Anion/Cation Synergy-Reinforced Electrode/Electrolyte Interphases via Ionic Liquid Electrolyte Engineering for Ultralong Cycling High-Voltage Potassium Batteries

The pursuit of safe high-energy potassium batteries (PBs) encounters critical challenges stemming from unstable interphases at both the anode and cathode and flammable electrolytes. Herein, we engineered a nonflammable ionic liquid (IL) electrolyte that revolutionizes interfacial chemistry through bidirectional anion–cation coordination. This distinctive solvation structure drives the spontaneous formation of inorganic-dominated solid-electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI), enabling dendrite-free K anodes (98.0% Coulomb efficiency over 800 cycles in K//Cu cell, 4800 h ultralong cycling in K//K symmetric cell) and high-voltage Prussian blue cathodes (stable operation at 4.6 V for 2200 cycles). The synergy between FSI^– decomposition and PY13⁺ electrostatic shielding yields an ultrastable graphite//Prussian blue analogue (PBA) full-battery configuration, achieving a record energy density of 148.5 Wh kg^–1 with exceptional cyclability exceeding 3600 cycles, outperforming state-of-the-art systems. This work presents a new design concept for nonflammable, long-cycling, high-energy PBs.