Temperature-Robust Solvation Enabled by Solvent Interactions for Low-Temperature Sodium Metal Batteries

The broad temperature adaptability associated with the desolvation process remains a formidable challenge for organic electrolytes in rechargeable metal batteries, especially under low-temperature (LT) conditions. Although a traditional approach involves utilizing electrolytes with a high degree of anion participation in the solvation structure, known as weakly solvation electrolytes (WSEs), the solvation structure of these electrolytes is highly susceptible to temperature fluctuations, potentially undermining their LT performance. To address this limitation, we have devised an innovative electrolyte that harnesses the interplay between solvent molecules, effectively blending strong and weak solvents while incorporating anion participation in a solvation structure that remains mostly unchanged by temperature variations. Remarkably, the competitive coordination between the two solvent molecules introduces local disorder, which not only boosts ionic conductivity but also prevents salt precipitation and solidification. Therefore, this electrolyte has a conductivity of 3.12 mS cm^-1 at −40 °C. Na₃V₂(PO₄)₃||Na cells demonstrated a high reversible capacity of 95.9 mAh g^-1 at −40 °C, which is 87.6% of that at room temperature, as well as stable cycling for 3400 cycles with capacity retention of 98.2% at −20 °C and 5 C and 600 cycles with capacity retention of 96.1% at −40 °C and 1 C. This study provides a new perspective on designing LT electrolytes by regulating temperature-robust solvation structures.