Effect on electrochemical properties of phases in Ab-type ZrTiNbNi alloys as nickel-metal hydride batteries

Abstract

AB-type ZrTiNbNi alloys are good candidates as the negative electrode for Ni-metal hydride (MH) batteries because they have high discharge capacity around 330 mAh g11 at 303 K. The Zr0.49Ti0.5Nb0.01Ni alloy consists of two phases, the primary-phase with B33-type orthorhombic structure and the secondary-phase with B2-type cubic structure. To compare electrochemical properties of each phase with the mother alloy, we synthesized the primary-phase and secondary phase alloys with compositions of Zr0.54Ti0.47Nb0.01Ni0.98 and Zr0.47Ti0.52Nb0.01Ni, respectively. The discharge capacity was examined at 25 mA g11 and 303 K, showing that the primary-phase alloy has the highest value of 362 mAh g11 than the mother alloy (335 mAh g11) and the secondary-phase alloy (253 mAh g11). For cycle performance, all alloys were excellent (½95%) at 100 mA g11 and 303 K. For high-rate dischargeability, the secondary-phase alloy was the best, probably because the stability of hydride for the secondary-phase alloy was lower than that for the mother and the primary-phase alloy.