Constructing Robust Interphase Armor via A Fluorinated Alkyne Phosphate Ester Additive for Stable Cycling of Silicon‐Based Lithium‐Ion Batteries

Silicon‐based anodes are promising for high‐energy‐density lithium‐ion batteries but suffer from severe volume expansion and interfacial instability. Herein, a fluorine‐substituted unsaturated phosphate ester additive (PEFA‐3) is proposed to address these challenges. The PEFA‐3 exhibits tailored electronic properties and a low electrostatic potential difference, enabling its preferential oxidation at the cathode and reduction at the anode. This behavior facilitates the formation of robust, polyyne network enhanced interphases (SEI/CEI) on both electrodes. In the 1.6 Ah NCM811||S600 pouch cells, PEFA‐3 enhances cycling stability by achieving 94.6% capacity retention after 300 cycles with the average Coulombic efficiency >99.9%, while effectively suppressing gas evolution and silicon‐based anode failure. The Liquid Chromatography‐Quadrupole Time‐of‐Flight Mass Spectrometry (LC‐QTof‐MS) decouples the decomposition pathways of PEFA‐3 at the electrodes, which indicates that crucial species such as C 6 H 8 O 4 F 3 P in SEI/CEI are beneficial for reinforcing interfacial integrity and inhibiting electrolyte degradation. Our design concept for electrolyte additives provides a promising path to silicon‐based energy‐dense lithium‐ion batteries.