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

Abstract To determine the structure and electrochemical properties of La–Mg–Ni-based Pr 5 Co 19 -type super-stacking structure alloys, a La 0.84 Mg 0.16 Ni 3.80 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 Pr 5 Co 19 -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 ( HRD 1500 ) 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, Ce 2 Ni 7 -type or LaNi 5 secondary phase was introduced into the single-phase alloy by adjusting molar ratio of precursors. When the content of Ce 2 Ni 7 -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.% LaNi 5 phase in the alloy, the HRD 1500 increases to 56% and the surface exchange current density ( i 0 ) increases from 275.50 mA g −1 to 354.16 mA g −1 .