JP6164576B2 - Redox flow battery - Google Patents

Description

  The present invention relates to a redox flow battery.

In general, a redox flow battery uses a strongly acidic electrolyte. As an example of a strongly acidic electrolytic solution, an electrolytic solution containing a vanadium redox substance has been put into practical use. Since the metal redox ions in the strongly acidic electrolyte are stably dissolved even at a relatively high concentration, the energy density of the battery can be increased. In a strongly acidic electrolyte, the ion conductive carrier is H ⁺ ion or OH ⁻ ion. Since both the mobility of H ⁺ ions and the mobility of OH ⁻ ions are relatively high, the strongly acidic electrolyte has high conductivity. This increases the battery efficiency as a result of the reduced battery resistance. However, chemicals that can withstand a strongly acidic electrolyte are required for the components constituting the redox flow battery. As a component of a redox flow battery, for example, a diaphragm between a positive electrode electrolyte and a negative electrode electrolyte can be cited. Patent Document 1 discloses a composite membrane of a hydrophilic membrane and a porous membrane as a diaphragm for a redox flow battery. The hydrophilic film is composed of a cellulose polymer or an ethylene vinyl alcohol copolymer. The porous film is made of tetrafluoroethylene or vinyl chloride.

  On the other hand, for example, Patent Document 2 discloses a weakly acidic electrolytic solution. In the case of using a weakly acidic electrolyte, the chemical resistance required for the positive electrode electrolyte and the negative electrode electrolyte is less than in the case of using a strongly acidic electrolyte.

  Patent Document 3 discloses a negative electrode in which a copolymer of chloromethylstyrene and divinylbenzene is filled in the pores of a porous substrate made of polyolefin, and a quaternary ammonium group is introduced into the copolymer. An ion exchange membrane is disclosed.

Japanese Patent Laid-Open No. 62-223984 JP 56-42970 A JP 2009-144041 A

  In the redox flow battery, when an electrolyte solution having a pH in the range of 2 or more and 8 or less is used, the chemical resistance required for the battery parts is alleviated, so that the use of expensive materials can be avoided. Become. Therefore, it is possible to reduce the cost of the equipment, which is advantageous from the viewpoint of promoting further popularization of the redox flow battery.

  The present invention has been made by finding a suitable diaphragm in a redox flow battery using an electrolytic solution having a pH in the range of 2 or more and 8 or less. In addition, although the said patent document 3 is disclosed about the anion exchange membrane based on polyolefin, application of the anion exchange membrane to the redox flow battery using the electrolyte solution in the range of pH 2-8 Does not suggest about.

  The objective of this invention is providing the redox flow battery which has a suitable diaphragm at the point which exhibits battery performance, when using electrolyte solution in the range of 2 or more and pH 8 or less.

  In order to achieve the above object, in one embodiment of the present invention, a redox flow battery using a positive electrode electrolyte and a negative electrode electrolyte having a pH in the range of 2 or more and 8 or less, which is made of polypropylene and not porous An anion exchange membrane in which an anion exchange group is introduced into a graft chain of the graft polymer by reacting a graft polymer obtained by graft polymerization of halogenated methylstyrene on a substrate and a tertiary amine. Is provided as a diaphragm between the positive electrode electrolyte and the negative electrode electrolyte.

  In the redox flow battery, it is preferable that a graft ratio of the anion exchange membrane is in a range of 55% to 130%.

  In the redox flow battery, the non-porous substrate is preferably a biaxially stretched polypropylene film, and the graft ratio of the anion exchange membrane is more preferably in the range of 70% to 130%. preferable.

It is the schematic which shows the redox flow battery of embodiment of this invention. It is a graph which shows the relationship between the grafting rate of the anion exchange membrane obtained by manufacture examples 1-4, and the transmittance | permeability. It is a result of the charging / discharging test of Example 1, and is a graph which shows the relationship between time and a voltage. It is a result of the charging / discharging test of Examples 2-6, and is a graph which shows the relationship between a graft ratio and energy efficiency.

  Hereinafter, the redox flow battery according to the embodiment of the present invention will be described.

<Structure of redox flow battery>
As shown in FIG. 1, the redox flow battery includes a charge / discharge cell 11, a first tank 23 that stores a positive electrode electrolyte 22, and a second tank 33 that stores a negative electrode electrolyte 32. Further, the redox flow battery includes a first supply pipe 24 that supplies the positive electrode electrolyte 22 to the charge / discharge cell 11 and a second supply pipe 34 that supplies the negative electrode electrolyte 32 to the charge / discharge cell 11.

  The inside of the charge / discharge cell 11 is partitioned into a positive electrode side cell 21 and a negative electrode side cell 31 by a diaphragm 12.

