Rational Design of Single-Atom Mo2B2O2 MBene Cathodes for Li–S Batteries: Mechanistic Insights from First-Principles Calculations

Abstract

Li–S batteries offer high theoretical energy density and low material cost, but practical performance is severely limited by three key challenges: the shuttle effect of soluble lithium polysulfides (LiPSs), sluggish sulfur reduction reaction (SRR) kinetics, and slow Li2S decomposition during charging. Here, we employ first-principles calculations to systematically screen 19 single-atom (SA)-decorated Mo2B2O2 systems (SA-Mo2B2O2), spanning the 3d and 4d transition metal series, as cathode materials for Li–S batteries. SA decoration significantly enhances LiPS adsorption by forming strong SA–S bonds, with adsorption strengths varying across the transition metal series due to differences in electronic and structural properties. Correlation analysis, ligand field theory, and selective orbital coupling reveal that electronic factors, charge transfer, and d–p orbital occupancy govern adsorption in 3d SAs, while structural factors dominate in 4d SAs, producing distinct adsorption trends in each series. Most SA-Mo2B2O2 systems exhibit zero SRR overpotential, in contrast to pristine Mo2B2O2 which suffers a potential-limiting step with an overpotential of 2.16 V. Furthermore, Li2S decomposition proceeds without an energy barrier on all SA-Mo2B2O2 surfaces, facilitating efficient delithiation during charging. Among all candidates, V- and Nb-Mo2B2O2 stand out by combining the strongest LiPS adsorption, zero SRR overpotential, and fast delithiation kinetics. These findings provide a mechanistic basis and rational design strategy for SA-engineered MBene cathodes with improved cycling stability and energy efficiency in Li–S batteries.