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

Crystalline β-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 interstratification. These changes generate structural disorder within the sample and the phases are designated as βbc (bc-badly crystalline) nickel hydroxide. The structure, composition and morphology of these phases differ significantly compared to highly ordered crystalline β-nickel hydroxide. Crystalline β-nickel hydroxide exchanges 0.3e/Ni whereas stacking faulted β-nickel hydroxide and βbc-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 β-nickel hydroxide does not show any improvement in their electrochemical activity. Stacking faulted β-nickel hydroxide, βbc-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 °C.