Moderately Solvated Electrolyte Enabling Fast Charging of a Lithium-Ion Battery at Low Temperature.

Lithium-ion batteries operating under low-temperature conditions suffer from sluggish ion transport and hindered interfacial desolvation, which limit fast-charging capability and cycling stability. Herein, a moderate solvation strategy is adopted, which enables a rational balance between bulk ionic transport and interfacial kinetics through tuning solvent-Li+-anion interactions. Notably, the as-designed moderately solvated electrolyte (MSE), employing dimethyl sulfite (DMS) and dimethyl ketone (DMK), is enriched with contact ion pairs (CIPs), which simultaneously preserves sufficient ion transport and reduced interfacial desolvation barrier, leading to well-balanced electrochemical kinetics with remarkably fast charging performance under low temperature. Graphite||LiCoO2 full cells achieved 82.8% capacity retention after 1500 cycles at 1 C rate at -20 °C, and even at -40 °C, reversible cycling can still be achieved at a record-breaking rate of 0.5 C. The 1 Ah pouch cells can also achieve over 90% capacity retention at -40 °C. This work reveals how the evolution of electrolyte solvation structures intrinsically governs electrochemical performance and provides new insights into electrolyte design principles for advanced low-temperature energy storage systems.