Theoretical Investigation of Nonmetallic Single-Atom Catalysts for Polysulfide Immobilization and Kinetic Enhancement in Lithium–Sulfur Batteries

With the increasing interest in tackling the "shuttle effect" of lithium–sulfur (Li–S) batteries, there is a growing emphasis on investigating effective catalysts to improve redox kinetics and understand the associated reaction pathways. In this study, a series of nonmetal (B, N, Si, P, S, F, and Cl) single-atom-doped graphenes were theoretically investigated as the catalysts for the multistep reduction of S8 and the kinetic conversion of the rate-limiting step. Analysis of the Gibbs free energy for the S8 reduction process on these catalysts confirms that the rate-limiting step is the conversion of Li2S2 to Li2S. Subsequently, six kinetic reaction paths transforming Li2S2 to Li2S were constructed. Based on the optimal reaction path with LiS as the intermediate product, a volcano plot was built with the excellent descriptor, −ΔGad(LiS). The peak catalytic efficiency corresponds to a −ΔGad(LiS) value of 1.72 eV. Consequently, pyrrolic N- and Cl-doped graphene are identified as superior catalysts with energy barriers of 0.61 and 0.47 eV for the reversible conversion of Li2S2 to Li2S. Furthermore, the strong correlation between ΔGad(LiS) and ΔGad(Li2S) also enables the prediction of catalytic performance using ΔGad(Li2S). These findings have significant implications for future catalyst design and understanding of kinetic reaction pathways in Li–S batteries.