Effects of milling duration on electrochemical hydrogen storage behavior of as-milled Mg–Ce–Ni–Al-based alloys for use in Ni-metal hydride batteries

Abstract

Mg-based hydrogen storage alloys are regarded as ideal materials for use as the negative electrode in nickel-metal hydride batteries. However, their poor electrochemical de-/hydriding performance at room temperature is a problem. Methods comprising the partial substitution with Ce for Mg and surface modification by mechanical coating with Ni have been applied to address the problem. In this study, nanocrystalline and amorphous Mg1-xCexNi0.9Al0.1 (x = 0, 0.02, 0.04, 0.06, 0.08) + 50 wt%Ni (named Mg1-xCexNi0.9Al0.1 (x = 0, 0.02, 0.04, 0.06, 0.08) + 50Ni) alloys were synthesized by mechanical milling. Electrochemical testing showed that the samples exhibited outstanding electrochemical de-/hydriding performance at room temperature. The maximum discharge capacities were obtained after only one de-/hydriding cycle and without any need for activation. The discharge capacity and cycle stability increased with the milling duration. In particular, for the alloy where x = 0.04, the discharge capacity increased from 378.8 to 578.4 mAh/g, and the capacity retention rate after the 100th cycle increased from 51% to 69% as the milling duration increased from 5 to 30 h. Furthermore, measurements based on the high rate discharge ability, electrochemical impedance spectra, potentiodynamic polarization curves, and potential-step measurements demonstrated that the electrochemical kinetic properties of the alloys could be improved by extending the duration of milling.