Molecular Engineering-Regulated Donor-Acceptor 1D Covalent Organic Framework with Bipolar Redox-Active Centers for High-Performance Organic Li-ion Battery Cathodes

Covalent organic frameworks (COFs) possess numerous merits that position them as a promising class of electrode materials for energy storage. However, traditional two-dimensional (2D) or three-dimensional (3D) COFs exhibit inherent limitations. In this work, two donor-acceptor (D-A) type one-dimensional (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 COF was in situ grown on carbon nanotubes (CNT), yielding COF@CNT composites with a unique dendritic core-shell structure that maximises active-site exposure. The COF@BFPPQ-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. The COF@BFPPQ’s maximum capacity contribution reaches 421 mAh g⁻¹, surpassing previously reported values. Through capacity analysis, XPS, and DFT calculations, we propose that each COF@BFPPQ 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).