Influence of rapid quenching on the microstructure and electrochemical properties of Co-free hydrogen storage electrode alloy

Co-free LaNi 4.92 Sn 0.33 alloy samples were prepared by first induction melting and subsequent melt-spinning at different quenching rates, and their microstructure and electrochemical properties were comparatively investigated and compared. The results reveal that the as-cast alloy is of a coarse dendrite structure consisting of two distinct CaCu 5 major phases and a scattered minor Sn phase, has high volume expansion and pulverization rates on hydriding and noticeable composition segregation, resulting in a rather poor cycling stability ( S 200 = 42.7 % ). However, the melt-spun alloys prepared at higher quenching rates are highly homogeneous in composition, of the single CaCu 5 phase in very fine cellular structure, have lower volume expansion and pulverization rates on hydriding, leading to a noticeably improved cyclic stability ( S 200 = 62.5 – 78 % ), although their activation rate, initial capacity and high-rate dischargeability are slightly lowered. It is believed that the great improvement in cycling stability of the melt-spun alloys is mainly due to their lower degree of pulverization on hydriding and the higher uniformity in composition, and the relatively lower high-rate dischargeability is mainly due to the decrease in both the electrocatalytic activity and the hydrogen diffusion rate in the alloy bulk.