KR20190093507A - Secondary battery and porous separator for secondary battery - Google Patents

Abstract

The present invention is to provide a secondary battery having excellent battery performance (for example, a high discharge capacity maintenance rate, a low impedance, and excellent rapid charge performance in repeated charging and discharging), and a porous separator for a secondary battery used therefor. The present invention relates to a secondary battery comprising a porous separator, wherein the porous separator comprises a porous polyimide film including polyimide comprising a unit represented by chemical formula 1-1 and a unit represented by chemical formula 1-2. In the chemical formula, A^11 and A^12 each independently represent a tetravalent aromatic group derived from acid anhydride including aromatic tetracarboxylic anhydride, B^11 and B^12 each independently represent a divalent diamine moiety derived from aromatic diamine, and at least one selected from the group consisting of A^12 and B^12 includes a divalent spacer group in the structure thereof.

Description

Secondary battery and porous separator for secondary battery {SECONDARY BATTERY AND POROUS SEPARATOR FOR SECONDARY BATTERY}

The present invention relates to a secondary battery excellent in battery performance, and a porous separator for secondary batteries.

There is a demand for an excellent secondary battery having characteristics such as high efficiency, high output, high energy density, and light weight that can be applied to an electronic device or an electric vehicle.

As a secondary battery, a lithium ion secondary battery or the like is known. The positive electrode and the negative electrode of the lithium ion secondary battery are separated by a separator made of a porous polymer membrane, and have a structure of preventing electrical direct contact. Therefore, the separator for secondary batteries requires various characteristics such as film thickness (thinness), mechanical strength, ion conductivity (when electrolyte solution is contained), electrical insulation property, electrolyte resistance, liquid retention property against electrolyte solution, and wettability.

In the separator for secondary batteries having such properties, a polyolefin-based porous film such as polyethylene or polypropylene is generally used.

These porous films have random pores, have a porosity of about 35% to 40%, and are widely used as separators for lithium ion secondary batteries using carbon as a negative electrode. However, there was room for improvement in performance as a separator for secondary batteries.

On the other hand, polyimide resin has the characteristics excellent in mechanical strength, chemical stability, and heat resistance. The porous polyimide film which consists of polyimide resin which has these outstanding characteristics is attracting attention in various uses.

For example, Patent Literature 1 discloses a porous polyimide film containing a polyimide resin and a non-crosslinked resin other than a polyimide resin, in which generation of cracks is suppressed, as compared with a porous polyimide film containing only a polyimide resin. It is.

However, the porous polyimide film described in Citation Document 1 has room for improvement in performance as a separator for secondary batteries. In addition, the porous polyimide film described in Citation Document 1 is vulnerable to the force at the time of manufacture, can be produced only in single sheets, and the productivity is low.

Japanese Unexamined Patent Publication No. 2016-183273

The present invention has been made in view of the above-mentioned problems of the prior art, and is a secondary battery excellent in battery performance (for example, high discharge capacity retention rate in repeated charging and discharging, low impedance, and high fast charging performance), and It aims at providing the porous separator for secondary batteries used for it.

MEANS TO SOLVE THE PROBLEM The present inventors have shown that the porous polyimide film containing the polyimide containing the structural unit of a specific structure is excellent in wettability with respect to the electrolyte solution in a secondary battery, and battery performance (for example, high discharge capacity retention rate in repeated charge / discharge, , Low impedance, high rapid charging performance), and excellent porosity for tensile strength, winding, and the like during film production, even though it was porous, it was found to be excellent in productivity, and thus the present invention was completed. That is, this invention is as follows.

1st aspect of this invention is a secondary battery provided with a porous separator, The said porous separator is a polyimide containing the structural unit represented by following formula (1-1) and the structural unit represented by following formula (1-2). A secondary battery comprising a porous polyimide film containing a.

[Formula 1]

(In the above formula, A ¹¹ and A ¹² each independently represent a tetravalent aromatic group derived from an acid anhydride containing an aromatic tetracarboxylic anhydride, and B ¹¹ and B ¹² are each independently derived from aromatic diamine. Represents a divalent diamine residue and at least one selected from the group consisting of A ¹² and B ¹² contains a divalent spacer group in its structure)

A 2nd aspect of this invention is a secondary battery provided with a porous separator, Comprising: The polyimide which the said porous separator contains the structural unit represented by following formula (2-1) and the structural unit represented by following formula (2-2). A secondary battery comprising a porous polyimide film containing a.

[Formula 2]

(In the above formula, A ²¹ and A ²² each independently represent a tetravalent aromatic group derived from an acid anhydride containing an aromatic tetracarboxylic anhydride, and B ²¹ and B ²² are each independently derived from aromatic diamines. It represents a divalent diamine residue, the a ²² and B ²² satisfies at least one condition selected from the group consisting of (I) and (II),.

The electron affinity of the aromatic tetracarboxylic anhydride to induce (I) A ²² is 2.6 eV or less.

(II) The aromatic diamine inducing B ²² is an aromatic diamine different from the aromatic diamine inducing B ²¹ , and the solubility in water at 40 ° C. is 0.1 g / L or more.)

3rd aspect of this invention is a polyimide containing the structural unit represented by the said Formula (1-1), and the structural unit represented by the said Formula (1-2), or the structural unit represented by the said Formula (2-1), and the said It is a porous separator for secondary batteries containing the porous polyimide film containing the polyimide containing the structural unit represented by Formula (2-2).

The secondary battery of the present invention is excellent in battery performance (for example, high discharge capacity retention rate in repeated charging and discharging, low impedance and high fast charging performance).

The porous separator for secondary batteries of the present invention is a secondary battery having excellent wettability to the electrolyte solution in the secondary battery, strength (for example, tensile strength and bending strength) and productivity in the secondary battery, and excellent battery performance. Can provide.

EMBODIMENT OF THE INVENTION Hereinafter, although embodiment of this invention is described in detail, this invention is not limited to the following embodiment at all, It can implement by changing suitably within the range of the objective of this invention.

≪Secondary battery≫

The secondary battery which concerns on a 1st and 2nd aspect is provided with the porous separator.

The porous separator can pass liquid and / or ionic molecules or maintain an electrolyte solution.

The configuration of the secondary batteries according to the first and second aspects is not particularly limited. As for the structure of the secondary battery which concerns on a 1st and 2nd aspect, the structure in which electrolyte solution and a porous separator are arrange | positioned between a negative electrode and a positive electrode is preferable, The battery element laminated | stacked so that electrolyte solution and a porous separator are arrange | positioned between a negative electrode and a positive electrode. The structure in which the electrolyte solution is impregnated and this is enclosed in the exterior is more preferable.

The type of secondary batteries according to the first and second aspects is not particularly limited either. Examples of the secondary battery according to the first and second aspects include a lithium ion secondary battery, a nickel cadmium secondary battery, a nickel hydride battery, a metal secondary battery, and the like, and a lithium ion secondary battery or a metal secondary battery from the viewpoint of battery performance. Is preferably.

In the case of a metal secondary battery, it may be a metal air battery using oxygen in the atmosphere as the positive electrode active material.

As a negative electrode of a secondary battery, the structure in which the negative electrode mixture which consists of a negative electrode active material, a conductive support agent, and a binder was shape | molded on the electrical power collector can be taken. For example, as a negative electrode active material, a cadmium hydroxide can be used in the case of a nickel cadmium battery, and a hydrogen storage alloy can be used in the case of a nickel hydrogen battery. In the case of a lithium ion secondary battery, a material capable of electrochemically doping lithium can be employed. As such a negative electrode active material, a carbon material, silicon, aluminum, tin, a wood alloy, etc. are mentioned, for example.

Examples of the conductive aid constituting the negative electrode include carbon materials such as acetylene black and Ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride, carboxymethyl cellulose, and the like. Copper foil, stainless steel foil, nickel foil etc. can be used for an electrical power collector.

As a metal negative electrode in the case of a metal secondary battery, the alloy of lithium (Li), magnesium (Mg), sodium (Na), and these and other metal can be used.

For example, when the secondary battery is a lithium metal secondary battery, in addition to lithium (metal lithium), the negative electrode includes lithium-aluminum, lithium-lead, lithium-bismuth, lithium-indium, lithium-gallium, lithium-indium-gallium, or the like. You may use the negative electrode comprised from the lithium alloy of. Specifically, these lithium or lithium alloy can be crimped to a current collector to form a negative electrode. In the case of a lithium alloy, it is preferable that content of lithium is about 90 mass% or more.

The thickness of a negative electrode is not specifically limited, It can set and use in a well-known range. In the secondary batteries according to the first and second aspects, when the porous separator including the porous polyimide film containing the polyimide containing the predetermined structural unit is used, the surface of the negative electrode is stabilized, so that the thickness of the negative electrode is reduced. It is also possible to increase the capacity utilization rate of the negative electrode metal with respect to the positive electrode. For example, what is necessary is just to be 15 micrometers or more and 700 micrometers or less as thickness except an electrical power collector. Preferably it is 600 micrometers or less, More preferably, it is 100 micrometers or less.

