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This study introduces a nucleophilic fluorination strategy targeting the termination phase of Solid Electrolyte Interphase (SEI) formation to suppress parasitic reactions and reduce irreversible lithium loss. By using phosphorus pentafluoride (PF₅) to chemically modify surface hydroxyl groups on TiO₂ anodes, the method successfully limits excessive organic SEI growth while preserving a beneficial LiF-rich inner layer. Consequently, the fluorinated anode achieves an initial Coulombic efficiency of 92.1%, significantly outperforming the pristine material's 74.1%.

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Coulombic efficiency2.1%

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Abstract

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.

Key findings

  • Traditional SEI modification strategies often consume excess lithium ions and yield limited improvements by focusing on the generation process rather than termination.
  • Nucleophilic fluorination suppresses parasitic reactions between PF₅ and surface hydroxyl groups, effectively terminating SEI formation early in the cycle.
  • The approach reduces organic SEI components while maintaining a LiF-rich inner layer, resulting in an initial Coulombic efficiency of 92.1% for TiO₂ anodes.

Keywords

Faraday efficiencyElectrolyteAnodeInterphaseElectrodeChemical engineering

Identifiers

DOI
10.1002/adma.202508647
PubMed
40557521
Journal
Advances in Materials
Year
2025