Cooperative effects of Sm and Mg on electrochemical performance of La–Mg–Ni-based alloys with A2B7- and A5B19-type super-stacking structure

• Cooperative effect of Sm and Mg on A-site is meaningful but scarcely reported.
• Super-stacking phase abundance is increased and crystal grains are refined.
• Cycling stability and HRD is remarkably improved.
• Grain refinement and stacking phase increase contribute to good properties.

The cooperative effects of Sm and Mg on the electrochemical properties of La0.85−x(Sm0.75Mg0.25)xMg0.15Ni3.65 (x = 0, 0.1, 0.15, 0.2, 0.25) alloys were investigated. It was found that the alloys mainly contained (La,Mg)2Ni7, (La,Mg)5Ni19 and LaNi5 phases. Partial replacement of Sm and Mg for La increased the total abundance of (La,Mg)2Ni7 and (La,Mg)5Ni19 super-stacking phases, refined crystal grains and decreased cell volumes. It was proved that Mg contributed to increasing the total abundance of super-stacking phases so that the discharge capacity and high rate dischargeability (HRD) were enhanced. Sm was favorable to the refinement of crystal grains, which contributed to better HRD and cycling stability. The joint effects of Sm and Mg in improving the overall electrochemical properties of the alloy electrodes were remarkable. The electrochemical cycle life for the alloy with x = 0.20 reached 280 cycles, more than two times that of the pristine alloy. Meanwhile the HRD1500 was increased by 12.3% and the maximum discharge capacity was also improved.