Moreover, the positive electrode can be made into the structure which the positive electrode mixture which consists of a positive electrode active material, a conductive support agent, and a binder was shape | molded on the electrical power collector. For example, as the positive electrode active material, nickel hydroxide may be used in the case of nickel cadmium batteries, and nickel hydroxide or nickel oxyhydroxide may be used in the case of nickel hydrogen batteries.

Moreover, the positive electrode which uses manganese dioxide as an active material can also be used. Specifically, the positive electrode etc. of the structure which formed the positive electrode mixture layer containing manganese dioxide which is an active material, a conductive support agent, and a binder on the single side | surface or both surfaces of a positive electrode electrical power collector can be used.

On the other hand, in the case of a lithium ion secondary battery or a lithium metal secondary battery, lithium oxide, lithium phosphate, lithium sulfide, a lithium containing transition metal oxide etc. are mentioned as a positive electrode active material. Specifically, LiCoO ₂ , LiNiO ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCo _0.5 Ni _0.5 O ₂ , LiAl _0.25 Ni _0.75 O _2, etc. may be mentioned.

Conductive aids include carbon materials such as carbon black, flaky graphite, acetylene black, Ketjen black, fibrous carbon and the like. Examples of the binder include organic polymers, and examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, styrene butadiene rubber, and the like.

Aluminum foil, stainless steel foil, titanium foil, etc. can be used for an electrical power collector.

As the electrolyte, for example, in the case of a nickel cadmium battery or a nickel hydrogen battery, an aqueous potassium hydroxide solution is used. The electrolyte solution of a lithium ion secondary battery becomes the structure which melt | dissolved lithium salt in the non-aqueous solvent. Examples of lithium salts include LiPF ₆ , LiBF ₄ , LiClO ₄ , and the like. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone and vinylene carbonate. These may be used alone or in combination.

In the case where the secondary battery according to the first and second aspects is a metal air battery, the positive electrode used preferably comprises a catalyst layer and a current collector which serve to absorb oxygen from air and convert it into hydroxide ions. The catalyst layer contains a current collector therein. The current collector may be in the center of the catalyst layer or may exist in a layered manner on one side of the catalyst layer.

As a current collector of a positive electrode, materials of the form conventionally used as an electrical power collector, such as porous structures, such as carbon paper and a metal mesh, a mesh-like structure, a fiber, a nonwoven fabric, can be used, without particular limitation. For example, a metal mesh formed of SUS, nickel, aluminum, iron, titanium, or the like can be used. As another positive electrode current collector, a metal foil having an oxygen supply hole can also be used.

The catalyst layer contains an air cathode catalyst material. As the cathode catalyst material, any of various catalysts can be used as long as it is a substance that receives electrons generated from the anode and reduces oxygen. For example, perovskite-type complex oxides such as lanthanum manganite represented by La _(1-x) A _x MnO ₃ (0.05 <x <0.95; A = Ca, Sr, Ba), Mn ₂ O ₃ , Mn ₃ Manganese lower oxides such as O ₄ , or carbon-based materials such as activated carbon, carbon, and carbon nanotubes have both oxygen reducing ability and conductivity and are preferable.

Examples of the packaging material include metal cans and aluminum laminate packs.

The shape of the battery is rectangular, cylindrical, coin-shaped, and the like. The secondary battery according to the first and second aspects can be preferably applied to the shape of any battery.

Moreover, since the secondary battery which concerns on a 1st and 2nd aspect is excellent in the intensity | strength (for example, tensile strength and bending strength) of a separator, it can apply to both a laminated type and a winding type.

In the case where the secondary batteries according to the first and second aspects are metal air batteries, the battery case may be an open air type or a sealed type. The battery case of the open air type has a structure in which at least the air electrode can sufficiently contact the air. On the other hand, in the case of a closed type, it is preferable to form an introduction pipe and an exhaust pipe of oxygen (air) which are positive electrode active materials.

The secondary battery which concerns on a 1st aspect is a porous polyimide film containing the polyimide containing the structural unit represented by following formula (1-1) and the structural unit represented by following formula (1-1) as said porous separator. Include.

[Formula 3]

(In the above formula, A ¹¹ and A ¹² each independently represent a tetravalent aromatic group derived from an acid anhydride containing an aromatic tetracarboxylic anhydride, and B ¹¹ and B ¹² are each independently derived from aromatic diamine. Represents a divalent diamine residue and at least one selected from the group consisting of A ¹² and B ¹² contains a divalent spacer group in its structure)

At least one selected from the group consisting of A ¹² and B ¹² includes a divalent spacer group in its structure, thereby providing good wettability to the electrolyte solution in the secondary battery, and good strength in the secondary battery (eg, tensile strength and bending). Strength) and good battery performance, and good productivity (productivity of secondary batteries, separators, and porous polyimide films) can be achieved. By the said good wettability, favorable battery performance (for example, high discharge capacity retention rate in repeated charge / discharge, low impedance, and quick charge performance are high) can be achieved.

In view of more reliably achieving the wettability, the strength, the battery performance, and the productivity, it is preferable that A ¹² includes a divalent spacer group in its structure.

The aromatic tetracarboxylic dianhydride which induces a tetravalent aromatic group related to A ¹¹ and A ¹² has conventionally been used as long as at least one selected from the group consisting of A ¹² and B ¹² includes a divalent spacer group in its structure. It can select suitably from the aromatic tetracarboxylic dianhydride currently used as a synthesis raw material of polyamic acid.

Preferred specific examples of the aromatic tetracarboxylic dianhydride include 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, 9,9-bis fluorene anhydride, 3,3 ', 4,4'-diphenylsulfontetracarboxylic dianhydride, 2,2-bis (3,4- Dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3 , 3-hexafluoropropane 2 anhydride, 2,2-bis (2,3-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane 2 anhydride, 3,3 ', 4 , 4'-benzophenonetetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, 2,2 ', 3,3' -Benzophenonetetracarboxylic dianhydride, 4,4- (p-phenylenedioxy) diphthalic acid dianhydride, 4,4- (m-phenylenedioxy) diphthalic acid dianhydride, pyromellitic Acid dianhydride (PMDA), 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3', 4'-biphenyltetracarboxylic dianhydride, 2, 2,6,6-biphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3 , 6,7-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3, 6,7-anthracene tetracarboxylic dianhydride, 1,2,7,8-phenanthrene tetracarboxylic dianhydride, etc. are mentioned. These tetracarboxylic dianhydrides can also be used individually or in mixture of 2 or more types.

Moreover, as long as at least 1 selected from the group which consists of A <^12> and B <^12> contains the divalent spacer group in the structure, the aromatic diamine which induces the divalent diamine residue which concerns on B <^11> and B <^12> is polyamide conventionally It can select suitably from the aromatic diamine used as a raw material of an acid synthesis.

As an aromatic diamine, the diamino compound which two amino groups couple | bonded with the cyclic ring which the benzene ring or 2 or more and 10 or less benzene rings couple | bonded and / or condensed is mentioned. The benzene ring or polycyclic ring in the aromatic diamine may have a substituent. Specifically, phenylenediamine and derivatives thereof, diaminobiphenyl compounds and derivatives thereof, diaminodiphenyl compounds and derivatives thereof, diaminotriphenyl compounds and derivatives thereof, diaminonaphthalene and derivatives thereof, aminophenylaminoindan and Derivatives thereof, diaminotetraphenyl compounds and derivatives thereof, diaminohexaphenyl compounds and derivatives thereof, and cardo-type fluorenediamine derivatives.

Phenylenediamine is m-phenylenediamine (MDA), p-phenylenediamine (PDA), and the like. As a phenylenediamine derivative, it is the diamine which alkyl groups, such as a methyl group and an ethyl group, couple | bonded. The phenylenediamine derivative is, for example, 2,4-diaminotoluene, 2,4-triphenylenediamine, or the like.

The diaminobiphenyl compound is a compound in which two aminophenyl groups are bonded to each other. The diaminobiphenyl compound is, for example, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis (trifluoromethyl) biphenyl, and the like.

The diaminodiphenyl compound is a compound in which two aminophenyl groups are bonded via a divalent linking group. The divalent linking group is an oxy group (-O-), a sulfonyl group, a thio group (-S-), an alkylene group or a derivative group thereof, an imino group, an azo group (-N = N-), a phosphine oxide group (-P ( = O) R-, R: hydrogen atom couple | bonded with the phosphorus atom, or monovalent organic group), an amide group (-CONH-), a ureylene group (-NH-CO-NH-), etc. The alkylene group is a group having 1 to 6 carbon atoms, and the derivative group is a group in which at least one hydrogen atom of the alkylene group is substituted with a halogen atom or the like.

