Abstract: Effect of stoichiometry on microstructures, electrochemical properties and PCT characteristics of the alloys Ml(Ni0.71Co0.15-Al0.06Mn0.08)x (Ml=Lanthanum-rich Michmetal, x=4.6-5.2) have been investigated. The lattice constants a, c and cell volumes of non-stoichiometric alloys are bigger than those of the stoichiometric alloy. With the increasing stoichiometry x, the value of a decreases, and the value of c and cell volume increases except for those of the stoichiometric alloy; the plateau pressure of PCT curve, discharge capacity and cycling stability all increase. The alloy with x=5.2 shows the highest discharge capacity and the best cycling stability among the studied alloys.

Key words: Hydrogen storage alloy, Metal hydride electrode, Rare earth, Electrochemical property, Stoichiometry