ELECTROCHEMICAL BALANCE IN A VANADIUM FLOW BATTERY

1 . A flow cell system, comprising:

a stack of flow cells;

a plurality of electrolyte storage tanks coupled to provide electrolyte to the stack and to receive electrolyte from the stack; and

a rebalance system coupled to adjust the electrolyte stored in the plurality of electrolyte storage tanks.

2 . The flow cell system of claim 1 , wherein the rebalance system introduces a reducing agent to the electrolyte to correct a positive imbalance.

3 . The flow cell system of claim 2 , wherein the reducing agent includes a mild organic reducing agent comprising at least one of alcohol, methanol, ethylene glycol, glycerol, organic acid, formic acid, oxalic acid and glycerol.

4 . The flow cell system of claim 1 , wherein the rebalance system introduces oxidation to correct a negative imbalance.

5 . The flow cell system of claim 4 , wherein the rebalance system includes an air pump coupled to an injector tube.

6 . The flow cell system of claim 4 , wherein the rebalance system includes a Venturi pump, and a valve coupled to an injector tube.

7 . The flow cell system of claim 4 , wherein the rebalance system introduces an oxidizing agent to the electrolyte to correct the negative imbalance.

8 . The flow cell system of claim 7 , wherein the oxidizing agent is comprised of at least one of oxygen, hydrogen peroxide, chlorine, or vanadium ion in oxidation state 5+ or 4+

9 . The flow cell system of claim 1 , wherein electrolyte having V 4+ /V 5+ are exchanged with electrolyte having V 2+ /V 3+ to correct the positive imbalance.

10 . The flow cell system of claim 1 , wherein electrolyte having V 2+ /V 3+ are exchanged with electrolyte having V 4+ /V 5+ to correct the negative imbalance.

11 . The flow cell system of claim 1 , wherein the rebalance system is controlled by a controller and integrated into a firmware.

12 . A method of rebalancing a positive imbalance in a flow cell system, comprising reducing excessive V 5+ .

13 . The method of claim 12 , wherein reducing the excessive V 5+ includes

introducing a reducing agent to electrolyte having V 4+ /V 5+ ;

reducing the excessive V 5+ ; and

adjusting molar amount of V 5+ to achieve rebalanced molar amount between V 2+ and V 5+ .

14 . The method of claim 13 , wherein the reducing agent includes a mild organic reducing agent, the mild organic reducing agent comprising at least one of alcohol, methanol, ethylene glycol, glycerol, organic acid, formic acid, oxalic acid and glycerol.

15 . The method of claim 12 , wherein reducing the excessive V 5+ includes

exchanging electrolyte having V 4+ /V 5+ with electrolyte having V 2+ /V 3+ ; and

adjusting molar amount of V 5+ to achieve rebalanced molar amount between V 2+ and V 5+ .

16 . A method of rebalancing a negative imbalance in a flow cell system, comprising oxidizing excessive V 2+ .

17 . The method of claim 16 , wherein oxidizing the excessive V 2+ includes

introducing an oxidizing agent to electrolyte having V 3+ /V 2+ ;

oxidizing the excessive V 2+ ; and

adjusting molar amount of V 2+ to achieve rebalanced molar amount between V 2+ and V 5+ .

18 . The method of claim 17 , wherein the oxidizing agent is comprised of at least one of oxygen gas, hydrogen peroxide, chlorine, or vanadium ions in oxidation state 5+ or 4+

19 . The method of claim 16 , wherein oxidizing the excessive V 2+ includes

introducing air into the flow cell system;

oxidizing the excessive V 2+ ; and

adjusting molar amount of V 2+ to achieve the rebalanced molar amount between V 2+ and V 5+ .

20 . The method of claim 16 , wherein the oxidation of the excessive V 2+ includes

exchanging electrolyte having V 2+ /V 3+ with electrolyte having V 4+ /V 5+ ; and

adjusting molar amount of V 2+ to achieve the rebalanced molar amount between V 2+ and V 5+ .