In Situ Construction of Uniform and Elastic Solid–Electrolyte Interphase for High‐Performance Potassium Batteries

Abstract Solid electrolyte interphase (SEI) plays a crucial role in a battery. This study leverages the assistance of weak interactions to construct a uniform and elastic SEI for potassium batteries. The caffeic acid phenethyl ester (CAPE) is introduced into the electrolyte, and the weak interactions between CAPE and anodes enable CAPE to contact electrons preferentially during cycling. The unsaturated carbon═carbon double bonds in CAPE molecules receive electrons and undergo polymerization reactions on the anode surface, forming a uniform and elastic SEI. Such SEI exhibits good uniformity and excellent mechanical elasticity, enabling the SEI to adapt well to the huge volume changes of the anode to maintain structural stability during cycling. As a result, the graphite anode exhibits over 1500 stable cycles at a current density of 100 mA g⁻¹. The potassium metal full battery based on a Prussian blue (PB) cathode cycles over 5700 times at a current density of 1000 mA g⁻¹. In addition, the pouch potassium‐ion full battery based on a graphite anode and a PB cathode also shows excellent electrochemical performance, which operates stably for over 600 cycles without significant attenuation in capacity at a current density of 200 mA g⁻¹, showing potential practical value.