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

Polycrystalline hydrogen storage alloys based on lanthanum (La) are commercially used as negative electrode materials for the nickel-metal hydride (Ni-MHx) batteries. In this paper, mechanical alloying (MA) was used to synthesize nanocrystalline LaNi4-xMn0.75Al0.25Cox (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 degreesC for 0.5 h, XRD confirmed the formation of the CaCu5-type structures with a crystallite sizes of about 25 nm. The nanocrystalline materials were used as negative electrodes for a Ni-MHx battery. Cobalt substituting nickel in LaNi4Mn0.75Al0.25 greatly improved the discharge capacity and cycle life of the LaNi5 material. For example, in the nanocrystalline LaNi3.75Mn0.75Al0.25Co0.25 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 LaNi5-type alloy powders for electrochemical energy storage. (C) 2002 Elsevier Science B.V. All rights reserved.