JP2010086935A - Redox flow battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new redox flow battery. <P>SOLUTION: The redox flow battery includes a positive electrode cell and a negative electrode cell, an ion exchange membrane to separate both the cells, a first tank in which electrolytic solution A containing an active material and ion liquid for the positive electrode cell is stored, a second tank in which the electrolytic solution B containing the active material and the ion liquid for the negative electrode cell, first piping connected so that the electrolytic solution A can be circulated between the first tank and the positive electrode cell, second piping connected so that the electrolytic solution B can be circulated between the second tank and the negative electrode cell, and electrolytic solution circulation pumps respectively installed in the middle of the first piping and the second piping. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a redox flow battery using an ionic liquid.

  Renewable energies such as solar power, wind power and hydropower are expected to become major energy sources for this century. However, these energy sources have the disadvantage of large output fluctuations. For this reason, when these energy sources are connected to the power system, it has been studied to temporarily store power for output smoothing. The use of batteries for the storage of electric power is being studied, and among the batteries, redox flow batteries are one of the leading options from the viewpoint of good adaptability to time fluctuations.

Currently, a vanadium redox flow battery, which is a kind of redox flow battery, is in the practical application stage (for example, Vol. 63, No. 4, No. 5 of Non-Patent Document 1). Further, for example, in Japanese Patent Application Laid-Open No. 2005-209525 (Patent Document 1), an aprotic organic solvent is used to obtain a high electromotive force, U ⁴⁺ / U ^{3+ for} a negative electrode reaction, and UO ₂ ⁺ / UO for a positive electrode reaction. Uranium redox flow batteries using ₂ ²⁺ have been proposed.

JP 2005-209525 A Electronic Technology Research Institute Vocabulary Vol. 63, No. 4, 5

However, the battery uses an aqueous sulfuric acid solution or an aprotic organic solvent as an electrolytic solution. Therefore, if it is used continuously for 10 to 20 years as a power storage battery, it is necessary to perform maintenance such as replenishment of water or an organic solvent. Therefore, it is desired to suppress the number of maintenance as much as possible.
In addition, the vanadium redox flow battery can only obtain an electromotive force within a range in which electrolysis of water does not occur.
Furthermore, the uranium redox flow battery also has a problem of ignition due to generation of combustible gas.
As described above, there is no maintenance such as replenishment of electrolyte solvent for long-term use, high safety, low polarization of the positive electrode during charging, high efficiency, and sufficiently high electromotive force can be generated. It has been desired to provide a novel redox flow battery.

  The inventors of the present invention have intensively studied to solve the above-mentioned problems, and as a result, by using an ionic liquid as a solvent for the electrolytic solution, there is no redox flow battery that does not evaporate or ignite the electrolyte and has a high electromotive force. As a result, the present invention was found.

  Thus, according to the present invention, a positive electrode cell and a negative electrode cell, an ion exchange membrane for separating the two cells, a first tank in which an electrolytic solution A containing an active material for the positive electrode cell and an ionic liquid is stored, A second tank in which an electrolytic solution B containing an active material for the negative electrode cell and an ionic liquid is stored, and a first tank that is connected so that the electrolytic solution A can circulate between the first tank and the positive electrode cell. 1 pipe, a second pipe connected so that the electrolyte B can circulate between the second tank and the negative electrode cell, and an electrolyte provided in the middle of the first pipe and the second pipe, respectively. A redox flow battery comprising a circulation pump is provided.

According to the present invention, since an ionic liquid having substantially no vapor pressure is used as a solvent for the electrolytic solution, there is no maintenance such as replenishment of the electrolytic solution solvent over a long period of use, and the safety is high. A redox flow battery can be provided. Moreover, since the polarization of the positive electrode during charging is low, it is possible to provide a redox flow battery capable of generating a sufficiently high electromotive force with high efficiency.
Moreover, if a hydrophilic ionic liquid is used, the solubility of the metal ion used as the active material of a positive electrode and / or a negative electrode can be improved. As a result, a redox flow battery with higher energy density can be provided. If an ionic liquid having a contact angle on glass of 80 degrees or less is used, a redox flow battery having a higher energy density can be provided.
Furthermore, if any one of the potential window, viscosity, and ionic conductivity is at least a specific range, a redox flow battery with higher energy density can be provided.

Moreover, the solubility of the metal ion used as an active material can be improved because one or both of electrolyte solution A and B contains the ionic liquid containing an aliphatic cation or the ionic liquid containing an aromatic cation. As a result, a redox flow battery with higher energy density can be provided. Further, the ionic liquid is 1-ethyl-3-methylimidazolium-trifluoromethanesulfonic acid, N, N, N-trimethyl-N-propylammonium-trifluoromethanesulfonic acid and N-methyl-N-propylpiperidinium. -By containing at least an ionic liquid selected from trifluoromethanesulfonic acid, a redox flow battery with higher energy density can be provided.
Furthermore, the solubility of the metal ion used as an active material can be improved because the electrolytic solution contains triethylene glycol dimethyl ether and / or tetraethylene glycol dimethyl ether. As a result, a redox flow battery with higher energy density can be provided.

