Ion exchange membrane, membrane electrode assembly, cell for redox flow batteries, and redox flow battery

Abstract

An ion exchange membrane comprising a resin composition that contains a cation exchange resin and a side chain heteroaromatic resin having a structural unit represented by general formula 1 (in the formula, R1, R2, and R3 may be the same or different from each other, and each represent a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1-10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6-10 carbon atoms, R4 represents a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1-10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6-10 carbon atoms, and Hc represents a substituted or unsubstituted heteroaromatic group having 4-30 carbon atoms, having at least one nitrogen atom in the heteroaromatic ring structure, and including a 5-membered ring and / or 6-membered ring structure.).

Description

Ion exchange membrane, membrane electrode assembly, redox flow battery cell, and redox flow battery

[0001] The present invention relates to an ion exchange membrane, a membrane electrode assembly, a cell for a redox flow battery, and a redox flow battery.

[0002] Redox flow batteries are secondary batteries that store and discharge electricity, and are suitable for large-scale stationary batteries used to level out electricity consumption. Redox flow batteries have a structure in which a cathode electrolyte (cathode cell) containing a cathode and a cathode redox active material and an anode electrolyte (anode cell) containing a cathode and a cathode redox active material are separated by a diaphragm, and charge and discharge are performed using the oxidation-reduction reaction of both redox active materials. Large capacity can be achieved by circulating the electrolyte containing both redox active materials from a storage tank to an electrolytic cell.

[0003] Examples of redox active materials contained in the electrolyte include iron / chromium, chromium / bromine, zinc / bromine, and vanadium, which utilizes differences in charge. In particular, vanadium-based redox flow batteries are being developed in earnest because of their advantages, such as high electromotive force, fast electrode reactions of vanadium ions, low hydrogen generation as a side reaction, and high output.

[0004] In vanadium-based redox flow batteries, the divalent (V) 2+ ) / trivalent (V 3+ ) and the tetravalent of vanadium (V) in the positive electrode cell 4+ ) / Pentavalent (V 5+) oxidation-reduction reaction. Because the redox active material contained in the electrolytes of the positive and negative cells is the same type of vanadium ion, even if the electrolytes are mixed through the diaphragm, it can be regenerated by an electrical process, making it superior in terms of long-term use. However, since permeation of the redox active material neutralizes the stored charge and reduces current efficiency, it is desirable for the diaphragm to minimize permeation of the redox active material. On the other hand, since protons contained in the electrolyte can easily permeate the diaphragm, reducing the battery resistance and increasing voltage efficiency, it is desirable for the diaphragm to minimize the obstruction of proton permeation. In other words, there is a need for a diaphragm that can achieve both high current efficiency and high voltage efficiency, i.e., high power efficiency (power efficiency is the product of current efficiency and voltage efficiency).

[0005] Processing of ion exchange membranes to suppress permeation of redox active materials and achieve high power efficiency has been disclosed (Patent Documents 1 to 3). Patent Document 1 discloses that alternately laminating cation exchange base layers and anion exchange base layers results in excellent initial power efficiency. Patent Document 2 discloses that the use of a membrane containing a sulfonated polymer and a heterocyclic molecule containing multiple nitrogen atoms results in low proton area resistivity and excellent vanadium ion permeation selectivity. Patent Document 3 discloses that the use of a polymer electrolyte membrane having an internal crossover prevention layer, which is a metal layer formed by reducing a cationic metal, results in excellent discharge capacity, current efficiency, voltage efficiency, and power efficiency. Patent Document 4 discloses that the use of a redox flow battery membrane comprising, in this order, a first ion exchange resin layer, an anion exchange resin layer containing an anion exchange compound, and a second ion exchange resin layer suppresses curling and results in excellent power efficiency.

[0006] Patent Document 5 discloses a 5% by mass solution of a fluororesin having acidic groups dissolved in a 50:50 mass ratio of ethanol to water. Patent Document 6 discloses that a polymer electrolyte solution in which a fluororesin having acidic groups is dissolved in a hydrophilic, high-boiling-point polar solvent can be used to obtain a thin film that is high in strength, has good adhesion to the substrate, and has good chemical resistance. Patent Document 7 and Non-Patent Document 1 disclose that when attempting to produce a polymer with a large proportion of sulfonic acid groups from a specific fluororesin having acidic groups, it is difficult to sufficiently increase the molecular weight of the polymer and to produce a polymer electrolyte membrane with sufficient mechanical strength. Patent Document 8 discloses that co-extrusion of a perfluorosulfonic acid polymer precursor with an incompatible polymer can form a multilayer film having a perfluorosulfonic acid polymer precursor layer with a reduced thickness supported on an incompatible polymer layer, and that a proton exchange membrane with a reduced thickness can be obtained.

[0007] Japanese Patent Publication No. 11-260390 International Patent Publication No. 2017 / 155648 International Patent Publication No. 2016 / 163773 International Patent Publication No. 2021 / 215126 Japanese Patent Publication No. 07-296634 Japanese Patent Publication No. 2004-164854 International Patent Publication No. 2008 / 090990 International Patent Publication No. 2013 / 091073

[0008] W. Vielstich, H. A. Gasteiger, A. Lamm, eds., "Handbook of Fuel Cells, vol. 3," John Wiley & Sons, Ltd., USA, 2003, Chapter 30, pp. 351-352

[0009] The embodiments of the present invention are as follows: <1> A side chain heteroaromatic resin having a structural unit represented by the following general formula 1, and (In the formula, R １ , R ２ , and R ３may be the same or different and each represent a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms; R ４ is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, and Hc is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, which has at least one nitrogen atom in the heteroaromatic ring structure and includes a 5-membered ring and / or a 6-membered ring structure.) An ion exchange membrane comprising a resin composition containing a cation exchange resin. <2> The ion exchange membrane according to <1>, wherein a weight ratio of the side chain heteroaromatic resin to the cation exchange resin is 1:100 to 100:1. <3> The ion exchange membrane according to <1> or <2>, wherein the cation exchange resin is a fluororesin. <4> The fluororesin has a structural unit represented by the following general formula G1: (In the formula, X ５ , X ６ , X ７ , and X ８ may be the same or different and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X ５ and X ６ , or X ５ and X ７ may be bonded to each other to form a cyclic structure, R ５ , and R ６ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X ９ is -COOZ, -SO ３ Z, -PO ３ Z ２ , or -PO ３A group represented by HZ, wherein Z is at least one selected from the group consisting of a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, and an amine; ９ The fluororesins may be crosslinked by ionic crosslinking via an intervening linkage, h and p represent molar ratios in all structural units contained in the resin, and are numbers that satisfy 0≦h<1, 0<p≦1, and h+p=1, i is an integer of 0 to 8, j is 0 or 1, k, l, and m may be the same or different, and are integers of 0 to 6, provided that when k, l, and m are simultaneously 0, X ９ is CF (CF ２ X １０ ) ２ and X １０ is -COOZ, -SO ３ Z, -PO ３ Z ２ , or -PO ３ The ion exchange membrane according to <3>, wherein <5> a layer (L) containing the resin composition and a structural unit represented by the following general formula G1: (In the formula, the definition of each substituent is the same as in the above-mentioned general formula G1.) The ion exchange membrane according to any one of <1> to <4>, having at least one layer (L) and one layer (M) containing a fluororesin, alternating with each other. <6> The ion exchange membrane according to <5>, having one layer (L) and one layer (M). <7> The ion exchange membrane according to <5> or <6>, having the layer (L), the layer (M), and the layer (L) in this order. <8> The ion exchange membrane according to any one of <1> to <4>, comprising a side-chain heteroaromatic resin having a structural unit represented by the following general formula 2: (In the formula, R １ , R ２ , and R ３ may be the same or different and each represent a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms; R ４represents a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms; Hc represents a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms and containing a 5-membered ring and / or 6-membered ring structure, which has at least one nitrogen atom in the heteroaromatic ring structure; Rf represents an aliphatic hydrocarbon group substituted with at least one fluorine atom; X － is a counter anion.) <9> An ion exchange membrane comprising a layer (L) containing the side chain heteroaromatic resin and a structural unit represented by the following general formula G1: (wherein the definition of each substituent is the same as in the above-mentioned general formula G1.) The ion exchange membrane according to <8>, having at least one layer (M) containing a fluororesin, and at least one layer (L) alternately. <10> The ion exchange membrane according to <9>, having one layer each of the layer (L) and the layer (M). <11> The ion exchange membrane according to <9>, having the layer (L), the layer (M), and the layer (L) in this order. <12> The ion exchange membrane according to any one of <9> to <11>, wherein the layer (L) further contains a cation exchange resin. <13> The ion exchange membrane according to <12>, wherein the weight ratio of the side chain heteroaromatic resin to the cation exchange resin is 1:100 to 100:1. <14> The ion exchange membrane according to <12> or <13>, wherein the cation exchange resin is a fluororesin. <15> The fluororesin has a structural unit represented by the following general formula G1, (In the formula, the definition of each substituent is the same as in the above-mentioned general formula G1.) <16> The ion exchange membrane according to <14>. <16> The side chain heteroaromatic resin further has a structural unit represented by the following general formula 2: (In the formula, R １ , R ２ , and R ３ may be the same or different and each represent a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms; R ４represents a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms; Hc represents a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms and containing a 5-membered ring and / or 6-membered ring structure, which has at least one nitrogen atom in the heteroaromatic ring structure; Rf represents an aliphatic hydrocarbon group substituted with at least one fluorine atom; X － is a counter anion.) The ion exchange membrane according to <1>. <17> The ion exchange membrane according to <16>, wherein the molar ratio of the structural unit represented by the general formula 1 to the structural unit represented by the general formula 2 is 1:100 to 100:1. <18> The ion exchange membrane according to <16> or <17>, wherein the weight ratio of the side chain heteroaromatic resin to the cation exchange resin is 1:100 to 100:1. <19> The ion exchange membrane according to any one of <16> to <18>, wherein the cation exchange resin is a fluororesin. <20> The fluororesin has a structural unit represented by the following general formula G1: (wherein the definition of each substituent is the same as in the above-mentioned general formula G1.) <16> to <19>. <21> The ion exchange membrane according to any one of <16> to <19>. <22> The ion exchange membrane according to any one of <16> to <19>, (wherein the definition of each substituent is the same as in the above-mentioned general formula G1.) The ion exchange membrane according to <20>, having at least one layer (L1) containing a heteroaromatic structure-containing fluororesin, having a structural unit represented by the following general formula A1, a saponified product thereof, or a salt thereof, alternating with at least one layer (M). <22> The ion exchange membrane according to <21>, having one layer each of the layer (L) and the layer (M). <23> The ion exchange membrane according to <21>, having the layer (L), the layer (M), and the layer (L) in this order. <24> A layer (L1) containing a heteroaromatic structure-containing fluororesin having a structural unit represented by the following general formula A1, a saponified product thereof, or a salt thereof, (In the formula, X １ , X ２ , X ３ , and X ４may be the same or different and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X １ and X ２ , or X １ and X ３ may be bonded to each other to form a cyclic structure, R １ , R ２ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; R ３ is a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms; R ４ is NR ３ and Hc, and is a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms; １０ is -CO ２ -, -SO ２ -, a divalent group represented by the formula: Hc is a substituted or unsubstituted heteroaromatic group containing at least one nitrogen atom, having a 5-membered ring and / or a 6-membered ring structure, and having 4 to 30 carbon atoms; a and g represent molar ratios in all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1; b is an integer from 0 to 8; c is 0 or 1; d, e, and f may be the same or different, and are integers from 0 to 6, provided that d, e, and f are not simultaneously 0. An ion exchange membrane comprising: a layer (M1) containing a fluororesin (G1) having a structural unit represented by the following general formula G1; (wherein the definition of each substituent is the same as in the above-mentioned general formula G1.) <25> The ion exchange membrane according to <24>, having three or more layers of the layer (L1) and the layer (M1) alternately. <26> The ion exchange membrane according to <24> or <25>, wherein the layer (L1) has a thickness of 10 μm or less. <27> The ion exchange membrane according to any one of <24> to <26>, wherein the ion exchange membrane has a thickness of 200 μm or less. <28> A layer (L3) containing a fluororesin having a nitrogen atom in a side chain, having a structural unit represented by the following general formula A3, a saponified product thereof, or a salt thereof, (In the formula, X ２０ , X ２１ , X ２２ , and X ２３ may be the same or different and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X ２０ and X ２１ , or X ２０ and X ２２ may form a cyclic structure, R ２０ , and R ２１ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; R ２２ , and R ２４ is a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms; R ２６ , and R ２７ is a hydrogen atom or a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, and R ２６ , and R ２７ at least one of R is a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms; ２３ , and R ２５may be the same or different, and each represents a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms; when h is 2 or more, the repeated R ２３ may be the same or different, X ２４ is -CO ２ - or -SO ２ a and g represent molar ratios in all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1; b is an integer of 0 to 8; c is 0 or 1; d, e, f, and h may be the same or different and are integers of 0 to 6, provided that d, e, and f are not simultaneously 0. A layer (M3) containing a fluororesin (G1) having a structural unit represented by the following general formula G1; (wherein the definition of each substituent is the same as in the general formula G1 above). <29> The ion exchange membrane according to <28>, having three or more layers of the layer (L3) and the layer (M3) alternately. <30> The ion exchange membrane according to <28> or <29>, wherein the layer (L3) has a thickness of 10 μm or less. <31> The ion exchange membrane according to any one of <28> to <30>, wherein the ion exchange membrane has a thickness of 200 μm or less. <32> The ion exchange membrane according to any one of <1> to <31>, which is for a redox flow battery. <33> A membrane electrode assembly comprising the ion exchange membrane according to any one of <1> to <31> and at least one electrode joined together. <34> The membrane electrode assembly according to <33>, which is for a redox flow battery. <35> A redox flow battery cell comprising: a first electrolytic solution containing a first redox active material; a second electrolytic solution containing a second redox active material; a first electrode in contact with the first electrolytic solution; a second electrode in contact with the second electrolytic solution; and a diaphragm disposed between the first electrolytic solution and the second electrolytic solution, wherein the diaphragm is the ion exchange membrane according to any one of <1> to <31>. <36> The redox flow battery cell according to <35>, which is a membrane electrode assembly in which the diaphragm and at least one electrode are joined. <37> The redox flow battery cell according to <35> or <36>, in which at least one of the first electrode and the second electrode is a carbon electrode. <38> The cell for a redox flow battery according to any one of <35> to <37>, wherein at least one of the first redox active material and the second redox active material is at least one selected from the group consisting of a metal redox active material, a non-metal redox active material, and an organic redox active material. <39> A redox flow battery, in which the cells for a redox flow battery according to any one of <35> to <38> are stacked.<40> A redox flow battery cell comprising: a first electrolytic solution containing a first redox active material, a second electrolytic solution containing a second redox active material, a first electrode in contact with the first electrolytic solution, a second electrode in contact with the second electrolytic solution, and a diaphragm disposed between the first electrolytic solution and the second electrolytic solution, wherein the diaphragm has at least a first cation exchange resin layer and an anion exchange resin layer, wherein the equivalent weight of the diaphragm is 1150 g / eq or less, and the thickness of the anion exchange resin layer is 0.001 μm or more and less than 5 μm, and the anion exchange resin layer of the diaphragm is disposed on the electrode side acting as a negative electrode. <41> The redox flow battery cell according to <40>, wherein the first cation exchange resin layer is disposed on the electrode side acting as a positive electrode relative to the anion exchange resin layer. <42> The distance D between the anion exchange resin layer of the diaphragm and the electrode acting as the negative electrode. ｎｅｇ and a distance D between the anion exchange resin layer of the diaphragm and the electrode acting as a positive electrode. ｐｏｓ and show the following relationship: D ｎｅｇ / D ｐｏｓ <1> The cell for a redox flow battery according to <40> or <41>. <43> The cell for a redox flow battery according to any one of <40> to <42>, wherein the thickness of the first cation exchange resin layer is 1 μm or more and 150 μm or less. <44> The cell for a redox flow battery according to any one of <40> to <43>, wherein the first cation exchange resin layer contains a fluororesin. <45> The cell for a redox flow battery according to any one of <40> to <44>, wherein the first cation exchange resin layer has at least one functional group selected from the group consisting of a sulfo group, a carboxyl group, and a phosphate group. <46> The first cation exchange resin layer contains a fluororesin having a structural unit represented by the following general formula G1: (In the formula, the definition of each substituent is the same as in the general formula G1 above.) The cell for redox flow battery according to any one of <40> to <45>. <47> The cell for redox flow battery according to any one of <40> to <46>, wherein the anion exchange resin layer contains at least one selected from the group consisting of: a primary amino group, a secondary amino group, a tertiary amino group, an amino salt structure which is a reaction product of at least one amino group selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group, and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, a nitrogen atom-containing heterocyclic structure, a nitrogen atom-containing heterocyclic salt structure which is a reaction product of a nitrogen-containing heterocyclic structure and at least one selected from the group consisting of an acidic substance and a halogen atom-containing aliphatic hydrocarbon compound, and a quaternary ammonium group. <48> The cell for a redox flow battery according to any one of <40> to <47>, wherein the diaphragm comprises the first cation exchange resin layer, the anion exchange resin layer, and a second cation exchange resin layer in this order, and the thickness of the first cation exchange resin layer is greater than the thickness of the second cation exchange resin layer. <49> The cell for a redox flow battery according to <48>, wherein the first cation exchange resin layer is disposed closer to the electrode acting as a positive electrode than the anion exchange resin layer. <50> The cell for a redox flow battery according to <50>, wherein the distance D between the anion exchange resin layer of the diaphragm and the electrode acting as a negative electrode is ｎｅｇ and a distance D between the anion exchange resin layer of the diaphragm and the electrode acting as a positive electrode. ｐｏｓ and show the following relationship: D ｎｅｇ / D ｐｏｓ<1> The cell for a redox flow battery according to <48> or <49>. <51> The cell for a redox flow battery according to any one of <48> to <50>, wherein the second cation exchange resin layer contains a fluororesin. <52> The cell for a redox flow battery according to any one of <48> to <51>, wherein the thickness of the second cation exchange resin layer is 0.01 μm or more and less than 150 μm. <53> The cell for a redox flow battery according to any one of <48> to <52>, wherein the value obtained by dividing the thickness of the second ion exchange resin layer by the thickness of the first cation exchange resin layer is less than 0.7. <54> The cell for a redox flow battery according to any one of <40> to <53>, wherein at least one of the first electrode and the second electrode is a carbon electrode. <55> The cell for redox flow batteries according to any one of <40> to <54>, wherein at least one of the first redox active material and the second redox active material is at least one selected from the group consisting of a metal redox active material, a non-metal redox active material, and an organic redox active material. <56> The cell for redox flow batteries according to any one of <40> to <55>, wherein at least one of the first electrode and the second electrode is a membrane electrode assembly joined to a membrane. <57> A redox flow battery comprising a stack of cells for redox flow batteries according to any one of <40> to <56>. <58> A method for producing a diaphragm comprising at least a first cation exchange resin layer and an anion exchange resin layer, wherein the diaphragm has an equivalent weight of 1150 g / eq or less, and the anion exchange resin layer has a thickness of 0.001 μm or more and less than 5 μm, the method comprising: a step of forming the first cation exchange resin layer; and a step of forming the anion exchange resin layer.<59> A process of reacting a fluororesin precursor layer, which serves as a precursor of the first cation exchange resin layer and contains at least one selected from the group consisting of a halogenated sulfonyl group, an acyl halide group, and a halogenated phosphate group, with a modifying compound having at least two nitrogen atom-containing groups, wherein the nitrogen atom-containing groups include at least one selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, an amino salt structure which is a reaction product of at least one amino group selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group with at least one selected from the group consisting of an acidic substance and a halogenated aliphatic hydrocarbon compound, a nitrogen atom-containing heterocyclic structure, a nitrogen atom-containing heterocyclic salt structure which is a reaction product of a nitrogen-containing heterocyclic structure and at least one selected from the group consisting of an acidic substance and a halogenated aliphatic hydrocarbon compound, and a quaternary ammonium group; <58>, the method for producing a diaphragm according to <58>, comprising, after the step, converting at least one selected from the group consisting of a halogenated sulfonyl group, an acyl halide group, and a halogenated phosphate group contained in the fluororesin precursor layer to at least one selected from the group consisting of a sulfo group, a carboxyl group, and a phosphate group. <60> A method for producing a diaphragm comprising the first cation exchange resin layer, the anion exchange resin layer, and a second cation exchange resin layer, in this order, and wherein the thickness of the first cation exchange resin layer is greater than the thickness of the second cation exchange resin layer, the method comprising: forming the first cation exchange resin layer, forming the anion exchange resin layer, and forming the second cation exchange resin layer. <61> The method for producing a diaphragm according to <60>, comprising: stacking the anion exchange resin layers of membranes each having the first cation exchange resin layer and the anion exchange resin layer.<62> A polymer electrolyte solution comprising: a fluororesin having a structural unit represented by the following general formula G1, and having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq; and a solvent containing water, an aliphatic alcohol, and an aliphatic carboxylic acid, wherein the mass ratio of the total of the aliphatic carboxylic acid and its reactant to the total mass of the solvent is 100:1 to 100:50. (wherein the definition of each substituent is the same as in the above-mentioned general formula G1.) <63> The polymer electrolyte solution according to <62>, wherein a mass ratio of the aliphatic carboxylic acid to the aliphatic alcohol is 100:1 to 1:100. <64> An ion exchange membrane comprising a fluororesin having a structural unit represented by the following general formula G1, and having an equivalent weight of 500 g / eq or more but less than 1,000 g / eq, wherein the number of crack defects per unit area of ​​the ion exchange membrane is 10 / m ２ An ion exchange membrane that is less than (wherein the definition of each substituent is the same as in the above-mentioned general formula G1.) <65> The ion exchange membrane according to <64>, wherein the orientation ratio OR in the membrane plane direction measured by X-ray scattering measurement is 1.0 or more and less than 1.1. <66> The ion exchange membrane according to <64> or <65>, wherein the average membrane thickness is 75 μm or less. <67> The ion exchange membrane according to any one of <64> to <66>, wherein the average membrane thickness is 25 μm or more. <68> The ion exchange membrane according to any one of <64> to <67>, wherein the minimum membrane thickness is 90% or more of the average membrane thickness and the maximum membrane thickness is 110% or less of the average membrane thickness. <69> A wound body formed by winding the ion exchange membrane according to any one of <64> to <68>. <70> The wound body according to <68>, wherein the width of the ion exchange membrane is 50 mm or more and 5,000 mm or less. <71> The wound body according to <69> or <70>, wherein the length of the ion exchange membrane is 100 mm or more. <72> A membrane electrode assembly comprising the ion exchange membrane according to any one of <64> to <68> and at least one electrode joined together. <73> The ion exchange membrane according to any one of <64> to <68>, which is for a redox flow battery. <74> The membrane electrode assembly according to <72>, which is for a redox flow battery. <75> A cell for a redox flow battery, comprising: a first electrolytic solution containing a first redox active material; a second electrolytic solution containing a second redox active material; a first electrode in contact with the first electrolytic solution; a second electrode in contact with the second electrolytic solution; and a diaphragm disposed between the first electrolytic solution and the second electrolytic solution, wherein the diaphragm is the ion exchange membrane according to any one of <64> to <68>. <76> The redox flow battery cell according to <75>, wherein the diaphragm and at least one electrode are joined. <77> The redox flow battery cell according to <75> or <76>, wherein at least one of the first electrode and the second electrode is a carbon electrode. <78> The redox flow battery cell according to any one of <75> to <77>, wherein at least one of the first redox active material and the second redox active material is at least one selected from the group consisting of metal redox active materials, non-metal redox active materials, and organic redox active materials.<79> A redox flow battery comprising a stack of cells for a redox flow battery according to any one of <75> to <78>. <80> An ion exchange membrane comprising a fluororesin having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq and having a structural unit represented by the following general formula G1, the ion exchange membrane having a crack defect count of 10 / m per unit area, the ion exchange membrane comprising a step of applying and drying the polymer electrolyte solution according to <62> or <63>: ２ The method for producing an ion exchange membrane, (In the formula, the definition of each substituent is the same as in the above-mentioned general formula G1.)

[0010] FIG. 1 shows an example of a schematic diagram of a redox flow battery using the redox flow battery membrane of this embodiment.

[0011] Below, a form for implementing the present invention (hereinafter referred to as the "present embodiment") will be described in detail, but the present invention is not limited to the following description and can be implemented in various modifications within the scope of its gist.

[0012] First Embodiment First, the first embodiment will be described.

[0013] Patent Document 1 discloses the use of an aromatic polysulfone polymer as an anion exchange base layer to improve current efficiency and power efficiency. However, although the current efficiency is excellent, it has been shown that the cell resistance increases and the voltage efficiency decreases. Therefore, an anion exchange base layer with a well-balanced current efficiency, voltage efficiency, and current efficiency is needed. Patent Document 2 discloses Nafion® 117 reacted with several heterocyclic molecules to improve vanadium ion permeation selectivity while suppressing an increase in proton surface resistance. However, attempts to reduce proton surface resistance result in reduced vanadium ion permeation selectivity, while attempts to increase vanadium ion permeation selectivity result in increased proton surface resistance. Thus, achieving both has remained a challenge. Furthermore, the examples do not involve evaluation as a redox flow battery, and the current efficiency, voltage efficiency, and power efficiency are unknown. However, since the proton surface resistance in the examples is higher than that of Nafion® 117, it can be inferred that the voltage efficiency is lower than that of Nafion® 117. For these reasons, there is a demand for a material that exhibits excellent and well-balanced current efficiency, voltage efficiency, and current efficiency. Patent Document 3 discloses the provision of a crossover prevention layer, which is a metal layer formed by reducing a cationic metal, inside a polymer electrolyte membrane in order to improve at least one of the properties of discharge capacity, current efficiency, voltage efficiency, and power efficiency. However, even higher properties are required. Patent Document 4 discloses the use of several polymer compounds as an anion exchange resin layer in order to achieve high power efficiency. However, it has been shown that when an anion exchange resin layer is not positioned between the ion exchange resin layer and the anion exchange resin layer, high power efficiency may be obtained as an initial property, but high power efficiency cannot be obtained after 100 cycles. For this reason, there is a demand for the anion exchange compound contained in the anion exchange resin layer used in Patent Document 4 to have even higher properties.

[0014] The present invention relates to a side-chain heteroaromatic resin, a resin composition, an ion exchange membrane, a membrane electrode assembly, and a redox flow battery cell using the same, which are capable of producing a redox flow battery cell having a well-balanced excellent current efficiency and voltage efficiency and high power efficiency, and a redox flow battery cell using the same.

[0015] As a result of intensive investigations into the above-mentioned problems, the present inventors have found that by using a side-chain heteroaromatic resin having a specific structural unit as a diaphragm for a redox flow battery cell, it is possible to obtain a well-balanced current efficiency and voltage efficiency as well as high power efficiency.

[0016] The ion exchange membrane according to the first embodiment contains the following resin composition: a side-chain heteroaromatic resin having a structural unit represented by the following general formula 1; (In the formula, R １ , R ２ , and R ３ may be the same or different and each represent a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms; R ４ is a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms; and Hc is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, which has at least one nitrogen atom in the heteroaromatic ring structure and includes a 5-membered ring and / or a 6-membered ring structure.) Cation exchange resin. According to this embodiment, it is possible to provide a side-chain heteroaromatic resin having a novel specific structural unit. Furthermore, according to this embodiment, it is possible to provide a side-chain heteroaromatic resin, a resin composition, an ion exchange membrane, a membrane electrode assembly, and a redox flow battery cell and a redox flow battery using these, which exhibit well-balanced current efficiency and voltage efficiency and high power efficiency.

[0017] The ion exchange membrane according to the first embodiment contains a side-chain heteroaromatic resin having a structural unit represented by the following general formula 2. (In the formula, R１ , R ２ , and R ３ may be the same or different and each represent a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms; R ４ represents a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms; Hc represents a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms and containing a 5-membered ring and / or 6-membered ring structure, which has at least one nitrogen atom in the heteroaromatic ring structure; Rf represents an aliphatic hydrocarbon group substituted with at least one fluorine atom; X － is the counter anion.)

[0018] <Side Chain Heteroaromatic Resin> The side chain heteroaromatic resin in the first embodiment has a structural unit represented by the following general formula 1. (In the formula, R １ , R ２ , and R ３ may be the same or different and each represent a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms; R ４ represents a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms; and Hc represents a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, which has at least one nitrogen atom in the heteroaromatic ring structure and includes a 5-membered ring and / or a 6-membered ring structure.

[0019] R in the above general formula 1 １ , R ２ , and R ３ may be the same or different and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms.

[0020] In the case of a substituted aliphatic hydrocarbon group or a substituted aromatic hydrocarbon group, the substituent is not particularly limited, but examples thereof include halogen atoms such as fluorine atoms, chlorine atoms, and bromine atoms, nitrile groups (—CN), alkoxy groups (—OR ａ ), alkyl carbonate group (—OCO ２ R ａ ), alkyl ester group (—CO ２ R ａ ), acyl group (—COR ａ ), sulfide group (-SR ａ ), sulfoxide group (—SOR ａ ), sulfonic acid group (—SO ２ R ａ ), and a urethane group (—NHCO ２ R ａ ) etc. ａ is an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms. In the case of an aliphatic hydrocarbon group, the substituent may be an aromatic hydrocarbon group having 6 to 10 carbon atoms, and in the case of an aromatic hydrocarbon group, the substituent may be an aliphatic hydrocarbon group having 1 to 10 carbon atoms. In the case of having a substituent, the substituent may be one type alone or multiple types.

[0021] R １ , R ２ , and R ３ As the alkyl group, a hydrogen atom or a substituted or unsubstituted aliphatic hydrocarbon group is preferred, and a hydrogen atom or an unsubstituted aliphatic hydrocarbon group is more preferred, since the raw material compounds are easily available when producing a side-chain heteroaromatic resin, and a hydrogen atom is even more preferred, since the raw material compounds are highly reactive when producing a side-chain heteroaromatic resin, and production costs tend to be reduced.

