Effect of Ni content on the electrochemical characteristics of the LaNi5-based hydrogen storage alloys

The effects of Ni content on the electrochemical characteristics of the LaNix(Co,Mn,Al)5−x (Co:Mn:Al=3:1:1; 3.6≦x≦4.2) electrodes were examined. The lattice cell parameters, discharge characteristics, high rate charging or discharging performance and cyclic stability of the series of alloys were all evaluated. The experimental results show that the LaNix(Co,Mn,Al)5−x electrodes had a capacity as high as 325–335 mAh g−1. A higher Ni content in the alloys could give a higher discharge cell voltage. But the cyclic stability of the metal hydride electrodes would be lowered by increasing the Ni content in the alloys. Replacing the Ni by substitutional elements (Co, Mn and Al) in the alloys could cause an expansion of the lattice cell volume and assist hydrogen diffusion in the metal hydride electrodes, which subsequently promoted the high rate charging performance. Under high rate discharging condition, the electrodes had optimum performance when the Ni content had an atomic ratio of 4 (x=4) in the LaNix(Co,Mn,Al)5−x alloys.