WO2015119272A1

WO2015119272A1 - Ion-exchange membrane for redox battery, complex, and redox battery

Info

Publication number: WO2015119272A1
Application number: PCT/JP2015/053519
Authority: WO
Inventors: 良平岩原; 真佐子吉岡; 西本　晃; 小林　真申
Original assignee: 東洋紡株式会社
Priority date: 2014-02-07
Filing date: 2015-02-09
Publication date: 2015-08-13
Also published as: JPWO2015119272A1; JP6447520B2

Abstract

[Problem] To provide an ion-exchange membrane for a redox battery that has excellent resistance to oxidation and that is highly energy efficient. [Solution] An ion-exchange membrane for a vanadium redox battery, the membrane characterized by containing a polybenzimidazole that includes a structural component that is represented by general formula (1). In formula (1), R¹ represents a tetravalent aromatic unit that can form an imidazole ring, and R² represents a bivalent aromatic group. X represents one or more ionic group selected from a sulfonic acid group and a metal salt thereof, a phosphonic acid group and a metal salt thereof, a hydroxyl group and a metal salt thereof, a carboxyl group and a metal salt thereof, and an ammonium salt; and m represents an integer from 1 to 4.

Description

Ion exchange membrane for redox battery, composite, and redox battery

The present invention is useful for redox batteries or redox flow batteries, and is particularly composed of a polybenzimidazole useful for vanadium-based redox flow batteries, or a composition containing polybenzimidazole and a polymer having an acidic ionic group. The present invention relates to an ion exchange membrane.

In recent years, new secondary batteries excellent in energy efficiency and environmental performance have attracted attention. In particular, in order to store natural energy such as sunlight and wind power, a large secondary battery is strongly demanded. Among these, the redox flow battery is excellent in charge / discharge cycle resistance and safety, and is optimal for a large-sized secondary battery.

A redox flow battery is generally a battery that obtains energy by causing a redox reaction of vanadium in a vanadium sulfate solution by circulation of a pump. In this redox flow battery, a cation exchange membrane or an anion exchange membrane is used in order to maintain the ion balance between both electrodes.

As anion exchange membrane, Selemion APS manufactured by Asahi Glass Co., Ltd. is used. However, since an anion exchange membrane needs to pass ions having a large ion radius such as sulfate anion, there is a problem that resistance is high.

In addition to ion conductivity, the ion exchange membrane must have properties such as prevention of permeation of the electrolyte and mechanical strength. Examples of such an ion exchange membrane include a membrane containing a perfluorocarbon sulfonic acid polymer introduced with a sulfonic acid group represented by Nafion (registered trademark) manufactured by DuPont of the United States, and a neoceptor manufactured by Tokuyama. A membrane containing a crosslinked polystyrene sulfonate is used.

A membrane containing a perfluorocarbon sulfonic acid polymer such as Nafion has advantages of excellent chemical durability, high proton conductivity, and low cell resistance. However, Nafion also has a problem of poor ion permeation selectivity. Specifically, vanadium ions are also allowed to pass during charging / discharging, so that the amount of active material in the electrolytic solution is reduced and the charging / discharging cycle is significantly deteriorated. In addition, there are problems of high cost and large environmental load at the time of disposal.

On the other hand, a membrane containing a polystyrene sulfonate cross-linked product such as neoceptor has advantages such as low cost, low vanadium ion permeability, and excellent ion permeation selectivity. However, since the strength of the membrane is insufficient, there is a problem that measures such as fiber reinforcement must be taken. Furthermore, there are problems in chemical durability and heat resistance, such as sulfonic acid groups being eliminated during hydrolysis and heat generation.

In a vanadium redox battery, pentavalent vanadium is generated on the positive electrode side during charging. This pentavalent vanadium has a very strong oxidizing power, so that it significantly deteriorates the ion exchange membrane. In general, hydrocarbon ion exchange membranes have excellent initial energy efficiency, but have poor oxidation resistance and low resistance to pentavalent vanadium. On the other hand, the perfluorocarbon sulfonic acid polymer such as Nafion described above has excellent resistance to pentavalent vanadium, but has poor ion permeation selectivity and tends to have low initial energy efficiency. Thus, it has been extremely difficult to achieve both initial energy efficiency and oxidation resistance.

Therefore, several methods for achieving both initial characteristics and oxidation resistance have been proposed. For example, in Patent Documents 1 to 3, a sulfonic acid group is introduced into an aromatic polymer to improve mechanical strength and heat resistance. However, even ion exchange membranes prepared by these methods dissolve when the ion exchange membrane is immersed in pentavalent vanadium for a long period of time, and the oxidation resistance is insufficient for use as a vanadium-based redox battery. It was.

Patent Documents 4 to 6 propose a method in which an ion exchange resin is combined with a porous base material that is a reinforcing material to compensate for deterioration due to pentavalent vanadium with the reinforcing material. However, these methods cannot suppress deterioration of the polymer itself and can maintain the shape as a diaphragm, but when used over a long period of time, deterioration of the initial characteristics due to a decrease in strength or ion exchange resin is inevitable. .

Japanese Patent No. 3928611 JP-T-2004-509224 JP 2006-137772 A Japanese Patent No. 3729296 JP-A-6-271688 JP 11-335473 A

Therefore, in view of such circumstances, an object of the present invention is to provide an ion exchange membrane for a redox battery that is excellent in oxidation resistance and excellent in initial energy efficiency.

The inventors of the present invention have intensively studied to achieve the above-mentioned object. The present invention has been completed by finding that an ion exchange membrane comprising a composition containing a functional group is excellent in oxidation resistance and high in energy efficiency.

1. An ion exchange membrane for a redox battery comprising polybenzimidazole containing a constituent represented by the following general formula (1).

However, R ¹ represents a tetravalent aromatic unit capable of forming an imidazole ring, and R ² represents a divalent aromatic group. X represents one or more ionic groups selected from a sulfonic acid group, a phosphonic acid group, a hydroxyl group, a carboxyl group, and metal salts and ammonium salts thereof, and m represents an integer of 1 to 4.

2. 2. The ion exchange membrane for redox battery according to 1, wherein the constituent of the general formula (1) includes constituents represented by the following general formula (2) and the following general formula (3).

However, n shows the copolymerization ratio of General formula (2), and satisfy | fills the formula of 20 <= n <= 100. R ² represents a divalent aromatic group, X represents one or more ionic groups selected from a sulfonic acid group, a phosphonic acid group, a hydroxyl group, a carboxyl group, and metal salts and ammonium salts thereof, and m represents 1 To an integer of 4 to 4, wherein Z is at least one selected from the group consisting of O, SO ₂ , C (CH ₃ ) ₂ , C (CF ₃ ) ₂ , and OPhO (where Ph represents an aromatic group). It represents the above.

3. An ion exchange membrane for a redox battery comprising 10 to 100% by mass of the polybenzimidazole according to any one of the above items 1 and 2.
4). Polybenzimidazole (A) containing the structural component represented by the general formula (1), and at least one acidic ion selected from a sulfonic acid group, a phosphonic acid group, a carboxyl group, or a metal salt thereof, or an ammonium salt It comprises a composition containing a polymer (B1) having a functional group and not containing the structure of formula (1), wherein the ion exchange capacity of (B1) is 1.5 mmeq / g or more. The ion exchange membrane for redox batteries of 1 or 2.
5. Polybenzimidazole (A) containing the structural component represented by the general formula (1), and a sulfonic acid group, phosphonic acid group, hydroxyl group, carboxyl group or a metal thereof which does not contain the structure of the formula (1) It consists of a composition containing the aromatic hydrocarbon polymer (B2) which has at least 1 or more types of acidic ionic groups chosen from a salt and ammonium salt, Any one of Claim 1, 2, 4 characterized by the above-mentioned. The ion exchange membrane for redox batteries described in 1.

6). Polybenzimidazole (A) containing the structural component represented by the general formula (1), and a sulfonic acid group, phosphonic acid group, hydroxyl group, carboxyl group or a metal thereof which does not contain the structure of the formula (1) Any one of 1, 2, 4 comprising a polymer (B3) having a repeating unit containing at least one acidic ionic group selected from a salt and an ammonium salt. An ion exchange membrane for a redox battery according to claim 1.
7). Polybenzimidazole (A) containing the structural component represented by the general formula (1), and a sulfonic acid group, phosphonic acid group, hydroxyl group, carboxyl group or a metal thereof which does not contain the structure of the formula (1) 1. A composition comprising a polymer (B4) having at least one acidic ionic group selected from a salt and an ammonium salt, wherein the polymer (B4) has a repeating unit having 12 or more carbon atoms, The ion exchange membrane for redox batteries according to any one of 2 and 4.

8). 6. The redox battery according to any one of 4 and 5, wherein in the composition, the polymer (B1) or the polymer (B2) contains a component represented by the following general formulas (4) and (5): Ion exchange membrane.

Here, Ar represents a divalent aromatic group, Y represents a sulfonyl group or a carbonyl group, Z represents an O atom, an S atom, or a direct bond, and X represents H or a monovalent cation species.

However, Z represents either an O atom or an S atom, and Ar ′ represents a divalent aromatic group.

9. 9. The composition according to any one of 4 to 8, comprising the polybenzimidazole (A) and at least one polymer selected from the group consisting of the polymers (B1) to (B4). The ion exchange membrane for a redox battery according to any one of 4 to 8, wherein the total content of the polymer (B1) to the polymer (B4) is 10 to 80% by mass of the composition.
10. 9. The composition according to any one of 4 to 8, comprising the polybenzimidazole (A) and at least one polymer selected from the group consisting of the polymers (B1) to (B4). The redox battery according to any one of 4 to 8, wherein the total content of the polymer (A) and the polymers (B1) to (B4) is 10 to 100% by mass of the composition Ion exchange membrane.

11. 11. The ion exchange membrane for a redox battery according to any one of 1 to 10, which is an ion exchange membrane for a redox flow battery.
12 The ion exchange membrane for redox battery according to any one of 1 to 11, which is used for a redox battery using vanadium ions as an active material of the battery.
13. 13. An ion exchange membrane / electrode composite for a redox battery comprising the ion exchange membrane according to any one of 1 to 12 above and an electrode.
14 13. A redox battery comprising the ion exchange membrane according to any one of 1 to 12 above.
15. 14. A redox battery comprising the ion exchange membrane / electrode composite as described in 13 above.

By an ion exchange membrane containing a polymer having an ionic group introduced into the polybenzimidazole of the present invention, and an ion exchange membrane comprising a polymer having an ionic group introduced into the polybenzimidazole and a composition containing an acidic ionic group, It is possible to provide a material exhibiting outstanding performance as an ion exchange membrane for a redox battery, which is excellent not only in initial energy efficiency but also in heat resistance, workability and oxidation resistance.

The schematic of a vanadium type redox flow battery is shown.

