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 La_0.8Mg_0.2Ni_3.3Co_0.2Si _x (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.

Keywords

A₂B₇-type electrode alloy / Si addition / annealing temperature / structure / electrochemical performances

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