Polarity Gradient CEI Driven Rapid Desolvation for Extreme Fast‐Charging Potassium‐Ion Batteries

Abstract Potassium‐ion batteries (PIBs) offer an opportunity for superior fast‐charging compared to lithium‐ion batteries, owing to their faster K + transport in electrolyte. However, severe side reactions at the cathode electrolyte interphase (CEI), sluggish K + transport, and cathode structural degradation hinder the development of fast‐charging PIBs. Herein, we tailor‐design a polarity gradient CEI via an electrolyte additives modification strategy. Specifically, the outer B–F/B–O species assist in withdrawing solvent molecules around K + during the desolvation process, while abundant K 2 CO 3 and KF throughout the CEI facilitate K + transport and structural stability. Consequently, the KFeHCF/graphite full cell demonstrates improved charge transfer and diffusion kinetics, with suppressed Fe dissolution, enhancing stability of both the cathode bulk structure and interphase under fast‐charging conditions. The full cell with optimized CEI delivers high reversible capacities of 126.5 mAh g −1 at 0.02 A g −1 and 95.8 mAh g −1 at 1 A g −1 (a charging time of 7.5 min for 80% of the capacity), and maintains 67 mAh g −1 at 5 A g −1 as well as good long cycle life. Moreover, it retains 85.1 mAh g −1 and exhibits good rate performance even at –10 °C. Our work reveals the critical role of rationally regulating CEI components and structure for fast‐charging PIBs.