Quasi-Crowding Solvation Design of Ionic Liquid Electrolytes for Stable High-Temperature Potassium-Ion Batteries

A quasi-crowding solvation structure design principle was proposed to develop phosphate-mediated ionic liquid electrolyte (PILE), enabling high ionic conductivity, low desolvation energy barrier, enhanced anion-dominant nature of the inner solvation sheath, and re-stabilization of organic cations in the outer solvation sheath. As a result, the Prussian Blue (PB) cathode in PILE delivered a highly maintained specific capacity of 62.0 mAh/g after 800 cycles at 500 mA/g and 20°C, which can be further improved to be 80.7 mAh/g after 500 cycles at 40°C. The synergistic effect from the quasi-crowding solvation design guaranteed stability, and elevating working temperatures enhanced kinetics, which was revealed to be responsible for the improved K-storage performance, mainly via transforming the cathode-electrolyte-interphase (CEI) formation mechanism from organic-cation-dominated to fluorine-rich-anion-dominated oxidation, and significantly reducing ion transport and charge transfer impedances, respectively. The developed PB||PILE||graphite (Gr) full cell also output a significantly improved energy density of 269.6 Wh/kg and power density of 609.9 W/kg at 200 mA/g and 60°C, attributing to the efficient activation of low-spin Fe-C sites for deep and high-voltage K-storage. These principles and validations will significantly advance the understanding of fundamental electrolyte chemistry and inspire the rational design of high-performance potassium-ion batteries (PIBs) for extreme applications.