Delocalization‐Driven Activation of Inert Imine Linkages in Covalent Organic Frameworks for Reversible Magnesium Storage

Imine‐linked covalent organic frameworks (COFs) are promising cathodes for rechargeable magnesium batteries (RMBs), yet their abundant imine linkages (C═N) typically remain electrochemically inert, serving merely as structural connectors. Here, we reveal that the redox inactivity of imine linkages arises from insufficient π‐electron delocalization, and we demonstrate that enhancing local delocalization can switch these bonds into highly reversible redox centers. Through precise fluorine substitution in a triazine‐based COF, we achieve localized π‐delocalization without disrupting the overall conjugated framework. This delocalization‐driven activation lowers the LUMO level and stabilizes the reduced state of imine linkages (C–N − ), enabling a reversible C═N ⇄ C–N − conversion—a function never realized before in magnesium batteries. The activated imine sites become kinetically preferred Mg 2+ migration channels, cutting the diffusion barrier by half (from 1.61 to 0.81 eV) and switching the transport pathway from triazine to imine. Consequently, the optimized COF cathode delivers a high specific capacity of 203.6 mAh g −1 , outstanding rate capability, and exceptional cycling stability (72.9% retention after 9000 cycles). This work establishes π‐delocalization engineering as a general strategy and a redox switch to unlock latent redox functions in organic frameworks, providing a mechanistic blueprint for activating inert bonds in multivalent energy storage systems beyond magnesium batteries.