A Temperature-Adapted Ultraweakly Solvating Electrolyte for Cold-Resistant Sodium-Ion Batteries

Sodium-ion batteries are applied to cold-resistant energy storage hindered by phase transitions and sluggish Na⁺ migration of traditional carbonate-based electrolytes at low temperatures. The desolvation of Na⁺ is a crucial step in impeding the transport of Na⁺, which primarily attributes to the robust solvent coordination of Na⁺. Herein, a low-temperature adaptive electrolyte with an ultraweakly coordinated 1,3-dioxolane (DOL) is designed for constructing anion-rich solvation structure in a diglyme (G2)-based electrolyte. The electronegativity of the oxygen atoms of G2 is attenuated by dipole-dipole interaction between DOL and G2. As the temperature drops, the weakened Na⁺‒O (G2) interaction leads to increased anionic coordination and less solvent coordination, facilitating the desolvation of Na⁺. This anionic-enhanced solvation structure contributes to the formation of stable solid electrolyte interface at the hard carbon (HC) anode, which accelerates Na⁺ transport and diminishing the voltage polarization at low temperatures. Consequently, the HC anode can retain a high capacity of 203.9 mAh g^‒1 (1 C) at ‒50 °C, and the pouch cell composed of HC||Na₃V₂(PO₄)₃ at ‒30 °C achieves a capacity retention of 92.43% after 100 cycles at 0.1 C. This strategy guides the design of ultra-low temperature electrolytes and broadens the range of applications for sodium-ion batteries.