[0022] The number of carbon atoms in the substituted or unsubstituted aliphatic hydrocarbon group is 1 to 10. In view of the ease of availability of raw material compounds for producing a side-chain heteroaromatic resin, the number of carbon atoms is preferably 1 to 6, more preferably 1 to 4, even more preferably 1 or 2, and even more preferably 1.

[0023] The number of carbon atoms in the substituted or unsubstituted aromatic hydrocarbon group is 6 to 10. In view of the ease of availability of raw material compounds for producing a side-chain heteroaromatic resin, the number of carbon atoms is preferably 6 to 10, more preferably 6 to 8, and even more preferably 6.

[0024] R in the above general formula 1 ４ represents a direct bond, a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms. The substituents here are the same as those described above.

[0025] Here, the direct bond is a bond between Hc and R ３ This means that the carbon atom constituting the main chain bonded to R is directly bonded to R. ４ The same meaning applies to descriptions related to the above.)

[0026] The number of carbon atoms in the substituted or unsubstituted divalent aliphatic hydrocarbon group is 1 to 10. In view of the ease of availability of raw material compounds for producing a side-chain heteroaromatic resin, the number of carbon atoms is preferably 1 to 6, more preferably 1 to 4, even more preferably 1 or 2, and even more preferably 1.

[0027] The carbon number of the substituted or unsubstituted divalent aromatic hydrocarbon group is 6 to 10. In view of the ease of availability of raw material compounds for producing a side-chain heteroaromatic resin, the carbon number is preferably 6 to 10, more preferably 6 to 8, and even more preferably 6.

[0028] R in the above general formula 1 ４ As R, a direct bond or a substituted or unsubstituted aliphatic hydrocarbon group is preferred because raw material compounds are easily available when producing a side-chain heteroaromatic resin, a direct bond or an unsubstituted aliphatic hydrocarbon group is more preferred, and a direct bond is even more preferred because the reactivity of the raw material compounds when producing a side-chain heteroaromatic resin is high and production costs tend to be reduced. ４ When the bond is a direct bond, the structural unit represented by general formula 1 is represented by the following general formula 1-2: Here, the substituents are the same as those described above. (In the formula, the definition of each substituent is the same as in General Formula 1 above.)

[0029] Hc in the above general formula 1 is a substituted or unsubstituted heteroaromatic group having 4 to 30 carbon atoms, which has at least one nitrogen atom in the heteroaromatic ring structure and includes a 5-membered ring and / or a 6-membered ring structure.

[0030] The 5-membered ring and / or 6-membered ring structure in Hc of general formula 1 above is not particularly limited, and examples thereof include an imidazole structure, a benzimidazole structure, an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a pyridazine structure, a pyrimidine structure, a cinnoline structure, a quinazoline structure, a phthalazine structure, a quinoxaline structure, a pteridine structure, a purine structure, a 2,2'-bipyridyl structure, a 2,3'-bipyridyl structure, a 2,4'-bipyridyl structure, a 1,7-phenanthroline structure, a 1,10-phenanthroline structure, and a 2,2':6',2''-terpyridine structure. The above-exemplified structures of Hc may be of one type alone or may include a plurality of types of structures.

[0031] Since Hc has at least one nitrogen atom in the heteroaromatic ring structure, among the above-mentioned 5-membered ring and / or 6-membered ring structures, it is preferable that Hc has an imidazole structure, a benzimidazole structure, an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a 2,2'-bipyridyl structure, a 2,3'-bipyridyl structure, a 2,4'-bipyridyl structure, a 1,7-phenanthroline structure, or a 1,10-phenanthroline structure, and it is preferable that Hc has an imidazole structure, a benzimidazole structure, or a 1,10-phenanthroline structure. It is more preferable that the side-chain heteroaromatic resin has an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a 2,2'-bipyridyl structure, or a 1,10-phenanthroline structure, and when the side-chain heteroaromatic resin is used in a redox flow battery cell, durability tends to be improved. Therefore, it is even more preferable that the side-chain heteroaromatic resin has an imidazole structure, a benzimidazole structure, an imidazopyridine structure, or a pyridine structure, and it is particularly preferable that the side-chain heteroaromatic resin has an imidazole structure or a pyridine structure.

[0032] H Ｃ The substituents in are the same as those described above.

[0033] Examples of Hc include an imidazolyl group, a benzimidazolyl group, an imidazopyridinyl group, a pyridinyl group, an oxazolyl group, a thiazolyl group, a pyridazinyl group, a pyrimidinyl group, a cinnolinyl group, a quinazolinyl group, a phthalazinyl group, a quinoxalinyl group, a pteridinyl group, a purinyl group, a 2,2'-bipyridinyl group, a 2,3'-bipyridinyl group, a 2,4'-bipyridinyl group, a 1,7-phenanthrolinyl group, a 1,10-phenanthrolinyl group, and a 2,2':6',2''-terpyridinyl group. Among these, an imidazolyl group or a pyridinyl group is preferred.

[0034] When Hc is an imidazolyl group, the structural unit represented by general formula 1 is a structural unit represented by the following general formula 1-3.

[0035] When Hc is a pyridinyl group, the structural unit represented by general formula 1 is a structural unit represented by the following general formula 1-4.

[0036] The structural unit represented by the above general formula 1 is preferably a structural unit represented by the following general formula 1-5 or 1-6.

[0037]

[0038] The side chain heteroaromatic resin preferably further has a structural unit represented by the following general formula 2. (In the formula, R １ , R ２ , R ３ , R ４ , Hc, and n are defined as in general formula 1, Rf is an aliphatic hydrocarbon group substituted with at least one fluorine atom, and X － is the counter anion.)

[0039] When the side chain heteroaromatic resin further has a structural unit represented by general formula 2, the water resistance, chemical resistance, acid resistance, and alkali resistance tend to be improved.

[0040] The aliphatic hydrocarbon group in Rf preferably has 1 to 20 carbon atoms, more preferably 3 to 16 carbon atoms, even more preferably 3 to 11 carbon atoms, and even more preferably 3 to 9 carbon atoms.

[0041] The number of fluorine atoms substituted on the aliphatic hydrocarbon group in Rf is preferably 1 to 41, more preferably 3 to 25, and even more preferably 5 to 18.

[0042] Rf is a group represented by the formula: -(CH ２ ) ｏ -(CF ２ ) ｐ -CF ３ (wherein o+p is 1 to 19, and o is 0 to 19) is preferred. o and p may be integers. o+p is preferably 1 to 19, more preferably 2 to 15, even more preferably 2 to 10, and even more preferably 2 to 8. From the same viewpoint, o is preferably 0 to 19, more preferably 1 to 10, and from the viewpoint of further improving the water resistance and chemical resistance of the side-chain heteroaromatic resin, it is more preferably 2 to 4, and even more preferably 2. From the viewpoints of easy availability of a compound that serves as a precursor of Rf and suppressing the production cost of the side-chain heteroaromatic resin, p is preferably 0 to 19, more preferably 2 to 10, even more preferably 3 to 7, and even more preferably 4 to 6.

[0043] More specifically, Rf may be, for example, —(CH ２ ) ２ (CF ２ ) ３ CF ３ , -(CH ２ ) ２ (CF ２ ) ４ CF ３ , -(CH ２ ) ２ (CF ２ ) ６ CF ３ Examples include:

[0044] X － As for F － , Cl － ,Br － , I－ , HSO4 ― , (SO ４ ２－ ) １／２ , NO ３ ― , O.H. － Examples include:

[0045] The structural unit represented by general formula 2 is preferably a structural unit represented by the following general formula 2-2.

[0046] The structural unit represented by general formula 2 is preferably a structural unit represented by the following general formula 2-3 or 2-4.

[0047]

[0048] More preferred examples of the structural unit represented by general formula 2 include structures represented by the following general formula 2-5 and general formula 2-6.

[0049]

[0050] The side chain heteroaromatic resin preferably has a structural unit represented by general formula 2, and more preferably has a structural unit represented by general formula 1 and a structural unit represented by general formula 2.

[0051] <Cation Exchange Resin> The resin composition of the present embodiment preferably contains a cation exchange resin. The cation exchange resin is a resin having ion exchange ability for cations (hereinafter also referred to as "positive ions").

[0052] The cation exchange resin is not particularly limited, but may be either a hydrocarbon resin or a fluororesin. For applications requiring reduced production costs, hydrocarbon resins are preferred, while for applications requiring long-term durability, fluororesins are preferred. The hydrocarbon resin and the fluororesin may be used alone or in combination.

[0053] The cation exchange resin preferably contains a functional group having ion exchange ability. The functional group having ion exchange ability is not particularly limited, but may be a sulfo group (SO３ H), carboxyl group (CO ２ H), phenolic hydroxyl group (OH), phosphate group (PO ３ H ２ ), a thiol group (SH), and alkali metal salts, alkaline earth metal salts, or transition metal salts of these functional groups. The functional group having ion exchange ability may be one type alone or multiple types of functional groups.

[0054] Among functional groups having ion exchange capacity, at least one selected from a sulfo group, a carboxyl group, and a phosphate group is preferred, as these tend to have excellent ion exchange capacity, and at least one selected from a sulfo group and a carboxyl group is more preferred, with a sulfo group being particularly preferred.

[0055] The hydrocarbon resin is not particularly limited, but examples thereof include polystyrene, polyphenylene ether, polybenzimidazole, polyether ether ketone, polyimide, polyetherimide, polyaryletherketone, polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylsulfone, and the like, and includes resins having functional groups with ion exchange capacity. The hydrocarbon cation exchange resin may be crosslinked or may be a copolymer, and may have various substituents (e.g., halogen atoms such as fluorine atoms, chlorine atoms, and bromine atoms; aliphatic hydrocarbon groups such as nitrile groups, methyl groups, ethyl groups, vinyl groups, allyl groups, 1-methylvinyl groups, n-propyl groups, isopropyl groups, n-butyl groups, isobutyl groups, sec-butyl groups, and tert-butyl groups; aromatic hydrocarbon groups such as benzyl groups, phenyl groups, and nitrile-substituted phenyl groups; amino groups; nitro groups; hydroxyl groups; silyl groups, and the like). The hydrocarbon resin may be used alone or in combination of two or more types.

[0056] The fluororesin is not particularly limited, but examples thereof include partially fluorinated resins and fully fluorinated resins having functional groups with ion exchange capacity. Resins in which at least one, but not all, of the hydrogen atoms on carbon contained in the hydrocarbon cation exchange resin are substituted with a fluorine atom, and resins in which all hydrogen atoms on carbon are substituted with fluorine atoms are exemplified as partially fluorinated resins and fully fluorinated resins.

[0057] The fluororesin is preferably a fluororesin having a structural unit represented by the following general formula G1 (hereinafter also referred to as "fluororesin G1"). (In the formula, X ５ , X ６ , X ７ , and X ８ may be the same or different and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X ５ and X ６ , or X ５ and X ７ may be bonded to each other to form a cyclic structure, R ５ , and R ６ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X ９ is -COOZ, -SO ３ Z, -PO ３ Z ２ , or -PO ３ A group represented by HZ, wherein Z is at least one selected from the group consisting of a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, and an amine; ９The fluororesins may be crosslinked by ionic crosslinking via an intervening linkage, h and p represent molar ratios in all structural units contained in the resin, and are numbers that satisfy 0≦h<1, 0<p≦1, and h+p=1, i is an integer of 0 to 8, j is 0 or 1, k, l, and m may be the same or different, and are integers of 0 to 6, provided that when k, l, and m are simultaneously 0, X ９ is CF (CF ２ X １０ ) ２ and X １０ is -COOZ, -SO ３ Z, -PO ３ Z ２ , or -PO ３ HZ, where Z is the same as defined above.

[0058] X ５ , X ６ , X ７ , and X ８ may be the same or different and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X ５ and X ６ , or X ５ and X ７ may be bonded to each other to form a cyclic structure.

[0059] The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, and even more preferably 1 to 3. The perfluoroalkyl group may be linear or branched. Examples of the perfluoroalkyl group include a trimethylfluoromethyl group and a pentafluoroethyl group.

[0060] The number of carbon atoms in the cyclic perfluoroalkyl group is preferably 6 to 8. Examples of the cyclic perfluoroalkyl group include a perfluorocyclohexyl group.

[0061] X ５ , X ６ , X ７, and X ８ As the alkyl group, a fluorine atom and an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms are preferred, from the viewpoint that raw materials are easily available and the production cost of the fluororesin tends to be reduced. Furthermore, from the viewpoint that the chemical stability of the fluororesin, such as resistance to oxidation and deterioration, tends to be improved, a fluorine atom and a trifluoromethyl group are more preferred, and a fluorine atom is even more preferred.

[0062] X ５ and X ６ , or X ５ and X ７ are bonded to each other to form a cyclic structure, the cyclic structure may be, for example, a substituted or unsubstituted cyclic perfluoroalkyl structure having 5 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroether structure having 4 to 9 carbon atoms.

[0063] R ５ , and R ６ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. ５ , R ６ As the alkyl group, a fluorine atom and an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms are preferred, from the viewpoint that raw materials are easily available and the production cost of the fluororesin tends to be reduced. Furthermore, from the viewpoint that the chemical stability of the fluororesin, such as resistance to oxidation and deterioration, tends to be improved, a fluorine atom and a trifluoromethyl group are more preferred, and a fluorine atom is particularly preferred.

[0064] X ９ is -COOZ, -SO ３ Z, -PO ３ Z ２ , or -PO ３ A group represented by HZ, wherein Z is at least one selected from the group consisting of a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, and an amine; ９ The fluororesins may be crosslinked to each other by ionic crosslinking via the fluororesin.

[0065] The alkali metal atom is not particularly limited, and examples thereof include lithium atom, sodium atom, potassium atom, rubidium atom, cesium atom, and francium atom. Among these, lithium atom, sodium atom, and potassium atom are preferred from the viewpoints that raw materials are easily available and that the production cost of the fluororesin tends to be reduced, and from the same viewpoint, sodium atom and potassium atom are more preferred.

[0066] The alkaline earth metal atom is not particularly limited, and examples thereof include beryllium atoms, magnesium atoms, calcium atoms, strontium atoms, barium atoms, and radium atoms. Among these, magnesium atoms and calcium atoms are preferred from the viewpoints that raw materials are easily available and the production costs of the fluororesin G1 tend to be reduced.

[0067] The amines are not particularly limited and include NH ４ , N.H. ３ R ３０ , N.H. ２ R ３０ R ３１ , N.H.R. ３０ R ３１ R ３２ , N.R. ３０ R ３１ R ３２ R ３３ The structure of R ３０ , R ３１ , R ３２ , R ３３ may be the same or different and are substituted or unsubstituted aliphatic hydrocarbon groups having 1 to 10 carbon atoms, or substituted or unsubstituted aromatic hydrocarbon groups having 6 to 10 carbon atoms. Among these, from the viewpoint of easy availability of raw materials and tendency to reduce the production cost of the fluororesin, unsubstituted aliphatic hydrocarbon groups having 1 to 6 carbon atoms and phenyl groups are preferred, unsubstituted aliphatic hydrocarbon groups having 1 to 4 carbon atoms are more preferred, and methyl groups or ethyl groups are even more preferred. ９ When the fluororesins are ionically crosslinked with each other via an ionic crosslink, Z is an alkaline earth metal atom.

[0068] h and p are numbers that satisfy 0≦h<1, 0<p≦1, and h+p=1. i is an integer from 0 to 8. j is 0 or 1. k, l, and m may be the same or different and are integers from 0 to 6 (however, when k, l, and m are simultaneously 0, X ９ is CF (CF ２ X １０ ) ２ and X １０ is -COOZ, -SO ３ Z, -PO ３ Z ２ , -PO ３ HZ, where Z is the same as above. In the case of "substitution", the substituent is the same as the substituent exemplified in general formula 1.

[0069] From the viewpoint that the chemical stability such as oxidation degradation resistance of the fluororesin tends to be improved, and the production cost of the fluororesin tends to be reduced, the fluororesin G1 preferably contains at least one selected from the structural unit represented by the following general formula G2, the structural unit represented by the following general formula G3, the structural unit represented by the following general formula G4, and the structural unit represented by the following general formula G5. -(CF ２ -CF ２ ) - [G2] - (CF ２ -CF(-O-(CF ２ CFXO) Ｎ -A))- [G3] (wherein X is F or a perfluoroalkyl group having 1 to 3 carbon atoms, N is an integer of 0 to 5, and A is (CF ２ ) Ｍ -SO ３ H (M is an integer from 0 to 6. However, N and M cannot be 0 at the same time.) -(CF ２ -CF(-O-(CF ２ ) Ｐ -CFX(-O-(CF ２ ) Ｋ -SO ３ H)))-[G4] (wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, P represents an integer of 0 to 12, and K represents an integer of 1 to 5, provided that P and K are not both 0.) -(CF ２ -CF(-O-(CF２ ) Ｑ -CFX(-(CF ２ ) Ｌ -O-(CF ２ ) ｏ -SO ３ H)))-[G5] (wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, Q represents an integer of 0 to 12, L represents an integer of 1 to 5, and o represents an integer of 0 to 6, provided that Q and O are not 0 at the same time.)

[0070] The fluororesin G1 more preferably contains a structural unit represented by general formula G2 and at least one selected from structural units represented by general formula G3, structural units represented by general formula G4, and structural units represented by general formula G5; even more preferably contains a structural unit represented by general formula G2 and a structural unit represented by general formula G3 (wherein X is F or a trifluoromethyl group, N is an integer of 0 to 2, and M is an integer of 1 to 4); and even more preferably contains a structural unit represented by general formula G2 and a structural unit represented by general formula G3 (wherein X is F or a trifluoromethyl group, N is 0 or 1, and M is an integer of 2 to 4).

[0071] The structural unit represented by general formula G1 in fluororesin G1 is preferably a structural unit represented by general formula G1-2 below, and more preferably a structural unit represented by general formula G1-3 below.

[0072] (In the formula, h and p represent molar ratios of all structural units contained in the resin, and are numbers that satisfy 0≦h<1, 0<p≦1, and h+p=1. i is 0 or 1.)

[0073] (In the formula, h and p represent molar ratios of all structural units contained in the resin, and are numbers that satisfy 0≦h<1, 0<p≦1, and h+p=1.)

[0074] The fluororesin G1 may be obtained by directly or indirectly partially crosslinking some of the molecules of the functional groups having ion exchange capacity contained therein. The partial crosslinking tends to suppress the solubility in the electrolyte solution and the excessive swelling, which may be preferable in some cases.

[0075] Even when fluororesin G1 has a high melt flow index (hereinafter also referred to as "MFI", measured in accordance with ASTM: D1238 (measurement conditions: temperature 270°C, load 2160 g)) (when it has a low molecular weight), the partial crosslinking increases intermolecular entanglement and reduces solubility and excessive swelling.

[0076] Examples of the partial crosslinking reaction include a reaction between a functional group having ion exchange capacity and a functional group or main chain of another molecule, a reaction between functional groups having ion exchange capacity, and a crosslinking reaction (covalent bond) via a low molecular weight compound, oligomer, or polymeric substance having excellent oxidation resistance, and in some cases, a reaction with a substance that forms a salt (including an ionic bond with the functional group having ion exchange capacity). Examples of the low molecular weight compound, oligomer, or polymeric substance having excellent oxidation resistance include polyhydric alcohols and organic diamines.

[0077] The equivalent weight of fluororesin G1 is not particularly limited, but from the viewpoint of a tendency toward excellent ion exchange capacity, it is preferably 2000 g / eq or less, more preferably 1500 g / eq or less, and even more preferably 1100 or less. For applications in which fluororesin G1 is in the form of a film and the property of cation migration within the film is utilized, the equivalent weight is even more preferably 1050 g / eq or less, and even more preferably 1000 or less, since the resistance to cation migration tends to be reduced. The equivalent weight of fluororesin G1 is even more preferably 500 g / eq or more, and even more preferably 700 g / eq or more, since the water resistance and chemical resistance of the fluororesin tend to be further improved. For applications in which the fluororesin is used in the form of a film, the equivalent weight is preferably 800 g / eq or more, more preferably 880 g / eq or more, since the mechanical strength of the film tends to be improved. In addition, the equivalent weight is the dry mass (grams) of an ion exchange resin, which is a resin having ion exchange capacity, per equivalent of an ion exchange group having ion exchange capacity, and in the case of a fluororesin, it is the dry mass (grams) of a fluororesin per equivalent of an ion exchange group possessed by the fluororesin. Hereinafter, in this embodiment, the expression "equivalent weight" will be used as appropriate. In addition, the equivalent weight can be measured by a method in which the fluororesin is subjected to salt substitution and the resulting solution is back-titrated with an alkaline solution. The equivalent weight can be appropriately adjusted by the copolymerization ratio of the monomers that are the raw materials for the fluororesin G1, the selection of the monomer types, etc.

[0078] <Method for producing fluororesin G1> The method for producing fluororesin G1 is not particularly limited, but an example is a method in which a copolymer containing a fluorinated olefin monomer represented by the following general formula G8 and at least one fluorinated vinyl ether compound represented by the following general formula G9, the following general formula G10, and the following general formula G11 is used as a fluororesin G1 precursor, and the copolymer is subjected to the hydrolysis treatment and acid treatment described below. １ =CZ ２ Z ３ [G8] (In the formula, Z １ , Z ２ , Z ３may be the same or different and are a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a cyclic perfluoroalkyl group, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom.) CF ２ =CF-O-(CF ２ CFXO) Ｎ -A [G9] (wherein X is F or a perfluoroalkyl group having 1 to 3 carbon atoms, N is an integer of 0 to 5, and A is (CF ２ ) Ｍ -W (M is an integer of 0 to 6, and N and M cannot be 0 at the same time), and W is converted to -SO by hydrolysis and acid treatment. ３ CF is a functional group that can be converted to a H group. ２ =CF-O-(CF ２ ) Ｐ -CFX(-O-(CF ２ ) Ｋ -W) [G10] (wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, P represents an integer of 0 to 12, K represents an integer of 1 to 5 (provided that P and K are not 0 at the same time), and W is a group that has been converted to -SO by hydrolysis treatment and acid treatment. ３ CF is a functional group that can be converted to a H group. ２ =CF-O-(CF ２ ) Ｑ -CFX(-(CF ２ ) Ｌ -O-(CF ２ ) ｍ -W)

[11] (wherein X is a perfluoroalkyl group having 1 to 3 carbon atoms, Q is an integer of 0 to 12, L is an integer of 1 to 5 (provided that Q and L are not 0 at the same time), m is an integer of 0 to 6 (Q, L, and m are not 0 at the same time), and W is a group that has been converted to -SO by hydrolysis treatment and acid treatment. ３ It is a functional group that can be converted to an H group.

[0079] The method for producing fluororesin G1 is preferably a method in which a copolymer consisting of a fluorinated olefin monomer represented by general formula G8 and at least one fluorinated vinyl ether compound selected from the group consisting of general formula G9, general formula G10, and general formula G11 is used as a fluororesin G1 precursor, and the copolymer is subjected to hydrolysis and acid treatment. From the viewpoint of tending to improve the chemical stability of fluororesin G1, such as oxidation degradation resistance, and tending to reduce the production cost of fluororesin G1, the copolymer of general formula G8 (where Z １ , Z ２ , and Z ３ is F) and a fluorinated vinyl ether compound represented by the general formula G9 (wherein X is F or a trifluoromethyl group, N is an integer of 0 to 2, and M is an integer of 1 to 4), and １ , Z ２ , and Z ３ is F) and a fluorinated vinyl ether compound represented by the general formula G9 (wherein X is F or a trifluoromethyl group, N is 0 or 1, and M is an integer of 2 to 4). １ , Z ２ , and Z ３ is F.) and a fluorinated vinyl ether compound represented by the general formula G9 (wherein X is a trifluoromethyl group, N is 1, and M is 2).

[0080] As the fluorinated olefin monomer represented by the general formula G8, a fluorinated olefin monomer represented by the following general formula G12 is preferred, a fluorinated olefin monomer represented by the following general formula G13 is more preferred, and a fluorinated olefin monomer represented by the following general formula G14 is even more preferred: CF ２ CFZ [G12] (wherein Z is H, Cl, F, a perfluoroalkyl group having 1 to 10 carbon atoms, or a cyclic perfluoroalkyl group which may contain oxygen as a ring-constituting atom). ２CF =CFZ [G13] (wherein Z is F or a perfluoroalkyl group having 1 to 3 carbon atoms) ２ =CF ２ [G14] As the fluorinated vinyl ether compound represented by at least one selected from the group consisting of general formulas G9, G10, and G11, a fluorinated vinyl ether compound represented by the following general formula G15 is preferred, and a fluorinated vinyl ether compound represented by the following general formula G16 is more preferred: CF ２ =CF-O-(CF ２ CFXO) ｎ -A [G15] (wherein X is F or a trifluoromethyl group, n is 0 or 1, and A is (CF ２ ) ｍ -W (m is an integer of 2 to 4, and n and m are not 0 at the same time), and W is converted to -SO by hydrolysis and acid treatment. ３ CF is a functional group that can be converted to a H group. ２ =CF-O-(CF ２ CFXO) ｎ -A [G16] (wherein X is a trifluoromethyl group, n is 1, and A is (CF ２ ) ｍ -W (m is 2), and W is converted to -SO by hydrolysis and acid treatment. ３ In the above general formulae G9 to G11, G15, and G16, the —SO 3 group is a functional group that can be converted to a —H group by hydrolysis and acid treatment. ３ The functional group W that can be converted to an H group is not particularly limited, but may be SO ２ F, SO ２ Cl, SO ２ Br and the like are exemplified, and SO ２ F, SO ２ Cl is preferred, SO ２ F is more preferred.

[0081] The fluororesin G1 precursor of this embodiment can be produced by known means, for example, by polymerizing a mixture containing a fluorinated olefin monomer represented by the general formula G8 and at least one fluorinated vinyl ether compound selected from the group consisting of general formulas G9, G10, and G11, in the presence of a radical generator such as a peroxide. The polymerization method is not particularly limited, and examples thereof include a method of polymerizing the fluorinated olefin monomer gas and a fluorinated vinyl ether compound or the like by filling and dissolving them in a polymerization solvent such as a fluorinated hydrocarbon and reacting them (solution polymerization), a method of polymerizing the fluorinated vinyl ether compound as the polymerization solvent without using a solvent such as a fluorinated hydrocarbon (bulk polymerization), a method of polymerizing the fluorinated olefin monomer gas and a fluorinated vinyl ether compound or the like using an aqueous solution of a surfactant as a medium (emulsion polymerization), a method of emulsifying and polymerizing the fluorinated olefin monomer gas and a fluorinated vinyl ether compound or the like using an aqueous solution of a surfactant and an alcohol or other co-emulsifier as a medium (emulsion polymerization), and a method of suspending and reacting the fluorinated olefin monomer gas and a fluorinated vinyl ether compound or the like using an aqueous solution of a suspension stabilizer as a medium (suspension polymerization). The fluororesin G1 precursor of this embodiment may be prepared by any of the above-mentioned polymerization methods. Alternatively, the fluororesin G1 precursor may be a block-shaped or tapered polymer obtained by adjusting the polymerization conditions, such as the amount of fluorinated olefin monomer supplied. The fluororesin G1 precursor may be one obtained by treating impure terminals formed in the resin molecular structure during the polymerization reaction or structurally easily oxidized portions (CO groups, H-bond portions, etc.) under fluorine gas by a known method, thereby fluorinating the portions ...urity terminals formed in the resin molecular structure during the polymerization reaction or structurally easily oxidized portions (CO groups, H-bond portions, etc.) under fluorine gas by a known method, thereby fluorinating the portions. The fluororesin G1 precursor may be one obtained by treating impurity terminals formed in the resin molecular structure during the polymerization reaction or structurally easily oxidized portions (CO groups, H-bond portions, etc.) under fluorine gas by a known method, thereby fluorinating the portions. ２ A part of the F groups may be partially (including intermolecularly) imidized (such as alkylimidized).

[0082] The molecular weight of the fluororesin G1 precursor is not particularly limited, but the melt flow index (MFI) measured in accordance with ASTM D1238 (measurement conditions: temperature 270°C, load 2160 g) is preferably 0.05 g / 10 min or more, more preferably 0.1 g / 10 min or more, and even more preferably 0.5 g / 10 min or more. The MFI value is preferably 100 g / 10 min or less, more preferably 80 g / 10 min or less, and even more preferably 60 g / 10 min or less.

[0083] The shape of the fluororesin G1 precursor is not particularly limited, but from the viewpoint of increasing the treatment speed in the hydrolysis treatment and acid treatment described later, it is preferable to use a shape of, for example, 0.5 cm ３ The fluororesin G1 precursor is preferably in the form of pellets, dispersion liquid, or powder particles as described below. Among these, it is more preferable to use a powder form after polymerization. From the viewpoint of cost, an extrusion-molded film-like fluororesin G1 precursor may also be used.

[0084] The method for producing the fluororesin G1 of this embodiment from the fluororesin G1 precursor is not particularly limited, but examples include melt-kneading the fluororesin G1 precursor, extruding it using an extruder nozzle or die, and then subjecting it to the hydrolysis treatment described below; or polymerizing the fluororesin G1 precursor and leaving it as a dispersion, or precipitating and filtering it into a powder, and then subjecting it to the hydrolysis treatment described below. These hydrolysis treatments produce a fluororesin G1 in which Z in the general formula G1 is an alkali metal atom or alkaline earth metal atom. Acid treatment of this fluororesin G1 (Z = alkali metal atom or alkaline earth metal atom) produces a fluororesin G1 in which Z in the general formula G1 is a hydrogen atom. Furthermore, reaction of this fluororesin G1 (Z = hydrogen atom) with an amine produces a fluororesin G1 in which Z in the general formula G1 is an amine.

