The interaction of subunits inside superlattice structure and its impact on the cycling stability of AB4-type La–Mg–Ni-based hydrogen storage alloys for nickel-metal hydride batteries

Abstract Satisfactory cycling stability is demanded for commercialization of new-type anode of La–Mg–Ni-based hydrogen storage alloys for nickel metal hydride batteries. The late-model AB4-type alloy is an attractive candidate among various alloys owing to the superior cycling stability and preferable rate performance. The admirable properties strongly associated with its inherently crystal structure layered by [A2B4], [AB5]-1 and [AB5]-2 subunits where the relationship is required to be further studied. Herein, we reveal the interaction among the subunits which affects the structural stability of the AB4-type superlattice structure based on a ternary La–Mg–Ni system. It is found the specific [AB5]-2 subunit away from the [A2B4] subunit not only has great flexibility of expansion/contraction upon hydrogenation/dehydrogenation, but more importantly it relieves the mismatch between the [A2B4] subunit and its adjacent [AB5]-1 subunit, strengthens the structural stability and constrains the amorphization of the alloy. As a result of the stable crystal structure, the AB4-type ternary La–Mg–Ni alloy delivers a high discharge capacity of 340.0 mAh g−1 after 100 cycles with a retention rate of 88.2%. We expect the work can motivate novel thoughts of developing desirable hydrogen storage alloys with high-performance by optimizing the crystal structure of the alloys.