A Symmetric Aqueous Magnesium Ion Supercapattery Based on Covalent Organic Frameworks.

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 Mg2+ ions results in sluggish solid‐state diffusion kinetics, which significantly limits the number of host materials suitable for effective Mg2+ ion storage. Here, for the first time, covalent organic frameworks (COFs) are explored as host materials for high‐rate aqueous Mg2+ ion batteries. Combining electrochemical and spectral characterization with theoretical simulation, a synergistic charge storage mechanism involving the reaction of nitrogen and oxygen bridged by Mg2+ ions is revealed. Using electrochemical analysis, it is shown that the Mg2+ 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 Mg2+ ions in COF host materials. [ABSTRACT FROM AUTHOR]