Study on phase structure and electrochemical properties of Ml1−xMgxNi2.80Co0.50Mn0.10Al0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) hydrogen storage alloys

Phase structure and electrochemical properties of the Ml1−xMgxNi2.80Co0.50Mn0.10Al0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) (Ml = La-rich mixed lanthanide) alloys were studied. X-ray diffraction (XRD) analysis and Rietveld refinement show that the alloys consist mainly of LaNi5 and (La,Mg)Ni3 phase. Due to variation in phases of the alloys, the maximum discharge capacity, the high rate dischargeability (HRD), and the low temperature dischargeability increase first and then decrease. The maximum discharge capacity increases from 322 mAh g−1 (x = 0.08) to 375 mAh g−1 (x = 0.12), and then decreases to 351 mAh g−1 (x = 0.28) with increasing x. As the case of x = 0.20, HRD at 1200 mA g−1 and discharge capacity at 233 K reaches 41.7% and 256 mAh g−1, respectively. The cycling stability is improved by substituting La with Ml and B-site multi-alloying, and the capacity retention of Ml0.72Mg0.28Ni2.80Co0.50Mn0.10Al0.10 at the 200th cycle is 71%.