Charge Storage Mechanism of an Anthraquinone-Derived Porous Covalent Organic Framework with Multiredox Sites as Anode Material for Lithium-Ion Battery

Design and construction of high-capacity covalent organic frameworks (COFs)-based electrode materials and research on the energy storage mechanism still present challenges. In this study, an anthraquinone-derived porous covalent organic framework (DAAQ-COF) with dual-redox active sites of C═N and C═O groups is synthesized by the condensation of 2,6-diaminoanthraquinone (DAAQ) and 1,3,5-benzenetricarboxaldehyde (Tb). The extra C═O groups contribute to the increase of the theoretical capacity of DAAQ-COF. The porous structure provides an open channel for ionic transportation and exposes storage sites for Li+. As the anode material for lithium-ion batteries (LIBs), the DAAQ-COF shows remarkable performance and continuous "activation" behavior with a high discharge capacity of 787 mA h g–1 after 500 cycles at 1 A g–1. On the basis of the characterization of the cycled electrode, we speculate that lithium ions absorption/desorption due to the layered structure contributes to the partial capacity of DAAQ-COF. Meanwhile, the gradual lithiation of not only the C═N and C═O bonds but also the aromatic C═C bonds results in the increasing exceptional capacity. Therefore, a combined charge storage mechanism including multiredox processes and an ions absorption/desorption process is proposed for the DAAQ-COF. This work deepens the understanding of the energy storage mechanism of high-capacity COFs.