Hereinafter, the present invention will be described in detail. The present invention provides a polymer material useful as an ion exchange membrane for a redox battery, which is excellent not only in initial energy efficiency but also in heat resistance, workability and oxidation resistance. That is, an ion exchange membrane containing a polymer in which polybenzimidazole having excellent oxidation resistance is used as a main chain skeleton and an ionic group such as a sulfonic acid group or a phosphonic acid group is introduced into the main chain skeleton is used. More preferably, an ion exchange membrane made of a composition containing a polymer having an ionic group introduced into the polybenzimidazole and a polymer having an acidic ionic group is used. Due to intramolecular acid-base interaction between imidazole and acidic ionic groups, an extremely strong polymer structure can be obtained. As a result, an ion exchange membrane having high ion permeation selectivity, low resistance, and high durability is provided. be able to.

That is, the ion exchange membrane for a redox battery of the present invention contains polybenzimidazole (A) including a component containing an acidic ionic group of the general formula (1).

However, R ¹ represents a tetravalent aromatic unit capable of forming an imidazole ring, R ² represents a divalent aromatic group, and R ¹ and R ² are both monocyclic aromatic rings, It may be a conjugate of an aromatic ring, may have a condensed ring or a heterocyclic ring, and may have a stable substituent such as an alkyl group or an aromatic group. X represents one or more ionic groups selected from a sulfonic acid group, a phosphonic acid group, a hydroxyl group, a carboxyl group, and metal salts and ammonium salts thereof, and m represents an integer of 1 to 4.

The method for synthesizing the acidic group-containing polybenzimidazole (A) of the present invention containing the structure represented by the above formula (1) is not particularly limited, but aromatic tetramines capable of forming an imidazole ring in the compound by a conventional method. And one or more compounds selected from the group consisting of derivatives thereof and one or more compounds selected from the group consisting of aromatic dicarboxylic acids and derivatives thereof. At that time, by using dicarboxylic acids containing sulfonic acid groups or phosphonic acid groups or salts thereof in the dicarboxylic acids to be used, sulfonic acid groups or phosphonic acid groups are introduced into the resulting polybenzimidazole. be able to. Dicarboxylic acids containing a sulfonic acid group or a phosphonic acid group can be used alone or in combination of two or more. For example, a sulfonic acid group-containing dicarboxylic acid and a phosphonic acid group-containing dicarboxylic acid can be used simultaneously. It is also possible to use it. Moreover, when using a carboxyl group, tri or tetracarboxylic acid can also be used.

Here, a benzimidazole-based binding unit that is a constituent element of the polybenzimidazole (A) used in the ion exchange membrane of the present invention, an aromatic dicarboxylic acid binding unit having a sulfonic acid group and / or a phosphonic acid group, a sulfone The aromatic dicarboxylic acid bonding unit having no acid group or phosphonic acid group and other bonding units are preferably bonded by random polymerization and / or alternating polymerization. Moreover, these polymerization formats are not limited to one type, and two or more polymerization types may coexist in the same compound.

In the ion exchange membrane for a redox battery of the present invention, it is preferable that the constituent of the general formula (1) includes constituents represented by the following general formulas (2) and (3).

However, n shows the copolymerization ratio of General formula (2), and satisfy | fills the formula of 20 <= n <= 100. R ² represents a divalent aromatic group, X represents one or more ionic groups selected from a sulfonic acid group, a phosphonic acid group, a hydroxyl group, a carboxyl group, and metal salts and ammonium salts thereof, and m represents 1 To an integer from 4 to Z, and at least one selected from the group consisting of O, SO ₂ , C (CH ₃ ) ₂ , C (CF ₃ ) ₂ , and OPhO (where Ph represents an aromatic group). It represents the above.

The amount of the acidic ionic group to be introduced is preferably 20 mol% or more, and more preferably 40 mol% or more with respect to the imidazole unit. That is, when there is one acidic ionic group introduced into R ₂ , n is preferably 40 or more, and more preferably 80 or more. When the acidic ionic group introduced into R ₂ is 2 or more, n is preferably 20 or more, and more preferably 40 or more.
Furthermore, Z is preferably SO ₂ or C (CF ₃ ) ₂ in view of oxidation resistance and solubility in organic solvents. For the oxidation resistance, it is better to lower the electron density in the polymer skeleton. To that end, SO ₂ or C (CF ₃ ) ₂ which is an electron withdrawing group is preferable. In general, when an acidic ionic group is introduced into polyimidazole, the solubility in an organic solvent decreases due to an acid / base interaction in the molecule. Therefore, it is preferable that Z is SO ₂ or C (CF ₃ ) _{2 because} it can be dissolved in an organic solvent such as N-methyl 2-pyrrolidone or dimethyl sulfoxide and the processing becomes easy.

The ion exchange membrane for a redox battery of the present invention contains a polyimidazole (A) having the above general formula (1) as a constituent component, but a structural unit other than that represented by the above general formula (1) (for example, sulfone). A structural unit that does not contain an acid group-containing component) may be included. At this time, the structural unit other than that represented by the general formula (1) is preferably 60 parts by mass or less when the polyimidazole (A) represented by the general formula (1) is 100 parts by mass. By setting it to 60 parts by mass or less, the characteristics of the ion exchange membrane for a redox battery of the present invention can be utilized.

Specific examples of the aromatic tetramines that give the sulfonic acid group-containing polybenzimidazole (A) containing the structural component represented by the general formula (1) and constitute R ₁ are not particularly limited. Are, for example, 1,2,4,5-tetraaminobenzene, 3,3′-diaminobenzidine, 3,3 ′, 4,4′-tetraaminodiphenyl ether, 3,3 ′, 4,4′-tetraamino Diphenylthioether, 3,3 ′, 4,4′-tetraaminodiphenylsulfone, 2,2-bis (3,4-diaminophenyl) propane, bis (3,4-diaminophenyl) methane, 2,2-bis ( 3,4-diaminophenyl) hexafluoropropane, 1,4-bis (3,4-diaminophenoxy) benzene, and the like and their derivatives. Among these, 3,3 ′, 4,4′-tetraaminodiphenyl ether, 3,3 ′, 4,4 ′, which can form a binding unit represented by general formula (2) or general formula (3). -Tetraaminodiphenyl sulfone, 2,2-bis (3,4-diaminophenyl) propane, 2,2-bis (3,4-diaminophenyl) hexafluoropropane, 1,4-bis (3,4-diaminophenoxy) ) Polybenzimidazole obtained from benzene and derivatives thereof can be used in aprotic polar solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, hexamethylphosphonamide and the like. It is particularly preferable from the viewpoint of ease of workability of the ion exchange membrane.

Specific examples of these aromatic tetramine derivatives include salts with acids such as hydrochloric acid, sulfuric acid and phosphoric acid. These compounds may be used alone or in combination. Furthermore, these compounds may contain known antioxidants such as tin (II) chloride and phosphorous acid compounds as necessary.

Examples of the ionic group (X) in the ionic group-containing dicarboxylic acid that gives the structure of the above formula (1) include a sulfonic acid group, a phosphonic acid group, a hydroxyl group, and a carboxyl group. Of these, sulfonic acid groups and phosphonic acid groups having a high degree of proton dissociation are preferred. By using a sulfonic acid group or a phosphonic acid group, the ion conductivity is increased and a low resistance ion exchange membrane can be obtained.
Further, in the present invention, since the ionic group (X) is bonded to the polymer main chain, there is an advantage that an acid immersion treatment after forming the polymer into a film is not particularly required.

The ionic group-containing dicarboxylic acid that gives the structure of the above formula (1) can be selected from those containing 1 to 4 ionic groups in the aromatic dicarboxylic acid. For example, 2,5-dicarboxybenzenesulfonic acid, 2,5-dicarboxybenzenephosphonic acid, 3,5-dicarboxybenzenesulfonic acid, 3,5-dicarboxybenzenephosphonic acid, 2,5-dicarboxy- 1,4-benzenedisulfonic acid, 4,6-dicarboxy-1,3-benzenedisulfonic acid, 2,2′-disulfo-4,4′-biphenyldicarboxylic acid, 3,3′-disulfo-4,4 ′ -Biphenyl dicarboxylic acid, (3,3'-disulfo-4,4'-dicarboxylic acid) diphenyl ether, (2,6-disulfo) -1,5-naphthalenedicarboxylic acid, etc. Acid group-containing dicarboxylic acids, phosphonic acid group-containing dicarboxylic acid, and may be derivatives thereof. Examples of the derivatives include alkali metal salts such as sodium and potassium, ammonium salts, and alkyl ammonium salts. The structure of the sulfonic acid group-containing dicarboxylic acid or phosphonic acid group-containing dicarboxylic acid is not particularly limited thereto. M in the above formula (1) is selected from an integer of 1 to 4. If m is 5 or more, the water resistance of the polymer tends to decrease, such being undesirable.

These compounds may be used alone or in combination. Furthermore, these compounds may contain known antioxidants such as tin (II) chloride and phosphorous acid compounds as necessary.

The ionic group-containing dicarboxylic acids can be introduced not only by themselves but also as R ^{2 in} the form of copolymerization with dicarboxylic acids not containing ionic groups. Examples of dicarboxylic acids that can be used with ionic group-containing dicarboxylic acids include terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, biphenyl dicarboxylic acid, terphenyl dicarboxylic acid, 2,2-bis (4 -Carboxyphenyl) General dicarboxylic acids reported as polyester raw materials such as hexafluoropropane can be used, and are not limited to those exemplified here. Among these dicarboxylic acids, those having no electron donating property such as an ether bond are preferable in order to improve oxidation resistance. For example, it is preferable to use derivatives such as terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenylsulfone dicarboxylic acid and the like.

When using a dicarboxylic acid not containing an ionic group together with an ionic group-containing dicarboxylic acid, clarifying the effect of the ionic group by setting the ionic group-containing dicarboxylic acid to 20 mol% or more of the total dicarboxylic acid. Can do. Especially, in order to draw out the remarkable effect of a sulfonic acid group or a phosphonic acid group, it is more preferable that it is 40 mol% or more. The remarkable effect is that an extremely strong polymer structure can be obtained due to intramolecular acid-base interaction between imidazole and acidic ionic groups. As a result, ion exchange membranes exhibit high ion permeation selectivity and high durability. It becomes. In addition, since the ion conductivity is improved by introducing an acidic ionic group, a low-resistance ion exchange membrane is obtained. When the content of the aromatic dicarboxylic acid having a sulfonic acid group or phosphonic acid group is less than 20 mol%, the ionic conductivity and acid-base interaction of the polybenzimidazole compound of the present invention are reduced, and the resistance is high. Durability tends to decrease.

The ion exchange membrane for redox of the present invention is one of the preferred embodiments containing 10 to 100% by mass of polyimide benzoxazole (A).

