Microstructures and electrochemical performances of La0.75Mg0.25Ni3.5Mx (M = Ni, Co; x = 0-0.6) hydrogen storage alloys

The cycle stability of the alloy (M = Co) monotonously increases with rising M content, but it first decreases slightly then increases for the alloy (M = Ni). The discharge potential of the alloy (M = Ni) drops with growing M content (x > 0.2), but the result is contrary for the alloy (M = Co). The substitution of Co for Ni significantly ameliorates the electrochemical performances. For a fixed M content (x = 0.2), the Co substitution enhances the discharge capacity from 365.7 to 401.8 mAh/g, the capacity retention ratio (S100) from 50.32 to 53.26% after 100 charging-discharging cycles and the HRD from 88.65 to 90.69%, respectively. It significantly enhances the discharge potential of the alloy and improves the activation performance.