diethylformamide, N, N-dimethylacetamide (DMAc), N, N-diethylacetamide, and N-methyl-2. -Pyrrolidone, N-ethyl-2-pyrrolidone, N, N, N', N'-tetramethylurea (TMU), N, N, N', N'-tetraethylurea, N-methylcaprolactam, 1,3- Examples thereof include dimethyl-2-imidazolidinone (DMI), dimethyl sulfoxide, hexamethylphosphoric triamide, and acetonitrile.

The amount of the solvent (S) used in the composition for forming a porous film is appropriately adjusted in consideration of the film thickness of the porous film to be formed, the viscosity which is easy to apply, and the like. The amount of the solvent (S) used in the composition for forming a porous film is a residual amount with respect to the total amount of the components described above and the amounts of other components described below.

<Other ingredients>
The composition for forming a porous film has other components other than the insulating fiber (A), the binder resin (B), the fine particles (C), and the solvent (S) described above, as long as the object of the present invention is not impaired. May include.
Examples of other components include surfactants, antifoaming agents, leveling agents and the like.

<Method for producing a composition for forming a porous film>
The method for producing the composition for forming a porous film is particularly limited as long as the insulating fiber (A) can be uniformly dispersed in the composition and each component can be dissolved or dispersed in the solvent (S). Not limited.
As a specific example of the method for producing the composition for forming a porous membrane, a predetermined amount of each component contained in the composition for forming a porous membrane is added to the solvent (S), treated with a disperser, and insulated. Examples thereof include a method of obtaining a composition for forming a porous film in which components such as the sex fiber (A) are uniformly dispersed.
Preferable examples of the disperser include ball mills, bead mills, sand mills, double rolls, triple rolls, roll mills, colloid mills, jet mills, kneaders, homogenizers and the like.
By adjusting the dispersion conditions, the particle size (dispersion diameter, volume average particle size) and particle size distribution of the insulating fibers in the composition for forming a porous film can be adjusted.

Further, after the insulating fibers (A) are dispersed in the solvent (S), components other than the insulating fibers (A) are added to the solvent (S) to prepare a composition for forming a porous film. May be good.

The volume average particle size of the hydrophobically modified insulating fiber (A) in the composition for forming a porous membrane obtained through the above dispersion treatment is that of ions such as lithium ions when the porous membrane is used as a separator. From the viewpoint of permeability, 10 μm or more is preferable, and 30 μm or more is more preferable. The volume average particle size of the hydrophobically modified insulating fiber (A) in the composition for forming a porous film is preferably 500 μm or less, more preferably 200 μm or less, and particularly preferably 100 μm or less.
In the porous membrane, the insulating fibers (A) are distributed so that the direction of the major axis is substantially parallel to the plane direction of the porous membrane. Therefore, there is no problem even if the volume average particle size of the insulating fiber (A) is larger than the film thickness of the porous film.

As described above, the porous film formed by removing the solvent (S) from the film made of the composition for forming a porous film described above is suitably used as a separator in an electrochemical element such as a secondary battery. In addition, since the distribution of the opening diameter is narrow and the film thickness is uniform, it is also suitably used as a filter for filtering liquids or gases.
Further, as the secondary battery, a lithium battery or a lithium ion battery is particularly preferable because a separator that satisfactorily permeates lithium ions can be easily formed by using the composition for forming a porous film described above.

≪Separator≫
The separator is formed from the above-mentioned composition for forming a porous film. That is, after forming the coating film made of the above-mentioned composition, the solvent (S) is removed from the formed coating film to form a separator which is a porous film.
Therefore, the separator includes a non-woven fabric-like porous portion in which the above-mentioned hydrophobically modified insulating fibers (A) are entangled.

The separator is a porous film that is peeled off from the base material after removing the solvent (S) from the coating film formed by applying the above-mentioned composition for forming a porous film on a base material such as a glass substrate. You may. In this case, the separator is placed in a predetermined position in the electrochemical element to manufacture the electrochemical element.
The separator is formed by applying the above-mentioned composition for forming a porous film on the surface of the electrochemical element on which the separator should be arranged to form a coating film, and then removing the solvent (S) from the coating film. Is preferable.
The separator is usually placed on the electrode. Therefore, typically, by applying the composition for forming a porous film on the electrode, a separator is directly formed on the electrode.
In this case, since the separator that adheres very well to the electrode can be formed without forming a gap, the concentration of the electric field at the interface between the separator and the electrode is suppressed. As a result, the growth of lithium dendrite, which adversely affects the life and performance of the electrochemical device, is suppressed, and a high-quality electrochemical device can be formed.

