Enhanced Electrochemical Cycle Stability of RE-Mg-Ni System A<sub>2</sub>B<sub>7</sub>-Type Alloys by Melt Spinning and Substituting La with Pr

Abstract

It has come to light that the poor electrochemical cycle stability of RE-Mg-Ni based AB3and A2B7-types electrode alloys limited their practical application as the negative electrode materials of Ni-MH battery. In order to improve the electrochemical cycle stability of the La-Mg-Ni system A2B7-type electrode alloys, La in the alloy is partially substituted by Pr and the melt-spinning technology was used for preparing La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1(x = 0-0.4) electrode alloys. The microstructures and electrochemical cycle stability of the as-cast and spun alloys were investigated. The results obtained by XRD, SEM and TEM show that the as-cast and spun alloys have a multiphase structure which consists of two main phases (La, Mg)2Ni7and LaNi5as well as a residual phase LaNi2. The substitution of Pr for La gives rise to a visible grain refinement of the as-cast alloys instead of changing the phase structure of the alloys. The electrochemical measurement indicates that the cycle stability of the alloy remarkably grows with increasing both Pr content and spinning rate.