(Configuration of redox flow battery)
The redox flow battery of the present invention includes a positive electrode cell and a negative electrode cell, an ion exchange membrane that separates the two cells, a first tank in which an electrolyte solution A for the positive electrode cell is stored, and an electrolyte solution B for the negative electrode cell. The electrolytic solution B circulates between the second tank, the first pipe connected so that the electrolytic solution A can circulate between the first tank and the positive electrode cell, and the second tank and the negative electrode cell. A second pipe connected in a manner that can be obtained, and an electrolyte circulation pump provided in the middle of the first pipe and the second pipe. Further, the electrolytic solution contains an ionic liquid as a solvent. In addition, a positive electrode and a negative electrode may be collectively called an electrode.

FIG. 4 is a schematic configuration diagram of the redox flow battery of the present invention. This redox flow battery includes a positive electrode cell and a negative electrode cell. The positive electrode cell has a configuration capable of holding the positive electrode plate 10 and a positive electrode electrolyte solution A (hereinafter referred to as a positive electrode solution). On the other hand, the negative electrode cell has a configuration capable of holding the negative electrode plate 11 and a negative electrode electrolyte B (hereinafter referred to as negative electrode solution). The positive electrode cell and the negative electrode cell are separated by an ion exchange membrane 12.
The positive electrode solution is circulated through the first pipe 14 by the electrolytic solution circulation pump 13 between the first tank 8 holding the positive electrode solution and the positive electrode cell. Similarly, the negative electrode liquid is circulated through the second pipe 15 by the electrolyte circulation pump 13 between the second tank 9 holding the negative electrode liquid and the negative electrode cell.

The positive electrode solution and the negative electrode solution are respectively supplied between the positive electrode plate 10 and the ion exchange membrane 12 and between the negative electrode plate 11 and the ion exchange membrane 12 and subjected to a predetermined redox reaction.
For example, in a redox flow battery using an electrode solution in which vanadium salt is dissolved in an ionic liquid as an active material, oxidation of V ⁴⁺ → V ⁵⁺ + e ⁻ is performed during charging in the cathode solution using the ionic liquid on the cathode side. Reaction occurs, and a reduction reaction of V ⁵⁺ + e ⁻ → V ⁴⁺ occurs during discharge. On the other hand, in the negative electrode solution using the ionic liquid on the negative electrode side, a reduction reaction of V ³⁺ + e ⁻ → V ²⁺ occurs during charging, and an oxidation reaction of V ²⁺ → V ³⁺ + e ⁻ occurs during discharging. . Therefore, an electromotive force of about 1.3 V is obtained with charging / discharging based on the above-described redox reaction in the battery.

(Cathode and Anode solution)
The positive electrode solution and the negative electrode solution contain an ionic liquid. In the present specification, the ionic liquid means a salt which is substantially non-volatile in vapor pressure and is non-volatile, and is composed of a cation and an anion and is generally in the range of −95 to 430 ° C.
(1) Ionic liquid Any ionic liquid can be used as long as it does not interfere with the electrochemical reaction of the redox flow battery. The ionic liquid for the positive electrode cell and the ionic liquid for the negative electrode cell may be the same or different.

The ionic liquid preferably has hydrophilicity in order to increase the solubility of the active material. Here, having hydrophilicity means having compatibility with a polar solvent. The presence or absence of hydrophilicity can be evaluated, for example, by measuring the contact angle according to JIS R3257. In detail, it can evaluate by measuring a contact angle with the ionic liquid on glass. The contact angle is an angle formed between a solid surface and a liquid surface when a small droplet is placed on the solid material, and represents the wettability of the solid and the liquid. That is, the smaller the contact angle, the higher the hydrophilicity. Specifically, it is measured by the following method.
-Drop 1 to 4 μL of droplets on the glass and read the contact angle from the projection after 1 minute.
・ Measure 7 points per sample, and use the average value of 5 points excluding the maximum and minimum values as the contact angle.
The ionic liquid preferably has a contact angle of 80 degrees or less.

More preferred ionic liquids are those having a potential window, viscosity and / or ionic conductivity in the following ranges.
The potential window of the ionic liquid is −2.5 to 2.0 Vvs. Ag / Ag ⁺ is preferred. When the potential on the low potential side is higher than −2.5 V, it becomes difficult to use an alkali metal such as sodium or potassium or an alkaline earth metal such as magnesium, calcium or strontium as an active material. When the potential on the high potential side is lower than 2.0 V, it becomes difficult to use materials such as uranium and sulfur as the active material. A more preferred potential window is -2.0 to 1.5 Vvs. It is a range of Ag / Ag ⁺ . When the potential on the low potential side is higher than −2.0 V, the potential becomes higher than the hydrogen generation potential, and the merit of the ionic liquid with respect to the aqueous electrolyte may be reduced. Further, when the potential on the high potential side is lower than 1.5 V, the merit of the ionic liquid with respect to the aqueous electrolyte may be reduced. If it is this range, the battery of higher electromotive force can be comprised. The potential window means a value obtained by performing cyclic voltammetry and measuring a potential at which an oxidation current and a reduction current are rapidly detected.

