Phase Constitution and Electrochemical Characteristics of La2Mg0.9Al0.1Ni7.5-xCo1.5Mnx Hydrogen Storage Alloys

Effect of Mn substitution for Ni on phase constitution and electrochemical characteristics of La2Mg0.9Al0.1Ni7.5-xCo1.5Mnx (x=0, 0.3, 0.6, 0.9) hydrogen storage alloys was studied. It is found that Mn substitution will change phase composition and phase constitution of the alloys. LaNi3 phase disappears; the components of αLa2Ni7 first increases with Mn content from x=0 to x=0.3 and then decreases from x=0.6 to 0.9. Both component of LaMgNi4 phase and La5Ni19 phase increase as x increases in the alloys. Replacement of Ni by Mn will lower hydrogen storage capacity, maximum electrochemical discharge capacity and activation property of the alloy electrodes. La2Mg0.9Al0.1Ni7.2Co1.5Mn0.3 hydride electrode shows the best cycle stability. The high rate dischargeability of the alloys decreases with the increase of Mn content, which would be attributed to the decrease of exchange current density (I0) and diffusion coefficient of the hydrogen atom (D).