Characteristics of nickel-metal hydride cells containing metal hydride alloys prepared by an atomization technique

We have studied effects of inert gas atomization and optional annealing of hydride-forming alloys on the alloy performance as the anode material of an Ni/MHx cell. Metal hydride electrodes were prepared using atomized powder of several hydride-forming alloys and studied for their performances in a flooded electrolyte Ni/MHx cell. Their performance was compared, at various temperatures, with that of corresponding non-atomized alloys. The performance studied included: specific capacity as a function of discharge rates; rate capability; cycle performance; particle size, and physical degradation with cycling. The atomized alloys showed lower specific capacity and slower activation with cycling than corresponding non-atomized alloys. A post-atomization annealing treatment improved both in specific capacity and activation process, but the improvement was not sufficient enough to match the performance of the non-atomized alloys. Rate capability of La0.7Ce0.3Ni3.2Co1.0Mn0.6Al0.2 alloy was not affected significantly by the atomization. Rate capability at 20 °C of another alloy with only a slight variation in composition, La0.7Ce0.3Ni3.3Co1.0Mn0.4Al0.3, was reduced a little by the atomization, while that at 2 °C was not affected. A direct observation of the physical degradation process of alloy particles was possible using the atomized powder particles due to their well defined spherical geometry.