Patent ID: 8137830

Claim:
A method of operating an electrochemical energy storage device, comprising charging a plurality of aqueous electrolyte electrochemical cells connected electrically in series, such that a charge storage capacity of an anode electrode in at least one of the plurality of cells is exceeded on charging, wherein water in the aqueous electrolyte electrolyzes to form hydrogen and OH − species at the anode electrode of the at least one of the plurality of cells when the charge storage capacity of the anode electrode of the at least one of the plurality of cells is exceeded on charging the at least one of the plurality of cells, wherein: each of the plurality of cells further comprises a cathode electrode; the charge storage capacity of the anode electrode is less than a charge storage capacity of the cathode electrode in each of the plurality of cells; each of the plurality of cells is a secondary hybrid aqueous energy storage cell; the cathode electrode in operation reversibly intercalates alkali metal cations; and the anode electrode is a capacitive electrode which stores charge through a nonfaradiac reaction of the alkali metal cations on a surface of the anode electrode or a pseudocapacitive electrode which undergoes a partial charge transfer surface interaction with the alkali metal cations on the surface of the anode electrode.