A Compact‐Solvation Electrolyte Under Low Concentration for High‐Energy Density and Stable Potassium‐Ion Batteries

The development of potassium-ion batteries (PIBs) faces significant challenges due to the lack of suitable electrolytes to achieve satisfactory energy density and long-term stability. This work reports an innovative compact-solvation electrolyte (CSE) strategy leveraging ionic liquid-induced manipulation of solvation structures under low concentration for high-performance PIBs. The CSE, formulated with a low-salt concentration of 0.8 M, simultaneously exhibits compact solvation structures with abundant F-rich anions, high-ionic conductivity, and low-desolvation energy. These features lead to enhanced K-storage thermodynamics and kinetics through the formation of a robust KF-rich solid electrolyte interphase (SEI) as well as accelerated K⁺ transport kinetics. Consequently, the graphite electrode in CSE delivers a high-reversible capacity of 252 mAh g^-1 with an average Coulombic efficiency of 99.5% after 300 cycles at 50 mA g. Furthermore, the designed CSE enables the Prussian blue||graphite full cell to operate for over 1450 cycles at 50 mA g^-1, maintaining an impressive capacity retention of 88%. This work represents a significant advance in the development of safe and compatible electrolytes for advanced PIBs.