DEGRADATION MECHANISMS OF NICKEL-OXIDE ELECTRODES IN ZINC NICKEL-OXIDE CELLS WITH LOW-ZINC-SOLUBILITY ELECTROLYTES

Nickel oxide electrodes that suffered capacity degradation during exte nded cycling in zinc/nickel oxide cells were examined by a variety of chemical and physical techniques. Nickel hydroxyzincates, which have b een speculated to cause such capacity degradation, were also examined. Powder X-ray diffraction experiments indicated that the intersheet di stance between layers of turbostratic nickel hydroxide increased when zinc was incorporated. Photoelectron spectra (XPS) showed that this ma terial is probably a mixture of Ni(OH)(2) and ZnO or Zn(OH)(2). Raman spectroscopy data also supported this conclusion. XPS indicated that t he form of zinc in degraded-nickel oxide electrodes is probably ZnO or Zn(OH)(2). Significant increases in resistivity were found in cycled nickel oxide electrodes, and optical microscopy provided visible evide nce of mechanical damage during cycling. These results suggest that th e observed capacity degradation was largely mechanical in nature, and not due to the formation of nickel-zinc double hydroxides, as had been reported by others. Cell-cycling experiments indicated that the mecha nical degradation is largely irreversible.