Electrolyte solution for redox flow battery and redox flow battery comprising same

Abstract

The provided are an electrolyte for redox flow battery and a redox flow battery comprising the same, wherein the electrolyte for redox flow battery comprises a solute and a solvent, wherein said solute comprises at least one of anode active material and cathode active material, wherein said anode active material comprises at least one of organic compounds having a carbonyl group such as benzophenone-, benzoquinone-, dimethyl terephthalate-, and 1,4-diacetylbenzene-based organic compounds, and said cathode active material comprises at least one of amine-, tetrathiafulvalene-, and N,N,N′,N′-tetramethyl-p-phenylenediamine-based organic compounds.

Claims

1. A redox flow battery comprising a cathode active material, and further comprising a metal-ligand compound or an anode active material, wherein the cathode active material comprises a N,N,N′,N′-tetramethyl-p-phenylenediamine-based organic compound, wherein the redox flow battery provides 1.4V or more of potential difference between an oxidation reaction and a reduction reaction of the metal-ligand compound or an anode electrolyte comprising the anode active material and a cathode electrolyte comprising the cathode active material.

2. The redox flow battery of claim 1, wherein the cathode active material comprises at least one of hydrogen, a methyl group, an ethyl group, a benzyl group, a butoxycarbonylmethyl group, a carboxymethyl group, or an aminocarbonylmethyl group.

3. The redox flow battery of claim 1, wherein the metal-ligand compound constitutes an anode and the cathode electrolyte comprising the cathode active material constitutes a cathode.

4. The redox flow battery of claim 1, wherein the anode electrolyte comprising the anode active material constitutes an anode and the cathode electrolyte comprising the cathode active material constitutes a cathode.

5. The redox flow battery of claim 1, further comprising a solvent.

6. The redox flow battery of claim 5, wherein the solvent comprises an organic solvent.

7. The redox flow battery of claim 6, wherein the organic solvent comprises at least one of acetonitrile, dimethylcarbonate, diethylcarbonate, dimethylsulfoxide, dimethylformamide, propylene carbonate, ethylene carbonate, N-methyl-2-pyrrolidone and fluoroethylene carbonate.

8. The redox flow battery of claim 6, wherein the solvent further comprises an aqueous solvent.

9. The redox flow battery of claim 8, wherein the aqueous solvent comprises at least one of sulfuric acid, hydrochloric acid and phosphoric acid.

10. The redox flow battery of claim 5, wherein a solubility of the cathode active material in the solvent is 0.1M to 10M.

11. The redox flow battery of claim 1, wherein the anode active material comprises at least of one of a benzophenone-based organic compound and a benzoquinone-based organic compound.

12. The redox flow battery of claim 11, wherein the anode active material comprises at least one of hydrogen, a methyl group, an ethyl group, a benzyl group, a butoxycarbonylmethyl group, a carboxylmethyl group, or an aminocarbonylmethyl group.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a current-voltage curve of Example 1 by a cyclic voltammetry method.

(2) FIG. 2 is a current-voltage curve showing the life properties of Example 1.

(3) FIG. 3 is a current-voltage curve of Example 2 by a cyclic voltammetry method.

(4) FIG. 4 is a current-voltage curve of Example 3 by a cyclic voltammetry method.

(5) FIG. 5 is a current-voltage curve of Example 4 by a cyclic voltammetry method.

(6) FIG. 6 is a current-voltage curve showing the life properties of Example 4.

(7) FIG. 7 is a current-voltage curve of Example 5 by a cyclic voltammetry method

(8) FIG. 8 is a current-voltage curve showing the life properties of Example 5.

(9) FIG. 9 is current-voltage curve of Example 6 by a cyclic voltammetry method.

(10) FIG. 10 is a current-voltage curve of Example 7 by a cyclic voltammetry method.

(11) FIG. 11 is a current-voltage curve Example 8 by a cyclic voltammetry method.

(12) FIG. 12 is a current-voltammetry curve of Example 9 by a cyclic voltammetry method.

(13) FIG. 13 is a graph showing energy densities and maximum reaction voltages of a combination of Examples 1 and 4, a combination of Examples 1 and 5, and Comparative Example 1.

