HYDROGEN ABSORPTION DESORPTION CHARACTERISTICS OF TI0.35ZR0.65NIXV2-X-YMNY ALLOYS WITH C-14 LAVES PHASE FOR NICKEL METAL HYDRIDE BATTERIES

The properties of Ti0.35Zr0.65NixV2-x-yMny (1.0 less than or equal to x less than or equal to 1.2, 0.2 less than or equal to y less than or equal to 0.4) alloys including crystallographic parameters, the enthalpy for hydride formation, pressure-composition-temperature (P-C-T) curves and electrochemical discharge capacities were investigated. Based on scanning electron microscopy results, with the exception of alloy A (x=1.0, y=0.2) which forms two distinguishable phases, alloys B (x=1.0, y=0.4), C (x=1.2, y=0.2) and D (x=1.2, y=0.4) all form single uniform phase. Structure contraction took place owing to partial replacement by nickel and/or manganese, but alloys B to D all exhibited C14 type Laves phases. The content of absorbed hydrogen increased as the d-electron concentration (DEC) of the alloys diminished. Although alloy A has the largest hydrogen absorption ability compared with the other alloys, this is not the case with respect to the hydrogen desorption ability of alloys. This can be attributed to the poor reversibility of hydriding-dehydriding of alloy A. It was found that the discharge capacities of alloys were affected not only by the content of absorbed hydrogen but also by the resistance to hydrogen release. Alloy C, Ti0.35Zr0.65Ni1.2V0.6Mn0.2, possessing good hydriding-dehydriding properties in gas and liquid media, is a promising electrode material.