A preferred embodiment of the present invention is a redox ion comprising a composition containing a polyimide benzoxazole (A) containing the component represented by the formula (1) and a second polymer (B) having an acidic ionic group. It is an ion exchange membrane for a battery.
The 2nd polymer (B) which has an acidic ionic group is a polymer which does not contain the structure of said (1) Formula. All of the polymers (B1) to (B4) described below show preferred modes of the polymer (B). The content thereof (that is, the total content of the polymers (B1) to (B4)) is preferably 80% by weight or less, more preferably 60% by weight or less and 10% by weight or more based on the composition. . By setting it as the range, high ion permeation selectivity and low resistance can be expressed. When it is 80% by weight or more based on polybenzimidazole, the characteristics of the second polymer (B) having an acidic ionic group become too large, and the ion permeation selectivity and water resistance are lowered. May not be expressed. On the other hand, if it is 10% by weight or less, the characteristics of the polybenzimidazole (A) become too large, the resistance becomes high, and all of the above performance may not be exhibited. When the second polymer (B) having an acidic ionic group is mixed with the acidic ionic group-containing polybenzimidazole (A), an ionic bridge is formed between the imidazole of (A) and the acidic ionic group of (B). . By this effect, the interaction between the mixed different types of polymers is strengthened, and as a result, the above performance is exhibited. At this time, even if it is polybenzimidazole which does not have an acidic ionic group, the said effect can be expressed by mixing the 2nd polymer (B) which has an acidic ionic group similarly. However, in the case of polybenzimidazole having no acidic ionic group, if the polybenzimidazole content is increased, a uniform solution is unlikely to be obtained, and the second polymer (B) having an acidic ionic group is preliminarily amined. In many cases, a salt solution or the like finally becomes a uniform solution, and a complicated manufacturing process that requires acid treatment after film formation is required.
In the above-described embodiment in which the composition containing polybenzimidazole (A) and the second polymer (B) having an acidic ionic group is used, the total amount of both is preferably 10 to 100% by mass.

Examples of the second polymer (B) having an acidic ionic group include polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyamides such as nylon 6, nylon 6,6, nylon 6,10, and nylon 12. Acrylate resins such as polymethyl methacrylate, polymethacrylic acid esters, polymethyl acrylate, polyacrylic acid esters, polyacrylic acid resins, polymethacrylic acid resins, polyethylene, polypropylene, polystyrene and diene polymers Various polyolefins, polyurethane resins, cellulose resins such as cellulose acetate and ethyl cellulose, polyarylate, aramid, polycarbonate, polyphenylene sulfide, polyphenylene oxide Aromatic hydrocarbon polymers such as polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyimide, polyamideimide, polybenzoxazole, polybenzthiazole, and fluorine-based polymers such as polytetrafluoroethylene and polyvinylidene fluoride There is no particular limitation as long as it is a polymer in which an ionic group as described above is introduced into a resin, an epoxy resin, a phenol resin, a novolac resin, a benzoxazine resin, or the like.

More preferably, it is an aromatic hydrocarbon polymer exhibiting high current efficiency, low resistance, heat resistance, and high mechanical strength. Specifically, polyarylate, aramid, polycarbonate, polyphenylene sulfide, polyphenylene oxide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyimide, polyamideimide, polybenzimidazole, polybenzoxazole, and polybenzthiazole. Preferably exemplified. A polymer obtained by sulfonating these polymers is more preferable.

More preferred are sulfonated polymers such as polyarylate, polyphenylene sulfide, polyphenylene oxide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, and polyimide. In the case of these polymers, since the polymer structure is more rigid, more excellent heat resistance and mechanical strength are exhibited.

The polymer (B1) which is a preferred embodiment of the polymer (B) has an ion exchange capacity of 1.5 mmeq / g or more, and more preferably 2.0 mmeq / g or more. By setting it as said range, the amount of acidic ionic groups in a film | membrane increases, and resistance falls as a result. If it is 1.5 mmeq / g or less, the amount of acidic ionic groups in the film is insufficient and the resistance increases, which is not preferable. When the ion exchange capacity is increased with a normal hydrocarbon-based polymer, although the resistance is lowered, the ion permeation selectivity is lowered, and further, the aquatic resistance is greatly lowered such as dissolution in water. By making a mixture of a polymer (A) in which an ionic group is introduced into polybenzimidazole and a polymer (B1) having an acidic ionic group as in the present invention, ionic crosslinking is performed between the imidazole and the acidic ionic group. Even if it is formed and the ion exchange capacity is increased, the above-mentioned problems can be solved.

The polymer (B2), which is a preferred embodiment of the polymer (B), is an aromatic hydrocarbon polymer that does not contain the structure of the formula (1). When the film is formed from the polymer, the tensile strength in the film forming direction is 50 MPa. It is preferable that it is the polymer which is the above. When the polymer (B2) having an acidic ionic group is mixed with the acidic ionic group-containing polyimidazole (A), an ionic bridge is formed between the imidazole of (A) and the acidic ionic group of (B2). By this effect, the interaction between the mixed different polymers is strengthened, and as a result, high ion permeation selectivity, low resistance, and high durability can be expressed. At this time, even if it is polybenzimidazole which does not have an acidic ionic group, the said effect can be expressed by mixing the polymer (B2) which has an acidic ionic group similarly. However, in the case of polybenzimidazole having no acidic ionic group, if the polybenzimidazole content is increased, a uniform solution is unlikely to be obtained, and the second polymer (B2) having acidic ionic group is preliminarily amined. In many cases, a salt solution or the like finally becomes a uniform solution, which requires a complicated manufacturing process that requires acid treatment after film formation.

Examples of the polymer (B2) having an acidic ionic group include polyarylate, aramid, polycarbonate, polyphenylene sulfide, polyphenylene oxide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyimide, polyamideimide, and polybenzimidazole. Aromatic hydrocarbon polymers such as polybenzoxazole and polybenzthiazole are preferably used because of their excellent heat resistance and mechanical strength, and polymers containing ionic groups as described above are used. More preferably, it is a sulfonated polymer or composition. More preferred are sulfonated polymers such as polyarylate, polyphenylene sulfide, polyphenylene oxide, polysulfone, polyethersulfone, polyetheretherketone. These polymers are preferably used because they exhibit excellent current efficiency and low resistance as ion exchange membranes.

The polymer (B3) which is a preferred embodiment of the polymer (B) is a polymer not containing the structure of the formula (1), and a sulfonic acid group, a phosphonic acid group, a hydroxyl group, a carboxyl group or these in the repeating unit. At least one or more acidic ionic groups selected from metal salts and ammonium salts. When the polymer (B3) having an acidic ionic group is mixed with the acidic ionic group-containing polyimidazole (A), an ionic bridge is formed between the imidazole of (A) and the acidic ionic group of (B3). By this effect, the interaction between the mixed different polymers is strengthened, and as a result, high ion permeation selectivity, low resistance, and high durability can be expressed. At this time, even if it is polybenzimidazole which does not have an acidic ionic group, the said effect can be expressed by mixing the polymer (B3) which has an acidic ionic group similarly. However, in the case of polybenzimidazole having no acidic ionic group, if the polybenzimidazole content is increased, it becomes difficult to form a uniform solution, and the polymer (B3) having an acidic ionic group is previously converted to an amine salt or the like. In many cases, the solution finally becomes a uniform solution, which requires a complicated manufacturing process that requires acid treatment after film formation.

Examples of the polymer (B3) having an acidic ionic group include polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polyamides such as nylon 6, nylon 6,6, nylon 6,10, and nylon 12, poly Acrylate resins such as methyl methacrylate, polymethacrylates, polymethyl acrylate, polyacrylates, polyacrylic resins, polymethacrylic resins, polyethylene, polypropylene, various polyolefins including polystyrene and diene polymers, Cellulose resins such as polyurethane resin, cellulose acetate, ethyl cellulose, polyarylate, aramid, polycarbonate, polyphenylene sulfide, polyphenylene oxide, Aromatic hydrocarbon polymers such as resulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyimide, polyamideimide, polybenzimidazole, polybenzoxazole, polybenzthiazole, polytetrafluoroethylene, polyvinylidene fluoride The polymer is not particularly limited as long as it is a polymer in which an ionic group as described above is introduced into a fluorine resin, an epoxy resin, a phenol resin, a novolac resin, a benzoxazine resin, or the like. Of these, acrylate resins such as polymethyl methacrylate, polymethacrylates, polymethyl acrylate, polyacrylates, polyacrylic resins, polymethacrylic resins, polyethylene, polypropylene, polystyrene and diene polymers Polymers such as various polyolefins, including polyurethane resins, cellulose resins such as cellulose acetate and ethyl cellulose are preferably used from the viewpoint of ease of processing such as solubility in organic solvents, and these sulfonated polymers or compositions are used. More preferably. More preferred are sulfonated polymers such as polyethylene, polypropylene, polystyrene and diene polymers. These polymers are preferably used because they do not have an electron donating group such as an ether bond and can improve oxidation resistance. In particular, polystyrene sulfonated polymers are preferably used because of their high ion exchange capacity and low resistance.

The polymer (B4) which is a preferred embodiment of the polymer (B) does not contain the structure of the above formula (1), and is composed of a sulfonic acid group, a phosphonic acid group, a hydroxyl group, a carboxyl group, or a metal salt or ammonium salt thereof. It is a polymer having at least one selected acidic ionic group and having a repeating unit having 12 or more carbon atoms. By having a repeating unit having 12 or more carbon atoms, an appropriate strength can be obtained as an ion exchange membrane. When the polymer (B4) having an acidic ionic group is mixed with the acidic ionic group-containing polyimidazole (A), an ionic bridge is formed between the imidazole of (A) and the acidic ionic group of (B4). By this effect, the interaction between the mixed different polymers is strengthened, and as a result, high ion permeation selectivity, low resistance, and high durability can be expressed. At this time, even if it is polybenzimidazole which does not have an acidic ionic group, the said effect can be expressed by mixing the polymer (B4) which has an acidic ionic group similarly. However, in the case of polybenzimidazole having no acidic ionic group, if the polybenzimidazole content is increased, a uniform solution is unlikely to be obtained, and the polymer (B4) having acidic ionic group is previously converted to an amine salt or the like. In many cases, the solution finally becomes a homogeneous solution, and a complicated manufacturing process that requires acid treatment after film formation is required.

Examples of the second polymer (B4) having an acidic ionic group include polyesters such as polybutylene terephthalate and polyethylene naphthalate, polyamides such as nylon 6,6, nylon 6,10, and nylon 12, and polymethacrylates. , Acrylate resins such as polyacrylic acid esters, polyacrylic acid resins, polymethacrylic acid resins, various polyolefins including polystyrene and diene polymers, polyurethane resins, cellulose acetates such as cellulose acetate, ethyl cellulose, Polyarylate, aramid, polycarbonate, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyimide, polyamideimide, polybenzimidazole, polybenzoxazole, Aromatic hydrocarbon-based polymers such as Li benzthiazole, epoxy resins, phenolic resins, novolak resins, as long as the polymer obtained by introducing an ionic group such as the such as the benzoxazine resin is not particularly limited. Of these, aromatic hydrocarbons such as polyarylate, aramid, polycarbonate, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyimide, polyamideimide, polybenzimidazole, polybenzoxazole, and polybenzthiazole. Polymers are preferably used because of their excellent heat resistance and mechanical strength, and are more preferably sulfonated polymers. More preferred is a polymer obtained by sulfonating a polymer such as polyarylate, polysulfone, polyethersulfone, polyetheretherketone or polystyrene. These polymers are preferably used because they exhibit excellent current efficiency and low resistance as ion exchange membranes.

