The cause of residual capacity in nickel oxyhydroxide electrodes

Abstract

Chemical analysis, X-ray diffraction and linear sweep voltammetry have been used to examine the cause of the secondary discharge plateau associated with the inefficient reduction of sintered plate NiOOH electrodes. The techniques confirm the presence ofβ-Ni(OH)2,β-NiOOH andγ-NiOOH in electrodes after failure at high rates. No evidence was obtained in support of the plateau arising from a new intrinsically less active compound. In disagreement with previous claims theγ-phase formed on overcharging was found to discharge as efficiently as theβ-phase. Inefficient discharge is considered to be caused by an insulating barrier layer ofβ-Ni(OH)2 between the charged active material and the current collector. The complex non-linear current-potential behaviour, exhibited by the secondary discharge plateau near −200 mV, is considered to be caused by the removal of Ni3+ or Ni3+ defects from the electronically conducting Ni(OH)2 prior to returning it to the poorly conducting divalent state.