First-Principles Study on a Layered Antiperovskite Li₇O₂Br₃ Solid Electrolyte

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.