Inhibition mechanism of capacity degradation in Mg-substituted LaY2-xMgxNi9 hydrogen storage alloys

To elucidate the effect of Mg substitution on the electrochemical properties of LaY2Ni9 alloys and its thermodynamic mechanisms, the cyclic stability, maximum discharge capacity (MDC), microstructure evolution, hydrogen induced amorphization (HIA), pulverization, formation energy, and amorphization formation criteria of LaY2-xMgxNi9 (x = 0, 0.25, 0.50, 0.75, and 1.00) alloys are investigated. The calculated formation energy indicates that Mg substitution destabilizes LaY2Ni9 phases and is responsible for decrement of phase fraction of LaY2Ni9 phases. The consumption of LaY2Ni9 phase and the generation of (La, Y)(2)Ni-7 phase improve the cyclic stability by inhibiting the pulverization but reduce the MDC of the alloys. The amorphization formation criterion demonstrates that Mg substitution inhibits the HIA as verified by transmission electron microscopy results, which benefits both the MDC and cyclic stability of the alloys. The LaY1.25Mg0.75Ni9 alloy exhibits good overall electrochemical properties with the MDC of 308.4 mAh/g and capacity retention after 100 cycles of 69.0%. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study investigates the effect of Mg substitution on LaY2Ni9 alloys and finds that Mg substitution destabilizes LaY2Ni9 phases, inhibits pulverization, and improves cyclic stability, while also affecting the maximum discharge capacity of the alloys. Furthermore, Mg substitution inhibits hydrogen-induced amorphization, leading to overall improved electrochemical properties of the alloys.