High-energy-density, aqueous, metal-polyiodide redox flow batteries
Improved metal-based redox flow batteries (RFBs) can utilize a metal and a divalent cation of the metal (M 2+ ) as an active redox couple for a first electrode and electrolyte, respectively, in a first half-cell. For example, the metal can be Zn. The RFBs can also utilize a second electrolyte having I − , anions of I x (for x≧3), or both in an aqueous solution, wherein the I − and the anions of I x (for x≧3) compose an active redox couple in a second half-cell.
1. A redox flow battery (RFB) comprising:
a first electrolyte comprising Zn 2+ in an aqueous solution and a first electrode comprising Zn, wherein the Zn and the Zn 2+ compose a first active redox couple at a first half-cell;
a second electrolyte comprising I − , anions of I x (x≧3), or both in the aqueous solution, wherein the I − and the anions of I x compose a second active redox couple at a second half-cell; and
a membrane or separator between the first and second half-cells;
wherein the RFB has an energy density (based on the positive electrolyte) greater than 60 Wh/L and the aqueous solution contains substantially no I 2 .
2. The RFB of claim 1 , wherein the aqueous solution has a pH greater than 3.
3. The RFB of claim 1 , wherein the first electrode comprises the Zn on a porous, conductive material.
4. The RFB of claim 3 , wherein the porous conductive material comprises conductive carbon, graphite fibers, graphene, or a metallic material.
5. The RFB of claim 1 , wherein the first electrode comprises M on a dense solid conductive material.
6. The RFB of claim 1 , wherein the membrane comprises an ion-exchange membrane, or a solid-state membrane.
7. The RFB of claim 1 , wherein the anions of I x comprise I 3 − .
8. The RFB of claim 1 , wherein the anions of I x comprise I 4 − .
9. The RFB of claim 1 , wherein the anions of I x comprise I 6 − .
10. The RFB of claim 1 , wherein the anions of I x comprise I − 2n+p , wherein n and p are positive integers and 1≦p≦4.
11. The RFB of claim 1 , wherein the separator comprises a microporous separator.