  In the positive electrode side cell 21, a positive electrode 21a and a positive electrode side current collecting plate 21b are arranged in contact with each other. In the negative electrode side cell 31, a negative electrode 31 a and a negative electrode current collector 31 b are arranged in contact with each other. The positive electrode 21a and the negative electrode 31a are made of, for example, carbon felt. The positive electrode side current collector plate 21b and the negative electrode side current collector plate 31b are made of, for example, a glassy carbon plate. The positive electrode side current collector plate 21 b and the negative electrode side current collector plate 31 b are electrically connected to the charge / discharge device 10. The redox flow battery is provided with a temperature adjusting device for adjusting the temperature around the charge / discharge cell 11 as necessary.

  A first tank 23 is connected to the positive electrode side cell 21 via a first supply pipe 24 and a first recovery pipe 25. The first supply pipe 24 is equipped with a first pump 26. By the operation of the first pump 26, the positive electrolyte solution 22 in the first tank 23 is supplied to the positive electrode side cell 21 through the first supply pipe 24. At this time, the positive electrode electrolyte 22 in the positive electrode side cell 21 is recovered to the first tank 23 through the first recovery pipe 25. Thus, the positive electrode electrolyte 22 circulates between the first tank 23 and the positive electrode side cell 21.

  A second tank 33 is connected to the negative electrode side cell 31 via a second supply pipe 34 and a second recovery pipe 35. The second supply pipe 34 is equipped with a second pump 36. By the operation of the second pump 36, the negative electrolyte solution 32 in the second tank 33 is supplied to the negative electrode side cell 31 through the second supply pipe 34. At this time, the negative electrode electrolyte 32 in the negative electrode side cell 31 is recovered in the second tank 33 through the second recovery pipe 35. Thus, the negative electrode electrolyte 32 circulates between the second tank 33 and the negative electrode side cell 31.

  A first gas pipe 13 a is connected to the first tank 23 and the second tank 33. The first gas pipe 13 a supplies the inert gas supplied from the inert gas generator into the positive electrode electrolyte 22 in the first tank 23 and the negative electrode electrolyte 32 in the second tank 33. Thereby, the contact with the positive electrode electrolyte solution 22 and the negative electrode electrolyte solution 32, and oxygen in air | atmosphere is suppressed. The oxygen concentration in the gas phase in the first tank 23 and the second tank 33 is kept substantially constant by adjusting the supply amount of the inert gas.

  For example, nitrogen gas is used as the inert gas. Examples of the inert gas that can be used include carbon dioxide gas, argon gas, and helium gas in addition to nitrogen gas. The inert gas supplied to the first tank 23 and the second tank 33 is exhausted through the exhaust pipe 14. A water seal portion 15 that seals the front end opening of the exhaust pipe 14 is provided at the distal end of the exhaust pipe 14 on the discharge side. The water seal 15 prevents the air from flowing back into the exhaust pipe 14 and keeps the pressure in the first tank 23 and the second tank 33 constant.

  The redox flow battery of this embodiment includes a case 41. The case 41 surrounds the charge / discharge cell 11, the first tank 23, and the second tank 33. The case 41 is connected to the second gas pipe 13b. The second gas pipe 13 b supplies the inert gas supplied from the inert gas generator to the periphery of the charge / discharge cell 11. Thereby, the contact with the charging / discharging cell 11 and oxygen in air | atmosphere is suppressed. The oxygen concentration in the case 41 is kept substantially constant by adjusting the supply amount of the inert gas.

  At the time of charging, an oxidation reaction is performed in the positive electrode electrolyte solution 22 in contact with the positive electrode 21a, and a reduction reaction is performed in the negative electrode electrolyte solution 32 in contact with the negative electrode 31a. That is, the positive electrode 21a emits electrons and the negative electrode 31a receives electrons. At this time, the positive collector plate 21b supplies the electrons discharged from the positive electrode 21a to the charging / discharging device 10. The negative electrode current collector 31b supplies the electrons received from the charge / discharge device 10 to the negative electrode 31a. The negative electrode current collector 31b collects the electrons emitted from the negative electrode 31a and supplies them to the charging / discharging device 10.

  At the time of discharge, a reduction reaction is performed in the positive electrode electrolyte solution 22 in contact with the positive electrode 21a, and an oxidation reaction is performed in the negative electrode electrolyte solution 32 in contact with the negative electrode 31a. That is, the positive electrode 21a receives electrons and the negative electrode 31a emits electrons. At this time, the positive collector plate 21b supplies the electrons received from the charge / discharge device 10 to the positive electrode 21a.

<Configuration of diaphragm 12>
The diaphragm 12 suppresses permeation of the active material between the positive electrode side cell 21 and the negative electrode side cell 31. The diaphragm 12 is composed of an anion exchange membrane. The diaphragm 12 transmits the anions in the negative electrode side cell 31 to the positive electrode side cell 21 during charging, and transmits the anions in the positive electrode side cell 21 to the negative electrode side cell 31 during discharge.

