The effect of Al substitution for Ni on the structure and electrochemical properties of AB3-type La2Mg(Ni1−xAlx)9 (x=0–0.05) alloys

Abstract The effect of replacing part of Ni by Al in La 2 MgNi 9 alloy on the structure and electrochemical properties of the thus formed La 2 Mg(Ni 1− x Al x ) 9 ( x = 0 – 0.05 ) quaternary alloys was investigated. All alloys consisted of a main phase with hexagonal PuNi 3 -type structure and a small quantity of an impurity phase (La 2 Ni 7 ). The increase of Al content in the alloys leads to an increase in both the cell volume and the hydride stability, and leads to a noticeable decrease in cell volume expansion rate ( Δ V / V ) on hydriding. The increase of Al content leads to some decrease in both the discharge capacity and the high-rate dischargeability (HRD) but leads to a significant improvement in cycling stability of the alloys. The decrease of HRD of the alloys is ascribed to the decrease of electrocatalytic activity for the hydrogen electrode reaction and the lower diffusion rate of hydrogen in the bulk of the alloys, while the improvement in cycling stability is mainly attributed to the decrease of V H of the hydride phase.