Fluorine-Rich Covalent Organic Framework to Boost Electrochemical Kinetics and Storages of K+ Ions for Potassium-Ion Battery

Covalent organic frameworks (COFs), featuring ordered nanopores with numerous accessible redox sites, have drawn much attention as promising electrode materials for rechargeable batteries. Thus far, however, COF-based battery electrodes have exhibited limited capacity and unsatisfactory cycling stability due to the unwanted side reactions over their large surface area. Herein, a fluorine-rich covalent organic framework (F-COF) as an electrode material with improved stability and performance for potassium-ion batteries is developed. The fluorinated COF not only stabilizes intercalation kinetics of K+ ions but also reinforces its electron affinity and conductivity, improving the reversibility of bond transitions during discharge-charge cycles. As a result, F-COF affords a high specific capacity (95 mAh g(-1) at fast rates up to 5 C) and excellent cycling stability (5000 cycles with approximate to 99.7% capacity retention), outperforming the pristine COF-based electrodes devoid of F atoms. Notably, the experimental capacity of F-COF approaches its theoretical value, confirming that a large proportion of electroactive sites are being actively utilized. Altogether, this work addresses the significant role of F atoms in improving the K+-ion storage capability of COFs and provides the rational design principles for the continued development of stable and high-performance organic electrode materials for energy storage devices.