  The anion exchange membrane is obtained by reacting a graft polymer obtained by graft polymerization of halogenated methylstyrene with a non-porous polypropylene base material and a tertiary amine. The reaction between the graft polymer and the tertiary amine introduces an anion exchange group into the graft chain of the graft polymer.

  As the non-porous substrate made of polypropylene, a commercially available film or sheet, for example, a biaxially stretched polypropylene film or an unstretched polypropylene film is used. Among non-porous substrates, a biaxially stretched polypropylene film is preferable.

  The thickness of the polypropylene non-porous substrate is preferably in the range of 10 μm or more and 300 μm or less. The content of polypropylene in the non-porous substrate is preferably 60% by mass or more, and more preferably 70% by mass or more. Resins other than polypropylene may be blended with the non-porous substrate. Examples of the resin other than polypropylene include polyethylene. The non-porous substrate may contain an additive such as a plasticizer.

  The halogenated methylstyrene is graft-polymerized on a non-porous substrate made of polypropylene. As a result, a graft polymer is obtained in which poly (halogenated methylstyrene) is introduced as a graft chain into the polypropylene constituting the non-porous substrate. Examples of the halogenated methyl styrene include chloromethyl styrene and bromomethyl styrene.

  The tertiary amine to be reacted with the graft polymer is not particularly limited as long as it is a tertiary amine capable of reacting with a halogenated methyl group. Suitable tertiary amines include amines having 3 to 12 carbon atoms such as trimethylamine, dimethylethylamine, dimethylpropylamine, dimethylbutylamine, triethylamine, tripropylamine, and tributylamine.

  The graft chain of the anion exchange membrane is a vinyl polymer having a benzyltrialkylammonium salt as a side chain, and the side chain of the graft chain has a quaternary ammonium cation as an anion exchange group.

  The graft ratio of the anion exchange membrane is preferably in the range of 55% to 130%, more preferably in the range of 70% to 130%.

The graft ratio of the anion exchange membrane is expressed by the following formula (A) when the mass of the polypropylene non-porous substrate is W ₀ and the mass of the anion exchange membrane after reacting with the tertiary amine is W _1. It is calculated by substituting for.

Graft rate (%) = 100 × (W ₁ −W ₀ ) / W ₀ (A)
<Manufacture of diaphragm 12 (anion exchange membrane)>
The diaphragm 12 (anion exchange membrane) is manufactured through a polymerization process and a substitution reaction process.

  In the polymerization step, a graft chain is introduced into the radical active site generated on the non-porous substrate using halogenated methylstyrene. The radical active site can be generated, for example, by use of a radical polymerization initiator, irradiation with ionizing radiation, irradiation with ultraviolet rays, irradiation with ultrasonic waves, irradiation with plasma, or the like. Among the methods for generating radical active sites, the polymerization step using ionizing radiation has the advantage that the production process is simple, safe and has a low environmental impact.

  Examples of the ionizing radiation include α rays, β rays, γ rays, electron rays, X rays and the like. Among the ionizing radiations, for example, γ rays emitted from cobalt 60, electron beams emitted from an electron beam accelerator, X-rays, and the like are preferable from the viewpoint of easy industrial use.

  Irradiation with ionizing radiation is preferably performed in an inert gas atmosphere such as nitrogen gas, neon gas, or argon gas from the viewpoint of suppressing the reaction between radical active sites and oxygen. The absorbed dose of ionizing radiation is, for example, in the range of 1 kGy to 300 kGy. The graft ratio can be changed by adjusting the absorbed dose of ionizing radiation.

  In the polymerization step, a solution containing halogenated methylstyrene is brought into contact with the non-porous substrate where radical active sites are generated. In this contact, the radical polymerization reaction can be promoted by shaking or heating the non-porous substrate immersed in the solution containing methyl halide styrene.

  As the solvent of the solution containing halogenated methylstyrene, for example, a hydrophilic ketone such as acetone is preferably used.

  The graft ratio can be easily changed by adjusting the concentration of the halogenated methylstyrene in the solution containing the halogenated methylstyrene. The concentration of the halogenated methylstyrene in the solution containing the halogenated methylstyrene is, for example, in the range of 1% by mass to 70% by mass. The time for which the solution containing halogenated methylstyrene is brought into contact with the non-porous substrate where the radical active site is generated is, for example, in the range of 30 minutes or more and 48 hours or less.

  As with the case of irradiation with ionizing radiation, an inert gas such as nitrogen gas, neon gas, argon gas, carbon dioxide gas, etc. is used for contact between the non-porous base material where radical active sites are generated and a solution containing halogenated methylstyrene. It is preferable to carry out in an atmosphere.

  The graft polymer obtained by the polymerization step is subjected to a substitution reaction step after being washed as necessary.

  In the substitution reaction step, an anion exchange group is introduced into the side chain of the graft chain of the graft polymer by bringing the solution containing the tertiary amine into contact with the graft polymer. In this contact, the substitution reaction can be promoted by shaking or heating the graft polymer immersed in the solution containing the tertiary amine.

