Fluorinated Aromatic Nitrile Electrolyte Additive for Simultaneous Stabilization of Anode and Cathode Interphases for High‐Performance Sodium‐Ion Batteries

ABSTRACT Sodium‐ion batteries (SIBs) are attractive for large‐scale energy storage owing to the abundance of sodium, long cycle life, and high safety. However, the electrochemical performance is largely hindered by unstable electrode–electrolyte interphases, particularly in high capacity layered oxide cathodes, where electrolyte decomposition, transition‐metal dissolution, and structural degradation occur. Here, we report 2,3,5,6‐tetrafluoro‐1,4‐terephthalonitrile (TFTPN) as a fluorine‐, nitrile‐, and aromatic ring‐functionalized additive that simultaneously stabilizes the solid electrolyte interphase (SEI) on hard carbon and the cathode electrolyte interphase (CEI) on layered oxides. The fluorinated aromatic framework promotes the formation of a dense and robust NaF‐rich interphase, while the nitrile groups enhance interfacial interaction with transition‐metal centers and contribute to lattice stabilization. Electrochemical and theoretical analyses reveal that TFTPN participates in interfacial reactions at both electrodes, leading to the formation of thin (<30 nm), uniform, and chemically robust interphases that suppress parasitic reactions and maintain structural stability. Hard carbon//Na[Ni 1/3 Fe 1/3 Mn 1/3 ]O 2 pouch full cells with TFTPN deliver outstanding cycling stability (95.2% capacity retention after 800 cycles), high‐rate capability (75.7% retention at 8C), and excellent low‐temperature performance (90.4% retention at −20°C). This work presents simple and novel design strategy of multifunctional electrolyte additives to engineer both anode and cathode interphases for high‐performance SIBs.