Effects of rapid quenching on structure and electrochemical characteristics of La 0.5Ce 0.2Mg 0.3Co 0.4Ni 2.6– xMn x ( x=0–0.4) electrode alloys

Abstract

The La-Mg-Ni system PuNi 3-type La 0.5Ce 0.2Mg 0.3Co 0.4Ni 2.6– x Mn x ( x=0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by casting and rapid quenching. The effects of the rapid quenching on the structure and electrochemical characteristics of the alloys were studied. The results obtained by XRD, SEM and TEM indicate that the as-cast and quenched alloys mainly consist of two major phases, (La, Mg)Ni 3 and LaNi 5, as well as a residual phase LaNi. The rapid quenching does not exert an obvious influence on the phase composition of the alloys, but it leads to an increase of the LaNi 5 phase and a decrease of the (La, Mg)Ni 3 phase. The as-quenched alloys have a nano-crystalline structure, and the grain sizes of the alloys are in the range of 20–30 nm. The results by the electrochemical measurements indicate that both the discharge capacity and the high rate discharge(HRD) ability of the alloy first increase and then decrease with the variety of quenching rate and obtain the maximum values at the special quenching rate which is changeable with the variety of Mn content. The rapid quenching significantly improves the cycle stabilities of the alloys, but it slightly impairs the activation capabilities of the alloys.