Electrochemical hydrogen storage performances of the Si added La-Mg-Ni-based A2B7-type electrode alloys for Ni/MH battery application

Abstract

The casting and annealing technologies were applied to fabricate the La0.8Mg0.2Ni3.3Co0.2Six (x = 0–0.2) electrode alloys. The effects of Si content and annealing temperature on the structure and electrochemical performances of the alloys were investigated systematically. The analyses of XRD and SEM show that all the alloys possess a multiphase structure, involving two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi3. The addition of Si brings on an evident increase in the LaNi5 phase and a decrease in the (La, Mg)2Ni7 phase, without altering the main phase component of the alloy, which also makes the lattice constants and cell volumes of the alloy enlarged. Likewise, the annealing treatment engenders the same action on the lattice constants and cell volumes as adding Si. Simultaneously, it gives rise to the variation of the phase abundance and the coarsening of the alloy grains. The electrochemical measurements indicate that the addition of Si ameliorates the cycle stability of the as-cast and annealed alloys significantly, but impairs their discharge capacities clearly. Similarly, the annealing treatment makes a positive contribution to the cycle stability of the alloy evidently, and the discharge capacity of the alloy shows a maximum value with annealing temperature rising. Furthermore, the high rate discharge ability (HRD) first augments and then declines with the rising of Si content and annealing temperature.