DETAILED DESCRIPTION

(14) Hereinafter, an electrolyte for a redox flow battery and a redox flow battery comprising the same according to the present invention will be explained in detail with reference to the drawings. The present invention can be better understood by referring to the following embodiments. However, the embodiments are intended to illustrate the present invention, but not to limit the scope of the present invention which is defined by the claims.

(15) First, the electrolyte for redox flow battery according to the present invention may comprise a solute and a solvent, wherein said solute may comprise at least one of an anode active material and a cathode active material.

(16) The anode active material may comprise at least one of organic compounds having carbonyl group such as benzophenone-, benzoquinone-, dimethyl terephthalate-, and 1,4-diacetylbenzene-based compounds. Preferably, the compounds may comprise at least one of substituents of hydrogen, methyl group, ethyl group, benzyl group, butoxycarbonylmethyl group, carboxylmethyl group and aminocarbonylmethyl group.

(17) For example, the anode active material may be at least one of the compounds represented by the following formulas:

(18) ##STR00001##

(19) The term “an anode active material” refers to a redox couple dissolved in an anode electrolyte, and when reduced to the lower of two oxidation states of the redox couple, a battery is charged.

(20) Furthermore, the cathode active material may comprise at least one of amine-, tetrathiafulvalene-, and N,N,N′,N′-tetramethyl-p-phenylenediamine-based organic compounds. Preferably, the compounds may comprise at least one of substituents of hydrogen, methyl group, ethyl group, benzyl group, butoxycarbonylmethyl group, carboxymethyl group and aminocarbonylmethyl group.

(21) For example, the cathode active material may be at least one of the compounds represented by the following formulas:

(22) ##STR00002##

(23) The term “a cathode active material” refers to a redox couple dissolved in a cathode electrolyte, and when it is oxidated to the higher state of two oxidation states of the redox couple, a battery is charged.

(24) The anode active material, the cathode active material and their derivatives perform a stable electrochemical reaction in the redox flow battery, and in the case of organic compound with ketone function group, an electrochemical reduction occurs at a very low voltage, thus when this compound and other cathode material are combined, a very high operating voltage can be expected.

(25) Said anode active material and said cathode active material can be combined with metal-ligand compounds, and in order to achieve a preferable energy density level, each operating voltage obtained from the oxidation and reduction of such combination should be higher than a maximum operating voltage of an aqueous system of 1.23V.

(26) Therefore, it is preferred that a maximum reduction potential of the anode electrolyte has a more negative value than −2.0V compared to Fc/Fc.sup.+(Ferrocene/Ferrocenium) reference electrode, a maximum oxidation potential of the cathode electrolyte has a more positive value than −0.5V compared to Fc/Fc.sup.+ reference electrode, and a potential difference between an oxidation reaction and a reduction reaction of the anode electrolyte wherein said anode active material is dissolved in said solvent and the cathode electrolyte wherein said cathode active material is dissolved in said solvent is 1.4V or more.

(27) Furthermore, all redox couples have a high electrochemical reversibility, and thus the difference between an oxidation potential and an reduction potential should be small. If not, when constructing a final battery, the voltage difference between charging and discharging becomes too high, which may decrease an energy efficiency of the battery. Therefore, the difference in voltage (peak potential) between the oxidation and reduction reactions of an anode active material and a cathode active material should be small.

(28) Therefore, in the present invention, when a redox reaction of said solute of 0.01M is analyzed using cyclic voltammetry which is a representative electrochemical analysis method for measuring potential in a redox reaction, at a scanning speed of 100 mV s−1, the difference between the oxidation potential and the reduction potential (Epa-Epc) where each peak current of said redox reaction is confirmed should preferably be 0.5V or less. This is because the small difference in the potentials is preferable in terms of the energy efficiency realized in a battery.

(29) Next, as the solvent to dissolve the solute, it is preferable to use an organic solvent, but the organic solvent can be used in combination with an aqueous solvent.

(30) Preferably, to maximize the solubility of the solute, said organic solvent may include at least one of acetonitrile, dimethylcarbonate, diethylcarbonate, dimethylsulfoxide, dimethylformamide, propylene carbonate, ethylene carbonate, N-methyl-2-pyrrolidone, and fluoroethylene carbonate.

