Decoupling Ion Transport and Desolvation via Spatially Heterogeneous Solvation Structure for Wide‐Temperature Sodium‐Ion Batteries

ABSTRACT

Despite competitive room‐temperature performance, sodium‐ion batteries suffer from sluggish kinetics and unstable interphases at ultralow temperatures. Herein, a single‐ether (diethylene glycol dibutyl ether, DGDE)‐based electrolyte featuring a spatially heterogeneous solvation structure across both the bulk and interfacial regions is successfully constructed by introducing a strongly polar sulfonate ester additive, 2,2,2‑trifluoroethyl trifluoromethanesulfonate (TTMS). In the bulk, DGDE chelates Na ⁺ via its multiple coordination sites to form a solvent‑separated ion pair dominated solvation structure, thereby enhancing ion dissociation and ionic conductivity. At the electrode–electrolyte interface, TTMS preferentially adsorbs onto the cathode surface, reconstructing the electric double layer into a compact, anion‐rich configuration dominated by contact ion pairs and aggregates. Meanwhile, TTMS in the inner Helmholtz plane provides desolvation‐active sites, lowering the charge‐transfer barrier and enabling the formation of a robust, inorganic‐rich interphase. This spatially heterogeneous solvation structure enables the decoupling of fast bulk ion transport and rapid interface desolvation. Consequently, at −40°C, the Na||NaNi _1/3 Fe _1/3 Mn _1/3 O ₂ cell with the optimized electrolyte delivers an initial specific capacity of 109.9 mAh g ⁻¹ and sustains reversible cycling for 140 cycles with a capacity retention of 87.3%. Moreover, the cell demonstrates reliable electrochemical operation over a wide‐temperature range from −60°C to 55°C.