Electrolyte Compositions Comprising Distinct Redox-Active Species and Uses Thereof

Abstract

The present invention relates to electrolyte compositions comprising distinct redox-active compounds, namely, a redox-active compound, which is phenazine or a phenazine derivative, and a distinct redox-active compound, which is not phenazine or a phenazine derivative. The present invention also relates to the use of such electrolyte compositions as redox flow battery electrolytes. Accordingly, the invention further provides a redox flow battery comprising said compositions.

Claims

1. An electrolyte composition comprising (i) a first redox active compound, which is characterized by General Formula (I), or a salt thereof: ##STR00015## wherein: R.sup.1 and R.sup.2 are selected independently from each other from the group consisting of R.sub.a—R.sub.d, R.sub.a—R.sub.b—R.sub.c, R.sub.a—R.sub.d—R.sub.c, R.sub.b—R.sub.c, R.sub.b—R.sub.a—R.sub.b—R.sub.c, R.sub.b—R.sub.a—R.sub.d—R.sub.c, R.sub.b—R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.b—R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.b—N(R.sub.b—R.sub.c).sub.3X, R.sub.e, R.sub.d, R.sub.d—R.sub.c, R.sub.d—R.sub.a—R.sub.b—R.sub.c, R.sub.d—R.sub.a—R.sub.d—R.sub.c, R.sub.d—R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.d—R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.d—N(R.sub.d—R.sub.c).sub.3X, R.sub.d—N(R.sub.b—R.sub.c).sub.3X, R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c)(R.sub.b—R.sub.c), —N(R.sub.b—R.sub.1).sub.3X, and —N(R.sub.d—R.sub.c).sub.3X, wherein R.sub.a is selected from the group consisting of —SO.sub.3—, —SO.sub.2(NH)—, —(NH)SO.sub.2—, —SO.sub.2(NR.sub.d)—, —(NR.sub.d)SO.sub.2—, —OSO.sub.3—, —OSO.sub.2(NH)—, —(NH)SO.sub.2O—, —OSO.sub.2NR.sub.d—, —(NR.sub.d)SO.sub.2O—, —PO.sub.3H—, —PO.sub.2H(NH)—, —PO.sub.2HNR.sub.d—, —OPO.sub.3H—, —OPO.sub.2H(NH)—, —OPO.sub.2HNR.sub.d—, —C(═O)O—, —CO(NH)—, —(NH)CO—, —CONR.sub.d—, —(NR.sub.d)CO—, —O—, —NH—, -heteroaryl, and -heterocyclyl, R.sub.b is selected from the group consisting of —CH.sub.2C(OH)HR.sub.d—, —R.sub.d—O—R.sub.d—, —R.sub.d—(OC.sub.2H.sub.4).sub.n—, and R.sub.d—(OCH.sub.2C(CH.sub.3)H).sub.n—, wherein n is an integer selected from 1 to 50, R.sub.c is selected from the group consisting of —H, —OH, —OR.sub.d, —OC(═O)R.sub.d, —NH.sub.2, —NH(R.sub.d), —N(R.sub.d).sub.2, —N(R.sub.d).sub.3X, —C(═O)NH.sub.2, —C(═O)(NH)R.sub.d, —C(═O)OH, —C(═O)R.sub.b—H, —SO.sub.3H, —SO.sub.3R.sub.d, —SO.sub.2NH.sub.2, —SO.sub.2(NH)R.sub.d, —OSO.sub.3H, —OSO.sub.3R.sub.d, —OSO.sub.2NH.sub.2, —OSO.sub.2(NH)R.sub.d, —PO.sub.3H.sub.2, —PO.sub.3HR.sub.d, —PO.sub.3(R.sub.d).sub.2, —OPO.sub.3H.sub.2, —OPO.sub.3HR.sub.d, —OPO.sub.3(R.sub.d).sub.2, -halogen, -aryl, —CHO, —CN, -heteroaryl, and -heterocyclyl, R.sub.d is a linear or branched, saturated or unsaturated C.sub.1-C.sub.9 chain, R.sub.e is selected from the group consisting of —PO.sub.3—, —OPO.sub.2—, and —N—, and X is selected from the group consisting of —Cl, —Br, —I, and ½-SO.sub.4; and wherein m and p are selected independently from each other from any integer of 0, 1, 2, 3, and 4; (ii) a second redox active compound, which is not characterized by General Formula (I); and (iii) a solvent.

