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.