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.