Examples of the diaminodiphenyl compound include 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether and 3,3'-diaminodi Phenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4 '-Diaminodiphenylmethane, 4,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylketone, 3,4'-diaminodiphenylketone, 2,2-bis (p- Aminophenyl) propane, 2,2'-bis (p-aminophenyl) hexafluoropropane, 4-methyl-2,4-bis (p-aminophenyl) -1-pentene, 4-methyl-2,4- Bis (p-aminophenyl) -2-pentene, iminodioline, 4-methyl-2,4-bis (p-aminophenyl) pentane, bis (p-aminophenyl) phosphineoxide, 4,4'-dia Minoazobenzene, 4,4'-diaminodiphenylurea, 4,4'-diaminodiphenylamide, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy ) Benzene, 1,3-bis (3-aminophenoxy) Benzene, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2, 2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, etc. are mentioned.

The diaminotriphenyl compound is a compound in which two aminophenyl groups and one phenylene group are bonded via a divalent linking group. The linking group is the same as the diaminodiphenyl compound. Examples of the diaminotriphenyl compound include 1,3-bis (m-aminophenoxy) benzene, 1,3-bis (p-aminophenoxy) benzene, 1,4-bis (p-aminophenoxy) benzene Etc. can be mentioned.

Examples of diaminonaphthalene include 1,5-diaminonaphthalene and 2,6-diaminonaphthalene.

Examples of aminophenylaminoindans include 5-amino-1- (p-aminophenyl) -1,3,3-trimethylindane and 6-amino-1- (p-aminophenyl) -1,3,3-trimethyl Indane may be mentioned.

Examples of the diaminotetraphenyl compound include 4,4'-bis (p-aminophenoxy) biphenyl, 2,2'-bis [p- (p'-aminophenoxy) phenyl] propane, 2,2 ' -Bis [p- (p'-aminophenoxy) biphenyl] propane, 2,2'-bis [p- (m-aminophenoxy) phenyl] benzophenone, etc. are mentioned.

As an example of a cardo-type fluorenediamine derivative, 9,9-bis (4-aminophenyl) fluorene etc. are mentioned.

The aromatic diamine may be a compound in which a hydrogen atom bonded to a position other than the amino groups in these diamines is substituted with at least one substituent selected from the group of a halogen atom, a methyl group, a methoxy group, a cyano group, and a phenyl group.

Examples of the divalent spacer group include an oxy group (-O-), a thio group (-S-), a carbonyl group, an alkylene group, an alkylene fluoride group, a sulfonyl group, and a fluorenylene group (fluorene-9,9-diyl group ( And two groups formed by removing two hydrogen atoms bonded to a carbon atom at the 9 position of fluorene.

As said alkylene group, it is preferable that it is a C1-C5 linear or branched alkylene group. As a specific example of a C1-C5 linear or branched alkylene group, a methylene group, an ethylene group, a propylene group, a dimethyl methylene group, etc. are mentioned.

As said alkyl fluoride group, it is preferable that it is a C1-C5 linear or branched alkylene fluoride group. As a specific example of a C1-C5 linear or branched alkylene fluoride group, a difluoromethylene group, tetrafluoroethylene group, bis (trifluoromethyl) methylene group, etc. are mentioned.

When A <^12> contains a bivalent spacer group in the structure, A <^12> can be represented by following formula (1-2-1).

In the case, including the B ^12, a divalent spacer in the structure, B ¹² can be represented by the following formula (1-2-2).

[Formula 4]

(In the formula, A ¹²¹ and A ¹²² each independently represent a trivalent aromatic group, B ¹²¹ and B ¹²² each independently represent a divalent aromatic group, and X ¹ and X ² each independently represent a divalent spacer. Group, * represents a bonding hand)

As a trivalent aromatic group, a benzene triyl group, a naphthalene triyl group, etc. are mentioned. Especially, benzene triyl group is preferable. As the benzenetriyl group, a benzene-1,2,4-triyl group is preferable.

As a bivalent aromatic group, a phenylene group, a naphthylene group, etc. are mentioned. Especially, a phenylene group is preferable. As a phenylene group, p-phenylene group or m-phenylene group is preferable and p-phenylene group is more preferable.

Specific examples of the divalent spacer group are as described above.

When A <^12> contains a bivalent spacer group in the structure, As a specific example of the aromatic tetracarboxylic anhydride which induces the tetravalent aromatic group which concerns on A <^12> , 1, 1-bis (2, 3- dicarboxy phenyl) Ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 9,9-bis fluoric anhydride (BPAF), 3,3 ' , 4,4'-diphenylsulfontetracarboxylic dianhydride (DSDA), 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl Propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA), 2,2-bis (2, 3-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride (BTDA), bis ( 3,4-dicarboxyphenyl) ether dianhydride (ODPA), bis (2,3-dicarboxyphenyl) ether dianhydride, 2,2 ', 3,3'-benzophenonete Tracarboxylic acid dianhydride, 4, 4- (p-phenylenedioxy) diphthalic acid dianhydride, 4, 4- (m-phenylenedioxy) diphthalic acid dianhydride, etc. are mentioned.

When the B ^12, comprises a divalent spacer in the structure, as a specific example of the aromatic diamine, for example, to drive a bivalent diamine residue involved in B ¹² is, 3,3'-diaminodiphenyl ether, 3,4'- Diaminodiphenylether, 4,4'-diaminodiphenylether (ODA), 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodi Phenylsulfone (DDS), 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane (DDM), 4,4'-diaminodi Phenylsulfide, 3,3'-diaminodiphenylketone, 3,4'-diaminodiphenylketone, 2,2-bis (p-aminophenyl) propane, 2,2'-bis (p-aminophenyl ) Hexafluoropropane, 4-methyl-2,4-bis (p-aminophenyl) -1-pentene, 4-methyl-2,4-bis (p-aminophenyl) -2-pentene, iminodioline, 4-methyl-2,4-bis (p-aminophenyl) pentane, bis (p-aminophenyl) phosphine oxide, 4,4'-diaminoazobenzene, 4,4'-diaminodiphenylurea, 4,4'-diaminodiphenylamide, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy ) Benzene, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2 , 2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, and the like.

As content of the structural unit represented by the said Formula (1-1) in the said polyimide, it is 40 mol% from the wettability with respect to the electrolyte solution in a secondary battery, the viewpoint of the strength and battery performance in a secondary battery, and productivity. It is preferable that it is the above, It is more preferable that it is 50 mol% or more, It is further more preferable that it is 60 mol% or more.

There is no restriction | limiting in particular as an upper limit of content of the structural unit represented by said formula (1-1) unless the effect of this invention is impaired. 99 mol% or less may be sufficient as content of the structural unit represented by Formula (1-1), 95 mol% or less may be sufficient, and typically 90 mol% or less may be sufficient as it.

As content of the structural unit represented by the said Formula (1-2) in the said polyimide, it is 60 mol% from the wettability with respect to the electrolyte solution in a secondary battery, the viewpoint of the strength and battery performance in a secondary battery, and productivity. It is preferable that it is the following, It is more preferable that it is 50 mol% or less, It is further more preferable that it is 40 mol% or less.

There is no restriction | limiting in particular as a lower limit of content of the structural unit represented by said formula (1-2) unless the effect of this invention is impaired. 1 mol% or more may be sufficient as content of the structural unit represented by Formula (1-2), 5 mol% or more may be sufficient, and typically 10 mol% or more may be sufficient as it.

The secondary battery which concerns on a 2nd aspect is a porous polyimide film containing the polyimide containing the structural unit represented by following formula (2-1) and the structural unit represented by following formula (2-1) as said porous separator. Include.

[Formula 5]

(In the above formula, A ²¹ and A ²² each independently represent a tetravalent aromatic group derived from an acid anhydride containing an aromatic tetracarboxylic anhydride, and B ²¹ and B ²² are each independently derived from aromatic diamines. It represents a divalent diamine residue, the a ²² and B ²² satisfies at least one condition selected from the group consisting of (I) and (II),.

The electron affinity of the aromatic tetracarboxylic anhydride to induce (I) A ²² is 2.6 eV or less.

(II) The aromatic diamine inducing B ²² is an aromatic diamine different from the aromatic diamine inducing B ²¹ , and the solubility in water at 40 ° C. is 0.1 g / L or more.)

When A ²² and B ²² satisfy at least one condition selected from the group consisting of the above (I) and (II), good wettability with respect to the electrolyte in the secondary battery, good strength and good battery performance in the secondary battery, And good productivity can be achieved. By the good wettability, good battery performance can be achieved.

From the viewpoint of more reliably achieving the wettability, the strength, the battery performance, and the productivity, it is preferable that A ²² satisfies the condition (I).

The aromatic tetracarboxylic dianhydride which induces the tetravalent aromatic group related to A ²¹ and A ²² is so long as A ²² and B ²² satisfy at least one condition selected from the group consisting of the above (I) and (II). It can select suitably from aromatic tetracarboxylic dianhydride conventionally used as a synthesis raw material of polyamic acid.

As an example of aromatic tetracarboxylic dianhydride which induces the tetravalent aromatic group which concerns on A <^21> and A <^22> , As an example of aromatic tetracarboxylic dianhydride which derives the tetravalent aromatic group which concerns on A <^11> and A <^12> The compound similar to the compound mentioned above is mentioned.

