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 Co3+/2+ ↔ Co0 and S2 2- ↔ S2- 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.