Insights into the effect of Y substitution on superlattice structure and electrochemical performance of A5B19-type La-Mg-Ni-based hydrogen storage alloy for nickel metal hydride battery

Abstract

La-Mg-Ni-based hydrogen storage alloys with superlattice structures are the new generation anode material for nickel metal hydride (Ni-MH) batteries owing to the advantages of high capacity and exceptional activation properties. However, the cycling stability is not currently satisfactory enough which plagues its application. Herein, a strategy of partially substituting La with the Y element is proposed to boost the capacity durability of La-Mg-Ni-based alloys. Furthermore, phase structure regulation is implemented simultaneously to obtain the A5B19-type alloy with good crystal stability specifically. It is found that Y promotes the phase formation of the Pr5Co19-type phase after annealing at 985 °C. The alloy containing Y contributes to the superior rate capability resulting from the promoted hydrogen diffusion rate. Notably, Y substitution enables strengthening the anti-pulverization ability of the alloy in terms of increasing the volume match between [A2B4] and [AB5] subunits, and effectively enhances the anti-corrosion ability of the alloy due to high electronegativity, realizing improved long-term cycling stability of the alloy from 74.2 % to 78.5 % after cycling 300 times. The work is expected to shed light on the composition and structure design of the La-Mg-Ni-based hydrogen storage alloy for Ni-MH batteries.