Pyrene-4,5,9,10-tetraone-based covalent organic framework/carbon nanotube composite as sodium-ion cathodes with high-rate capability

A novel pyrene-4,5,9,10-tetraone (PTO)-based covalent organic framework grown on multi-walled carbon nanotubes via in situ polycondensation (Tp-PTO-COF@CNTs) were prepared and the composite displays the excellent electrochemical properties for sodium-ion batteries (SIBs). [Display omitted] •Tp-PTO-COF@CNTs was fabricated via in-situ acid-catalyzed polycondensation reaction.•The cathode displays a high specific capacity of 223.2 mA h g−1 at 0.1 A g−1.•Ultra-long cyclicity (93.7% retention over 5000 cycles at 5 A g−1) could be realized.•The ex-situ XPS and FT-IR tests prove sodium storage mechanism with C=O groups. Covalent organic frameworks (COFs) have attracted significant interest in the field of rechargeable batteries on account of their unique properties, including robust frameworks, well-defined porosity, abundant redox-active sites, and flexible structure designability. However, the limited active site utilization and low electrical conductivity always bring about poor electrochemical performance, thereby hindering practical applications. Herein, we reported a pyrene-4,5,9,10-tetraone-based covalent organic framework composite (Tp-PTO-COF@CNTs) grown on multi-walled carbon nanotubes via in-situ polycondensation. The Tp-PTO-COF@CNTs with numerous active sites (C=O groups) and strong π-π interaction between CNTs and COFs could accommodate more Na-ions and boost structural stability. Moreover, the existence of 1D CNTs could improve electronic conductivity, which facilitates fast transport of electrons and enhances reaction kinetics. In view of the two synergistic effects, Tp- PTO-COF@CNTs cathode displays an outstanding sodium-ion storage property with high initial capacity of 223.2 mA h/g at 0.1 A/g, remarkable rate capability at as high as 20 A/g, and ultra-long cycling stability (163.0 mA h/g exceeding 5000 cycles at 5 A/g). Furthermore, the ex-situ measurements are proposed to better confirm the role of carbonyl groups as redox-active centers. Such ultra-stable structural advantage might inspire the development of COF cathode materials for sodium-ion batteries.