Nanocrystalline LaNi4−xMn0.75Al0.25Cox electrode materials prepared by mechanical alloying (0≤x≤1.0)

Polycrystalline hydrogen storage alloys based on lanthanum (La) are commercially used as negative electrode materials for the nickel–metal hydride (Ni–MH x ) batteries. In this paper, mechanical alloying (MA) was used to synthesize nanocrystalline LaNi 4− x Mn 0.75 Al 0.25 Co x ( x =0, 0.25, 0.5, 0.75 and 1.0) hydrogen storage materials. XRD analysis showed that, after 30 h milling, the starting mixture of the elements decomposed into an amorphous phase. Following the annealing in high purity argon at 700 °C for 0.5 h, XRD confirmed the formation of the CaCu 5 -type structures with a crystallite sizes of about 25 nm. The nanocrystalline materials were used as negative electrodes for a Ni–MH x battery. Cobalt substituting nickel in LaNi 4 Mn 0.75 Al 0.25 greatly improved the discharge capacity and cycle life of the LaNi 5 material. For example, in the nanocrystalline LaNi 3.75 Mn 0.75 Al 0.25 Co 0.25 powder, discharge capacities up to 258 mA h g −1 (at 40 mA g −1 discharge current) were measured. Mechanical alloying is a suitable procedure to obtain LaNi 5 -type alloy powders for electrochemical energy storage.