Effects of V substitution and annealing on Zr-based AB2 alloys as anode material of metal hydride batteries

Present paper investigates Ti(0.25)Zr(0.25)Ni(1.35-x)Mn(0.65)Vx (x = 0, 0.05, 0.1, and 0.15) alloys as anode active ma-terials of metal hydride batteries. The AB2 Laves-type alloys are prepared using arc melting and annealing. The as-cast alloys contain the major C15 and/or C14 intermetallic compounds together with the Ti-Ni and Zr-Ni secondary phases. The annealing promotes the homogeneity of the alloys and dismisses the non-Laves phases. As the V contents increase, the C15-type Laves phase transforms to the C14 structure. In addition, the unit cells of the Laves phase increase as the V contents in the alloys increase. All the studied alloy electrodes reach their maximum discharge capacities during the first 10 activation cycles. After charge/discharge 100 cycles at 300 mAg(-1), the discharge capacity retentions of all the studied alloy electrodes keep more than 75%. Annealing treatment and V substitution increase the full discharge capacity from similar to 230 mAg(-1) for N1 alloy to similar to 430 mAhg(-1) for A4 alloy. The synthetic effects between V substitution and annealing are studied on improving the phase structure and the electrochemical properties of AB2-type Laves phase alloys.