  The viscosity of the ionic liquid is preferably in the range of 1 to 500 mPa · s at 20 ° C. If it is lower than 1 mPa · s, the stability of the ionic liquid may be lowered. If it is higher than 500 mPa · s, the load on the pump for circulating the ionic liquid may become too high. A more preferable viscosity is in the range of 10 to 150 mPa · s. Within this range, the penetration of the ionic liquid into the positive electrode and the negative electrode (hereinafter collectively referred to as electrodes) can be improved. The viscosity means a value measured by AR2000 manufactured by TA Instruments.

  The ionic conductivity of the ionic liquid is preferably in the range of 0.05 to 25 mS / cm at 25 ° C. If it is lower than 0.05 mS / cm, the electric resistance of the battery becomes too high, and the energy efficiency of charge / discharge may be lowered. If it is higher than 25 mS / cm, the leakage current increases and the energy storage property may be lowered. More preferable ionic conductivity is in the range of 1 to 15 mS / cm, and within this range, the charge / discharge reaction of the redox flow battery can be made better. The ion conductivity means a value obtained by measuring an alternating current impedance of 1000 Hz using a Solartron 1280Z type electrochemical measurement system.

Examples of ionic liquids include aromatic cations and borofluoride anions (BF ₄ ⁻ ), hexafluorophosphate anions (PF ₆ ⁻ ), trifluoromethanesulfonate anions (CF ₃ SO ₃ ⁻ ) (TF), bis Molten salt of (trifluoromethanesulfonyl) imide anion (N (CF ₃ SO ₂ ) ₂ ⁻ ) (TFSI) or iodide ion (I ⁻ ), aliphatic cation and BF ₄ ⁻ , PF ₆ ⁻ , TF, TFSI Alternatively, a molten salt with I ⁻ can be used. In addition, aromatic here means benzene and a compound similar in chemical behavior to benzene.

Aromatic cations include 1-ethyl-3-methylimidazolium (EMI) ion, 1-butyl-3-methylimidazolium (BMI) ion, 1-hexyl-3-methylimidazolium (HMI) ion, 1 Imidazolium-based cations and pyridinium-based cations such as -propyl-3-methylimidazolium (MPI) ion and 1,2-dimethyl-3-propylimidazolium (DMPI) ion can be preferably used.
Aliphatic cations include tetraethylammonium (TEA) ions, triethylmethylammonium (TEMA) ions, quaternary ammonium cations such as trimethylpropylammonium (TMPA) ions, methylpropylpiperidinium (MPPi) ions, and butylmethyl. Piperidinium cations such as piperidinium (BMPi) ions, pyrrolidinium cations such as methylpropylpyrrolidinium (MPPy) ions and butylmethylpyrrolidinium (BMPy) ions can be suitably used.

  Among these ionic liquids, TMPA-TFSI, MPPy-TFSI, EMI-TFSI, EMI-TF, TMPA-TF, and MPPi-TF are preferred because of their wide potential window for redox. In particular, EMI-TF, TMPA-TF, and MPPi-TF are preferable as the ionic liquid because of low viscosity at room temperature, high solubility of metal ions, and high permeability to electrodes.

(2) Other components The positive electrode solution and the negative electrode solution may contain an active material, a nonaqueous solvent, a supporting electrolyte, and the like as other components.
(2-1) Active material As the active material, transition metals such as vanadium, uranium, iron and chromium, alkali metals such as zinc, sodium and potassium, alkaline earth metals such as magnesium, calcium and strontium, chlorine, bromine, Sulfur etc. are mentioned. Of these, vanadium, iron, sodium, bromine, and sulfur are preferable from the viewpoint of low environmental load.

  The amount of the active material added is preferably in the range of 0.001 to 10 mol / liter with respect to the entire electrode solution. If it is less than 0.001 mol / liter, the battery may have a low energy density. When the amount is more than 10 mol / liter, the active material may be precipitated and may not function as an energy storage medium. A more preferable addition amount is in the range of 0.1 to 5 mol / liter.

  The active material is present in the positive electrode solution and the negative electrode solution in the form of chloride, sulfide, sulfate, nitrate, trihalomethanesulfonate, bis (trifluoromethanesulfonyl) imide salt, and the like. Examples of the combination of the positive electrode active material and the negative electrode active material include a combination of sulfide and chloride, a combination of sulfate and nitrate, a combination of trihalomethanesulfonate and bis (trifluoromethanesulfonyl) imide salt, and the like.

(2-2) Non-aqueous solvent For the purpose of improving the solubility of metal ions, which are active materials, in the ionic liquid and improving the permeability of the electrode liquid into the electrode. Can be added.

  Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate; dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, dipropyl carbonate, and the like. Chain carbonates, γ-butyrolactone (hereinafter sometimes abbreviated as GBL), lactones such as γ-valerolactone, furans such as tetrahydrofuran and 2-methyltetrahydrofuran, diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, dioxane, ethers such as triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dimethyl sulfoxide, sulfolane, methyl sulfate Examples include holan, acetonitrile, methyl formate, and methyl acetate.

Among them, glyme such as 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc. that have high compatibility with ionic liquids and high coordination ability to metal ions. Are preferred. In particular, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether are preferable because they have a very low vapor pressure, are highly safe even when added to an ionic liquid, and do not impair the advantages of no liquid evaporation.
The addition amount of the non-aqueous solvent is preferably 0.5 to 50 wt% with respect to the total weight of the ionic liquid, from the viewpoint that evaporation of the non-aqueous solvent can be suppressed, and more preferably 1 to 30 wt%.

(2-3) Support Electrolyte In order to improve the ionic conductivity of the electrode solution and constitute a redox flow battery using an ionic liquid having high output characteristics, a support electrolyte can be added to the electrode solution.
Examples of the supporting electrolyte include proton acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, formic acid, hydrofluoric acid, perchloric acid, trihalomethanesulfonic acid, lithium perchlorate, lithium borofluoride (LiBF ₄ ), and phosphorus hexafluoride. Lithium such as lithium acid (LiPF ₆ ), lithium trifluoroacetate (LiCF ₃ COO), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis (trifluoromethanesulfonyl) imide (LiN (CF ₃ SO ₂ ) ₂ ) Salt can be used. Further, at least one selected from cations of sodium, potassium, rubidium, cesium and tetramethylammonium, a borofluoride anion (BF ₄ ⁻ ), a hexafluorophosphate anion (PF ₆ ⁻ ), a trifluoromethanesulfonate anion (CF ₃ SO ₃ ⁻ ) (TF), a bis (trifluoromethanesulfonyl) imide anion (N (CF ₃ SO ₂ ) ₂ ⁻ ) (TFSI), and a salt comprising at least one anion selected from iodide ion (I ⁻ ) Can also be used.

  The amount of supporting electrolyte added is preferably in the range of 0.01 to 2 mol / liter with respect to the entire electrode solution. In particular, in order to construct a redox flow battery using an ionic liquid having high output characteristics, a range of 0.1 to 1 mol / liter is more preferable.

(Positive electrode plate and negative electrode plate)
The positive electrode cell includes a positive electrode plate, and the negative electrode cell includes a negative electrode plate. The electrode plate is provided with a circuit for discharging by flowing an electric current to the outside and for charging by taking in an electric current from the outside.
Examples of the material for the electrode plate include metal materials, carbonaceous materials, and conductive inorganic materials.

  As the metal material, a material having electronic conductivity and resistance to corrosion in an acidic atmosphere is preferable. Specifically, noble metals such as Au, Pt, Pd, metals such as Ti, Ta, W, Nb, Ni, Al, Cr, Ag, Cu, Zn, Su, Si, and nitrides and carbides of these metals, Examples of the alloy include stainless steel, Cu—Cr, Ni—Cr, and Ti—Pt. It is more preferable that the metal material contains at least one element selected from the group consisting of Pt, Ti, Au, Ag, Cu, Ni, and W from the viewpoint that there are few other chemical side reactions. These metal materials have a small specific resistance and can suppress a decrease in voltage even when a current is extracted in the surface direction.

As the carbonaceous material, a chemically stable and conductive material is preferable. Examples thereof include carbon powders and carbon fibers such as acetylene black, vulcan, ketjen black, furnace black, VGCF, carbon nanotube, carbon nanohorn, and fullerene.
Examples of the inorganic material having conductivity include tin oxide, indium tin oxide (ITO), and antimony oxide-doped tin oxide.

  Furthermore, when using a metal material having poor corrosion resistance under an acidic atmosphere such as Cu, Ag, Zn, etc., noble metals and metals having corrosion resistance such as Au, Pt, Pd, carbon, graphite, glassy carbon, The surface of the metal having poor corrosion resistance may be coated with a conductive polymer, a conductive nitride, a conductive carbide, a conductive oxide, or the like. In addition, examples of the conductive polymer include polyacetylene, polythiophene, polyaniline, polypyrrole, polyparaphenylene, polyparaphenylene vinylene, and the like, and examples of the conductive nitride include carbon nitride, silicon nitride, gallium nitride, indium nitride, and nitride. Germanium, titanium nitride, zirconium nitride, thallium nitride, etc. are listed, and conductive carbides include tantalum carbide, silicon carbide, zirconium carbide, titanium carbide, molybdenum carbide, niobium carbide, iron carbide, nickel carbide, hafnium carbide, tungsten carbide. , Vanadium carbide, chromium carbide, and the like. Examples of the conductive oxide include tin oxide, indium tin oxide (ITO), and antimony oxide-doped tin oxide.

