An asymmetric hybrid nonaqueous energy storage cell

A nonaqueous asymmetric electrochemical cell technology is presented where the positive electrode stores charge through a reversible nonfaradaic or ps eudocapacitive reaction of anions on the surface of an activated carbon pos itive electrode. The negative electrode is a crystalline intercalation comp ound which supports the fast reversible intercalation of lithium ions. Usin g a positive electrode material of activated carbon and newly developed neg ative electrode material of nanostructured Li4Ti5O12 we obtain a cell which exhibits a sloping voltage profile from 3 to 1.5 V, 90% capacity utilizati on at 10C charge/discharge rates, and 10-15% capacity loss after 5000 cycle s. Electrolyte oxidation on the activated carbon positive electrode was cha racterized in a Li metal asymmetric hybrid cell by cyclic voltammetry. Oxid ation during the anodic scan was found to decrease significantly after surf ace passivation at high voltage and elevated temperatures. We also introduc e the asymmetric hybrid technology in a bonded flat plate plastic cell conf iguration where packaged energy densities were calculated to be in excess o f 20 Wh/kg. In addition, a practical method for three-electrode analysis of Li cells by use of a Ag quasi-reference electrode wire is discussed. (C) 2 001 Telcordia Technologies.