Molecular descriptor-guided design of weakly solvating electrolytes for low-temperature sodium-ion batteries

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The development of sodium-ion batteries (SIBs) for low-temperature applications is hindered by sluggish interfacial kinetics, primarily due to the high desolvation energy barrier of Na + . This study introduces a rational electrolyte design strategy that modulates the coordination strength solely by varying the molecular chain length of ether solvents (from diethylene glycol dimethyl ether to tetraglycol dimethyl ether, G2 to G4) while keeping functional groups constant. We establish the solvent electrostatic potential (ESP) and its binding energy with Na + as effective molecular descriptors for screening weakly coordinating solvents. Theoretical and experimental analyses reveal that increasing chain length reduces solvent ESP and weakens Na + -solvent interaction, which promotes the formation of CIP dominated solvation structures and lowers the desolvation barrier. The optimized electrolyte with the solvent (G4) with the weakest negative ESP value and the smallest binding energy with Na + enables superior low-temperature performance at −20 °C, delivering a high reversible capacity of 141.4 mAh g −1 at 2 C and retaining 95.3% capacity after 200 cycles, significantly outperforming its shorter-chain counterparts. This performance is attributed to the formation of a stable, inorganic-rich solid-electrolyte interphase derived from anion participation, which facilitates fast Na + transport. This work provides a novel and generalizable solvent design paradigm for high-performance, low-temperature energy storage systems.