Synthesis and electrochemical performance of mixed phase α/β nickel hydroxide by codoping with Ca2+ and PO4 3−

Abstract

Nickel hydroxide with a unique mixed phase α/β-Ni(OH)2 was prepared by partially substituting Ca2+ for Ni2+ with supersonic co-precipitating method firstly. The crystal structure and morphology of the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The results show that the Ca-substituted Ni(OH)2 by adding PO4 3− is α/β mixed phase, while the undoped Ni(OH)2 and the Ca-substituted Ni(OH)2 without adding PO4 3− are pure β phase. Furthermore, the Ca-substituted Ni(OH)2 by adding PO4 3− exhibits irregular shape and contains many intercalated water molecules and anions as proven by SEM and FT-IR. Meanwhile, the prepared samples were added into micro-sized beta nickel hydroxide to form biphase electrode materials for Ni-MH battery. The electrochemical performances of the biphase electrodes were characterized by cyclic voltammetry (CV) and charge/discharge tests. The results demonstrate that the biphase electrode with mixed phase α/β-Ni(OH)2 exhibits higher electrochemical activity, better electrochemical reversibility and charge efficient, higher discharge potential, and better cyclic stability. The specific discharge capacity of Ca-substituted α/β-Ni(OH)2 electrode can retain 271.7 and 238 mAh/g after 80 cycles at 0.2 and 0.5 C, respectively. This indicates that it may be a promising positive active material for alkaline secondary batteries. The results reported in this work may be useful for the designing and synthesizing of nickel hydroxide materials with superior performance.