2. The electrolyte composition of claim 1, wherein R.sup.1 and R.sup.2 are selected independently from each other from the group consisting of R.sub.a—R.sub.b—R.sub.e, R.sub.a—R.sub.d—R.sub.c, R.sub.b—R.sub.c, R.sub.c, R.sub.d, R.sub.d—R.sub.c, R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c)(R.sub.b—R.sub.c), —N(R.sub.b—R.sub.c).sub.3X, and —N(R.sub.d—R.sub.c).sub.3X.

3. The electrolyte composition of claim 1, wherein R.sub.a is selected from the group consisting of —PO.sub.3H—, —CO(NH)—, —(NH)CO—, —CONR.sub.d—, —(NR.sub.d)CO—, —O—, —NH—, -heteroaryl, and -heterocyclyl.

4. The electrolyte composition of claim 1, wherein R.sub.b is selected from the group consisting of —CH.sub.2C(OH)HR.sub.d—, —R.sub.d—O—R.sub.d—, and —R.sub.d—(OC.sub.2H.sub.4).sub.n.

5. The electrolyte composition of claim 1, wherein R.sub.c is selected from the group consisting of —H, —OH, —OR.sub.d, —NH.sub.2, —N(R.sub.d).sub.3X, —C(═O)NH.sub.2, —C(═O)OH, —SO.sub.3H, —OSO.sub.3H, —PO.sub.3H.sub.2, -halogen, -aryl, —CN, -heteroaryl, and -heterocyclyl.

6. The electrolyte composition of claim 1, wherein Rd is a linear or branched, saturated C1-C9 chain.

7-10. (canceled)

11. The electrolyte composition of claim 1, wherein R.sup.1 and R.sup.2 are selected independently from each other from the group consisting of R.sub.a—R.sub.b—R.sub.c, R.sub.a—R.sub.d—R.sub.c, R.sub.b—R.sub.c, R.sub.c, R.sub.d, R.sub.d—R.sub.c, R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c)(R.sub.b—R.sub.c), —N(R.sub.b—R.sub.c).sub.3X, and —N(R.sub.d—R.sub.c).sub.3X, wherein R.sub.a is selected from the group consisting of —CO(NH)—, —(NH)CO—, —CONR.sub.d—, —(NR.sub.d)CO—, —O—, —NH—, -heteroaryl, and -heterocyclyl, R.sub.b is selected from the group consisting of —CH.sub.2C(OH)HR.sub.d—, —R.sub.d—O—R.sub.d—, and —R.sub.d—(OC.sub.2H.sub.4).sub.n—, wherein n is an integer selected from 1 to 20, R.sub.c is selected from the group consisting of —H, —OH, —OR.sub.d, —NH.sub.2, —N(R.sub.d).sub.3X, —C(═O)NH.sub.2, —C(═O)OH, —SO.sub.3H, —OSO.sub.3H, —PO.sub.3H.sub.2, -halogen, -aryl, —CN, -heteroaryl, and -heterocyclyl, R.sub.d is a linear or branched, saturated C.sub.1-C.sub.9 chain, R.sub.e is —N—, and X is selected from the group consisting of —Cl, —Br, and ½-SO.sub.4; and wherein m is an integer selected from 0, 1, 2, and 3; and p is an integer selected from 0, 1, and 2.

12. The electrolyte composition of claim 1, wherein: R.sup.1 and R.sup.2 are selected independently from each other from the group consisting of R.sub.a—R.sub.b—R.sub.c, R.sub.a—R.sub.d—R.sub.c, R.sub.c, R.sub.d, R.sub.d—R.sub.c, R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c)(R.sub.b—R.sub.c), and —N(R.sub.b—R.sub.c).sub.3X, wherein R.sub.a is —O— or —NH—, R.sub.b is —CH.sub.2C(OH)HR.sub.d— or —R.sub.d—(OC.sub.2H.sub.4).sub.n—, wherein n is an integer selected from 1 to 5, R.sub.c is selected from the group consisting of —H, —OH, —NH.sub.2, —C(═O)OH, —SO.sub.3H, -aryl, —CN, -heteroaryl, and -heterocyclyl, R.sub.d is a linear or branched, saturated C.sub.1-C.sub.5 chain, R.sub.e is —N—, and X is —Cl or ½-SO.sub.4; and wherein m is an integer selected from 0, 1, and 2; and p is 0 or 1.

