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, a highly-solvating electrolyte is reported 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, It is revealed 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_0.5MnO₂ cathode and a soft carbon (SC) anode, a high energy density (202.3 Wh kg^-1) is achieved with an exceptional cycle lifespan (92.5% capacity retention after 500 cycles) in a SC||K_0.5MnO₂ full cell, setting new performance benchmarks for PIBs.