Fluorinated Weakly Coordinating Solvent Enables High-Areal-Capacity Low-Temperature Sodium Batteries

High areal capacity and stable low-temperature operation are critical for the practical implementation of sodium-ion batteries, yet their development is hindered by sluggish charge/mass transfer kinetics at low temperatures and interfacial instability during cycling. Herein, we incorporate the weakly coordinating solvent ethoxy(pentafluoro)cyclotriphosphazene (PFPN) into the conventional NaPF₆-PC/DEC electrolyte. PFPN competitively binds to Na⁺ with PC/DEC through its steric hindrance effect, weakening solvent-ion interactions to enhance Na⁺ migration kinetics at low temperatures. Concurrently, it coordinates with highly electronegative PF₆^- anions, facilitating their redistribution and the formation of a stable anion-derived electrode-electrolyte interphase. At a high areal capacity of 2.0 mAh cm^-2 (N/P = 1.29) and -40 °C, the NaNi_1/3Fe_1/3Mn_1/3O₂∥hard carbon batteries utilizing the PFPN-modified electrolyte exhibit stable cycling with 89.9% capacity retention over 200 cycles, while the pouch cell delivers a high energy density of 112.5 Wh kg^-1. This work offers valuable insights for the design of high-areal-capacity sodium batteries tailored for cold regions.