13. The electrolyte composition of claim 1, wherein R.sup.1 is positioned at ring position 7 and/or 8.

14. The electrolyte composition of claim 1, wherein R.sup.2 is positioned at ring position 2 and/or 3.

15. The electrolyte composition of claim 1, wherein m is 2 and R1 is positioned at ring position 7 and 8.

16. The electrolyte composition of claim 1, wherein m is 1 and R1 is positioned at ring position 7 or 8.

17. The electrolyte composition of claim 1, wherein p is 2 and R2 is positioned at ring position 2 and 3.

18. The electrolyte composition of claim 1, wherein p is 1 and R2 is positioned at ring position 2 or 3.

19. The electrolyte composition of claim 1, wherein the composition comprises at least one compound according to Formula (I)(a) (reduced state) and at least one corresponding compound of Formula (I)(b) (oxidized state).

20. The electrolyte composition of claim 1, wherein the composition comprises at least two distinct redox active compounds characterized by General Formula (I).

21. (canceled)

22. The electrolyte composition of claim 1, wherein the electrolyte composition does not comprise 2,5-dihydroxy-1,4-benzoquinone.

23. The electrolyte composition of claim 1, wherein the second redox active compound is selected from the group consisting of inorganic ions (e.g., metal ions, halogen ions), metal complexes, polysulfide/sulfur systems, and metal-free organic compounds not according to General Formula (I).

24-25. (canceled)

26. The electrolyte composition of claim 1, wherein the second redox active compound is characterized by any one of General Formulas (II) to (IV): ##STR00016## wherein each of R.sup.1-R.sup.4 in formula (II); R.sup.1-R.sup.6 in formula (III); and/or R.sup.1-R.sup.8 in formula (IV) is independently selected from hydrogen; hydroxyl; carboxy; optionally substituted C.sub.1-6 alkyl optionally comprising at least one heteroatom selected from N, O and S, including —C.sub.nH.sub.2nOH, —C.sub.nH.sub.2nNH.sub.2 and —C.sub.nH.sub.2nSO.sub.3H, wherein n is an integer selected from 1, 2, 3, 4, 5, or 6; carboxylic acids; esters; halogen; optionally substituted C.sub.1-6 alkoxy, including methoxy and ethoxy; optionally substituted amino, including primary, secondary, tertiary and quaternary amines; amide; nitro; carbonyl; phosphoryl; phosphonyl; cyanide; and sulfonyl (—SO.sub.3H); or an alkali salt thereof.

27-32. (canceled)

33. The electrolyte composition of claim 1, wherein the composition comprises at least two distinct redox active compounds selected from compounds having one of General Formulas (II) to (IV) ##STR00017## wherein each of R.sup.1-R.sup.4 in formula (II); R.sup.1-R.sup.6 in formula (III); and/or R.sup.1-R.sup.8 in formula (IV) is independently selected from hydrogen: hydroxyl; carboxy; optionally substituted C.sub.1-6 alkyl optionally comprising at least one heteroatom selected from N, O and S, including —C.sub.nH.sub.2nOH, —C.sub.nH.sub.2nNH.sub.2 and —C.sub.nH.sub.2nSO.sub.3H, wherein n is an integer selected from 1, 2, 3, 4, 5, or 6; carboxylic acids; esters; halogen; optionally substituted C.sub.1-6 alkoxy, including methoxy and ethoxy; optionally substituted amino, including primary, secondary, tertiary and quaternary amines; amide; nitro; carbonyl; phosphoryl; phosphonyl; cyanide; and sulfonyl (—SO.sub.3H); or an alkali salt thereof.

34. (canceled)

35. The electrolyte composition of claim 1, wherein the composition is an aqueous composition.

36. The electrolyte composition of claim 1, wherein the composition comprises an organic solvent.

37. The electrolyte composition according to claim 36, wherein the organic solvent is selected from the group consisting of dimethyl sulfoxide, anisole, 1,4-dioxane, ethylene glycol, glycerol, tetrahydrofuran, diethylene glycol, triethylene glycol, dimethoxyethane, bis(2-methoxyethyl)ether, triethylene glycol dimethyl ether, a fatty alcohol ethoxylate having a C.sub.12-C.sub.18 chain and an ethoxylation degree of 2-30, and a monoalcohol of General Formula (V):
HO—R.sup.9  (V) wherein R.sup.9 is a saturated or partially unsaturated, linear or branched C.sub.1-C.sub.18 alkyl chain, or a condensed or annulated aromatic moiety having 6-14 carbon atoms.

38-45. (canceled)

46. A redox flow battery half-cell comprising the electrolyte composition of claim 1.

47. A redox flow battery comprising: a first half-cell comprising a first electrolyte composition, wherein the first electrolyte composition is of claim 1; and a second half-cell comprising a second electrolyte composition, wherein the second electrolyte composition is distinct from the first electrolyte composition.

