Breaking Kinetic Bottlenecks in Rechargeable Magnesium Batteries: Interfacial Sb Doping for Dual‐Function Desolvation and Reconversion in CuS Cathodes

ABSTRACT Rechargeable magnesium batteries (RMBs) represent a promising post‐lithium technology, yet their advancement is fundamentally limited by the sluggish desolvation of Mg 2+ and the irreversibility of conversion reactions in high‐capacity cathodes. Herein, we report a rational interfacial antimony (Sb) doping strategy for copper sulfide (Sb‐CuS) that concurrently addresses both kinetic bottlenecks. Combined theoretical calculations and experiments demonstrate that Sb dopants not only create charge‐redistributed regions that significantly lower the Mg 2+ desolvation barrier (7.22 eV), but also participate in forming Mg 3 Sb 2 nanoalloys that catalyze the decomposition of MgS during charging. This synergistic interplay enables highly reversible and rapid bidirectional CuS/MgS conversion kinetics and effectively mitigates the diffusion of Cu species toward the anode. Consequently, the Sb‐CuS cathode delivers a high reversible capacity of 365 mAh g − 1 at 50 mA g − 1 and exceptional long‐term cycling stability (107 mAh g − 1 after 800 cycles at 1 A g − 1 , corresponding to 91% capacity retention). Furthermore, a functional pouch cell demonstrates its practical viability. This work elucidates a general interfacial‐engineering paradigm applicable to conversion‐type chalcogenide cathodes, providing a critical pathway toward high‐performance multivalent batteries.