Feasibility study of LiSiH₃ as hydrogen storage material

Abstract

Solid state hydrogen storage materials must simultaneously satisfy both gravimetric, volumetric, and stability requirements to be viable for onboard energy applications. In this work, first principles density functional theory (DFT) calculations are employed to investigate the structural, electronic, mechanical, thermodynamic and dynamical properties of the complex hydride LiSiH3 as a candidate hydrogen storage medium. From the crystal structure indicate a gravimetric capacity of about 7.9 wt% H2 (≈2.7 kWh kg−1) and a volumetric energy density of ≈4.6 kWh L−1, substantially exceeding the 2025 U.S. Department of Energy targets and outperforming compressed hydrogen at 700 bar. Electronic band structure and projected density of states analyses reveal strong Si–H covalent bonding and a largely ionic interaction between Li+ and the SiH−3 framework, consistent with a lightweight, hydrogen rich lattice. Elastic constants satisfy the Born criteria, confirming mechanical stability, although the calculated Pugh’s ratio and Poisson’s ratio indicate intrinsically brittle behaviour. Thermodynamic functions from the quasi harmonic Debye model approach the classical limits at high temperature, while phonon dispersion curves exhibit pronounced imaginary modes, signalling dynamical instability of the studied phase at ambient conditions. Overall, LiSiH3 offers highly attractive storage capacities.