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

Abstract

ABSTRACT 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.