Two-dimensional conjugated N-rich covalent organic frameworks for superior sodium storage

Sodium-ion batteries (SIBs) are considered as a promising next-generation energy storage system. To achieve the large-scale application of SIBs, it is crucial to develop cost-effective anode materials with high Na-ion storage capacity. Herein two-dimensional (2D) conjugated covalent organic frameworks (cCOFs) with N-rich phthalocyanine (Pc) units fused via benzene moieties (named MPc-2D-cCOFs) were explored as the SIBs anode materials. Electrochemical tests reveal their high reversible capacities of 538 and 342 mA h g(-1) at 50 and 1000 mA g(-1), respectively, good rate performance, and excellent stability, comparable to the state-of-the-art anode materials of SIBs, indicating their outstanding Na-ion storage performance. Ex situ X-ray photoelectron and Fourier transform infrared spectroscopies together with theoretical calculations disclose the N atoms at the pore channels and conjugated pyrrole moieties of MPc-2D-cCOFs provide abundant Na-ion storage sites. This, in cooperation with the enhanced electrical conductivity owing to the 2D conjugated structure, contributes to the outstanding Na-ion storage capacity of MPc-2D-cCOFs. The present result is surely helpful for developing high-performance and cost-effective COFs as electroactive materials for SIBs.