When the composition for forming a porous film is applied onto the electrode to form a separator, the surface of the electrode in contact with the separator, that is, the surface on which the composition for forming a porous film is applied on the electrode has irregularities. May be. According to the method of applying the composition for forming a porous film to the surface of the electrode to form a separator, even if the surface of the electrode has irregularities, the separator is in good contact with the surface of the electrode. A separator having a shape that conforms to the surface shape of the electrode can be formed.
In this case, by increasing the surface area of the electrode and the contact area between the electrode and the separator, charging at extremely high speed is possible, and a high-capacity electrochemical element can be formed.

Further, the separator preferably has a contact angle of 25 ° or less with the electrolytic solution when measured under the condition of 2 seconds after dropping the droplets of the electrolytic solution containing dimethyl carbonate on the surface.
The separator is mainly composed of the insulating fiber (A). Since the insulating fiber (A) has undergone the above-mentioned hydrophobic denaturation, it is easily wetted with an electrolytic solution containing dimethyl carbonate. Therefore, by using the above-mentioned composition for forming a porous film, it is possible to form a separator having a contact angle of 25 ° or less with an electrolytic solution containing dimethyl carbonate measured under the above-mentioned predetermined conditions.
The method for adjusting the contact angle is not particularly limited, but for example, in the hydrophobic modification of the insulating fiber (A), the amount of the modifier used is increased or the modifier is changed to a modifier having a higher hydrophobic effect. There is a way to do it.

When the contact angle between the separator and the electrolytic solution containing dimethyl carbonate satisfies the above range, the electrolytic solution quickly and satisfactorily penetrates into the separator, and the movement of ions such as lithium ions between the electrodes is particularly high. It progresses well. Therefore, a high-performance electrochemical element can be formed.

The film thickness of the separator is not particularly limited and may be appropriately selected depending on the design of the electrochemical element. In general, the thinner the separator is, the more preferable it is because it can be charged at high speed and it is easy to manufacture a high-capacity electrochemical element. Specifically, the film thickness of the separator is preferably 1 to 100 μm or less, more preferably 2 to 50 μm.

≪Electrochemical element≫
The electrochemical device may have a conventionally known and well-known configuration for an electrochemical device, in addition to the above-mentioned separator.
The above-mentioned separator constitutes an element of an electrochemical element as an electrode composite composited with an electrode.

Examples of the electrochemical element include batteries or capacitors such as lithium ion secondary batteries, polymer lithium batteries, aluminum electrolytic capacitors (capacitors), electric double layer capacitors, and lithium ion capacitors.
The electrode composite in which the above-mentioned separator and electrode are combined is preferably used for a secondary battery, and more preferably used for a lithium ion secondary battery.

The configuration of the battery as an electrochemical element can be exactly the same as that of a conventional battery except that an electrode composite in which a separator and an electrode are composited is used as a unit battery layer. The structure of the electrochemical element is not particularly limited, and examples thereof include a laminated type, a cylindrical type, a square type, and a coin type.
For example, a lithium ion secondary battery as an electrochemical element can include a unit battery layer in which a porous film (separator) in an electrode composite is impregnated with an electrolytic solution.

Further, a capacitor as an electrochemical element, for example, an electric double layer capacitor can also include a unit cell in which a porous film (separator) in an electrode composite is impregnated with an electrolytic solution.

In a lithium ion secondary battery or an electric double layer capacitor, for example, a plurality of the unit battery layers or unit cells are laminated or wound to form an element, and then the element is housed in an exterior material and a current collector is externally mounted. It can be manufactured by connecting to an electrode, impregnating with a conventionally known electrolytic solution, and then sealing an exterior material.

≪Manufacturing method of electrode composite≫
As described above, a porous film that functions as a separator can be formed by a method including a coating step of applying the composition for forming a porous film onto an electrode, whereby an electrode composite containing the electrode and the separator is produced. NS.

