Tuning phase structure and electrochemical hydrogen storage properties of A5B19-type La–Y–Ni–Mn-based superlattice alloys by partial Al substitution

Abstract

Rare earth-based superlattice alloys are essential anodes for high-performance nickel-metal hydride (Ni-MH) batteries. This study aimed to improve the overall electrochemical hydrogen storage properties of (La0.33Y0.67)5Ni18.1-xMn0.9Alx alloys by adjusting the Al content. The alloys predominantly consist of the 2H–Pr5Co19 phase, with Al atoms mainly occupying the 12k2 site at the [AB5]-1/[AB5]-2 boundary and subsequently the 12k1 site at the [A2B4]/[AB5]-1 boundary. As a result, a minimum subunit volume difference of 2.08 Å3 is observed at x = 0.6. Therefore, the Al substitution is responsible for the decrease in the dehydriding plateau pressure and the increase in discharge capacity. Among them, the alloy (La0.33Y0.67)5Ni17.5Mn0.9Al0.6 presents a discharge capacity of 361.2 mAh/g, a higher capacity retention S200 of 69.80 %, and better rate performance owning to the enhanced hydrogen diffusion rate through the multi-phase interface. This work demonstrates the potential of the (La0.33Y0.67)5Ni17.5Mn0.9Al0.6 alloy as high-performance Ni-MH battery anode.