Unlocking Inert Material to Durable Cathode for Magnesium Storage Inspired via Synergistic Spin‐Orbital Reconfiguration and Adaptive Crystal Transformation

ABSTRACT High polarity of Mg 2+ results in unsatisfied interactions with the cathode host lattice, giving rise to sluggish Mg 2+ diffusion and thus surface “self‐passivation” caused by irreversible insertion/extraction of Mg 2+ , impeding development of magnesium metal batteries (MMBs). Herein, we pioneer a Defect Chemistry‐Inspired synergistic strategy of synchronously Spin‐State Modulation and Adaptive Microstructural Reformation, thereby resolving the inherent thermodynamic–kinetic conflict to improve Mg 2+ storage. Combining first‐principles calculations with advanced characterization, the intrinsic inertness of the V‐3d 0 orbital in Cu 3 VS 4 was activated by filling electrons to induce a spin state change after introducing Na + , which enhanced the electron hopping process for rapid charge compensation to unlock Mg 2+ storage ability. Furthermore, the cathode undergoes a self‐driven structural evolution into a microcrystalline/amorphous hybrid, improved the cathode‐electrolyte interface and Internal reaction site to balance subsequent Mg 2+ adsorption and mobility. The optimized material, C@A‐N‐0.5, delivers a high specific capacity of 140 mAh g −1 at 40 mA g −1 (92% of capacity over rarely reported 300 cycles), and it had over 100 mAh g −1 at 200 mA g −1 for 1000 cycles, far outperforming the unmodified Cu 3 VS 4 with negligible Mg 2+ storage. This work provides mechanistic insights and materials design pathways for high‐performance MMBs cathodes based on transition metal sulfides.