The second polymer (B) having an acidic ionic group contained in the composition of the present invention is a polymer not containing the structure of the formula (1), and the content thereof is 100 parts by mass of the composition. Is preferably 80 parts by mass or less, more preferably 60 parts by mass or less and 10 parts by mass or more. By setting it as the range, high ion permeation selectivity, low resistance, and high durability can be expressed. If the amount is 80 parts by mass or more based on the composition, the characteristics of the second polymer (B) having an acidic ionic group may become too large to exhibit all the above performance. On the other hand, if it is 10 parts by mass or less, all of the above performance may not be exhibited.

In the composition, the polymer (B1) or (B2) preferably contains constituents represented by the following general formulas (4) and (5).

Here, Ar represents a divalent aromatic group, Y represents a sulfone group or a carbonyl group, Z represents an O atom, an S atom, or a direct bond, and X represents H or a monovalent cation species.

In addition, polymers other than (A) and (B) can be used in the composition of the present invention. For example, in order to improve flexibility, styrene-butadiene rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, nitrile rubber, etc. A rubber component may be added, or a crosslinking component may be introduced to improve mechanical strength and chemical resistance.

Using one or more compounds selected from the group consisting of the aromatic tetramines and derivatives thereof and one or more compounds selected from the group consisting of aromatic dicarboxylic acids and derivatives thereof, sulfonic acid groups and / or phosphones A method for synthesizing a polybenzimidazole compound having an acid group is not particularly limited. F. Wolfe, Encyclopedia of Polymer Science and Engineering, 2nd Ed. , Vol. 11, p. 601 (1988), and can be synthesized by dehydration and cyclopolymerization using polyphosphoric acid as a solvent. Further, polymerization by a similar mechanism using a mixed solvent system of methanesulfonic acid / phosphorus pentoxide instead of polyphosphoric acid can be applied. In order to synthesize a polybenzimidazole compound having high thermal stability, polymerization using polyphosphoric acid that is commonly used is preferred.

Furthermore, in order to obtain the polybenzimidazole (A) used for the ion exchange membrane of the present invention, for example, a precursor polymer having a polyamide structure or the like in a reaction in a suitable organic solvent or mixed raw material monomer melt is used. A method of synthesizing and then converting to the target polybenzimidazole structure by a cyclization reaction by appropriate heat treatment or the like can also be used.

The molecular weight of the polybenzimidazole (A) containing an acidic ionic group of the present invention is not particularly limited, but is preferably 1,000 or more, more preferably 3,000 or more. The molecular weight is preferably 1,000,000 or less, more preferably 200,000 or less. When the molecular weight is less than 1,000, it may be difficult to obtain a molded product having good properties from the polybenzimidazole compound due to a decrease in viscosity. On the other hand, when the molecular weight exceeds 1,000,000, it may be difficult to mold the polybenzimidazole compound due to an increase in viscosity. Moreover, the molecular weight of the polybenzimidazole compound containing an acidic ionic group can be evaluated substantially by the logarithmic viscosity when measured in concentrated sulfuric acid. The logarithmic viscosity is preferably 0.25 or more, and more preferably 0.40 or more. The logarithmic viscosity is preferably 10 or less, more preferably 8 or less. When the logarithmic viscosity is less than 0.25, it is difficult to obtain a molded product having good properties from the polybenzimidazole compound due to the decrease in viscosity. On the other hand, when the molecular weight exceeds 10, it becomes difficult to mold a polybenzimidazole compound due to an increase in viscosity. The acidic ionic group preferably has a sulfonic acid group and / or a phosphonic acid group.

In addition, the reaction time for synthesizing the polybenzimidazole (A) containing an acidic ionic group of the present invention cannot be specified unconditionally because there is an optimum reaction time depending on the combination of individual raw material monomers. In a reaction that takes a long time as described above, in a system containing a raw material monomer such as an aromatic dicarboxylic acid having a sulfonic acid group and / or a phosphonic acid group, the thermal stability of the obtained polybenzimidazole compound is low. In this case, it is preferable to shorten the reaction time within a range where the effects of the present invention can be obtained. The reaction time is preferably 48 hours or less, and more preferably 24 hours or less. By shortening the reaction time in this way, a polybenzimidazole compound having a sulfonic acid group and / or a phosphonic acid group can also be obtained in a highly heat stable state.

The reaction temperature when synthesizing the polybenzimidazole (A) containing the acidic ionic group of the present invention cannot be defined unconditionally because there is an optimum reaction temperature depending on the combination of individual raw material monomers, but it has been reported in the past. In a reaction involving a high temperature as described above, in a system including a raw material monomer such as an aromatic dicarboxylic acid having a sulfonic acid group and / or a phosphonic acid group, the sulfonic acid group and / or the resulting polybenzimidazole compound is obtained. In some cases, it becomes impossible to control the amount of phosphonic acid groups introduced. In this case, it is preferable to lower the reaction temperature within a range where the effects of the present invention can be obtained. The reaction temperature is preferably 300 ° C. or lower, more preferably 250 ° C. or lower. By lowering the reaction temperature in this way, it is possible to control the amount of sulfonic acid group and / or phosphonic acid group introduced into the polybenzimidazole compound having a large amount of acidic groups.

In addition, the ion exchange membrane of the present invention can be used as necessary, for example, an antioxidant, a heat stabilizer, a lubricant, a tackifier, a plasticizer, a crosslinking agent, a viscosity modifier, an antistatic agent, an antibacterial agent, and an antifoaming agent. In addition, various additives such as a dispersant and a polymerization inhibitor may be contained.

The ion exchange membrane for a redox battery of the present invention can be formed into a membrane by any method such as extrusion, rolling or casting. Among these, it is preferable to mold from a solution dissolved in an appropriate solvent. Examples of the solvent include aprotic polar solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone and hexamethylphosphonamide, and strong acid such as phosphoric acid and sulfuric acid. A suitable solvent can be selected from alcohols such as methanol, ethanol and the like, but is not limited thereto. A plurality of these solvents may be used as a mixture within a possible range.

Among these solvents, aprotic polar solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone and hexamethylphosphonamide are easy to process, This is preferable because acid resistance is not necessary.

The compound solid concentration in the solution is preferably in the range of 0.1 to 50% by mass. If the compound concentration in the solution is less than 0.1% by mass, it tends to be difficult to obtain a good molded product, and if it exceeds 50% by mass, the workability tends to deteriorate. A method of obtaining a molded body from a solution can be performed using a conventionally known method. For example, the film can be obtained by removing the solvent by heating, drying under reduced pressure, or immersing in a compound non-solvent that can be mixed with the solvent that dissolves the compound. When the solvent is an organic solvent, the solvent is preferably distilled off by heating or drying under reduced pressure. When combined with a compound having a similar dissolution behavior, it is preferable in that good molding can be achieved. The sulfonic acid group in the molded article thus obtained may contain a salt form with a cationic species, but it can be converted to a free sulfonic acid group by acid treatment as necessary. You can also.

The most preferable method for forming an ion exchange membrane from the ionic group-containing polybenzimidazole (A) of the present invention or a composition thereof is casting from a solution, and the solvent is removed from the cast solution as described above. Thus, an ion exchange membrane for a redox battery can be obtained. As the solution, a solvent using an organic polar solvent such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, dimethyl sulfoxide, or a strong acid solution or an alcohol solvent may be used depending on the case. . The removal of the solvent is preferably by drying in view of the uniformity of the ion exchange membrane for vanadium redox batteries. Moreover, in order to avoid decomposition | disassembly and alteration of a compound or a solvent, it can also dry at the lowest temperature possible under reduced pressure. Further, when the viscosity of the solution is high, when the substrate or the solution is heated and cast at a high temperature, the viscosity of the solution is lowered and the casting can be easily performed. The thickness of the solution at the time of casting is not particularly limited, but is preferably 10 to 1000 μm. More preferably, it is 50 to 500 μm. If the thickness of the solution is less than 10 μm, the form as an ion exchange membrane for a redox battery tends not to be maintained, and if it is thicker than 1000 μm, a non-uniform ion exchange membrane tends to be easily formed. As a method for controlling the cast thickness of the solution, a known method can be used. For example, the thickness can be controlled with the amount and concentration of the solution with a constant thickness using an applicator, a doctor blade, or the like, and with a cast area constant using a glass petri dish or the like. The cast solution can obtain a more uniform film by adjusting the solvent removal rate. For example, in the case of heating, the evaporation rate can be reduced by lowering the temperature in the first stage. In addition, when immersed in a non-solvent such as water, the coagulation rate of the compound can be adjusted by leaving the solution in air or an inert gas for an appropriate time.

The ion exchange membrane for a redox battery of the present invention can have any film thickness depending on the purpose, but is preferably as thin as possible from the viewpoint of ion conductivity. Specifically, the thickness is preferably 5 to 200 μm, more preferably 5 to 50 μm, and most preferably 5 to 20 μm. If the thickness of the ion exchange membrane for redox batteries is less than 5 μm, the handling of the ion exchange membrane becomes difficult, and a short circuit or the like tends to occur when a vanadium redox battery is produced. However, the energy efficiency of the redox battery tends to decrease. When used as an ion exchange membrane for vanadium-based redox batteries using vanadium ions as the active material of the battery, the sulfonic acid groups in the membrane may include those in the form of metal salts, but free by appropriate acid treatment. It can also be converted to sulfonic acid. In this case, it is also effective to immerse the membrane in an aqueous solution of sulfuric acid, hydrochloric acid, etc. with or without heating. The ion conductivity of the ion exchange membrane is preferably 1.0 × 10 ⁻³ S / cm or more. When the ionic conductivity is 1.0 × 10 ⁻³ S / cm or more, a redox flow battery using the ion exchange membrane tends to provide good output, and less than 1.0 × 10 ⁻³ S / cm. In some cases, the output of the redox battery tends to decrease.

The 3% weight reduction temperature of the ion exchange membrane of the present invention is preferably 300 ° C to 500 ° C. When the temperature is 300 ° C. or lower, durability may be insufficient when the temperature is increased.

The redox battery in the present invention is a battery that charges and discharges by an oxidation-reduction reaction of active materials having different valences (for example, vanadium), and includes a redox flow battery described later. A vanadium-based redox battery is a preferred embodiment of the present invention. In this case, the ion exchange membrane is used as a diaphragm for adjusting the ion balance in the positive electrode and the negative electrode and preventing mixing of vanadium having different valences. The ion exchange membrane for a vanadium redox battery of the present invention may be used in a redox flow battery in which an aqueous electrolyte is charged and discharged by circulating a pump, or vanadium hydrate is used as a carbon electrode instead of an aqueous electrolyte. It may be used as a redox battery impregnated with. A redox flow battery that charges and discharges aqueous electrolyte solution by circulating a pump has a diaphragm disposed between a pair of current collector plates facing each other with a gap interposed therebetween, for example. An electrode material is sandwiched between at least one of the diaphragms, and the electrode material includes an electrolytic cell having a structure including an electrolytic solution made of an aqueous solution containing an active material.

