Effects of Mn and Fe elements on the electrochemical hydrogen storage properties of the A5B19-type La-Y-Mg-Ni-Al alloy for nickel metal hydride battery

Abstract

Rare earth–Mg–Ni-based alloys with superlattice structures are novel anode materials for nickel metal hydride batteries, wherein A5B19-type alloys have been regarded as the replacement of the current commercialized A2B7-type alloys due to the superior discharge ability at high rates and cycling stability. However, it is still a challenge to further improve the hydrogen storage properties of the A5B19-type alloys in a low-cost approach. Herein, we select low-cost Mn and Fe elements to substitute Ni to further reduce the cost of an A5B19-type La0.72Y0.13Mg0.15Ni3.70Al0.15 alloy and focus on their effects on the alloy's structure and hydrogen storage properties. Results show that the La0.72Y0.13Mg0.15Ni3.65Al0.15Fe0.05 alloy features increased intrinsic gas-solid hydrogen storage ability of 1.44 wt% and hydrogen absorption enthalpy change of −22.9 kJ mol–1, which have been altered by 0.21 wt% and 7.3 kJ mol–1 in contrast to the La0.72Y0.13Mg0.15Ni3.70Al0.15 alloy, respectively. Furthermore, the Fe substitution benefits capacity retention during electrochemical cycling compared to Mn, which maintains 87.5% and 62.4% after cycling 100 and 500 times. The Mn substitution results in superior rate capability compared to the alloy containing Fe. The work provides guidance for designing hydrogen storage alloys with superlattice structures to improve the electrochemical performance.