Interface Stability\nand Reaction Mechanisms of Li<sub>3</sub>YCl<sub>5</sub>Br with High-Voltage\nCathodes and Li Metal\nAnode: Insights from Ab Initio Simulations

Recent advancements in battery technology emphasize the\ncritical\nrole of solid electrolytes in enhancing the performance and safety\nof next-generation batteries. In this study, we investigate the interface\nstability and reaction mechanisms of Li<sub>3</sub>YCl<sub>5</sub>Br, a promising halide-based solid electrolyte, in contact with high-voltage\nNi–Mn–Co (NMC) cathodes and a Li metal anode using ab\ninitio molecular dynamics simulations. Our findings reveal that Li<sub>3</sub>YCl<sub>5</sub>Br reacts with charged NMC cathodes. This reaction\ninvolves changes in the oxidation states of Br<sup>–</sup> anions\nin Li<sub>3</sub>YCl<sub>5</sub>Br and d-element cations in NMC, as\nwell as the diffusion of Li ions from the solid electrolyte to the\ncathode to maintain charge balance. The reaction is confined to the\ninterface, suggesting bulk stability. Conversely, the Li/Li<sub>3</sub>YCl<sub>5</sub>Br interface exhibits significant instability, with\na chemical reaction that results in substantial structural changes\nand the formation of LiCl and LiBr at the solid electrolyte surface\nand metallic Y at the Li anode surface. These insights provide valuable\ninformation for optimizing interfacial design, aiming at improving\nthe performance and reliability of all-solid-state batteries using\nhalide solid electrolytes.