Aromatic diamines which induce divalent diamine residues relating to B ¹¹ and B ¹² have conventionally been made of poly, as long as A ²² and B ²² satisfy at least one condition selected from the group consisting of the above (I) and (II). It can select suitably from the aromatic diamine used as a raw material of amic acid synthesis.

Specific examples of the aromatic diamine, for example, to drive a bivalent diamine residue related to B ¹¹ and B ¹² are, in the same compound as the above-described compound as a specific example of the aromatic diamine to derive a bivalent diamine residue related to B ¹¹ and B ¹² Can be.

For the above (I), Ea of the aromatic tetracarboxylic anhydride which induces A ²² is described in POLYIMIDES Thermally Stable Polymers (manufactured by MI Bessonov, MM KotoN, VV Kudryavtsev, LA Laius), VM Svetlichnyi, KK Kalnin 'from CONSULTANTS BUREAU. sh, VV Kudryavtsev, and MM Kotton, Dokl. Akad. Nauk., 237, 612-615 (1977) and the like.

It is preferable that the electron affinity (Ea) of the aromatic tetracarboxylic anhydride which induces A <^22> is 2.3 eV or less.

There is no restriction | limiting in particular as a lower limit of Ea. Ea may be 1.0 eV or more, and typically 1.3 eV or more may be sufficient as it.

The structure of the aromatic tetracarboxylic anhydride which guides A <^22> and its electron affinity are illustrated below. The aromatic tetracarboxylic anhydride which induces A ²² is not limited to the following compounds.

In addition, in the following example, the numerical value in brackets is electron affinity.

[Formula 6]

In the above (II), "solubility in water at 40 ° C of 0.1 g / L or more '' means a limit amount (g) in which the aromatic diamine inducing B ²² is dissolved in 1 L (liter) of 40 ° C. do. This value can be easily retrieved by SciFinder (registered trademark) known as a search service based on a database such as Chemical Abtract. Here, among the solubility under various conditions, the pH at 7 calculated by Advanced Chemistry Development (ACD / Labs) Software V11.02 (Copyright 1994-2011 ACD / Labs) can be adopted.

The solubility of the aromatic diamine to induce B ²² is preferably not less than 0.5 g / ℓ, more preferably 1.0 g / ℓ or more.

There is no restriction | limiting in particular as an upper limit of solubility. The solubility may be 500 g / L or less, and typically 400 g / L or less.

Although the structure of the aromatic diamine which guides B <^22> and its solubility to water at 40 degreeC is illustrated below, this invention is not limited to these.

In addition, in the following example, the numerical value in parentheses is solubility with respect to water of 40 degreeC.

[Formula 7]

As content of the structural unit represented by said Formula (2-1) in the said polyimide, it is 40 mol% from the wettability with respect to the electrolyte solution in a secondary battery, the viewpoint of the strength and battery performance in a secondary battery, and productivity. It is preferable that it is the above, It is more preferable that it is 50 mol% or more, It is further more preferable that it is 60 mol% or more.

There is no restriction | limiting in particular as an upper limit of content of the structural unit represented by said formula (2-1), unless the effect of this invention is impaired. 99 mol% or less may be sufficient as content of the structural unit represented by Formula (2-1), 95 mol% or less may be sufficient, and typically 90 mol% or less may be sufficient as it.

As content of the structural unit represented by the said Formula (2-2) in the said polyimide, it is 60 mol% from the wettability with respect to the electrolyte solution in a secondary battery, the viewpoint of the strength and battery performance in a secondary battery, and productivity. It is preferable that it is the following, It is more preferable that it is 50 mol% or less, It is further more preferable that it is 40 mol% or less.

There is no restriction | limiting in particular as a lower limit of content of the structural unit represented by said formula (2-2), unless the effect of this invention is impaired. Content of the structural unit represented by Formula (2-2) may be 1 mol% or more, 5 mol% or more, and typically 10 mol% or more may be sufficient.

There is no restriction | limiting in particular as mass average molecular weight (Mw) of the polyimide contained in the said porous polyimide film, unless the effect of this invention is impaired. The mass average molecular weight (Mw) of the polyimide contained in the porous polyimide film is the wettability with respect to the electrolyte solution in a secondary battery, the strength (for example, tensile strength and bending strength) in a secondary battery, a viewpoint of battery performance, and productivity It is preferable that it is 5000 or more from a viewpoint, It is more preferable that it is 8000 or more, It is still more preferable that it is 10,000 or more, It is especially preferable that it is 15,000 or more.

Moreover, when the polyimide precursor solution mentioned later contains the organic solvent, Mw of a polyimide does not have a restriction | limiting in particular, unless the effect of this invention is impaired. Mw of a polyimide may be 30,000 or more from a viewpoint of the wettability with respect to the electrolyte solution in a secondary battery, the strength of a secondary battery, a battery performance, and a viewpoint of productivity, and it is preferable that it is 50,000 or more.

There is no restriction | limiting in particular as an upper limit of Mw of a polyimide, unless the effect of this invention is impaired. 100,000 or less are preferable and, as for Mw of a polyimide, 80,000 or less are more preferable.

In this specification, a mass mean molecular weight (Mw) is a measured value by polystyrene conversion of gel permeation chromatography (GPC).

The porous polyimide film has a plurality of openings irregularly formed on the surface of the film, and a plurality of irregularly formed on the back surface of the film, from the viewpoints of wettability to the electrolyte solution in the secondary battery, viewpoints of strength and battery performance in the secondary battery, and productivity. It is preferable that it is porous having an opening of.

It is preferable that the said porous polyimide film is porous provided with the communication hole which communicates a film surface and a film back surface from a wettability with respect to the electrolyte solution in a secondary battery, a viewpoint of the strength and battery performance in a secondary battery, and productivity. . Specifically, it is preferable that at least a part of the plurality of openings formed on the film surface and at least part of the plurality of openings formed on the back surface of the film communicate with each other inside the polyimide film.

The porous polyimide film is used as a porous separator in a secondary battery.

The porous polyimide film preferably has a porosity of 50% or more, more preferably a porosity of 55% or more, even more preferably a porosity of 60% or more, and a porosity of 65%, from the viewpoint of the communicability as the porous separator for secondary batteries. It is especially preferable that it is above.

There is no restriction | limiting in particular as an upper limit of porosity. It is preferable that it is 90% or less, and, as for a porosity, from a viewpoint of the intensity | strength of a porous polyimide film, it is more preferable that it is 80% or less.

Porosity shows the ratio of the pore per unit volume of a porous polyimide film, for example. The porosity can be calculated by, for example, the following formula (A).

Porosity (%) = {volume of test piece (cm 3)-[weight of test piece (g) / specific gravity of polyimide (g / cm 3)]} / volume of test piece (cm 3) × 100... (A)

As described later, the desired porosity can be achieved by appropriately adjusting the particle diameter and content of the fine particles used when producing the porous polyimide film.

There is no restriction | limiting in particular as thickness of the porous polyimide film contained in a porous separator. The thickness is preferably 1 µm or more and 500 µm or less, more preferably 3 µm or more and 200 µm or less, still more preferably 5 µm or more and 100 µm or less, particularly preferably 7 µm or more and 80 µm or less.

There is no restriction | limiting in particular as the length and width of the film of the porous polyimide film contained in a porous separator, It can set suitably.

In the secondary batteries according to the first and second aspects, the porous polyimide film used as the porous separator is characterized in terms of strength and productivity in the secondary battery (for example, in a roll-to-roll manufacturing method). From the viewpoint of application preferably), the tensile strength specified by ASTM standard D638 is preferably 45 MPa or more, more preferably 70 MPa or more, still more preferably 80 MPa or more, particularly preferably 90 MPa or more, and 100 MPa It is most preferable that it is above.

There is no restriction | limiting in particular as an upper limit of the said tensile strength unless the effect of this invention is impaired. The tensile strength may be 300 MPa or less, and typically 200 MPa or less.

In the secondary batteries according to the first and second aspects, the porous polyimide film used as the porous separator is, from the viewpoint of strength and productivity in the secondary battery (for example, from the viewpoint of being preferably applied to the roll-to-roll manufacturing method). It is preferable that the bending strength prescribed | regulated by ASTM specification D790 is 60 Mpa or more, It is more preferable that it is 70 Mpa or more, It is more preferable that it is 80 Mpa or more, It is especially preferable that it is 90 Mpa or more, It is especially preferable that it is 100 Mpa or more, 110 Most preferably, it is MPa or more.

There is no restriction | limiting in particular as an upper limit of the said bending strength, unless the effect of this invention is impaired. The bending strength may be 400 MPa or less, and typically 300 MPa or less.

This invention is also invention regarding the porous separator for secondary batteries.

The porous separator for secondary batteries which concerns on a 3rd aspect is a polyimide containing the structural unit represented by Formula (1-1) and the structural unit represented by Formula (1-2), or a structural unit represented by Formula (2-1), and a formula The porous polyimide film containing the polyimide containing the structural unit represented by (2-2) is included.

