Aqueous redox flow batteries featuring improved cell design characteristics
This invention is directed to aqueous redox flow batteries comprising ionically charged redox active materials and separators, wherein the separator is less than about 100 microns and the flow battery is capable of operating with high energy densities and voltage efficiencies.
1. A flow battery, comprising:
(a) a first aqueous electrolyte comprising a first metal ligand coordination compound;
(b) a second aqueous electrolyte comprising a second metal ligand coordination compound;
(c) a separator positioned between said first and second aqueous electrolytes, the separator comprising an ionomer membrane; and
(d) a mobile ion;
wherein the separator has a thickness of less than 100 microns and each of the first and second metal ligand coordination compound, in both oxidized and reduced forms, and the ionomer membrane have an associated net charge that is the same sign.
2. The flow battery of claim 1 , wherein at least one of the first or second metal ligand coordination compound is of the formula M(L1) 3-x-y (L2) x (L3) y m , x and y are independently 0, 1, 2, or 3, such that 3-x-y is not less than zero;
m is −5, −4, −3, −2, −1, +1, +2, +3, +4, or +5; and
M is Al, Cr, Fe, or Ti; and
L1, L2, and L3 are each independently ascorbate, a catecholate, a pyrogallate, lactate, gluconate, or citrate.
3. The flow battery of claim 2 , wherein if x is 0, y is not 0.
4. The flow battery of claim 1 , wherein both of the first and second metal ligand coordination compounds comprise at least one ascorbate, catecholate, citrate, gluconate, lactate, or pyrogallate ligand.
5. The flow battery of claim 1 , wherein at least one of the metal ligand coordination compounds comprises at least one catecholate or pyrogallate ligand.
6. The flow battery of claim 1 , wherein at least one of the metal ligand coordination compounds comprises at least one ascorbate, citrate, gluconate, or lactate ligand.
7. The flow battery of claim 1 , wherein one of the metal ligand coordination compounds is a chromium, cobalt, iron, manganese, molybdenum, or ruthenium cyanide compound.
8. The flow battery of claim 7 , wherein one of the metal ligand coordination compounds is a chromium, iron, or manganese hexacyanide compound.
9. The flow battery of claim 1 , wherein the flow battery exhibits an open circuit potential of at least 0.8 V.
10. The flow battery of claim 9 , wherein the flow battery exhibits an open circuit potential of at least 0.8 V.
11. The flow battery of claim 10 , wherein the flow battery exhibits an open circuit potential of at least 1.0 V.
12. The flow battery of claim 11 , wherein the flow battery exhibits an open circuit potential of at least 1.2 V.
13. The flow battery of claim 12 , wherein the flow battery exhibits an open circuit potential of at least 1.4 V.
14. The flow battery of claim 1 , wherein at least one of the first or the second metal ligand coordination compounds is present in its respective electrolyte at a concentration of at least about 0.75 M.
15. The flow battery of claim 1 , wherein the energy density of the electrolytes is at least about 10 Wh/L.
16. The flow battery of claim 15 , wherein the energy density of the electrolytes is at least about 20 Wh/L.
17. The flow battery of claim 16 , wherein the energy density of the electrolytes is at least about 30 Wh/L.
18. The flow battery of claim 1 , further comprising at least one electrode in each of the aqueous electrolytes, wherein at least one of the electrodes presents a surface of an allotrope of carbon to the respective electrolyte.
19. The flow battery of claim 1 , wherein each electrolyte has a pH in a range of about 1 to about 13.
20. The flow battery of claim 1 , wherein the mobile ion comprises one or more of Li + , K + , Na + , Mg 2+ , Ca 2+ , Sr 2+ , Cl − , Br − , I − , OH − or a combination thereof.
21. The flow battery of claim 1 , wherein either the first or second active material diffuses through the separator at a rate of less than about 1×10 −5 mol/cm 2 -day.
22. The flow battery of claim 1 , which when operating, the molar flux of either the first or second active metal ligand coordination compound passing through the membrane is less than about 3% of the total molar flux of all ions passing through the ionomer membrane.
23. The flow battery of claim 1 , wherein the separator has a thickness of less than 50 microns.
24. The flow battery of claim 23 , wherein the separator has a thickness of less than 35 microns.
25. The flow battery of claim 24 , wherein the separator has a thickness of less than 25 microns.
26. The flow battery of claim 1 , wherein the flow battery is capable of operating, or is operating, with a current density greater than 50 mA/cm 2 while exhibiting a round trip voltage efficiency greater than 70%.
27. The flow battery of claim 26 , wherein the flow battery is capable of operating, or is operating, with a current density greater than 100 mA/cm 2 while exhibiting a round trip voltage efficiency greater than 70%.
28. The flow battery of claim 27 , wherein the flow battery is capable of operating, or is operating, with a current density greater than 200 mA/cm 2 while exhibiting a round trip voltage efficiency greater than 70%.