[0085] Specifically, the fluororesin G1 precursor obtained as described above and molded as necessary can be subsequently immersed in a basic reaction liquid and subjected to hydrolysis treatment. The basic reaction liquid used for the hydrolysis treatment is not particularly limited, but examples include aqueous solutions of amine compounds such as dimethylamine, diethylamine, monomethylamine, and monoethylamine, and aqueous solutions of alkali metal or alkaline earth metal hydroxides. Among these, aqueous solutions of sodium hydroxide or potassium hydroxide are preferred. When an alkali metal or alkaline earth metal hydroxide is used, its content is not particularly limited, but is preferably 10% by mass or more and 30% by mass or less based on the total basic reaction liquid. It is more preferred that the basic reaction liquid further contains a swelling organic compound such as methyl alcohol, ethyl alcohol, acetone, or dimethyl sulfoxide. The content of the swelling organic compound is preferably 1% by mass or more and 60% by mass or less based on the total basic reaction liquid.

[0086] The fluororesin G1 precursor is hydrolyzed in a basic reaction liquid, thoroughly washed with warm water, etc., if necessary, and then subjected to acid treatment to produce a fluororesin having a structural unit in the general formula G1 where Z is a hydrogen atom. The acid used in the acid treatment is not particularly limited, but examples include mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid, and trifluoroacetic acid. Mixtures of these acids with water are preferred. The acids may be used alone or in combination. The basic reaction liquid used in the hydrolysis treatment may be removed before the acid treatment by treatment with a cation exchange resin, for example. The hydrolyzed and acid-treated fluororesin G1 may be dispersed or dissolved in a protic organic solvent, water, or a mixture of the two, and may be formed into a suspension or solution.

[0087] Since the mechanical strength of the fluororesin G1 can be improved in some cases, it may be preferable to use a composition of two or more types of fluororesin G1 in which the structures of the raw materials constituting the fluororesin are different. By mixing two or more types of fluororesins, it may be possible to exhibit excellent properties by combining the functions of each fluororesin. From the viewpoint of increasing crystallinity and improving mechanical strength, when mixing two or more types of fluororesins, the ratio of the fluororesin having the larger equivalent weight is preferably greater than 50 mass%, more preferably greater than 55 mass%, and even more preferably greater than 60 mass%.

[0088] <Resin Composition> The resin composition according to this embodiment contains a side-chain heteroaromatic resin and a cation exchange resin. The weight ratio of the side-chain heteroaromatic resin to the cation exchange resin in the resin composition is not particularly limited, but is preferably 1:100 to 100:1. While this varies depending on the application of the resin composition according to this embodiment, when the resin composition is used as a diaphragm for a redox flow battery, the weight ratio of the side-chain heteroaromatic resin to the cation exchange resin is preferably 10:90 or more, more preferably 20:80 or more, and even more preferably 30:70 or more, from the viewpoint of suppressing elution of the side-chain heteroaromatic resin into the electrolyte. While this varies depending on the application of the mixture, when the resin composition is used as a diaphragm for a redox flow battery, the weight ratio of the side-chain heteroaromatic resin to the cation exchange resin is preferably 90:10 or less, more preferably 80:20 or less, and even more preferably 70:30 or less, because the side-chain heteroaromatic resin tends to improve power efficiency.

[0089] The resin composition according to this embodiment is preferably a styrene resin, a vinyl chloride resin, a chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a polyether ether ketone resin, a polysulfone resin, a polyether sulfone resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a polyphenylene ether resin, a polyphenylene sulfide resin, a syndiotactic polystyrene resin, a polyetherimide, a siloxane-modified polyetherimide resin, a polyamide-imide resin, a cycloolefin resin, a cycloolefin copolymer, a polyether ketone ether ketone ketone resin, a polyaryl ether ketone resin, or a perfluororesin, and may further include a styrene resin, a vinyl chloride resin, a chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a syndiotactic polystyrene resin, a cycloolefin resin, or a cycloolefin copolymer. The resins that may be included in the resin composition according to this embodiment may be used alone or in combination of two or more.

[0090] <Ion Exchange Membrane> The ion exchange membrane according to this embodiment contains a side chain heteroaromatic resin having a structural unit represented by General Formula 1, a side chain heteroaromatic resin having a structural unit represented by General Formula 2, or the resin composition according to this embodiment.

[0091] When molding a side chain heteroaromatic resin having a structural unit represented by general formula 1, a side chain heteroaromatic resin having a structural unit represented by general formula 2, or the resin composition according to this embodiment into a film, the molding method is not particularly limited, and examples include a method in which a substance containing the side chain heteroaromatic resin or the resin composition according to this embodiment is melted and extruded using an extruder nozzle or die to form a film, or a method in which the side chain heteroaromatic resin or the resin composition according to this embodiment is melted and applied to a substrate using a die, gravure roll, knife, or spray, and then dried to form a film. The resulting film of the side chain heteroaromatic resin or the resin composition according to this embodiment is also referred to as a side chain heteroaromatic resin film hereinafter. The solvent that can be used to prepare a solution of the side chain heteroaromatic resin or the resin composition is not particularly limited, and examples thereof include saturated hydrocarbon compounds such as n-pentane, n-hexane, n-octane, n-decane, cyclopentane, cyclohexane, and cyclooctane; aromatic hydrocarbon compounds such as benzene, toluene, xylene, and ethylbenzene; halogenated hydrocarbon compounds such as methylene chloride, chloroform, carbon tetrachloride, chlorobenzene, and dichlorobenzene; alcohols such as methanol, ethanol, propanol, isopropanol, butanol, hexanol, cyclohexanol, and benzyl alcohol; acetone, ethyl methyl ketone, methyl butyl ketone, methyl isobutyl ketone, and cyclohexanone. and ketones such as ethyl acetate, butyl acetate, and methyl benzoate; ethers such as diethyl ether, dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, and dioxane; polyols such as ethylene glycol, propylene glycol, and glycerin, and polymers of compounds of these polyols having two hydroxyl groups, as well as polyols; and esterified compounds of the above polymers, nitriles such as acrylonitrile and benzonitrile; nitromethane; N,N-dimethylformamide; dimethyl sulfoxide; hexamethylphosphoric triamide; carbon disulfide; fluorine-based compounds (for example, Novec (trademark) manufactured by 3M Company, Asahiklin manufactured by Asahi Glass Co., Ltd., etc.); and the like. These solvents may be used alone or in combination.

[0092] A substrate can also be used when molding the side-chain heteroaromatic resin according to this embodiment or the resin composition according to this embodiment into a film. Using a substrate may allow for more stable production of a film of the side-chain heteroaromatic resin according to this embodiment or the resin composition according to this embodiment. The material used for the substrate is not particularly limited, and examples include polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, cycloolefin polymer, polycarbonate, polyamide, polyimide, polyamideimide, polyvinyl chloride, polystyrene, polyphenylene ether, polyetheretherketone, polysulfone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyetherimide, polyimide resin, polyetherketoneetherketoneketone, polyaryletherketone, and the like. The above-mentioned materials may be modified, and may be used alone or in combination of two or more.

[0093] The ion exchange membrane according to this embodiment includes a layer (L) containing the resin composition described above and a structural unit represented by the following general formula G1: (wherein the definition of each substituent is the same as in the above-mentioned general formula G1) and a layer (M) containing a fluororesin, which are alternately provided.

[0094] By using a film containing a fluororesin (hereinafter also referred to as a fluororesin film) as the substrate for the layer (M), an ion exchange membrane having a fluororesin film (layer (M)) and a side-chain heteroaromatic resin film (layer (L)) can be obtained. Note that the layer (M) does not have to contain a side-chain heteroaromatic resin. The ion exchange resin according to this embodiment may have one layer (L) and one layer (M) (a film having one layer (M) and one layer (L) is also referred to as a "bipolar membrane"). The laminated film can be an ion exchange membrane having the properties of both the fluororesin film and the side-chain heteroaromatic resin film. Note that hereinafter, in the laminated state, the fluororesin film will also be referred to as a fluororesin layer, and the side-chain heteroaromatic resin film will also be referred to as a side-chain heteroaromatic resin layer.

[0095] The interface between the layer (L) containing the side-chain heteroaromatic resin in the ion exchange membrane and the layer (M) containing the fluororesin having a structural unit represented by general formula G1 is determined by measuring the maximum signal intensity of the peak characteristic of the side-chain heteroaromatic resin by a time-of-flight secondary ion mass spectrometer with reference to JIS K 0146:2002, where the maximum signal intensity is 1 / 10. The region where the maximum signal intensity of the peak characteristic of the side-chain heteroaromatic resin is 1 / 10 or more is called layer (L), and the region where the maximum signal intensity of the peak characteristic of the side-chain heteroaromatic resin is less than 1 / 10 is called layer (M).

[0096] The method for producing the fluororesin film (layer (M)) is not particularly limited, and can be obtained by processing a resin composition containing fluororesin G1 into a film, or by processing a resin composition containing a fluororesin G1 precursor having functional groups with ion exchange capacity by hydrolysis into a film, followed by the aforementioned hydrolysis treatment and acid treatment. For example, a method can be used in which a resin composition containing a fluororesin is melt-kneaded and then extruded using an extruder through a nozzle or a die to form a film. Another method can be used in which a resin composition containing a fluororesin G1 precursor is melt-kneaded and then extruded using an extruder through a nozzle or a die to form a film, followed by hydrolysis treatment and acid treatment to form ion exchange groups. Alternatively, a substance containing a fluororesin can be dispersed in a solvent and then cast onto a substrate to form a film.

[0097] The layer (L) can be produced by a molding method in which a side chain heteroaromatic resin having a structural unit represented by the above-mentioned general formula 1, a side chain heteroaromatic resin having a structural unit represented by the above-mentioned general formula 2, or the resin composition according to this embodiment is molded into a film.

[0098] By repeatedly applying the method for producing a side-chain heteroaromatic resin film and the method for producing a fluororesin film to the laminated film, a film in which multiple side-chain heteroaromatic resin films and fluororesin films are laminated can be produced.

[0099] A multi-layered membrane can be produced by alternately stacking bipolar membrane side-chain heteroaromatic resin membranes and fluororesin membranes and then pressing the membranes together. A three-layered membrane can also be produced by laminating two bipolar membrane side-chain heteroaromatic resin membranes or two fluororesin membranes together and then pressing the membranes together.

[0100] The side-chain heteroaromatic resin membrane of this embodiment and the ion exchange membrane having a side-chain heteroaromatic resin membrane and a fluororesin membrane (the ion exchange membrane is not particularly limited as long as it has two or more layers, and the same applies hereinafter) can be used in various applications. Examples of such applications include redox flow batteries, fuel cells, salt electrolysis, alkaline water electrolysis, and carbon dioxide reduction electrolysis. Among these, use in cells for redox flow batteries and redox flow batteries is preferred. Use in cells for redox flow batteries and redox flow batteries tends to provide superior power efficiency compared to conventionally used diaphragms.

[0101] The total thickness of the ion exchange membrane of this embodiment is not particularly limited, but in the redox flow battery cell and redox flow battery exemplified as suitable applications, it is preferably 0.01 μm or more and 200 μm or less, and more preferably 1 μm or more because the membrane tends to have improved handleability and mechanical strength. In particular, when the membrane pulsates significantly and high mechanical strength is required, it is even more preferably 10 μm or more, and particularly preferably 20 μm or more. The total thickness of the ion exchange membrane of this embodiment is more preferably 150 μm or less, even more preferably 130 μm or less, and particularly preferably 100 μm or less, because the electrical resistance when the redox flow battery cell and redox flow battery are operated tends to be suppressed and the power efficiency tends to be improved.

[0102] The thickness of layer (L) (side-chain heteroaromatic resin film) in the ion exchange membrane of this embodiment is not particularly limited, but in the redox flow battery cell and redox flow battery exemplified as suitable applications, it is preferably 0.01 μm or more and 10 μm or less. When used in a redox flow battery cell and redox flow battery, it tends to be possible to further suppress permeation of redox active substances through the membrane, so it is more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. When the side-chain heteroaromatic resin film has large pulsation and high mechanical strength is required, the thickness of layer (L) (side-chain heteroaromatic resin film) is particularly preferably 0.3 μm or more, even more particularly preferably 0.4 μm or more. When the redox flow battery cell and redox flow battery are operated, it tends to suppress electrical resistance and improve power efficiency, so it is more preferably 7 μm or less, even more preferably 5 μm or less, particularly preferably 3 μm or less, and even more particularly preferably 2 μm or less.

[0103] The equivalent weight of the ion exchange membrane is not particularly limited, but is preferably 500 g / eq or more and 2000 g / eq or less, more preferably 700 g / eq or more and even more preferably 800 g / eq or more, since the handleability and mechanical strength of the membrane tend to be improved. In particular, when the membrane pulsates significantly and high mechanical strength is required, the equivalent weight is particularly preferably 880 g / eq or more and even more preferably 900 g / eq or more. The equivalent weight of the ion exchange membrane is more preferably 1500 g / eq or less, even more preferably 1400 g / eq or less, particularly preferably 1200 g / eq or less, and even more particularly preferably 1150 g / eq or less, since the electrical resistance when the redox flow battery cell and the redox flow battery are operated tends to be suppressed and the power efficiency tends to be improved.

[0104] Second Embodiment Next, a second embodiment will be described.

[0105] Patent Document 1 discloses the use of an aromatic polysulfone polymer as an anion exchange base layer to improve current efficiency and power efficiency. However, although the current efficiency is excellent, it has been shown that the cell resistance increases and the voltage efficiency decreases. Therefore, an anion exchange base layer with a well-balanced current efficiency, voltage efficiency, and current efficiency is needed. Patent Document 2 discloses Nafion® 117 reacted with several heterocyclic molecules to improve vanadium ion permeation selectivity while suppressing an increase in proton surface resistance. However, attempts to reduce proton surface resistance result in reduced vanadium ion permeation selectivity, while attempts to increase vanadium ion permeation selectivity result in increased proton surface resistance. Thus, achieving both has remained a challenge. Furthermore, the examples do not involve evaluation as a redox flow battery, and the current efficiency, voltage efficiency, and power efficiency are unknown. However, since the proton surface resistance in the examples is higher than that of Nafion® 117, it can be inferred that the voltage efficiency is lower than that of Nafion® 117. For these reasons, there is a demand for a material that exhibits excellent and well-balanced current efficiency, voltage efficiency, and current efficiency. Patent Document 3 discloses the provision of a crossover prevention layer, which is a metal layer formed by reducing a cationic metal, inside a polymer electrolyte membrane in order to improve at least one of the properties of discharge capacity, current efficiency, voltage efficiency, and power efficiency. However, even higher properties are required. Patent Document 4 discloses the use of several polymer compounds as an anion exchange resin layer in order to achieve high power efficiency. However, it has been shown that when an anion exchange resin layer is not positioned between the ion exchange resin layer and the anion exchange resin layer, high power efficiency may be obtained as an initial property, but high power efficiency cannot be obtained after 100 cycles. For this reason, there is a demand for the anion exchange compound contained in the anion exchange resin layer used in Patent Document 4 to have even higher properties.

[0106] The object of the present embodiment relates to an ion exchange membrane, a membrane electrode assembly, a cell for a redox flow battery, and a redox flow battery that can provide a cell for a redox battery having a well-balanced excellent current efficiency and voltage efficiency and high power efficiency.

[0107] As a result of intensive research into the above-mentioned problems, the present inventors have found that by using a heteroaromatic structure-containing fluororesin having a specific structural unit, a saponified product thereof, or a salt thereof as an ion exchange membrane, it is possible to provide a redox battery cell that has a well-balanced excellent current efficiency and voltage efficiency and also has high power efficiency.

[0108] <Ion Exchange Membrane According to Second Embodiment> The ion exchange membrane according to the second embodiment includes a layer (L1) containing a heteroaromatic structure-containing fluororesin having a structural unit represented by the following general formula A1, a saponified product thereof, or a salt thereof; (In the formula, X １ , X ２ , X ３ , and X ４ may be the same or different and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X １ and X ２ , or X １ and X ３ may be bonded to each other to form a cyclic structure, R １ , R ２ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; R ３ is a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 1 to 10 carbon atoms; R ４ is NR ３and Hc, and is a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms; １０ is -CO ２ -, -SO ２ -, a divalent group represented by the formula: Hc is a substituted or unsubstituted heteroaromatic group containing at least one nitrogen atom, having a 5-membered ring and / or a 6-membered ring structure, and having 4 to 30 carbon atoms; a and g represent molar ratios in all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1; b is an integer from 0 to 8; c is 0 or 1; d, e, and f may be the same or different, and are integers from 0 to 6, provided that d, e, and f are not simultaneously 0.) The present invention has a layer (M1) containing a fluororesin (G1) having a structural unit represented by general formula G1, and

[0109] According to the present embodiment, it is possible to provide an ion exchange membrane, a membrane electrode assembly, a cell for a redox flow battery, and a redox flow battery that can provide a cell for a redox battery having a well-balanced excellent current efficiency and voltage efficiency and high power efficiency.

[0110] <Fluororesin Having a Heteroaromatic Structure> The fluororesin having a heteroaromatic structure according to this embodiment has a structural unit represented by the following general formula A1.

[0111] X １ , X ２ , X ３ , and X ４ may be the same or different and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X １ and X ２ , or X １ and X ３ may be bonded to each other to form a cyclic structure. １ , X ２ , X３ and X ４ As the substituent, a fluorine atom or an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms is preferred, from the viewpoint that raw materials are easily available and the production cost of the heteroaromatic structure-containing fluororesin tends to be reduced. Furthermore, from the viewpoint that the chemical stability such as oxidation degradation resistance of the heteroaromatic structure-containing fluororesin tends to be improved, a fluorine atom or a trifluoromethyl group is more preferred, and a fluorine atom is particularly preferred.

[0112] R １ , and R ２ may be the same or different and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, chlorine atom, bromine atom, or iodine atom. １ , and R ２ As the substituent, a fluorine atom or an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms is preferred, from the viewpoint that raw materials are easily available and the production cost of the heteroaromatic structure-containing fluororesin tends to be reduced. Furthermore, from the viewpoint that the chemical stability of the heteroaromatic structure-containing fluororesin, such as resistance to oxidation and deterioration, tends to be improved, a fluorine atom or a trifluoromethyl group is more preferred, and a fluorine atom is particularly preferred.

[0113] In the case of "substitution", the substituent is the same as the substituent exemplified in general formula 1.

[0114] R ３ R is a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms. ３As the substituent, from the viewpoints of easy availability of raw materials and tendency to be able to suppress the production cost of the heteroaromatic structure-containing fluororesin, a hydrogen atom or an aliphatic hydrocarbon group having 1 to 10 carbon atoms is preferred, and a hydrogen atom or an unsubstituted aliphatic hydrocarbon group having 1 to 4 carbon atoms is more preferred. From the viewpoint of suppressing the production cost of the heteroaromatic structure-containing fluororesin, a hydrogen atom is more preferred, and from the viewpoint of improving the stability of the heteroaromatic structure-containing fluororesin under alkaline conditions, an unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms is even more preferred. In the case of "substitution", the substituent is the same as the substituent exemplified in general formula 1.

[0115] R ４ is NR ３ and Hc, and is a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms. ４ As the substituent, from the viewpoints of easy availability of raw materials and tendency to suppress the production cost of the heteroaromatic structure-containing fluororesin, an unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms is preferred, an unsubstituted aliphatic hydrocarbon group having 1 to 6 carbon atoms is more preferred, and an unsubstituted aliphatic hydrocarbon group having 1 to 4 carbon atoms is even more preferred. From the viewpoint of tendency to improve the chemical stability of the heteroaromatic structure-containing fluororesin, such as resistance to oxidation and deterioration, an unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms is particularly preferred, and an unsubstituted aliphatic hydrocarbon group having 1 carbon atom is even more particularly preferred. In addition, when "substituted", the substituent is the same as the substituent exemplified in general formula 1.

[0116] X １０ is -CO ２ -, -SO ２ From the viewpoint that the chemical stability such as oxidation deterioration resistance of the heteroaromatic structure-containing fluororesin tends to be improved, -SO ２ A divalent group represented by the formula: - is preferred.

[0117] Hc is a substituted or unsubstituted heteroaromatic group containing at least one nitrogen atom, a 5-membered ring and / or a 6-membered ring structure, and having 4 to 30 carbon atoms. The 5-membered ring and / or 6-membered ring structure in Hc is not particularly limited, and examples thereof include an imidazole structure, a benzimidazole structure, an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a pyridazine structure, a pyrimidine structure, a cinnoline structure, a quinazoline structure, a phthalazine structure, a quinoxaline structure, a pteridine structure, a purine structure, a 2,2'-bipyridyl structure, a 2,3'-bipyridyl structure, a 2,4'-bipyridyl structure, a 1,7-phenanthroline structure, a 1,10-phenanthroline structure, and a 2,2':6',2''-terpyridine structure. The above-exemplified structures of Hc may be one type alone, or multiple types may be present. The above-exemplified Hc structures may be used alone or in combination of two or more structures.

[0118] Since Hc has at least one nitrogen atom in the heteroaromatic ring structure, among the above-mentioned 5-membered ring and / or 6-membered ring structures, it is preferably an imidazole structure, a benzimidazole structure, an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a 2,2'-bipyridyl structure, a 2,3'-bipyridyl structure, a 2,4'-bipyridyl structure, a 1,7-phenanthroline structure, or a 1,10-phenanthroline structure, and it is preferably an imidazole structure, a benzimidazole structure, an imidazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a 2,2'-bipyridyl structure, a 2,3'-bipyridyl structure, a 2,4'-bipyridyl structure, a 1,7-phenanthroline structure, or a 1,10-phenanthroline structure. The heteroaromatic structure-containing fluororesin preferably has a midazopyridine structure, a pyridine structure, an oxazole structure, a thiazole structure, a 2,2′-bipyridyl structure, or a 1,10-phenanthroline structure, and more preferably has an imidazole structure, a benzimidazole structure, an imidazopyridine structure, or a pyridine structure, and particularly preferably has an imidazole structure or a pyridine structure, since durability tends to be improved when the heteroaromatic structure-containing fluororesin is used in a redox flow battery cell.

[0119] H Ｃ The substituents in are the same as those exemplified in general formula 1.

[0120] Examples of Hc include an imidazolyl group, a benzimidazolyl group, an imidazopyridinyl group, a pyridinyl group, an oxazolyl group, a thiazolyl group, a pyridazinyl group, a pyrimidinyl group, a cinnolinyl group, a quinazolinyl group, a phthalazinyl group, a quinoxalinyl group, a pteridinyl group, a purinyl group, a 2,2'-bipyridinyl group, a 2,3'-bipyridinyl group, a 2,4'-bipyridinyl group, a 1,7-phenanthrolinyl group, a 1,10-phenanthrolinyl group, and a 2,2':6',2''-terpyridinyl group. Among these, an imidazolyl group or a pyridinyl group is preferred.

[0121] In the above heteroaromatic structure-containing fluororesin, from the viewpoint that the chemical stability such as oxidation degradation resistance of the heteroaromatic structure-containing fluororesin tends to be improved, and from the viewpoint that the production cost of the heteroaromatic structure-containing fluororesin can be reduced, and the production cost of the redox flow battery cell tends to be reduced, it is preferable that the heteroaromatic structure-containing fluororesin contains at least one structural unit selected from the group consisting of a structural unit represented by the following general formula A4, a structural unit represented by the following general formula A5, and a structural unit represented by the following general formula A6. -(CF ２ -CF ２ ) - [A2] - (CF ２ -CF(-O-(CF ２ CFXO) Ｎ -Ag))- [A4] (wherein X represents F or a perfluoroalkyl group having 1 to 3 carbon atoms. Ag represents the (CF ２ ) ｆ -X １０ -NR ３ -R ４ -Hc. N represents an integer of 0 to 5. ) ), -(CF ２ -CF(-O-(CF ２ ) Ｐ -CFX(-O-(CF ２ ) Ｋ -SO ２ NX ４１ Ax)))-[A5] (wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms. X ４１represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group; Ax represents -R ４ -Hc. P represents an integer from 0 to 12, and K represents an integer from 1 to 5. However, P and K cannot be 0 at the same time.) -(CF ２ -CF(-O-(CF ２ ) Ｑ -CFX(-(CF ２ ) Ｌ -O-(CF ２ ) ｏ -SO ２ NX ４１ Ax)))-[A6] (wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms. X ４１ represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group; Ax represents -R ４ -Hc. Q represents an integer of 0 to 12, L represents an integer of 1 to 5, and o represents an integer of 0 to 6. However, Q and O cannot be 0 at the same time.

[0122] The heteroaromatic structure-containing fluororesin more preferably comprises at least one selected from the group consisting of a structural unit represented by general formula A2, a structural unit represented by general formula A4, a structural unit represented by general formula A5, and a structural unit represented by general formula A6, still more preferably comprises a structural unit represented by general formula A2 and a structural unit represented by general formula A4 (wherein X is F or a trifluoromethyl group, N is an integer of 0 to 2, and f is an integer of 1 to 4), and particularly preferably comprises a structural unit represented by general formula A2 and a structural unit represented by general formula A4 (wherein X is F or a trifluoromethyl group, N is 0 or 1, and f is an integer of 2 to 4).

[0123] The heteroaromatic structure-containing fluororesin more preferably contains a structural unit represented by the following general formula A1-1, and even more preferably contains a structural unit represented by the following general formula A1-2: -[CF ２ CF ２ ]ａ -[CF ２ -CF((-O-CF ２ -(CF(CF ３ ))) ｂ -O-(CF ２ ) ２ -SO ２ NX ４１ Ax)] ｇ - [A1-1] (wherein, X ４１ represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group; Ax represents -R ４ -Hc. a and g represent the molar ratios of all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1. b is 0 or 1.) -[CF ２ CF ２ ] ａ -[CF ２ -CF((-O-CF ２ -(CF(CF ３ )))-O-(CF ２ ) ２ -SO ２ NX ４１ Ax)] ｇ - [A1-2] (wherein, X ４１ represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group; Ax represents -R ４ -Hc. a and g represent the molar ratios of all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1.)

[0124] In the above general formulae A5, A6, A1-1, and A1-2, from the viewpoint that raw materials are easily available and the production cost of the heteroaromatic structure-containing fluororesin tends to be reduced, X ４１is preferably a hydrogen atom or an aliphatic hydrocarbon group having 1 to 10 carbon atoms, more preferably a hydrogen atom or an unsubstituted aliphatic hydrocarbon group having 1 to 4 carbon atoms. From the viewpoint of reducing the production cost of the heteroaromatic structure-containing fluororesin, a hydrogen atom is more preferred, and from the viewpoint of improving the stability of the heteroaromatic structure-containing fluororesin under alkaline conditions, an unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms is more preferred.

[0125] The method for producing the heteroaromatic structure-containing fluororesin is not particularly limited, but an example is a method in which a fluororesin precursor described below is reacted with a modifying compound. The modifying compound has at least two nitrogen atom-containing groups. At least one of the nitrogen atom-containing groups is a substituted or unsubstituted heteroaromatic group (corresponding to Hc) containing at least one nitrogen atom, including a 5-membered ring and / or a 6-membered ring structure, and having 4 to 30 carbon atoms. Furthermore, at least one of the nitrogen atom-containing groups is a primary amino group or a secondary amino group. From the viewpoint of improving the reactivity of the modifying compound with the fluororesin precursor, a primary amino group is preferred, and from the viewpoint of improving the stability of the heteroaromatic structure-containing fluororesin, a secondary amino group is preferred. Other examples of the nitrogen-containing group that may be contained in the modifying compound include an amino salt structure of at least one amino group selected from the group consisting of primary amino groups, secondary amino groups, and tertiary amino groups with at least one selected from the group consisting of acidic substances and halogen-containing aliphatic hydrocarbon compounds, a salt structure of a nitrogen-containing heterocyclic structure with at least one selected from the group consisting of acidic substances and halogen-containing aliphatic hydrocarbon compounds, and a quaternary ammonium group, etc. However, the quaternary ammonium group is a quaternary ammonium group different from the amino salt structure and the salt structure.

[0126] More specific examples of the modified compounds include 1-(3-aminopropyl)imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4-(ethylaminomethyl)pyridine, 4-(4-piperidyl)pyridine, 2-methyltryptamine, 5-methoxytryptamine, 6-methoxytryptamine, necrostatin-1, alosetron, sulfamethoxypyridazine, 1-(3-chloroanilino)-4-phenylpropanol, and the like. Examples of the modified compounds include quinolazine, 4-amino-5-aminomethyl-2-methylpyrimidine, 2-(aminomethyl)-5-methylpyrazine, 2-(4-piperidinyl)benzimidazole, 2-(4-aminophenyl)benzimidazole, 5-amino-2-(4-aminophenyl)benzimidazole, 6-(aminomethyl)quinoline, 2-methyl-7-[phenyl(phenylamino)methyl]-8-quinolinol, and 1-(2-amino-1-naphthyl)isoquinoline. These modified compounds may be used alone or in combination.

[0127] From the viewpoints that modified compounds are easily available and that the production cost of the heteroaromatic structure-containing fluororesin tends to be reduced, 1-(3-aminopropyl)imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4-(ethylaminomethyl)pyridine, 4-(2-aminoethyl)pyridine, 4-(4-piperidyl)pyridine, 2-(4-piperidinyl)benzimidazole, 2-(4-aminophenyl)benzimidazole, and 5-amino-2-(4-aminophenyl)benzimidazole are preferred. Preferably, it is at least one selected from the group consisting of 1-(3-aminopropyl)imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4-(4-piperidyl)pyridine, and 2-(4-aminophenyl)benzimidazole, more preferably, it is at least one selected from the group consisting of 1-(3-aminopropyl)imidazole, 4-picolylamine, and 4-(2-aminoethyl)pyridine.

[0128] The heteroaromatic structure-containing fluororesin of this embodiment has a sulfonamide bond (—SO ２ The presence of a sulfonamide bond in the heteroaromatic structure-containing fluororesin can be determined by a general analytical method, and examples of analytical devices that can be used include FT-IR and TOF-SIMS.

