Neighboring Copper Atoms Enhance Valence‐Adaptive Catalysis of Cobalt for Boosted Polysulfide Redox Kinetics

ABSTRACT Reversible polysulfide redox kinetics critically govern the capacity, rate capability, and cycle life of sodium–sulfur (Na–S) batteries. Here we report a single‐atom catalyst featuring S‐bridged Cu–Co dual sites anchored on N‐doped Ti 3 C 2 S 2 MXene. The sulfur cathode delivers a high specific capacity of 573.8 mAh g −1 at 5.0 A g −1 with an ultralow capacity decay of ≈0.0037% per cycle over 15,000 cycles. Experimental and DFT calculations reveal that Co serves as the valence‑adaptive catalytic center, donating electrons to sulfur species during discharge and accepting them during charge, corresponding to the Co 1.32+ ↔ Co 1.58+ valence transition. Neighboring Cu atoms amplify this behavior by modulating the electronic structure of Co, as evidenced by a larger Co valence fluctuation in CuCo‑NSM (Δ = 0.26) than in Co‑NSM (Δ = 0.18). Additionally, the Cu–Co dual sites accelerate sodium‐ion diffusion and facilitate the reverse polysulfide conversion (Na 2 S→Na 2 S 2 ) during charge. The synergistic valence‑adaptive catalysis arising from the Cu–Co dual‑metal sites significantly promotes the kinetics of polysulfide conversion, offering a feasible atomic‐level design strategy for high‐performance metal–sulfur batteries.