Materials for flow battery energy storage and methods of using

1. A catholyte mixture comprising:

a mediator having a first redox potential;

an cathode material having a second redox potential that is less than the first redox potential; and

a cation, wherein:

the cathode material is in a form comprising a solid particulate,

the cathode material has a first condition comprising a first oxidation state, where the cation is intercalated within the cathode material,

the cathode material has a second condition comprising a second oxidation state that is higher than the first oxidation state, where the cathode material is substantially free of the cation,

the mediator has a first condition comprising a third oxidation state and a second condition comprising a fourth oxidation state that is higher than the third oxidation state,

the cathode material is capable of being reversibly cycled between the first condition of the cathode material and the second condition of the cathode material, and

the mediator is capable of being reversibly cycled between its first condition and its second condition.

2. The catholyte mixture of claim 1 , wherein the mediator comprises an organic radical group.

3. The catholyte mixture of claim 2 , wherein the organic radical group comprises a nitroxide group.

4. The catholyte mixture of claim 1 , wherein the mediator has a molecular weight less than 10,000 g/mol.

5. The catholyte mixture of claim 1 , wherein the mediator comprises at least one of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, (1-oxyl-2,2,6,6-tetramethyl-4-hydroxypiperidine), a nitronyl nitroxide, a azephenylenyl, a percholorophenylmethyl radical, tris(2,4,6-trichlorophenyl)methyl radical, poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate), or poly[4-(nitronylnitroxyl)styrene].

6. The catholyte mixture of claim 3 , wherein, when in the first condition of the mediator, the mediator comprises

and when in the second condition of the mediator, the mediator comprises

7. The catholyte mixture of claim 3 , wherein the mediator includes a structure comprising at least one of

8. The catholyte mixture of claim 1 , wherein the cathode material further comprises a gel.

9. The catholyte mixture of claim 1 , wherein the solid particulate has a particle size between 1 nanometer and 1000 micrometers.

10. The catholyte mixture of claim 1 , wherein the cathode material comprises at least one of cobalt, nickel, manganese, aluminum, titanium, vanadium, or iron.

11. The catholyte mixture of claim 10 , wherein the cathode material further comprises at least one of an oxide or a phosphate.

12. The catholyte mixture of claim 11 , wherein the cathode material comprises at least one of a cobalt oxide, a nickel cobalt oxide, a manganese cobalt oxide, or an iron phosphate.

13. The catholyte mixture of claim 11 , wherein the cathode material comprises at least one of CoO 2 , FePO 4 , or Fe 0.5 Mn 0.5 PO 4 .

14. The catholyte mixture of claim 1 , wherein the cation comprises at least one of a Group 1 element, a Group 2 element, or a Group 13 element.

15. The catholyte mixture of claim 1 , wherein the cation comprises at least one of lithium, magnesium, aluminum, or beryllium.

16. The catholyte mixture of claim 1 , further comprising a salt, wherein the salt provides at least a portion of the cation.

17. The catholyte mixture of claim 16 , wherein the salt comprises at least one of LiPF 6 , LiBF 4 , or LiClO 4 .

18. The catholyte mixture of claim 16 , further comprising a solvent, wherein the mediator and the salt are substantially soluble in the solvent.

19. The catholyte mixture of claim 18 , wherein the mixture has an energy storage density greater than or equal to 300 Wh/L, when the cathode material is in the second condition of the cathode material, and the mediator is in the second condition of the mediator.

20. A method comprising transferring energy to a catholyte mixture by applying a voltage to the catholyte mixture, wherein:

the catholyte mixture comprises a mediator having a first redox potential, an cathode material having a second redox potential that is less than the first redox potential, a cation, and a solvent,

the cathode material is in a form comprising a solid particulate,

the voltage transforms the mediator from a first condition having a first oxidation state to a second condition having a second oxidation state that is higher than the first oxidation state, and

when in the second condition, the mediator oxidizes the cathode material, thereby transforming the cathode material from a first condition comprising a third oxidation state where the cation is intercalated within the cathode material, to a second condition comprising a fourth oxidation state that is higher than the third oxidation state where the cathode material is substantially free of the cation,

the cathode material is capable of being reversibly cycled between the first condition of the cathode material and the second condition of the cathode material, and

the mediator is capable of being reversibly cycled between the first condition of the mediator and the second condition of the mediator.

21. The method of claim 20 , further comprising applying a load to the catholyte mixture, wherein the load transforms the cathode material from the second condition of the cathode material to the first condition of the cathode material.