(31) Preferably, said aqueous solvent may include at least one of sulfuric acid, hydrochloric acid, and phosphoric acid.

(32) Further, the electrolyte may further comprise a supporting electrolyte to additionally provide the conductivity to the electrolyte. Preferable examples of the supporting electrolyte may include at least one of ammonium salt-, lithium salt-, and sodium salt-based supporting electrolytes.

(33) Furthermore, it is preferable that the solubility of the solute in the solvent may be 0.1 M to 10 M, and more preferably 1 M to 10 M. If the concentration of the solute dissolved in the electrolyte is 0.1M or more, it is more advantageous than conventional organic-based electrolyte systems, but in order to have a higher energy density than vanadium-based aqueous systems, it is preferable that 1M or more of the solute is dissolved in the electrolyte. If it is less than 0.1M, the energy density is significantly low so that there is a difficulty to achieve the effects by the present invention, and if it exceeds 10M, the viscosity of the electrolyte will be high so that pumping the electrolyte is difficult, and a solute sedimentation can occur in the supersaturated electrolyte solution.

(34) Furthermore, to realize a higher operating voltage, a cell may be constructed using the anode active material of the present invention which has a very low reaction voltage and a metal-ligand compound which has a high reaction voltage, or in the opposite, using the cathode active material of the present invention which has a high reaction voltage and a metal-ligand compound with a low reaction voltage.

(35) For the metal-ligand compound, it is preferable to use at least one of metal-acetylacetonates, metal-biphenyls, and metal-tetradendate tetradecane-based nitrogen-ligand compounds.

(36) Next, a redox flow battery according to the present invention may comprise at least two of metal-ligand compound, the anode active material of the present invention and the cathode active material of the present invention.

(37) In preferable embodiment, the redox flow battery according to the present invention may be constructed using the metal-ligand compound as a cathode and an electrolyte comprising the anode active material as an anode; or the metal-ligand compound as an anode and an electrolyte comprising the cathode active material as a cathode; or an electrolyte comprising the anode active material as an anode and an electrolyte comprising the cathode active material as a cathode. The redox flow battery may further comprise the solvent.

(38) In other words, the present invention relates to a redox flow battery electrolyte comprising a solvent and a solute, wherein the solute comprises an organic compound which can perform a stable electrochemical reaction, migrate one or more electrons during the reaction, and stably be dissolved in the solvent.

(39) Each of the following embodiments of the present invention includes a process for preparing electrolyte in which the organic compound is dissolved in the organic solvent, and the electrolyte prepared by the same, wherein when a redox reaction of the compound occurs, one or more electrons migrate, and stable radicals are generated by an electrochemical reaction and exist in the electrolyte in a stable state. This means that any sedimentation does not take place in the electrolyte.

(40) Hereinafter, to prove the superiority the redox flow battery electrolyte and redox flow battery comprising the same according to the present invention, various experiments on Examples and Comparative example were conducted, of which results are as follows.

Example 1

Electrolyte Comprising Benzophenone

(41) 0.01M of benzophenone purchased from Daejung Chemicals was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium to prepare the electrolyte.

Example 2

Electrolyte Comprising Menadione

(42) 0.01M of menadione purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium to prepare the electrolyte.

Example 3

Electrolyte Comprising 1,4-Naphthoquinone

(43) 0.01M of 1,4-Naphthoquinone purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium to prepare the electrolyte.

Example 4

Electrolyte Comprising N,N,N′N′-Tetramethyl-P-Phenylenediamine

(44) 0.01M of N,N,N′N′-tetramethyl-p-phenylenediamine purchased from Alfa aesar was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium to prepare the electrolyte.

Example 5

Electrolyte Comprising Tetrathiafulvalene

(45) 0.01M of Tetrathiafulvalene purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium to prepare the electrolyte.

Example 6

Electrolyte Comprising N,N-Dimethyl-P-Phenylenediamine

(46) 0.01M of N,N-dimethyl-p-phenylenediamine purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium to prepare the electrolyte.

