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-N_x 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.