Aging in chemically prepared divalent silver oxide electrodes for silver/zinc reserve batteries

The instability of silver(II) oxide electrodes used in silver/zinc reserve batteries is the well known cause of capacity loss and delayed activation i n reserve batteries after they are stored in the dry, unactivated state fur extended periods of time. Metal contaminants in sintered/ electroformed el ectrodes destabilize the oxide and the solid state reaction between AgO and elemental silver results in the formation of the lower capacity monovalent oxide Ag2O. Chemically prepared (CP) AgO can be used to avoid the metal co ntaminants and to minimize the interfacial contact area between AgO and Ag, thus minimizing the affects of aging on the electrodes. Electrodes were fa bricated with CP AgO and polytetrafluoroethylene (PTFE) binder and expanded silver metal current collectors. Experimentally, both electrode active mat erial compacts (AgO and binder only) and electrodes complete with AgO/binde r and silver current collector were tested to evaluate the influence of the current collector on aging. The electrode samples: were discharged at a co nstant rate of 50 mA cm(-2) before and after storage at 60 degreesC for 21 days as well as after storage at room ambient temperature conditions for 91 months. The results indicate that the affects of aging upon the AgO/binder compacts are insignificant for long term storage at room temperature. Howe ver, thermally accelerated aging at high temperature (60 degreesC) affects both transient and stabilized load voltage as well as capacity. In terms of capacity, the AgO/binder mix itself looses about 5% capacity after 21 days dry storage at 60 degreesC while electrodes complete with current collecto r loose about 8%. The 60% increase in capacity loss is attributed to the so lid state reaction between AgO and elemental silver. (C) 2001 Elsevier Scie nce B.V. All rights reserved.