First-principles study on the physical properties of double perovskites LiX3H8 (X = Ni and Mn) for hydrogen storage

Abstract

This study explores for the first time the physical properties of novel hydrides LiX₃H₈ (where X = Ni and Mn) as promising candidates for hydrogen storage applications, with particular emphasis on their ionic conductivity behavior under temperature variation. Using density functional theory (DFT)-based simulations, a comprehensive analysis covering structural, electronic, elastic, thermodynamic, ion diffusion, and hydrogen storage properties was performed. The materials exhibit mechanical and thermodynamic stability, as confirmed by phonon spectra (absence of imaginary frequencies), compliance with Born and Huang criteria, and negative formation energies. LiMn₃H₈ demonstrates enhanced mechanical rigidity, with higher compressibility, shear modulus, and Young's modulus compared to LiNi₃H₈. Both compounds show ductile behavior, as revealed by Poisson's ratio and Pugh's B/G ratio, which is desirable for hydrogen storage systems. The hydrogen storage capacities are estimated at 4.23 wt% for LiNi₃H₈ and 4.49 wt% for LiMn₃H₈, with corresponding desorption temperatures of 325.02 K and 325.82 K, respectively. Hydride ion (H⁻) migration barriers are calculated as 0.275 eV for LiNi₃H₈ and 0.299 eV for LiMn₃H₈, indicating efficient diffusion, particularly in LiNi₃H₈. At room temperature (300 K), ionic conductivities reach 0.321 S/cm for LiNi₃H₈ and 0.145 S/cm for LiMn₃H₈, confirming their suitability for fast ion transport. Hydride materials LiX₃H₈ (where X = Ni and Mn) are positioned as attractive materials for next-generation hydrogen storage devices based on these discoveries.