<Method for producing the porous polyimide film>

Although there is no restriction | limiting in particular as a manufacturing method of the said porous polyimide film,

After applying the composition containing polyamic acid which is a polyimide precursor, and microparticles | fine-particles (henceforth simply a "polyimide precursor solution") to a base material, and forming a coating film, the said coating film is dried and the said polyimide precursor and microparticles | fine-particles are A film forming step of forming a film comprising, and

A firing step of firing the coating,

The firing process also serves as a fine particle removing step of removing the fine particles, or further includes the fine particle removing step,

It is productive to manufacture by the manufacturing method including the peeling process which peels the said film or manufactured porous polyimide film from the said base material before the said baking process after the said film formation process, after the said baking process, or after the said microparticle removal process. It is preferable at the point of view.

It is preferable to manufacture a porous polyimide film by roll-to-roll from a viewpoint of productivity.

(Film forming step)

Polyamic acid

The said polyimide precursor is a polyamic acid containing the structural unit represented by Formula (3-1), and the structural unit represented by Formula (3-2), or the structural unit represented by Formula (4-1), and Formula (4-2) It is preferable that it is a polyamic acid containing the structural unit represented by).

[Formula 8]

(In the above formula, A ¹¹ , A ¹² , B ^11, and B ¹² have the same meanings as their abbreviations in the formulas (1-1) and (1-2), and in the group consisting of A ¹² and B ¹² ) At least one selected comprises a divalent spacer group in its structure)

[Formula 9]

(In the above formula, A ²¹ , A ²² , B ^21, and B ²² have the same meanings as their abbreviations in the formulas (2-1) and (2-2), and A ²² and B ²² represent the above ( Satisfies at least one condition selected from the group consisting of I) and (II))

Aromatic tetracarboxylic dianhydride can be suitably selected from the aromatic tetracarboxylic dianhydride conventionally used as a synthesis raw material of polyamic acid. You may use aromatic tetracarboxylic dianhydride in combination of 2 or more type.

As a specific example of aromatic tetracarboxylic dianhydride, the compound similar to the compound mentioned above is mentioned as an example of aromatic tetracarboxylic dianhydride which induces the tetravalent aromatic group which concerns on A <^11> and A <^12> .

Aromatic diamine can be suitably selected from the aromatic diamine conventionally used as a synthetic raw material of polyamic acid. You may use aromatic diamine in combination of 2 or more type.

Specific examples of the aromatic diamine, as a specific example of the aromatic diamine, for example, to drive a bivalent diamine residue related to B ¹¹ and B ¹² may be mentioned the same compounds as the aforementioned compound.

There is no restriction | limiting in particular in the means for manufacturing the polyamic acid used by this invention, For example, well-known methods, such as the method of making aromatic tetracarboxylic dianhydride and aromatic diamine react in an organic solvent, can be used.

Reaction of aromatic tetracarboxylic dianhydride and aromatic diamine is normally performed in the organic solvent. The organic solvent used for reaction of aromatic tetracarboxylic dianhydride and aromatic diamine can dissolve aromatic tetracarboxylic dianhydride and aromatic diamine, and is organic which does not react with aromatic tetracarboxylic dianhydride and aromatic diamine. It will not specifically limit, if it is a solvent. An organic solvent can be used individually or in mixture of 2 or more types.

Examples of the organic solvent used for the reaction of the aromatic tetracarboxylic dianhydride and the aromatic diamine include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, Nitrogen-containing polar solvents such as N-dimethylformamide, N, N-diethylformamide, N-methylcaprolactam, N, N, N ', N'-tetramethylurea; lactone polar solvents such as β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, and ε-caprolactone; Dimethyl sulfoxide; Acetonitrile; Fatty acid esters such as ethyl lactate and butyl lactate; Ethers such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane, tetrahydrofuran, methyl cellosolve acetate, and ethyl cellosolve acetate; Phenolic solvents, such as cresols, are mentioned. These organic solvents can be used individually or in mixture of 2 or more types. Especially, the combination of the said nitrogen-containing polar solvent and a lactone polar solvent is preferable. There is no restriction | limiting in particular in the usage-amount of the organic solvent. As for the usage-amount of the organic solvent, the quantity whose content of the polyamic acid to produce | generate is 5 mass% or more and 50 mass% or less is preferable.

Among these organic solvents, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, Nitrogen-containing polar solvents such as N, N-diethylformamide, N-methylcaprolactam, N, N, N ', N'-tetramethylurea are preferred. Moreover, it is good also as a mixed solvent which added lactone polar solvents, such as (gamma) -butyrolactone, from a viewpoint of film-forming property, It is preferable that 1 mass% or more and 20 mass% or less are added with respect to the whole organic solvent, 5 Mass% or more and 15 mass% or less are more preferable.

Polymerization temperature is generally -10 degreeC or more and 120 degrees C or less, Preferably they are 5 degreeC or more and 30 degrees C or less. Although polymerization time changes with raw material composition to be used, it is usually 3 hours or more and 24 hours or less.

(Particulates)

As a material of the microparticles | fine-particles contained in a polyimide precursor solution, it is insoluble in the solvent contained and if it is a material which can be removed from a porous polyimide film in a subsequent microparticle removal process, it will not specifically limit, A well-known material can be employ | adopted.

When the material of the fine particles is an inorganic material, the material of the inorganic fine particles is not particularly limited as long as the inorganic fine particles can be removed by a method such as chemical treatment or heating. Examples of the material of the inorganic fine particles include metal oxides such as silica (silicon dioxide), calcium carbonate, titanium oxide, and alumina (Al ₂ O ₃ ). Preferable inorganic fine particles include silica fine particles such as calcium carbonate and colloidal silica.

When the material of the fine particles is an organic material, examples of the material of the organic fine particles include high molecular weight olefin polymers (polypropylene, polyethylene, polybutadiene, polyisoprene, polytetrafluoroethylene, etc.), aromatic vinyl polymers such as polystyrene and acrylic resins. (Acrylic acid, methyl acrylate, methyl methacrylate, isobutyl methacrylate, polymethyl methacrylate (PMMA), etc.), an epoxy resin, cellulose, polyvinyl alcohol, polyvinyl butyral, polyester, polyether and the like A polymer is mentioned. These organic polymers may be copolymers (for example, copolymers of methyl methacrylate and styrene, copolymers of acrylic acid and styrene). Moreover, you may use combining organic fine particles of different materials.

It is preferable that the ratio of the mass of microparticles | fine-particles with respect to the total mass of polyamic acid and microparticles | fine-particles in a polyimide precursor solution is 35 mass% or more, and it is more preferable that it is 40 mass% or more.

There is no restriction | limiting in particular as an upper limit of the ratio of the mass of microparticles | fine-particles. It is preferable that it is 90 mass% or less, and, as for the mass of microparticles | fine-particles, it is more preferable that it is 85 mass% or less.

The shape of the fine particles is not particularly limited, and may be spherical particles or plate-shaped particles. As microparticles | fine-particles, spherical particle is preferable and spherical particle with a high sphericity is more preferable.

The particle size (average diameter or median diameter) of the fine particles is not particularly limited. For example, 10 nm or more and 2000 nm or less are preferable, as for an average diameter or median diameter, 50 nm or more and 1500 nm or less are more preferable, and 100 nm or more and 1000 nm or less are more preferable.

It is preferable that the particle size distribution index (d25 / d75) of the said microparticles | fine-particles is 1 or more and 6 or less, It is more preferable that it is 1 or more and 5 or less, It is more preferable that it is 1 or more and 3 or less.

Here, d25 and d75 represent the particle diameter whose cumulative degree of particle size distribution is 25% and 75%, respectively, and d25 is a larger particle diameter.

As a solvent which can be contained in a polyimide precursor solution, water, the aqueous solution of an organic solvent, and an organic solvent are mentioned.

As an example of the organic solvent, the organic solvent illustrated as a solvent used for reaction of aromatic tetracarboxylic dianhydride and aromatic diamine is mentioned. The organic solvent may be used alone or in combination of two or more thereof.

As an organic solvent in the case of making it into the aqueous solution of an organic solvent, a polar solvent and a water-soluble solvent are mentioned. Specific examples of the polar solvent and the water-soluble solvent include methyl alcohol, ethyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 1-pentanol, and 2-pentanol Alcohols such as 4-methyl-2-pentanol, 1,1-dimethylethanol, 2,2-dimethyl-1-propanol and tetrahydrofurfuryl alcohol; Glycols, such as ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and diethylene glycol, etc. are mentioned. The organic solvent is preferably alcohols.

Also, when the B ²² satisfy the above (II), as a solvent that can be included in the polyimide precursor solution, the water or the aqueous solution of the organic solvent is preferred.

When using organic fine particles as microparticles | fine-particles, it is preferable that a solvent is water or the aqueous solution of the said organic solvent.