Example 7

Electrolyte Comprising Triphenylamine

(47) 0.01M of Triphenylamine purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium to prepare the electrolyte.

Example 8

Electrolyte Comprising 4-Hydroxydiphenylamine

(48) 0.01M of 4-hydroxydiphenylamine purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium to prepare the electrolyte.

Example 9

Electrolyte Comprising 4-Amino-Diphenylamine

(49) 0.01M of 4-amino-diphenylamine purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium to prepare the electrolyte.

Example 10

Experiment on Solubility of Benzophenone

(50) Benzophenone purchased from Daejung Chemicals was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium and the maximum amount of benzophenone that can be dissolved was checked.

Example 11

Experiment on Solubility of Menadione

(51) Menadione purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium and the maximum amount of Menadione that can be dissolved was checked.

Example 12

Experiment on Solubility of 1,4-Naphthoquinone

(52) 1,4-Naphthoquinone purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium and the maximum amount of 1,4-Naphthoquinone that can be dissolved was checked.

Example 13

Experiment on Solubility of N,N,N′N′-Tetramethyl-P-Phenylenediamine

(53) N,N,N′N′-tetramethyl-p-phenylenediamine purchased from Alfa aesar was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium and the maximum amount of N,N,N′N′-tetramethyl-p-phenylenediamine that can be dissolved was checked.

Example 14

Experiment on Solubility of Tetrathiafulvalene

(54) Tetrathiafulvalene purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium and the maximum amount of tetrathiafulvalene that can be dissolved was checked.

Example 15

Experiment on Solubility of N,N-Dimethyl-P-Phenylenediamine

(55) N,N-dimethyl-p-phenylenediamine purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium and the maximum amount of N,N-dimethyl-p-phenylenediamine that can be dissolved was checked.

Example 16

Experiment on Solubility of Triphenylamine

(56) Triphenylamine purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium and the maximum amount of triphenylamine that can be dissolved was checked.

Example 17

Experiment on Solubility of 4-Hydroxydiphenylamine

(57) 4-Hydroxydiphenylamine purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium and the maximum amount of 4-hydroxydiphenylamine that can be dissolved was checked.

Example 18

Experiment on Solubility of 4-Amino-Diphenylamine

(58) 4-Amino-diphenylamine purchased from Sigma Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium and the maximum amount of 4-amino-diphenylamine that can be dissolved was checked.

Comparative Example 1

Aqueous Electrolyte Comprising VOSO.SUB.4

(59) Energy density was calculated based on the data from Journal of Power Sources, 160, 716-32, published in 2006 by C.Ponce de Le'on.

Comparative Example 2

Electrolyte Comprising Thianthrene

(60) Thianthrene purchased from Aldrich was dissolved in propylene carbonate solution comprising tetrafluoroborate tetraethylammonium and the maximum amount of thianthrene that can be dissolved was checked.

(61) Cyclic Voltammetry

(62) [Checking a Reaction Voltage of Electrolyte]

(63) Experiments were conducted using electrolytes obtained from said Examples 1-9 at electric potential scanning speed of 100 mV s.sup.−1.

(64) The voltage ranges used for conducting the experiments are as follows: −1.05 V-−2.45 V (vs. Fc/Fc.sup.+) for Example 1; −2 V-0 V (vs. Ag wire) for Example 2; −2.2 V-−0.2 V (vs. Fc/Fc.sup.+) for Example 3; −1 V-1 V (vs. Fc/Fc.sup.+) for Example 4; −0.45 V-0.55 V (vs. Fc/Fc.sup.+) for Example 5; −0.25 V-0.55 V (vs. Fc/Fc.sup.+) for Example 6; 0 V-1.5 V (vs. Ag wire) for Example 7; −0.5 V-0.6 V (vs. Fc/Fc.sup.+) for Example 8; and 0 V-1.0 V (vs. Ag wire) for Example 9. Ag wire was used as a reference electrode or it was corrected to Fc/Fc.sup.+ reference electrode. Glassy carbon electrode was used as a working electrode and white gold was used for a counter electrode. Electrochemical cell was prepared using such construction and the cyclic voltammetry experiment was conducted thereon.

