Co∕Yb Hydroxide Coating of Spherical Ni(OH)[sub 2] Cathode Materials for Ni–MH Batteries at Elevated Temperatures

Abstract

Cobalt/ytterbium hydroxide was used for surface coating of spherical to improve its high-temperature performance. The coated spherical was prepared by coprecipitation of hydroxide on the surface of spherical . The optimum coating content of ytterbium was around 0.75% (atomic concentration) to obtain high discharge capacity at both 25 and . The scanning electron microscope and X-ray photoelectron spectroscopy analysis showed that the coating layer uniformly covered the surface of spherical . The cyclic voltammetry analysis of spherical showed that the oxidation potential, the oxygen evolution potential, and the difference between them increased after the coating both at room temperature and . This increase was much bigger at . The high-temperature performances of sealed AA-sized Ni–MH batteries using hydroxide-coated spherical were much better than those using uncoated or only -coated spherical electrodes. The capacity retention for 2% Co/0.75% Yb hydroxide-coated spherical reached 90% at , where the capacity retentions for uncoated and only -coated were only 46 and 48%, respectively. It has shown that the hydroxide coating is an effective way to improve the high-temperature performance of spherical for nickel–metal hydride batteries.