[0129] The heteroaromatic structure-containing fluororesin of the present embodiment may be a saponified product thereof or a salt thereof.

[0130] The saponified product of the heteroaromatic structure-containing fluororesin is a saponified product obtained by reacting the heteroaromatic structure-containing fluororesin with an alkaline substance. Examples of the basic substance include amine compounds such as dimethylamine, diethylamine, monomethylamine, and monoethylamine, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkaline earth metal hydroxides. Among these, sodium hydroxide or potassium hydroxide is preferred.

[0131] The salt of the heteroaromatic structure-containing fluororesin is a salt of the heteroaromatic structure-containing fluororesin with an acidic substance, such as mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid, and trifluoroacetic acid.

[0132] <Fluororesin G1> The heteroaromatic structure-containing fluororesin of this embodiment may be used as a resin composition mixed with other resins. The resin composition may contain the heteroaromatic structure-containing fluororesin of this embodiment and fluororesin G1. In this embodiment, a mixture of fluororesins, such as a composition containing the heteroaromatic structure-containing fluororesin and fluororesin G1, is referred to as a resin composition. The fluororesin G1 is a fluororesin having ion exchange ability for cations (hereinafter also referred to as "positive ions").

[0133] The fluororesin G1 has a structural unit represented by the following general formula G1. (In the formula, the definition of each substituent is the same as in the general formula G1 described above.) The preferred fluororesin G1 is also as described above.

[0134] The weight ratio of the heteroaromatic structure-containing fluororesin to the fluororesin G1 in the resin composition is not particularly limited, but is preferably 1:100 to 100:1. Although it varies depending on the application of the resin composition according to this embodiment, when used as a diaphragm for a redox flow battery, from the viewpoint of suppressing elution of the heteroaromatic structure-containing fluororesin into the electrolyte, the weight ratio of the heteroaromatic structure-containing fluororesin to the fluororesin G1 is preferably 5:95 or more, more preferably 10:90 or more, and even more preferably 15:85 or more. Although it varies depending on the application of the mixture, when used as a diaphragm for a redox flow battery, the weight ratio of the heteroaromatic structure-containing fluororesin to the fluororesin G1 tends to improve power efficiency, so it is preferably 90:10 or less, more preferably 80:20 or less, and even more preferably 70:30 or less.

[0135] The content of the heteroaromatic structure-containing fluororesin in the resin composition is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Although it varies depending on the application of the mixture, when used as a diaphragm for a redox flow battery, the heteroaromatic structure-containing fluororesin tends to improve power efficiency, so the content of the heteroaromatic structure-containing fluororesin in the resin composition is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0136] When a heteroaromatic structure-containing fluororesin having a structural unit represented by general formula A1 is used, the ratios of the various resins are exemplified as follows: The weight ratio of the side-chain nitrogen atom-containing fluororesin to the fluororesin G1 in the resin composition is not particularly limited, but is preferably 1:100 to 100:1. Although it varies depending on the application of the resin composition according to this embodiment, when used as a diaphragm for a redox flow battery, from the viewpoint of suppressing elution of the heteroaromatic structure-containing fluororesin into the electrolyte, the weight ratio of the side-chain nitrogen atom-containing fluororesin to the fluororesin G1 is preferably 10:90 or more, more preferably 20:80 or more, and even more preferably 30:70 or more. Although it varies depending on the application of the mixture, when used as a diaphragm for a redox flow battery, the weight ratio of the side-chain nitrogen atom-containing fluororesin to the fluororesin G1 tends to improve power efficiency due to the side-chain nitrogen atom-containing fluororesin, so it is preferably 90:10 or less, more preferably 80:20 or less, and even more preferably 70:30 or less.

[0137] The content of the fluororesin having a nitrogen atom in a side chain in the resin composition is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. Although it varies depending on the application of the mixture, when used as a diaphragm for a redox flow battery, the fluororesin having a nitrogen atom in a side chain tends to improve power efficiency, so the content of the fluororesin having a nitrogen atom in a side chain in the resin composition is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0138] The resin composition according to this embodiment is preferably a styrene resin, a vinyl chloride resin, a chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a polyether ether ketone resin, a polysulfone resin, a polyether sulfone resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a polyphenylene ether resin, a polyphenylene sulfide resin, a syndiotactic polystyrene resin, a polyetherimide, a siloxane-modified polyetherimide resin, a polyamideimide resin, a cycloolefin resin, a cycloolefin copolymer, a polyether ketone ether ketone ketone resin, a polyaryl ether ketone resin, or a fluororesin, and may further include a styrene resin, a vinyl chloride resin, a chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a syndiotactic polystyrene resin, a cycloolefin resin, or a cycloolefin copolymer. The resins that may be included in the resin composition according to this embodiment may be used alone or in combination.

[0139] <Ion Exchange Membrane> The ion exchange membrane according to this embodiment contains the heteroaromatic structure-containing fluororesin or the resin composition according to this embodiment.

[0140] When the resin composition that contains the fluororesin containing heteroaromatic structure is molded into film, molding method is not particularly limited, and can be made into film by the method that the resin composition that contains the fluororesin containing heteroaromatic structure is made into a molten state, and extruded by the nozzle or die etc. of an extruder, or the method that the resin composition that contains the fluororesin containing heteroaromatic structure is made into a solution state, and is applied to a substrate by a die, a gravure roll, a knife or a spray, and is dried, and is made into film.The film of the fluororesin that obtains the fluororesin containing heteroaromatic structure is also referred to below as the fluororesin film that contains heteroaromatic structure.

[0141] The solvent that can be used when preparing a solution of the heteroaromatic structure-containing fluororesin is not particularly limited, and examples thereof include saturated hydrocarbon compounds such as n-pentane, n-hexane, n-octane, n-decane, cyclopentane, cyclohexane, and cyclooctane; aromatic hydrocarbon compounds such as benzene, toluene, xylene, and ethylbenzene; halogenated hydrocarbon compounds such as methylene chloride, chloroform, carbon tetrachloride, chlorobenzene, and dichlorobenzene; alcohols such as methanol, ethanol, propanol, isopropanol, butanol, hexanol, cyclohexanol, and benzyl alcohol; acetone, ethyl methyl ketone, methyl butyl ketone, methyl isobutyl ketone, and cyclohexanone. and ketones such as ethyl acetate, butyl acetate, and methyl benzoate; ethers such as diethyl ether, dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, and dioxane; polyols such as ethylene glycol, propylene glycol, and glycerin, and polymers of compounds of these polyols having two hydroxyl groups, as well as polyols; and esterified compounds of the above polymers, nitriles such as acrylonitrile and benzonitrile; nitromethane; N,N-dimethylformamide; dimethyl sulfoxide; hexamethylphosphoric triamide; carbon disulfide; fluorine-based compounds (for example, Novec (trademark) manufactured by 3M Company, Asahiklin manufactured by Asahi Glass Co., Ltd., etc.); and the like. The solvent may be used alone or in combination.

[0142] When forming a composition containing a heteroaromatic structure-containing fluororesin into a film, a substrate can also be used. By using a substrate, a film of a composition containing a heteroaromatic structure-containing fluororesin can sometimes be more stably produced. The material used for the substrate is not particularly limited, and examples include polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, cycloolefin polymer, polycarbonate, polyamide, polyimide, polyamideimide, polyvinyl chloride, polystyrene, polyphenylene ether, polyetheretherketone, polysulfone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyetherimide, polyimide resin, polyetherketoneetherketoneketone, polyaryletherketone, etc. The material used for the substrate may be modified, and may be used alone or in combination of multiple types.

[0143] The ion exchange membrane according to this embodiment comprises a layer (L1) containing the above-described heteroaromatic structure-containing fluororesin and a layer (L2) having a structural unit represented by the following general formula G1: (wherein the definition of each substituent is the same as in the above-mentioned general formula G1) and a layer (M1) containing a fluororesin, and the layer (M2) and the layer (M3) are alternately provided.

[0144] By using a membrane containing fluororesin G1 (hereinafter also referred to as fluororesin membrane) as the substrate for layer (M1), an ion exchange membrane having a fluororesin membrane (M1) and a heteroaromatic structure-containing fluororesin membrane (L1) can be obtained. Note that layer (M1) does not have to contain a heteroaromatic structure-containing fluororesin. The ion exchange resin according to this embodiment may have one layer (L1) and one layer (M1) (an ion exchange membrane having one layer (L1) and one layer (M1) is also referred to as a "bipolar membrane"). The laminated membrane can be an ion exchange membrane having the properties of both the fluororesin G1 and the heteroaromatic structure-containing fluororesin. Note that hereinafter, in the laminated state, the fluororesin membrane will also be referred to as a fluororesin layer, and the heteroaromatic structure-containing fluororesin membrane will also be referred to as a heteroaromatic structure-containing fluororesin layer.

[0145] The interface between the layer (L1) containing the heteroaromatic structure-containing fluororesin contained in the ion exchange membrane and the layer (M1) containing the fluororesin having a structural unit represented by the general formula G1 is measured by a time-of-flight secondary ion mass spectrometer with reference to JIS K 0146:2002. ２ The presence or absence of an interface is determined from the value at which the maximum signal intensity (m / z 78, two peaks are detected but the lower mass peak is used) is 1 / 10. ２ The region where the maximum signal intensity of the peak is 1 / 10 or more is called the layer (L), and the NSO ２ The region where the maximum signal intensity of the peak is less than 1 / 10 is defined as a layer (M).

[0146] The method for producing the fluororesin film is as described above.

[0147] As a method for forming a heteroaromatic structure-containing fluororesin into a film, a heteroaromatic structure-containing fluororesin film can be produced by reacting a fluororesin G1 precursor film with a modifying compound and then hydrolyzing the resulting film. Furthermore, an acid treatment can also be performed. That is, a saponified product of the heteroaromatic structure-containing fluororesin film can be obtained by hydrolysis, and a salt of the heteroaromatic structure-containing fluororesin film can be obtained by acid treatment. The hydrolysis and acid treatments are similar to those of the general formula G1. When using this method, by controlling the reaction between the fluororesin G1 precursor and the modifying compound, a film in which the heteroaromatic structure-containing fluororesin film and the fluororesin film are integrated can be obtained, which is suitable for cases where it is desired to improve the adhesion between the heteroaromatic structure-containing fluororesin film and the fluororesin film. In addition, in the film obtained by this method, the distribution of the heteroaromatic structure-containing fluororesin within the film can also be controlled by controlling the reaction between the fluororesin precursor and the modifying compound. To give a specific example, the reaction proceeds from the point where the fluororesin G1 precursor film and the modified compound come into contact, so that a film can be formed in which the concentration of the heteroaromatic structure-containing fluororesin has a gradient from the point of contact.

[0148] The ion exchange membrane containing the heteroaromatic structure-containing fluororesin membrane of this embodiment, and the ion exchange membrane containing the heteroaromatic structure-containing fluororesin membrane and the fluororesin membrane (the ion exchange membrane is not particularly limited as long as it has two or more layers, and the same applies hereinafter) can be used in various applications. Examples of such applications include redox flow batteries, fuel cells, salt electrolysis, alkaline water electrolysis, and carbon dioxide reduction electrolysis, and among these, use in cells for redox flow batteries and redox flow batteries is preferred. Use in cells for redox flow batteries and redox flow batteries tends to provide superior power efficiency compared to conventionally used diaphragms.

[0149] The total thickness of the ion exchange membrane according to the present embodiment is not particularly limited, but in the case of a cell for a redox flow battery and a redox flow battery, which are exemplified as suitable applications, it is preferably 0.01 μm or more and 200 μm or less, and more preferably 1 μm or more because this tends to improve the handleability and mechanical strength of the membrane. In particular, when the membrane pulsates significantly and high mechanical strength is required, it is even more preferably 10 μm or more, and particularly preferably 20 μm or more. In order to suppress the electrical resistance when the cell for a redox flow battery and the redox flow battery are operated and to tend to improve the power efficiency, it is more preferably 150 μm or less, even more preferably 130 μm or less, and particularly preferably 100 μm or less.

[0150] The thickness of layer (L1) (heteroaromatic structure-containing fluororesin membrane) in the ion exchange membrane according to this embodiment is not particularly limited, but in the redox flow battery cell and redox flow battery exemplified as suitable applications, it is preferably 0.001 μm or more and 10 μm or less. When used in a redox flow battery cell and a redox flow battery, the thickness of layer (L1) tends to be able to further suppress the permeation of the redox active substance through the membrane, so it is more preferably 0.01 μm or more, and even more preferably 0.1 μm or more. When the pulsation of the heteroaromatic structure-containing fluororesin membrane is large and high mechanical strength is required, it is particularly preferably 0.2 μm or more, and even more particularly preferably 0.3 μm or more. The thickness of the layer (L1) is more preferably 7 μm or less, further preferably 5 μm or less, particularly preferably 3 μm or less, and even particularly preferably 1 μm or less, because electrical resistance is suppressed and power efficiency tends to improve when the redox flow battery cell and the redox flow battery are operated.

[0151] The equivalent weight of the ion exchange membrane according to the present embodiment is not particularly limited, but is preferably 500 g / eq or more and 2000 g / eq or less, more preferably 700 g / eq or more and even more preferably 800 g / eq or more, since the handleability and mechanical strength of the membrane tend to be improved. In particular, when the membrane pulsates significantly and high mechanical strength is required, the equivalent weight is particularly preferably 880 g / eq or more and even more particularly preferably 900 g / eq or more. The equivalent weight of the ion exchange membrane according to the present embodiment is more preferably 1500 g / eq or less, even more preferably 1400 g / eq or less, particularly preferably 1200 g / eq or less, and even more particularly preferably 1150 g / eq or less, since the electrical resistance during operation of the redox flow battery cell and the redox flow battery tends to be suppressed and the power efficiency tends to be improved.

[0152] The ion exchange membrane of the second embodiment according to another embodiment includes a layer (L3) containing a fluororesin having a nitrogen atom in a side chain and a structural unit represented by the following general formula A3, a saponified product thereof, or a salt thereof; (In the formula, X ２０ , X ２１ , X ２２ , and X ２３ may be the same or different and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X ２０ and X ２１ , or X ２０ and X ２２ may form a cyclic structure, R ２０ , and R ２１ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; R ２２ , and R ２４ is a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms; R ２６ , and R ２７ is a hydrogen atom or a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, and R ２６ , and R ２７ at least one of R is a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms; ２３ , and R ２５ may be the same or different, and each represents a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms; when h is 2 or more, the repeated R ２３ may be the same or different, X ２４ is -CO ２ - or -SO２ a and g represent molar ratios in all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1; b is an integer of 0 to 8; c is 0 or 1; d, e, f, and h may be the same or different and are integers of 0 to 6, provided that d, e, and f are not simultaneously 0. A layer (M3) containing a fluororesin (G1) having a structural unit represented by the following general formula G1; (wherein the definition of each substituent is the same as in the above-mentioned general formula G1).

[0153] <Fluororesin A3 Having a Nitrogen Atom in a Side Chain> The fluororesin A3 having a nitrogen atom in a side chain has a structural unit represented by the following general formula A3: Hereinafter, the fluororesin having a nitrogen atom in a side chain and a structural unit represented by the general formula A3 will also be referred to as "fluororesin A3 having a nitrogen atom in a side chain".

[0154] X ２０ , X ２１ , X ２２ , and X ２３ may be the same or different and are each a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X ２０ and X ２１ , or X ２０ and X ２２ may form a cyclic structure. ２０ , X ２１ , X ２２ , and X ２３ As the alkyl group, a fluorine atom and an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms are preferred, from the viewpoint that raw materials are easily available and the production cost of the fluororesin having a nitrogen atom in a side chain tends to be reduced. Furthermore, from the viewpoint that the chemical stability of the fluororesin having a nitrogen atom in a side chain tends to be improved, such as resistance to oxidation and deterioration, a fluorine atom and a trifluoromethyl group are more preferred, and a fluorine atom is particularly preferred.

[0155] R２０ , and R ２１ may be the same or different and are each a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, chlorine atom, bromine atom, or iodine atom. ２０ , and R ２１ As the alkyl group, a fluorine atom and an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms are preferred, from the viewpoints that raw materials are easily available and that the production cost of the fluororesin having a nitrogen atom in a side chain tends to be reduced. Furthermore, from the viewpoint that the chemical stability of the fluororesin having a nitrogen atom in a side chain tends to be improved, such as resistance to oxidation and deterioration, a fluorine atom and a trifluoromethyl group are more preferred, and a fluorine atom is particularly preferred.

[0156] R ２２ , and R ２４ may be the same or different and are each a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms. ２２ , and R ２４ As R, from the viewpoints that raw materials are easily available and that the production cost of the side chain nitrogen atom-containing fluororesin tends to be suppressed, a hydrogen atom or an unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms is preferred, and a hydrogen atom or an unsubstituted aliphatic hydrocarbon group having 1 to 4 carbon atoms is more preferred. ２４ is more preferably a hydrogen atom or an unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms, and particularly preferably a hydrogen atom. ２２ is more preferably a hydrogen atom from the viewpoint of suppressing the production cost of the fluororesin having a nitrogen atom in a side chain, and is more preferably an unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms from the viewpoint of improving the stability of the fluororesin having a nitrogen atom in a side chain under alkaline conditions.

[0157] R ２６ , and R ２７ R is a hydrogen atom or a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms. ２６ , and R ２７When at least one of R is a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, the current efficiency, voltage efficiency, and power efficiency tend to be well-balanced and excellent when used in a redox flow battery cell and a redox flow battery. ２６ , and R ２７ and R are more preferably both substituted or unsubstituted aliphatic hydrocarbon groups having 1 to 10 carbon atoms. ２６ , and R ２７ is preferably an unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, more preferably an unsubstituted aliphatic hydrocarbon group having 1 to 6 carbon atoms, and even more preferably an unsubstituted aliphatic hydrocarbon group having 1 to 4 carbon atoms, because when used in a redox flow battery cell and a redox flow battery, the current efficiency, voltage efficiency, and power efficiency tend to be well-balanced and excellent.

[0158] R ２３ , and R ２５ may be the same or different, and each represents a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms. ２３ may be the same or different. ２３ , R ２５ As the alkyl group, from the viewpoints of easy availability of raw materials and tendency to suppress the production cost of the fluororesin containing a nitrogen atom in a side chain, an unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms is preferred, an unsubstituted aliphatic hydrocarbon group having 2 to 6 carbon atoms is more preferred, an unsubstituted aliphatic hydrocarbon group having 2 to 4 carbon atoms is even more preferred, and an unsubstituted aliphatic hydrocarbon group having 2 to 3 carbon atoms is particularly preferred.

[0159] In the case of "substitution", the substituent is the same as the substituent exemplified in general formula 1.

[0160] X ２４ is -CO ２ -, -SO ２ From the viewpoint that the chemical stability such as oxidation deterioration resistance of the fluororesin containing a nitrogen atom in a side chain tends to be improved, -SO ２A divalent group represented by the formula: - is preferred.

[0161] From the viewpoint that the chemical stability such as oxidation degradation resistance of the fluororesin containing a nitrogen atom in a side chain tends to be improved, and from the viewpoint that the production cost of the fluororesin containing a nitrogen atom in a side chain tends to be reduced, and the production cost of the cell for a redox flow battery tends to be reduced, it is preferable that the fluororesin contains at least one structural unit selected from the group consisting of a structural unit represented by the following general formula A2, a structural unit represented by the following general formula A17, a structural unit represented by the following general formula A18, and a structural unit represented by the following general formula A19. -(CF ２ -CF ２ ) - [A2] - (CF ２ -CF(-O-(CF ２ CFXO) Ｎ -Bg))- [A17] (wherein X represents F or a perfluoroalkyl group having 1 to 3 carbon atoms. Ag represents the ((CF ２ ) ｆ -X ２４ -NR ２２ - (R ２３ -NR ２４ ) ｈ -R ２５ -NR ２６ R ２７ ), where N is an integer of 0 to 5. ), -(CF ２ -CF(-O-(CF ２ ) Ｐ -CFX(-O-(CF ２ ) Ｋ -SO ２ NX ５１ Bx)))- [A18] (wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms. X ５１ represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group; Bx represents -(R ２３ -NR ２４ ) ｈ -R ２５ -NR ２６ R ２７), where P is an integer between 0 and 12, and K is an integer between 1 and 5. However, P and K cannot be 0 at the same time. ) -(CF ２ -CF(-O-(CF ２ ) Ｑ -CFX(-(CF ２ ) Ｌ -O-(CF ２ ) ｏ -SO ２ NX ５１ Bx)))- [A19] (wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms. X ４１ represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group; Ax represents -(R ２３ -NR ２４ ) ｈ -R ２５ -NR ２６ R ２７ ), where Q represents an integer of 0 to 12, L represents an integer of 1 to 5, and o represents an integer of 0 to 6. However, Q and O cannot be 0 at the same time.

[0162] The side chain nitrogen atom-containing fluororesin more preferably comprises a structural unit represented by general formula A2 and at least one selected from the group consisting of a structural unit represented by general formula A17, a structural unit represented by general formula A18, and a structural unit represented by general formula A19; from the same viewpoint, it is even more preferable that it contains a structural unit represented by general formula A2 and a structural unit represented by general formula A17 (wherein X is F or a trifluoromethyl group, n is an integer of 0 to 2, and m is an integer of 1 to 4), and it is particularly preferable that it contains a structural unit represented by general formula A2 and a structural unit represented by general formula A17 (wherein X is F or a trifluoromethyl group, n is 0 or 1, and m is an integer of 2 to 4).

[0163] The fluororesin having a nitrogen atom in a side chain more preferably has a structural unit represented by the following general formula A20, and even more preferably has a structural unit represented by the following general formula A21: -[CF ２ CF ２ ] ａ-[CF ２ -CF((-O-CF ２ -(CF(CF ３ ))) ｂ -O-(CF ２ ) ２ -SO ２ NX ５１ Bx)] ｇ - [A20] (wherein, X ５１ represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group; Ax represents -(R ２３ -NR ２４ ) ｈ -R ２５ -NR ２６ R ２７ a and g represent the molar ratios of all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1. b is 0 or 1. ) -[CF ２ CF ２ ] ａ -[CF ２ -CF((-O-CF ２ -(CF(CF ３ )))-O-(CF ２ ) ２ -SO ２ NX ５１ Bx)] ｇ - [A21] (wherein, X ５１ represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group; Ax represents -(R ２３ -NR ２４ ) ｈ -R ２５ -NR ２６ R ２７ a and g represent the molar ratios of all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1.

[0164] The method for producing the side-chain nitrogen atom-containing fluororesin is not particularly limited, but an example is a method of reacting the above-mentioned fluororesin G1 precursor with the modifying compound described below. The modifying compound has at least two nitrogen atoms. Of the nitrogen atoms, the functional group containing the first nitrogen atom is a primary amino group or a secondary amino group. From the viewpoint of improving the reactivity between the modifying compound and the side-chain nitrogen atom-containing fluororesin precursor, a primary amino group is preferred. From the viewpoint of improving the stability of the side-chain nitrogen atom-containing fluororesin, a secondary amino group is preferred. Of the at least two nitrogen atoms contained in the modifying compound, the functional group containing the second nitrogen atom is at least one functional group selected from the group consisting of a secondary amino group, a tertiary amino group, and a combination of the amino group and an acidic substance. If it is desired to suppress side reactions in the reaction between the acidic fluororesin precursor and the modifying compound, a secondary amino group or a tertiary amino group is preferred, and a tertiary amino group is more preferred.

[0165] Examples of the modifying compound include N-methylethylenediamine, N-ethylethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N,N'-trimethylethylenediamine, N,N-diethylethylenediamine, N-benzylethylenediamine, N,N-dibutylethylenediamine, 1,2-diphenylethylenediamine, N,N-dicyclohexyl-1,2-ethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethyldipropylenetriamine, and N,N-dibutylethylenediamine. Examples of the modifying compound include N,N-dimethyldipropylenetriamine, N,N-diethyl-1,3-propanediamine, N,N-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, N,N-dimethyl-1,4-cyclohexanediamine, 3-aminopiperidine, isophoronediamine, 4-(aminomethyl)piperidine, 3-aminopyrrolidine, 4-aminopiperidine, 3-aminopyrrolidine, N,N-dimethyltrimethylenediamine, and N,N-dibutyltrimethylenediamine. The modifying compound may be used alone or in combination of two or more.

[0166] Among the modifying compounds, N-methylethylenediamine, N-ethylethylenediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethyldipropylenetriamine, N,N-dibutyldipropylenetriamine, N,N-diethyl-1,3-propanediamine, N,N-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, N,N-dimethyl-1,4-cyclohexanediamine, N,N-dimethyltrimethylenediamine, and N,N-dibutyltrimethylenediamine are more preferred because the modifying compounds are easily available and the production cost of the ion exchange membrane for redox flow batteries containing a fluororesin having a nitrogen atom in a side chain tends to be reduced.

[0167] Among the modifying compounds, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethyldipropylenetriamine, N,N-dibutyldipropylenetriamine, N,N-dimethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, and N,N-dimethyltrimethylenediamine are particularly preferred because they tend to be excellent in balance of current efficiency, voltage efficiency, and power efficiency when an ion exchange membrane for a redox flow battery containing a fluororesin having a nitrogen atom in a side chain is used as a cell for a redox flow battery or a diaphragm of a redox flow battery, or when used in a cell for a redox flow battery or a redox flow battery.

[0168] From the same viewpoint, N,N-dimethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyldipropylenetriamine, and N,N-dimethyltrimethylenediamine are more particularly preferred.

[0169] In this embodiment, the fluororesin having a nitrogen atom in a side chain has a sulfonamide bond (—SO ２The presence of a sulfonamide bond in the heteroaromatic structure-containing fluororesin can be determined by a general analytical method, and examples of analytical devices that can be used include FT-IR and TOF-SIMS.

[0170] The fluororesin having nitrogen atoms in its side chains in this embodiment may be a saponified product thereof or a salt thereof.

[0171] The saponified product of the fluororesin having a nitrogen atom in the side chain is a saponified product obtained by reacting the fluororesin having a nitrogen atom in the side chain with an alkaline substance. Examples of the basic substance include amine compounds such as dimethylamine, diethylamine, monomethylamine, and monoethylamine, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkaline earth metal hydroxides. Among these, sodium hydroxide or potassium hydroxide is preferred.

[0172] The salt of the fluororesin having a nitrogen atom in a side chain is a salt of the fluororesin having a nitrogen atom in a side chain with an acidic substance, such as mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid, and trifluoroacetic acid.

[0173] <Fluororesin G1> The fluororesin having a nitrogen atom in a side chain in this embodiment may be used as a resin composition mixed with other resins. The resin composition may contain the fluororesin having a nitrogen atom in a side chain in this embodiment and fluororesin G1. In this embodiment, a mixture of fluororesins, such as a composition containing the fluororesin having a nitrogen atom in a side chain and fluororesin G1, is referred to as a fluororesin composition. Fluororesin G1 is a fluororesin having ion exchange ability with cations (hereinafter also referred to as "positive ions").

[0174] The fluororesin G1 has a structural unit represented by the following general formula G1. (In the formula, the definition of each substituent is the same as in the general formula G1 described above.) The preferred fluororesin G1 is also as described above.

[0175] When a fluororesin having a side chain nitrogen atom and a structural unit represented by general formula A3 is used, the ratio of the various resins is exemplified as follows. The weight ratio of the fluororesin having a side chain nitrogen atom to the fluororesin G1 in the resin composition is not particularly limited, but is preferably 1:100 to 100:1. Although it varies depending on the application of the resin composition according to this embodiment, when used as a diaphragm for a redox flow battery, from the viewpoint of suppressing elution of the fluororesin having a side chain nitrogen atom into the electrolyte, the weight ratio of the fluororesin having a side chain nitrogen atom to the fluororesin G1 is preferably 5:95 or more, more preferably 10:90 or more, and even more preferably 15:85 or more. Although it varies depending on the application of the mixture, when used as a diaphragm for a redox flow battery, the weight ratio of the fluororesin having a side chain nitrogen atom to the fluororesin G1 tends to improve power efficiency by the fluororesin having a side chain nitrogen atom, so it is preferably 90:10 or less, more preferably 70:30 or less, and even more preferably 60:40 or less.

[0176] The content of the fluororesin having a nitrogen atom in a side chain in the resin composition is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Although it varies depending on the application of the mixture, when used as a diaphragm for a redox flow battery, the fluororesin having a nitrogen atom in a side chain tends to improve power efficiency, so the content of the fluororesin having a nitrogen atom in a side chain in the resin composition is preferably 90% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0177] The resin composition according to this embodiment is preferably a styrene resin, a vinyl chloride resin, a chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a polyether ether ketone resin, a polysulfone resin, a polyether sulfone resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a polyphenylene ether resin, a polyphenylene sulfide resin, a syndiotactic polystyrene resin, a polyetherimide, a siloxane-modified polyetherimide resin, a polyamideimide resin, a cycloolefin resin, a cycloolefin copolymer, a polyether ketone ether ketone ketone resin, a polyaryl ether ketone resin, or a fluororesin. It may further contain a styrene resin, a vinyl chloride resin, a chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a syndiotactic polystyrene resin, a cycloolefin resin, or a cycloolefin copolymer. The resins that may be contained in the resin composition according to this embodiment may be used alone or in combination.

[0178] <Ion Exchange Membrane> The ion exchange membrane according to this embodiment contains a fluororesin containing a nitrogen atom in a side chain or the resin composition according to this embodiment.

[0179] When molding the resin composition containing the fluororesin containing a side chain nitrogen atom into a film, the molding method is not particularly limited, and examples include the method of melting the resin composition containing the fluororesin containing a side chain nitrogen atom, and extruding it with a nozzle or die using an extruder to process it into a film, or the method of applying the resin composition containing the fluororesin containing a side chain nitrogen atom into a solution state to a substrate with a die, gravure roll, knife or spray, and drying it to process it into a film.The obtained film of the fluororesin containing a side chain nitrogen atom is also referred to as the fluororesin film containing a side chain nitrogen atom below.

