Lattice dynamics of lithium anti-perovskite solid-state electrolytes Li3OX (X = Cl, Br): An insight into thermal management from first-principles study

In this study, we have employed first-principles calculations based on density functional theory to investigate the thermal properties derived from lattice dynamics of lithium anti-perovskite solid-state electrolytes Li3OX (X = Cl, Br). Given the pronounced anharmonicity in their structures, we have examined the phonon spectra considering both harmonic and anharmonic effects at finite temperatures, as accurate phonon spectra are essential for the subsequent determination of thermal properties. The linear and volumetric thermal expansion coefficients have been evaluated using the quasi-harmonic approximation (QHA). Furthermore, we have assessed the macroscopic and phonon-mode Gruneisen parameters to quantify their anharmonicity. Incorporating higher-order anharmonic effects, we have performed phonon self-consistent calculations (SCPH) to determine the thermal conductivity and factors related to the phonon-gas model, including phonon group velocity, mean free path, and phonon lifetime. Our findings elucidate the underlying mechanisms governing the thermal behavior of antiperovskites, offering useful insights for thermal management of solid-state electrolytes.