  As the solvent of the solution containing the tertiary amine, for example, a hydrophilic solvent such as water is preferably used. The concentration of the tertiary amine in the solution containing the tertiary amine is, for example, in the range of 1% by mass to 70% by mass. The time for the substitution reaction is, for example, in the range of 30 minutes to 48 hours.

  The anion exchange membrane obtained in the substitution reaction step is used as the diaphragm 12 after being washed as necessary.

<Electrolyte>
The pH of the positive electrode electrolyte 22 and the pH of the negative electrode electrolyte 32 are in the range of 2 or more and 8 or less. The pH of the positive electrode electrolyte 22 and the pH of the negative electrode electrolyte 32 are preferably in the range of 4 or more and 7 or less.

  As the pH of the positive electrode electrolyte 22 and the negative electrode electrolyte 32, an aqueous solution containing an active material capable of performing a redox reaction within the above pH range is used. When the pH of the positive electrode electrolyte 22 and the pH of the negative electrode electrolyte 32 are 2 or more, corrosion resistance is easily ensured. When the pH of the positive electrode electrolyte 22 and the pH of the negative electrode electrolyte 32 are 8 or less, for example, the solubility of the active material is easily ensured.

  Examples of the active material include an iron redox material, a titanium redox material, a chromium redox material, a manganese redox material, and a copper redox material. The “redox substance” described in the present application refers to a metal ion, a metal complex ion, or a metal generated by a metal redox reaction.

  The active material is preferably contained in the electrolytic solution as a metal complex in order to suppress precipitation within the above pH range. The chelating agent for forming the metal complex is capable of forming a complex with the active material, and examples thereof include amines, citric acid, lactic acid, aminocarboxylic chelating agents, and polyethyleneimine.

  Hereinafter, details of an example of the positive electrode electrolyte 22 and the negative electrode electrolyte 32 will be described.

  The cathode electrolyte 22 contains an iron redox material and an acid. The acid is citric acid or lactic acid.

  In the positive electrode electrolyte 22, iron functions as an active material. For example, oxidation from iron (II) to iron (III) occurs during charging, and reduction from iron (III) to iron (II) occurs during discharging. Is presumed to occur. The positive electrode electrolyte 22 contains the acid described above, so that a practical electromotive force can be easily obtained.

  The concentration of the iron redox substance (iron ions) in the positive electrode electrolyte 22 is preferably 0.2 mol / L or more, more preferably 0.3 mol / L or more, from the viewpoint of increasing the energy density. More preferably 0.4 mol / L or more. The concentration of the iron redox substance (iron ions) in the positive electrode electrolyte 22 is preferably 1.0 mol / L or less.

  The molar ratio of the acid to the iron redox substance in the positive electrode electrolyte 22 is preferably in the range of 1 or more and 4 or less. When the molar ratio is 1 or more, the electrical resistance of the positive electrode electrolyte 22 becomes lower, so that the Coulomb efficiency and the utilization rate of the positive electrode electrolyte 22 can be easily increased. When the molar ratio is 4 or less, both economic efficiency and practicality can be easily achieved.

  The pH of the positive electrode electrolyte 22 is preferably in the range of 1 or more and 7 or less, more preferably 2 or more and 5 or less, for example, since it is easy to ensure the solubility of the iron redox material and the acid. Is within the range. The pH is a value measured at 20 ° C., for example.

  The positive electrode electrolyte solution 22 may contain, for example, an inorganic acid salt or a chelating agent as necessary.

  The negative electrode electrolyte 32 is an electrolyte containing a redox material of titanium and an acid. The acid is citric acid or lactic acid.

  In the negative electrode electrolyte 32, titanium functions as an active material. For example, reduction from titanium (IV) to titanium (III) occurs during charging, and oxidation from titanium (III) to titanium (IV) occurs during discharging. Is presumed to occur. The negative electrode electrolyte solution 32 is complexed by containing the above acid, and the potential of about 0.2 V is lowered, so that a practical electromotive force is easily obtained.

  The concentration of the titanium redox material (titanium ions) in the negative electrode electrolyte 32 is preferably 0.2 mol / L or more, more preferably 0.3 mol / L or more, from the viewpoint of increasing the energy density. More preferably 0.4 mol / L or more. The concentration of the titanium redox substance (titanium ions) in the negative electrode electrolyte solution 32 is preferably 1.0 mol / L or less.

  The molar ratio of the acid to the redox material of titanium in the negative electrode electrolyte solution 32 is preferably in the range of 1 or more and 4 or less. When the molar ratio is 1 or more, the electric resistance of the negative electrode electrolyte 32 becomes lower, so that the Coulomb efficiency and the utilization factor of the negative electrode electrolyte 32 are easily increased. When the molar ratio is 4 or less, both economic efficiency and practicality can be easily achieved.

