The effect of tap density on the reversible charge storage capacity of nickel hydroxide electrodes

Abstract

β-Nickel hydroxide crystallizes in brucite structure with a stacking of charge neutral Ni(OH) 2 layers represented by AbC. A and C represent the hydroxide ions while b denotes the nickel ion. Crystalline nickel hydroxide having ideal composition will have the stacking sequence of AbC AbC AbC … . When the stacking sequence of nickel hydroxide is different from that of the ideal i.e. AbC AbC BcA …, then the sample is stacking faulted. Highly disordered β bc-nickel hydroxide comprises of an intergrowth of α-phase of nickel hydroxide in β-nickel hydroxide. These disorders introduce a significant changes in their structure composition and morphological features in contrast to crystalline phase of β-nickel hydroxide. The tap densities of all these nickel hydroxide samples were investigated. Electrochemical performance of crystalline phase β-nickel hydroxide with high tap density exchanges 0.3 e/Ni while nickel hydroxide samples with stacking disorder or compositional disorder exchanges 0.8–0.9 e/Ni. These samples have lower tap densities compared to crystalline β-nickel hydroxide. The results clearly show that the better electrochemical activity is mainly dictated by the structural disorder and is not associated to tap density of nickel hydroxide.