Breaking Anionic Solvation Barrier for Safe and Durable Potassium-ion Batteries Under Ultrahigh-Voltage Operation.

Ultrahigh-voltage potassium-ion batteries (PIBs) with cost competitiveness represent a viable route towards high energy battery systems. Nevertheless, rapid capacity decay with poor Coulombic efficiencies remains intractable, mainly attributed to interfacial instability from aggressive potassium metal anodes and cathodes. Additionally, high reactivity of K metal and flammable electrolytes pose severe safety hazards. Herein, a weakly solvating fluorinated electrolyte with intrinsically nonflammable feature is successfully developed to enable an ultrahigh-voltage (up to 5.5 V) operation. Through breaking the anionic solvation barrier, synergistic interfacial modulation can be achieved by the formation of robust anion-derived inorganic-rich electrode-electrolyte interfaces on both the cathode and anode. As proof of concept, a representative KVPOF cathode can sustain 1600 cycles with 84.4 % of capacity retention at a high cutoff voltage of 4.95 V. Meanwhile, K plating/stripping process in our designed electrolyte also demonstrates optimized electrochemical reversibility and stability with effectively inhibited potassium dendrites. These findings underscore the critical impact of anion-dominated solvation configuration on synergistic interfacial modulation and electrochemical properties. This work provides new insights into rational design of ultrahigh-voltage and safe electrolyte for advanced PIBs.