  The pH of the negative electrode electrolyte 32 is preferably in the range of 1 or more and 7 or less because, for example, it is easy to ensure the solubility of the redox material of titanium and the acid. The pH of the negative electrode electrolyte solution 32 is more preferably in the range of 2 or more and 5 or less.

  The negative electrode electrolyte solution 32 can contain, for example, inorganic acid salts and various chelating agents as required.

  The positive electrode electrolyte 22 and the negative electrode electrolyte 32 can be prepared by a known method. It is preferable that the water used for the positive electrode electrolyte 22 and the negative electrode electrolyte 32 has a purity equal to or higher than that of distilled water.

  In the redox flow battery configured as described above, the amount of dissolved oxygen in the negative electrode electrolyte solution 32 in the second tank 33 is preferably set to 1.5 mg / L or less. The dissolved oxygen amount is more preferably 1.0 mg / L or less. Furthermore, the oxygen concentration in the case 41 is preferably 10% by volume or less. In addition, the oxygen concentration in the gas phase in the second tank 33 is preferably 1% by volume or less.

  The amount of dissolved oxygen in the positive electrode electrolyte 22 in the first tank 23 may also be set to 1.5 mg / L or less, or may be set to 1.0 mg / L or less. The oxygen concentration in the gas phase in the first tank 23 may also be set to 1% by volume or less.

<Action of redox flow battery>
Since the redox flow battery using the positive electrode electrolyte 22 and the negative electrode electrolyte 32 having a pH in the range of 2 or more and 8 or less has the above-described anion exchange membrane as the diaphragm 12, it is easy to exhibit battery performance. Become. According to the redox flow battery of this embodiment, it becomes easy to exhibit practical energy efficiency, for example.

  The performance of the redox flow battery can be evaluated by, for example, charge / discharge cycle characteristics (reversibility), Coulomb efficiency, voltage efficiency, energy efficiency, electrolyte utilization factor, electromotive force, and electrolyte potential. Hereinafter, one charge / discharge of the redox flow battery is referred to as one cycle.

  The charge / discharge cycle characteristics (reversibility) are calculated by substituting the coulomb amount (A) for the first cycle discharge and the coulomb amount (B) for the tenth cycle discharge into the following equation (1).

Charging / discharging cycle characteristics [%] = B / A × 100 (1)
The charge / discharge cycle characteristics are preferably 80% or more.

  The coulomb efficiency is calculated by substituting the coulomb amount (C) for charging and the coulomb amount (D) for discharging in a predetermined cycle into the following equation (2).

Coulomb efficiency [%] = D / C × 100 (2)
The coulomb efficiency is preferably 90% or more in a value calculated from the coulomb amount at the 10th cycle, for example.

  The voltage efficiency is calculated by substituting the average terminal voltage (E) for charging and the average terminal voltage (F) for discharging in a predetermined cycle into the following formula (3).

Voltage efficiency [%] = F / E × 100 (3)
The voltage efficiency is preferably 70% or more in a value calculated from the terminal voltage at the 10th cycle, for example.

  The energy efficiency is calculated by substituting the electric energy (G) for charging and the electric energy (H) for discharging in a predetermined cycle into the following formula (4).

Energy efficiency [%] = H / G × 100 (4)
The energy efficiency is preferably 70% or more in the value calculated from the electric energy at the 10th cycle.

  The utilization rate of the electrolytic solution is obtained by multiplying the number of moles of the active material of the electrolytic solution supplied to the positive electrode 21a side or the negative electrode 31a side by the Faraday constant (96500 coulomb / mol) to obtain the amount of coulomb (I) and the tenth cycle. Is calculated by substituting the coulomb amount (I) and the coulomb amount (J) into the following equation (5). In addition, when the number of moles of the active material of the electrolytic solution supplied to the positive electrode 21a side is different from the number of moles of the active material of the electrolytic solution supplied to the negative electrode 31a side, a smaller number of moles is adopted.

Utilization rate of electrolytic solution [%] = J / I × 100 (5)
The utilization factor of the electrolytic solution is preferably 35% or more in a value calculated from the discharge coulomb amount at the 10th cycle.

  The electromotive force is a terminal voltage when switching from charging to discharging (when the current is 0 mA) in a predetermined cycle.

  The electromotive force is preferably 0.8 V or more at the terminal voltage at the 10th cycle.

  According to this embodiment described above, the following effects are obtained.

  (1) In the redox flow type battery of the present embodiment, the pH of the positive electrode electrolyte 22 and the negative electrode electrolyte 32 is in the range of 2 or more and 8 or less. This redox flow battery has an anion exchange membrane as the diaphragm 12 of the positive electrode electrolyte 22 and the negative electrode electrolyte 32. The anion exchange membrane is obtained by reacting a graft polymer obtained by graft polymerization of halogenated methylstyrene with a non-porous polypropylene base material and a tertiary amine. The reaction between the graft polymer and the tertiary amine introduces an anion exchange group into the graft chain of the graft polymer. The redox flow battery having this anion exchange membrane as the diaphragm 12 is suitable in that the battery performance is exhibited when an electrolyte solution having a pH in the range of 2 or more and 8 or less is used.