Examples of the aqueous electrolyte used in the redox battery and redox flow battery of the present invention include iron-chromium, titanium-manganese-chromium, chromium-chromium, iron-titanium, in addition to the vanadium electrolyte as described above. The vanadium electrolyte is preferable. In particular, the carbon electrode material assembly of the present invention uses a vanadium-based electrolyte having a viscosity of 0.005 Pa · s or more at 25 ° C. or a vanadium-based electrolyte containing 1.5 mol / l or more of vanadium ions. Useful for redox flow batteries.

Hereinafter, the present invention will be specifically described using examples, but the present invention is not limited to these examples. Various measurements were performed as follows.

Solution viscosity: The polymer powder was dissolved in methanesulfonic acid at a concentration of 0.5 g / dl, the viscosity was measured using a Ubbelohde viscometer in a constant temperature bath at 30 ° C., and the logarithmic viscosity ln [ta / tb] / c ) (Ta is the number of seconds that the sample solution falls, tb is the number of seconds that the solvent is dropped, and c is the polymer concentration).

TGA: Using a thermogravimetry meter (TGA-50) manufactured by Shimadzu Corporation, measurement was performed in an argon atmosphere at a heating rate of 10 ° C./min (while maintaining at 150 ° C. for 30 minutes to sufficiently remove moisture) . The 3% weight reduction temperature was the temperature at which the weight decreased by 3% with respect to the weight after the temperature was raised to 200 ° C.

Battery characteristics: A small cell having an electrode area of 10 cm ² of 10 cm in the vertical direction (liquid flow direction) and 1 cm in the width direction is formed, and charging and discharging are repeated at a constant current density, current efficiency, cell resistance, energy efficiency, voltage efficiency Was calculated as follows. Moreover, a 2.5 mol / l sulfuric acid aqueous solution of 1.5 mol / l vanadium oxysulfate was used for the positive electrode electrolyte, and a 2.5 mol / l sulfuric acid aqueous solution of 1.5 mol / l vanadium sulfate was used for the negative electrode electrolyte. It was. The amount of the electrolytic solution was excessively large with respect to the cell and the piping. The liquid flow rate was 6.2 ml per minute, and the measurement was performed at 30 ° C.

(A) Current efficiency: η _I
In a one-cycle test that starts with charging and ends with discharging, the current density is 80 mA / cm 2 (1260 mA) per electrode geometric area, and the amount of electricity required for charging up to 1.6 V is constant at Q ₁ coulomb and 1.0 V. The amount of electricity taken out by the current discharge is defined as Q ₂ coulomb, and the current efficiency ηI is obtained by Equation 1.

(B) Cell resistance: R
The ratio of the amount of electricity taken out by discharge with respect to the theoretical amount of electricity Q _th necessary to completely reduce V ³⁺ in the negative electrode solution to V ²⁺ is taken as the charging rate, and the charging rate is obtained by Equation 2.

Charging voltage V _C50 of the charging rate corresponding to the quantity of electricity at _50% electric quantity discharge voltage V _D50 - calculated respectively from the voltage curves, the cell resistance to the electrode geometry area than the formula 3 R (Ω · cm ²
)

(C) Voltage efficiency: η _V
Using the cell resistance R obtained by the above method, the voltage efficiency η _V is obtained by the simple method of Equation 4.

Here, E is a cell open circuit voltage of 1.432 V (measured value) when the charging rate is 50%, and I is a current value of 1.260 A in constant current charge / discharge.

(D) Energy efficiency: η _E
Using the current efficiency η _I and the voltage efficiency η _V described above, the energy efficiency η _E is obtained by Equation 5.

NMR measurement: The polymer was dissolved in a solvent, and ¹ H-NMR was measured at room temperature using UNITY-500 manufactured by VARIAN. Heavy dimethyl sulfoxide was used as the solvent. From the peak area value derived from the structural formula (2) and the peak area value derived from the structural formula (3), the molar ratio of the constituent components was calculated, and the value of n was calculated.

Oxidation resistance test: The membrane was immersed in an electrolytic solution composed of 4.0 mol / l sulfuric acid containing 0.9 mol / l of pentavalent vanadium ions and incubated at 70 ° C. for 24 hours. About the film | membrane after a test, after confirming the presence or absence of a film | membrane shape, it was immersed in 2.5 mol / l sulfuric acid overnight or more, and the acid component was removed by immersing in pure water for further 1 hour. Then, according to the above-mentioned method, (eta) I was calculated | required according to the above-mentioned method, and the current efficiency loss was calculated | required according to Numerical formula 6.

Here, Δη _I is the current efficiency loss, η _II is the current efficiency before the immersion test, and η _I2 is the current efficiency after the immersion test.

(Polymerimidazole (A) polymerization)
3,3 ′, 4,4′-tetraaminodiphenylsulfone (abbreviation: TAS) 1.500 g (5.389 × 10 −3 mole), monosodium 2,5-dicarboxybenzenesulfonate (abbreviation: STA, purity 99%) 1.445 g (5.389 × 10 −3 mole), 20.48 g of polyphosphoric acid (phosphorus pentoxide content 75%), and 16.41 g of phosphorus pentoxide are weighed in a polymerization vessel. Flow nitrogen and raise the temperature to 100 ° C while stirring gently on an oil bath. 10
After maintaining at 0 ° C. for 1 hour, the temperature was raised to 150 ° C. for 1 hour, and the temperature was raised to 200 ° C. for 4 hours for polymerization. After completion of the polymerization, the mixture was allowed to cool, and water was added to take out the polymerized product, followed by repeated washing with a home mixer until the pH test paper was neutral. The obtained polymer was dried under reduced pressure at 80 ° C. overnight. The logarithmic viscosity of the polymer was 1.71. The obtained polymer is referred to as polymer 1 and the structural formula is shown below.

Example 1
1 g of the polymer 1 obtained above was weighed, dissolved in 10 ml of NMP, cast on a glass plate on a hot plate to a thickness of about 200 μm, NMP was distilled off until a film was formed, and then immersed in water overnight. The thickness of the obtained film was 15 μm. The 3% weight loss temperature (measured based on the sample weight at 200 ° C.) by thermogravimetry of this film was 453 ° C.

(Example 2)
1 g of the polymer 1 obtained above was weighed, dissolved in 10 ml of NMP, cast on a glass plate on a hot plate to a thickness of about 150 μm, NMP was distilled off until a film was formed, and then immersed in water overnight. The thickness of the obtained film was 10 μm.

Example 3
1 g of the polymer 1 obtained above was weighed, dissolved in 10 ml of NMP, cast on a glass plate on a hot plate to a thickness of about 300 μm, NMP was distilled off until a film was formed, and then immersed in water overnight. The thickness of the obtained film was 20 μm.

(Example 18)
TAS 10.000 g (0.03567 mole), 2,6 − 9.665 g (0.03567 mole) dicarboxybenzenesulfonic acid monosodium, 122.5 g polyphosphoric acid (phosphorus pentoxide content 75%), phosphorus pentoxide 20. Weigh 73 g into a polymerization vessel. The temperature is raised to 100 ° C. while slowly stirring on an oil bath while flowing nitrogen. After maintaining at 100 ° C. for 1 hour, the temperature was raised to 150 ° C. for 1 hour, and the temperature was raised to 200 ° C. and polymerized for 4 hours. After completion of the polymerization, the mixture was allowed to cool, and water was added to take out the polymerized product, followed by repeated washing with a home mixer until the pH test paper was neutral. The obtained polymer was dried under reduced pressure at 80 ° C. overnight. The logarithmic viscosity of the polymer was 1.10. The structural formula of the obtained polymer is shown below. The resulting polymer is referred to as polymer 8.

1 g of the obtained polymer was dissolved in 10 ml of NMP, cast on a glass plate on a hot plate to a thickness of about 300 μm, NMP was distilled off until a film was formed, and then immersed in water overnight. The thickness of the obtained film was 15 μm. The 3% weight loss temperature (measured based on the sample weight at 200 ° C.) by thermogravimetry of the film was 433 ° C.

(Example 19)
TAS 10.000 g (0.03567 mole), 2,5 − monosodium dicarboxybenzenesulfonate 2.899 g (0.01070 mole), 2,6 − 6.208 g (0.02497 mole) dicarboxybenzenephosphonic acid 122.5 g of polyphosphoric acid (phosphorus pentoxide content 75%) and 20.73 g of phosphorus pentoxide are weighed into a polymerization vessel. The temperature is raised to 100 ° C. while slowly stirring on an oil bath while flowing nitrogen. After maintaining at 100 ° C. for 1 hour, the temperature was raised to 150 ° C. for 1 hour, and the temperature was raised to 200 ° C. and polymerized for 4 hours. After completion of the polymerization, the mixture was allowed to cool, and water was added to take out the polymerized product, followed by repeated washing with a home mixer until the pH test paper was neutral. The obtained polymer was dried under reduced pressure at 80 ° C. overnight. The logarithmic viscosity of the polymer was 1.33. The structural formula of the obtained polymer is shown below. The resulting polymer is referred to as polymer 9.

1 g of the obtained polymer was dissolved in 10 ml of NMP, cast on a glass plate on a hot plate to a thickness of about 200 μm, NMP was distilled off until a film was formed, and then immersed in water overnight. The thickness of the obtained film was 15 μm. The 3% weight loss temperature (measured based on the sample weight at 200 ° C.) by thermogravimetry of the film was 433 ° C.

(Example 20)
<Monomer synthesis>
2,8.7 'of 4,4'-oxydibenzoic acid was reacted in 60 ml of fuming sulfuric acid at 110 ° C for 2 hours. The reaction system was dropped into cooling water, and sodium chloride was added to this solution to precipitate a precipitate (salting out). The precipitate was filtered, and the resulting solid was purified by recrystallization from water to obtain 2.2'-disulfo-4.4'-oxydibenzoic acid with a purity of 99.8%.
<Polymer polymerization>
TAS 10.000 g (0.03567 mole), 2.2'-disulfo-4.4'-oxydibenzoic acid 16.511 g (0.03567 mole), polyphosphoric acid (phosphorus pentoxide content 75%) 122.5 g, pentoxide Weigh 20.73 g of phosphorus into the polymerization vessel. The temperature is raised to 100 ° C. while slowly stirring on an oil bath while flowing nitrogen. After maintaining at 100 ° C. for 1 hour, the temperature was raised to 150 ° C. for 1 hour, and the temperature was raised to 200 ° C. and polymerized for 4 hours. After completion of the polymerization, the mixture was allowed to cool, and water was added to take out the polymerized product, followed by repeated washing with a home mixer until the pH test paper was neutral. The obtained polymer was dried under reduced pressure at 80 ° C. overnight. The logarithmic viscosity of the polymer was 0.99. The structural formula of the obtained polymer is shown below.

1 g of the obtained polymer was dissolved in 10 ml of NMP, cast on a glass plate on a hot plate to a thickness of about 200 μm, NMP was distilled off until a film was formed, and then immersed in water overnight. The thickness of the obtained film was 15 μm. Moreover, the 3% weight reduction | decrease temperature (measured on the basis of the sample weight in 200 degreeC) by thermogravimetry of this film was 411 degreeC.

