Recent Progress of Hydrogen-Absorbing Alloys for Nickel-Metal Hydride Rechargeable Batteries

Abstract

Major activities in the direction of developing a commercial nickel-metal hydride rechargeable batteries occurred in the middle 1980s and some Japanese companies started to commercialize these batteries for small computer and electronic appliances in the early 1990s. For most of batteries, MmNi5 (Mm = misch metal) based alloys are exclusively utilized. As metal hydride electrodes could ideally replace the cadmium electrode of nickel-cadmium battery and had much higher electrode capacities, these batteries were easily accepted in commercial. After that, annual production of hydrogen-absorbing alloys has risen drastically. Main research and development for hydrogen-absorbing alloys used in commercial nickel-metal hydride batteries is now directed toward lower price and higher capacity. MmNi5-based alloys are still under development to improve their electrode performances and to reduce the cost of raw materials. Other hydrogen absorbing alloys with higher capacities such as Zr-Mn-Ni, Ti-V-Ni and Mg-Ni systems are also under investigation at both the fundamental and applied levels.