Structural and electrochemical properties of Ti1.5Zr5.5VxNi10−x

Quaternary alloys with the formula Ti1.5Zr5.5VxNi10−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 Zr7Ni10 structure to a Zr9Ni11 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 Zr7Ni10 and Zr9Ni11 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 Ti1.5Zr5.5V2.5Ni7.5 and mainly C14 structure. Testing also shows the high rate dischargeability is controlled by the surface reaction and Ti1.5Zr5.5V0.5Ni9.5 has the best high rate dischargeability.