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

摘要

Covalent organic frameworks (COFs), featuring ordered nanopores withnumerous accessible redox sites, have drawn much attention as promisingelectrode materials for rechargeable batteries. Thus far, however, COF-basedbattery electrodes have exhibited limited capacity and unsatisfactory cyclingstability due to the unwanted side reactions over their large surface area.Herein, a fluorine-rich covalent organic framework (F-COF) as an electrodematerial with improved stability and performance for potassium-ion batteriesis developed. The fluorinated COF not only stabilizes intercalation kinetics ofK~+ ions but also reinforces its electron affinity and conductivity, improving thereversibility 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) andexcellent cycling stability (5000 cycles with ≈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 activelyutilized. Altogether, this work addresses the significant role of F atoms inimproving the K~+-ion storage capability of COFs and provides the rationaldesign principles for the continued development of stable andhigh-performance organic electrode materials for energy storage devices.