  As the structure of the electrode plate, a plate shape, a foil shape, a rod shape, a mesh shape, a lath plate shape, a porous plate shape, a porous rod shape, a woven fabric shape, a nonwoven fabric shape, a fiber shape, and a felt shape can be suitably used. Further, a grooved electrode in which the surface of the felt-like electrode is pressure-bonded in a groove shape is preferable because electric resistance and flow resistance of the electrode liquid can be reduced.

(Ion exchange membrane)
As the ion exchange membrane, any membrane known in the art can be used, and generally a proton conductive membrane, a cation exchange membrane, an anion exchange membrane or the like can be used.
(1) Proton conductive membrane The material of the proton conductive membrane is not particularly limited as long as it is a material having proton conductivity and electrical insulation, and a polymer membrane, an inorganic membrane or a composite membrane is used. Can do.

Examples of the polymer membrane include perfluorosulfonic acid electrolyte membranes such as Nafion (manufactured by DuPont), Aciplex (manufactured by Asahi Kasei), Flemion (manufactured by Asahi Glass), polystyrene sulfonic acid, sulfonated poly Examples thereof include hydrocarbon electrolyte membranes such as ether ether ketone.
Examples of the inorganic film include films made of phosphate glass, cesium hydrogen sulfate, polytungstophosphoric acid, ammonium polyphosphate, and the like.
Examples of composite membranes include membranes made of sulfonated polyimide polymers, composites of inorganic materials such as tungstic acid and organic materials such as polyimide, and specifically, Gore Select membranes (manufactured by Gore) and pore filling electrolyte membranes. Etc.

Furthermore, when the battery is used in a high temperature environment (for example, 100 ° C. or more), sulfonated polyimide, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), sulfonated polybenzimidazole, phosphonated polybenzimidazole. , Cesium hydrogen sulfate, ammonium polyphosphate, and the like. The ion exchange membrane preferably has a proton conductivity of 10 ⁻⁵ S / cm or more, and more preferably has a proton conductivity of 10 ⁻³ S / cm or more such as perfluorosulfonic acid polymer or hydrocarbon polymer. It is more preferable to use a polymer electrolyte membrane.

  For example, a film of Nafion (manufactured by DuPont), Aciplex (manufactured by Asahi Kasei Co., Ltd.), Flemion (manufactured by Asahi Glass Co., Ltd.), or the like can be used. PTFE and PVDF may be added to impart water repellency, and silica particles, hygroscopic resin, and the like may be added to impart hydrophilicity.

(2) Cation exchange membrane As a cation exchange membrane, what is necessary is just the solid polymer electrolyte which can move a cation. Specifically, fluorine ion exchange membranes such as perfluorocarbon sulfonic acid membranes and perfluorocarbon carboxylic acid membranes, polybenzimidazole membranes impregnated with phosphoric acid, polystyrene sulfonic acid membranes, sulfonated styrene / vinylbenzene copolymers A film etc. can be mentioned.

(3) Anion exchange membrane When the anion transport number of the supporting electrolyte solution is high, an anion exchange membrane can be used. As the anion exchange membrane, a solid polymer electrolyte capable of transferring anions can be used. Specifically, a polyorthophenylenediamine film, a fluorine ion exchange film having an ammonium salt derivative group, a vinylbenzene polymer film having an ammonium salt derivative group, and a chloromethylstyrene / vinylbenzene copolymer on the positive and negative electrode plates The film | membrane etc. which were made into are mentioned.

(4) Ew value It is preferable that the ion exchange membrane has Ew value of the range of 400-2000. In particular, in the case of an ion exchange membrane made of Nafion, the Ew value is preferably in the range of 800 to 1200. If the Ew value is low, the resistance of the battery may be high, and if the Ew value is high, the film strength may be low in a battery using a fluid such as a redox flow battery.
The Ew value is a value defined by the following formula.
Ew = dry weight of ion exchange membrane per equivalent of functional group = (dry weight of ion exchange membrane) / (number of functional groups having ion exchange ability)

The dry weight of the ion exchange membrane was determined by weighing the ion exchange membrane after vacuum drying at 60 ° C. for 72 hours.
The number of functional groups having ion exchange capacity was determined by a sodium chloride titration method. Specifically, sodium chloride is added, the pH value is measured, and the active functional group is quantified.

(5) Production method of ion exchange membrane The ion exchange membrane can be formed by a known method. For example, a method of coating the electrode plate by an electrolytic polymerization method, a plasma polymerization method, a liquid phase polymerization method, a solid phase polymerization method, or the like can be given. These methods can be appropriately selected according to the selection of the monomer for film production. Furthermore, the electrode plate can be directly immersed in the polymer solution constituting the ion exchange membrane and adhered to the surface. In general, the coating amount is preferably at least 1 mg / cm ² or more or 2 mg / cm ² or more.

