Superior electrochemical performance of La-Mg-Ni-based alloys with novel A2B7-A7B23 biphase superlattice structure

Abstract

Nickel metal hydride (Ni-MH) rechargeable batteries hold an important position in the new-energy vehicle market owing to their key technology advantages. Their negative electrode materials—hydrogen storage alloys (HSAs) are always on the spotlight and are the key to compete with the burgeoning Li-ion batteries. Here, for the first time we report a series of biphase supperlattice HSAs with a (La,Mg)2Ni7 matrix phase and a novel (La,Mg)7Ni23 secondary phase. The biphase alloys show discharge capacities of 402–413 mAh g−1 compared with 376–397 mAh g−1 of the other multi- or single-phase alloys. These values are among the highest for superlattice HSAs. In addition, the alloy with 15.4 wt.% (La,Mg)7Ni23 phase exhibits good high rate dischargeability due to the proper compromise between the amount of crystal boundaries and equilibrium plateau voltage. The cycling stability of the biphase alloys is lower than that of the single-phase alloy but is till higher than the multiphase alloy. The novel superlattice biphase alloys with superior overall electrochemical properties are expected to inspire further design and development of HSAs as advanced electrode materials for power batteries.