Ionothermal Synthesis of Fully Conjugated Covalent Organic Frameworks for High‐Capacity and Ultrastable Potassium‐Ion Batteries

Fully aromatic conjugated covalent organic frameworks (FAC-COFs) with excellent physicochemical stability have been emerging as active semiconductors for diverse potential applications. Developing efficient synthesis methods for fabricating FAC-COFs will significantly facilitate the exploration over their material and photonic/electronic functionalities. Herein, a facile solvent-free strategy is developed for the synthesis of 2D phthalocyanine-based FAC-COFs (FAC-Pc-COFs). Cyclopolymerization of benzo[1,2-b:4,5-b']bis[1,4]benzodioxin-2,3,9,10-tetracarbonitrile (BBTC) and quinoxalino[2',3':9,10]phenanthro[4,5-abc]phenazine-6,7,15,16-tetracarbonitrile (QPPTC) in ZnCl2 leads to the fast formation and isolation of BB-FAC-Pc-COF and QPP-FAC-Pc-COF, respectively. Powder X-ray diffraction and electron microscopy analysis reveal their crystalline nature with sql topology and AA stacking configuration. Thermogravimetric analysis and immersion experiment indicate their excellent stability. The conductivity test demonstrates their high conductivity of 0.93-1.94 × 10-4 S cm-1 owing to the fully π-conjugated electronic structural nature. In particular, the as-prepared FAC-Pc-COFs show high-performance K+ storage in potassium-ion batteries due to their excellent conductivity, highly ordered and robust structure, and N/O-rich framework nature. Impressively, QPP-FAC-Pc-COF shows a large reversible capacity of 424 mA h g-1 after 100 cycles at 50 mA g-1 and a capacity retention of nearly 100% at 2000 mA g-1 for over 10 000 cycles.