Effects of particle size and heat treatment on the electrode performance of a low-cobalt atomized AB 5-type hydrogen storage alloy

Abstract

A low-cobalt hydrogen storage alloy with a composition of MLNi 3.8Co 0.3Fe 0.2Mn 0.4Al 0.3 was prepared by a vacuum induction casting method followed by gas atomization processing. The results showed that the atomized powders had lower discharge capacity and poorer activation kinetics but better cycling stability than the as-cast sample. The high amount of oxygen and nitrogen present in the atomized powder and the presence of amorphous phase were the main reasons for the observed low discharge capacity and poor activation performance. The atomized powder with a large particle size showed a lower oxygen content and therefore higher discharge capacity than that with a small particle size. However the favorable effect of the atomization processing on the durability of the hydrogen storage alloy was eliminated after heat treatment at 850°C for 6 h.