Single-Atom Catalysts as Promising Cathode Materials for Lithium–Sulfur Batteries

A major challenge toward the practical application of lithium–sulfur (Li–S) batteries is the lithium polysulphide (LiPS) shuttling, caused by the rapid LiPS migration in the electrolyte and slow reaction kinetics. Single-atom catalyst (SAC) materials hold the promise of strong LiPS binding to the cathode and improved reaction kinetics in Li–S batteries. In this study, we examine the electrocatalytic properties of four SAC materials with TM–N4–C (TM = Co, Fe, V, and W) formation, from simulations based on the density functional theory. We study for the first time a W-based SAC as the Li–S cathode host and calculate the adsorption energy of five LiPS intermediates (Li2Sn, n = 1, 2, 4, 6, and 8). We explore the mechanism for the conversion of Li2S2 to Li2S and present the energy profiles based on the Gibbs free energy for the LiPS reaction pathway from S8 to Li2S. V- and W-based SACs provide high LiPS binding, of up to 6.0 times of pristine graphene, and largely improved reaction kinetics by lowering the S dissociation barrier of the Li2S2 decomposition by ∼2.5 times compared to pristine graphene. Our work provides a detailed investigation into the adsorption and conversion of LiPSs on SAC cathode hosts, highlighting their potential on improving the electrochemical performance of Li–S batteries and mitigating the LiPS "shuttle" effect.