When inorganic fine particles are used as the fine particles, the organic solvent that can be included in the polyimide precursor solution is preferably an organic solvent that can dissolve polyamic acid, polyimide, and the like, and does not dissolve the inorganic fine particles.

5 mass% or more and 50 mass% or less are preferable, and, as for solid content concentration of a polyimide precursor solution, More preferably, they are 10 mass% or more and 40 mass% or less.

As said base material, films, such as PET (polyethylene terephthalate) or PEN (polyethylene naphthalate), SUS board | substrate are mentioned, for example, It is preferable that it is PET film.

After forming a coating film by apply | coating (for example, apply | coating) a polyimide precursor solution on the said substrate, and drying (prebaking) the said coating film, the method of forming a film is 0 degreeC or more and 120 degreeC under normal pressure or a vacuum. The method of drying and forming a coating film below (preferably 0 degreeC or more and 90 degrees C or less), More preferably, normal pressure 10 degreeC or more and 100 degrees C or less (more preferably 10 degreeC or more and 90 degrees C or less) is mentioned.

(Firing process)

By the baking process which calcinates the said film containing polyamic acid which is a polyimide precursor, polyamide acid can be closed-closed, polyimide can be formed, and it can be set as a polyimide film.

For example, the structural unit and formula which show the polyamic acid containing the structural unit represented by Formula (3-1) and the structural unit represented by Formula (3-2) by a baking process by Formula (1-1) ( The polyamic acid which can be ring-closed by the polyimide containing the structural unit represented by 1-2), and which contains the structural unit represented by Formula (4-1) and the structural unit represented by Formula (4-2) is represented by Formula (2) It can be ring-closed by the polyimide containing the structural unit represented by -1) and the structural unit represented by Formula (2-2).

It is preferable that baking temperature is 120 degreeC or more and 500 degrees C or less, and it is more preferable that it is temperature of 150 degreeC or more and 450 degrees C or less.

The firing conditions are, for example, after raising the temperature from room temperature to 420 ° C. for 3 hours, and then maintaining the temperature at 420 ° C. for 20 minutes, or increasing the temperature to 420 ° C. at 20 ° C. in steps of 20 ° C. (maintaining each step for 20 minutes), It is also possible to use a stepwise dry-thermal imidization method such as keeping at 420 ° C. for 20 minutes.

The atmosphere in the system at the time of baking may be under the same oxygen-containing atmosphere as in the atmosphere, or may be under an inert atmosphere such as under nitrogen atmosphere, under reduced pressure, or under vacuum. However, inert atmosphere is preferable in terms of polyimide membrane properties. Moreover, it is preferable that the oxygen concentration in the system at the time of baking is 5% or less, for example from a point of a polyimide membrane characteristic or a battery characteristic, and 3% or less is more preferable. Although the lower limit of oxygen concentration is so preferable that it is low, it is not specifically limited, For example, it is 0.001% or more.

(Particle Removal Process)

The manufacturing method may further comprise a particulate removal process.

Inorganic fine particles can be removed by contacting an aqueous solution of hydrofluoric acid (HF) with inorganic fine particles such as silica to dissolve the inorganic fine particles. In the case where the inorganic fine particles are calcium carbonate, an aqueous hydrochloric acid solution may be used instead of the aqueous hydrofluoric acid solution.

When microparticles | fine-particles are organic microparticles | fine-particles and non-crosslinked resin microparticles | fine-particles, a non-crosslinked resin particle can be dissolved and removed by the organic solvent in which a non-crosslinked resin particle is soluble, without melt | dissolving a polyimide film. As such an organic solvent, For example, ether, such as tetrahydrofuran; Aromatics such as toluene; Ketones such as acetone; Esters such as ethyl acetate; Can be mentioned. Among these, ethers, such as tetrahydrofuran, are preferable and it is more preferable to use tetrahydrofuran.

When the firing step also serves as the fine particle removal step, the fine particles are preferably organic fine particles.

If the organic material of the organic fine particles is a material decomposed at a lower temperature than the polyimide, only the organic fine particles can be lost without causing thermal damage to the polyimide.

For example, the resin fine particle which consists of a linear polymer and a known depolymerizable polymer is mentioned. In conventional linear polymers, the molecular chain of the polymer is randomly cleaved during thermal decomposition, and the depolymerizable polymer is a polymer in which the polymer is decomposed into monomers upon thermal decomposition. All are lost from the polyimide membrane by decomposing to low molecular weight or CO ₂ . It is preferable that the decomposition temperature of the resin fine particle used is 200 degreeC or more and 400 degrees C or less, for example.

(Peeling process)

The said manufacturing method includes the peeling process of peeling the said film or manufactured porous polyimide film from the said base material before the said baking process after the said film formation process, after the said baking process, or after the said microparticle removal process.

Moreover, in the said manufacturing method, although there is no restriction | limiting in particular as the film length of a porous polyimide film, It is preferable that it is long (for example, 1 m or more) from a viewpoint of productivity, It is more preferable that it is 5 m or more, 10 It is more preferable that it is m or more, It is especially preferable that it is 30 m or more, It is most preferable that it is 40 m or more.

Although there is no restriction | limiting in particular as an upper limit of film length, For example, it is 2000 m or less, and is typically 1000 m or less.

In the said manufacturing method, it is preferable to further include the process of winding up the manufactured porous polyimide film by the winding core of 2.5 cm (1 inch) or more and 25 cm (10 inches) or less in diameter. Thereby, the winding length per film roll becomes long, productivity improves, and transport storage cost is suppressed.

As diameter of a winding core, 5 cm (2 inches) or more and 10 cm (4 inches) or less are preferable.

Although there is no restriction | limiting in particular as a material of a winding core, Stainless steel (for example, SUS product), a polyethylene terephthalate (PET) agent, etc. are mentioned.

Example

EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, the scope of the present invention is not limited to these Examples.

Synthesis of Polyamic Acid

The aromatic tetracarboxylic anhydride shown in Table 1 and aromatic diamine are made to react, and the polyamic acid 1-3 containing the acid anhydride residue and diamine residue in the composition ratio (mol%) of following Table 1 and the comparative polyamic acid 1 and 2 was obtained.

In the following Table 1, "solubility" shows the solubility (g / L) in water of 40 degreeC.

Preparation Example 1

Using a homogenizer, 42 g of spherical silica (median average particle diameter 280 nm, particle size distribution index (d25 / d75) 1.5 or less) was uniformly dispersed in 42 g of dimethylacetamide (DMAC) to obtain 84 g of a silica dispersion.

The DMAC solution (20 mass% of concentration of polyamic acid 1) of the obtained polyamic acid 1 was prepared, 52.5 g of this solution, 84 g of the said silica dispersions, and 13.5 g of DMAC were mixed, and it was rent-a-ro (brand name, Shinki company (Manufacture) was uniformly mixed to obtain a polyimide precursor solution (composition) of Preparation Example 1 (about mass ratio, spherical silica: polyamic acid = 80: 20, volume ratio is spherical silica: polyamic acid = 73). : 27).

[Comparative Preparation Examples 1 and 2]

Instead of DMAC solution of polyamic acid 1, DMAC solution of comparative polyamic acid 1 (concentration 20 mass% of comparative polyamic acid 1), DMAC solution of comparative polyamic acid 2 (concentration 20 mass% of comparative polyamic acid 2) ) Was used in the same manner as in Preparation Example 1, except that the polyimide precursor solutions of Comparative Preparation Examples 1 and 2 were obtained.

Preparation Example 2

Polystyrene particle aqueous dispersion (40 mass%) containing the spherical particle of polystyrene (PS) (median mean particle diameter 260 nm, particle size distribution index (d25 / d75) 1.5 or less, hereinafter simply called "polystyrene particle"), and the said obtained An aqueous solution of polyamic acid 1 (concentration 15% by mass of polyamic acid 1) was mixed, and pure water was further added, and the mixture was uniformly mixed so that the solid content concentration was 23% by mass, thereby preparing the polyimide precursor solution of Preparation Example 2 (The mass ratio was polystyrene particles: polyamic acid = 60: 40, and the volume ratio was polystyrene particles: polyamic acid = 68: 32).

Preparation Example 3

Instead of the aqueous solution of the obtained polyamic acid 1 (concentration of 15% by mass of polyamic acid 1), the aqueous solution of water / IPA (isopropanol) of the obtained polyamic acid 1 (concentration of 15% by mass of polyamic acid 1, water / IPA Except using = 9/1 (mass ratio)), it carried out similarly to the preparation example 2, and obtained the polyimide precursor solution of the preparation example 3.

Preparation Example 4

Instead of the aqueous solution of the obtained polyamic acid 1 (concentration 15% by mass of polyamic acid 1), the water / NMP (N-methylpyrrolidone) aqueous solution of the obtained polyamic acid 1 (concentration 15 mass of Polyamic Acid 1) % And water / NMP = 9/1 (mass ratio)) except that the polyimide precursor solution of Preparation Example 4 was obtained in the same manner as in Preparation Example 2.

