Regulating Ion-Dipole Interactions in Weakly Solvating Electrolyte towards Ultra-Low Temperature Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are recognized as promising energy storage devices. However, they suffer from rapid capacity decay at ultra-low temperatures due to high Na+ desolvation energy barrier and unstable solid electrolyte interphase (SEI). Herein, a weakly solvating electrolyte (WSE) with decreased ion-dipole interactions is designed for stable sodium storage in hard carbon (HC) anode at ultra-low temperatures. 2-methyltetrahydrofuran with low solvating power is incorporated into tetrahydrofuran to regulate the interactions between Na+ and solvents. The reduced Na+-dipole interactions facilitate more anionic coordination in the first solvation sheath, which consistently maintains anion-enhanced solvation structures from room to low temperatures to promote inorganic-rich SEI formation. These enable WSE with a low freezing point of -83.3 degree celsius and faster Na+ desolvation kinetics. The HC anode thus affords reversible capacities of 243.2 and 205.4 mAh g(-1) at 50 mA g(-1) at -40 and -60 degree celsius, respectively, and the full cell of HC||Na3V2(PO4)(3) yields an extended lifespan over 250 cycles with high capacity retention of similar to 100 % at -40 degree celsius. This work sheds new lights on the ion-dipole regulation for ultra-low temperature SIBs.