(Piping, tank, pump)
Two tanks, a first tank and a second tank, are used as the tank, and the shape of the tank can be determined as appropriate according to the application, use place, etc. of the battery. Further, the capacity of the tank can be appropriately determined according to the desired capacity of the battery. Furthermore, the material constituting the tank is not particularly limited as long as it can hold the electrolytic solution.
The pipe is connected so that the electrolyte can circulate between the first tank and the negative electrode cell, and the first pipe connected so that the electrolyte can circulate between the first tank and the positive electrode cell. Second piping. The shape of the piping can be appropriately determined according to the use of the battery, the place of use, and the like. Moreover, the material which comprises piping is not specifically limited if it can hold | maintain electrolyte solution.
The pump is used for flowing an electrolytic solution between the electrode cell and the tank, and the configuration and type of the pump are not limited as long as it has this function. For example, it is preferable to use a pump having a function capable of discharging the electrolytic solution at a flow rate of 0.1 ml / min or more.

EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to an Example.
Example 1
A half battery using an ionic liquid having the configuration shown in FIG. 1 was produced. In a beaker type container, 0.1 g of vanadyl sulfate (VOSO ₄ ) was added to EMI-TF (hydrophilicity expressed by a contact angle of 40 degrees, potential window −2.0 to 1.5 Vvs. Ag / Ag ⁺ , viscosity 38 mPa · s. Electrolytic solution 4 dissolved in 10 ml of ionic conductivity 9.8 mS / cm was put, glassy carbon test electrode 1 (0.5 cm width × 0.5 cm length × 1 mm thickness) and platinum counter electrode 3 (3 cm width) × 3 cm length × 0.5 mm thickness) was fixed with a Teflon (registered trademark) lid 7 so as to be immersed in the electrolyte solution 4. The silver wire reference electrode 2 (0.5 mmΦ) 2 was fixed in a glass tube 5 filled with a reference electrode solution separated from the electrolyte solution 4 by a porous glass film 6. The reference electrode solution was an EMI-TF solution of 0.01 mol / l silver trifluoromethanesulfonate.

With respect to the obtained half-cell, -1.0 to 1.0 Vvs. FIG. 2 shows the results of cyclic voltammetry performed on the Ag / Ag ⁺ potential range at a scanning speed of 0.05 V / sec. About 0.08V oxidation peak of V ⁴⁺ ⇒V ⁵⁺ is confirmed, the reduction peak of V ⁵⁺ ⇒V ⁴⁺ has been confirmed in about -0.08V.
A half cell using an ionic liquid having the same structure as described above was prepared except that the electrolyte solution 4 was obtained by dissolving 0.1 g of vanadium chloride (VCl ₃ ) in 10 ml of EMI-TF. For this half-cell, -0.2 to -2.0 Vvs. FIG. 3 shows the results of cyclic voltammetry performed on the Ag / Ag ⁺ potential range at a scanning speed of 0.05 V / sec. About -1.5V reduction peak of V ³⁺ ⇒V ²⁺ has been confirmed, the oxidation peak of V ²⁺ ⇒V ³⁺ was confirmed at about -0.9V.
From the above, it is possible to configure a redox flow battery using an ionic liquid by making the half battery showing the result of FIG. 2 the reaction on the positive electrode cell side and the half battery showing the result of FIG. 3 on the negative electrode cell side. I understood.

Example 2
A redox flow battery using an ionic liquid having the configuration shown in FIG. 4 was produced. The first tank 8 on the positive electrode cell side holds an electrolytic solution in which 0.2 g of vanadyl sulfate (VOSO ₄ ) is dissolved in 20 ml of EMI-TF and 1 wt% of 36N sulfuric acid is added. The second tank 9 on the negative electrode cell side holds an electrolytic solution in which 0.2 g of vanadium chloride (VCl ₃ ) is dissolved in 20 ml of EMI-TF and 1 wt% of 36N sulfuric acid is added. The positive electrode plate 10 and the negative electrode plate 11 were glassy carbon plates (3 cm width × 3 cm length × 1 mm thickness). As the ion exchange membrane 12, a Nafion membrane (thickness 170 μm, Ew value 1000) was used. In order to circulate the electrolyte solution on the positive electrode cell side and the electrolyte solution on the negative electrode cell side, the electrolyte solution circulation pump 13 was used, and the flow rate was 5 ml / min. The open circuit voltage was 1.3V.
When this battery was charged at a constant current of 3 mA for 12 hours and discharged at a constant current of 3 mA for 10 hours, the open circuit voltage was 1.3 V.

Example 3
As an electrolyte on the positive electrode cell side, a solution obtained by dissolving 0.3 g of vanadyl sulfate (VOSO ₄ ) in 20 ml of EMI-TF and adding 2 wt% of 36N sulfuric acid was used. As an electrolyte on the negative electrode cell side, vanadium chloride ( A redox flow battery using an ionic liquid having the same configuration as in Example 2 was prepared, except that 0.3 g of VCl ₃ ) dissolved in 20 ml of EMI-TF was added with 2 wt% of 36N sulfuric acid. . The flow rate of the electrolyte was 5 ml / min. The open circuit voltage was 1.3V.
When this battery was charged at a constant current of 6 mA for 8 hours and discharged at a constant current of 3 mA for 12 hours, the open circuit voltage was 1.4 V.

