Enhancing Wide-Temperature Performance of Lithium Batteries with a LiFSI-KFSI Dual-Salt Electrolyte

The synergistic combination of lithium hexafluorophosphate (LiPF₆) and multicomponent carbonates extends the low-temperature liquid range and enhances electrolyte performance at subambient temperatures. However, the solvation structure dominated by solvent-separated ion pairs (SSIPs), along with poor lithium deposition, sluggish intercalation kinetics, and limited thermal stability, hinder further application over a wide temperature range. Herein, a dual-salt electrolyte comprising lithium bis(fluorosulfonyl)imide (LiFSI) and potassium bis(fluorosulfonyl)imide (KFSI) is developed to tailor solvation chemistry and improve interfacial kinetics. The FSI⁻ anion and K⁺ electrostatic shielding synergistically promote the formation of a uniform and robust solid electrolyte interphase (SEI), ensuring enhanced interfacial stability. As a result, the electrolyte supports stable operation from -70 °C to 60 °C. At -40 °C, LiFePO₄ (LFP)|Li and Li₄Ti₅O₁₂ (LTO)|Li cells retain 75.3% and 90.2% of their room temperature capacity, respectively, while the LFP|graphite pouch cell delivers a high discharge capacity of 323 mAh. Furthermore, Ah-level LFP|graphite pouch cells exhibit excellent cycling performance, with 82.9% capacity retention after 1200 cycles at 25 °C and 78.1% after 200 cycles at 60 °C. This study offers a practical electrolyte design strategy to realize lithium-ion batteries with wide-temperature adaptability and long-term durability.