ZINC ELECTRODE CYCLE-LIFE PERFORMANCE IN ALKALINE ELECTROLYTES HAVING REDUCED ZINC SPECIES SOLUBILITY

Electrolytes having 3.5 M hydroxide-ion concentration were tested in 1.35 Ah Zn/NiOOH cells to evaluate their ability to reduce the extent of zinc species migration and slow the rate of cell capacity decline. Alkaline-fluoride and alkaline-borate electrolytes, in which ZnO solubility is approximately 25% of that in standard 7.4 M KOH electrolyte, exhibited 0.09-0.14%/cycle zinc-electrode area loss, which may be compared to a value of 0.46%/cycle observed in standard electrolyte. In addition, no zinc penetration of the separator occurred in cells that employed alkaline-fluoride and alkaline-borate electrolytes, even when zinc-electrode overpotentials reached 290 mV at the end of charge. Less than 2% of the zinc remaining after cycling was electrochemically inactive.