An Investigation on the Electrochemical Cycle Stability of La<sub>0.75−x</sub>Zr<sub>x</sub>Mg<sub>0.25</sub>Ni<sub>3.2</sub>Co<sub>0.2</sub>Al<sub>0.1</sub> (x = 0-0.2) Alloys Prepared by Melt Spinning

Abstract

In order to improve the electrochemical cycle stability of the La-Mg-Ni system A2B7-type electrode alloys, La in the alloy was partially substituted by Zr. The melt-spinning technology was used for preparing La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1(x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys. 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 in detail. The structure analysis of XRD, SEM and TEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7and LaNi5as well as a residual phase LaNi2. The substitution of Zr for La facilitates to form a like amorphous structure in the as-spun alloy without altering the structures of two major phases. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning remarkably improves cycle stability of the alloys. The capacity retaining rate (S100) of the Zr0.2alloy at 100th charging/discharging cycle is enhanced from 76.69 to 85.18% by growing spinning rate from 0 (as-cast was defined as the spinning rate of 0 m/s) to 30 m/s. And that of the as-spun (10 m/s) alloys is increased from 69.25 to 83.09% by rising Zr content from 0 to 0.2.