Engineering Directional Ion Transport Channels in Three-Dimensional Covalent Organic Frameworks for High-Performance Sodium-Ion Batteries.

Covalent organic frameworks (COFs) with abundant redox-active sites are promising electrode materials for sodium-ion batteries (SIBs). However, conventional design strategies are often limited by sluggish Na+ transport and low utilization of active sites. Here, we report a pair of 3D COFs (COF-O and COF-H). In COF-O, the C═O groups are precisely oriented toward the pore channels, allowing the O atoms to serve as effective Na+ storage sites. In contrast, COF-H contains only C-H groups within the pores, which lack Na+ storage capability. When employed as an anode material in SIBs, COF-O exhibits a high specific capacity of 318 mAh/g (1.9 times that of COF-H) and excellent cycling stability over 6000 cycles. In situ spectroscopic studies combined with theoretical calculations reveal that the C═O groups in COF-O act as efficient Na+ storage sites, effectively enhancing the capacity and accelerating Na+ transport kinetics. This work demonstrates that precisely orienting functional groups in 3D COFs can create effective ion transport channels, providing a promising strategy for designing advanced organic electrode materials for SIBs.