Cooperative effects of Sm and Mg on electrochemical performance of La-Mg-Ni-based alloys with A_2B_7- and A_5B_(19)-type super-stacking structure

摘要

The cooperative effects of Sm and Mg on the electrochemical properties of La_(0.85-x)(Sm_(0.75)Mg_(0.25))_xMg_(0.15)Ni_(3.65) (x = 0, 0.1, 0.15, 0.2, 0.25) alloys were investigated. It was found that the alloys mainly contained (La,Mg)_2Ni_7, (La,Mg)_5Ni_(19) and LaNi_5 phases. Partial replacement of Sm and Mg for La increased the total abundance of (La,Mg)_2Ni_7 and (La,Mg)_5Ni_(19) 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 HRD_(1500) was increased by 12.3% and the maximum discharge capacity was also improved.