Highly‐Solvating Electrolyte Enables Mechanically Stable and Inorganic‐Rich Cathode Electrolyte Interphase for High‐Performing Potassium‐Ion Batteries

Abstract

AbstractCathode–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 K0.5MnO2 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||K0.5MnO2 full cell, setting new performance benchmarks for PIBs.