Bidirectional Soft Catalysts for Improved Power Performance of Li-S Batteries.

Lithium-sulfur (Li-S) batteries are attractive for next-generation energy storage owing to their high theoretical energy density and low cost, yet their practical performance is limited by sluggish redox kinetics. Here, we introduce a soft catalyst in which a polymer-metal complex is directly integrated into the binder, creating a catalytically active microenvironment that enables efficient and bidirectional sulfur catalysis. A polyvinyl alcohol (PVA) scaffold stabilizes metal ions through chelation with the electron-donating -OH groups of PVA, forming homogeneously distributed catalytic domains in the sulfur cathode. Among the systems investigated, PVA-Cu exhibits the highest catalytic activity, arising from optimal sulfur binding energies, Cu-S d-p hybridization, and additional electronic states near the Fermi level. As a result, the PVA-Cu cells deliver high capacities at 3 mg cm-2 of 1,100 mAh g-1 at 1 C with 82% capacity retention over 300 cycles, while at higher loadings of 9 mg cm-2, the cells deliver 813 mAh g-1 (7.3 mAh cm-2) at 0.5 C. In a pouch cell prototype, stable cycling at 0.5 C delivers a discharge capacity of 790 mAh g-1 and a power density of 150 W kg-1, which lies within the upper range of reported Li-S pouch-cell performance in terms of operating rate and power density.