  (2) When the graft ratio of the anion exchange membrane is in the range of 55% or more and 130% or less, it becomes easy to further increase the energy efficiency. That is, when the graft ratio of the anion exchange membrane is 55% or more, anions easily pass through, and energy efficiency is likely to increase. When the graft ratio of the anion exchange membrane is 130% or less, the permeation of the redox material is easily suppressed, so that the energy efficiency is easily increased.

  (3) When the non-porous substrate is a biaxially stretched polypropylene film, it becomes easy to further increase energy efficiency. When a biaxially stretched polypropylene film is used, it is advantageous that the graft ratio of the anion exchange membrane is in the range of 70% or more and 130% or less from the viewpoint of further improving energy efficiency.

  (4) Since the anion exchange membrane of this embodiment can be manufactured using readily available raw materials, it can contribute to cost reduction of the membrane of a redox flow battery. For this reason, it is possible to reduce the cost of the equipment, which is advantageous from the viewpoint of promoting further spread of the redox flow battery.

  (5) A method for producing an anion exchange membrane includes a polymerization step in which halogenated methylstyrene is graft-polymerized on a polypropylene non-porous substrate, and a substitution reaction in which the obtained graft polymer is reacted with a tertiary amine. Process. Since the polymerization process is a polymerization process using ionizing radiation, it has the advantage that the manufacturing process is simple, safe and has a low environmental impact.

(Example of change)
The embodiment may be modified as follows.

  The anion exchange membrane may include a support having higher permeability of ions serving as ion-conducting carriers than the anion exchange membrane. That is, the diaphragm 12 may be a laminate having an anion exchange membrane and a support that supports the membrane.

  The shape, arrangement, or number of the charge / discharge cells 11 included in the redox flow battery and the capacities of the first tank 23 and the second tank 33 may be changed according to the performance required for the redox flow battery. Further, the supply amount of the positive electrode electrolyte 22 and the negative electrode electrolyte 32 to the charge / discharge cell 11 can also be set according to, for example, the capacity of the charge / discharge cell 11. For example, the case 41 may be omitted in the case of an electrolyte having a small influence of oxygen concentration.

  Next, the present invention will be described in more detail with reference to examples and comparative examples.

(Production Example 1)
A biaxially stretched polypropylene film (trade name: pyrene film-OT, P2161, thickness 50 μm, dimensions 80 × 80 mm, manufactured by Toyobo Co., Ltd.) was sealed in a bag, and the inside of the bag was purged with nitrogen. This was irradiated with an electron beam under the conditions of an acceleration voltage of 750 kV and an absorbed dose of 200 kGy, and then 20 mL of a 40% by mass chloromethylstyrene-acetone solution was injected into the bag. Next, the bag was shaken in a constant temperature bath at 50 ° C. for 2 hours. Thereby, the graft polymer which graft-polymerized 4-chloromethyl styrene on the biaxially stretched polypropylene film was obtained.

  Next, the obtained graft polymer was taken out of the bag, washed with acetone and water, and then sealed again in a bag purged with nitrogen. 20 mL of a 5 mass% trimethylamine aqueous solution was injected into the bag. The graft polymer and trimethylamine were reacted by shaking this for 2 hours in a thermostat at 50 ° C. As a result, an anion exchange membrane having an anion exchange group introduced into the graft chain was obtained.

The obtained anion exchange membrane was removed from the bag, washed with water, and dried. A premeasured biaxially mass of oriented polypropylene film (W _0), was calculated grafting rate by substituting the mass (W ₁₎ and the equation described above the anion exchange membrane (A).

(Production Examples 2 to 4)
In Production Examples 2 to 4, anion exchange membranes having different graft rates were obtained in the same manner as Production Example 1 except that the concentration of the chloromethylstyrene-acetone solution was changed.

(Production Example 5 and Production Example 6)
In Production Example 5 and Production Example 6, an unstretched polypropylene film (trade name: Orphan PP sheet P23S, thickness 250 μm, dimensions 80 × 70 mm, manufactured by OJK Corporation) instead of the biaxially stretched polypropylene film of Production Example 1 Using. Anion exchange membranes having different graft rates were obtained in the same manner as in Production Example 1 except that the concentration of the chloromethylstyrene-acetone solution was adjusted.

(Comparison of transmittance of ions in electrolyte)
About the anion exchange membrane obtained by the said manufacture example 1, the transmittance | permeability of the ion in electrolyte solution was measured as follows. First, the opening of the glass container containing the electrolytic solution was sealed with an ion exchange membrane. As an electrolytic solution, a 0.2 mol / L iron (II) -citric acid complex aqueous solution was used.