(Comparative Example 1)
Cast a N, N-dimethylacetamide solution of polybenzimidazole manufactured by Sato Light Kogyo Co., Ltd. onto a glass plate on a hot plate while adjusting the thickness, distill off the solvent until a film is formed, and then immerse in water overnight Thus, a film having an average thickness of 10 μm was prepared. Its structural formula is shown below.

(Comparative Example 2)
4.3220 g (0.00875 mole) of 3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: S-DCDPS) and 4.6-dichlorobenzonitrile (abbreviation: DCBN) 1847 g (0.02426 mole), 4,4′-biphenol 6.1494 g (0.03300 mole), and 5.0171 g (0.03630 mole) of potassium carbonate were weighed into a 100 ml four-necked flask and flushed with nitrogen. After adding 30 ml of NMP and stirring at 150 ° C. for 1 hour, the reaction was continued by raising the reaction temperature to 195-200 ° C. and sufficiently increasing the viscosity of the system (about 5 hours). After standing to cool, the precipitated molecular sieve was removed and the mixture was precipitated in water as a strand. The obtained polymer was washed in boiling water for 1 hour and then dried. The polymer structural formula is shown below.

The NMP solution of the polymer obtained in Comparative Example 2 was cast on a glass plate on a hot plate by adjusting the thickness, and after the NMP was distilled off until it became a film, it was immersed in water for more than one night. A film having an average thickness of 30 μm was prepared. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component. The 3% weight loss temperature (measured based on the sample weight at 200 ° C.) by thermogravimetry of this film was 380 ° C.

(Comparative Example 3)
4.4560 g (0.00902 mole) of 3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: S-DCDPS) and 3,6-dichlorobenzonitrile (abbreviation: DCBN) of 3. Polymerization was conducted in the same manner as in Comparative Example 2 except that 1583 g (0.01831 mole), 4,4′-biphenol 5.0912 g (0.02732 mole), and potassium carbonate 4.1538 g (0.03005 mole). Of polymer was obtained.

The NMP solution of the polymer obtained in Comparative Example 3 was cast on a glass plate on a hot plate by adjusting the thickness, and after NMP was distilled off until it became a film, it was immersed in water for more than one night. A film having an average thickness of 30 μm was prepared. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component. The 3% weight loss temperature (measured based on the sample weight at 200 ° C.) by thermogravimetry of this film was 384 ° C.

(Comparative Example 4)
3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: S-DCDPS) 5.000 g (0.01012 mole), 2,6-dichlorobenzonitrile (abbreviation: DCBN) 2.2215 g ( 0.01288 mole), 4,4′-biphenol 4.2846 g (0.02299 mole), potassium carbonate 3.4957 g (0.02529 mole), and molecular sieve 2.61 g. And a polymer having the following structure was obtained.

The NMP solution of the polymer obtained in Comparative Example 4 was cast on a glass plate on a hot plate by adjusting the thickness, and after the NMP was distilled off until it became a film, it was immersed in water overnight or longer. A film having an average thickness of 30 μm was prepared. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component. The 3% weight loss temperature (measured based on the sample weight at 200 ° C.) by thermogravimetry of this film was 393 ° C.

(Comparative Example 5)
3,3′-Disulfo-4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: S-DCDPS) 5.000 g (0.01012 mole), 4,4′-dichlorodiphenylsulfone (abbreviation: DCDPS) 2.9140 g (0.01012 mole), 4,4′-biphenol 3.7704 g (0.02023 mole), potassium carbonate 3.0762 g (0.02226 mole), and molecular sieve 2.61 g. To obtain a polymer having the following structure.

The NMP solution of the polymer obtained in Comparative Example 5 was cast on a glass plate on a hot plate by adjusting the thickness, and after the NMP was distilled off until it became a film, it was immersed in water for more than one night. A film having an average thickness of 30 μm was prepared. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component. The 3% weight loss temperature (measured based on the sample weight at 200 ° C.) by thermogravimetry of this film was 354 ° C.

The ion exchange membranes produced in Examples 1 to 3 and Comparative Examples 1 to 5 were sandwiched between carbon electrode materials (XF30A manufactured by Toyobo Co., Ltd.) to assemble a cell as shown in FIG. A small cell having an electrode area of 10 cm ² of 10 cm in the vertical direction (liquid passing direction) and 1 cm in the width direction was prepared, charge and discharge were repeated at a constant current density, and the ion exchange membrane performance was tested. The current value at the time of charging / discharging was set to 1280 mA, and the current density was set to 80 mA / cm ² . The upper limit voltage during charging was 1.6 V, and the lower limit voltage during discharging was 1.0 V. A 2.5 mol / l sulfuric acid aqueous solution of 1.5 mol / l vanadium oxysulfate was used for the positive electrode electrolyte, and a 2.5 mol / l sulfuric acid aqueous solution of 1.5 mol / l vanadium sulfate was used for the negative electrode electrolyte. The amount of the electrolytic solution was excessively large with respect to the cell and the piping. The liquid flow rate was 6.2 ml per minute, and the measurement was performed at 30 ° C.

Using the ion exchange membranes produced in Examples 1 to 3 and Comparative Examples 1 to 5, charging and discharging were performed for 2 to 4 cycles. As other comparative examples, the same measurement was performed using Nafion 115CS manufactured by DuPont of the United States and Selemion DMV manufactured by Asahi Glass (Comparative Examples 6 and 7). Furthermore, an oxidation resistance test was also performed, and the results were as shown in Table 1.

As is clear from the results in Table 1, the ion exchange membranes comprising the ionic group-containing polybenzimidazoles of Examples 1 to 3 exhibited a low resistance and a very high current efficiency, resulting in a high energy efficiency. Furthermore, although the film thickness was thinner than the other comparative examples, the film shape was maintained even after the oxidation resistance test, and almost no current efficiency loss was observed. From this result, it was found that the ion exchange membrane made of ionic group-containing polybenzimidazole has high energy efficiency and very good oxidation resistance.

In contrast, the ion exchange membrane made of polybenzimidazole containing no ionic group (Comparative Example 1) was very high in resistance and inferior in energy efficiency. Furthermore, the oxidation resistance was insufficient. From this result, it is considered that the effect of introducing the acidic ionic group is expressed. In Comparative Examples 2 to 5, sulfonic acid groups are introduced into conventional aromatic polymers. Although these initial energy efficiencies are equivalent to those of Examples 1 to 3, the film was fragmented or dissolved in the oxidation resistance test, and none of the films could maintain the film shape. On the other hand, in the perfluoro-type ion exchange membrane as in Comparative Example 6, although the oxidation resistance was excellent, the initial energy efficiency was low because the current efficiency was low. Further, in the commercially available ion exchange membrane (Comparative Example 7), the same results as in Comparative Examples 2 to 5 were obtained.

(Polymerization of polymer (B) having acidic ionic group)
(Polymerization Example 1: Polymer polymerization of IEC = 2.1 mmeq / g)
3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: S-DCDPS) 5.000 g (0.01012 mole), 2,6-dichlorobenzonitrile (abbreviation: DCBN) 2.2215 g ( 0.01288 mole), 4,4′-biphenol 4.2846 g (0.02299 mole), and potassium carbonate 3.4957 g (0.02529 mole) were weighed into a 100 ml four-necked flask and flushed with nitrogen. After adding 40 ml of NMP and stirring at 150 ° C. for 1 hour, the reaction was continued by raising the reaction temperature to 195-200 ° C. and sufficiently increasing the viscosity of the system (about 5 hours). After cooling, it was precipitated in strands in water. The obtained polymer was washed in boiling water for 1 hour and then dried. A polymer having the following structure was obtained by NMR measurement. The following polymer is referred to as Polymer 2. The thermogravimetric 3% weight loss temperature of this polymer (measured based on the sample weight at 200 ° C.) was 389 ° C. The logarithmic viscosity of polymer 2 was 1.43 dl / g. The IEC determined by titration was 2.03 meq / g.

(Polymerization Example 2: Polymer polymerization of IEC = 2.4 mmeq / g)
2.4450 g (0.00495 mole) of 3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: S-DCDPS) and 0.26 of 2,6-dichlorobenzonitrile (abbreviation: DCBN). Polymerization was conducted in the same manner as in Polymerization Example 1 except that 6983 g (0.00405 mole) was obtained, and a polymer having the following structural formula was obtained. The polymer structural formula is shown below. The following polymer is referred to as Polymer 3. The thermogravimetric 3% weight loss temperature of this polymer (measured based on the sample weight at 200 ° C.) was 393 ° C. The logarithmic viscosity of Polymer 3 was 1.33 dl / g. The IEC determined by titration was 2.41 meq / g.

(Polymerization Example 3: Polymer polymerization of IEC = 2.6 mmeq / g)
3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: S-DCDPS) 1.500 g (0.00304 mole), 2,6-dichlorobenzonitrile (abbreviation: DCBN) 0.2820 g ( 0.00163 mole), 4,4′-biphenol 0.8701 g (0.00467 mole), and potassium carbonate 0.7099 g (0.00514 mole). A polymer was obtained. The following polymer is referred to as Polymer 4. The thermogravimetric 3% weight loss temperature of this polymer (measured based on the sample weight at 200 ° C.) was 389 ° C. The logarithmic viscosity of polymer 4 was 1.54 dl / g. The IEC determined by titration was 2.61 meq / g.

(Polymerization Example 4: Polymer polymerization of IEC = 1.4 mmeq / g)
4.3220 g (0.00875 mole) of 3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: S-DCDPS) and 4.6-dichlorobenzonitrile (abbreviation: DCBN) Polymerization was conducted in the same manner as in Polymerization Example 1 except that 1847 g (0.02426 mole), 4,4′-biphenol 6.1494 g (0.03300 mole), and potassium carbonate 5.0171 g (0.03630 mole). A polymer of the formula was obtained. The logarithmic viscosity of the polymer was 1.43 dl / g. The polymer structural formula is shown below. The following polymer is referred to as Polymer 5. The thermogravimetric 3% weight loss temperature of this polymer (measured based on the sample weight at 200 ° C.) was 388 ° C. The logarithmic viscosity of polymer 5 was 1.35 dl / g. The IEC determined by titration was 1.39 meq / g.

Example 4
1 g of polymer 1 was weighed and dissolved in 10 ml of NMP (solution A). Further, 1 g of polymer 2 was weighed and dissolved in 10 ml of NMP (solution B). Both solutions were mixed so that the weight ratio was Solution A: Solution B = 4: 6, defoamed, cast on a glass plate on a hot plate to a thickness of about 200 μm, and NMP was distilled off until a film was formed. Soaked in water for more than one night. The thickness of the obtained film was 15 μm.

(Example 5)
A film was obtained in the same manner as in Example 4 except that both solutions were mixed so that the weight ratio was Solution A: Solution B = 2: 8. The thickness of the obtained film was 15 μm.

