Platinum single-atom alloy catalyst for fast lithium polysulfide conversion.

The practical application of LiS batteries is severely limited by sluggish polysulfide redox kinetics and the shuttle effect. In this work, a phase-engineered PdBi-Pt single-atom alloy (SAA) that features isolated Pt atoms embedded in a hexagonal close-packed PdBi intermetallic lattice is rationally designed. It is further loaded onto carbon (PdBi-Pt SAA/C) and employed as a functional modification layer for polypropylene separators in LiS batteries. Structural characterizations confirm the atomic dispersion and stable coordination environment of Pt single atoms within the PdBi matrix. Density functional theory calculations reveal that the incorporation of single-atom Pt markedly enhances d-p orbital coupling, enhances polysulfide adsorption, and shifts the rate-determining step of polysulfide conversion to an earlier liquid-solid transformation stage, accelerating reaction kinetics. Consequently, LiS batteries equipped with a PdBi-Pt SAA/C-modified separator achieve a high discharge capacity of 1253.5 mAh g-1 at 0.2C and exhibit exceptional cycling stability with a capacity decay rate of only 0.035% per cycle over 800 cycles at 2C. Notably, a practical pouch-cell configuration achieves a high initial energy density of 453.6 Wh kg-1. This work demonstrates the effectiveness of SAA catalysts in regulating polysulfide redox chemistry and provides a viable strategy for realizing high-performance, practically relevant LiS batteries.