48. (canceled)

49. A redox flow battery comprising: a first electrolyte composition, wherein the first electrolyte composition is of claim 1; a first electrode in contact with the first electrolyte composition; a second electrolyte composition, wherein the second electrolyte composition is distinct from the first electrolyte composition; a second electrode in contact with the second electrolyte composition; and a separator interposed between the first and the second electrode and separating the first electrolyte composition from the second electrolyte composition.

50-57. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0268] In the following a brief description of the appended figures will be given. The figures are intended to illustrate the present invention in more detail. However, they are not intended to limit the subject matter of the invention in any way.

[0269] FIG. 1 shows cell polarization and performance with cells with an electrolyte composition of the invention (“DHPS+AQ”) and a comparative electrolyte composition (“DHPS”).

[0270] FIG. 2 shows a charge and discharge curve for a cell with an electrolyte composition of the invention (“DHPS+AQ”) and a comparative electrolyte composition (“DHPS”).

EXAMPLES

[0271] In the following, particular examples illustrating various embodiments and aspects of the invention are presented. However, the present invention shall not to be limited in scope by the specific embodiments described herein. The following preparations and examples are given to enable those skilled in the art to more clearly understand and to practice the present invention. The present invention, however, is not limited in scope by the exemplified embodiments, which are intended as illustrations of single aspects of the invention only, and methods which are functionally equivalent are within the scope of the invention. Indeed, various modifications of the invention in addition to those described herein will become readily apparent to those skilled in the art from the foregoing description, accompanying figures and the examples below. All such modifications fall within the scope of the appended claims.

Example 1

Flow-By Cells (FB Cell):

[0272] For electrochemical characterization, a small laboratory cell is used. A cell assembly with pressed carbon electrodes (80% graphite-20% PP electrodes with carbon black surface, 41 mm×41 mm×0.72 mm, regularly rhombus shaped surface pattern with maximal height of structures of 1.4 mm) as both the positive and negative electrode is employed. The gap between the base electrode surface and membrane is 1.5 mm on each side of the cell. A cation exchange membrane (620PE, supplier: fumatech) is used to separate the positive and negative electrolytes. The membrane is conditioned in 0.5 M KOH/NaOH (KOH/NaOH=1:1) for at least 150 h prior to each test. 25 mL of negolyte electrolyte composition (sum of active material is 0.5 M) and 54 mL of Na.sub.2K.sub.2Fe(CN).sub.6 as posolyte (0.68 M, in 0.25 M Na/KOH, Na.sup.+/K.sup.+=1:1) is used. Two distinct negolyte electrolyte compositions were tested, namely an electrolyte composition according to the invention (“DHPS+AQ”) and a comparative electrolyte composition (“DHPS”): [0273] “DHPS+AQ”: 0.4 M 7,8-dihydroxyphenazine-2-sulfonic acid, 0.1 M 2,6-dihydroxyanthraquinone, 0.95 M NaOH, 0.95 KOH [0274] “DHPS”: 0.5 M 7,8-dihydroxyphenazine-2-sulfonic acid, 1.0 M NaOH, 1.0 KOH

[0275] According to Faraday's law, a maximum capacity of 26.8 Ah/L is achievable. Electrolytes are pumped by peristaltic pumps (Drifton BT100-1 L, Cole Parmer Ismatec MCP and BVP Process IP 65) at a rate of 72 mL/min to the corresponding electrodes, respectively. The electrolyte reservoirs are purged with N.sub.2 gas for 1 h before start of charging and the inert atmosphere is maintained during the experiments.

[0276] Electrochemical testing is performed on a BaSyTec (BaSyTec GmbH, 89176 Asselfingen, Germany) or a Bio-Logic (Bio-Logic Science Instruments, Seyssinet-Pariset 38170, France) battery test system. In the beginning, polarization curves are obtained by galvanostatic discharging holds after potentiostatic charging to 1.6V (1.5 mA/cm.sup.2 current limitation). The cell is afterwards cycled potentiostatically (1.6-1.0V, 1.5 mA/cm.sup.2) for 5 cycles, followed by galvanostatic cycling with a current density of 20 mA/cm.sup.2 (1.7-1.0V).

[0277] The results are summarized in Table 1 below:

TABLE-US-00001 TABLE 1 Electrochemical performance data for the distinct electrolyte compositions used as negolyte. DHPS DHPS + AQ Cell resistance [Ωcm.sup.2] 5.8 4.6 Maximum performance [mW/cm.sup.2] 92 105 RTE [%] 80% 83% Average discharging voltage [V] 1.24 1.29 Average charging voltage [V] 1.48 1.49

[0278] These data show that the electrolyte composition of the present invention is superior to a comparative electrolyte composition comprising only a phenazine (derivative) as redox active compound.