(65) [Checking a Reaction Voltage of an Anode Active Material]

(66) The results from the experiment on Example 1 showed that the oxidation voltage and reduction voltage were 1.85 V and −2.21 V (vs. Fc/Fc.sup.+) respectively, and thus it can be used as an anode active material for redox flow battery of voltage of −2.03 V (vs. Fc/Fc.sup.+).

(67) The results from the experiment on Example 2 showed that the oxidation voltage and reduction voltage were 0.56 V and −0.75 V (vs. Ag wire) respectively, and thus it can be used as an anode active material for redox flow battery of voltage of −0.66 V (vs. Ag wire).

(68) The results from the experiment on Example 3 showed that the oxidation voltage and reduction voltage were 1.49 V and −1.62 V (vs. Fc/Fc.sup.+) respectively, and thus it can be used as an anode active material for redox flow battery of voltage of −1.56 V (vs. Fc/Fc.sup.+).

(69) [Checking a Reaction Voltage of a Cathode Active Material]

(70) The results from the experiment on Example 4 showed that the reduction voltage and oxidation voltage were −0.56 V, −0.10 V, 0 V, and 0.48 V (vs. Fc/Fc+) in that order, and thus it can be used as an cathode active material for redox flow battery performing two electrons reaction at −0.33 V and 0.24 V (vs. Fc/Fc.sup.+).

(71) The results from the experiment on Example 5 showed that the reduction voltage and oxidation voltage were −0.27 V, −0.17 V, 0.06 V, and 0.15 V (vs. Fc/Fc+) in that order, and thus it can be used as an cathode active material for redox flow battery performing two electrons reaction at −0.22 V and 0.11 V (vs. Fc/Fc.sup.+).

(72) The results from the experiment on Example 6 showed that the maximum reduction voltage and maximum oxidation voltage were 0.16 V and 0.30 V respectively, and thus it can be used as an cathode active material for redox flow battery performing one electron reaction at 0.23 V (vs. Fc/Fc.sup.+).

(73) The results from the experiment on Example 7 showed that the maximum reduction voltage and maximum oxidation voltage were 0.85 V and 0.30 V (vs. Ag wire) respectively, and thus it can be used as an cathode active material for redox flow battery performing one electron reaction at 0.96 V (vs. Ag wire).

(74) The results from the experiment on Example 8 showed that the maximum reduction voltage and maximum oxidation voltage were −0.26 V, −0.19 V, 0.27 V, and 0.35 V (vs. Fc/Fc.sup.+) in that order, and thus it can be used as an cathode active material for redox flow battery performing two electrons reaction at −0.23 V and 0.31 V (vs. Fc/Fc.sup.+).

(75) The results from the experiment on Example 9 showed that the maximum reduction voltage and maximum oxidation voltage were 0.20 V, 0.29 V, 0.66 V, and 0.80 V (vs. Ag wire) in that order, and thus it can be used as an cathode active material for redox flow battery performing two electrons reaction at 0.25 V and 0.73 V (vs. Ag wire).

(76) The maximum oxidation and reduction voltages measured from Examples 1-9 are shown in Table 1.

(77) TABLE-US-00001 TABLE 1 1 Electron 2 Electron Oxidation Reduction Oxidation Reduction maximum maximum maximum maximum voltage voltage voltage voltage Example 1 −1.85/V −2.21/V — — (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) Example 2 −0.56/V −0.75/V — — (vs. Ag wire) (vs. Ag wire) Example 3 −1.49/V −1.62/V — — (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) Example 4 −0.10/V −0.56/V 0.48/V 0.0/V (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) Example 5 −0.17/V −0.27/V 0.15/V 0.06/V (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) Example 6 0.30/V 0.16/V — — (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) Example 7 1.07/V 0.85/V — — (vs. Ag wire) (vs. Ag wire) Example 8 −0.19/V −0.26/V 0.35/V 0.27/V (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) Example 9 0.29/V 0.20/V 0.80/V 0.66/V (vs. Ag wire) (vs. Ag wire) (vs. Ag wire) (vs. Ag wire)

(78) Half-wave potentials measured from Examples 1-3 which are considered as the oxidation-reduction reaction voltages of the electrolytes are shown in Table 2.