Specifically, the solvent (S) is removed from the coating film formed by applying the composition for forming a porous film onto the electrode to form a separator in close contact with the electrode surface, and an electrode composite is obtained. Be done.
The electrode to which the composition for forming a porous film is applied may be a positive electrode or a negative electrode.
The coating device is not particularly limited, and a contact transfer type coating device such as a roll coater, a reverse coater, or a bar coater, or a non-contact type coating device such as a curtain flow coater, a die coater, a slit coater, or a spray may be used.
Even when the surface of the electrode has irregularities, it is easy to form a coating film having a uniform film thickness. Therefore, a spray method, for example, a method using a rotary atomization type coating device is preferable as the coating method. As the rotary atomization type coating device, for example, those described in Japanese Patent Application Laid-Open No. 2013-115181 can be used.

The solvent (S) is removed from the coating film formed by the above method. The method for removing the solvent (S) is not particularly limited, but a method for heating the coating film on the electrode is preferable. The coating film may be heated under atmospheric pressure or reduced pressure. The heating temperature is not particularly limited, and is appropriately set within a temperature range in which thermal deterioration of the separator does not occur in consideration of the boiling point of the solvent (S).

Hereinafter, the present invention will be specifically described with reference to Examples, but the scope of the present invention is not limited to the Examples shown below.

Hereinafter, in the examples, cellulose fibers coated with a fluorene compound having a cardo structure were used as the hydrophobically modified insulating fibers.
As the fluorene compound having a cardo structure, fluorene cellulose (Lot. WSAC-0001) manufactured by Osaka Gas Co., Ltd. was used.

[Examples 1-36]
10 parts by mass of the above hydrophobized cellulose fiber and 0.4 parts by mass of polyvinylidene fluoride were mixed in the solvent shown in Table 1 so that the solid content concentration was about 1% by mass.
The obtained mixture was dispersed using a bead mill for 10 minutes to obtain a composition for forming a porous membrane.
The composition for forming a porous film after the dispersion treatment was visually observed, and the dispersed state of the hydrophobically modified cellulose fibers in the composition for forming a porous film was evaluated according to the following criteria. The evaluation results are shown in Table 1.
⊚: Cellulose fibers are well dispersed.
◯: Cellulose fibers are dispersed, but gradual sedimentation is observed.
X: Separation and sedimentation of cellulose fibers are observed.

According to Table 1, it can be seen that the cellulose fibers hydrophobized and modified with the fluorene compound having a cardo structure are well dispersed in the composition for forming a porous film containing various solvents.

[Example 37]
The composition for forming a porous film of Example 22 is applied to the surface of a negative electrode (LTO, lithium-titanium oxide) formed on an aluminum sheet using a rotary atomization type coating device, and then the coating film is heated. Then, NMP was removed to form a separator having a film thickness of 4 μm.
The volume average particle size of the hydrophobically modified cellulose fibers in the composition for forming a porous film of Example 22 was 40 μm.

When a droplet of the electrolytic solution containing dimethyl carbonate was dropped on the surface of the formed separator, the electrolytic solution permeated into the separator 2 seconds after the dropping, and the contact angle of the electrolytic solution could not be measured.
From this, it can be seen that the contact angle of the surface of the separator with the above-mentioned electrolytic solution is clearly 25 ° or less.

A positive electrode (lithium) was provided on the separator formed by the above method to prepare a battery cell.
When the prepared battery cell was subjected to charge / discharge evaluation (3 cycles) based on the discharge capacity (mAh / g), good results were obtained.

[Comparative Example 1]
A composition for forming a porous film was obtained in the same manner as in Example 22 except that the solvent was changed to water.
Using the obtained composition for forming a porous film, a battery cell was prepared in the same manner as in Example 37.
When the obtained battery cell was subjected to charge / discharge evaluation (3 cycles) in the same manner as in Example 37, it was significantly inferior to the evaluation result of Example 37.

[Example 38]
A composition for forming a porous film was obtained in the same manner as in Example 22 except that polyvinylidene fluoride was changed to styrene-butadiene rubber.
Using the obtained composition for forming a porous film, a battery cell was prepared in the same manner as in Example 37.
When the obtained battery cell was subjected to charge / discharge evaluation (3 cycles) in the same manner as in Example 37, the same good result as the evaluation result of Example 37 was obtained.