[0180] The solvent that can be used to prepare a solution of the fluororesin containing a nitrogen atom in a side chain is not particularly limited, and examples thereof include saturated hydrocarbon compounds such as n-pentane, n-hexane, n-octane, n-decane, cyclopentane, cyclohexane, and cyclooctane; aromatic hydrocarbon compounds such as benzene, toluene, xylene, and ethylbenzene; halogenated hydrocarbon compounds such as methylene chloride, chloroform, carbon tetrachloride, chlorobenzene, and dichlorobenzene; alcohols such as methanol, ethanol, propanol, isopropanol, butanol, hexanol, cyclohexanol, and benzyl alcohol; and ketones such as acetone, ethyl methyl ketone, methyl butyl ketone, methyl isobutyl ketone, and cyclohexanone. and esters such as ethyl acetate, butyl acetate, and methyl benzoate; ethers such as diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, and dioxane; polyols such as ethylene glycol, propylene glycol, and glycerin, and polymers of compounds of these polyols having two hydroxyl groups, and polyols; and esterified compounds of the above polymers, and nitriles such as acrylonitrile and benzonitrile; nitromethane; N,N-dimethylformamide; dimethyl sulfoxide; hexamethylphosphoric triamide; carbon disulfide; fluorine-based compounds (for example, Novec (trademark) manufactured by 3M Company, Asahiklin manufactured by Asahi Glass Co., Ltd., etc.); and the like. The solvent may be used alone or in combination.

[0181] A substrate can also be used when forming a composition containing a side-chain nitrogen atom-containing fluororesin into a film. Using a substrate may allow for more stable production of a film of a composition containing a side-chain nitrogen atom-containing fluororesin. The material used for the substrate is not particularly limited, and examples include polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, cycloolefin polymer, polycarbonate, polyamide, polyimide, polyamideimide, polyvinyl chloride, polystyrene, polyphenylene ether, polyetheretherketone, polysulfone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyetherimide, polyimide resin, polyetherketoneetherketoneketone, polyaryletherketone, etc. The material used for the substrate may be modified, and may be used alone or in combination of two or more types.

[0182] The ion exchange membrane according to this embodiment includes a layer (L3) containing the above-described fluororesin having a nitrogen atom in a side chain and a structural unit represented by the following general formula G1: (wherein the definition of each substituent is the same as in the above-mentioned general formula G1) and a layer (M3) containing a fluororesin, and at least one layer each of these layers are alternately provided.

[0183] By using a membrane containing fluororesin G1 (hereinafter also referred to as fluororesin membrane) as the substrate for layer (M3), an ion exchange membrane having a fluororesin membrane (M3) and a side-chain nitrogen atom-containing fluororesin membrane (L3) can be obtained. Note that layer (M3) does not have to contain a heteroaromatic structure-containing fluororesin. The ion exchange resin according to this embodiment may have one layer (L3) and one layer (M3) (an ion exchange membrane having one layer (L3) and one layer (M3) is also referred to as a "bipolar membrane"). The laminated membrane can be an ion exchange membrane having the properties of both the fluororesin G1 and the heteroaromatic structure-containing fluororesin. Note that hereinafter, in the laminated state, the fluororesin membrane will also be referred to as a fluororesin layer, and the side-chain nitrogen atom-containing fluororesin membrane will also be referred to as a side-chain nitrogen atom-containing fluororesin layer.

[0184] The interface between the layer (L3) containing the fluororesin having a nitrogen atom in the side chain contained in the ionic membrane and the layer (M3) containing the fluororesin having a structural unit represented by the general formula G1 is measured by a time-of-flight secondary ion mass spectrometer, and is measured by NSO 0146:2002 with reference to JIS K 0146:2002. ２ The presence or absence of an interface is determined from the value at which the maximum signal intensity (m / z 78, two peaks are detected but the lower mass peak is used) is 1 / 10. ２ The region where the maximum signal intensity of the peak is 1 / 10 or more is called the layer (L), and the NSO ２ The region where the maximum signal intensity of the peak is less than 1 / 10 is defined as a layer (M).

[0185] The method for producing the fluororesin film is as described above.

[0186] As a method for forming a fluororesin having a side chain nitrogen atom into a film, a fluororesin G1 precursor film can be reacted with a modifying compound and then hydrolyzed to produce a fluororesin film having a side chain nitrogen atom. Acid treatment can also be performed. That is, a saponified product of a fluororesin film having a heteroaromatic structure can be obtained by hydrolysis, and a salt of a fluororesin film having a heteroaromatic structure can be obtained by acid treatment. The hydrolysis and acid treatments are similar to those for general formula G1. This method allows for the control of the reaction between the fluororesin G1 precursor and the modifying compound to produce a film in which the fluororesin film having a side chain nitrogen atom and the fluororesin film are integrated, making this a suitable film for when increased adhesion between the fluororesin film having a side chain nitrogen atom and the fluororesin film is desired. In addition, in the film obtained by this method, the distribution of the fluororesin having a side chain nitrogen atom within the film can also be controlled by controlling the reaction between the fluororesin G1 precursor and the modifying compound. To give a specific example, the reaction proceeds from the point where the fluororesin G1 precursor film and the modified compound come into contact, and therefore a film can be formed in which the concentration of the fluororesin containing nitrogen atoms in the side chains has a gradient from the point of contact.

[0187] The ion exchange membrane having the side-chain nitrogen atom-containing fluororesin of this embodiment and the ion exchange membrane containing the side-chain nitrogen atom-containing fluororesin membrane and the fluororesin membrane (the ion exchange membrane is not particularly limited as long as it has two or more layers, and the same applies hereinafter) can be used in various applications. Examples of such applications include redox flow batteries, fuel cells, salt electrolysis, alkaline water electrolysis, and carbon dioxide reduction electrolysis, and among these, use in cells for redox flow batteries and redox flow batteries is preferred. Use in cells for redox flow batteries and redox flow batteries tends to provide superior power efficiency compared to conventionally used diaphragms.

[0188] The total thickness of the ion exchange membrane according to the present embodiment is not particularly limited, but in the case of a cell for a redox flow battery and a redox flow battery, which are exemplified as suitable applications, it is preferably 0.01 μm or more and 200 μm or less, and more preferably 1 μm or more because this tends to improve the handleability and mechanical strength of the membrane. In particular, when the membrane pulsates significantly and high mechanical strength is required, it is even more preferably 10 μm or more, and particularly preferably 20 μm or more. In order to suppress the electrical resistance when the cell for a redox flow battery and the redox flow battery are operated and to tend to improve the power efficiency, it is more preferably 150 μm or less, even more preferably 130 μm or less, and particularly preferably 100 μm or less.

[0189] The thickness of layer (L3) (side-chain nitrogen atom-containing fluororesin membrane) in the ion exchange membrane according to this embodiment is not particularly limited, but in the redox flow battery cell and redox flow battery exemplified as suitable applications, it is preferably 0.001 μm or more and 10 μm or less. When used in a redox flow battery cell and a redox flow battery, the thickness of layer (L3) tends to be more effectively inhibited from permeating the membrane of redox active substances, so it is more preferably 0.003 μm or more, and even more preferably 0.005 μm or more. When the heteroaromatic structure-containing fluororesin membrane has large pulsation and high mechanical strength is required, it is particularly preferably 0.01 μm or more, and even more particularly preferably 0.04 μm or more. The thickness of the layer (L3) is more preferably 7 μm or less, further preferably 5 μm or less, particularly preferably 3 μm or less, and further particularly preferably 1.5 μm or less, because electrical resistance is suppressed and power efficiency tends to improve when the redox flow battery cell and the redox flow battery are operated.

[0190] The equivalent weight of the ion exchange membrane according to the present embodiment is not particularly limited, but is preferably 500 g / eq or more and 2000 g / eq or less, more preferably 700 g / eq or more and even more preferably 800 g / eq or more, since the handleability and mechanical strength of the membrane tend to be improved. In particular, when the membrane pulsates significantly and high mechanical strength is required, the equivalent weight is particularly preferably 880 g / eq or more and even more particularly preferably 900 g / eq or more. The equivalent weight of the ion exchange membrane according to the present embodiment is more preferably 1500 g / eq or less, even more preferably 1400 g / eq or less, particularly preferably 1200 g / eq or less, and even more particularly preferably 1150 g / eq or less, since the electrical resistance during operation of the redox flow battery cell and the redox flow battery tends to be suppressed and the power efficiency tends to be improved.

[0191] <Redox Flow Battery Cell> A redox flow battery cell, exemplified as a suitable application of the ion exchange membrane of this embodiment, includes a first electrolyte solution containing a first redox active material, a second electrolyte solution containing a second redox active material, a first electrode in contact with the first electrolyte solution, a second electrode in contact with the second electrolyte solution, and a diaphragm disposed between the first and second electrolyte solutions. The cell may also include elements other than those commonly used by those skilled in the art, as well as elements known from publicly available literature and patents related to redox flow battery cells. Examples of such elements include bipolar plates, frames, compressible seals, conductive additives, and balancing cells.

[0192] FIG. 1 shows an example of a schematic diagram of the redox flow battery cell. The redox flow battery cell 10 has a cell chamber 2 containing an electrode 1 (positive electrode in FIG. 1 ) made of a first electrode, a cell chamber 4 containing an electrode 3 (negative electrode in FIG. 1 ) made of a second electrode, and an electrolytic cell 6 containing a diaphragm 5 separating the cell chamber 2 from the cell chamber 4. The cell chamber 2 and the cell chamber 4 contain an electrolyte containing a redox active material. The electrolyte containing the redox active material is stored in an electrolyte tank 7 and a tank 8, respectively, and supplied to each cell chamber by a pump or the like. The current generated by the redox flow battery cell may be converted from DC to AC via an AC / DC converter 9, or may be converted from AC to DC via the AC / DC converter 9 and used to fill the redox flow battery cell. The redox flow battery cell of this embodiment is preferably a redox flow secondary battery cell.

[0193] <Redox Flow Battery> A redox flow battery can be formed by stacking the redox flow battery cells. When stacking, electrical current can be passed between the redox flow battery cells via bipolar plates. The material of the bipolar plate is not particularly limited, and examples thereof include carbon, graphite, and metal. The material may also contain dispersed carbon particles, carbon fibers, metal particles, metal fibers, graphene, and carbon nanotubes. One type of material may be used alone, or multiple types may be used in combination. The bipolar plate may have various flow channels, which may improve contact between the electrodes and the electrolyte. The flow channels are not particularly limited, and examples thereof include serpentine, interdigitated, parallel, multi-parallel, discontinuous, and combinations of the above flow channels.

[0194] <Electrolyte> The electrolyte in this embodiment is a liquid containing a redox active material and a solvent. The redox active material is a substance that has redox activity that directly contributes to the electromotive force in a redox flow battery cell. The redox active material used in this embodiment is not particularly limited, but includes metal-based redox active materials, non-metal-based redox active materials, and organic redox active materials, all of which may be neutral or ionic compounds. The metal-based redox active material is a substance containing at least one metal atom, and may contain multiple atoms of the same metal or multiple atoms of different metals. The metal atom used in the metal-based redox active material is not particularly limited, but includes aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin, lead, and cerium, among which titanium, vanadium, chromium, manganese, iron, and cerium are preferred. From the viewpoint of enabling the first redox active material and the second redox active material to be of the same type, vanadium, iron, copper, and tin are preferred, vanadium and iron are more preferred, and vanadium is particularly preferred. The metal-based redox active material may have a commonly used active material ligand, examples of which include cyanide ion, acetylacetone, ethylenediamine, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, carbon monoxide, bipyridine, bipyrazine, ethylene glycol, propylene glycol, ethanedithiol, butanedithiol, terpyridine, diethylenetriamine, triazacyclononane, tris(hydroxymethyl)aminomethane, ascorbic acid, citric acid, glycolic acid, gluconic acid, acetic acid, formic acid, benzoic acid, malic acid, maleic acid, phthalic acid, sarcosinic acid, salicylic acid, oxalic acid, urea, aminophenolate, and lactic acid. The active material ligand may be one kind alone or a combination of two or more kinds. The substance used for the non-metallic redox active material is not particularly limited, but examples thereof include chlorine, bromine, sulfur, polysulfide, and the like.Examples of organic redox active materials include, but are not limited to, viologen, derivatives thereof, and compounds having a viologen structure in a polymer side chain, 2,2,6,6-tetramethyl-1-piperidinyloxy radical, derivatives thereof, and compounds having a 2,2,6,6-tetramethyl-1-piperidinyloxy radical structure in a polymer side chain, ferrocene, derivatives thereof, and compounds having a ferrocene structure in a polymer side chain, quinone, derivatives thereof, and compounds having a quinone structure in a polymer side chain, anthraquinone, derivatives thereof, and compounds having an anthraquinone structure in a polymer side chain, quinoxaline, derivatives thereof, and compounds having a quinoxaline structure in a polymer side chain, etc. The redox active materials may be used alone or in combination.

[0195] When the redox active material is used in a redox flow battery cell, the redox active material used in the positive electrode electrolyte and the redox active material used in the negative electrode electrolyte can be combined according to the desired characteristics. The combination of redox active materials is not particularly limited, but examples include vanadium / vanadium, iron / iron, lead / lead, copper / copper, iron / chromium, chromium / bromine, zinc / bromine, polysulfide / bromine, zinc / cerium, zinc / nickel, zinc / cerium, zinc / iodine, titanium / manganese, vanadium / cerium, and vanadium / manganese. Among these, vanadium / vanadium, iron / iron, iron / chromium, chromium / bromine, zinc / bromine, and titanium / manganese are preferred because they provide a high electromotive force and excellent charge / discharge stability. Vanadium / vanadium, iron / iron, and zinc / bromine are more preferred, and vanadium / vanadium is particularly preferred. When the redox active materials of the positive electrode and the negative electrode are both vanadium, the battery is also referred to as a vanadium redox flow battery cell or a vanadium redox flow battery. ２＋ / VO ２ ＋ , and at the negative electrode, V ２＋ / V ３＋Charging and discharging are performed by utilizing an oxidation-reduction reaction using a redox couple. During charging, the oxidation-reduction reaction causes an excess of protons (H+) in the positive electrode cell chamber, while the negative electrode cell chamber is deficient in protons (H+). The diaphragm selectively transfers the excess protons in the positive electrode cell chamber to the negative electrode chamber, maintaining electrical neutrality. During discharging, the reverse reaction occurs, maintaining electrical neutrality.

[0196] The solvent used in the electrolyte solution is not particularly limited, but examples thereof include water, alcohols, nitriles, esters, ketones, ethers, aliphatic hydrocarbons, aromatic hydrocarbons, etc. Among these, water is preferred from the viewpoint of improving safety during operation of the redox flow battery cell. Specific examples of the solvent include alcohols such as methanol, ethanol, propanol, butanol, hexanol, cyclohexanol, ethylene glycol, diethylene glycol, and glycerol, nitriles such as acetonitrile, propionitrile, and benzonitrile, esters such as ethyl acetate and butyl acetate, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, ethers such as diethyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, ethylene glycol diethyl ether, and diethylene glycol dimethyl ether, aliphatic hydrocarbons such as pentane, hexane, cyclohexane, heptane, octane, chloroform, dichloromethane, and tetrachloromethane, and aromatic hydrocarbons such as benzene, toluene, xylene, chlorobenzene, dichlorobenzene, phenol, and cresol. The solvent used in the electrolytic solution may be one type alone or a combination of two or more types.

[0197] The electrolytic solution may further contain an electrolyte. The electrolyte is a substance that dissociates into ions in the electrolytic solution and improves the electrical conductivity of the electrolytic solution. Examples of the electrolyte include, but are not limited to, sulfuric acid, hydrochloric acid, nitric acid, acetic acid, phosphoric acid, sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium acetate. The electrolyte used in the electrolytic solution may be one type alone or a combination of multiple types.

[0198] Additives may be added to the electrolyte solution depending on the desired properties of the electrolyte solution. Examples of additives include, but are not limited to, ethylene glycol, diethylene glycol, polyethylene glycol, glycerol, mannitol, sorbitol, pentaerythritol, tris(hydroxymethyl)aminomethane, corn starch, corn syrup, gelatin, glycerol, guar gum, pectin, surfactants, etc. The additives used in the electrolyte solution may be used alone or in combination.

[0199] <Electrode> The electrode of this embodiment is not particularly limited. Examples of the electrode include a metal electrode and a carbon electrode. The material of the metal electrode is not particularly limited, but includes aluminum, gold, silver, copper, chromium, molybdenum, nickel, thallium, titanium, iridium, zinc, tin, and composites of these metals. The shape of the metal electrode is not particularly limited, but includes plate-like, lattice-like, mesh-like (diamond-shaped, tortoiseshell-shaped), linear, and rod-like. The carbon electrode is not particularly limited, but includes glassy carbon electrodes, pyrolytic carbon electrodes, carbon felt electrodes, carbon paper electrodes, carbon foam electrodes, carbon cloth electrodes, carbon knit electrodes, carbon nanofiber sheet electrodes, activated carbon fiber sheet electrodes, and the like. For applications in which a liquid or gas flows through the electrode, the electrode preferably has continuous pores, and more preferably is a porous body with continuous pores. Examples of carbon electrodes with continuous pores include carbon felt electrodes, carbon paper electrodes, carbon foam electrodes, carbon cloth electrodes, carbon knit electrodes, carbon nanofiber sheet electrodes, activated carbon fiber sheet electrodes, and the like. Among these, carbon felt, carbon paper, and carbon foam are preferred, with carbon foam being more preferred, from the viewpoint of reducing resistance due to high flexibility and a large surface area. Carbon foam preferably has a structure in which the carbon portion is three-dimensionally continuous. Carbon foam preferably has linear portions and bonding portions that bond the linear portions, as this allows for high flexibility and a large surface area. Specific examples of carbon felt and carbon paper include the SIGRACELL (registered trademark) KFD series, GFA series, GFD series, SGL series, and SIGRACET (registered trademark) series manufactured by SGL CARBON, carbon felt manufactured by Toyobo Co., Ltd. (e.g., XF30A, BW-309), CARBORON (registered trademark) GF series manufactured by Nippon Carbon Co., Ltd. (e.g., GF-20, GF-3F), TORAYCA (trademark) TGP series manufactured by Toray Industries, Inc., PYROFIL (trademark) series and GRAFIL (trademark) series manufactured by Mitsubishi Chemicals Corporation, VGCF (registered trademark) sheet manufactured by Showa Denko K.K., carbon felt and graphite felt manufactured by MERSEN, and the like.These may be subjected to activation treatment such as oxidation as necessary. The carbon foam can be produced by known methods (WO 2018 / 096895, WO 2018 / 168741, WO 2020 / 045645). The electrode may be used alone or in combination of two or more types.

[0200] <Membrane Electrode Assembly> The membrane electrode assembly of this embodiment has a structure in which an ion exchange membrane (hereinafter, the ion exchange membrane may also be referred to as an assembly membrane) and at least one electrode are joined together. The joining refers to joining the assembly membrane and at least one electrode, and the assembly membrane and at least one electrode can be integrated by joining them. For example, a membrane electrode assembly including an assembly membrane and two electrodes may be preferably used in assembling a redox flow battery cell because it eliminates the need for a step of assembling the electrode, assembly membrane, and electrode in order, allowing for a single step, which tends to reduce manufacturing costs. The method for joining the assembly membrane and at least one electrode is not particularly limited, but examples include a method using heat pressing and / or heat roll pressing. The temperature during bonding is not particularly limited, but is preferably room temperature or higher, since insufficient bonding between the assembly film and the electrode tends to reduce the elastic modulus of the assembly film and improve the bonding between the assembly film and the electrode. Since deterioration of the assembly film tends to be suppressed, the temperature during bonding is preferably 250°C or lower, more preferably 200°C or lower, even more preferably 170°C or lower, and particularly preferably 150°C or lower. The pressure during bonding is not particularly limited, but is a pressure exceeding 0 MPa. Since deterioration of the assembly film and the electrode tends to be improved, the pressure is preferably 0.01 MPa or higher, more preferably 0.05 MPa or higher, even more preferably 0.08 MPa or higher, and particularly preferably 0.1 MPa or higher. Since deterioration of the electrode tends to be suppressed, the pressure is preferably 100 MPa or lower, more preferably 50 MPa or lower, even more preferably 20 MPa or lower, and particularly preferably 10 MPa or lower. The bonding time is not particularly limited, but is preferably a time exceeding 0 seconds. Since this tends to improve the bonding between the membrane for bonding and the electrode, the time is preferably 0.01 seconds or more, more preferably 0.1 seconds or more, even more preferably 0.5 seconds or more, and particularly preferably 1 second or more.Since the cost of producing a membrane electrode assembly tends to be reduced, the time is preferably 10 hours or less, more preferably 5 hours or less, even more preferably 2 hours or less, and particularly preferably 1 hour or less. The atmosphere during bonding is not particularly limited, but examples include air, nitrogen, and argon. Since the cost of producing a membrane electrode assembly tends to be reduced, air and nitrogen are preferred, and air is more preferred.

[0201] The membrane electrode assembly of the present embodiment can be used for various purposes, but suitable examples include use in a cell for a redox flow battery and a redox flow battery. Use in a cell for a redox flow battery and a redox flow battery tends to result in superior power efficiency compared to conventionally used combinations of a membrane and an electrode.

[0202] In the redox flow battery cell and redox flow battery of this embodiment, when a side-chain heteroaromatic resin film, a heteroaromatic structure-containing fluororesin film, and a side-chain nitrogen atom-containing fluororesin film are used as the diaphragm, if a well-balanced current efficiency, voltage efficiency, and high power efficiency are required, the side-chain heteroaromatic resin layer, the heteroaromatic structure-containing fluororesin film, and the side-chain nitrogen atom-containing fluororesin film are preferably disposed on the electrode side acting as the negative electrode, and preferably disposed proximal to the electrode side. Proximal means that the side-chain heteroaromatic resin layer, the heteroaromatic structure-containing fluororesin film, and the side-chain nitrogen atom-containing fluororesin film are closer to the electrode acting as the negative electrode than to the electrode acting as the positive electrode. Although the reason why the above-mentioned special effect is obtained by arranging the side-chain heteroaromatic resin layer, the heteroaromatic structure-containing fluororesin film, and the side-chain nitrogen atom-containing fluororesin film proximal to the electrode acting as the negative electrode is unclear, it is presumed that this is because the amount of redox active material that moves from the positive electrode to the negative electrode is different from the amount of redox active material that moves from the negative electrode to the positive electrode, and the side-chain heteroaromatic resin layer, the heteroaromatic structure-containing fluororesin layer, and the side-chain nitrogen atom-containing fluororesin layer function more effectively with respect to the redox active material that moves more. Furthermore, when higher current efficiency is required, it is preferable to arrange the side-chain heteroaromatic resin layers on both sides of the diaphragm.

[0203] The redox flow battery cell and redox flow battery of this embodiment can be used to smooth out power supply and demand and provide a mechanism for stabilizing fluctuating power from renewable energy sources such as solar and wind energy. More specifically, they can provide power integration from renewable energy sources, peak load shifting, grid stabilization, baseload power, energy arbitrage, weak grid support, frequency regulation, and any combination thereof. They can also be used as power sources for off-grid remote camps, forward operating bases, power transmission and distribution telecommunications, remote sensors, and the like. The redox flow battery cell and redox flow battery of this embodiment can be equipped with a control system and a power conditioning unit. The control system can be used to control the operation of various valves, pumps, circulation circuits, sensors, mitigation devices, other electronic / hardware control devices, safety protection devices, and the like. By using the power conditioning unit, the voltage and current of the input power can be converted into a form optimal for the redox flow battery cell and / or the redox flow battery, and the voltage and current of the output power can be converted into a form optimal for any application. For example, when the redox flow battery cell and / or the redox flow battery is connected to a power grid, the power conditioning unit can convert the input AC power into DC power of an appropriate voltage and current during the charge cycle. Also, during the discharge cycle, the redox flow battery cell and / or the redox flow battery generates DC power, and the power conditioning unit can convert the DC power into AC power of an appropriate voltage and frequency for transmission to the power grid.

[0204] Third Embodiment Next, a third embodiment will be described.

[0205] Patent Document 1 discloses alternately stacking cation exchange base layers and anion exchange base layers to improve initial power efficiency, but does not disclose anything about the thickness of the cation exchange base layer or the anion exchange base layer, except in the examples. Furthermore, while it discloses a preferred range of the ion exchange capacity of an ion exchange membrane composed of an ion exchanger layer having ion exchange groups and a porous support layer not having ion exchange groups, it does not disclose any reasons why that range is preferred or any examples demonstrating that it is preferred. Furthermore, the examples do not disclose anything about the ion exchange capacity of the copolymer having structural formula (1) in Patent Document 1. Furthermore, it discloses that the cation exchange base layer in the ion exchange base layer can be arranged on the positive electrode liquid side, thereby extending the life of the ion exchange base layer, but does not disclose anything about arranging the anion exchange base layer.

[0206] Patent Document 2 discloses modifying Nafion® 117 with multiple nitrogen-containing heterocyclic molecules. However, because Nafion® 117 has a large membrane thickness, even if it has the same proton area resistivity, a lower proton area resistivity is required when actually used in a redox flow battery. It also discloses using a support to form a thin membrane, but the proton area resistivity is higher than that of Nafion® 117. Similarly, when actually used in a redox flow battery, a lower proton area resistivity is required. However, there is no disclosure regarding the operation of a redox flow battery using the disclosed membrane. It also discloses that the side to which the multiple nitrogen-containing heterocyclic molecules are bonded may be optionally located closer to the negative half-cell of the battery to improve membrane performance, but there is no disclosure or example of what performance is improved. There is no disclosure regarding the thickness of the multiple nitrogen-containing heterocyclic molecules within the membrane.

[0207] Patent Document 3 discloses the provision of a crossover prevention layer, which is a metal layer formed by reducing a cationic metal inside a polymer electrolyte membrane, in order to improve at least one of the properties of discharge capacity, current efficiency, voltage efficiency, and power efficiency. However, even higher properties are desired. Furthermore, the document indicates that the thickness of the formed metal layer is preferably in a relatively large range of 10 μm to 50 μm. There is no indication regarding the preferred range of the equivalent weight (EW) of the polymer electrolyte membrane. Regarding the location of the crossover prevention layer inside the polymer electrolyte membrane, it is indicated that it is located at a distance of 10% to 90% of the thickness of the electrolyte membrane from the surface of the polymer electrolyte membrane. However, there is no indication regarding whether the crossover prevention layer should face the positive electrode or the negative electrode when used in a flow battery.

[0208] Patent Document 4 discloses that in order to suppress curling, the value obtained by dividing the thickness of the first ion exchange resin layer by the thickness of the second ion exchange resin layer is set to 0.7 to 1.3, and shows that the thicknesses of the first ion exchange resin layer and the second ion exchange resin layer are equal, that is, the anion exchange resin layer is located at the center of the thickness direction of the entire membrane. Furthermore, even if the thicknesses of the first ion exchange resin layer and the second ion exchange resin layer are not equal, there is no disclosure as to whether the anion exchange resin layer is located on the positive electrode side or the negative electrode side in the redox flow battery cell.

[0209] The object of this embodiment relates to a redox battery cell, a redox flow battery, and a method for manufacturing a diaphragm, which have high power efficiency.

[0210] As a result of intensive research into the above-mentioned problems, the present inventors have surprisingly found that when a diaphragm constituting a redox flow battery cell includes at least a first cation exchange resin layer and an anion exchange resin layer, and the anion exchange resin layer is located on the electrode side acting as the negative electrode, higher power efficiency can be obtained than when the anion exchange resin layer is located on the electrode side acting as the positive electrode. Furthermore, the present inventors have found that particularly high power efficiency can be obtained by setting the equivalent weight of the diaphragm and the thickness of the anion exchange resin layer within specific ranges.

[0211] The redox flow battery cell according to this embodiment includes: a first electrolytic solution containing a first redox active material, a second electrolytic solution containing a second redox active material, a first electrode in contact with the first electrolytic solution, a second electrode in contact with the second electrolytic solution, and a diaphragm disposed between the first electrolytic solution and the second electrolytic solution, wherein the diaphragm has at least a first cation exchange resin layer and an anion exchange resin layer, wherein the equivalent weight of the diaphragm is 1150 g / eq or less, and the thickness of the anion exchange resin layer is 0.001 μm or more and less than 5 μm, and the anion exchange resin layer of the diaphragm is disposed on the electrode side acting as a negative electrode. According to this embodiment, it is possible to provide a redox battery cell, a redox flow battery, and a diaphragm having high power efficiency.

[0212] <Redox Flow Battery Cell> The redox flow battery cell of this embodiment includes a first electrolyte solution containing a first redox active material, a second electrolyte solution containing a second redox active material, a first electrode in contact with the first electrolyte solution, a second electrode in contact with the second electrolyte solution, and a diaphragm disposed between the first and second electrolyte solutions. The redox flow battery cell may also include elements other than the above components that are commonly used by those skilled in the art, as well as elements known from publicly available information, such as published literature and patents, related to redox flow battery cells. Examples of such elements include bipolar plates, frames, compressible seals, conductive additives, and balancing cells.

[0213] FIG. 1 shows an example of a schematic diagram of a redox flow battery cell according to this embodiment. The redox flow battery cell 10 according to this embodiment includes a cell chamber 2 containing an electrode 1 (positive electrode in FIG. 1 ) made of a first electrode, a cell chamber 4 containing an electrode 3 (negative electrode in FIG. 1 ) made of a second electrode, and an electrolytic cell 6 containing a diaphragm 5 separating the cell chamber 2 from the cell chamber 4. The cell chambers 2 and 4 contain an electrolyte containing a redox active material. The electrolyte containing the redox active material is stored in, for example, an electrolyte tank 7 and a tank 8, respectively, and supplied to each cell chamber by a pump or the like. The current generated by the redox flow battery cell may be converted from DC to AC via an AC / DC converter 9, or may be converted from AC to DC via the AC / DC converter 9 before filling the redox flow battery cell. The redox flow battery cell of this embodiment is preferably a redox flow secondary battery cell.

