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 NaNi1/3Fe1/3Mn1/3O2∥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.