Sodium ion based aqueous electrolyte electrochemical secondary energy storage device

1. A method of operating a hybrid aqueous energy storage device comprising an anode electrode, a cathode electrode, a separator, and a sodium containing aqueous electrolyte, the method comprising:

providing the storage device in which the cathode electrode comprises an active cathode electrode material comprising lithium manganate cubic spinel material having a formula Li x Mn 2-z Al z O 4 where 1≦x<1.1 and 0≦z<0.1;

deintercalating lithium ions from the active cathode electrode material during initial charging of the device to form a substantially lithium free cubic spinel λ-manganate active cathode electrode material;

reversibly intercalating sodium ions from the electrolyte into the active cathode electrode material during a subsequent discharge cycle to form a cubic spinel λ-manganate active cathode electrode material having a formula A y Mn 2-z Al z O 4 where A comprises at least 80 atomic percent Na, 0≦y<1, and 0≦z<0.1; and

reversibly deintercalating sodium ions from the active cathode electrode into the electrolyte during a subsequent charge cycle.

2. The method of claim 1 , wherein a cation concentration of the electrolyte is substantially constant during the subsequent discharge cycle and the subsequent charge cycle of the device.

3. The method of claim 1 , wherein the spinel λ-manganate active cathode electrode material has a formula Na y Mn 2 O 4 where 0≦y<1 during the subsequent discharge cycle and the subsequent charge cycle of the device.

4. The method of claim 1 , wherein the anode electrode comprises porous activated carbon, graphite, mesoporous carbon, carbon nanotubes, disordered carbon, Ti-oxide material, V-oxide material, phospho-olivine material, mesoporous ceramic material or a composite thereof.

5. The method of claim 1 , wherein the electrolyte comprises aqueous Na 2 SO 4 , NaNO 3 , NaClO 4 , Na 3 PO 4 , Na 2 CO 3 , NaCl, NaOH, or combination thereof.

6. The method of claim 1 , wherein the anode electrode comprises porous activated carbon and the electrolyte consists essentially of aqueous Na 2 SO 4 .

7. The method of claim 6 , wherein the device exhibits a specific energy of greater than 20 Wh per kg of active cathode material when cycled between potentials of 0.60 and 1.9 V in 1 M Na 2 SO 4 at C/10 rate or slower.

8. The method of claim 6 , wherein the device comprises an activated carbon anode material, and exhibits a specific energy of between 10 and 105 Wh per kg of active cathode material for a specific power of between 20 to 1000 W per kg of active cathode material at 23° C. at 0.1 C rate.

9. The method of claim 8 , wherein the device exhibits a specific energy of between 40 and 60 Wh per kg of active cathode material at −5 to 23° C. at 1 C rate.

10. The method of claim 6 , wherein the device exhibits greater than or equal to about 75 mAh per gram of active cathode material specific capacity with Na 2 SO 4 electrolyte.

11. The method of claim 1 , wherein the hybrid energy storage device operates between 5000 and 10000 cycles to full discharge with less than 20% loss of initial capacity.

12. The method of claim 1 , wherein a charge containing electrochemical double layer is formed near the surface of an anode electrode during device charging, and the active charged species in this electrochemical double layer comprises Na ions.

13. The method of claim 1 , wherein a partial charge transfer interaction occurs near the surface of a pseudocapacitive anode electrode during device charging, and the active charged species in this partial charge transfer interaction comprises Na ions.

14. The method of claim 1 , wherein the active cathode electrode material does not intercalate or deintercalate electrolyte anions during the subsequent discharge cycle and the subsequent charge cycle of the device.

15. The method of claim 1 , wherein the active cathode material only reversibly intercalates and deintercalates alkali cations and does not intercalate and deintercalate protons during the subsequent discharge cycle and the subsequent charge cycle of the device.

16. The method of claim 1 , wherein the cathode electrode further comprises a doped or undoped Na 0.44 MnO 2 active cathode electrode material in addition to the cubic spinel λ-manganate active cathode electrode material.

17. The method of claim 16 , wherein the cathode electrode comprises 80 to 90% active cathode material, 0 to 10% conductive additive, and 0 to 10% binder material, and the anode electrode comprises 80 to 90% active anode material, 0 to 10% conductive additive, and 0 to 10% binder material.

18. The method of claim 17 , wherein the conductive additive comprises one or more of carbon black, graphite, a non-reactive metal, and a conductive polymer, and the binder comprises one or more of PTFE, PVC, cellulose-based material, PVDF, or other non-reactive non-corroding polymer material.

19. The method of claim 17 , wherein the binder material for one or more of the cathode electrode and anode electrode comprises hydrated birnessite.

20. The method of claim 1 , wherein the substantially lithium free cubic spinel λ-manganate active cathode electrode material contains 0 to 5 atomic percent lithium.