Preparation Example 5 and 6 and Comparative Preparation Example 3

Instead of the aqueous solution of polyamic acid 1, the aqueous solution of polyamic acid 2 (concentration 15% by mass of polyamic acid 2), the aqueous solution of polyamic acid 3 (concentration 15% by mass of polyamic acid 3), comparative poly A polyimide precursor solution of Preparation Examples 5 and 6 and a polyimide of Comparative Preparation Example 3 were prepared in the same manner as in Preparation Example 2, except that an aqueous solution of Amic Acid 2 (concentration 15 mass% of Comparative Polyamic Acid 2) was used, respectively. The mid precursor solution was obtained.

Preparation Example 7

An aqueous dispersion (21 mass%) containing the non-crosslinked styrene acrylic copolymer (henceforth simply "A / St") of 0.1 micrometer of average particle diameters,

The aqueous solution of the obtained polyamic acid 1 (concentration 21% by mass of polyamic acid 1) was uniformly mixed to obtain a polyimide precursor solution of Preparation Example 7 (about the mass ratio, A / St: polyamic acid = 50: 50 and A / St: polyamic acid = 57: 43 for the volume ratio).

Preparation Example 8

The aqueous dispersion (40 mass%) containing calcium carbonate fine particles (average particle diameter 700 nm) obtained by the manufacturing method mentioned later, and the aqueous solution of the obtained polyamic acid 1 (30 mass% of polyamic acid 1 concentration) are mixed uniformly, , The polyimide precursor solution of Preparation Example 8 was obtained (about the mass ratio, the calcium carbonate particles: polyamic acid = 73: 27, and the volume ratio was the calcium carbonate particles: polyamic acid = 40: 60).

[Dispersion liquid of calcium carbonate fine particles]

To 50 g of isopropyl alcohol, 10 g of surface unmodified calcium carbonate fine particles (bathelite type, average particle diameter: 700 nm) were added, and stirred with an stirrer for 1 hour while cooling with ice water, and isopropyl alcohol suspension of calcium carbonate fine particles. Was prepared. On the other hand, 0.2 g of adipic acid was added to 23 g of isopropyl alcohol, and stirred for 10 minutes to completely dissolve it, thereby preparing an isopropyl alcohol solution. The isopropyl alcohol suspension and the isopropyl alcohol solution were stirred at room temperature for 2 hours to obtain a slurry containing calcium carbonate fine particles and isopropyl alcohol surface-modified adipic acid. After filtering the slurry using a Kiriyama funnel (manufactured by Kiriyama Co., Ltd.) and a cellulose filter paper having a collecting particle diameter of 1 μm, the filtrate was dried at 120 ° C. for 1 hour to produce calcium carbonate fine particles whose surface was modified with adipic acid. Got it. 7.2 g of the calcium carbonate fine particles were added to 10.8 g of pure water, and homogenized using a homogenizer for 40 seconds at 20% of pulverization power, followed by 40 seconds at 30% of pulverization power to obtain a calcium carbonate fine particle dispersion.

(Film forming step and peeling step)

The final film thickness (film thickness of porous polyimide film fabric) of the obtained polyimide precursor solution (composition) of Preparation Examples 1 to 8 and Comparative Preparation Examples 1 to 3 was applied on the PET film. It coated so that it might become 25 micrometers, the coating film was formed, the PET film in which the coating film was formed was put into the baking, and it dried at 80 degreeC for 5 minutes, and formed the film.

The obtained film was peeled from the PET film.

(Sintering process of the film after peeling)

The coating film was baked at the furnace temperature of 420 degreeC for 5 minutes (However, Preparation Example 7 was 380 degreeC for 5 minutes) using the kiln, and the polyimide film was formed. In addition, the atmosphere of the kiln was nitrogen atmosphere, and the oxygen concentration in the system was about 1%.

About the film formed from the polyimide precursor solution of the preparation examples 2-6, the said baking process also serves as a microparticle removal process, and can carry out the burning of a polystyrene particle completely by the said baking, and, thereby, the preparation example 2-the film thickness of 25 micrometers 6 porous polyimide film was obtained.

(Particle Removal Process)

About the polyimide membrane formed from the polyimide precursor solution of the preparation example 1, it is immersed in 10 mass% hydrofluoric acid (HF) aqueous solution for 10 minutes, and a silica is melt | dissolved and the porous polyimide of the preparation example 1 with a film thickness of 25 micrometers. Mid film was obtained.

About the polyimide membrane formed from the polyimide precursor solution of the preparation example 7, it immersed similarly except using tetrahydrofuran (THF) instead of the 10 mass% hydrofluoric acid aqueous solution, and A / St was dissolved and prepared. 7 porous polyimide film was obtained.

About the polyimide membrane formed from the polyimide precursor solution of the preparation example 8 except having used 10 mass% hydrochloric acid instead of the 10 mass% hydrofluoric acid aqueous solution, it immersed similarly and dissolved calcium carbonate, and was prepared. A porous polyimide film was obtained.

As a result of measuring the porosity of the porous polyimide film of the obtained preparation examples 1-6, all the films existed in 60 to 70% of range. Preparation Example 7 and Preparation Example 8 were in a range of 50% or more and 60% or less.

Tensile strength and bending strength test

Tensile strength and bending strength were measured based on the following standard method about the test piece of the porous polyimide film of the said preparation example 1-8 and comparative preparation examples 1-3 (tensile strength measuring instrument: EZ-TEST / CE ( Manufactured by SHIMAZU)).

Tensile Strength: ASTM D638

Bending Elastic Modulus: ASTM D790

The results are shown in Table 2 below.

As is evident from the results shown in Table 2 above, the requirement "to include the structural unit represented by the formula (3-1) and the structural unit represented by the formula (3-2)" and the configuration represented by the formula (4-1) In Comparative Preparation Examples 1 to 3 using Comparative Polyamic Acids 1 and 2 which do not satisfy both the requirements of “including the unit and the structural unit represented by the formula (4-2)”, the tensile strength did not reach 45 MPa, Bending strength also did not reach 60 MPa.

On the other hand, with the requirement that "the structural unit represented by Formula (3-1) and the structural unit represented by Formula (3-2) is included, and the" structural unit represented by Formula (4-1), and Formula (4-2) In the porous polyimide film of the preparation examples 1-8 which used any one of the polyamic acid 1-3 which satisfy | fills at least one of the requirements of "containing the structural unit to show," both tensile strength (45 Mpa or more) and bending strength (60 MPa or more) was excellent.

Formulation example 1 using the polyamic acid 1 whose content of the structural unit represented by Formula (3-2) or the structural unit represented by Formula (4-2) is 60 mol% or less, and the structural unit represented by Formula (3-2), or From the comparison of the preparation example 6 using the polyamic acid 3 whose content of the structural unit represented by Formula (4-2) exceeds 60 mol%, it is a structural unit represented by Formula (3-2) or Formula (4-2). It is understood that the content of the structural unit represented is 60 mol% or less, which is excellent in tensile strength and bending strength.

[Preparation of Porous Polyimide Film for Reference Example 1]

(Preparation of the composition for film formation)

(1) the first composition

Into a separable flask equipped with a stirrer, a stirring blade, a reflux condenser, and a nitrogen gas introduction tube, 6.5 g of PMDA, tetracarboxylic dianhydride, 6.7 g of diamine, and 30 g of DMAC were charged. Nitrogen was introduced into the flask from the nitrogen gas introduction pipe, and the flask was placed in a nitrogen atmosphere. Subsequently, PMDA and ODA were made to react at 50 degreeC for 20 hours, stirring the contents of the flask, and the polyamic-acid solution was obtained. To the obtained polyamic acid solution, 75 g of silica having an average particle diameter of 300 nm was added and stirred to prepare a first composition having a volume ratio of polyamic acid and silica fine particles to 22:78 (mass ratio is 15:85). In addition, the ratio of all the organic solvent DMAC in a composition was adjusted so that it might become 70 mass%.

(2) a second composition

The volume ratio of polyamic acid and silica microparticles was 28:72 (mass ratio is 20:80) in the same manner as (1) except that 53g of silica having an average particle diameter of 700 nm was added to the obtained polyamic acid solution. 2 compositions were prepared.

(Formation of Film (Polyimide-Particle Composite Film))

The prepared 1st composition was formed into a film on the glass plate which apply | coated the peeling agent using the applicator. This layer (about 1 μm) forms the first layered region. Then, the 2nd composition prepared similarly was formed into a film using the applicator on the 1st layered area | region. This layer forms a second layered region. Prebaking was carried out at 70 degreeC for 5 minutes, and the unbaked composite film with a film thickness of 20 micrometers was formed.

After peeling the said unbaked composite film from the base material, the peeling agent was removed with ethanol, heat-processed at 320 degreeC for 15 minutes, and imidation was completed and it was set as the film (polyimide microparticle composite film). In addition, the atmosphere of the kiln at the time of heat processing was nitrogen atmosphere, and the oxygen concentration in system was about 1%.

