Asymmetric Glycol-Ether Molecule Design Enables Temperature-Adaptive Anion Coordination for Durable High-Temperature Sodium Batteries

High-voltage and high-temperature sodium-ion batteries (SIBs) promise cost-effective energy storage applications in extreme scenarios, but a critical dilemma persists: the chemical and electrochemical instability of conventional electrolytes. The intensified electrolyte consumption, electrode failure, and interface damage result from aggressive H+ corrosion, especially in NaPF6-based electrolytes. To address this challenge, this study proposes a molecular design strategy based on an asymmetric glycol-ether (F3Si) cosolvent. Leveraging its steric hindrance effect, we modulate the Na+ coordination environment, thereby altering traditional solvation structures and promoting anion participation in constructing a stable, inorganic-rich cathode-electrolyte interphase (CEI). Experimental and theoretical simulation results demonstrate that the involvement of F3Si in the Na+ solvation sheath exhibits temperature-adaptive characteristics: as temperature increases, more anions are incorporated into the coordination sphere, facilitating the formation of a high-modulus, inorganic-rich CEI. Meanwhile, the F3Si cosolvent effectively captures adverse acidic species via Si–O bonding, interrupting subsequent chain-like side reactions. Consequently, the developed electrolyte enables the 4.3 V–Na3V2(PO4)2O2F cathode to demonstrate exceptional cycling stability under extreme thermal conditions─retaining 88.9% of capacity after 2000 cycles at 70 °C and maintaining 98.5% of capacity over 400 cycles at 90 °C. This work elucidates a temperature-responsive interface stabilization mechanism rooted in solvent molecular geometry and anion solvation, offering innovative electrolyte design principles for developing high-performance SIBs in harsh temperature regimes.