Effect of Ni/(La plus Mg) Ratio on Structure and Electrochemical Performance of La-Mg-Ni Alloy System

As the alloy with the most suitable Ni/(La+Mg) ratio has higher capacity and good cycle stability, the effects of Ni/(La+Mg) ratios on the electrochemical performances of the La0.80Mg0.20Nix (x = 3.5 to 5.0) alloys have been investigated to find the most suitable Ni/ ( La + Mg) ratio. The results of XRD and SEM observations show that the phase composition of the alloys varies with different Ni/(La+Mg) ratios. When Ni/(La+Mg) is not more than 4.25, all the alloys contain LaNi5 and (La, Mg)(2) Ni-7 phases, in addition, the LaMg and (La, Mg) Ni-3 phases exist in the x = 3.5 and 3.75 alloys, respectively. The LaMg2Ni9 phase exists in the x = 4.25 alloy. There are the LaNi5 and LaMg2Ni9 phases in the x = 4.5, 4.75, and 5.0 alloys. The phase abundance and cell volume change with different Ni content. When the Ni/(La+Mg) ratio is not more than 4.25, the alloys possess excellent activation capability, however, the activation capabilities of the alloys decrease with a further increase in the Ni/(La+Mg ratio. With increasing the Ni/(La+Mg) ratio, the maximum discharge capacities, the medium voltages, and the cycle stabilities of the alloys first increase and then decrease. When the Ni/(La+Mg) ratio is 3.75, the corresponding alloy has the maximum discharge capacity among all the alloys. However, the cycle stability of the Ni/(La+Mg) = 4.0 alloy is better than that of the others.