Air-breathing aqueous sulfur rechargeable batteries

1. An electrochemical apparatus comprising:

a catholyte comprising at least one metal salt dissolved in water, thereby providing at least one metal ion;

an anolyte comprising a polysulfide solution; and

a separator, disposed between the anolyte and the catholyte, permeable to the at least one metal ion,

wherein the catholyte, the anolyte, and/or the separator are configured such that:

during a charging process of the electrochemical apparatus, oxygen is generated in the catholyte, the polysulfide in the polysulfide solution undergoes a reduction reaction in the anolyte, and the at least one metal ion moves from the catholyte to the anolyte, and

during a discharging process of the apparatus, the oxygen is consumed in the catholyte, the polysulfide oxidizes in the anolyte, and the at least one metal ion moves from the anolyte to the catholyte.

2. The apparatus of claim 1 , wherein the at least one metal salt comprises Li 2 SO 4 and the metal ion comprises Li + ion.

3. The apparatus of claim 2 , wherein the separator comprises a lithium superionic conductor.

4. The apparatus of claim 1 , wherein the at least one metal salt comprises Na 2 SO 4 and the metal ion comprises Na + ion.

5. The apparatus of claim 4 , wherein the separator comprises a sodium superionic conductor.

6. The apparatus of claim 1 , wherein the catholyte is acidic and the apparatus has a cell voltage of about 1.26 V to about 1.68 V.

7. The apparatus of claim 1 , wherein the polysulfide solution comprises a solution of at least one of a lithium polysulfide or a sodium polysulfide.

8. The apparatus of claim 1 , wherein the catholyte is alkaline and the apparatus has a cell voltage of about 0.85 V to about 1.26 V.

9. The apparatus of claim 1 , wherein the pH value of the anolyte is substantially equal to or greater than 12.

10. The apparatus of claim 1 , wherein the anolyte further comprises at least one of LiOH or NaOH to increase the pH value of the anolyte.

11. The apparatus of claim 1 , wherein at least one of the catholyte or the anolyte comprises a percolating network of an electronic conductor.

12. The apparatus of claim 1 , wherein a level of reduction of the polysulfide after the reduction reaction is no more than S 4 2− .

13. The apparatus of claim 1 , further comprising a cathode current collector operably coupled to the catholyte and an anode current collector operably coupled to the anolyte.

14. The apparatus of claim 13 , wherein the cathode current collector comprises a carbon-based material.

15. The apparatus of claim 13 , wherein the anode current collector comprises at least one of a transition metal, a transition metal alloy, graphite, hard carbon, carbon fiber, reticulated carbon, disordered carbon, carbon black, fullerene, graphene, graphene oxide, transition metal oxide, reduced titanium oxide, or indium tin oxide.

16. The apparatus of claim 13 , wherein at least one of the cathode current collector or the anode current collector comprises a corrugated plate, a fiber weave, an open cell foam, sintered particulates, or a packed particle bed.

17. The apparatus of claim 13 , wherein at least one of the cathode current collector or the anode current collector comprises a redox mediator to increase a charge transfer rate within the at least one of the cathode current collector or the anode current collector.

18. The apparatus of claim 13 , wherein the cathode current collector comprises an oxygen evolution reaction (OER) catalyst to decrease the over-potential for oxygen gas formation.

19. The apparatus of claim 18 , wherein the OER catalyst comprises at least one IrO 2 or RuO 2 .

20. The apparatus of claim 13 , wherein the cathode current collector comprises an oxygen reduction reaction (ORR) catalyst to decrease the over-potential for oxygen reduction.

21. The apparatus of claim 20 , wherein the ORR catalyst comprises at least one of Pt black or Pt 3 Ni.

22. The apparatus of claim 1 , further comprising:

a catholyte chamber containing the catholyte;

a catholyte pump, operably coupled to the catholyte chamber, to transport the catholyte into and out of the catholyte chamber;

an anolyte chamber containing the anolyte; and

an anolyte pump, operably coupled to the anolyte chamber, to transport the anolyte into and out of the anolyte chamber so as to form a flow battery cell.

23. The apparatus of claim 1 , further comprising:

a gas pump, operably coupled to the catholyte, to provide an oxygen gas into the catholyte.

24. A method comprising:

charging the electrochemical apparatus of claim 1 by coupling the apparatus to an external circuit,

whereby oxygen is generated in the catholyte; and

the polysulfide is reduced in the polysulfide solution.

