Hydrogen Storage Alloys for Nickel — Metal Hydride Battery*

— 2 times higher energy density per unit volume and longer cycle life than Ni —Cd cells with almost comparable rate capability and charge retention. A very unique feature of the hydrogen battery is a self-protective mechanism for overdischarge. The hydrogen produced on the nickel electrode is absorbed on the MH electrode and then oxidized to water, keeping the cell voltage around —0.2 V. No oxidation and degradation of alloy occurs during overdischarge if the recombination reaction is fast enough to keep up with the discharge rate. This good overdischarge protection is very advantageous for the series stacking of many cells, i.e., for high voltage applications such as electric vehicles (EV) [6]. Secondly, AB5 (A = rare earth, Zr, B = Ni, Co, Fe, Mn, Al) and AB2 (A = Ti, Zr, B = Ni, V, Fe, Co, Mn, Al) type alloys do not contain hazardous materials, being safe from the standpoint of environmental and safety regulations [7].

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