A beaker containing 100 mL of distilled water was prepared, and the anion exchange membrane attached to the glass container was immersed in distilled water, and the distilled water was stirred for 24 hours using a stirrer. Next, the iron ion concentration in distilled water was measured. This iron ion concentration was converted into a concentration per 1 cm ² of an anion exchange membrane area, 1 mol of an electrolyte solution, and 1 hour, and the converted value was defined as a transmittance.

  The anion obtained in Production Example 1 for each of the anion exchange membranes obtained in Production Examples 2 to 6 and a commercially available anion exchange membrane (AHA, manufactured by Astom Corp.) that does not use a polypropylene porous substrate. The transmittance was determined in the same manner as the ion exchange membrane.

FIG. 2 shows the relationship between the graft ratio and transmittance of the anion exchange membrane obtained in each production example. The plot shown by “A” in FIG. 2 shows the results of Production Examples 1 to 4, and the plot shown by “B” in FIG. 2 shows the results of Production Examples 5 and 6. The thick line in the graph of FIG. 2 indicates the level of transmittance (transmittance = 2.0 × 10 ⁻⁷ ) of a commercially available anion exchange membrane.

Example 1
<Redox flow battery>
The redox flow battery shown in FIG. 1 was used. As a positive electrode and a negative electrode, the electrode area was set to 10 cm ² using carbon felt (trade name: GFA5, manufactured by SGL). As the current collector plate, pure titanium having a thickness of 1.0 mm was used. As the diaphragm, an anion exchange membrane (graft rate 71%) produced in the same manner as in Production Example 1 was used.

  Glass containers with a capacity of 30 mL were used as the first tank and the second tank. Silicone tubes were used as the supply tubes, the recovery tubes, the gas tubes, and the exhaust tubes. As each pump, a micro tube pump (MP-1000, manufactured by Tokyo Rika Kikai Co., Ltd.) was used. As the charge / discharge device, a charge / discharge battery test system (PFX200, manufactured by Kikusui Electronics Co., Ltd.) was used.

<Preparation of aqueous solution of iron (II) -citric acid complex>
0.04 mol (8.4 g) of citric acid was dissolved in 50 mL of distilled water. The pH was adjusted to 3 by adding 0.01 mol (0.4 g) of NaOH to this aqueous solution. Further, 0.02 mol (5.56 g) of FeSO ₄ .7H ₂ O was dissolved in this aqueous solution. Next, distilled water was added to the aqueous solution so that the total amount became 100 mL. As a result, an aqueous solution having an iron (II) -citrate complex concentration of 0.2 mol / L was obtained.

<Preparation of aqueous solution of titanium (IV) -citric acid complex>
0.04 mol (8.4 g) of citric acid was dissolved in 50 mL of distilled water. The pH was adjusted to 6 by adding 0.12 mol (4.8 g) of NaOH to this aqueous solution. Further, 16 g (corresponding to 0.02 mol of titanium sulfate) of a 30% by mass titanium sulfate solution was added to the aqueous solution, and the solution was stirred until the aqueous solution became transparent. Next, 0.2 mol (11.69 g) of NaCl was dissolved in this aqueous solution, and distilled water was added so that the total amount became 100 mL. As a result, an aqueous solution having a titanium (IV) -citrate complex concentration of 0.2 mol / L was obtained.

<Adjustment of oxygen concentration>
An iron (II) -citrate complex aqueous solution was used as the positive electrode electrolyte, and a titanium (IV) -citrate complex aqueous solution was used as the negative electrode electrolyte. By supplying nitrogen gas from the first gas pipe, each electrolyte solution was bubbled, and the amount of dissolved oxygen in each electrolyte solution was adjusted to 0.8 mg / L (about 10% of the saturated oxygen concentration) or less. The supply of nitrogen gas from the first gas pipe was continued during the subsequent charge / discharge test.

  Next, the oxygen concentration in the ambient atmosphere of the charge / discharge cell was adjusted to 1% or less by supplying nitrogen from the second gas pipe into the case. The supply of nitrogen gas from the second gas pipe was continued during the subsequent charge / discharge test.

  The amount of dissolved oxygen was measured using a dissolved oxygen meter (“B-506” manufactured by Iijima Electronics Co., Ltd.). The oxygen concentration was measured using an oxygen concentration meter (manufactured by Shin Cosmos Electric Co., Ltd., “XPO-318”).

<Charge / discharge test>
The charge / discharge test was started from charging, and was first charged with a constant current of 50 mA for 60 minutes (total 180 coulombs). Next, the battery was discharged at a constant current of 50 mA with a final discharge voltage of 0V.

  The above charging / discharging was made into 1 cycle, and charging / discharging was repeated 100 cycles.

  The redox reaction at the time of charging / discharging is estimated as follows.

