Molecular Traffic Control: Fast Mg²⁺ Transport via Carbonyl-Induced Ion-Dipole Interactions in Covalent Organic...

Rechargeable magnesium batteries (RMBs) have garnered significant attention due to their high energy density, abundant resources, and inherent safety. However, developing cathode materials with both high specific capacity and excellent kinetic performance remains a significant challenge. In this study, two carbonyl-functionalized covalent organic frameworks (COFs), namely Tp-DAAQ COF and Tp-DAA COF, were successfully synthesized via a molecular engineering strategy. Among them, the Tp-DAAQ COF, with a higher density of carbonyl sites, exhibits superior performance in terms of specific capacity and rate capability. Mechanistic investigations revealed that reversible storage of Mg²⁺ is achieved through the enolization reaction of carbonyl groups. Furthermore, molecular dynamics simulations and theoretical calculations indicated that the carbonyl oxygen acts as a negatively charged center, facilitating Mg²⁺ dissociation via ion-dipole interactions and modulating the ion distribution within the COF channels. This significantly reduces the diffusion energy barrier for Mg²⁺ within the porous framework. As a result, the Tp-DAAQ COF cathode exhibits not only a high ion diffusion rate but also exceptional cycling stability, maintaining 72% capacity retention over 4000 cycles at 1000 mA g^-1. This work highlights carbonyl-rich COFs potential as RMBs cathode, elucidates their high kinetics mechanism, and provides insights into RMBs advanced organic cathode structural design.