Investigation on the Electrochemical Cycle Stability of La–Mg–Ni-based A<sub>2</sub>B<sub>7</sub>-type Alloys Prepared by Melt Spinning

Abstract

In order to improve the electrochemical cycle stability of the La–Mg–Ni system A2B7-type electrode alloys, the partial substitution of Zr for La has been performed. The La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys were fabricated by casting and melt-spinning. The influences of both the substitution of Zr for La and the melt spinning on the structures and the electrochemical cycle stability of the alloys were investigated. The structure characterization of XRD, SEM and HRTEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)2 Ni7 and LaNi5 as well as a residual phase LaNi2. The substitution of Zr for La results in an evident refinement of the grains of the alloys instead of changing the structures of two major phases. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning remarkably ameliorate electrochemical cycle stability of the alloys. The capacity retaining rate (R100) of the as-spun (5 m/s) alloys at 100th charging/discharging cycle is enhanced from 67.43% to 79.22% by increasing Zr content from 0 to 0.2. And that of the Zr0.1 alloy is increased from 73.21% to 82.07% by growing spinning rate from 0 (as-cast was defined as the spinning rate of 0 m/s) to 20 m/s.