Positive electrode: Iron (II) -citric acid complex ⇔ Iron (III) -citric acid complex + e ⁻
Negative electrode: Titanium (IV) -citric acid complex + 2e ^- ⇔ Titanium (III) -citric acid complex In the charge / discharge test, charge / discharge cycle characteristics (reversibility), Coulomb efficiency, voltage efficiency, energy efficiency, electrolyte utilization rate And the electromotive force.

  The charge / discharge cycle characteristics (reversibility) were determined from the coulomb amount (A) of the first cycle discharge and the coulomb amount (B) of the tenth cycle discharge.

  Coulomb efficiency was determined from the amount of coulomb at the 10th cycle.

  The voltage efficiency was determined from the average terminal voltage at the 10th cycle.

  The energy efficiency was determined from the amount of power at the 10th cycle.

  The utilization factor of the electrolytic solution was determined from the coulomb amount at the 10th cycle.

  The electromotive force was the terminal voltage at the 10th cycle.

(Result of charge / discharge test)
Table 1 shows the results of the charge / discharge test in Example 1.

図３には、実施例１の充放電試験において、８サイクル目から９サイクル目までの充放電した際の電池電圧の推移を示している。これにより、レドックスフロー電池としての実用性を有することが確認された。

In FIG. 3, the transition of the battery voltage at the time of charging / discharging from the 8th cycle to the 9th cycle in the charging / discharging test of Example 1 is shown. Thereby, it was confirmed that it has the utility as a redox flow battery.

(Examples 2 to 4)
In Example 2 and Example 3, an anion exchange membrane was obtained in the same manner as in Production Example 1. In Example 4, an anion exchange membrane was obtained in the same manner as in Production Example 1 except that the concentration of the chloromethylstyrene-acetone solution was changed. The graft rate of the anion exchange membrane of Example 2 is 78%, the graft rate of the anion exchange membrane of Example 3 is 83%, and the graft rate of the anion exchange membrane of Example 4 is 121%. is there.

  In Examples 2 to 4, a charge / discharge test was performed in the same manner as in Example 1 to determine energy efficiency.

(Example 5 and Example 6)
In Example 5 and Example 6, instead of a biaxially stretched polypropylene film, an unstretched polypropylene film (trade name: Orphan PP sheet P23S, thickness 250 μm, dimensions 80 × 70 mm, manufactured by OJK Corporation) Anion exchange membranes having different graft rates were obtained in the same manner as in Production Example 1 except that the concentration of the chloromethylstyrene-acetone solution was changed. The graft rate of the anion exchange membrane of Example 5 is 52%, and the graft rate of the anion exchange membrane of Example 6 is 88%.

  In Example 5 and Example 6 as well, the charge / discharge test was performed in the same manner as in Example 1 to determine the energy efficiency.

  In FIG. 4, the relationship between the grafting rate of the anion exchange membrane in Examples 2-6 and the energy efficiency of a redox flow battery is shown. The plot indicated by “A” in FIG. 4 indicates the results of Examples 2 to 4, and the plot indicated by “B” indicates the results of Example 5 and Example 6. The thick line “C” in the graph of FIG. 4 is the same as in Example 1 except that a commercially available anion exchange membrane (AHA, manufactured by Astom Corp.) that does not use a polypropylene porous substrate is used as a diaphragm. The level of energy efficiency (energy efficiency = 70%) when performed is shown. The thick line “D” in the graph of FIG. 4 uses a commercially available cation exchange membrane (CMS, manufactured by Astom Corp.) as a diaphragm, and 0.2 mol (11.69 g) of NaCl is further added to the positive electrode electrolyte. Except for being dissolved, the level of energy efficiency (energy efficiency = 72%) when performing a charge / discharge test in the same manner as in Example 1 is shown.

  From the results shown in FIG. 4, it was confirmed that the energy efficiency of the redox flow batteries of Examples 2 to 6 was suitable as the energy efficiency of the redox flow battery using a commercially available ion exchange membrane.

Claims (4)

A redox flow battery in which a positive electrode electrolyte having a pH of 2 or more and 8 or less and a negative electrode electrolyte having a pH of 2 or more and 8 or less are used, and halogenated on a non-porous substrate made of polypropylene An anion exchange membrane formed by introducing an anion exchange group into a graft chain of the graft polymer by reacting a graft polymer obtained by graft polymerization of methylstyrene with a tertiary amine is obtained as a positive electrode electrolyte. A redox flow battery characterized by having a diaphragm between the anode and the negative electrode electrolyte.   The redox flow battery according to claim 1, wherein a graft ratio of the anion exchange membrane is in a range of 55% or more and 130% or less.   The redox flow battery according to claim 1, wherein the non-porous substrate is a biaxially stretched polypropylene film.   The redox flow battery according to claim 3, wherein a graft ratio of the anion exchange membrane is in a range of 70% to 130%.

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