Phase Transformation and Electrochemical Feature of an AB4-Type La0.60Sm0.20Mg0.20Ni3.50Al0.20 Hydrogen Storage Alloy for Ni/MH Batteries

Abstract

La–Mg–Ni-based alloys with a novel AB4-type superlattice structure is supposed as potential anode materials for nickel metal hydride (Ni/MH) batteries due to the excellent discharge ability at high rates and long cycling life. However, it is still challenging to achieve high phase content of the AB4-type structure during annealing due to the complex peritectic reaction of virous superlattice structures. Herein, we study the phase transformation of the AB4-type structure upon annealing and elucidate its effect on electrochemical characteristics based on a La0.60Sm0.20Mg0.20Ni3.50Al0.20 alloy. It is found that the AB4-type phase forms between 970 °C–1000 °C by a peritectic reaction of A5B19- and CaCu5-type phases. The existence of AB4-type phase drives the alloy a higher discharge capacity of 366 mAh g–1 at 60 mA g–1, and 135 mAh g–1 at 1800 mA g–1 owing to the advantages of charge transfer and hydrogen diffusion. Moreover, high capacity retentions of 88.7% and 79.3% at the 100th and 200th cycles are respectively achieved. Besides, the alloy with the AB4-type phase shows improved tolerance at a low temperature of –40 °C. We expect that our finding can provide guidance for developing AB4-type hydrogen storage alloy for Ni/MH.