Rigid vs Flexible COFs: Skeleton Engineering Strategies for Enhancing Lithium‐Ion Storage

ABSTRACT Covalent organic frameworks (COFs) are promising lithium‐ion battery electrodes because of their tunable structures and porous architectures. However, research on COF‐based lithium‐ion battery (LIB) electrodes has primarily focused on rigid frameworks, with limited attention to flexible COFs. In this work, two types of COFs with distinctly different mechanical properties—rigid (Rig) and flexible (Flx)—were synthesized via a skeleton engineering strategy. To overcome low electronic conductivity, the COFs were grown in situ on carbon nanotubes (CNT) to form conductive composites. Both COFs exhibited high crystallinity, large surface areas, and well‐defined pore structures. Comparative electrochemical studies revealed that Flx‐4C delivered improved long‐term capacity retention and rate performance, reaching a maximum capacity of 582 mAh·g − 1 at 2 C, surpassing the theoretical capacity of commercial graphite. Cross‐sectional SEM and confined powder compaction tests show that the flexible framework undergoes smaller thickness growth and higher mechanical energy dissipation, indicating improved buffering of cycling‐induced deformation. Ex situ XPS and DFT calculations suggest that quinone/hydroxyl, imine, triazine, and ether‐related sites participate in lithium storage, consistent with a 24‐electron redox process per repeating unit of Flx. This work offers critical insights into the structure–performance relationship of rigid vs flexible COFs, guiding the design of advanced organic electrode materials.