Cobalt/ytterbium hydroxide was used for surface coating of spherical Ni(OH)(2) to improve its high-temperature performance. The coated spherical Ni (OH)(2) was prepared by coprecipitation of Co/Yb hydroxide on the surface of spherical Ni (OH)(2). The optimum coating content of ytterbium was around 0.75% (atomic concentration) to obtain high discharge capacity at both 25 and 60 C. The scanning electron microscope and X-ray photoelectron spectroscopy analysis showed that the coating layer uniformly covered the surface of spherical Ni (OH)(2). The cyclic voltammetry analysis of spherical Ni (OH)(2) showed that the oxidation potential, the oxygen evolution potential, and the difference between them increased after the coating both at room temperature and 60 degrees C. This increase was much bigger at 60 degrees C. The high-temperature performances of sealed AA- sized Ni -MH batteries using Co/Yb hydroxide-coated spherical Ni (OH)(2) were much better than those using uncoated or only Co(OH)(2)-coated spherical Ni (OH)(2) electrodes. The capacity retention for 2% Co/0.75% Yb hydroxide-coated spherical Ni (OH)(2) reached 90% at 60 degrees C, where the capacity retentions for uncoated and only Co (OH)(2)-coated Ni (OH)(2) were only 46 and 48%, respectively. It has shown that the Co/Yb hydroxide coating is an effective way to improve the high-temperature performance of spherical Ni (OH)(2) for nickel - metal hydride batteries. (c) 2006 The Electrochemical Society.