Electrochemical performances of as-cast and annealed La0.8-x Nd x Mg0.2Ni3.35Al0.1Si0.05 (x = 0–0.4) alloys applied to Ni/metal hydride (MH) battery

Abstract

The La–Mg–Ni-based A2B7-type La0.8-x Nd x Mg0.2Ni3.35Al0.1Si0.05 (x = 0, 0.1, 0.2, 0.3, and 0.4) electrode alloys were prepared by casting and annealing. The influence of the partial substitution of Nd for La on the structure and electrochemical performances of the alloys was investigated. The structural analysis of X-ray diffraction and scanning electron microscopy reveals that the experimental alloys consist of two major phases: (La,Mg)2Ni7 with the hexagonal Ce2Ni7-type structure and LaNi5 with the hexagonal CaCu5-type structure as well as some residual phases of LaNi3 and NdNi5. The electrochemical measurements indicate that an evident change of the electrochemical performance of the alloys is associated with the substitution of Nd for La. The discharge capacity of the alloy first increases then decreases with the growing Nd content, whereas their cycle stability clearly grows all the time. Furthermore, the measurements of the high rate discharge ability, the limiting current density, and hydrogen diffusion coefficient all demonstrate that the electrochemical kinetic properties of the alloy electrodes first augment then decline with the rising amount of Nd substitution.