Early Terminating Solid Electrolyte Interphase Formation via Nucleophilic Fluorination to Achieve High Initial Coulombic Efficiency.

The initial Coulombic efficiency (ICE) of lithium-ion batteries, quantifying the irreversible Li+ loss during the first cycle, is critical for determining practical energy density. Many electrode materials exhibit substandard ICEs (<90%) due to excessive formation of solid electrolyte interphase (SEI). Traditional strategies modifying SEI formation mainly focus on the generating process but often consume extra Li+ and yield limited improvements. Here, a strategy is introduced that targets the terminating process of SEI formation, usually impeded by interfacial parasitic reactions, to achieve ICEs exceeding 90%. Using TiO2 as a model electrode, it is demonstrated that equivalent chemical fluorination suppresses the parasitic reaction between phosphorus pentafluoride (PF₅) and surface hydroxyl groups (─OH), early terminating SEI formation. Interfacial analysis and theoretical simulations reveal that this approach reduces organic SEI formation while preserving the beneficial LiF-rich inner SEI layer. As a result, the fluorinated TiO2 anode exhibits an ICE of 92.1%, significantly higher than the 74.1% of pristine TiO2, without compromising other electrochemical performance metrics. Pouch cell tests confirm the practical applicability of the method. This work provides deep insights into mechanisms of terminating SEI formation and opens a new pathway for optimizing the battery performances through inherent SEI manipulation.