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

Abstract The synergistic combination of lithium hexafluorophosphate (LiPF 6 ) 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, LiFePO 4 (LFP)|Li and Li 4 Ti 5 O 12 (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.