Example 4
As an electrolytic solution on the positive electrode cell side, a solution in which 0.2 g of vanadyl sulfate (VOSO ₄ ) was dissolved in 20 ml of EMI-TF was added with 1 wt% of 36N sulfuric acid, and further 5 wt% of triethylene glycol dimethyl ether was used. as the electrolyte of the negative electrode cell side, except that the vanadium chloride (VCl ₃₎ 1 g was added 1 wt% of 36N sulfuric acid obtained by dissolving the EMI-TF20ml, triethylene glycol dimethyl ether was used which was added 5 wt%, A redox flow battery using an ionic liquid having the same configuration as in Example 2 was produced. The flow rate of the electrolyte was 5 ml / min. The open circuit voltage was 1.3V.
When this battery was charged at a constant current of 6 mA for 6 hours and discharged at a constant current of 6 mA for 5 hours, the open circuit voltage was 1.3 V.

Example 5
A half cell A using the ionic liquid having the configuration shown in FIG. 1 was produced. In a beaker-type container, 0.1 g of vanadyl sulfate (VOSO ₄ ) is added to TMPA-TF (hydrophilicity represented by a contact angle of 60 degrees, potential window from −2.9 to 2.2 Vvs. Ag / Ag ⁺ , viscosity of 70 mPa · s. Electrolyte solution 4 dissolved in 10 ml of ion conductivity 3.4 mS / cm is put, glassy carbon test electrode 1 (0.5 cm width × 0.5 cm length × 1 mm thickness) and platinum counter electrode 3 (3 cm width) × 3 cm length × 0.5 mm thickness) was fixed with a Teflon (registered trademark) lid 7 so as to be immersed in the electrolyte solution 4. The silver wire reference electrode 2 (0.5 mmΦ) 2 was fixed in a glass tube 5 filled with a reference electrode solution separated from the electrolyte solution 4 by a porous glass film 6. The reference electrode solution was a 0.01 mol / l silver trifluoromethanesulfonate TMPA-TF solution.
With respect to the obtained half battery A, -1.0 to 1.0 Vvs. When cyclic voltammetry was performed in the Ag / Ag ⁺ potential range at a scanning speed of 0.05 V / sec, an oxidation peak of V ⁴⁺ ⇒ V ⁵⁺ was confirmed at about 0.08 V, and about −0.08 V. A reduction peak of V ⁵⁺ ⇒ V ⁴⁺ was confirmed.
A half cell B using an ionic liquid having the same structure as described above was prepared except that the electrolyte solution 4 was obtained by dissolving 0.1 g of vanadium chloride (VCl ₃ ) in 10 ml of TMPA-TF. For this half-cell, -0.2 to -2.0 Vvs. When cyclic voltammetry was performed in the Ag / Ag ⁺ potential range at a scanning speed of 0.05 V / sec, a reduction peak of V ³⁺ ⇒ V ²⁺ was confirmed at about −1.5 V, and about −0.9 V The oxidation peak of V ²⁺ ⇒ V ³⁺ was confirmed.
As mentioned above, it turned out that the redox flow battery using an ionic liquid can be comprised by making the half battery A into the reaction of the positive electrode cell side and the half battery B as the negative electrode cell side.

Example 6
A redox flow battery using an ionic liquid having the configuration shown in FIG. 4 was produced. In the first tank 8 on the positive electrode cell side, 0.2 g of vanadyl sulfate (VOSO ₄ ) is added to MPPi-TF (hydrophilicity expressed by a contact angle of 70 degrees, potential window from −2.9 to 2.2 V vs. Ag / Ag. ⁺ , An electrolyte obtained by adding 1 wt% of 36N sulfuric acid to a solution dissolved in 20 ml of a viscosity of 150 mPa · s and an ionic conductivity of 1.7 mS / cm) is held. The second tank 9 on the negative electrode cell side holds an electrolytic solution in which 0.2 g of vanadium chloride (VCl ₃ ) is dissolved in 20 ml of MPPi-TF and 1 wt% of 36N sulfuric acid is added. The positive electrode plate 10 and the negative electrode plate 11 were glassy carbon plates (3 cm width × 3 cm length × 1 mm thickness). As the ion exchange membrane 12, a Flemion membrane (thickness 170 μm, Ew value 1100) was used. In order to circulate the electrolyte solution on the positive electrode cell side and the electrolyte solution on the negative electrode cell side, the electrolyte solution circulation pump 13 was used, and the flow rate was 5 ml / min. The open circuit voltage was 1.3V.
When this battery was charged at a constant current of 4 mA for 10 hours and discharged at a constant current of 3 mA for 12 hours, the open circuit voltage was 1.3V.

