Unravelling the critical role of electrochemical deposition parameters in determining cycling reversibility of alpha-nickel hydroxide in alkaline electrolyte

Abstract

Nickel hydroxide (α-Ni(OH)2) with large interlayer spacing is a promising pseudocapacitive material with high theoretical capacitance and good rate capability. However, the phase transition reversibility between α-Ni(OH)2 and γ-NiOOH in alkaline electrolyte upon charging/discharging is still vague. In this study, the cycling reversibility of α-Ni(OH)2 has been systematically investigated via adjusting the electrochemical deposition parameters. Structure characterizations and electrochemical analysis clearly revealed that the precursor concentration, deposition voltage and time significantly affect the mass loading of active material, the thicknesses of deposited films and their morphologies. Increasing the precursor concentration, deposition voltage and time lead to high mass loading, thick film and agglomerated nanosheets, which deteriorated the charge transfer and ion diffusion that lead to inferior cycling reversibility. In contrast, thin film with small mass loading and vertically-aligned nanosheets can be obtained upon deposition under low precursor concentration, small deposition voltage and short time, which shows facilitated charge transfer, ion diffusion and thereby high phase transition reversibility. Therefore, choosing appropriate deposition parameters would be beneficial to improve the electrode's cycling reversibility, which can effectively guide the development of more metal hydroxides with enhanced charge storage capability.