Phase Transformation and Electrochemical Feature of an AB<sub>4</sub>-Type La<sub>0.60</sub>Sm<sub>0.20</sub>Mg<sub>0.20</sub>Ni<sub>3.50</sub>Al<sub>0.20</sub> Hydrogen Storage Alloy for Ni/MH Batteries
Hang Lu, Yanan Guo, Qing Wang, Anyi Zhang, Yuan Li, Ning Xi, Xiaomei Zhu, Shumin Han, Lu Zhang
Abstract
La–Mg–Ni-based alloys with a novel AB 4 -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 AB 4 -type structure during annealing due to the complex peritectic reaction of virous superlattice structures. Herein, we study the phase transformation of the AB 4 -type structure upon annealing and elucidate its effect on electrochemical characteristics based on a La 0.60 Sm 0.20 Mg 0.20 Ni 3.50 Al 0.20 alloy. It is found that the AB 4 -type phase forms between 970 °C–1000 °C by a peritectic reaction of A 5 B 19 - and CaCu 5 -type phases. The existence of AB 4 -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 AB 4 -type phase shows improved tolerance at a low temperature of –40 °C. We expect that our finding can provide guidance for developing AB 4 -type hydrogen storage alloy for Ni/MH.