Phase Distribution and Electrochemical Properties of Al-Substituted Nickel Hydroxides

Abstract

Substituting small contents of aluminum for nickel in nickel hydroxides by a chemical coprecipitation and a\nsubsequent hydrothermal process can yield stable positive electrode materials. Detailed studies on the structural\nevolution were conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission\nelectron microscopy (TEM). The electrochemical properties of Al-substituted nickel hydroxides in alkaline\nsolution were examined by charge−discharge experiments and cyclic voltammetric (CV) measurements.\nHydrothermal treatments improved the crystallinity of Al-substituted nickel hydroxides, which exhibited much\nbetter electrode performance than the untreated samples. The sample with 10% (in mol) Al substitution having\na mixture structure with α- and β-phases after hydrothermal treatments showed the maximum discharge capacity\nof 333 mAh/g, corresponding to 1.46 exchanged electrons per Ni atom in α-phase nickel hydroxides. The\nphase distribution in the mixture has a great influence on the particle morphology, discharge capacity, potential\nplateau, and redox potentials of nickel hydroxide electrodes.