Ionic covalent organic frameworks with tailored anionic redox chemistry and selective ion transport for high-performance Na-ion cathodes

Employing cathode materials with multiple redox couples and electrolytes with efficient cation transport kinetics are two effective approaches to improving the electrochemical performance of batteries. In this work, for the first time, we present a design strategy of simultaneously realizing reversible cationic and anionic redox chemistries as well as selective anion/cation transport in the viologen-based COFs (BAV-COF:X, coordinated anions of X = Cl-, Br-, I-, and ClO4-) for high-performance Na-ion cathodes. Besides the cationic redox of viologen segments, the different redox activities of anions effectively tune the total capacities of the COFs. Meanwhile, electrochemical analysis and ab-initial molecular dynamics (AIMD) calculation illustrate that the anion/cation transport kinetics of electrolytes caged in the COFs' channels can be selectively tuned by the coordinated anions. As a result, combining high-potential Br-/Br2 redox couple, cationic redox of viologen segments, and enhanced Na' transport kinetics, the BAV-COF:Br- demonstrates stable performance with energy densities of 358.7 and 145.2 Wh kg -1 at power densities of 116.5 and 2124.1 W kg -1, respectively. This study offers new insight into the fabrication of organic cathodes with anionic redox and the advantages of COFs electrode materials in anion/cation transport selectivity for energy storage applications.(c) 2022 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press.

Automated summary

This study presents a design strategy for simultaneously achieving reversible cationic and anionic redox chemistries, as well as selective anion/cation transport in viologen-based COFs. By tuning the coordinated anions, the anion/cation transport kinetics of electrolytes caged in the COFs' channels can be selectively adjusted. The results demonstrate stable and high-performance sodium-ion cathodes using this design strategy.