Phase Distribution and Electrochemical Properties of Al-Substituted Nickel Hydroxides

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