Stabilizing Sodium‐Ion Batteries in Harsh Environments via a Versatile Additive Strategy

Abstract Sodium‐ion batteries (SIBs) encounter substantial operational challenges under elevated temperature and pressure conditions. Herein, a novel electrolyte is designed to stabilize the NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) cathode by adding Ethoxy(pentafluoro)cyclotriphosphazene (PFPN) as a functional additive. PFPN effectively modulates the solvation structure of Na⁺ in the first solvation shell, significantly lowering the desolvation energy barrier. Furthermore, PFPN promotes a robustcathode electrolyte interphase (CEI) film enriched with NaF, NaCl, and Na 3 N, which exhibits enhanced Young's modulus and ionic conductivity.The C‐F bonds from PFPN decompositionfurther enhance the CEI's thermal stability. Furthermore, PFPN suppresses sodium expansion and reduce the release of CO 2 and H 2 . Electrochemical tests demonstrate a dramatic enhancement in capacity retention i, from 43.34% to 78.07% after 300 cycles for NFM//Na coin cells at 45 °C, and 1 C/5 C (2–4.1 V). Moreover, PFPN enhances the wettability of highly loaded electrode materials and electrolytes, facilitating the application of modified electrolytes in NFM//HC full coin cellsand exhibiting excellent cycling stability over 1000 cycles, with a minimal weekly capacity attenuation rate of ≈0.02%. Furthermore, the Ah‐grade pouch cell exhibits excellent cycling stability with 83.79% capacity retention after 500 cycles.