The effect of cobalt on the electrochemical performance of β-nickel hydroxide electrodes

Crystalline beta-nickel hydroxide comprises of a periodic stacking of charge neutral nickel hydroxide layers. Translation or rotation of nickel hydroxide layers with respect to each other generates stacking faults while an intergrowth of one polymorphic modification in the other generates intef'Stratification. These changes generate structural disorder within the sample and the phases are designated as beta(bc)(bc-badly crystalline) nickel hydroxide. The structure, composition and morphology of these phases differ significantly compared to highly ordered crystalline beta-nickel hydroxide. Crystalline beta-nickel hydroxide exchanges 0.3e/Ni whereas stacking faulted beta-nickel hydroxide and beta(bc)-nickel hydroxide exchanges 0.8-0.9e/Ni. Inclusion of cobalt metal as a conducting additive during the electrode fabrication of pasted electrodes is expected to enhance the electrochemical performance of nickel hydroxide. In contrast to the literature reports, partial substitution of cobalt for graphite to highly ordered crystalline phase of beta-nickel hydroxide does not show any improvement in their electrochemical activity. Stacking faulted beta-nickel hydroxide, beta(bc)-nickel hydroxide and chemically substituted nickel hydroxide samples also does not show any enhancement in their reversible discharge capacity on inclusion of cobalt. This clearly demonstrates that the electrochemical activity is mainly dictated by the structural disorders at 25-30 degrees C. (c) 2008 Elsevier Ltd. All rights reserved.