A Symmetric Aqueous Magnesium Ion Supercapattery Based on Covalent Organic Frameworks

Abstract Aqueous magnesium ion‐based batteries have attracted significant research interest due to the two‐electron transfer process, small cation radius, low reduction potential as well as the inert hydrogen evolution reaction. However, the high surface charge density of divalent Mg 2+ ions results in sluggish solid‐state diffusion kinetics, which significantly limits the number of host materials suitable for effective Mg 2+ ion storage. Here, for the first time, covalent organic frameworks (COFs) are explored as host materials for high‐rate aqueous Mg 2+ ion batteries. Combining electrochemical and spectral characterization with theoretical simulation, a synergistic charge storage mechanism involving the reaction of nitrogen and oxygen bridged by Mg 2+ ions is revealed. Using electrochemical analysis, it is shown that the Mg 2+ ion diffusion kinetics are dominated by the surface pseudocapacitive behavior in COFs, which achieves a favorable rate performance and durable cyclic stability. This work offers a new perspective on the storage of Mg 2+ ions in COF host materials.