(Example 6)
1 g of the polymer 3 was weighed and dissolved in 10 ml of NMP (solution C). A film was obtained in the same manner as in Example 4 except that both solutions were mixed so that the weight ratio was Solution A: Solution C = 4: 6. The thickness of the obtained film was 17 μm.

(Example 7)
The membrane after casting was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component, and Example 6 A film was obtained in the same manner. The thickness of the obtained film was 17 μm.

(Example 8)
A film was obtained in the same manner as in Example 7 except that both solutions were mixed so that the weight ratio was Solution A: Solution C = 6: 4. The thickness of the obtained film was 15 μm.

Example 9
1 g of polymer 4 was weighed and dissolved in 10 ml of NMP (solution D). A film was obtained in the same manner as in Example 7 except that both solutions were mixed so that the weight ratio was Solution A: Solution D = 6: 4. The thickness of the obtained film was 16 μm.

(Example 10)
A film was obtained in the same manner as in Example 7 except that both solutions were mixed so that the weight ratio was Solution A: Solution D = 7: 3. The thickness of the obtained film was 15 μm.

(Comparative Example 8)
Using only solution B, cast it on a glass plate on a hot plate to a thickness of about 400 μm, distill off NMP until it becomes a film, and then immerse it in water for more than one night, then dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) ) For 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component. The thickness of the obtained film was 30 μm.

(Comparative Example 9)
A film was obtained in the same manner as in Comparative Example 8 except that only the solution D was used. The thickness of the obtained film was 30 μm.

(Comparative Example 10)
1 g of the polymer 5 was weighed and dissolved in 10 ml of NMP (solution E). Using only solution E, a film was obtained in the same manner as in Comparative Example 8. The thickness of the obtained film was 30 μm.

(Comparative Example 11)
Example 7 except that a 10 wt% N, N-dimethylacetamide solution (solution F) of polybenzimidazole manufactured by Sato Light Industry Co., Ltd. having the following structural formula was used and the weight ratio was set to solution F: solution B = 4: 6. A film was obtained in the same manner. The thickness of the obtained film was 16 μm. The following polymer is referred to as Polymer 6.

The ion exchange membranes produced in Examples 4 to 10 and Comparative Examples 8 to 10 were sandwiched between carbon electrode materials (XF30A manufactured by Toyobo Co., Ltd.) to assemble a cell as shown in FIG. A small cell having an electrode area of 16 cm ² of 10 cm in the vertical direction (liquid passing direction) and 1.6 cm in the width direction was prepared, and charge / discharge was repeated at a constant current density to test the ion exchange membrane performance. The current value at the time of charging / discharging was set to 1280 mA, and the current density was set to 80 mA / cm ² . The upper limit voltage during charging was 1.6 V, and the lower limit voltage during discharging was 1.0 V. A 2.5 mol / l sulfuric acid aqueous solution of 1.5 mol / l vanadium oxysulfate was used for the positive electrode electrolyte, and a 2.5 mol / l sulfuric acid aqueous solution of 1.5 mol / l vanadium sulfate was used for the negative electrode electrolyte. The amount of the electrolytic solution was excessively large with respect to the cell and the piping. The liquid flow rate was 6.2 ml per minute, and the measurement was performed at 30 ° C.

Using the ion exchange membranes produced in Examples 4 to 10 and Comparative Examples 8 to 10, charging and discharging were performed for 2 to 4 cycles. Further, as another comparative example, the same measurement was performed using Nafion 115CS manufactured by DuPont, USA and Selemion DMV manufactured by Asahi Glass Co., Ltd. (Comparative Examples 12 and 13). As a result, it became as shown in Table 2.

As is apparent from the results in Table 2, ions comprising a mixture of the ionic group-containing polybenzimidazoles of Examples 4 to 10 and a polymer containing acidic ionic groups having an ion exchange capacity of 1.5 mmeq / g or more. The exchange membrane exhibited a low resistance and very high current efficiency, resulting in high energy efficiency. In particular, Examples 4, 6, and 7 can achieve both a very low resistance value and high current efficiency. Thus, by forming an ionic bridge between the polybenzimidazole containing an acidic ionic group and the second polymer having an acidic ionic group, the interaction between the mixed different polymers is strengthened, The above performance is considered to have developed.

On the other hand, the film made of only polymer 2 resulted in low current efficiency (Comparative Example 8). The polymer 4 alone having a higher IEC than that of the polymer 2 was not able to be evaluated because the movement of vanadium was excessive during battery measurement (Comparative Example 9). The film consisting only of the polymer 5 having a low IEC had a high resistance and was inferior in energy efficiency (Comparative Example 10). Comparative Example 11 is a film made of polybenzimidazole and polymer 2 that do not contain an acidic ionic group. This was very high in resistance, and the effects as in Examples 4 to 10 were not exhibited. This shows that introduction of an acidic ionic group into polybenzimidazole is advantageous in terms of energy efficiency. Further, in the perfluoro-based ion exchange membrane as in Comparative Example 12, the initial energy efficiency was low because the current efficiency was low. Further, the resistance was also high in the commercially available ion exchange membrane (Comparative Example 13).

(Example 11)
10 g of polyetheretherketone was placed in a container containing 100 mL of 97% concentrated sulfuric acid and stirred at 40 ° C. for 3 hours or longer, and further stirred at 80 ° C. for 3 hours or longer to react. After completion of the reaction, the solution was allowed to cool and then poured into a container containing ice water. The remaining acid was removed until the pH test paper was neutral and the sulfonated polymer was recovered. The obtained polymer was dried under reduced pressure at 80 ° C. overnight. This sulfonated polyether ketone is referred to as polymer 7.

The NMP solution of the polymer 1 and the NMP solution of the sulfonated polyetheretherketone (polymer 7) obtained by the above method were mixed so that the weight ratio of the polymer was 6: 4. At this time, lithium chloride was added and mixed so as to be 20% by weight to 30% by weight with respect to the polymer weight. This mixed polymer solution was cast on a glass plate on a hot plate to a thickness of about 150 μm depending on the solution concentration, NMP was distilled off until it became a film, and then immersed in water overnight or longer. The thickness of the obtained film was 15 μm. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component.

The ion exchange membrane produced in Example 11 was sandwiched between carbon electrode materials (XF30A manufactured by Toyobo Co., Ltd.) to assemble a cell as shown in FIG. A small cell having an electrode area of 10 cm ² of 10 cm in the vertical direction (liquid passing direction) and 1 cm in the width direction was prepared, and charge / discharge was repeated at a constant current density to test the ion exchange membrane performance. The current value at charging / discharging was set to 1280 mA, and the current density was set to 80 mA / cm ² . The upper limit voltage during charging was 1.7 V, and the lower limit voltage during discharging was 1.0 V. A 2.5 mol / l sulfuric acid aqueous solution of 1.7 mol / l vanadium oxysulfate was used for the positive electrode electrolyte, and a 2.5 mol / l sulfuric acid aqueous solution of 1.7 mol / l vanadium sulfate was used for the negative electrode electrolyte. The amount of the electrolytic solution was excessively large with respect to the cell and the piping. The liquid flow rate was 6.2 ml per minute, and the measurement was performed at 30 ° C.

The oxidation resistance test was performed using the ion exchange membrane produced in Example 11, and the results are shown in Table 3. Moreover, the same measurement was performed using Asahi Glass Co., Ltd. Selemion APS4 as another comparative example (Comparative Example 14).

As is apparent from the results in Table 3, the ion exchange membrane comprising the polybenzimidazole (A) and the acidic ionic group-containing polymer (B) in Example 11 has a low resistance, and is a membrane even after the oxidation resistance test. The shape was maintained and almost no current efficiency loss was observed. From this result, it was found that the ion exchange membrane comprising the ionic group-containing polybenzimidazole (A) and the acidic ionic group-containing polymer (B) has very excellent initial characteristics and oxidation resistance. .
On the other hand, the commercially available ion exchange membrane as in Comparative Example 14 also showed high resistance.

Example 12
A poly (4-styrenesulfonic acid) solution (Mw: 75000, 18 wt% aqueous solution) manufactured by Sigma-Aldrich was dried to remove water, and the resulting solid poly (4-styrenesulfonic acid) was converted into NMP. Dissolved to prepare a 20 wt% to 25 wt% solution.

The NMP solution of polymer 1 and the NMP solution of poly (4-styrenesulfonic acid) were mixed so that the weight ratio of the polymer was 6: 4. At this time, lithium chloride was added and mixed so as to be 20% by weight to 30% by weight with respect to the polymer weight. This mixed polymer solution was cast on a glass plate on a hot plate to a thickness of about 150 to 250 μm depending on the concentration of the solution, NMP was distilled off until a film was formed, and then immersed in water overnight or longer. The thickness of the obtained film was 10 to 25 μm. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component.

(Example 13)
In Example 12, the same procedure as in Example 12 was performed, except that the NMP solution of polymer 1 and the NMP solution of poly (4-styrenesulfonic acid) were mixed so that the weight ratio of the polymer was 7: 3. It was.

(Example 14)
In Example 12, the same procedure as in Example 12 was performed, except that the NMP solution of polymer 1 and the NMP solution of poly (4-styrenesulfonic acid) were mixed so that the weight ratio of the polymer was 8: 2. It was.

The ion exchange membranes produced in Examples 12 to 14 were sandwiched between carbon electrode materials (XF30A manufactured by Toyobo Co., Ltd.) to assemble a cell as shown in FIG. A small cell having an electrode area of 10 cm ² of 10 cm in the vertical direction (liquid passing direction) and 1 cm in the width direction was prepared, and charge / discharge was repeated at a constant current density to test the ion exchange membrane performance. The current value at charging / discharging was set to 1280 mA, and the current density was set to 80 mA / cm ² . The upper limit voltage during charging was 1.7 V, and the lower limit voltage during discharging was 1.0 V. A 2.5 mol / l sulfuric acid aqueous solution of 1.7 mol / l vanadium oxysulfate was used for the positive electrode electrolyte, and a 2.5 mol / l sulfuric acid aqueous solution of 1.7 mol / l vanadium sulfate was used for the negative electrode electrolyte. The amount of the electrolytic solution was excessively large with respect to the cell and the piping. The liquid flow rate was 6.2 ml per minute, and the measurement was performed at 30 ° C.

The oxidation resistance test was performed using the ion exchange membranes produced in Examples 12 to 14. As a result, the results shown in Table 4 were obtained. Moreover, the same measurement was performed using Asahi Glass Co., Ltd. Selemion APS4 as another comparative example (Comparative Example 15).

As is clear from the results in Table 4, the ion exchange membranes comprising the polybenzimidazole (A) of Examples 12 to 14 and the acidic ionic group-containing polymer (B) have low resistance, and after the oxidation resistance test However, the film shape was maintained and almost no current efficiency loss was observed. From this result, it was found that the ion exchange membrane comprising the ionic group-containing polybenzimidazole (A) and the acidic ionic group-containing polymer (B) has very excellent initial characteristics and oxidation resistance. .

