Synergetic Electrolyte Chemistry Enables Flame-Retardancy, K+-Desolvation, Anti-Corrosion and Wide-Temperature-Tolerance in Potassium-Ion Batteries

Potassium-ion batteries (PIBs) have emerged as an appealing, sustainable and cost-effective candidate for grid-scale energy storage due to abundant K resources and reversible K⁺ de/intercalation in graphite anodes (KC₈, 279 mAh g^–1). However, their practical operation suffers from sluggish kinetics and severe capacity deterioration in traditional carbonate electrolytes. Herein, ethoxy (pentafluoro) cyclotriphosphazene (PFPN) and methyl (2,2,2-trifluoroethyl) carbonate (FEMC) are introduced as cosolvents to rejuvenate conventionally low-concentration (1 M) 1,2-dimethoxyethane (DME)-based electrolytes. In the resultant 1 M KFSI-DME/PFPN/FEMC (3 vol %) electrolyte, the cyclotriphosphazene group of PFPN is revealed to not only mitigate the flammability of DME but also diminish the K⁺-DME interaction through steric hindrance. While FEMC preempts the DME-induced corrosion of the potassium anode by facilitating the formation of a KF-enriched interface. Consequently, ether cointercalation into graphite is successfully suppressed in K||graphite cells, exhibiting 96% capacity retention over 1800 cycles (a running time of 402 days). When the temperature drops from 50 to −20 °C, the K-ion full device retains a capacity as high as 89%. The study introduces a novel electrolyte regulation strategy that harmonizes intrinsic safety, rapid kinetics at subzero temperatures, and enduring cycle stability at the same time, thereby advancing the practical implementation of PIBs for the future.