Highly Crystalline and Robust Donor‐Acceptor Type Covalent Organic Frameworks for Long‐life Sodium‐Ion Battery Cathodes

Covalent organic frameworks (COFs) hold great potential in sodium‐ion battery cathodes. However, most reported COF‐based electrodes show unsatisfying capacity and rate performance due to their limited redox site density, low crystallinity, and poor conductivity. Herein, a highly crystalline and robust donor‐acceptor type COF with abundant redox active sites is developed by the polymerization of donor unit benzo[1,2‐b:3,4‐b″:5,6‐b″']trithiophene‐2,5,8‐tricarbaldehyde) (BTT) and acceptor unit s‐indacene‐1,3,5,7(2H,6H)‐tetrone (ICTO) (denoted as BTT‐ICTO) for cathodic Na + storage. The BTT‐ICTO‐graphene composites (BTT‐ICTO@G) synthesized by in situ growth have a loose sheet structure with rough surfaces, contributing to the improved conductivity and active site utilization of BTT‐ICTO. Benefiting from the robustness of BTT‐ICTO linked by ethylene bonds, the BTT‐ICTO@G cathodes exhibit a high capacity of 325 mAh g −1 at 0.1 A g −1 with a high active site utilization of 80%, excellent rate performance of 190 mAh g −1 at 5.0 A g −1 , and exceptional cycle performances of 196 mAh g −1 over 10 000 cycles at 2.0 A g −1 with only 0.0015% decay per cycle. These properties make the BTT‐ICTO@G cathodes among the best‐reported COF‐based sodium‐ion battery cathodes. In addition, in situ Raman, ex situ Fourier transform infrared, and theoretical calculations disclose the reaction pathway of Na + storage.