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 LaNi_x(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 LaNi_x(Co,Mn,Al)_5-x electrodes had a capacity as high as 325-335 mAhg^-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 LaNi_x(Co,Mn,Al)_5-x alloys.