METAL HYDRIDE ANODES FOR NICKEL-HYDROGEN SECONDARY BATTERY

It has been found that the respective substitutions of La and Ni in LaNi5 by small amounts of Zr and Al remarkably improved the cycle life of the alloy anode, scarcely causing a lowering of capacity. In order to clarify the mechanism, the relations between chemical compositions and anode properties for La1-xZrxNi5-yAly, such as capacity, cycle life, rate capability, temperature behavior, and self-discharge character, were examined. With increasing Zr content in the presence of Al (y = 0.5) the cycle life (CL) increased greatly: CL = 180 for x = 0, CL = 580 for x = 0.1, CL = 690 for x = 0.15, and CL = 810 for x = 0.2. The self-discharge was also depressed by the Zr addition. However, hydrogen overpotentials showed a tendency to increase with increasing Zr content, leading to the lowering of discharge potentials and capacities at high currents and low temperatures. The results obtained here were discussed in terms of surface oxide film which worked as a barrier for preventing the diffusion of hydrogen and for protecting the alloy from further corrosion. It was suggested that the small amounts of substituted Zr and Al play an important role by getting the surface oxide film more dense and protective. © 1990, The Electrochemical Society, Inc. All rights reserved.