[Example 39]
Further, it is porous in the same manner as in Example 22 except that 10.4 parts by mass of a lithium ion conductive ceramic (LLTO) particle dispersion liquid (volume average particle diameter 0.5 μm (dispersed by NMP and PVDF)) is added. A film-forming composition was obtained.
Using the obtained composition for forming a porous film, a battery cell was prepared in the same manner as in Example 37.
When the obtained battery cell was subjected to charge / discharge evaluation (3 cycles) in the same manner as in Example 37, the same good result as the evaluation result of Example 37 was obtained.

[Impedance evaluation: Example 37, Example 40, Example 41, and Reference Example 1]
For Examples 40 and 41, a battery cell was prepared in the same manner as in Example 37, except that the film thickness of the separator was changed to the film thickness shown in Table 2. In Reference Example 1, a battery cell was produced in the same manner as in Example 37, except that a commercially available separator (Celgard (registered trademark) 2400) having a film thickness of 25 μm manufactured by Celgard was used.
The prepared battery cell was charged and discharged for two cycles under the following conditions, and then the impedance was measured under the following conditions. The impedance measurement results are shown in Table 2.
(Charging / discharging)
Charging: Constant current constant voltage charging (CCCV), end at 0.1C, 0.01C Pause: 10 minutes Discharge: Constant current (CC), end at 0.1C, 2.6V (impedance measurement)
Charge rate (SOC): 50%
Frequency: 1000kHz-10MHz
Voltage Va: 10 mV

According to Table 2, a separator formed by using a composition for forming a porous film containing a hydrophobically modified insulating fiber (A), a binder resin (B), and a solvent (S) is provided. It can be seen that the impedance value of the battery cell is higher than the impedance value of the battery cell provided with the commercially available separator.
In particular, according to a comparison between Examples 37 and 41 and Reference Example 1, the porous material containing the hydrophobically modified insulating fiber (A), the binder resin (B), and the solvent (S) is contained. It can be seen that the separator formed by using the film-forming composition exhibits better insulating properties than the commercially available separator even in a thin film.

[Impedance evaluation: Example 40, Example 42, and Example 43, and Reference Example 1]
For Example 42, a battery cell was prepared in the same manner as in Example 38, except that the film thickness of the separator was changed to the film thickness shown in Table 3.
For Example 43, a battery cell was prepared in the same manner as in Example 39, except that the film thickness of the separator was changed to the film thickness shown in Table 3.
Impedances of the battery cells of Example 40, Example 42, and Example 43, and the battery cell of Reference Example 1 were measured according to the above-mentioned method. The impedance measurement results are shown in Table 3.

According to Table 3, a separator formed by using a composition for forming a porous film containing a hydrophobically modified insulating fiber (A), a binder resin (B), and a solvent (S) is provided. It can be seen that the impedance value of the battery cell is high regardless of the type of the binder resin (B) and whether or not the composition for forming the porous film contains fine particles.
The battery cells of Examples 40, 42, and 43 showed better insulating properties than commercially available separators even if the separator was a thin film.

[Impedance evaluation: Example 40, Example 44, Example 45, and Reference Example 1]
For Example 44, a battery cell was formed in the same manner as in Example 40 by using the composition for forming a porous film prepared in the same manner as in Example 22 except that the dispersion treatment time was changed from 10 minutes to 3 minutes. bottom.
Regarding Example 45, a battery cell was formed in the same manner as in Example 40 by using the composition for forming a porous film prepared in the same manner as in Example 22 except that the dispersion treatment time was changed from 10 minutes to 30 minutes. bottom.
The impedance of the battery cells of Example 40, Example 44, Example 45, and Reference Example 1 was measured according to the method described above. The impedance measurement results are shown in Table 4.

According to Table 4, a separator formed by using a composition for forming a porous film containing a hydrophobically modified insulating fiber (A), a binder resin (B), and a solvent (S) is provided. It can be seen that the impedance value of the battery cell is high regardless of the dispersion time of the insulating fiber (A).
Further, it can be seen that the longer the dispersion time of the insulating fiber (A) is, the higher the impedance value is.
The battery cells of Examples 40, 44, and 45 showed better insulating properties than commercially available separators even if the separator was a thin film.

