Influence of material processing on crystallographic and electrochemical properties of cobalt-free LaNi_(4.95)Sn_(0.3) hydrogen storage alloy

摘要

The effects of the alloy preparation methods, including the conventional casting, annealing and melt-spinning, on the crystallographic and electrochemical properties of the Co-free LaNi_(4.95)Sn_(0.3) alloy samples were investigated. The results reveal that the as-cast alloy consists of a main phase of CaCu_5-type structure and a little second phase (Sn) with noticeable composition segregation and rather poor cycling stability (S_(200) = 40.l percent). While the annealed and melt-spun alloys are of single CaCu_5-type structure phase with a more homogeneous composition and lower cell volume expansion rate (DELTA V/V) on hydriding, and a dramatically improved cyclic stability (S_(200) = 73.6 percent - 76.2 percent), although their activation rate, initial capacity and high-rate dischargeability are lowered somewhat. It is found that the decrease in both the electrocatalytic activity and the hydrogen diffusion rate of the annealed and melt-spun alloys is the main cause for their relatively lower high-rate dischargeability, and the improved cycling stability is due to their lower volume expansion on hydriding and more uniform composition.