[0214] <Electrolyte> The electrolyte in this embodiment is a liquid containing a redox active material and a solvent. The redox active material is a substance that has redox activity that directly contributes to the electromotive force in a redox flow battery cell. The redox active material used in this embodiment is not particularly limited, but examples include metal-based redox active materials, non-metal-based redox active materials, and organic redox active materials, all of which may be neutral compounds or ionic compounds.

[0215] The metal-based redox active material is a substance containing at least one metal atom, and may contain multiple metal atoms of the same type or multiple metals of different types. Metal atoms used in the metal-based redox active material are not particularly limited, but examples include aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin, lead, and cerium. Among these, titanium, vanadium, chromium, manganese, iron, and cerium are preferred. Furthermore, from the viewpoint of enabling the first redox active material and the second redox active material to be the same type, vanadium, iron, copper, and tin are preferred, vanadium and iron are more preferred, and vanadium is particularly preferred.

[0216] The metal-based redox active material may have a commonly used active material ligand, examples of which include cyanide ion, acetylacetone, ethylenediamine, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, carbon monoxide, bipyridine, bipyrazine, ethylene glycol, propylene glycol, ethanedithiol, butanedithiol, terpyridine, diethylenetriamine, triazacyclononane, tris(hydroxymethyl)aminomethane, ascorbic acid, citric acid, glycolic acid, gluconic acid, acetic acid, formic acid, benzoic acid, malic acid, maleic acid, phthalic acid, sarcosinic acid, salicylic acid, oxalic acid, urea, aminophenolate, and lactic acid. The active material ligand may be used alone or in combination.

[0217] The substance used for the non-metallic redox active material is not particularly limited, but examples thereof include chlorine, bromine, sulfur, polysulfides, and the like.

[0218] Examples of organic redox active materials include, but are not limited to, viologen, derivatives thereof, and compounds having a viologen structure in a polymer side chain, 2,2,6,6-tetramethyl-1-piperidinyloxy radical, derivatives thereof, and compounds having a 2,2,6,6-tetramethyl-1-piperidinyloxy radical structure in a polymer side chain, ferrocene, derivatives thereof, and compounds having a ferrocene structure in a polymer side chain, quinone, derivatives thereof, and compounds having a quinone structure in a polymer side chain, anthraquinone, derivatives thereof, and compounds having an anthraquinone structure in a polymer side chain, quinoxaline, derivatives thereof, and compounds having a quinoxaline structure in a polymer side chain, etc. The redox active materials may be used alone or in combination.

[0219] When the redox active material is used in a redox flow battery cell, the redox active material used in the positive electrode electrolyte and the redox active material used in the negative electrode electrolyte can be combined according to the desired characteristics. The combination of redox active materials is not particularly limited, but examples include vanadium / vanadium, iron / iron, lead / lead, copper / copper, iron / chromium, chromium / bromine, zinc / bromine, polysulfide / bromine, zinc / cerium, zinc / nickel, zinc / cerium, zinc / iodine, titanium / manganese, vanadium / cerium, and vanadium / manganese. Among these, vanadium / vanadium, iron / iron, iron / chromium, chromium / bromine, zinc / bromine, and titanium / manganese are preferred because they provide a high electromotive force and excellent charge / discharge stability. Vanadium / vanadium, iron / iron, and zinc / bromine are more preferred, and vanadium / vanadium is particularly preferred.

[0220] When the redox active materials of the positive electrode and the negative electrode are both vanadium, the battery is also referred to as a vanadium redox flow battery cell or a vanadium redox flow battery. ２＋ / VO ２ ＋ , and at the negative electrode, V ２＋ / V ３＋ Charging and discharging are performed by utilizing an oxidation-reduction reaction using a redox couple. During charging, the oxidation-reduction reaction causes an excess of protons (H+) in the positive electrode cell chamber, while the negative electrode cell chamber is deficient in protons (H+). The diaphragm selectively transfers the excess protons in the positive electrode cell chamber to the negative electrode chamber, maintaining electrical neutrality. During discharging, the reverse reaction occurs, maintaining electrical neutrality.

[0221] The solvent used in the electrolyte solution is not particularly limited, but examples thereof include water, alcohols, nitriles, esters, ketones, ethers, aliphatic hydrocarbons, aromatic hydrocarbons, etc. Among these, water is preferred from the viewpoint of improving safety during operation of the redox flow battery cell. Specific examples of the solvent include alcohols such as methanol, ethanol, propanol, butanol, hexanol, cyclohexanol, ethylene glycol, diethylene glycol, and glycerol, nitriles such as acetonitrile, propionitrile, and benzonitrile, esters such as ethyl acetate and butyl acetate, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, ethers such as diethyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, ethylene glycol diethyl ether, and diethylene glycol dimethyl ether, aliphatic hydrocarbons such as pentane, hexane, cyclohexane, heptane, octane, chloroform, dichloromethane, and tetrachloromethane, and aromatic hydrocarbons such as benzene, toluene, xylene, chlorobenzene, dichlorobenzene, phenol, and cresol. The solvent used in the electrolytic solution may be one type alone or a combination of two or more types.

[0222] The electrolytic solution may further contain an electrolyte. The electrolyte is a substance that dissociates into ions in the electrolytic solution and improves the electrical conductivity of the electrolytic solution. Examples of the electrolyte include, but are not limited to, sulfuric acid, hydrochloric acid, nitric acid, acetic acid, phosphoric acid, sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium acetate. The electrolyte used in the electrolytic solution may be one type alone or a combination of multiple types.

[0223] Additives may be added to the electrolyte solution depending on the desired properties of the electrolyte solution. Examples of additives include, but are not limited to, ethylene glycol, diethylene glycol, polyethylene glycol, glycerol, mannitol, sorbitol, pentaerythritol, tris(hydroxymethyl)aminomethane, corn starch, corn syrup, gelatin, glycerol, guar gum, pectin, surfactants, etc. The additives used in the electrolyte solution may be used alone or in combination.

[0224] <Electrode> The electrode used in the redox flow battery cell of this embodiment is not particularly limited, but is preferably a carbon electrode. The carbon electrode preferably has continuous pores to allow the electrolyte to pass through, and is more preferably a porous material with continuous pores. Examples of carbon electrodes with continuous pores include carbon felt, carbon paper, carbon foam, carbon cloth, carbon knit, carbon nanofiber sheets, and activated carbon fiber sheets, with carbon felt, carbon paper, and carbon foam being preferred. Among these, carbon foam is preferred from the viewpoint of reducing resistance due to its high flexibility and large surface area. Carbon foam preferably has a three-dimensionally continuous carbon structure. Carbon foam preferably has linear segments and bonding segments that bond the linear segments, since high flexibility and a large surface area can be achieved, thereby achieving high power efficiency.

[0225] Specific examples of carbon felt and carbon paper include the SIGRACELL (registered trademark) KFD series, GFA series, GFD series, SGL series, and SIGRACET (registered trademark) series manufactured by SGL CARBON, carbon felt manufactured by Toyobo Co., Ltd. (e.g., XF30A, BW-309), CARBORON (registered trademark) GF series (e.g., GF-20, GF-3F) manufactured by Nippon Carbon Co., Ltd., TORAYCA (trademark) TGP series manufactured by Toray Industries, Inc., PYROFIL (trademark) series and GRAFIL (trademark) series manufactured by Mitsubishi Chemicals Corporation, VGCF (registered trademark) sheet manufactured by Showa Denko K.K., carbon felt and graphite felt manufactured by MERSEN GmbH, etc. These may be subjected to activation treatment such as oxidation, if necessary.

[0226] Carbon foam can be produced by known methods (WO 2018 / 096895, WO 2018 / 168741, WO 2020 / 045645).

[0227] The first electrode and the second electrode may be a single type of electrode or different electrodes, and within the first electrode and / or the second electrode, a single type of electrode or a combination of multiple types of electrodes may be used.

[0228] <Diaphragm> In the present embodiment, the diaphragm is a membrane disposed between a first electrolytic solution and a second electrolytic solution, and comprises at least a first cation exchange resin layer and an anion exchange resin layer, the diaphragm has an equivalent weight of 1150 g / eq or less, the anion exchange resin layer has a thickness of 0.001 μm or more and less than 5 μm, and in a redox flow battery cell, the anion exchange resin layer of the diaphragm is disposed on the side of the electrode acting as a negative electrode.

[0229] The equivalent weight of the diaphragm is not particularly limited, but is preferably 1150 g / eq or less, and more preferably 1100 g / eq or less, because this tends to reduce proton transfer resistance and improve power efficiency. It is more preferably 1050 g / eq or less, particularly preferably 1030 g / eq or less, and even particularly preferably 1000 g / eq or less, because this tends to improve the hydrophilicity of the diaphragm. It is preferably 500 g / eq or more, and more preferably 700 g / eq or more, because this tends to improve the solubility of the diaphragm in the electrolyte. It is more preferably 800 g / eq or more, and particularly preferably 880 g / eq or more, because this tends to improve the mechanical strength of the diaphragm against pulsation of the electrolyte, contact with the electrodes, and the like.

[0230] In addition, the equivalent weight refers to the dry mass (grams) of the ion exchange resin per equivalent of ion exchange groups having ion exchange capacity in the case of an ion exchange resin, which is a resin having ion exchange capacity. In the case of a first cation exchange resin layer, it refers to the dry mass (grams) of the first cation exchange resin layer per equivalent of ion exchange groups possessed by the first cation exchange resin layer. Hereinafter, the expression "equivalent weight" will be used appropriately in this embodiment. In addition, the equivalent weight can be measured by a method in which the ion exchange resin is subjected to salt substitution and the resulting solution is back-titrated with an alkaline solution. The equivalent weight can be appropriately adjusted by the copolymerization ratio of the monomers that are raw materials for the cation exchange resin, the selection of the monomer species, etc.

[0231] In this embodiment, the anion exchange resin layer included in the diaphragm is preferably disposed on the electrode side acting as the negative electrode, preferably proximal to the electrode side. Proximal means that the distance from the anion exchange resin layer to the electrode acting as the negative electrode is shorter than the distance from the electrode acting as the positive electrode. In this application, the inventors surprisingly discovered that disposing the anion exchange resin layer on the electrode side acting as the negative electrode improves power efficiency. While the reason for this improvement in power efficiency is unclear, it is speculated that the amount of redox active material that migrates from the positive electrode to the negative electrode differs from the amount of redox active material that migrates from the negative electrode to the positive electrode, and the anion exchange resin layer functions more effectively on the redox active material that migrates more. Furthermore, it is speculated that the effect of disposing the anion exchange resin layer on the electrode side acting as the negative electrode effectively affects the amount of redox active material that migrates from the negative electrode to the positive electrode.

[0232] Distance D between the anion exchange resin layer of the membrane and the electrode acting as the negative electrode ｎｅｇ and the distance D between the anion exchange resin layer of the diaphragm and the electrode acting as the positive electrode. ｐｏｓ and preferably have the following relationship: D ｎｅｇ / D ｐｏｓ <1 Here, the distance D ｎｅｇ means the distance from the surface of the anion exchange resin layer closest to the negative electrode to the surface of the negative electrode closest to the negative electrode. ｐｏｓ D means the distance from the surface of the anion exchange resin layer closest to the positive electrode to the surface closest to the positive electrode. ｎｅｇ / D ｐｏｓ From the viewpoint of further improving the power efficiency, D is preferably 0.8 or less, more preferably 0.7 or less, even more preferably 0.6 or less, and even more preferably 0.5 or less. ｎｅｇ / D ｐｏｓ The lower limit of is not particularly limited, but may be, for example, equal to or greater than 0. In other words, the anion exchange resin layer and the negative electrode may be in contact with each other.

[0233] From the viewpoint of further improving power efficiency, the first cation exchange resin layer is preferably disposed closer to the electrode acting as the positive electrode than the anion exchange resin layer.

[0234] <First cation exchange resin layer> The first cation exchange resin layer is a layer formed from a substance containing a resin (hereinafter also referred to as a "cation exchange resin") having ion exchange ability for cations (hereinafter also referred to as "positive ions").

[0235] The cation exchange resin is not particularly limited, but examples thereof include hydrocarbon resins and fluororesins. From the viewpoint of reducing the manufacturing cost of the redox flow battery cell, hydrocarbon resins are preferred, and from the viewpoint of improving the durability of the redox flow battery cell, fluororesins are preferred.

[0236] The hydrocarbon resin and the fluororesin may be used alone or in combination.

[0237] The functional group having ion exchange ability contained in the cation exchange resin is not particularly limited, but may be a sulfo group (SO ３ H), carboxyl group (CO ２ H), phenolic hydroxyl group (OH), phosphate group (PO ３ H ２ ), a thiol group (SH), and hydrogen in the functional group may be an alkali metal, an alkaline earth metal, a transition metal, etc. The functional group having ion exchange ability may be used alone or in combination of two or more types of functional groups.

[0238] Among functional groups having ion exchange capacity, sulfo groups, carboxyl groups, and / or phosphate groups are preferred, sulfo groups and / or carboxyl groups are more preferred, and sulfo groups are particularly preferred, as they tend to have excellent ion exchange capacity.

[0239] The hydrocarbon-based resin is not particularly limited, but examples thereof include polystyrene, polyphenylene ether, polybenzimidazole, polyether ether ketone, polyimide, polyetherimide, polyaryletherketone, polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylsulfone, and the like, and includes resins having functional groups with ion exchange capacity. Depending on the required physical properties, the resin may be crosslinked or may be a copolymer, and may have various substituents (e.g., halogen atoms such as fluorine atoms, chlorine atoms, and bromine atoms; aliphatic hydrocarbon groups such as nitrile groups, methyl groups, ethyl groups, vinyl groups, allyl groups, 1-methylvinyl groups, n-propyl groups, isopropyl groups, n-butyl groups, isobutyl groups, sec-butyl groups, and tert-butyl groups; aromatic hydrocarbon groups such as benzyl groups, phenyl groups, and nitrile-substituted phenyl groups; amino groups; nitro groups; hydroxyl groups; silyl groups, and the like). The hydrocarbon-based resins may be used alone or in combination of two or more types.

[0240] The fluororesin is not particularly limited, but examples thereof include partially fluorinated resins and fully fluorinated resins having functional groups with ion exchange capacity. Resins in which at least one, but not all, of the hydrogen atoms on carbon contained in the hydrocarbon cation exchange resin are substituted with a fluorine atom, and resins in which all hydrogen atoms on carbon are substituted with fluorine atoms are exemplified as partially fluorinated resins and fully fluorinated resins.

[0241] As the fluororesin, a fluororesin having a structural unit represented by general formula G1 (hereinafter also referred to as "fluororesin G1") is preferred, from the viewpoint that durability of the redox flow battery cell tends to be improved. (In the formula, the definition of each substituent is the same as in the above-mentioned general formula G1.)

[0242] The equivalent weight of the first cation exchange resin layer is not particularly limited, but is preferably less than 1100 g / eq, more preferably 1050 g / eq or less, since the proton transfer resistance tends to be reduced and the power efficiency tends to be improved. Furthermore, since the hydrophilicity of the first cation exchange resin layer tends to be improved, it is more preferably 1030 g / eq or less, and particularly preferably 1000 g / eq or less. Since the solubility in the electrolyte tends to be improved, it is preferably 500 g / eq or more, and more preferably 700 g / eq or more. Furthermore, since the mechanical strength against pulsation of the electrolyte, contact with the electrode, etc. tends to be improved, it is more preferably 800 g / eq or more, and particularly preferably 880 g / eq or more.

[0243] The thickness of the first cation exchange resin layer is not particularly limited, but is preferably 1 μm or more and 150 μm or less. Since proton transfer resistance tends to be reduced and power efficiency tends to be improved, 100 μm or less is more preferable, 80 μm or less is even more preferable, and 60 μm or less is particularly preferable. Since mechanical strength against pulsation of the electrolyte solution and contact with the electrodes tends to be improved, 5 μm or more is more preferable, 10 μm or more is even more preferable, 20 μm or more is particularly preferable, and 25 μm or more is even more particularly preferable.

[0244] The content of the cation exchange resin in the first ion exchange resin layer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. There is no particular upper limit to the content of the cation exchange resin, but it is preferably 100% by mass or less in the first ion exchange resin layer. It is more preferably 99.5% by mass or less, and even more preferably 99% by mass or less, because this tends to reduce the cost of removing substances other than the cation exchange resin in the first ion exchange resin layer and reduce the cost of the redox flow battery cell.

[0245] The method for producing the first cation exchange resin layer used in the diaphragm of this embodiment is not particularly limited, and the layer can be obtained by processing a cation exchange resin into a film, or by processing a cation exchange resin precursor having functional groups with ion exchange capacity by hydrolysis into a film, followed by the hydrolysis and acid treatment described above. For example, a method can be used in which the cation exchange resin is melt-kneaded and then extruded using an extruder through a nozzle or a die to form a film. Another method can be used in which the cation exchange resin precursor is melt-kneaded and then extruded using an extruder through a nozzle or a die to form a film, followed by hydrolysis and acid treatment to form ion exchange groups. Alternatively, a cation exchange resin can be dispersed in a solvent and then cast onto a substrate to form a film.

[0246] The method for producing the fluororesin G1 is as described above.

[0247] <Anion Exchange Resin Layer> The anion exchange resin layer is a layer containing an anion exchange compound. The anion exchange compound is a compound having a functional group and a molecular structure containing a nitrogen atom, such as a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, a pyridine ring structure and a derivative structure thereof, a pyridinium group, an imidazole ring structure and a derivative structure thereof, an imidazolium group, a pyrrole ring structure and a derivative structure thereof, and is a compound that is positively charged at least under acidic conditions.

[0248] The diaphragm of the present embodiment has an anion exchange resin layer, which imparts to the diaphragm an electrostatic repulsive force to the cations in the electrolyte, thereby suppressing permeation of the redox active material with a high charge density through the diaphragm while allowing protons with a low charge density to permeate the diaphragm, thereby improving power efficiency.

[0249] The anion exchange compound is not particularly limited, and examples thereof include polyvinylpyridine polymers and salts thereof, vinylpyridine / divinylbenzene copolymers and salts thereof, vinylpyridine / styrene copolymers and salts thereof, polyethyleneimine and salts thereof, vinylbenzyltrimethylammonium chloride polymers, polyvinylimidazole polymers and salts thereof, vinylimidazole / divinylbenzene copolymers and salts thereof, vinylimidazole / styrene copolymers and salts thereof, polyvinylpyrrolidone polymers and salts thereof, polybenzimidazole and salts thereof, polymers having a benzimidazole structure and salts thereof, polypyrrole and salts thereof, polyaniline, poly(4-aminostyrene) and salts thereof, poly (vinylcarbazole) and its salts, anion exchange polymers such as tetrabutylammonium, octyltrimethylammonium and other quaternary ammonium compounds having a quaternary ammonium group, pyridinium compounds having a pyridinium structure such as butylpyridinium, and derivatives thereof, trimethylamine and its salts, triethylamine and its salts, tributylamine and its salts, triethanolamine and its salts, pyrrole and its salts, pyrrole derivatives and its salts, 1,8-diazabicyclo[5.4.0]undecene-7 and its salts, 1,5-diazabicyclo[4.3.0]nonene-5 and its salts, 1,4-diazabicyclo[2.2.2]octane and its salts, 1-azabicyclo[2.2.2. ]octane and salts thereof, N,N,N',N'-tetramethylbutanediamine and salts thereof, ethylenediamine, N,N-dimethylethylenediamine, N-methylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyldipropylenetriamine, 1-(3-aminopropyl)imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, 4-aminopyridine, 1,2,3-triaminobenzene, hexamethylenetetramine, imidazole, oxazole, thiazole, pyrazole, aminobenzimidazole, 4-aminopiperidine, tetrafluoro-p-phenylenediamine, hexamethylenediamine, 4,4'-diaminodiphenyl ether, 4-benzylpyridine, and the like.

[0250] The anion exchange compound may be an anion exchange fluororesin represented by the following general formula B17, a saponified product thereof, or a salt thereof: -[CFX １ CX ２ X ３ ] ａ -[CF ２ -CF((-O-CF ２ -(CF(CF ２ X ４ ))) ｂ -O ｃ -(CFR １ ) ｄ -(CFR ２ ) ｅ -(CF ２ ) ｆ -Ae)] ｇ - [B17] (wherein, X １ , X ２ , X ３ and X ４ may be the same or different and are a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a cyclic perfluoroalkyl group, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X １ and X ２ , or X １ and X ３ may be a cyclic structure. １ , R ２ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group or a fluorochloroalkyl group having 1 to 10 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom or an iodine atom. Ae is -CONX ６ Ax, -SO ２ NX ６ Ax is a monovalent group represented by the formula ６is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or a substituted or unsubstituted aliphatic hydrocarbon group or aromatic hydrocarbon group having 1 to 10 carbon atoms; Ax is a substituted or unsubstituted aliphatic hydrocarbon group, aromatic hydrocarbon group, or heteroaromatic group having 1 to 20 carbon atoms containing at least one nitrogen atom. a and g represent molar ratios in all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1. b is an integer of 0 to 8. c is 0 or 1. d, e, and f may be the same or different, and are integers of 0 to 6 (however, when d, e, and f are simultaneously 0, Ae is -CF(CF ２ Az) ２ and Az is -CONX ６ Ax, -SO ２ NX ６ Ax and X are monovalent groups represented by the formula ６ The anion exchange compounds may be used singly or in combination of two or more.

[0251] In the case of "substitution", the substituent is the same as the substituent exemplified in general formula 1.

[0252] As the anion exchange compound, polyvinylpyridine polymers and salts thereof, vinylpyridine / divinylbenzene copolymers and salts thereof, vinylpyridine / styrene copolymers and salts thereof, polyethyleneimine and salts thereof, vinylbenzyltrimethylammonium chloride polymers, polyvinylimidazole polymers and salts thereof, vinylimidazole / divinylbenzene copolymers and salts thereof, vinylimidazole / styrene copolymers and salts thereof, polyvinylpyrrolidone polymers and salts thereof, polybenzimidazole and salts thereof, polymers having a benzimidazole structure and salts thereof, polypyrrole and salts thereof, polyaniline, poly(4-aminostyrene) and salts thereof, poly(vinylpyridine ... The anion exchange compound is preferably at least one selected from the group consisting of poly(vinylcarbazole) and salts thereof, an anion exchange fluororesin represented by general formula B17 and its saponification product or salts thereof, and more preferably at least one selected from the group consisting of polyvinylpyridine polymers and salts thereof, vinylpyridine / divinylbenzene copolymers and salts thereof, vinylpyridine / styrene copolymers and salts thereof, polyvinylimidazole polymers and salts thereof, vinylimidazole / divinylbenzene copolymers and salts thereof, vinylimidazole / styrene copolymers and salts thereof, polybenzimidazole and salts thereof, polymers having a benzimidazole structure and salts thereof, and anion exchange fluororesin represented by general formula B17.Since the electrostatic repulsion force of the anion exchange resin layer against cations increases and the power efficiency of the redox flow battery cell tends to improve, it is more preferable that the anion exchange compound be at least one selected from the group consisting of polyvinylpyridine polymers and salts thereof, polyvinylimidazole polymers and salts thereof, polybenzimidazole and salts thereof, polymers having a benzimidazole structure and salts thereof, and anion exchange fluororesins represented by general formula B17, and it is particularly preferable that the anion exchange compound be at least one selected from the group consisting of polyvinylpyridine polymers and salts thereof, polyvinylimidazole polymers and salts thereof, and anion exchange fluororesins represented by general formula B17.

[0253] The saponified anion-exchange fluororesin represented by general formula B17 is a saponified product obtained by reacting anion-exchange fluororesin with an alkaline substance. Examples of basic substances include amine compounds such as dimethylamine, diethylamine, monomethylamine, and monoethylamine, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkaline earth metal hydroxides. Among these, sodium hydroxide or potassium hydroxide is preferred.

[0254] The salt of an anion exchange fluororesin is a salt of an anion exchange fluororesin with an acidic substance, such as mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid, and trifluoroacetic acid.

[0255] In anion exchange fluororesin represented by the above general formula B17 that can be used as an anion exchange compound, from the viewpoint that the chemical stability of the anion exchange fluororesin, such as resistance to oxidation degradation, tends to be improved, and from the viewpoint that the production cost of the anion exchange fluororesin can be reduced, and the production cost of the redox flow battery cell tends to be reduced, it is preferable that the anion exchange fluororesin contains at least one selected from the group consisting of a structural unit represented by the following general formula B16, a structural unit represented by the following general formula B18, a structural unit represented by the following general formula B19, and a structural unit represented by the following general formula B20: -(CF ２ -CF２ ) - [B16] - (CF ２ -CF(-O-(CF ２ CFXO) Ｎ -Ag))- [B18] (wherein X represents F or a perfluoroalkyl group having 1 to 3 carbon atoms. Ag represents (CF ２ ) Ｍ -SO ２ NX ６ Ax (X ６ represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or a substituted or unsubstituted aliphatic hydrocarbon group or aromatic hydrocarbon group having 1 to 10 carbon atoms; Ax represents a substituted or unsubstituted aliphatic hydrocarbon group, aromatic hydrocarbon group, or heteroaromatic group having 1 to 20 carbon atoms containing at least one nitrogen atom; N represents an integer of 0 to 5; M represents an integer of 0 to 6; provided that N and M cannot be 0 at the same time; ) represents -(CF ２ -CF(-O-(CF ２ ) Ｐ -CFX(-O-(CF ２ ) Ｋ -SO ２ NX ６ Ax)))- [B19] (wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms. X ６ represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or a substituted or unsubstituted aliphatic hydrocarbon group or aromatic hydrocarbon group having 1 to 10 carbon atoms; Ax represents a substituted or unsubstituted aliphatic hydrocarbon group, aromatic hydrocarbon group, or heteroaromatic group having 1 to 20 carbon atoms containing at least one nitrogen atom; P represents an integer of 0 to 12; and K represents an integer of 1 to 5. However, P and K cannot be 0 at the same time. ) -(CF ２ -CF(-O-(CF ２ ) Ｑ -CFX(-(CF ２ ) Ｌ -O-(CF ２ ) ｏ -SO ２ NX ６ Ax)))-[B20] (wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms. X ６represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or a substituted or unsubstituted aliphatic hydrocarbon group or aromatic hydrocarbon group having 1 to 10 carbon atoms; Ax represents a substituted or unsubstituted aliphatic hydrocarbon group, aromatic hydrocarbon group, or heteroaromatic group having 1 to 20 carbon atoms containing at least one nitrogen atom; Q represents an integer of 0 to 12; L represents an integer of 1 to 5; and o represents an integer of 0 to 6, provided that Q and O cannot be 0 at the same time. The anion-exchange fluororesin is more preferably composed of a structural unit represented by general formula B16 and at least one selected from the group consisting of a structural unit represented by general formula B18, a structural unit represented by general formula B19, and a structural unit represented by general formula B20, and from the same viewpoint, it is even more preferable to contain a structural unit represented by general formula B16 and a structural unit represented by general formula B18 (wherein X is F or a trifluoromethyl group, n is an integer of 0 to 2, and m is an integer of 1 to 4), and it is particularly preferable to contain a structural unit represented by general formula B16 and a structural unit represented by general formula B18 (wherein X is F or a trifluoromethyl group, n is 0 or 1, and m is an integer of 2 to 4).

[0256] The anion-exchangeable fluororesin more preferably has a structural unit represented by the following general formula B21, and even more preferably has a structural unit represented by the following general formula B22: -[CF ２ CF ２ ] ａ -[CF ２ -CF((-O-CF ２ -(CF(CF ３ ))) ｂ -O-(CF ２ ) ２ -SO ２ NX ６ Ax)] ｇ - [B21] (wherein, X ６represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms; Ax represents a substituted or unsubstituted aliphatic hydrocarbon group, aromatic hydrocarbon group, or heteroaromatic group having 1 to 20 carbon atoms, containing at least one nitrogen atom. a and g represent molar ratios of all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1. b is 0 or 1.) -[CF ２ CF ２ ] ａ -[CF ２ -CF((-O-CF ２ -(CF(CF ３ )))-O-(CF ２ ) ２ -SO ２ NX ６ Ax)] ｇ - [B22] (wherein, X ６ represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or a substituted or unsubstituted aliphatic hydrocarbon group or aromatic hydrocarbon group having 1 to 10 carbon atoms; Ax represents a substituted or unsubstituted aliphatic hydrocarbon group, aromatic hydrocarbon group, or heteroaromatic group having 1 to 20 carbon atoms containing at least one nitrogen atom; a and g represent molar ratios of all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1.

[0257] In the above general formulas B17 to B22, the anion exchange fluororesin can be easily produced, and the production cost of the redox flow battery cell tends to be reduced. ６ is preferably a hydrogen atom or a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms. From the viewpoint of reducing the production cost of the anion exchange fluororesin, a hydrogen atom is more preferred, and from the viewpoint of improving the stability of the anion exchange fluororesin under alkaline conditions, an unsubstituted aliphatic hydrocarbon group having 1 to 2 carbon atoms is more preferred.

[0258] In the above general formulas B17 to B22, since raw material costs tend to be reduced and the production costs of redox flow battery cells can be suppressed, Ax is preferably an unsubstituted aliphatic hydrocarbon group, aromatic hydrocarbon group, or heteroaromatic group having 1 to 20 carbon atoms and containing at least one nitrogen atom, and more preferably an unsubstituted aliphatic hydrocarbon group or heteroaromatic group having 1 to 10 carbon atoms and containing at least one nitrogen atom. More specific preferred structures of the nitrogen atom contained in Ax include a primary amino group, a secondary amino group, a tertiary amino group, a pyridine ring structure and a derivative structure thereof, a pyridinium group, an imidazole ring structure and a derivative structure thereof, an imidazolium group, and a pyrrole ring structure and a derivative structure thereof, and a tertiary amino group, a pyridine ring structure and a derivative structure thereof, and an imidazole ring structure and a derivative structure thereof are more preferred.

