Rebalancing electrolyte concentration in flow battery using pressure differential

1. A method of rebalancing electrolyte concentrations in a flow battery, the method comprising:

(a) providing a flow battery that includes an electrochemical cell having first and second half-cells and an ion-exchange membrane separator there between, a first electrolyte circulable through the first half-cell and a second electrolyte circulable through the second half-cell, the first and second electrolytes including one or more types of electrochemically active species dissolved therein; and

(b) selectively establishing a fluid pressure differential across the ion-exchange membrane separator for a controlled amount of time to urge a concentration imbalance of the electrochemically active species between the first and second electrolytes toward a concentration balance, wherein establishing the fluid pressure differential is in response to the concentration imbalance.

2. The method as recited in claim 1 , wherein said step (b) includes establishing the fluid pressure differential according to a model of electrolyte flux through the ion-exchange membrane separator.

3. The method as recited in claim 1 , wherein said step (b) includes establishing the fluid pressure differential by using unequal flow rates between the first and second electrolytes in the flow battery.

4. The method as recited in claim 3 , wherein the flow rate of a less concentrated one of the first and second electrolytes is greater than the flow rate of a more concentrated one of first and second electrolytes, with respect to the concentrations of the one or more types of electrochemically active species.

5. The method as recited in claim 1 , wherein said step (b) includes establishing the fluid pressure differential with respect to electrolyte flux through the ion-exchange membrane separator.

6. The method as recited in claim 1 , wherein the active specie in first electrolyte is V(ii)/V(iii) and the active specie in second electrolyte is V(iv)/V(v).

7. A flow battery comprising:

an electrochemical cell having first and second half-cells and an ion-exchange membrane separator there between;

a first electrolyte circulable through the first half-cell;

a second electrolyte circulable through the second half-cell, the first and second electrolytes including one or more types of electrochemically active species dissolved therein;

a supply/storage system external of the electrochemical cell, the supply/storage system including first and second vessels, fluid lines connecting the first and second vessels to, respectively, the first and second half-cells, a plurality of pumps operable to circulate the first and second electrolytes, and a plurality of control valves operable to control flow of the first and second electrolytes; and

a controller connected to control operation of at least the supply/storage system, the controller configured to control the supply/storage system to selectively establish a fluid pressure differential across the ion-exchange membrane separator for a controlled amount of time to urge a concentration imbalance of the electrochemically active species between the first and second electrolytes toward a concentration balance.

8. The flow battery as recited in claim 7 , wherein the controller is configured to establish the fluid pressure differential in response to the concentration imbalance.

9. The flow battery as recited in claim 7 , wherein the controller is configured to establish the fluid pressure differential according to a model of electrolyte flux through the ion-exchange membrane separator.

10. The flow battery as recited in claim 7 , wherein the controller is configured to establish the fluid pressure differential establishing unequal flow rates between the first and second electrolytes.

11. The flow battery as recited in claim 10 , wherein the controller is configured to establish the flow rate of a less concentrated one of the first and second electrolytes to be greater than the flow rate of a more concentrated one of first and second electrolytes, with respect to the concentrations of the one or more types of electrochemically active species.

12. The flow battery as recited in claim 7 , wherein the controller is configured to establish the fluid pressure differential with respect to electrolyte flux through the ion-exchange membrane separator.

13. The flow battery as recited in claim 7 , wherein the active specie in first electrolyte is V(ii)/V(iii) and the active specie in second electrolyte is V(iv)/V(v).

14. A method of rebalancing electrolyte state-of-charge in a flow battery, the method comprising:

operating a flow battery to establish a controlled fluid pressure differential across an ion-exchange membrane separator such that there is a higher fluid pressure in a first half-cell than in a second half-cell of the flow battery to, by pressure-driven osmosis, dilute the more concentrated solution in the second half-cell and concentrate the more dilute solution in the first half-cell with respect to an electrochemically active specie dissolved in the solutions.

15. The method as recited in claim 14 , wherein operating the flow battery includes establishing the controlled fluid pressure differential in response to a concentration imbalance between the first solution, which is an anolyte solution, and the second solution, which is a catholyte solution.

16. The method as recited in claim 14 , wherein operating the flow battery includes establishing the controlled fluid pressure differential with respect to electrolyte flux through the ion-exchange membrane separator.

17. The method as recited in claim 14 , wherein the active specie in first solution is V(ii)/V(iii) and the active specie in second solution is V(iv)/V(v).

18. The method as recited in claim 1 , wherein said step (b) includes establishing the fluid pressure differential by using unequal flow rates between the first and second electrolytes in the flow battery such that the fluid pressure of a less concentrated one of the first and second electrolytes is greater than the fluid pressure of a more concentrated one of first and second electrolytes, with respect to the concentrations of the one or more types of electrochemically active species.

19. The method as recited in claim 18 , wherein the less concentrated one of the first and second electrolytes is an anolyte and the more concentrated one of first and second electrolytes is a catholyte.

20. The flow battery as recited in claim 7 , wherein the controller is configured to establish the fluid pressure differential by using unequal flow rates between the first and second electrolytes in the flow battery such that the fluid pressure of a less concentrated one of the first and second electrolytes is greater than the fluid pressure of a more concentrated one of first and second electrolytes, with respect to the concentrations of the one or more types of electrochemically active species.

21. The flow battery as recited in claim 20 , wherein the less concentrated one of the first and second electrolytes is an anolyte and the more concentrated one of first and second electrolytes is a catholyte.

22. The method as recited in claim 14 , wherein the establishing of the fluid pressure differential includes using unequal flow rates between first and second electrolytes in the flow battery such that the fluid pressure of a less concentrated one of the first and second electrolytes is greater than the fluid pressure of a more concentrated one of first and second electrolytes, with respect to the concentrations of the one or more types of electrochemically active species.

23. The method as recited in claim 22 , wherein the less concentrated one of the first and second electrolytes is an anolyte and the more concentrated one of first and second electrolytes is a catholyte.