Reactivating the Current Collector: A Catalytic Strategy for Carbon‐Free Sulfur‐Based Cathodes

The practical deployment of sulfur cathodes in rechargeable batteries is limited by sluggish redox kinetics and polysulfide dissolution, which impair energy efficiency and cycling stability. Conventional strategies-such as carbon-sulfur composites-mitigate these issues but require >30 wt.% of electrochemically inactive additives, reducing energy density. Here, a carbon-free sulfur-based cathode formed via a spontaneous solid-state reaction is presented between elemental sulfur and copper foil, catalyzed by layered mackinawite iron sulfide. By effectively lowering the reaction energy barrier, this catalyst accelerates the solid-phase reaction kinetics between sulfur and copper, thereby enabling the in situ formation of conductive covellite copper sulfide with pseudocapacitive behavior, which allows electrodes with 95 wt.% active material. The cathodes deliver remarkable kinetic performance, with a specific capacity of 1588 mAh g^-1 at 10 A g^-1, as well as exceptional long-term cycling stability, demonstrating 100% capacity retention over 1000 cycles at 5 A g^-1. Operando spectroscopy and first-principles calculations elucidate the structural and electronic evolution underlying the catalytic process. By reconfiguring the current collector as an active component, this strategy offers a scalable and generalizable framework for constructing high-energy, carbon-free sulfur-based cathodes.