Influence of Zr Addition on Structure and Performance of Rare Earth Mg-Based Alloys as Anodes in Ni/MH Battery

In this study, the substitution of Mg with Zr in La0.7Mg0.3(Ni0.85Co0.15)3.5 was carried out with the purpose of improving the electrochemical performances. The structural and hydrogen storage properties in both gas-solid reaction and the electrochemical system were systematically studied on La0.7(Mg0.3−xZrx)(Ni0.85Co0.15)3.5 (x = 0.05, 0.1, 0.2, 0.3) alloys. Each tested alloy is composed of LaNi3 phase, LaNi5 phase and ZrNi3 phase with different phase abundances. The electrochemical studies indicated that all Zr-substituted anodes possessed a much higher cycling capacity retention than pristine La0.7Mg0.3(Ni0.85Co0.15)3.5. However, the maximum discharge capacity was reduced with the increase of Zr content. The potential-step tests showed that the diffusion of hydrogen atoms inside the anodes was decelerated after the introduction of Zr.