[Fast charge evaluation: Example 37, Example 40, and Reference Example 1]
The battery cells of Example 37, Example 40, and Reference Example 1 were evaluated for rapid charging based on the charging capacity (mAh / g) at 2C. Table 5 shows the values of the charge capacity at 2C.

According to Table 5, a separator formed by using a composition for forming a porous film containing a hydrophobically modified insulating fiber (A), a binder resin (B), and a solvent (S) is provided. It can be seen that the quick charging characteristics of the battery cell are as good as those of a battery cell provided with a commercially available separator, regardless of the film thickness of the separator.

[Fast charge evaluation: Example 40, Example 43, and Reference Example 1]
The battery cells of Example 40, Example 43, and Reference Example 1 were evaluated for quick charging according to the method described above. Table 6 shows the values of the charge capacity at 2C.

According to Table 6, a separator formed by using a composition for forming a porous film containing a hydrophobically modified insulating fiber (A), a binder resin (B), and a solvent (S) is provided. It can be seen that the quick charging characteristics of the battery cell are as good as those of the battery cell provided with the commercially available separator, regardless of whether or not the composition for forming the porous film contains fine particles.

[Fast charge evaluation: Example 40, Example 44, and Reference Example 1]
The battery cells of Example 40, Example 44, and Reference Example 1 were evaluated for quick charging according to the method described above. Table 7 shows the values of the charge capacity at 2C.

According to Table 7, a separator formed by using a composition for forming a porous film containing a hydrophobically modified insulating fiber (A), a binder resin (B), and a solvent (S) is provided. It can be seen that the quick charging characteristics of the battery cell are as good as those of the battery cell provided with the commercially available separator, regardless of the dispersion time of the insulating fiber (A).

[Durability evaluation: Example 37, Example 40, Example 44, and Reference Example 1]
The battery cells of Example 37, Example 40, Example 44, and Reference Example 1 were charged and discharged for 300 cycles, and their durability was evaluated based on the discharge capacity retention rate (%).
As a result of the above test, in the battery cell of Reference Example 1, the discharge capacity retention rate (%) rapidly decreased to 80% or less after 150 cycles, and the discharge capacity retention rate decreased to about 20% in 200 cycles.
On the other hand, in the battery cells of Examples 37, 40, and 44, the discharge capacity retention rate of nearly 100% was maintained even in 150 cycles, and the discharge capacity retention rate of more than 80% was maintained even in 200 cycles.
That is, the durability of the battery cell including the separator formed by using the composition for forming a porous film containing the hydrophobically modified insulating fiber (A), the binder resin (B), and the solvent (S). The property is significantly superior to the durability of a battery cell provided with a commercially available separator.

Claims (13)

It contains a hydrophobically modified insulating fiber (A), a binder resin (B), and a solvent (S).
A composition for forming a porous film, wherein the hydrophobization modification is a surface modification with a compound having at least one selected from the group consisting of a cardo structure and a bisphenol structure. The composition according to claim 1, wherein the insulating fiber (A) is cellulose. The solvent (S) is glycol, glycol alkyl ether, glycol alkyl ether acetate, chain or cyclic ester, chain or cyclic ketone, solvent having a carbon-carbon double bond, ether other than the above, carbon atom other than the above. The composition according to claim 1 or 2 , which contains at least one selected from the group consisting of alcohols of number 7 or less, amine-based solvents, and aprotonic polar solvents other than the above. The composition according to any one of claims 1 to 3 , wherein the water content is 50% by mass or less. The composition according to any one of claims 1 to 4 , wherein the hydrophobically modified insulating fiber (A) has a volume average particle size of 10 μm or more. The composition according to any one of claims 1 to 5 , which is a coating type. The composition according to any one of claims 1 to 6 , wherein the porous membrane is a separator. A separator formed from the composition according to any one of claims 1 to 7. The separator according to claim 8 , wherein the contact angle with the electrolytic solution is 25 ° or less when measured under the condition of 2 seconds after the droplet of the electrolytic solution containing dimethyl carbonate is dropped on the surface. An electrochemical device comprising the separator according to claim 8 or 9. The element according to claim 10 , which is a secondary battery. The element according to claim 10 or 11 , which is a lithium battery or a lithium ion battery. A method for producing an electrode composite, comprising a coating step of applying the composition according to any one of claims 1 to 7 onto an electrode.