Structure and electrochemical properties of the mechanically alloyed La(Ni,M)5 materials

Mechanical alloying (MA) was used to synthesize LaNi5-type hydrogen storage materials. XRD analysis showed that, after 30 h milling, the starting mixture of the elements was 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 crystallite sizes of about 25 nm. The nanocrystalline materials were used as negative electrodes for a Ni-MHx battery. A partial substitution of Ni by Al or Mn in LaN5-xMx alloy leads to an increase in discharge capacity. On the other hand, alloying elements such as Al, Mn and Co greatly improved the cycle life of LaNi5 material. For example, in the nanocrystalline LaNi3.75Mn0.75Al0.25Co0.25 powder, discharge capacities of up to 258 mA h g(-1) (at 40 mA g(-1) discharge current) were measured. This nanocrystalline hydrogen storage alloy is attractive for Ni-MHx battery. (C) 2002 Elsevier Science B.V. All rights reserved.