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 A(2)B(7)-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)(2)Ni-7 phase, (La,Mg)(5)Ni-9 phase and LaNi5 phase, except for absence of LaNi5 phase in the non-substituted alloy. The (La,Mg)(5)Ni-9 phase and LaNi5 phase increased and the (La,Mg)(2)Ni-7 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.