Degradation mechanisms of nickel oxide electrodes in zinc/nickel oxide cells with low-zinc-solubility electrolytes

Nickel oxide electrodes that suffered capacity degradation during extended cycling in zinc/nickel oxide cells were examined by a variety of chemical and physical techniques. Nickel hydroxyzincates, which have been speculated to cause such capacity degradation, were also examined. Powder X-ray diffraction experiments indicated that the intersheet distance between layers of turbostratic nickel hydroxide increased when zinc was incorporated. Photoelectron spectra (XPS) showed that this material is probably a mixture of NiOH)₂ and ZnO or Zn(OH)₂. Raman spectroscopy data also supported this conclusion. XPS indicated that the 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 evidence of mechanical damage during cycling. These results suggest that the 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 mechanical degradation is largely irreversible.