[0259] The method for producing the anion exchange fluororesin is not particularly limited, but an example thereof is a method in which the fluororesin precursor is reacted with the anion exchange compound (hereinafter also referred to as "modified compound") excluding the anion exchange fluororesin.

[0260] Examples of the modified compound include modified compounds having at least two nitrogen atom-containing groups, and the nitrogen atom-containing groups include at least one selected from the group consisting of: a primary amino group, a secondary amino group, a tertiary amino group, an amino salt structure which is a reaction product of at least one amino group selected from the group consisting of primary amino groups, secondary amino groups, and tertiary amino groups with at least one selected from the group consisting of acidic substances and halogen-containing aliphatic hydrocarbon compounds, a nitrogen atom-containing heterocyclic structure, a nitrogen atom-containing heterocyclic salt structure which is a reaction product of a nitrogen-containing heterocyclic structure with at least one selected from the group consisting of acidic substances and halogen atom-containing aliphatic hydrocarbon compounds, and a quaternary ammonium group. Among these, at least one nitrogen atom-containing group is preferably a primary amino group or a secondary amino group, more preferably a primary amino group, because it tends to have improved reactivity with the fluororesin precursor. However, the quaternary ammonium group is a quaternary ammonium group different from the amino salt structure or the salt structure.

[0261] More specific examples of the modifying compound include ethylenediamine, N-methylethylenediamine, N-ethylethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N,N'-trimethylethylenediamine, N-benzylethylenediamine, N,N-dibutylethylenediamine, 1,2-diphenylethylenediamine, N,N'-dicyclohexyl-1,2-ethylenediamine, N,N-dimethyl-1,3-propanediamine, N, N-dimethyldipropylenetriamine, N,N-dibutyldipropylenetriamine, N,N-diethyl-1,3-propanediamine, N,N-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, N,N-dimethyl-1,4-cyclohexanediamine, 3-aminopiperidine, isophoronediamine, 4-(aminomethyl)piperidine, 3-aminopyrrolidine, 4-aminopiperidine, 3-aminopyrrolidine Lysine, N,N-dimethyltrimethylenediamine, N,N-dibutyltrimethylenediamine, 1-(3-aminopropyl)imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4-(ethylaminomethyl)pyridine, 4-(4-piperidyl)pyridine, 2-methyltryptamine, 5-methoxytryptamine, 6-methoxytryptamine, necrostatin-1, alosetron, sulfamethoxypyridazine, 1-(3-chloroanilino )-4-phenylphthalazine, 4-amino-5-aminomethyl-2-methylpyrimidine, 2-(aminomethyl)-5-methylpyrazine, 2-(4-piperidinyl)benzimidazole, 2-(4-aminophenyl)benzimidazole, 5-amino-2-(4-aminophenyl)benzimidazole, 6-(aminomethyl)quinoline, 2-methyl-7-[phenyl(phenylamino)methyl]-8-quinolinol, and 1-(2-amino-1-naphthyl)isoquinoline. The modifying compounds may be used alone or in combination of two or more.

[0262] As the modifying compound, ethylenediamine, N-methylethylenediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethyldipropylenetriamine, N,N-dibutyldipropylenetriamine, N,N-dimethyl-1,4-butanediamine, and N,N-dimethyl-1,6-hexanediamine are preferred because the raw materials are easily available and the production costs of the anion exchange fluororesin tend to be reduced. , N,N-dimethyltrimethylenediamine, N,N-dibutyltrimethylenediamine, 1-(3-aminopropyl)imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4-(ethylaminomethyl)pyridine, 4-(2-aminoethyl)pyridine, 4-(4-piperidyl)pyridine, 2-(4-piperidinyl)benzimidazole, 2-(4-aminophenyl)benzimidazole, and 5-amino-2-(4-aminophenyl)benzimidazole are preferred. When used in a battery cell for a redox flow battery, they tend to have a good balance of current efficiency, voltage efficiency, and power efficiency. Therefore, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethyldipropylenetriamine, N,N-dibutyldipropylenetriamine, N,N-dimethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, N,N-dimethyltrimethylenediamine, 1-(

[0111] N,N-dimethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyldipropylenetriamine, N,N-dimethyltrimethylenediamine, 1-(3-aminopropyl)imidazole, 4-(2-aminoethyl)pyridine, 4-picolylamine, isonicotinamide, 4-(4-piperidyl)pyridine, and 2-(4-aminophenyl)benzimidazole are more preferred, and from the same viewpoint, N,N-dimethylethylenediamine, N,N-dibutylethylenediamine, N,N-dimethyldipropylenetriamine, N,N-dimethyltrimethylenediamine, 1-(3-aminopropyl)imidazole, 4-picolylamine, and 4-(2-aminoethyl)pyridine are even more preferred.

[0263] The anion exchange resin layer is preferably a styrene resin, a vinyl chloride resin, a chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a polyether ether ketone resin, a polysulfone resin, a polyethersulfone resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a polyphenylene ether resin, a polyphenylene sulfide resin, a syndiotactic polystyrene resin, a polyetherimide, a siloxane-modified polyetherimide resin, a polyamideimide resin, a cycloolefin resin, a cycloolefin copolymer, a polyether ketone ether ketone ketone resin, a polyaryl ether ketone resin, or a fluororesin, and may further contain a styrene resin, a vinyl chloride resin, a chlorinated polyethylene, a polyamide resin, a polyphenylene ether / polystyrene resin, a high-density polyethylene resin, a low-density polyethylene resin, a linear low-density polyethylene resin, a syndiotactic polystyrene resin, a cycloolefin resin, a cycloolefin copolymer, or a fluororesin represented by the above general formula G1. The resin that may be contained in the anion exchange resin layer may be one type alone or a combination of two or more types.

[0264] From the viewpoint that durability of the redox flow battery cell tends to be improved, a fluororesin is preferred.

[0265] The content of the anion exchange compound contained in the anion exchange resin layer is not particularly limited, but from the viewpoint of enhancing the tendency to suppress permeation of the redox active material through the diaphragm, it is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. There is no particular upper limit to the content of the anion exchange compound contained in the anion exchange resin layer, and it is preferably 100% by mass or less. In order to facilitate availability and reduce the cost of forming the anion exchange resin layer, it is more preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99% by mass or less.

[0266] When the anion exchange resin layer contains an anion exchange compound and a fluororesin, the content of the anion exchange compound in the anion exchange resin layer is not particularly limited, but from the viewpoint of enhancing the tendency to suppress permeation of the redox active material through the diaphragm, it is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and particularly preferably 15% by mass or more. From the viewpoint of enhancing the tendency to improve the durability of the anion exchange resin layer, it is preferably 99% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and particularly preferably 70% by mass or less.

[0267] The thickness of the anion exchange resin layer is 0.001 μm or more and less than 5 μm. Because proton transfer resistance tends to be reduced and power efficiency tends to be improved, the thickness is preferably 4 μm or less, more preferably 3 μm or less, and even more preferably 1.5 μm or less. Because permeation of the redox active material through the diaphragm tends to be suppressed and power efficiency tends to be improved, the thickness is preferably 0.01 μm or more, more preferably 0.02 μm or more, and especially preferably 0.04 μm or more. Because mechanical strength against pulsation of the electrolyte solution, contact with the electrodes, etc. tends to be improved, the thickness is more preferably 0.1 μm or more, especially preferably 0.3 μm or more, and even especially preferably 0.4 μm or more.

[0268] A method for producing a diaphragm including at least the first cation exchange resin layer and the anion exchange resin layer of this embodiment can be achieved by a process including a step of forming the first cation exchange resin layer and a step of forming the anion exchange resin layer. The method for producing a diaphragm of this embodiment includes the steps of reacting a fluororesin precursor layer, which serves as a precursor of a first cation exchange resin layer and contains at least one group selected from the group consisting of a halogenated sulfonyl group, an acyl halide group, and a halogenated phosphate group, with a modifying compound having at least two nitrogen atom-containing groups, the nitrogen atom-containing groups being at least one selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, an amino salt structure which is a reaction product of at least one amino group selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group with at least one group selected from the group consisting of an acidic substance and a halogenated aliphatic hydrocarbon compound, a nitrogen atom-containing heterocyclic structure, a nitrogen atom-containing heterocyclic salt structure which is a reaction product of a nitrogen-containing heterocyclic structure and at least one group selected from the group consisting of an acidic substance and a halogenated aliphatic hydrocarbon compound, and a quaternary ammonium group; It is preferable to include, after the above step, a step of converting at least one selected from the group consisting of a halogenated sulfonyl group, an acyl halide group, and a halogenated phosphate group contained in the fluororesin precursor layer into at least one selected from the group consisting of a sulfo group, a carboxyl group, and a phosphate group. However, the quaternary ammonium group is a quaternary ammonium group different from the amino salt structure and the salt structure. The fluororesin precursor layer is a layer that serves as a precursor of the first cation exchange resin layer and contains at least one selected from the group consisting of a halogenated sulfonyl group, an acyl halide group, and a halogenated phosphate group.

[0269] The method for producing the anion exchange resin layer is not particularly limited, and examples include a method in which an anion exchange compound or a mixture containing an anion exchange compound is molten and extruded using an extruder through a nozzle or die to form a film, or a method in which an anion exchange compound or a mixture containing an anion exchange compound is put into a solution state and applied to a substrate using a die, gravure roll, knife, or spray, and then dried to form a film.

[0270] After forming the anion exchange resin layer, the anion exchange resin layer and the first cation exchange resin layer are laminated to produce a diaphragm. The lamination method is not particularly limited, but examples include a lamination method using hot pressing and / or hot roll pressing.

[0271] The fluororesin precursor is melt-kneaded and extruded using an extruder through a nozzle or a die to form a film, which is then brought into contact with a mixture containing a modifying compound to form a layer containing an anion exchange fluororesin. The resulting film is then hydrolyzed to form a fluororesin, thereby forming a layer containing a fluororesin that will become the first cation exchange resin layer and a layer containing an anion exchange fluororesin that will become the anion exchange resin layer, thereby producing a diaphragm.

[0272] When producing the diaphragm, a substrate may be used. By using a substrate, the first cation exchange resin layer and / or the anion exchange resin layer may be produced more stably in some cases.

[0273] The material used for the substrate is not particularly limited, and examples thereof include polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, cycloolefin polymer, polycarbonate, polyamide, polyimide, polyamideimide, polyvinyl chloride, polystyrene, polyphenylene ether, polyether ether ketone, polysulfone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyetherimide, polyimide resin, polyether ketone ether ketone ketone, polyaryl ether ketone, etc. The above materials may be modified as necessary, and may be used alone or in combination of two or more types.

[0274] The solvent used to prepare a solution of the mixture containing the anion exchange compound is not particularly limited, and examples thereof include saturated hydrocarbon compounds such as n-pentane, n-hexane, n-octane, n-decane, cyclopentane, cyclohexane, and cyclooctane; aromatic hydrocarbon compounds such as benzene, toluene, xylene, and ethylbenzene; halogenated hydrocarbon compounds such as methylene chloride, chloroform, carbon tetrachloride, chlorobenzene, and dichlorobenzene; alcohols such as methanol, ethanol, propanol, isopropanol, butanol, hexanol, cyclohexanol, and benzyl alcohol; acetone, ethyl methyl ketone, methyl butyl ketone, methyl isobutyl ketone, and cyclohexanol. ketones such as benzophenone; esters such as ethyl acetate, butyl acetate, and methyl benzoate; ethers such as diethyl ether, dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, and dioxane; polyols such as ethylene glycol, propylene glycol, and glycerin, and polymers of compounds of these polyols having two hydroxyl groups, and polyols; esterified compounds of the above polymers, and nitriles such as acrylonitrile and benzonitrile; nitromethane; N,N-dimethylformamide; dimethyl sulfoxide; hexamethylphosphoric triamide; carbon disulfide; fluorine-based compounds (e.g., Novec (trademark) manufactured by 3M Company, Asahiklin manufactured by Asahi Glass Co., Ltd.); and the like. These solvents may be used alone or in combination.

[0275] <Second cation exchange resin layer> The diaphragm of the present embodiment may further include a second cation exchange resin layer. In the diaphragm, the second cation exchange resin layer may include a first cation exchange resin layer, an anion exchange resin layer, and a second cation exchange resin layer in this order.

[0276] In a diaphragm using a second cation exchange resin layer, the thickness of the first cation exchange resin layer is greater than the thickness of the second cation exchange resin layer. The thickness of the second cation exchange resin layer is not particularly limited as long as it is smaller than the thickness of the first cation exchange layer, but is preferably 0.01 μm or more and less than 150 μm. Since proton transfer resistance tends to be reduced and power efficiency tends to be improved, the thickness is more preferably 100 μm or less, even more preferably 50 μm or less, and particularly preferably 20 μm or less. Since mechanical strength against pulsation of the electrolyte, contact with electrodes, etc. tends to be improved, the thickness is more preferably 0.1 μm or more, even more preferably 0.5 μm or more, and particularly preferably 1 μm or more.

[0277] The value obtained by dividing the thickness of the second ion exchange resin layer by the thickness of the first cation exchange resin layer is not particularly limited, but is preferably less than 0.7. The anion exchange resin layer can be disposed closer to the electrode acting as the negative electrode, which tends to suppress permeation of the redox active material through the diaphragm and improve power efficiency. Therefore, the value obtained by dividing the thickness of the second ion exchange resin layer by the thickness of the first cation exchange resin layer is more preferably 0.6 or less, and even more preferably 0.5 or less. The value obtained by dividing the thickness of the second ion exchange resin layer by the thickness of the first cation exchange resin layer may be any value greater than 0. From the viewpoint of simplifying the production of the second ion exchange resin layer, the value is preferably 0.0001 or more. The value is more preferably 0.001 or more, and particularly preferably 0.01 or more, because mechanical strength against pulsation of the electrolyte and contact with the electrode tends to be improved.

[0278] The second cation exchange resin layer, like the first cation exchange resin layer, is a layer formed of a substance containing a cation exchange resin. The cation exchange resin used in the second cation exchange resin layer is not particularly limited, but the cation exchange resin preferably used is the same as that used in the first cation exchange resin layer. From the viewpoint that the durability of the redox flow battery cell tends to be improved, the second cation exchange resin layer more preferably contains a fluorine-based cation exchange resin. The cation exchange resin contained in the first cation exchange resin layer and the cation exchange resin contained in the second cation exchange resin layer may be the same or different.

[0279] The method for producing a membrane comprising a first cation exchange resin layer, an anion exchange resin layer, and a second cation exchange resin layer is not particularly limited, and examples thereof include a method in which a cation exchange resin to be the second cation exchange resin layer is melt-kneaded onto a two-layer membrane comprising a first cation exchange resin layer and an anion exchange resin layer, and then extruded using an extruder with a nozzle or a die to form a film, a method in which a cation exchange resin precursor to be the second cation exchange resin layer is melt-kneaded, and then extruded using an extruder with a nozzle or a die to form a film, and then subjected to the above-mentioned hydrolysis treatment and acid treatment to form ion exchange groups, and a method in which a cation exchange resin to be the second cation exchange resin layer is dispersed in a solvent, and then cast-formed into a film, etc. A two-layer membrane comprising two types of cation exchange resin layers and an anion exchange resin layer can also be produced by overlapping the anion exchange resin layers simultaneously. When the anion exchange resin layers are laminated together, heat pressing and / or heat roll pressing can be used since this tends to reduce peeling between the anion exchange resin layers.

[0280] The diaphragm of this embodiment can also use a support. The support is not particularly limited, and examples thereof include supports made of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, cycloolefin polymer, polyamide, polyimide, polyamideimide, polyvinyl chloride, polystyrene, polyphenylene ether, polyether ether ketone, polysulfone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyetherimide, polyimide resin, polyetherketone ether ketone ketone, polyaryl ether ketone, and fluororesin. It is preferable not to use a support because voids may form between the cation exchange resin layer or the anion exchange resin layer and the support, which may reduce the performance of the redox flow battery cell.

[0281] <Membrane Electrode Assembly> The membrane electrode assembly in this embodiment has a structure in which at least one of a first electrode and a second electrode is joined to a diaphragm. The joining refers to connecting the at least one of the first electrode and the second electrode to the diaphragm, and by joining, the at least one of the first electrode and the second electrode and the diaphragm can be integrated. For example, a membrane electrode assembly including a first electrode, a second electrode, and a diaphragm may be preferably used when assembling a redox flow battery cell because it eliminates the need for a step of assembling the first electrode, the diaphragm, and the second electrode in order, allowing for a single step, which tends to reduce production costs.

[0282] The method for bonding at least one of the first electrode and the second electrode to the diaphragm is not particularly limited, but examples include a method using hot pressing and / or hot roll pressing.

[0283] The temperature during bonding is not particularly limited, but is preferably room temperature or higher, because if the bonding between the diaphragm and the electrode is insufficient, the elastic modulus of the diaphragm will decrease, tending to improve the bonding between the diaphragm and the electrode.The temperature during bonding is preferably 250°C or lower, more preferably 200°C or lower, even more preferably 170°C or lower, and particularly preferably 150°C or lower, because this tends to prevent deterioration of the diaphragm.

[0284] The pressure during bonding is not particularly limited, but is a pressure exceeding 0 MPa. Since bonding between the diaphragm and the electrode tends to be improved, the pressure is preferably 0.01 MPa or more, more preferably 0.05 MPa or more, even more preferably 0.08 MPa or more, and particularly preferably 0.1 MPa or more. Since deterioration of the electrode tends to be suppressed, the pressure is preferably 100 MPa or less, more preferably 50 MPa or less, even more preferably 20 MPa or less, and particularly preferably 10 MPa or less.

[0285] The bonding time is not particularly limited, but is preferably more than 0 second. Because bonding between the diaphragm and the electrode tends to be improved, the bonding time is preferably 0.01 second or more, more preferably 0.1 second or more, even more preferably 0.5 second or more, and particularly preferably 1 second or more. Because costs for producing the membrane electrode assembly tend to be reduced, the bonding time is preferably 10 hours or less, more preferably 5 hours or less, even more preferably 2 hours or less, and particularly preferably 1 hour or less.

[0286] The atmosphere during bonding is not particularly limited, but examples thereof include air, nitrogen, and argon. Air and nitrogen are preferred, and air is more preferred, as they tend to reduce the cost of producing a membrane electrode assembly.

[0287] <Redox flow battery> A redox flow battery can be formed by stacking the redox flow battery cells of this embodiment. When stacking, electricity can be passed between the redox flow battery cells via bipolar plates.

[0288] The material of the bipolar plate is not particularly limited, and examples thereof include carbon, graphite, and metal. The material may contain dispersed carbon particles, carbon fibers, metal particles, metal fibers, graphene, and carbon nanotubes. One type of material may be used alone, or multiple types may be used in combination.

[0289] The bipolar plate may have various flow channels, which may improve contact between the electrodes and the electrolyte. The flow channels are not particularly limited, and examples include serpentine, interdigitated, parallel, multi-parallel, discontinuous, and combinations of the above flow channels.

[0290] The redox flow battery cell and redox flow battery of this embodiment can be used to provide a mechanism for smoothing power supply and demand and stabilizing fluctuating power obtained from renewable energy sources such as solar energy and wind energy. More specifically, they can provide integration of power obtained from renewable energy sources, power peak load shifting, grid stabilization, baseload power, energy arbitrage, weak grid support, frequency regulation, and any combination thereof. They can also be used as a power source for remote camps, forward operating bases, power transmission and distribution telecommunications, remote sensors, and other applications that do not use the power grid.

[0291] The redox flow battery cell and the redox flow battery of this embodiment can be equipped with a control system and a power conditioning unit.

[0292] A control system may be used to control the operation of various valves, pumps, circuits, sensors, mitigation devices, other electronic / hardware controls, safeguards, and the like.

[0293] By using the power conditioning unit, the voltage and current of the input power can be converted into a form optimal for the redox flow battery cell and / or the redox flow battery, and the voltage and current of the output power can be converted into a form optimal for any application. For example, when the redox flow battery cell and / or the redox flow battery is connected to a power grid, the power conditioning unit can convert the input AC power into DC power of an appropriate voltage and current during the charge cycle. Also, during the discharge cycle, the redox flow battery cell and / or the redox flow battery generates DC power, and the power conditioning unit can convert the DC power into AC power of an appropriate voltage and frequency for transmission to the power grid.

[0294] Fourth Embodiment Next, a fourth embodiment will be described.

[0295] In Patent Document 5, a solvent containing a large amount of ethanol, a protic solvent, is used (in the examples of Patent Document 1, the ethanol content is 50% by mass), and when the fluororesin content in the solution is increased, the viscosity of the solution tends to increase, making it difficult to store the solution in the optimum viscosity range for the film formation process by coating and drying.In addition, the solution viscosity tends to change significantly over time, making it difficult to store the solution in the optimum viscosity range for the film formation process by coating and drying.

[0296] In Patent Document 6, N,N-dimethylformamide is used as a hydrophilic, high-boiling solvent. When an ion exchange membrane is produced by applying a polymer electrolyte solution, drying the applied solution, and then heat-treating the solution, the N,N-dimethylformamide remaining in the ion exchange membrane decomposes to produce dimethylamine as an impurity in the ion exchange membrane. This causes a problem that the properties of the ion exchange membrane are deteriorated due to the impurity depending on the application.

[0297] Patent Document 7 and Non-Patent Document 1 state that it is difficult to increase the molecular weight of a perfluorosulfonic acid polymer with a large proportion of sulfonic acid groups sufficiently, and that when an ion exchange membrane is obtained by coating and drying a solution of a perfluorosulfonic acid polymer with a large proportion of sulfonic acid groups that does not have a sufficiently large molecular weight, a membrane with sufficient mechanical strength cannot be obtained with the solvent compositions of conventional known techniques, and therefore there is a need for a membrane of a perfluorosulfonic acid polymer with a large proportion of sulfonic acid groups that has sufficient mechanical strength.

[0298] In Patent Document 8, a perfluorosulfonic acid polymer precursor is co-extruded with an incompatible polymer to obtain an ion exchange membrane with a thickness of 25 μm or less, which is difficult to produce by conventional extrusion molding techniques. However, although the ion exchange membrane produced by this invention has reduced anisotropy compared to conventionally known extrusion-molded ion exchange membranes made of perfluorosulfonic acid polymer, in applications where the ion exchange membrane is used immersed in an electrolyte or solvent, such as redox flow batteries and water electrolysis, the in-plane anisotropy inherent in the molding method causes the polymer electrolyte membrane to swell in the electrolyte, resulting in anisotropic dimensional changes in the ion exchange membrane relative to the membrane surface, which may adversely affect its properties. In other words, there is a need for an ion exchange membrane containing a perfluorosulfonic acid polymer with reduced anisotropy.

[0299] As described above, it has been difficult with conventional known techniques to provide a polymer electrolyte solution in which the solution viscosity of a solution containing a fluororesin with a high ratio of sulfonic acid changes little over time and can be set in an optimum viscosity range for a membrane formation process by coating and drying, and an ion exchange membrane obtained by coating and drying the solution, which has sufficient mechanical strength, few cracks per unit area, an appropriate membrane thickness that allows for low electrical resistance, and small in-plane anisotropy of the electrolyte membrane.

[0300] An object of the present embodiment is to provide a novel polymer electrolyte solution for forming a polymer membrane.

[0301] The polymer electrolyte solution according to the present embodiment is a polymer electrolyte solution comprising: a fluororesin having a structural unit represented by the following general formula G1, whose equivalent weight is equal to or greater than 500 g / eq and less than 1,000 g / eq; and a solvent containing water, an aliphatic alcohol, and an aliphatic carboxylic acid, wherein the mass ratio of the total of the aliphatic carboxylic acid and its reaction product to the total mass of the solvent is 100:1 to 100:50. (In the formula, the definition of each substituent is the same as in the above-mentioned general formula G1.)

[0302] According to this embodiment, it is possible to provide a novel polymer electrolyte solution that forms a polymer membrane.

[0303] Furthermore, according to the above-described embodiments, a polymer electrolyte solution containing a fluororesin with a high sulfonic acid ratio can be provided, with little change in solution viscosity over time, and the solution viscosity can be set to an optimal viscosity range for a membrane formation process by coating and drying. It is also possible to provide an ion exchange membrane containing a fluororesin with a high sulfonic acid ratio that has sufficient mechanical strength, few cracks per unit area, an appropriate thickness that allows for low electrical resistance, small in-plane anisotropy of the electrolyte membrane, excellent thickness uniformity, and a sufficiently large area. Furthermore, a redox flow battery cell and a redox flow battery using the ion exchange membrane can be provided.

[0304] (Fluororesin G1) The fluororesin of this embodiment (hereinafter also referred to as "fluororesin G1") has a structural unit represented by the following general formula G1, having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq. (In the formula, the definition of each substituent is the same as in the above-mentioned general formula G1.)

[0305] In the fourth embodiment, the fluororesin G1 preferably has a structural unit represented by the following general formula C3: —[CF ２ CX １ X ２ ] ａ -[CF ２ -CF((-O-CF ２ -CF (CF ２ X ３)) ｂ -O ｃ -(CFR １ ) ｄ -(CFR ２ ) ｅ -(CF ２ ) ｆ -X ４ )] ｇ - [C3] (wherein, X １ , X ２ , and X ３ are each independently a halogen atom or a perfluoroalkyl group having 1 to 3 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. １ , R ２ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. ４ is -COOZ, -SO ３ Z, -PO ３ Z ２ , or -PO ３ a monovalent group represented by the formula HZ, or -COOMOOC-, -SO ３ MO ３ S-, -PO ３ M ２ O ３ P- or -PO ３ HMHO ３ X is a divalent group represented by the formula: ４ is a divalent group, X ４ The fluororesins G1 may be crosslinked to each other via a bond. Z is a hydrogen atom, an alkali metal atom, or an amine. M is an alkaline earth metal atom. X ４ Ga-PO ３ Z ２ When the formula is:

[0306] X １ , X ２ , and X ３are each independently a halogen atom or a perfluoroalkyl group having 1 to 3 carbon atoms, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. １ , X ２ , and X ３ As R, a fluorine atom, a chlorine atom, or a perfluoroalkyl group having 1 to 3 carbon atoms is preferred, a fluorine atom, a chlorine atom, or a perfluoroalkyl group having 1 carbon atom is more preferred, a fluorine atom or a chlorine atom is even more preferred, and a fluorine atom is particularly preferred, because raw materials are easily available and the production cost of the fluororesin G1 tends to be reduced. １ , R ２ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group, and the halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. １ , R ２ As X, a fluorine atom and an unsubstituted perfluoroalkyl group having 1 to 3 carbon atoms are preferred from the viewpoints that raw materials are easily available and that the production cost of the fluororesin G1 tends to be reduced. Furthermore, from the viewpoint that the chemical stability of the fluororesin G1, such as resistance to oxidation and deterioration, tends to be improved, a fluorine atom and a trifluoromethyl group are more preferred, and a fluorine atom is particularly preferred. ４ is -COOZ, -SO ３ Z, -PO ３ Z ２ , or -PO ３ a monovalent group represented by the formula HZ, or -COOMOOC-, -SO ３ MO ３ S-, -PO ３ M ２ O ３ P- or -PO ３ HMHO ３ X is a divalent group represented by the formula: ４ is a divalent group, X ４ The fluororesins G1 may be crosslinked to each other via a group represented by the formula: Z represents a hydrogen atom, an alkali metal atom, or an amine; M represents an alkaline earth metal atom; X ４ Ga-PO ３ Z２ In this case, the two Z's may be the same or different. The alkali metal is not particularly limited, and a lithium atom, a sodium atom, or a potassium atom is preferred, and a sodium atom or a potassium atom is more preferred. The amine is not particularly limited, and NH ４ , N.H. ３ R １０ , N.H. ２ R １０ R １１ , N.H.R. １０ R １１ R １２ , N.R. １０ R １１ R １２ R １３ The structure of R １０ , R １１ , R １２ , and R １３ may be the same or different and are not particularly limited as long as they have a commonly used structure, and examples thereof include an aliphatic hydrocarbon group and an aromatic hydrocarbon group. ｎ H ２ｎ＋１ (n represents an integer of 1 or more, preferably an integer of 1 to 20, and more preferably an integer of 1 to 10). As the aromatic hydrocarbon group, a phenyl group or a naphthyl group is preferred. M is an alkaline earth metal atom, and is not particularly limited, but a magnesium atom or a calcium atom is preferred. a and g are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1. b is an integer of 0 to 8. c is 0 or 1. d, e, and f are each independently an integer of 0 to 6 (however, d, e, and f are not all 0 at the same time).

[0307] In the fluororesin G1 having a structural unit represented by the above general formula C3, from the viewpoint of achieving a better balance between dispersibility and film strength, it is preferably represented by the following general formula C1 or the following general formula C4, and more preferably represented by the following general formula C4: -[CF ２ CF ２ ] ａ -[CF ２ -CF((-O-CF ２ -CF (CF３ )) ｂ -O-(CF ２ ) ｃ -SO ３ X) ] ｄ - [C1] (wherein a and d are 0≦a<1, 0≦d<1, and a+d=1; b is an integer of 1 to 8; c is an integer of 0 to 10; and X is a hydrogen atom or an alkali metal atom.) - [CF ２ CF ２ ] ｅ -[CF ２ -CF((-O-(CF ２ ) f -SO ３ X) ] ｇ - [C4] (wherein e and g are 0≦e<1, 0≦g<1, e+g=1. f is an integer of 0 to 10. Y is a hydrogen atom or an alkali metal atom.) The fluororesin G1 can be a prepared product prepared by a known method or a commercially available product.

