Characterization and improvement of electrochemical properties of Pr5Co19-type single-phase La0.84Mg0.16Ni3.80 alloy

To determine the structure and electrochemical properties of La-Mg-Ni-based Pr5Co19-type super-stacking structure alloys, a La0.84Mg0.16Ni3.80 alloy was designed and synthesized by step-wise powder sintering. X-ray diffraction (XRD) analysis and Rietveld refinement show that the alloy consists of a single Pr5Co19-type phase. Electrochemical studies show that the alloy has a mediocre discharge capacity of 338 mAh g−1 and good cycling stability. High rate dischargeability at 1500 mA g−1(HRD1500) reaches 51.5% and the corresponding discharge capacity remains 174 mAh g−1. To improve overall electrochemical properties of the alloy, especially the discharge capacity, Ce2Ni7-type or LaNi5 secondary phase was introduced into the single-phase alloy by adjusting molar ratio of precursors. When the content of Ce2Ni7-type phase increases from 0 to 40.6 wt.%, the maximum discharge capacity enhances from 338 to 388 mAh g−1 and the discharge capacity retention at the 100th cycle is improved from 77.0% to 85.3%. With the presence of 20.7 wt.% LaNi5 phase in the alloy, the HRD1500 increases to 56% and the surface exchange current density (i0) increases from 275.50 mA g−1 to 354.16 mA g−1.