(Formation of Porous Polyimide Film)

The fine particles contained in the film were removed by immersing the coating film (polyimide-fine particle composite film) in a 10% HF solution for 10 minutes.

(Chemical etching)

2.38 mass% aqueous solution of tetramethylammonium hydroxide (TMAH) was diluted so that it might become 1.04% with 50 mass% aqueous solution of methanol, and the alkaline etching liquid was prepared. A porous polyimide film was immersed in this etching liquid, a part of polyimide surface was removed, and it was set as the porous polyimide film for reference example 1.

[Example 1, Reference Example 1 and Comparative Example 1]

(Manufacture of Single Layer Laminate Cell Secondary Battery)

The porous polyimide film of the said Preparation Example 2 which is 52 mm x 56 mm as a positive electrode of 52 mm x 56 mm, and a porous separator was put into the aluminum laminate exterior in order, and electrolyte solution (solvent: ethylene carbonate: diethyl carbonate: dimethyl carbonate = 1) : 1: 1 (mass ratio), electrolyte salt: LiPF ₆ 1 mol / L) were added. Furthermore, the battery case was enclosed with the negative electrode (2 sheets) of 56 mm x 60 mm, and the lithium ion secondary battery of Example 1 was obtained.

Here, the positive electrode of nickel cobalt manganese ternary system and the negative electrode of artificial graphite system were used as an electrode.

Moreover, using the porous polyimide film for the reference example 1 prepared above, it carried out similarly to the above, and obtained the single layer laminated cell battery. This was used as the lithium ion secondary battery of Reference Example 1.

In addition, a single-layer laminate cell battery was obtained in the same manner as above using a commercially available polyethylene (PE) -based separator (CellGuard®). This was used as the lithium ion secondary battery of the comparative example 1.

<Cycle charge / discharge test>

For the lithium ion secondary batteries of Example 1 and Comparative Example 1, one cycle was performed using CC (constant current) / CV (constant voltage) = 80 mA / 4.2 (by using the charge / discharge measuring device TOSCAT-3000U (manufactured by Toyo System Co., Ltd.). The charge / discharge which is the charge of cut-off current 5 mA) and discharge of CC = 80 mA (cut-off voltage 2.7V) were repeated 500 cycles in a 25 degreeC thermostat.

For each of the lithium ion secondary batteries of Example 1 (n number = 3) and Comparative Example 1 (n number = 2), the discharge capacity retention rate after 500 cycles was measured and the average value was calculated. The results are shown in Table 3.

As apparent from the results shown in Table 3 above, the structural unit represented by the formula (1-1) and the structural unit represented by the formula (1-1) as the porous separator than the lithium ion secondary battery of Comparative Example 1 using a commercially available PE-based separator Lithium ion of Example 1 containing the polyimide containing a structural unit or the porous polyimide film containing the polyimide containing the structural unit represented by Formula (2-1), and the structural unit represented by Formula (2-2) It is found that the secondary battery has a high discharge capacity retention rate and is resistant to repeated charge / discharge use.

Impedance measurement

About the lithium ion secondary batteries of Example 1, the reference example 1, and the comparative example 1, the impedance (Ohm) originating in a separator part was measured using the charge / discharge measuring apparatus TOSCAT-3000U (made by Toyo Systems Co., Ltd.). The results are shown in Table 4 below.

As is clear from Table 4 above, the formulas (1-1) and (1) in the lithium ion secondary battery of Example 1 than the commercially available PE separators in the lithium ion secondary battery of Comparative Example 1 It can be seen that the porous separator including the polyimide containing the structural unit represented by -2) or the structural unit represented by the formula (2-1) and the structural unit represented by the formula (2-2) has a significantly small impedance. .

In particular, the structural unit represented by Formula (2-1) and the structural unit represented by Formula (2-1) are not included, without including the structural unit represented by said Formula (1-1) and (1-2) in the lithium ion secondary battery of Reference Example 1. It turns out that the porous separator in the lithium ion secondary battery of Example 1 has a smaller impedance than the porous separator which does not contain the structural unit shown by 2).

<Quick Charge (Rate) Test>

About the lithium ion secondary battery of Example 1, the reference example 1, and the comparative example 1, the quick charge (rate) test was done using the charge / discharge measuring apparatus TOSCAT-3000U (made by Toyo Systems Co., Ltd.).

Specifically, for each secondary battery, the charging rate 0.5 C (2 hours charge), 1 C (1 hour charge), 2 C (30 minutes charge), 5 C (12 minutes charge), 10 C (6 minutes charge) ) And the discharge capacity (mAh) at 20 C (3 minutes charge) was measured. The results are shown in Table 5 below.

As apparent from the results shown in Table 5 above, as the porous separator, the structural unit represented by the formula (1-1) and the formula (1-2) than the lithium ion secondary battery of Comparative Example 1 using a commercially available PE-based separator The lithium ion secondary battery of Example 1 containing the porous polyimide film containing the structural unit shown, or the porous polyimide film containing the structural unit represented by Formula (2-1), and the structural unit represented by Formula (2-2). It turns out that the discharge capacity is large large also in any of the charge rate 0.5C, 1C, 2C, 5C, 10C, and 20C, and it is excellent in quick charge performance.

In particular, the porous separator does not include the structural unit represented by the formula (1-1) and the structural unit represented by the formula (1-2), but the structural unit represented by the formula (2-1) and the formula (2-2). The lithium ion secondary battery of Example 1 has a charging rate of 0.5 C, 1 C, 2 C, 5 C, and 10 than the lithium ion secondary battery of Reference Example 1 containing a porous polyimide film containing no structural unit. It turns out that discharge capacity is large also in any of C and 20C, and it is excellent in quick charge performance.

Claims (7)

A secondary battery having a porous separator, wherein the porous separator comprises a porous polyimide film containing a polyimide containing structural units represented by the following formulas (1-1) and (1-2).
[Formula 1]

(In the above formula, A ¹¹ and A ¹² each independently represent a tetravalent aromatic group derived from an acid anhydride containing an aromatic tetracarboxylic anhydride, and B ¹¹ and B ¹² are each independently derived from aromatic diamine. Represents a divalent diamine residue and at least one selected from the group consisting of A ¹² and B ¹² contains a divalent spacer group in its structure) A secondary battery having a porous separator, wherein the porous separator comprises a porous polyimide film comprising a polyimide containing a structural unit represented by the following formula (2-1) and a structural unit represented by the following formula (2-2): Secondary battery included.
[Formula 2]

(In the above formula, A ²¹ and A ²² each independently represent a tetravalent aromatic group derived from an acid anhydride containing an aromatic tetracarboxylic anhydride, and B ²¹ and B ²² are each independently derived from aromatic diamines. It represents a divalent diamine residue, the a ²² and B ²² satisfies at least one condition selected from the group consisting of (I) and (II),.
The electron affinity of the aromatic tetracarboxylic anhydride to induce (I) A ²² is 2.6 eV or less.
(II) The aromatic diamine inducing B ²² is an aromatic diamine different from the aromatic diamine inducing B ²¹ , and the solubility in water at 40 ° C. is 0.1 g / L or more.) The method according to claim 1 or 2,
The secondary battery whose content of the structural unit represented by the said Formula (1-2) or (2-2) in the said polyimide is 60 mol% or less. The method according to claim 1 or 2,
The secondary battery whose tensile strength prescribed | regulated by ASTM specification D638 of the said porous polyimide film is 45 Mpa or more. The method according to claim 1 or 2,
The secondary battery whose bending strength prescribed | regulated by ASTM specification D790 of the said porous polyimide film is 60 Mpa or more. The method according to claim 1 or 2,
The secondary battery whose porosity of the said porous polyimide film is 60% or more. Represented by the polyimide containing the structural unit represented by following formula (1-1) and the structural unit represented by following formula (1-2), or the structural unit represented by following formula (2-1), and following formula (2-2) The porous separator for secondary batteries containing the porous polyimide film containing the polyimide containing a structural unit.
[Formula 3]

(In the above formula, A ¹¹ and A ¹² each independently represent a tetravalent aromatic group derived from an acid anhydride containing an aromatic tetracarboxylic anhydride, and B ¹¹ and B ¹² are each independently derived from aromatic diamine. Represents a divalent diamine residue and at least one selected from the group consisting of A ¹² and B ¹² contains a divalent spacer group in its structure)
[Formula 4]

(In the above formula, A ²¹ and A ²² each independently represent a tetravalent aromatic group derived from an acid anhydride containing an aromatic tetracarboxylic anhydride, and B ²¹ and B ²² are each independently derived from aromatic diamines. It represents a divalent diamine residue, the a ²² and B ²² satisfies at least one condition selected from the group consisting of (I) and (II),.
The electron affinity of the aromatic tetracarboxylic anhydride to induce (I) A ²² is 2.6 eV or less.
(II) The aromatic diamine inducing B ²² is an aromatic diamine different from the aromatic diamine inducing B ²¹ , and the solubility in water at 40 ° C. is 0.1 g / L or more.)