Abstract
Quaternary alloys with the formula Ti 1.5Zr 5.5V x Ni 10− x ( x between 0 and 3.0) were studied as a potential replacement for Laves phase alloys used as the negative electrode active material in nickel metal hydride batteries. The V-containing alloys all show multi-phase structures. The major phase shifts from a Zr 7Ni 10 structure to a Zr 9Ni 11 structure and finally to a C14 structure as the vanadium content increases. Other minor phases with C15 and ZrNi crystal structures are also present. The solubility of vanadium is high in AB2 phases (both C14 and C15), moderate for the ZrNi phase and very low for Zr 7Ni 10 and Zr 9Ni 11 phases. The bulk hydrogen transport property of the alloys is dominated by synergetic effects between major and minor phases. Electrochemical testing shows that the highest discharge capacity, 357 mAh/g, was obtained from an alloy with a chemical composition of Ti 1.5Zr 5.5V 2.5Ni 7.5 and mainly C14 structure. Testing also shows the high rate dischargeability is controlled by the surface reaction and Ti 1.5Zr 5.5V 0.5Ni 9.5 has the best high rate dischargeability.
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