The recent development of sodium-ion batteries (SIBs) represents one of the most significant technological advancements in the context of energy storage because of the high energy/power densities of SIBs and abundant sodium resources. Electroactive materials based on covalent organic frameworks (COFs) have demonstrated superior Na-ion storage capacities. Electrolytes can be absorbed into the nanometer-sized channels of the COFs, realizing intimate nanoscale contact between the electrolyte and electroactive sites on the COF skeleton. However, the preparation of COF materials with a variety of electroactive sites and enhanced redox kinetics is still a challenging endeavor.
Under the cooperation of Profs. Chun-Sing Lee and Yongbing Tang, affiliated with the City University of Hong Kong and Shenzhen Institute of Advanced Technology (CAS), respectively, a paper titled “Ionic covalent organic frameworks with tailored anionic redox chemistry and selective ion transport for high-performance Na-ion cathodes” was published in the Journal of Energy Chemistry in 2022. The authors prepared a series of viologen-based ionic COFs (BAV-COF:X, coordinated anions of X = Cl-, Br-, I-, and ClO4-). With these COFs, the reversible anionic redox chemistry and selective tuning of the anion/cation transport were achieved for the first time. Besides the cationic redox contributions from the pyridinium segments of the COF skeletons, coordinated anions, including redox halide ions (Cl-, Br-, and I-) and the non-electroactive ClO4-, were introduced for tuning the energy storage capacity of the COFs. Furthermore, based on electrochemical analysis and Ab initio molecular dynamic (AIMD) simulation, it was found that the coordinated anions can significantly affect Na+ transport in the electrolytes located in the COF channels via tuning of the Na+ solvation/de-solvation kinetics. As a result, BAV-COF:Br demonstrated superior energy density and cycling stability among the four prepared COFs.
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The Journal of Energy Chemistry is a publication that mainly reports on creative researches and innovativeapplications of chemical conversions of fossil energy, carbon dioxide, electrochemical energy and hydrogen energy,as well as the conversions of biomass and solar energy related with chemical issues to promote academicexchanges in the field of energy chemistry and to accelerate the exploration, research and development of energyscience and technologies.
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