Effects of Fe-substitution for cobalt on electrochemical properties of La-Mg-Ni-based alloys

In order to improve electrochemical properties, especially cycling stability, Co was partially substituted by Fe in A2B7-type La-Mg-Ni-based alloys. The La0.74Mg0.26Ni2.55Co0.65–xFex (x=0, 0.10, 0.20, 0.30) alloys were prepared by inductive melting, and their phase structure and electrochemical properties were studied. The XRD and SEM results showed that the alloys consisted mainly of (La, Mg)2Ni7 phase, (La, Mg)5Ni19 phase and LaNi5 phase, except for absence of LaNi5 phase in the non-substituted alloy. The (La, Mg)5Ni19 phase and LaNi5 phase increased and the (La, Mg)2Ni7 phase decreased as Fe content increased. The partial Fe substitution for Co decreased the maximum discharge capacity to some extent; however, the cycling stability was improved and the self-discharge was remarkably suppressed by Fe substitution. The linear polarization and cyclic voltammetry measurements showed that the electro-catalytic activity and hydrogen diffusibility were both deteriorated by Fe substitution and thus the high rate dischargeability decreased.