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 °C 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 °C, respectively, and the full cell of HC||Na 3 V 2 (PO 4 ) 3 yields an extended lifespan over 250 cycles with high capacity retention of ~100 % at −40 °C. This work sheds new lights on the ion‐dipole regulation for ultra‐low temperature SIBs.