Azo-linked covalent triazine-based framework as organic cathodes for ultrastable capacitor-type lithium-ion batteries

A highly stable 3D π-conjugation covalent triazine-cored framework (Azo-CTF) with triazine as the electron-rich center bridged by azo redox-active linkers is proposed and prepared as cathode materials for improving both rate performance and cycle stability of LIBs, two critical issues addressed in organic electrodes. The synchronous and orderly introduction of electron-withdrawing units and redox active units in conjugated polymer framework can effectively tune electronic structure and redox potential of materials, contributing to the improvement of electrical and electrochemical behavior. Attributed to abundant redox azo sites, resilient and accessible pores network, and good intramolecular and interfacial electron transfer ability, Azo-CTF cathode shows a large and reversible capacity output of 205.6 mAh g⁻¹, a ultralong cycle life (89.1% capacity retention after 5000 cycles), and a high power density of 4253 W kg⁻¹ even at an energy density of 258 Wh kg⁻¹, much better than many reported organic cathodes and even better than some commercial inorganic cathodes. In addition, in-situ Raman spectroscopy and theoretical calculations were done and further verified the redox process of azo active sites and the optimization of molecular orbital in covalent framework for better battery cathode, indicating the availability of molecular-level electronic structure tuning.