The effect of partial substitution of Si for Ni on the electrochemical properties of cobalt-free LaNi_4.2-xAl_0.35Mn_0.45Si_x (x = 0-0.35) alloys

The structure and electrochemical properties of a cobalt-free hydrogen storage electrode alloys LaNi_4.2-xAl_0.35Mn_0.45Si_x (0 ≤ x ≤ 0.35) have been investigated with small amount of Si in replacement of Ni. With the increase of Si content, the maximum discharge capacity and the high rate discharge (HRD) ability gradually decrease, however the cycle stability is improved correspondingly. The lowest capacity decay rate can remain 19.4% (x = 0.35) after 300 charge/discharge cycles. The lower corrosion current densities of the alloys with the addition of Si can explain the good cycle life for them. It is found that all of the alloys are single CaCu₅ phase structure through XRD analysis. But some white dot-like LaNi₃ phase separated out in the matrix only for the alloy x = 0.35 through further EDX analysis.