MnNi@NG: A Highly Promising Cathode for Accelerating Sulfur Redox Kinetics in Lithium-Sulfur Batteries

One of the primary challenges in the practical application of lithium-sulfur (Li-S) batteries lies in the sluggish kinetics of the sulfur reduction reaction (SRR). In this study, we propose a solution to this issue by introducing heteronuclear Mn-X (X = Fe, Co, Ni) catalysts supported on nitrogen-doped graphene (Mn-X@NG) as the cathode material for the Li-S battery. Using density functional theory calculations, we uncover the mechanism by which the incorporation of the X atom enhances the reactivity of the activity center at the Mn site by regulating its d orbital electronic configurations. Our investigation reveals the synergistic effects between the nitrogen ligand field and the electron negativity of the Mn-X off-site region, leading to a more localized distribution of d orbitals at the Mn active site. This localization facilitates enhanced orbital hybridization between the Mn-d(xz)/d(yz) and S-p orbitals, resulting in the weakening of the Li-S bond strength in the SRR intermediates. Importantly, we achieve significantly lower Gibbs free energy differences in the heteronuclear active site during the rate-limiting step of the SRR process compared to its single-atom catalyst counterparts. Among the catalysts studied, MnNi@NG emerges as the most promising candidate for accelerating the rate-limiting step of the SRR in Li-S batteries.