Highly-solvating Electrolyte Enables Mechanically Stable and Inorganic-rich Cathode Electrolyte Interphase for High-performing Potassium-ion Batteries.

Cathode-electrolyte interphase (CEI) is crucial for the reversibility of rechargeable batteries, yet receives less attention compared to solid-electrolyte interphase (SEI). The prevalent weakly-solvating electrolyte is usually proposed from the standing point of obtaining robust SEI, however, the resultant weak ion-solvent interaction gives rise to excessive free solvents and forms thick CEI with high kinetic barriers, which is disadvantageous for interfacial stability at the high working voltage. Herein, we report a highly-solvating electrolyte to immobilize free solvents by generating stable ternary complexes and facilitate the growth of homogeneous and ultrathin CEI to boost the electrochemical performances of potassium-ion batteries (PIBs). Through time-of-flight secondary ion mass spectrometry and cryogenic transmission electron microscopy, we reveal that the deliberately coordinated complexes are the key to forming mechanically stable and inorganic-rich CEI with superior diffusion kinetics for high-performing PIBs. Coupling with a K 0.5 MnO 2 cathode and a soft carbon (SC) anode, we achieve a high energy density (202.3 Wh kg -1 ) with an exceptional cycle lifespan (92.5% capacity retention after 500 cycles) in a SC||K 0.5 MnO 2 full cell, setting new performance benchmarks for PIBs. This article is protected by copyright. All rights reserved.