Electrochemical properties of Ml1−xMgxNi3.0Mn0.10Co0.55Al0.10 (x = 0.05–0.30) hydrogen storage alloys

The Ml1−xMgxNi3.0Mn0.10Co0.55Al0.10 (x = 0.05, 0.10, 0.15, 0.20, 0.30) (where Ml denotes La-rich mischmetal) alloys were prepared by inductive melting. The prepared alloys consist of LaNi5 phase and (La,Mg)Ni3 phase; the LaNi5 phase decreases and (La,Mg)Ni3 phase increases as x increases. Due to the change of the phase structure, the maximum discharge capacity, high rate dischargeability (HRD) and low temperature dischargeability (LTD) of the alloys increase and then decrease with increasing x. The maximum discharge capacity reaches up to 363 mAh/g at x = 0.20, and at x = 0.15, HRD and LTD reach 58.0% at 1200 mA/g and 75.8% at 233 K, respectively. The cycle stability decreases with increasing Mg content. However, by using Ml substitution for La as A-side component and multi-substituted B-side metals, the cycle stability is improved. The capacity retention of the alloys at the 200th cycle is up to 74.9% when x is 0.05.