(79) TABLE-US-00002 TABLE 2 1 Electron 2 Electron Reaction potential Reaction potential Example 1 −2.03/V — (vs. Fc/Fc.sup.+) Example 2 −0.66/V — (vs. Ag wire) Example 3 −1.56/V — (vs. Fc/Fc.sup.+) Example 4 −0.33/V 0.24/V (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) Example 5 −0.22/V 0.11/V (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) Example 6 0.23/V — (vs. Fc/Fc.sup.+) Example 7 0.96/V — (vs. Ag wire) Example 8 −0.23/V 0.31/V (vs. Fc/Fc.sup.+) (vs. Fc/Fc.sup.+) Example 9 0.25/V 0.73/V (vs. Ag wire) (vs. Ag wire)

(80) [Checking Life Property of Material]

(81) Experiments were conducted using electrolytes obtained from said Examples 1-9 at electric potential scanning speed of 300 mV s.sup.−1.

(82) The potential sweep ranges used for conducting the experiments are as follows: −1.05 V-−2.45 V (vs. Fc/Fc.sup.+) for Example 1; −2 V-0 V (vs. Ag wire) for Example 2; −2.2 V-−0.2 V (vs. Fc/Fc.sup.+) for Example 3; −1 V-1 V (vs. Fc/Fc.sup.+) for Example 4; −0.45 V-0.55 V (vs. Fc/Fc.sup.+) for Example 5; −0.25 V-0.55 V (vs. Fc/Fc.sup.+) for Example 6; 0 V-1.5 V (vs. Ag wire) for Example 7; −0.5 V-0.6 V (vs. Fc/Fc.sup.+) for Example 8; and 0 V-1.0 V (vs. Ag wire) for Example 9. Ag wire was used as a reference electrode or it was corrected to Fc/Fc.sup.+ reference electrode. Glassy carbon electrode was used as a working electrode and white gold was used for a counter electrode. Electrochemical cell was prepared using such construction and the cyclic voltammetry experiment was conducted thereon.

(83) Experiment results showed that after repeating 50 times of the redox reaction of each redox couple, there were no change in the reaction voltage and decrease in the current value. Through this, it was confirmed that even through repeated charging and discharging, the active materials of the present invention can perform the reaction stably and reversibly.

(84) [Comparison of Voltage and Energy Density using Electrolyte's Solubility and Reaction Potential]

(85) The maximum solubility of each electrolyte from Examples 10-18 is shown in Table 3. Even if it is the same organic active material, the organic active material of the present invention shows a higher solubility, and thus when used as an electrolyte for redox flow battery, can realize a higher capacity.

(86) TABLE-US-00003 TABLE 3 Solubility/M Example 10 5M Example 11 0.3M Example 12 0.5M Example 13 2M Example 14 0.6M Example 15 2M Example 16 Less than 0.1M Example 17 4M Example 18 4M Comparative example 2 0.1M

(87) Considering the operating voltage of battery calculated from Table 2 and the maximum solubility described in Table 3, the expected maximum energy density was calculated, and the result is listed in Table 4 together with the result of Comparative example 1.

(88) TABLE-US-00004 TABLE 4 Maximum 1 Electron 2 Electron energy Maximum Operating Operating density/ Combination solubility/M voltage/V voltage/V Wh L.sup.−1 Example 1 + 4M/2M 1.7 2.27 212.84 Example 4 Example 1 + 1.2M/0.6M 1.81 2.14 63.53 Example 5 Comparative 1M 1.23 — 32.97 example 1

(89) As shown in Table 4, the energy densities from the combination of Examples 1 and 4, and the combination of Example 1 and 5 are much higher than that of Comparative example 1. These results are represented as graphs in FIG. 13.

(90) The preferred examples were explained above, but various changes, modifications, and equivalents thereof can be applied for practicing the present invention. It is apparent that the examples in the present invention can be appropriately modified and applied. Therefore, the above disclosures do not limit the scope of the present invention defined by the appended claims.

INDUSTRIAL APPLICABILITY

(91) The electrolyte for redox flow battery and the redox flow battery comprising the same according to the present invention have many advantageous industrial applications.