Hyperbranched Polymer-Anchored CoS₂ Nanoclusters Enabling Stable Dual-Redox Mg-Storage Mechanism

Rechargeable magnesium batteries (RMBs) are promising for large-scale energy storage due to their intrinsic safety and abundant resources, yet their development remains critically hindered by the scarcity of high-performance cathodes. Conversion-type cathodes offer high theoretical capacity via multi-electron redox, but most rely solely on cationic redox, leading to sluggish kinetics, high activation barriers, and severe structural degradation from large volume changes. Here, we report a molecular anchoring strategy using an amine-terminated hyperbranched polymer (AHP) as a multifunctional template. The terminal -NH₂ groups coordinate Co²⁺ in situ, directing the formation of ultradispersed CoS₂ nanoclusters, while the AHP matrix uniformly permeates CoS₂ to form 3D flexible network that prevents nanocluster aggregation and provides elastic buffering to accommodate volumetric strain during conversion. Consequently, the CoS₂-AHP cathode delivers a high reversible capacity of 167.3  mAh g^-1 at 50 mA g^-1 and retains capacity retention of 91.8% after 300 cycles at 200 mA g^-1. Crucially, ex situ characterizations confirm a synergistic reversible anion-cation co-redox mechanism involving Co^3+/2+ ↔ Co⁰ and S₂ ^2- ↔ S^2- conversions. This work establishes a molecular anchoring strategy for anion-rich conversion materials to synergistically boost reaction kinetics and maintain structural integrity, enabling high capacity and superior cycling stability, and offering new insight for high-performance multivalent-ion battery cathodes.