Ultrastable Potassium Storage Performance Realized by Highly Effective Solid Electrolyte Interphase Layer

Abstract Potassium ion‐batteries (PIBs) have attracted tremendous attention recently due to the abundance of potassium resources and the low standard electrode potential of potassium. Particularly, the solid‐electrolyte interphase (SEI) in the anode of PIBs plays a vital role in battery security and battery cycling performance due to the highly reactive potassium. However, the SEI in the anode for PIBs with traditional electrolytes is mainly composed of organic compositions, which are highly reactive with air and water, resulting in inferior cycle performance and safety hazards. Herein, a highly stable and effective inorganic SEI layer in the anode is formed with optimized electrolyte. As expected, the PIBs exhibit an ultralong cycle performance over 14 000 cycles at 2000 mA g −1 and an ultrahigh average coulombic efficiency over 99.9%.