Microstructure and Electrochemical Properties of Al-Substituted Nickel Hydroxides Modified with CoOOH Nanoparticles

Abstract

Aluminum-substituted α-phase nickel hydroxide (Al−α-Ni(OH)2) microspheres with high structural stability are synthesized, and their surface modification by CoOOH nanoparticles is made subsequently in order to improve their electrochemical performance. The morphology, microstructure, and chemical state of the Al−α-Ni(OH)2 microspheres, before and after coating, are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectra (FTIR). It is found that CoOOH nanoparticles with a rod-like morphology are either dispersed randomly on the surface or intercalated between nanosheets of the Al−α-Ni(OH)2 microspheres. The effect of CoOOH nanoparticles on the electrochemical performance of Al−α-Ni(OH)2 microspheres is investigated by galvanostatic charge−discharge experiments and cyclic voltammetry (CV). It is demonstrated that the Al−α-Ni(OH)2 microspheres, coated with 7 wt % CoOOH nanoparticles, have an enhanced discharge capacity, high-rate discharge ability, discharge potential plateau, and cycle stability. The improvement of the electrochemical performance of Al−α-Ni(OH)2 microspheres is mainly attributed to formation of highly conductive CoOOH nanoparticles on the surface of Al−α-Ni(OH)2 microspheres and good electrochemical accessibility of the microspherical aggregates of Al−α-Ni(OH)2 nanosheets, which result in the good reversibility and high electrochemical activity of the positive materials.