Effects of γ-CoOOH coating on the high-temperature and high-rate performances of spherical nickel hydroxide electrodes

To improve the high-temperature and high-rate performances of nickel hydroxide electrodes in nickel-metal hydride (Ni/MH) batteries, γ-CoOOH is coated onto spherical Ni(OH)2 through surface modification. X-ray diffraction, scanning electron microscopy with energy dispersive X-ray, and X-ray photoelectron spectroscopy are used to characterize the synthesized products. The effects of γ-CoOOH on the electrochemical performance of nickel electrodes are investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and a charge/discharge test. It is found that the spherical γ-CoOOH-coated Ni(OH)2 electrode without adding any conductive additives exhibits superior electrode properties including excellent high-temperature and high-rate discharge abilities, and superior cycling reversibility. These performance improvements are ascribed to the enhancement of oxygen evolution over-potential, slower oxygen evolution rate and lower charge transfer resistance resulting from the high conductivity coating of γ-CoOOH.