25. A method comprising:

discharging the electrochemical apparatus of claim 1 by coupling the apparatus to an external circuit,

whereby oxygen is consumed in the catholyte; and

the polysulfide is oxidized in the polysulfide solution.

26. The method of claim 24 , wherein the metal salt comprises Li 2 SO 4 and the metal ion comprises Li + ion.

27. The method of claim 26 , wherein the separator comprises a lithium superionic conductor.

28. The method of claim 24 , wherein the metal comprises Na 2 SO 4 and the metal ion comprises Na + ion.

29. The method of claim 28 , wherein the separator comprises a sodium superionic conductor.

30. The method of claim 24 , wherein catholyte is acidic and the apparatus has a cell voltage of about 1.26 V to about 1.68 V.

31. The method of claim 24 , wherein the polysulfide solution comprises a solution of at least one of Li 2 S or Na 2 S.

32. The method of claim 24 , wherein the catholyte is alkaline and the apparatus has a cell voltage of about 0.85 V to about 1.26 V.

33. The method of claim 24 , further comprising:

changing the pH value of the catholyte so as to change a cell voltage of the apparatus.

34. The method of claim 24 , wherein the pH value of the anolyte is substantially equal to or greater than 12.

35. The method of claim 24 , wherein the anolyte further comprises at least one of LiOH or NaOH to increase the pH value of the anolyte.

36. The method of claim 24 , wherein at least one of the catholyte or the anolyte comprises a percolating network of an electronic conductor.

37. The method of claim 24 , wherein a level of reduction of the polysulfide after the reduction reaction is no more than S 4 2− .

38. The method of claim 24 , wherein applying the voltage onto the apparatus comprises applying the voltage via a cathode current collector operably coupled to the catholyte and an anode current collector operably coupled to the anolyte.

39. The method of claim 38 , wherein the cathode current collector comprises a carbon-based material.

40. The method of claim 38 , wherein the anode current collector comprises at least one of a transition metal, a transition metal alloy, graphite, hard carbon, carbon fiber, reticulated carbon, disordered carbon, carbon black, fullerene, graphene, graphene oxide, transition metal oxide, reduced titanium oxide, or indium tin oxide.

41. The method of claim 38 , wherein at least one of the cathode current collector or the anode current collector comprises a corrugated plate, a fiber weave, an open cell foam, sintered particulates, or a packed particle bed.

42. The method of claim 38 , wherein at least one of the cathode current collector or the anode current collector comprises a redox mediator to increase a charge transfer rate within the at least one of the cathode current collector or the anode current collector.

43. The method of claim 38 , wherein the cathode current collector comprises an oxygen evolution reaction (OER) catalyst to decrease the over-potential for oxygen gas formation.

44. The method of claim 43 , wherein the OER catalyst comprises.

45. The method of claim 38 , wherein the cathode current collector comprises an oxygen reduction reaction (ORR) catalyst to decrease the over-potential for oxygen reduction.

46. The method of claim 45 , wherein the ORR catalyst comprises Pt black.

47. The method of claim 24 , further comprising:

pumping the catholyte into and out of a catholyte chamber; and

pumping the anolyte into and out of an anolyte chamber so as to form a flow battery cell.

48. The method of claim 24 , further comprising:

pumping an oxygen gas into the catholyte.

49. An energy storage system comprising one or more electrochemical apparatuses of claim 1 , and further comprising:

a catholyte chamber containing the catholyte;

a catholyte pump, operably coupled to the catholyte chamber, to transport the catholyte into and out of the catholyte chamber;

a catholyte current collector operably coupled to the catholyte;

an anolyte chamber containing the anolyte;

an anolyte pump, operably coupled to the anolyte chamber, to transport the anolyte into and out of the anolyte chamber;

an anolyte current collector operably coupled to the anolyte;

wherein the system is configured such that:

during the charging process of the apparatus, oxygen generated in the catholyte is released from the energy storage system, and the anolyte containing reduced polysulfide is pumped from the anolyte chamber to an anolyte storage chamber, and

during the discharging process of the apparatus, the oxygen is consumed in the catholyte, and stored anolyte containing reduced polysulfide is pumped from the anolyte storage chamber to the anolyte chamber and oxidized, whereby electrical energy is supplied to an external circuit.