Fluorobenzene‐Mediated Dragging Effect Boosting Bulk/Interfacial Ion Transport Enables −50°C Operation of Long‐Life Potassium‐Ion Batteries

ABSTRACT

The small Stokes radius of K ⁺ in propylene carbonate (PC) (3.6 Å) potentially promotes fast migration both in the bulk electrolyte and interface. However, the practical applications of potassium‐ion batteries (PIBs) are still hindered by sluggish desolvation kinetics and interfacial instability under low‐temperature conditions. Herein, PC‐based electrolytes with fast ion mobility were designed by coupling the features of high‐concentration electrolytes with the “dragging effect” (non‐solvating interaction) between fluorobenzene (FB) and PC. The optimized electrolyte enriching with contact ion pairs (CIPs) and aggregates (AGGs) exhibits a threefold reduction of viscosity, 40% increased ionic conductivity (∼3.9 mS cm ⁻¹ at −10°C), 8% reduced desolvation activation energy (32.5 kJ mol ⁻¹ ), and a KF‐rich solid electrolyte interphase (SEI) with a thirteenfold increase of mechanical modulus (16.7 GPa). Consequently, the graphite // K‐FeHCFe full cells maintain over 51% of room‐temperature capacity even at −50°C and exhibit long‐term cycling stability at 25°C (77.4% after 1000 cycles) and −20°C (91.2% after 300 cycles). Furthermore, 70 mAh pouch cells deliver 90% capacity retention after 100 cycles at −10°C. This work elucidates the effects of solvation structure on desolvation kinetics and interfacial stability, providing a design strategy for high‐performance, low‐temperature PIBs.