Example 2

[0279] Next, further electrolyte compositions according to the present invention were tested with (i) DHPS (as first redox active compound) and (ii) different non-phenazine second redox active compounds as described in the following.

Flow-Through Cells (FT Cell):

[0280] For electrochemical characterization, a small laboratory cell is used. A graphite felt (with an area of 6 cm.sup.2, 6 mm in thickness, supplier: SGL Sigracell GFA 6EA) in combination with a bipolar plate (4.1 cm×4.1 cm, SGL Sigracell TF6) is employed as both the positive and negative electrode. A cation exchange membrane (630K or 620PE, supplier: fumatech) is used to separate the positive and negative electrolytes. The membrane is conditioned in an aqueous solution of 0.5 M base (KOH/NaOH=1:1) for at least 150 h prior to each test. As anolyte and catholyte, the aqueous solutions according to table 2 are used. The pH-values were adjusted using a 1:1 mixture of NaOH/KOH. The catholyte is always employed in stoichiometric excess in order to obtain charge limitation solely out of the anolyte (see table 2) Both electrolytes are pumped by peristaltic pumps (Drifton BT100-1 L, Cole Parmer Ismatec MCP and BVP Process IP 65) at a rate of 24 mL/min to the corresponding electrodes, respectively. The electrolyte reservoirs are purged with N.sub.2 gas for 1 h before start of charging and the inert atmosphere is maintained during the course of the experiments.

TABLE-US-00002 TABLE 2 Compositions of employed anolyte and catholyte aqueous solutions in Example 2. Anolyte composition Catholyte composition DHPS + 0.10M DHPS 0.29M Na.sub.2K.sub.2[Fe(CN).sub.6] Lawsone 0.03M Lawsone DHPS + 0.11M DHPS 0.53M Na.sub.2K.sub.2[Fe(CN).sub.6] Alizarin Red S 0.04M Alizarin Red S DHPS + 0.11M DHPS 0.30M Na.sub.2K.sub.2[Fe(CN).sub.6] Alizarin 0.04M Alizarin DHPS + 0.09M DHPS 0.29M Na.sub.2K.sub.2[Fe(CN).sub.6] Bislawsone 0.05M Bislawsone

Electrochemical Tests:

[0281] Electrochemical testing is performed on a BaSyTec (BaSyTec GmbH, 89176 Asselfingen, Germany) or a Bio-Logic (Bio-Logic Science Instruments, Seyssinet-Pariset 38170, France) battery test system. For galvanostatic cycling, the cell is charged at a current density of 25 mA/cm.sup.2 (FT) or 20 mA/cm.sup.2 (FB) up to 1.7 V and discharged at the same current density down to 1.0 or 0.8 V cut-off. A full potentiostatic cycle with voltage limitations of 1.6 V for charging and 1.0 or 0.8 V for discharging with <1.5 mA/cm.sup.2 current limitation is conducted in order to get maximum electrolyte exploitation and to calculate the accessible maximum charge per volume of used Phenazine electrolyte.

[0282] According to Faraday's law, a maximum capacity of 26.8 Ah/L is achievable. Electrolytes are pumped by peristaltic pumps (Drifton BT100-1 L, Cole Parmer Ismatec MCP and BVP Process IP 65) at a rate of 72 mL/min to the corresponding electrodes, respectively. The electrolyte reservoirs are purged with N.sub.2 gas for 1 h before start of charging and the inert atmosphere is maintained during the experiments.

[0283] The results are summarized in table 3:

TABLE-US-00003 TABLE 3 Electrochemical performance data for the distinct compositions, assigned to the respective anolyte solutions (RTE = round-trip efficiency, n.d. = not determined). DHPS DHPS + DHPS + DHPS + DHPS + DHPS + (Ex. 1) AQ (Ex. 1) Lawsone Alizarin Red S Alizarin Bislawsone Cell resistance 5.8 4.6 3.5 n.d. n.d. 3.4 [Ωcm.sup.2] Maximum 92 105 143 n.d. n.d. 120 performance [mW/cm.sup.2] RTE [%] 80 83 84 81 83 83 Average discharging 1.24 1.29 1.16 1.16 1.17 1.21 voltage [V] Average charging 1.48 1.49 1.36 1.40 1.39 1.02 voltage [V]

[0284] These data confirm that the electrolyte compositions of the present invention are superior to a comparative electrolyte composition comprising only one phenazine (derivative) as redox active compound by combining the first redox active compound with further exemplary non-phenazine second redox-active compounds.