Contra-Diffusion Engineering of Single-Atom Catalytic Interlayers Enables Reversible Sulfur Redox Chemistry.

Achieving durable lithium-sulfur batteries with minimal catalyst loading remains challenging, particularly for interlayer designs where catalytic efficiency is often compromised by nonuniform active-site utilization. Here we demonstrate that diffusion-regulated precursor growth enables the construction of atomically dispersed Co-Nx catalytic sites within a freestanding aramid nanofiber-derived carbon interlayer. By synchronizing the bidirectional diffusion of metal ions and ligands, this process enforces spatially confined nucleation and homogeneous precursor evolution, yielding a uniformly accessible single-atom catalytic architecture while preserving the intrinsic fibrous conduction network. The resulting interlayer simultaneously enhances polysulfide anchoring, accelerates bidirectional sulfur redox kinetics, and regulates Li2S nucleation and dissolution, as directly revealed by in situ Raman spectroscopy and electrochemical analyses. As a consequence, the system delivers exceptional cycling stability under high-rate operation despite a low Co loading, highlighting the importance of diffusion-regulated catalytic architectures for efficient sulfur redox regulation in lithium-sulfur batteries.