The electronic and electrochemical properties of the LaNi5-based alloys

Abstract

Mechanical alloying was used to synthesize LaNi5-type hydrogen storage materials. X-ray diffraction 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°C for 0.5 h, X-ray difraction confermed the formation of the CaCu5-type structures. The nanocrystalline materials were used as negative electrodes for a Ni-MH x battery. A partial substitution o Ni by Al or Mn in LaNi 5-xMx alloy leads to an increase in discharge capacity. On the other hand, the alloying elements such as Al, Mn and Co greatly improved the cycle life of LaNi5 material. For example, in the nanocrystalline LaNi 3.75Mn0.75Al0.25Co0.25 powder, discharge capacities of up to 258 mA h g-1 (at 40 mA g-1 discharge current) were measured. The band structure ab initio calculations showed that 3g sites are preferred by Al, Co, and Mn atoms in the unit cell.