[0308] (Polymer Electrolyte) The polymer electrolyte in this embodiment includes fluororesin G1, which is a type of polymer electrolyte. The ratio of fluororesin G1 to the polymer electrolyte is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more. When the ratio of fluororesin G1 to the polymer electrolyte is 70% by mass or more, the current efficiency of the fuel cell tends to be excellent when used in a fuel cell. The fluororesin G1 used in the polymer electrolyte may be used alone or in combination of multiple types.

[0309] The polymer electrolyte of this embodiment may contain, as a polymer electrolyte different from fluororesin G1, acidic polymers such as perfluorocarboxylic acid polymers, partially fluorinated sulfonic acid polymers, and partially fluorinated carboxylic acid polymers, and basic polymers such as azole polymers (including imidazole polymers) and amine polymers. The acidic polymers and basic polymers may be used alone or in combination. When the polymer electrolyte contains fluororesin G1 and the basic polymer, the resulting ion exchange membrane of a fuel cell tends to have improved chemical durability during fuel cell operation. The polymer electrolyte of this embodiment may contain a polymer such as polyethylene glycol, polyphenylene ether, polyphenylene sulfide, polyetherimide, polysulfone, polyether ketone, polyether ether ketone, polyether ether imide, polyamide, polyimide, or polyamide imide. The polymers may be used alone or in combination. The mass % of the optional polymer contained in the polymer electrolyte is preferably 5 mass % or less, more preferably 3 mass % or less, and even more preferably 1 mass % or less, since this tends to impart the properties of the optional polymer to the ion exchange membrane while suppressing a decrease in the mechanical strength of the ion exchange membrane.

[0310] The equivalent mass (hereinafter also referred to as "EW") of fluororesin G1 having a structural unit represented by general formula C1 is preferably at least 600 g / eq but less than 1,000 g / eq, more preferably at least 650 g / eq but not more than 980 g / eq, and even more preferably at least 700 g / eq but not more than 950 g / eq, from the viewpoints of reducing the electrical resistance of the diaphragm and improving the mechanical strength of the diaphragm when the ion exchange membrane containing fluororesin G1 is used as a diaphragm for a redox flow battery. The "equivalent mass (EW) of fluororesin G1" refers to the dry weight per equivalent of sulfonic acid groups.

[0311] When an ion exchange membrane containing fluororesin G1 is used as a diaphragm for a redox flow battery, the equivalent mass (EW) of the fluororesin G1 having a structural unit represented by general formula C4 is, from the viewpoint of reducing the electrical resistance of the diaphragm and improving the mechanical strength of the diaphragm, preferably from 400 g / eq to less than 1,000 g / eq, more preferably from 450 g / eq to 980 g / eq, even more preferably from 500 g / eq to 950 g / eq, still more preferably from 600 g / eq to 950 g / eq, and still more preferably from 700 g / eq to 950 g / eq.

[0312] The melt flow rate (hereinafter also referred to as "MFR") can be used as an indicator of the degree of polymerization of the fluororesin G1 precursor. The MFR of the fluororesin G1 precursor is not particularly limited, but is preferably 100 g / 10 min or less, more preferably 50 g / 10 min or less, and even more preferably 30 g / 10 min or less. An MFR of 100 g / 10 min or less tends to provide an ion exchange membrane with excellent mechanical strength. Furthermore, the MFR is preferably 0.01 g / 10 min or more, more preferably 0.1 g / 10 min or more, and even more preferably 0.3 g / 10 min or more. An MFR of 0.01 g / 10 min or more tends to provide more efficient, finer dispersion and dissolution of the fluororesin G1 when it is prepared into a solution. The MFR can be measured by the method described in the examples.

[0313] (Polymer electrolyte solution) The polymer electrolyte solution in this embodiment contains a fluororesin G1 having an equivalent weight of 500 g / eq or more and less than 1,000 g / eq, and a solvent containing water, an aliphatic alcohol, an aliphatic carboxylic acid, and an aliphatic ester. The dissolution equipment for obtaining a uniform, colorless, and transparent polymer electrolyte solution from an emulsion containing the fluororesin G1 and the solvent is not particularly limited, but it is preferable to use equipment that continuously dissolves the fluororesin G1 and the solvent. The continuous dissolution equipment is heated by a heating means described below, and depending on the conditions within the dissolution equipment, the perfluorosulfonic acid polymer in the emulsion passing through the dissolution equipment dissolves in the solvent, allowing a uniform polymer electrolyte solution to be discharged from the dissolution equipment.

[0314] The continuous dissolving equipment preferably includes a pump for continuously supplying an emulsion containing the fluororesin G1 and a solvent into the dissolving equipment, a dissolving equipment for continuously dissolving the fluororesin G1 in the solvent, a heating means for heating the dissolving equipment, and a cooling means.

[0315] The pump is used to continuously supply an emulsion containing the fluororesin G1 and a solvent into a dissolution facility. The type of pump is not particularly limited, but examples include turbo pumps, piston pumps, plunger pumps, diaphragm pumps, gear pumps, vane pumps, and screw pumps. Among these, from the viewpoint of safety, plunger pumps, diaphragm pumps, multiple pumps, and accumulators are preferred, as they have excellent pressure resistance, and from the viewpoint of productivity, they have high metering accuracy, and they have high discharge pressure. Furthermore, from the viewpoint of suppressing pulsation, multiple pumps and accumulators are more preferred. The pumps may be used alone or in combination.

[0316] The dissolution equipment is not particularly limited, but examples thereof include equipment in which the fluid flow within the dissolution equipment is of the plug flow type.

[0317] The shape of the dissolution equipment is not particularly limited, but for example, a tube is preferred. A tube shape tends to further improve productivity and dissolution efficiency. The tube shape is not particularly limited, and examples include a straight shape, a coil shape, and a square shape. Among these, a coil shape is preferred from the viewpoint of installation area and stable operation. From the viewpoint of productivity and dissolution efficiency, the outer diameter of the tube is preferably 1 / 16 to 2 inches, more preferably 1 / 4 to 1 / 2 inches. Note that commonly available commercially available pipes of 6A to 500A may also be used. From the viewpoint of productivity and dissolution efficiency, an in-line mixer, a wire mesh, a metal filler, or the like may be installed inside the tube.

[0318] The melting equipment is not particularly limited, but is preferably tubular and made of metal. The material of the melting equipment is not particularly limited, but an optimal material may be selected from the viewpoint of corrosion resistance, and examples thereof include SUS-based materials, Hastelloy-based materials, titanium-based materials, zirconia-based materials, and tantalum-based materials. Among these, SUS-based materials and materials with the same composition as Hastelloy (a registered trademark of Haynes Corporation, USA) are preferred because they offer an excellent balance between corrosion resistance and cost. Materials with the same composition as SUS316 and Hastelloy C are more preferred, and materials with the same composition as Hastelloy C276 are particularly preferred. The same composition as Hastelloy, Hastelloy C, and Hastelloy C276 refers to materials with a composition containing 56 to 60% by mass of Ni, 16 to 22% by mass of Cr, 13 to 16% by mass of Mo, 2 to 6% by mass of W, 3 to 8% by mass of Fe, and 2.5% by mass or less of Co. The use of such metal dissolving equipment makes it possible to carry out the dissolving step at high temperature and high pressure, and the perfluorosulfonic acid polymer contained in the obtained polymer electrolyte solution tends to have improved stability at the end of the main chain of the perfluorosulfonic acid polymer. The inner wall of the tube may be lined. The lining is not particularly limited, but examples include fluorine lining and glass lining. The use of such lined dissolving equipment makes it possible to carry out the dissolving step at relatively low temperature and low pressure, and the concentrations of F ions and Fe ions in the obtained polymer electrolyte solution tend to be kept low.

[0319] The tube wall thickness is not particularly limited, but an optimum thickness may be selected from the viewpoint of pressure resistance. The tube inner diameter is not particularly limited, but from the viewpoints of productivity and dissolution efficiency, it is preferably 1 to 50 mm, more preferably 4 to 50 mm.

[0320] The surface roughness of the tube inner wall is not particularly limited and may be uneven or mirror-finished. From the viewpoint of dissolution efficiency, the maximum height of the surface roughness of the tube inner wall is preferably 50 μm or less, more preferably 25 μm or less, and even more preferably 10 μm or less. The maximum height of the surface roughness of the tube inner wall is a value obtained by, for example, using a laser microscope, extracting a reference length from a roughness curve in the direction of its average line, and measuring the distance between the peak line and the valley line of this extracted portion in the direction of the vertical magnification of the roughness curve.

[0321] The tube length depends on the required dissolution time (residence time). Specifically, the tube length can be calculated based on the relationship with the tube inner diameter so that the product of the dissolution time (min) and the supply rate (L / min) is equal to or less than the internal volume of the heated tube. Dissolution time (min) × supply rate (L / min) ≦ Internal volume of the tube Internal volume of the tube = (inner diameter of the tube / 2) 2 × π × tube length

[0322] When a plurality of tubular melting equipment are used in series, the melting equipment may be provided with a uniform or irregular union, a T-type union, a check valve, a safety valve, a back pressure valve, a pressure gauge, a thermometer, etc., which connect the melting equipment to each other. It is also possible to increase productivity by using a plurality of melting equipment in parallel and increasing the internal volume.

[0323] The heating means of the melting equipment is used to heat the melting equipment. The heating method is not particularly limited, but examples include methods of heating the melting equipment using a heat medium such as hot air, hot water, steam, or silicone oil. The heat medium may be used alone or in combination with multiple types. Among heat mediums, hot air is preferred because it is easy to use, and the melting equipment can be placed in a thermostatic chamber set to an atmosphere at a specific temperature by hot air.

[0324] The pressure within the dissolution equipment in the continuous dissolution equipment is not particularly limited, but it is preferable that the equipment further includes a pressure adjustment means for adjusting the pressure so that it exceeds the vapor pressure of the solvent at the heating temperature of the dissolution equipment. The pressure adjustment means may be installed downstream of the dissolution equipment in the supply direction, upstream of the supply direction, both upstream and downstream, or within the dissolution equipment. Examples of the pressure adjustment means include, but are not limited to, a back pressure valve, an automatic pressure control valve (PIC), and the above-mentioned pump. By using a back pressure valve or an automatic pressure control valve (PIC), the pressure within the dissolution equipment can be kept constant, i.e., pressure fluctuations are minimized, which tends to improve the dispersibility of the polymer electrolyte solution and prevent clogging within the dissolution equipment. Furthermore, the dissolution equipment can be pressurized by using a pump. The entire area from the pump to the pressure adjustment means (back pressure valve) can be considered as a sealed container with constant pressure. The continuous dissolution equipment described above tends to further improve the dispersibility of the polymer electrolyte in the polymer electrolyte solution, and also tends to produce an electrolyte solution with improved dispersibility at a higher concentration and in a shorter time.

[0325] The continuous dissolution equipment preferably has a cooling means downstream of the dissolution equipment that cools the polymer electrolyte solution while maintaining a pressure that exceeds the vapor pressure of the solvent at the heating temperature inside the dissolution equipment. The presence of such a cooling means tends to further prevent clogging of the dissolution equipment when the polymer electrolyte solution is discharged. The cooling method is not particularly limited, but examples include a method in which the polymer electrolyte solution is cooled by passing it through a cooling tube, and a method in which the polymer electrolyte solution is air-cooled by passing it through a tube at room temperature without passing through a cooling tube.

[0326] <Solvent> The polymer electrolyte solution according to this embodiment contains water, an aliphatic alcohol, and an aliphatic carboxylic acid. The polymer electrolyte solution according to this embodiment may contain a reaction product of the aliphatic carboxylic acid. Examples of the reaction product of the aliphatic carboxylic acid include an aliphatic carboxylic acid ester obtained by condensation of an aliphatic carboxylic acid with an aliphatic alcohol.

[0327] The mass ratio of the total of the aliphatic carboxylic acid and its reaction product to the total mass of the solvent is 100:1 to 100:50. By setting the mass ratio within this range, the occurrence of crack defects in the resulting ion exchange membrane can be suppressed. The mass ratio is preferably 100:3 to 100:40, more preferably 100:4 to 100:35, and even more preferably 100:5 to 100:30.

[0328] (Aliphatic Carboxylic Acid) In the present embodiment, the aliphatic carboxylic acid is a compound having a carboxyl group (—COOH group), and the carbon number of the aliphatic carboxylic acid is preferably 1 to 5, and examples thereof include formic acid, acetic acid, propionic acid, butyric acid, and isobutyric acid. When water is coexisting during membrane formation using a polymer electrolyte solution, the aliphatic carboxylic acid more preferably has 1 to 4 carbon atoms, even more preferably 1 to 3 carbon atoms, and particularly preferably acetic acid, since this tends to provide an excellent balance between miscibility with water and solvation of the hydrophobic moiety of the polymer electrolyte. The boiling point of the carboxylic acid is preferably 165° C. or lower, and more preferably 150° C. or lower, since this tends to improve drying properties during membrane formation. The ratio of the aliphatic carboxylic acid to the amount of solvent in the polymer electrolyte solution is preferably 1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 40% by mass or less, and even more preferably 3% by mass or more and 30% by mass or less, because when water is coexisting in the polymer electrolyte solution during membrane formation, the balance between miscibility with water and solvation of the hydrophobic moiety of the polymer electrolyte tends to be excellent. When the ratio of the aliphatic carboxylic acid is 1% by mass or more, the rate of change over time in the solution viscosity of the polymer electrolyte solution tends to be small. When the ratio of the aliphatic carboxylic acid is 30% by mass or less, the drying property of the polymer electrolyte solution during cast membrane formation tends to be improved.

[0329] (Aliphatic Alcohol) In this embodiment, the aliphatic alcohol is a compound having a hydroxyl group (—OH group). The number of carbon atoms is preferably 1 to 10, more preferably 1 to 7, and even more preferably 1 to 4, from the viewpoint that when water is coexisting during membrane formation using a polymer electrolyte solution, the aliphatic alcohol tends to have an excellent balance between miscibility with water and solvation of the hydrophobic moiety of the polymer electrolyte. Specific examples of aliphatic alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and isobutanol. Of these, methanol, ethanol, 1-propanol, and 1-butanol are preferred. The boiling point of the alcohol is preferably 165°C or lower, more preferably 150°C or lower, because this improves drying properties during membrane formation. The ratio of the amount of aliphatic alcohol to the amount of solvent in the polymer electrolyte solution is preferably 5% by mass or higher and 70% by mass or lower, more preferably 5% by mass or higher and 60% by mass or lower, and even more preferably 5% by mass or higher and 50% by mass or lower. When the alcohol content is 5% by mass or more, the pin puncture strength of the ion exchange membrane tends to be improved, and when the alcohol content is 50% by mass or less, the rate of change in the solution viscosity of the polymer electrolyte solution over time tends to be small.

[0330] (Aliphatic Ester) In the present embodiment, the aliphatic ester is a compound having an ester group (-COOR group: R is a hydrocarbon group), and the number of carbon atoms is preferably 2 to 10, more preferably 2 to 8, and even more preferably 2 to 6, because when water is coexisting during membrane formation using a polymer electrolyte solution, the aliphatic ester tends to have an excellent balance of miscibility with water and solvation of the hydrophobic moiety of the polymer electrolyte. Specific examples of aliphatic esters include methyl formate, ethyl formate, n-propyl formate, isopropyl formate, n-butyl formate, sec-butyl formate, isobutyl formate, methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, sec-butyl acetate, isobutyl acetate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, n-butyl butyrate, sec-butyl butyrate, and isobutyl butyrate. Among these, methyl acetate, ethyl acetate, n-propyl acetate, and n-butyl acetate are preferred. The boiling point of the ester is preferably 160°C or lower, more preferably 150°C or lower, since this improves drying properties during membrane formation. The ratio of the aliphatic ester to the amount of solvent in the polymer electrolyte solution is preferably 1% by mass or higher and 40% by mass or lower, more preferably 1% by mass or higher and 35% by mass or lower, and even more preferably 1% by mass or higher and 30% by mass or lower. When the ester amount ratio is 1% by mass or higher, the pin puncture strength of the ion exchange membrane tends to be improved. When the ester amount ratio is 30% by mass or lower, the rate of change over time in the solution viscosity of the polymer electrolyte solution tends to be small.

[0331] The solution viscosity (25°C) of the polymer electrolyte solution is 10 mPa·s or more and 2,000 mPa·s or less, preferably 50 mPa·s or more and 1,000 mPa·s or less, and more preferably 100 mPa·s or more and 1,000 mPa·s or less. When the initial solution viscosity (25°C) of the polymer electrolyte solution is 10 mPa·s or more, the thickness of the polymer electrolyte solution tends to be uniform during coating. When the viscosity is 2,000 mPa·s or less, there is a tendency for fewer bubbles to form after coating, and / or for the thickness of the ion exchange membrane to be uniform. The pot life of the solution viscosity of a polymer electrolyte solution refers to the shorter of the number of days required for the viscosity (25°C) of a polymer electrolyte solution prepared within a viscosity range of 10 mPa·s or more and 2,000 mPa·s or less, when measured within 24 hours after preparation, to increase by at least two times, or the number of days required for the viscosity to exceed 2,000 mPa·s. In particular, in the case of perfluorocarbon sulfonic acids of the above general formula C4, conventional techniques have had the problem of short pot life within the above appropriate viscosity range. By using the solvent composition of the present invention, the pot life can be improved.

[0332] The solid content of the polymer electrolyte solution is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 35% by mass or less, and even more preferably 10% by mass or more and 30% by mass or less. When the solid content of the polymer electrolyte solution is 10% by mass or more, the time required for drying during application tends to be shortened. When the solid content of the polymer electrolyte solution is 35% by mass or less, the solution viscosity of the polymer electrolyte solution tends to be small, and the rate of increase in solution viscosity over time tends to be small.

[0333] (Ion Exchange Membrane) The ion exchange membrane of the present embodiment can be obtained, for example, by applying the polymer electrolyte solution of the present embodiment to a known substrate (application step), drying (drying step), optionally cooling (cooling step), and further heat-treating (heat-treating step). The term "application and drying" refers to a series of steps including at least the application step and the drying step.

[0334] The coating method in the coating step is not particularly limited, and known coating methods can be used. For example, coating onto the support can be performed using various devices such as blade coaters, roll coaters, air knife coaters, and bar coaters. The drying temperature in the drying step is not particularly limited, and may be, for example, room temperature to 200°C. Since thermal decomposition of the perfluorocarbon orosulfonic acid polymer tends to be suppressed, the drying temperature is preferably 150°C or less when the drying time is long. Furthermore, in high-speed coating with a short drying time, an ion exchange membrane can be obtained even with a short drying time by setting the drying temperature to 200°C or less. The drying time in the drying step is not particularly limited, and may be, for example, about 10 seconds to 120 minutes. The drying temperature may be changed in stages in the drying step. The drying means is not particularly limited, and examples include hot air drying and electromagnetic wave drying, and two or more drying means may be combined. The cooling temperature in the cooling step may be, for example, about room temperature, and the cooling time may be, for example, about 30 to 90 minutes. When the heat treatment step is carried out after the drying step, the heat treatment temperature in the heat treatment step may be, for example, about 100 to 200° C., and the heat treatment time may be about 5 to 15 minutes.

[0335] In dynamic light scattering particle size measurement, the polymer electrolyte solution has a scattering intensity ratio (A) of at least one particle size peak in the range of 0.1 μm or more and less than 5.0 μm to a scattering intensity (B) of at least one particle size peak in the range of 5.0 μm or more and 50.0 μm or less, but is not particularly limited to 1.0×10 －２ The scattering intensity ratio (A / B) is preferably 1.0×10 or more and 1.0×10 or less. －２ More preferably, it is 1.0 × 10 or less, and more preferably 1.0 × 10 or less. －１ More preferably, it is 5.0×10 －１It is particularly preferable that the scattering intensity ratio (A / B) is 1.0×10 or more and 2.0 or less. The scattering intensity ratio (A / B) in dynamic light scattering particle size measurement is used to determine the dispersibility of a polymer in a polymer electrolyte solution. In other words, it can be a measure of dissolution. The scattering intensity ratio (A / B) can be measured by the method described in the Examples below. When the ratio (A / B) of scattering intensities (1 / nm) is 1.0×10 or less, the dispersibility of the polymer electrolyte in the solvent tends to be further improved. In other words, as the scattering intensity (B) increases relative to the scattering intensity (A), the dispersibility of the polymer electrolyte in the solvent tends to be improved. When the scattering intensity ratio (A / B) is 1.0×10 －２ By being equal to or greater than this, decomposition of the polymer electrolyte and its degradation into smaller molecules tend to be suppressed. The scattering intensity ratio (A / B) can be increased by shortening the residence time or lowering the temperature during dissolution, and can be decreased by increasing the residence time or raising the temperature during dissolution, thereby achieving the desired scattering intensity ratio (A / B). As a criterion for determining the dissolution of a polymer electrolyte in a solvent, other than the scattering intensity ratio (A / B) in the dynamic light scattering particle size measurement, the transmittance at a wavelength of 800 nm in UV measurement of a polymer electrolyte solution having a solids content of 20% by mass can also be used. The transmittance of the polymer electrolyte solution is not particularly limited, but is preferably 90% T or more, more preferably 95% T or more, and even more preferably 98% T or more. When the transmittance of the polymer electrolyte solution is 90% T or more, the dispersibility of the polymer electrolyte in the solvent tends to be improved. The UV measurement can be performed by the method described in the Examples below.

[0336] The concentration of fluorine ions contained in the polymer electrolyte is not particularly limited, but is preferably 0.1 ppm (ppm represents parts per million) or more and 500 ppm or less relative to the solid weight of the fluororesin G1. By setting the fluorine ion concentration to 500 ppm or less, the hot water solubility resistance of the ion exchange membrane and, when the ion exchange membrane is used as an electrode catalyst layer for a fuel cell, the chemical durability of the fuel cell tend to be improved. The concentration of Fe contained in the ion exchange membrane is not particularly limited, but is preferably 0.010 ppm or more and 10 ppm or less, more preferably 0.050 ppm or more and 5 ppm or less, and even more preferably 0.10 ppm or more and 1 ppm or less, relative to the solid weight of the fluororesin G1. When the ion exchange membrane is used in a fuel cell, the Fe concentration that induces radical generation during fuel cell operation is reduced by setting the Fe concentration to 10 ppm or less, which tends to suppress deterioration of the ion exchange membrane and improve the chemical durability of the fuel cell.When the Fe concentration is 0.010 ppm or more, a polymer electrolyte solution and an ion exchange membrane can be produced without a step of removing Fe, which tends to improve productivity.

[0337] The structure of the polymer chain terminal of the fluororesin G1 contained in the ion exchange membrane is not particularly limited, but may be -CF ２ H group, -CF ３ group, —COOH group, —COONa group, etc. Among these, —CF ２ H group is preferred. ２ The amount of H groups is preferably 40% or more, more preferably 50% or more, and even more preferably 90% or more. ２ When the amount of H groups is 40% or more, the Fenton resistance is improved compared to ion exchange membranes having terminal -COOH groups or -COONa groups, and when the ion exchange membrane is used in a fuel cell, the chemical durability of the fuel cell tends to be improved. ３Compared to ion exchange membranes, which are the base, there is no need to go through a post-loading manufacturing process such as a fluorination step, so productivity tends to improve.

[0338] The converted puncture strength of the ion exchange membrane (the value obtained by converting the puncture strength in a wet state per 25 μm) is preferably 30 gf / 25 μm or more, more preferably 40 gf / 25 μm or more, and even more preferably 50 gf / 25 μm or more. By setting the converted puncture strength to 30 gf / 25 μm or more, the mechanical strength required for producing a thin ion exchange membrane tends to be obtained. In this embodiment, there is no particular upper limit to the converted puncture strength, but from the viewpoint of ensuring an appropriate moisture content, it is preferably 100 gf / 25 μm or less.

[0339] (Wound body) In this embodiment, the wound body refers to a strip-shaped film wound around a cylindrical core. The material of the core is not particularly limited, but examples thereof include resin and metal. Examples of resin include polyethylene, polypropylene, polystyrene, ABS resin, epoxy resin, polyester, polyvinyl chloride, polyvinylidene chloride, polyimide, polyamide, and polyamideimide.

[0340] (Width and Length of Ion Exchange Membrane Wound into a Roll) When a continuously produced ion exchange membrane is wound into a roll, the width of the ion exchange membrane is preferably 100 mm or more and 1,000 mm or less, more preferably 150 mm or more and 800 mm or less, and even more preferably 200 mm or more and 600 mm or less. When the ion exchange membrane has a width of 100 mm or more, for example, when the ion exchange membrane is used in a fuel cell or a redox flow battery, the cell area of ​​the fuel cell or the redox flow battery can be increased, thereby enabling a high output. When the width of the ion exchange membrane is 600 mm or less, the variation in the thickness of the ion exchange membrane tends to be reduced. The length of the ion exchange membrane is preferably 0.1 m or more and 1,000 m or less, more preferably 0.5 m or more and 700 m or less, and even more preferably 1.0 m or more and 500 m or less. By setting the length of the ion exchange membrane to 1 m or more, the thickness of the coated film of the polymer electrolyte solution becomes uniform, and the uniformity of the film thickness of the obtained ion exchange membrane tends to be improved. By setting the length of the ion exchange membrane to 500 m or less, the weight per obtained wound body tends to be reduced, and the handleability tends to be improved.

[0341] <Redox Flow Battery Cell> Examples of applications of the ion exchange membrane of this embodiment include redox flow battery cells, redox flow batteries, solid polymer electrol...

Claims

1. A layer (L1) containing a heteroaromatic structure-containing fluororesin having a structural unit represented by the following general formula A1, a saponification product thereof, or a salt thereof; 【Chemistry 1】 (In the formula, X １ , X ２ , X ３ , and X ４ may be the same or different, and each is a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X １ and X ２ , or X １ and X ３ may be bonded to each other to form a cyclic structure, R １ , R ２ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; R ３ represents a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, R ４ is N.R. ３ and Hc, which is a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, X １０ is -CO ２ -, -SO ２ - is a divalent group represented by the formula Hc is a substituted or unsubstituted heteroaromatic group containing at least one nitrogen atom, a 5-membered ring and / or a 6-membered ring structure, and having 4 to 30 carbon atoms; a and g each represent a molar ratio of all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1, b is an integer from 0 to 8; c is 0 or 1; d, e, and f may be the same or different and are integers from 0 to 6, provided that d, e, and f are not 0 at the same time. a layer (M1) containing a fluororesin (G1) having a structural unit represented by the following general formula G1; An ion exchange membrane having 【Chemistry 2】 (In the formula, the definition of each substituent is the same as in the above-mentioned general formula G1.)

2. The layer (L1), The layer (M1), The ion exchange membrane according to claim 1 , having three or more layers of the above alternating layers.

3. 2. The ion exchange membrane according to claim 1, wherein the layer (L1) has a thickness of 10 μm or less.

4. The ion exchange membrane according to claim 1 , wherein the thickness of the ion exchange membrane is 200 μm or less.

5. A layer (L3) containing a fluororesin having a nitrogen atom in a side chain and having a structural unit represented by the following general formula A3, a saponification product thereof, or a salt thereof; 【Chemistry 3】 (In the formula, X ２０ , X ２１ , X ２２ , and X ２３ may be the same or different, and each is a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted cyclic perfluoroalkyl group having 5 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; X ２０ and X ２１ , or X ２０ and X ２２ may form a cyclic structure, R ２０ , and R ２１ may be the same or different and are a hydrogen atom, a halogen atom, a substituted or unsubstituted perfluoroalkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted fluorochloroalkyl group having 1 to 10 carbon atoms, the halogen atom being a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; R ２２ , and R ２４ represents a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, R ２６ , and R ２７ is a hydrogen atom or a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms; R ２６ , and R ２７ at least one of is a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 10 carbon atoms, R ２３ , and R ２５ may be the same or different, and each represents a substituted or unsubstituted divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 10 carbon atoms. When h is 2 or more, the repeated R ２３ may be the same or different, X ２４ is -CO ２ - or -SO ２ is a divalent group represented by -, a and g each represent a molar ratio of all structural units contained in the resin, and are numbers that satisfy 0≦a<1, 0<g≦1, and a+g=1, b is an integer from 0 to 8; c is 0 or 1; d, e, f, and h may be the same or different and are integers from 0 to 6, provided that d, e, and f are not 0 at the same time. a layer (M3) containing a fluororesin (G1) having a structural unit represented by the following general formula G1; 【Chemistry 4】 (In the formula, the definition of each substituent is the same as in the above-mentioned general formula G1.) An ion exchange membrane comprising:

6. The layer (L3), The layer (M3), The ion exchange membrane according to claim 5 , having three or more layers of the above alternating layers.

7. The ion exchange membrane according to claim 5, wherein the layer (L3) has a thickness of 10 μm or less.

8. The ion exchange membrane according to claim 5 , wherein the ion exchange membrane has a thickness of 200 μm or less.

9. The ion exchange membrane according to any one of claims 1 to 8, which is for use in a redox flow battery.

10. The ion exchange membrane according to any one of claims 1 to 8 is joined to at least one electrode. Membrane electrode assembly.

11. For redox flow batteries, The membrane electrode assembly according to claim 10.

12. a first electrolyte solution including a first redox active material; a second electrolyte comprising a second redox active material; a first electrode in contact with the first electrolyte; a second electrode in contact with the second electrolyte; a diaphragm disposed between the first electrolytic solution and the second electrolytic solution; Including, The diaphragm is an ion exchange membrane according to any one of claims 1 to 8. Redox flow battery cell.

13. A membrane electrode assembly in which a diaphragm and at least one electrode are joined together. The cell for a redox flow battery according to claim 12.

14. At least one of the first electrode and the second electrode is a carbon electrode. The cell for a redox flow battery according to claim 12.

15. At least one of the first redox active material and the second redox active material is at least one selected from the group consisting of a metal-based redox active material, a non-metal-based redox active material, and an organic redox active material; The cell for a redox flow battery according to claim 12.

16. The redox flow battery cell according to claim 12, wherein the cell is stacked. Redox flow battery.

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