Ether-Enabled High-Concentration Ionic Liquid Electrolytes via Monodentate Coordination for Boosted Kinetics in Potassium-Ion Batteries

Ionic liquids (ILs)-based high-concentration electrolytes (HCEs) have the advantages of flame retardancy and abundant anion-rich solvation structures, demonstrating excellent compatibility with organic K-storage cathode materials. However, owing to the characteristics of strong electrostatic solvation networks and viscosity-driven conductivity reduction, the K-storage kinetics of organic cathodes in ILs-based HCEs are significantly impaired. In this work, an ether-enabled high-concentration IL electrolyte was designed to simultaneously address the kinetic and thermodynamic challenges in the K-storage process of the perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) cathode. The developed 2 M potassium bis(fluorosulfonyl)imide (KFSI)/N-propyl-N-methylpyrrolidinium bis(fluoromethanesulfonyl)imide (Pyr13FSI) electrolyte modified with organic ether solvent of 1,2-dimethoxyethane (DME) marked as HDILE demonstrated significantly enhanced ionic conductivity and ionic transfer number and reduced interfacial desolvation energy, ascribed to the broken strong electrostatic interaction network and the formation of a hybrid-coordinated solvation sheath with anions and monodentate coordinated DME. As a result, the optimized one-dimensional PTCDA (1D H-PTCDA) in HDILE delivered a high reversible capacity of 147 mAh g–1 at a current density of 50 mA g–1, with nearly 100% capacity retention after 50 cycles. Moreover, the remarkably reduced impedances in interfacial diffusion and a charge transfer process with a significantly enhanced K+ diffusion coefficient were revealed to be responsible for the enhanced K-storage kinetics in HDILE. The satisfactory specific capacity and rate performance for the assembled PTCDA||HDILE||Bi@C full battery further validate the practical application potential of the designed electrolyte.