Structural and electrochemical properties of the hydrogen storage alloys Zr0.8Ti0.2(Ni0.6Mn0.2V0.2Cr0.05)x

We studied a series of Zr0.8Ti0.2(Ni0.6Mn0.2V0.2Cr0.05) (x) alloys (x = 1.8 similar to 2.4) in order to reveal the effects of the stoichiometry on the phase structures and electrochemical properties. It was found that Zr0.8Ti0.2 (Ni0.6Mn0.2V0.2Cr0.05). alloys consist of C14 and C15 Laves phase, and secondary phase Zr7Ni10 or TiNi. With increasing x value, abundance of C14 phase decreases and C15 phase increases. Increase of x value leads to decrease of the lattice parameters of both C14 and C15 phases. As the x value increases the activation property, the discharge capacity and the high rate dischargeability are improved and the highest capacity is found for x = 2.2, (370 mAh/g). For the over - stoichiometrical alloys, the cycling stability is deteriorated with increasing of x value. A critical x value is found at x 2.2, and Zr0.8Ti0.2(Ni0.6Mn0.2V0.2Cr0.05)(2.2) alloy shows the best comprehensive electrochemical performances.