Investigation on the structures and electrochemical performances of La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x=0-0.2) electrode alloys prepared by melt spinning

In order to improve the electrochemical cycle stability of the La-Mg-Ni system A(2)B(7)-type electrode alloys, La in the alloy was partially substituted by Zr and the melt-spinning technology was used for preparing La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.05, 0.1. 0.15, 0.2) electrode alloys. The microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results obtained by XRD, SEM and TEM showed that the as-cast and quenched alloys have a multiphase structure which is composed of two main phases (La, Mg)Ni-3 and LaNi5 as well as a residual phase LaNi2. The substitution of Zr for La leads to an obvious increase of the LaNi5 phase in the alloys, and it also helps the formation of a like amorphous structure in the as-quenched alloy. The results of the electrochemical measurement indicated that the substitution of Zr for La obviously decreased the discharge capacity of the as-cast and quenched alloys, but it significantly improved their cycle stability. The discharge capacity of the alloys (x <= 0.1) first increased and then decreased with the variety of the quenching rate. The cycle stability of the alloys monotonously rose with increasing quenching rate. (C) 2009 Elsevier B.V. All rights reserved.