Redox of Dual-Radical Intermediates in a Methylene-Linked Covalent Triazine Framework for High-Performance Lithium-Ion Batteries

Covalent triazine frameworks (CTFs) are promising electrodes for rechargeable batteries due to their adjustable structures, rich redox sites, and tunable porosity. However, the CTFs usually exhibit inferior electrochemical stability because of the inactivation of the unstable radical intermediates. Here, a methylene-linked CTF has been synthesized and evaluated as a cathode for rechargeable lithium-ion batteries. Electron paramagnetic resonance (EPR) and in situ Raman characterizations demonstrated that the redox activity and reversibility of alpha-C and triazine radical intermediates are essentially important for the charging/discharging process, which have been efficiently stabilized by the synergetic pi conjugation and hindrance effect caused by the adjacent rigid triazine rings and benzene rings in the unique CTF-p framework. Additionally, the methylene groups provided extra redox-active sites. As a result, high capacity and cycling stability were achieved. This work inspires the rational modulation of the radical intermediates to enhance the electrochemical performance of organic electrode materials for the next-generation energy storage devices.