Molecular Engineering-Regulated Donor-Acceptor 1D Covalent Organic Frameworks with Bipolar Redox-Active Centers for...

Covalent organic frameworks (COFs) possess numerous merits that position them as a promising class of electrode materials for energy storage. However, traditional 2D or 3D COFs exhibit inherent limitations. In this work, two donor-acceptor (D-A) type 1D COFs with bipolar redox-active behavior are synthesized. By leveraging molecular engineering to regulate the energy gap of the 1D COFs, enhanced electronic conductivity is achieved. To further improve performance, the 1D COFs were in situ grown on carbon nanotubes (CNT), yielding COFs composites with a unique dendritic core-shell structure that maximizes active-site exposure. The BF-4C composite delivers exceptional long-term cycling stability, exhibiting a maximum capacity of 329 mAh g^{- 1} at 100 mA g^{- 1} and retaining about 100 mAh g^{- 1} even at 5000 mA g^{- 1}, and outstanding rate capability. Cathodes prepared with a high CNT ratio and in situ growth strategy outperform conventional composites. Through capacity analysis, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations, we propose that each BF unit participates in the reversible storage of two PF₆ ^- anions and eight Li-ions during the charge/discharge processes. This work highlights the potential of molecularly engineered 1D COFs as high-performance organic cathodes for next-generation lithium-ion batteries (LIBs).