Two dimensional Conjugated Metal-Organic Frameworks with Multiple Redox-Active Sites towards High-Performance Sodium-Ion Battery.

Two dimensional (2D) conjugated metal-organic frameworks (2D c-MOFs) have emerged as promising electroactive materials for energy storage owing to their high conductivity and large charge carrier mobility. However, their broader implementation is hindered by limitations in capacity and cycling stability, primarily due to the restricted density, diversity, and stability of the redox sites. In this study, a new 2D c-MOF (Cu-TTPQ) with multiple redox-active sites that incorporated quinone and pyrazine functionalities as cathode materials for sodium-ion batteries (SIBs) is developed. Notably, 2D layered Cu-TTPQ with a rigid skeleton is directly synthesized from a flexible precursor ligand through in situ cyclodehydrogenation and coordination assembly. Two other contrastive 2D c-MOF analogs (Cu-TBPQ and Cu-DDQP) sharing similar structural motifs with Cu-TTPQ but featuring distinct conductivities and energy band characteristics are prepared for systematic investigation. By contrast, Cu-TTPQ demonstrates a higher reversible capacity of 214.8 mAh g at 0.05 A g, along with high cycling stability, showing impressive cyclability with minimal capacity decay even after 1800 cycles at 5.0 A g. This work elucidates the rationality of introducing multiple redox-active sites to improve the overall performance of 2D c-MOFs as cathode materials for SIBs.