A Conformal Protective Skin Producing Stable Cathode‐Electrolyte Interface for Long‐Life Potassium‐Ion Batteries

Abstract The development of K‐based layered oxide cathodes is essential for boosting the competitiveness of potassium‐ion batteries (PIBs) in grid‐scale energy storage. However, their service life is dramatically limited by interfacial instability issues, which is still poorly understood. In this work, amorphous FePO 4 (a‐FP) is built on K 0.5 Ni 0.1 Mn 0.9 O 2 (KNMO) as the protective skin, whose elasticity for strain relaxation and the K‐conducting nature guarantee its integrity during fast and constant K‐ion insertion/extraction. The conformal coating leads to a robust interphase on the cathode surface, which qualifies excellent K‐transport ability and significantly suppresses the mechanical cracking and transition metal dissolution. Breakthrough in cycle life of the K‐based layered cathodes is therefore achieved, which of the amorphous FePO 4 coated K 0.5 Ni 0.1 Mn 0.9 O 2 (KNMO@a‐FP) reaches 2500 cycles. The insights gained from the surface protection layer construction and the in‐depth analysis of its working mechanism pave the way for further development of K‐based layered cathodes with both bulk structural and interfacial stability.