Construction of High‐Performance Anode of Potassium‐Ion Batteries by Stripping Covalent Triazine Frameworks with Molten Salt

Abstract Covalent triazine frameworks (CTFs) are promising battery electrodes owing to their designable functional groups, tunable pore sizes, and exceptional stability. However, their practical use is limited because of the difficulty in establishing stable ion adsorption/desorption sites. In this study, a melt‐salt‐stripping process utilizing molten trichloro iron (FeCl₃) is used to delaminate the layer‐stacked structure of fluorinated covalent triazine framework (FCTF) and generate iron‐based ion storage active sites. This process increases the interlayer spacing and uniformly deposits iron‐containing materials, enhancing electron and ion transport. The resultant melt‐FeCl₃‐stripped FCTF (Fe@FCTF) shows excellent performance as a potassium ion battery with a high capacity of 447 mAh g⁻¹ at 0.1 A g⁻¹ and 257 mAh g⁻¹ at 1.6 A g⁻¹ and good cycling stability. Notably, molten‐salt stripping is also effective in improving the CTF's Na⁺ and Li⁺ storage properties. A stepwise reaction mechanism of K/Na/Li chelation with C═N functional groups is proposed and verified by in situ X‐ray diffraction testing (XRD), ex‐situ X‐ray photoelectron spectroscopy (XPS), and theoretical calculations, illustrating that pyrazines and iron coordination groups play the main roles in reacting with K⁺/Na⁺/Li⁺ cations. These results conclude that the Fe@FCTF is a suitable anode material for potassium‐ion batteries (PIBs), sodium‐ion batteries (SIBs), and lithium‐ion batteries (LIBs).