Example 7
As the electrolyte solution on the positive electrode cell side, a solution obtained by dissolving 0.3 g of vanadyl sulfate (VOSO ₄ ) in 20 ml of TMPA-TF and adding 2 wt% of perchloric acid (70%) is used. As an example, an ionic liquid having the same configuration as in Example 2 was used except that 0.3 g of VCl ₃ dissolved in 20 ml of TMPA-TF was used with 2 wt% of perchloric acid (70%) added. A redox flow battery was produced. The flow rate of the electrolyte was 5 ml / min. The open circuit voltage was 1.3V.
When this battery was charged at a constant current of 3 mA for 12 hours and discharged at a constant current of 3 mA for 10 hours, the open circuit voltage was 1.3 V.

Comparative Example 1
As the electrolyte on the positive electrode cell side, 0.3 g of vanadyl sulfate (VOSO ₄ ) dissolved in 20 ml of 1N sulfuric acid aqueous solution was used. As the electrolyte on the negative electrode cell side, 0.3 g of vanadium chloride (VCl ₃ ) was added to 1N. A redox flow battery using an ionic liquid having the same configuration as in Example 2 was prepared, except that a solution dissolved in 20 ml of a hydrochloric acid aqueous solution was used. The flow rate of the electrolyte was 5 ml / min. The open circuit voltage was 1.2V.
When this battery was charged at a constant current of 3 mA for 12 hours and discharged at a constant current of 3 mA for 9 hours, the open circuit voltage was 1.2V.
When the batteries of Example 5 and Comparative Example 1 were stored in a constant temperature and humidity chamber with a temperature of 45 ° C. and a humidity of 30% for 60 days, the amount of electrolyte in the battery of Example 3 did not change, whereas the comparative example In the battery of No. 1, the amount of the positive electrode side electrolyte decreased from 20 ml to 19 ml, and the amount of the negative electrode side electrolyte decreased from 20 ml to 18 ml.
From the above, it has been found that a redox flow battery using an ionic liquid can constitute a battery that does not require maintenance such as replenishment of electrolyte compared to a redox flow battery using an aqueous solution.

Experimental Example When an electrolytic solution in which 0.2 g of vanadyl sulfate (VOSO ₄ ) was dissolved in 20 ml of PC and an electrolytic solution in which 0.2 g of vanadyl sulfate was dissolved in 20 ml of EMI-TF were infiltrated into the filter paper, The former burned but the latter did not.
From the above, it has been found that a redox flow battery using an ionic liquid can constitute a battery that is safe against fire and the like as compared with a redox flow battery using an organic solvent.

It is a schematic explanatory drawing of the half battery used in the Example. 4 is a graph showing the results of cyclic voltammetry of the half-cell of Example 1. 4 is a graph showing the results of cyclic voltammetry of the half-cell of Example 1. It is a schematic block diagram of the redox flow battery of this invention.

Explanation of symbols

1 Test Electrode, 2 Reference Electrode, 3 Counter Electrode, 4 Electrolyte, 5 Glass Tube, 6 Porous Glass Membrane, 7 Lid, 8 First Tank, 9 Second Tank, 10 Positive Electrode Plate, 11 Negative Electrode Plate, 12 Ion Exchange Membrane , 13 Electrolyte circulation pump, 14 1st piping, 15 2nd piping

Claims (7)

  A positive electrode cell, a negative electrode cell, an ion exchange membrane that separates the two cells, a first tank in which an electrolytic solution A containing an active material for the positive electrode cell and an ionic liquid is stored, and an active material for the negative electrode cell And a second tank in which an electrolyte B containing ionic liquid is stored, a first pipe connected so that the electrolyte A can circulate between the first tank and the positive electrode cell, and the second A second pipe connected so that the electrolyte B can circulate between the tank and the negative electrode cell; and an electrolyte circulation pump provided in the middle of the first pipe and the second pipe. Redox flow battery.   The redox flow battery according to claim 1, wherein one or both of the ionic liquids contained in the electrolytic solutions A and B have hydrophilicity.   The redox flow battery according to claim 2, wherein the hydrophilic ionic liquid is an ionic liquid having a contact angle on glass of 80 degrees or less. The ionic liquid is -2.5 to 2.0 Vvs. It has at least one of the following properties: a potential window in the range of Ag / Ag ⁺ , a viscosity in the range of 1 to 500 mPa · s (20 ° C.), and an ionic conductivity in the range of 0.05 to 25 mS / cm (25 ° C.). The redox flow battery according to any one of claims 1 to 3.   The redox according to any one of claims 1 to 4, wherein one or both of the ionic liquids contained in the electrolytic solutions A and B include an ionic liquid containing an aliphatic cation or an ionic liquid containing an aromatic cation. Flow battery.   One or both of the electrolytes A and B are 1-ethyl-3-methylimidazolium-trifluoromethanesulfonic acid, N, N, N-trimethyl-N-propylammonium-trifluoromethanesulfonic acid and N-methyl-N. The redox flow battery according to claim 5, comprising at least an ionic liquid selected from -propylpiperidinium-trifluoromethanesulfonic acid.   The redox flow battery according to any one of claims 1 to 6, wherein one or both of the electrolytic solutions A and B further contain triethylene glycol dimethyl ether and / or tetraethylene glycol dimethyl ether as a nonaqueous solvent. .

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