First-Principles Study on a Layered Antiperovskite Li 7 O 2 Br 3 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 Li 7 O 2 Br 3 exhibits superior Li + conductivity compared to cubic antiperovskite Li 3 OBr. However, the pure phase of Li 7 O 2 Br 3 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 Li 7 O 2 Br 3 . Our results reveal that Li 7 O 2 Br 3 is dynamically stable in its ground state, featuring electrical insulation with a wide bandgap of approximately 5.83 eV. Moreover, Li 7 O 2 Br 3 exhibits improved malleability compared to Li 3 OBr, making it favorable for material processing. Notably, the calculated energy barrier for Li + migration in Li 7 O 2 Br 3 is 0.26 eV, lower than that in Li 3 OBr (0.4 eV), primarily attributed to the softened phonons of Li at the edge layers within the Li 7 O 2 Br 3 lattice. We also investigated the impact of various defect types on Li + diffusion in Li 7 O 2 Br 3 , with the results indicating that LiBr defects effectively facilitate Li + mobility. Additionally, we constructed a pressure-temperature-Gibbs (PTG) free energy phase diagram for Li 7 O 2 Br 3 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.