Patent ID: 8741455

Claim:
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.