First principles exploration of high hydrogen storage capacity of lithium-based perovskite hydrides

The search for efficient solid-state hydrogen storage materials is essential for advancing clean energy technologies. In this work, Li-based perovskite hydrides (LiBH₃, LiCuH₃, LiMgH₃, and LiSiH₃) are studied using first-principles calculations. All compounds show negative formation energies, indicating thermodynamic stability. LiBH₃, LiCuH₃, and LiMgH₃ are dynamically stable, while LiSiH₃ is unstable due to imaginary phonon modes. Mechanical analysis confirms stability for all systems, with LiCuH₃ and LiMgH₃ showing higher rigidity. Electronic properties reveal metallic behavior for LiBH₃, LiCuH₃, and LiSiH₃, while LiMgH₃ is semiconducting with a 2.59 eV band gap. Hydrogen storage capacities are 14.56 wt% for LiBH₃, 4.11 wt% for LiCuH₃, 8.82 wt% for LiMgH₃, and 7.95 wt% for LiSiH₃. LiCuH₃ also shows the lowest desorption temperature (382.7 K), indicating favorable kinetics.

All calculations were performed within the framework of density functional theory (DFT) using the Quantum ESPRESSO package. The exchange-correlation energy was treated using the generalized gradient approximation in the Perdew-Burke-Ernzerhof (GGA-PBE) form, and electron-ion interactions were described using ultrasoft pseudopotentials. Valence configurations included Li (2s¹), H (1s¹), B (2s²2p¹), Cu (3d^9.54s^1.5), Mg (3s²), and Si (3s²3p²). Convergence tests determined a plane-wave cutoff energy of 55 Ry and a Monkhorst-Pack k-point mesh of 9 × 9 × 9, ensuring total energy convergence within 1-2 meV/atom. Structural optimizations were carried out using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm with convergence thresholds of 1 × 10⁻⁶ eV/atom for energy and 1 × 10⁻³ eV/Å for forces. Phonon dispersion, mechanical properties, and optical responses were evaluated using the thermo_pw package integrated with Quantum ESPRESSO.