Structural evolution and electrochemical hydrogen storage properties of single-phase A5B19-type (La0.33Y0.67)5Ni17.6Mn0.9Al0.5 alloy

La–Y–Ni-based superlattice alloys demonstrate the potential as high-capacity anodes for Nickel-metal hydride batteries. However, the usual multi-phase structure formed in A5B19-type La–Y–Ni-based alloys makes precise investigations of composition-structure-performance relationships difficult. This work optimizes the quenching temperature to obtain the single-phase (La0.33Y0.67)5Ni17.6Mn0.9Al0.5 alloy with a hexagonal 2H–Pr5Co19 structure. The single-phase alloy exhibits better overall electrochemical properties than multi-phase alloys, such as the maximum discharge capacity of 368.8 mAh g−1, the capacity retention at the 200th cycle of 73.4%, and the rate performance at a high discharge current of 1500 mA g−1 of 58.6%. The ex-situ X-ray diffraction research reveals that during charging, the single-phase alloy sequentially forms β and γ hydrides, with the β hydride exhibiting the highest lattice strain, mainly due to the asynchronous hydrogenation and expansion between [A2B4] and [AB5]-2 subunits. This work offers meaningful guidance for developing high-performance La–Y–Ni-based electrode alloys.