From this result, the polybenzimidazole of the polymer (A) and the sulfonic acid of the polymer (B) form a strong interaction, so that even when a water-soluble polymer is used as in the example, it is eluted. It is thought that it functions as a low resistance component. In the examples, it is considered that the polymer (B) is superior in oxidation resistance to the conventional hydrocarbon ion exchange membrane by using a polymer having no electron donating group. On the other hand, the resistance of the commercially available ion exchange membrane as in Comparative Example 15 was also high.

(Example 15)
The NMP solution of polymer 1 and the NMP solution of polymer 5 were mixed so that the weight ratio of the polymer was 7: 3. This mixed polymer solution was cast on a glass plate on a hot plate to a thickness of about 150 μm, NMP was distilled off until it became a film, and then immersed in water overnight. The thickness of the obtained film was 15 μm. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component.

(Example 16)
The NMP solution of polymer 1 and the NMP solution of polymer 2 were mixed so that the weight ratio of the polymer was 7: 3. This mixed polymer solution was cast on a glass plate on a hot plate to a thickness of about 150 μm, NMP was distilled off until it became a film, and then immersed in water overnight. The thickness of the obtained film was 15 μm. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component.

(Example 17)
The NMP solution of polymer 1 and the NMP solution of polymer 4 were mixed so that the weight ratio of the polymer was 7: 3. This mixed polymer solution was cast on a glass plate on a hot plate to a thickness of about 150 μm, NMP was distilled off until it became a film, and then immersed in water overnight. The thickness of the obtained film was 15 μm. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component.

(Comparative Example 16)
The N, N-dimethylacetamide solution of polymer 6 was cast on a glass plate on a hot plate while adjusting the thickness, the solvent was distilled off until it became a film, and then immersed in water for more than one night. A 10 μm film was prepared.

(Comparative Example 17)
The solution of polymer 6 described in Comparative Example 16 and the solution of polymer 5 described in Example 15 were mixed so that the weight ratio of the polymer was 4: 6. This mixed polymer solution was cast on a glass plate on a hot plate with the thickness adjusted, NMP was distilled off until it became a film, and then immersed in water overnight to adjust the film with an average thickness of 15 μm. did. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component.

(Comparative Example 18)
The NMP solution of polymer 5 was cast on a glass plate on a hot plate while adjusting the thickness, and after NMP was distilled off until it became a film, it was immersed in water overnight for a film with an average thickness of 30 μm. Prepared.

(Comparative Example 19)
The film obtained in Comparative Example 18 was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component.

(Comparative Example 20)
The NMP solution of polymer 2 was cast on a glass plate on a hot plate with the thickness adjusted, and after NMP was distilled off until it became a film, it was immersed in water for more than one night to form a film with an average thickness of 30 μm. It was adjusted. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component.

(Comparative Example 21)
The NMP solution of polymer 4 was cast on a glass plate on a hot plate while adjusting the thickness, and after NMP was distilled off until it became a film, it was immersed in water overnight for a film with an average thickness of 30 μm. It was adjusted. The obtained film was treated in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 hour to remove the salt, and then immersed in pure water for 1 hour to remove the acid component.

The ion exchange membranes produced in Examples 15 to 17 and Comparative Examples 16 to 21 were sandwiched between carbon electrode materials (XF30A manufactured by Toyobo Co., Ltd.) to assemble a cell as shown in FIG. A small cell having an electrode area of 10 cm ² of 10 cm in the vertical direction (liquid passing direction) and 1 cm in the width direction was prepared, and charge / discharge was repeated at a constant current density to test the ion exchange membrane performance. The current value at charging / discharging was set to 1280 mA, and the current density was set to 80 mA / cm ² . The upper limit voltage during charging was 1.6 V, and the lower limit voltage during discharging was 1.0 V. A 2.5 mol / l sulfuric acid aqueous solution of 1.5 mol / l vanadium oxysulfate was used for the positive electrode electrolyte, and a 2.5 mol / l sulfuric acid aqueous solution of 1.5 mol / l vanadium sulfate was used for the negative electrode electrolyte. The amount of the electrolytic solution was excessively large with respect to the cell and the piping. The liquid flow rate was 6.2 ml per minute, and the measurement was performed at 30 ° C.

The oxidation resistance test was performed using the ion exchange membranes produced in Examples 15 to 17 and Comparative Examples 16 to 21, and the results are shown in Table 1. As another comparative example, the same measurement was performed using Nafion 115CS manufactured by DuPont of the United States, and Selemion CSO and Selemion CMV manufactured by Asahi Glass (Comparative Examples 22 to 24).

As is clear from the results in Table 5, the ion exchange membranes comprising the ionic group-containing polybenzimidazole (A) and the polymer (B) in Examples 15 to 17 are thinner than the other comparative examples. Nevertheless, the film shape was maintained even after the oxidation resistance test, and almost no current efficiency loss was observed. From this result, it was found that the ion exchange membrane made of ionic group-containing polybenzimidazole had very excellent oxidation resistance.

On the other hand, the ion exchange membrane made of polybenzimidazole containing no ionic group (Comparative Example 16) had insufficient oxidation resistance. Furthermore, even the ion exchange membrane (Comparative Example 17) made of a polybenzimidazole containing no ionic group and a polymer containing an acidic ionic group had insufficient oxidation resistance. From this result, it is considered that the effect of introducing an ionic group into polybenzimidazole is expressed. In Comparative Examples 18 to 21, sulfonic acid groups are introduced into conventional aromatic polymers. In these oxidation resistance tests, the film was dissolved or fragmented, and none of the films could maintain the film shape. On the other hand, the perfluorocarbon sulfonic acid ion exchange membrane as in Comparative Example 22 is excellent in oxidation resistance, but the initial energy efficiency is 85.5% because of low current efficiency. It was low compared to 88.5%. Further, in the commercially available ion exchange membranes (Comparative Examples 23 and 24), the same results as in Comparative Examples 16 to 21 were obtained.

By using the ionic group-containing polybenzimidazole (A) or the composition thereof of the present invention as an ion exchange membrane for a redox battery, a redox battery exhibiting long life, low cell resistance, excellent voltage efficiency and energy efficiency is provided. be able to.

DESCRIPTION OF SYMBOLS 1 ... Current collector plate, 2 ... Spacer, 3 ... Ion exchange membrane, 4a, b ... Liquid passage, 5 ... Electrode material, 6 ... Positive electrode tank, 7 ... Negative electrode tank, 8, 9 ... Pump

Claims

An ion exchange membrane for a redox battery, comprising polybenzimidazole (A) containing a constituent represented by the following general formula (1).

However, R 1 represents a tetravalent aromatic unit capable of forming an imidazole ring, and R 2 represents a divalent aromatic group. X represents one or more ionic groups selected from a sulfonic acid group, a phosphonic acid group, a hydroxyl group, a carboxyl group, and metal salts and ammonium salts thereof, and m represents an integer of 1 to 4.
2. The ion exchange membrane for a redox battery according to claim 1, wherein the constituent of the general formula (1) includes constituents represented by the following general formula (2) and the following general formula (3).

However, n shows the copolymerization ratio of General formula (2), and satisfy | fills the formula of 20 <= n <= 100. R 2 represents a divalent aromatic group, X represents one or more ionic groups selected from a sulfonic acid group, a phosphonic acid group, a hydroxyl group, a carboxyl group, and metal salts and ammonium salts thereof, and m represents 1 To an integer of 4 to 4, wherein Z is at least one selected from the group consisting of O, SO 2 , C (CH 3 ) 2 , C (CF 3 ) 2 , and OPhO (where Ph represents an aromatic group). It represents the above.
An ion exchange membrane for a redox battery comprising 10 to 100% by mass of the polybenzimidazole (A) according to any one of claims 1 to 2.
Polybenzimidazole (A) containing the structural component represented by the general formula (1), and at least one acidic ion selected from a sulfonic acid group, a phosphonic acid group, a carboxyl group, or a metal salt thereof, or an ammonium salt It comprises a composition containing a polymer (B1) having a functional group and not containing the structure of formula (1), wherein the ion exchange capacity of (B1) is 1.5 mmeq / g or more. The ion exchange membrane for redox batteries of Claim 1 or 2.
Polybenzimidazole (A) containing the structural component represented by the general formula (1), and a sulfonic acid group, phosphonic acid group, hydroxyl group, carboxyl group or a metal thereof which does not contain the structure of the formula (1) It consists of a composition containing the aromatic hydrocarbon polymer (B2) which has at least 1 or more types of acidic ionic groups chosen from a salt and ammonium salt, Any one of Claim 1, 2, 4 characterized by the above-mentioned. The ion exchange membrane for redox batteries described in 1.
Polybenzimidazole (A) containing the structural component represented by the general formula (1), and a sulfonic acid group, phosphonic acid group, hydroxyl group, carboxyl group or a metal thereof which does not contain the structure of the formula (1) It consists of a composition containing the polymer (B3) which has a repeating unit which contains at least 1 or more types of acidic ionic groups chosen from a salt and ammonium salt, One or more, The ion exchange membrane for redox batteries of any one of these.
Polybenzimidazole (A) containing the structural component represented by the general formula (1), and a sulfonic acid group, phosphonic acid group, hydroxyl group, carboxyl group or a metal thereof which does not contain the structure of the formula (1) It consists of a composition containing a polymer (B4) having at least one acidic ionic group selected from a salt and an ammonium salt, and the polymer (B4) has a repeating unit having 12 or more carbon atoms. The ion exchange membrane for redox batteries according to any one of 1, 2, and 4.
In the said composition, a polymer (B1) or a polymer (B2) contains the structural component shown by following General formula (4) and (5), It is any one of Claim 4 or 5 characterized by the above-mentioned. Ion exchange membrane for redox batteries.

Here, Ar represents a divalent aromatic group, Y represents a sulfonyl group or a carbonyl group, Z represents an O atom, an S atom, or a direct bond, and X represents H or a monovalent cation species.

However, Z represents either an O atom or an S atom, and Ar ′ represents a divalent aromatic group.
The composition according to any one of claims 4 to 8, which contains the polybenzimidazole (A) and at least one polymer selected from the group consisting of the polymers (B1) to (B4). 9. The ion exchange for redox battery according to claim 4, wherein the total content of the polymer (B1) to the polymer (B4) is 10 to 80% by mass of the composition. film.
The composition according to any one of claims 4 to 8, which contains the polybenzimidazole (A) and at least one polymer selected from the group consisting of the polymers (B1) to (B4). The total content of the polymer (A) and the polymer (B1) to the polymer (B4) is 10 to 100% by mass of the composition, according to any one of claims 4 to 8. Ion exchange membrane for redox batteries.
11. The ion exchange membrane for a redox battery according to claim 1, which is an ion exchange membrane for a redox flow battery.
The ion exchange membrane for a redox battery according to any one of claims 1 to 11, which is used for a redox battery using vanadium ions as an active material of the battery.
An ion exchange membrane / electrode composite for a redox battery comprising the ion exchange membrane according to any one of claims 1 to 12 and an electrode.
A redox battery comprising the ion exchange membrane according to any one of claims 1 to 12.
A redox battery comprising the ion exchange membrane / electrode composite according to claim 13.