First-Principles Study on a Layered Antiperovskite Li7O2Br3 Solid Electrolyte.

Abstract

Lithium-rich antiperovskites (LiRAPs) have garnered recent attention as solid electrolytes for solid-state lithium-ion batteries (SSLIBs) with high safety and high energy density. Among them, the layered antiperovskite Li7O2Br3 exhibits superior Li+ conductivity compared to cubic antiperovskite Li3OBr. However, the pure phase of Li7O2Br3 has not been synthesized to date, impeding an in-depth investigation of its migration mechanism and electrochemical properties. Herein, we employ density functional theory (DFT) calculations to examine the physical and electrochemical properties of Li7O2Br3. Our results reveal that Li7O2Br3 is dynamically stable in its ground state, featuring electrical insulation with a wide bandgap of approximately 5.83 eV. Moreover, Li7O2Br3 exhibits improved malleability compared to Li3OBr, making it favorable for material processing. Notably, the calculated energy barrier for Li+ migration in Li7O2Br3 is 0.26 eV, lower than that in Li3OBr (0.4 eV), primarily attributed to the softened phonons of Li at the edge layers within the Li7O2Br3 lattice. We also investigated the impact of various defect types on Li+ diffusion in Li7O2Br3, with the results indicating that LiBr defects effectively facilitate Li+ mobility. Additionally, we constructed a pressure-temperature-Gibbs (PTG) free energy phase diagram for Li7O2Br3 to explore appropriate experimental synthesis conditions. These findings hold substantial promise for promoting the research and development of innovative solid electrolyte materials for advanced SSLIBs.