Lightweight alkali-induced lattice-dynamical stability and energy storage mechanism of quaternary Mg-based hydrides under pressure effect

Abstract

New-discovery compositions of the lightweight quaternary Mg-based hydrides at ambient pressure are found as NaLiMgH4, NaLiMg2H6, and Na3LiMg4H12, which their stabilities were determined by all positive modes of the phonon dispersion relation. The varying compositions of Na-Li-Mg-H were analyzed using the ab initio random structure searching technique and affirmed by mechanical stability and Born stability criteria. Besides, the effects of pressure on stable structures are considered also. High-gravimetric hydrogen capacity introduces us to study H-vacancy occurrence and H-diffusion kinetics in these lightweight quaternary hydrides. Our calculation results indicated that the NaLiMg2H6 in the P21/m system gave more suitable for hydrogen storage material due to lower energy barriers as well as the hydrogen diffusion kinetics in this lightweight hydride for its practical use in energy storage applications.