Basic studies on nickel-zinc batteries. Final report, September 29, 1978-November 28, 1979

Abstract

Experiments were conducted with an especially constructed, single-pore electrode designed to examine transport and electrochemical processes. Both the zinc and nickel electrodes were studied with the analog pore having an electrode-electrolyte spacing of only 20 ..mu..m. The primary goal was to provide information for nickel-zinc battery development. In situ and postmortem microscopic examinations were conducted to identify surface structural changes in terms of the influence of local current density gradations that arise under the diffusional limitations in small pores. With the zinc electrode, four major phenomena were examined that could possibly develop in commercial Ni-Zn cells: under discharge, four separate reaction fronts were found to move into the pore with 10M KOH, saturated ZnO in the following order: a front marked by the dissolution of zinc, a precipitation of gray ZnO, precipitation of black ZnO, and a solution of ZnO. Zinc dendrite growth was always found to be preceded by hydrogen gas formation under conditions of galvanostatic charging. Movement of zinc fragments by an electrochemical displacement was found to occur toward the anode at about 2 x 10/sup -4/ cm s/sup -1/ at 1000 mA cm/sup -2/. After severe electrolysis between two zinc electrodes, spontaneous growth of mossy zinc occurredmore » at open circuit on the electrode that had previously been the cathode. This process can be identified with perturbations of the hydroxide ion concentration in the pore. With the nickel electrode, exfoliation of the reactive layer on the nickel could be seen after dismantling single-pore cells after 150 cycles. After the 40th cycle, during a prolonged cycling to 150 cyles, a change in the discharge slope was noted, which remained the same thereafter. At the same time, a loss in capacity occurred. 37 figures, 4 tables.« less