Unraveling the Catalytic Potential of 2D Nb2Se2C for Lithium Polysulfide Conversion: A DFT Study

The effective adsorption and conversion of sulfur species are essential to the performance of lithium–sulfur (Li–S) batteries. In this work, we designed a TMD-MXene-like material, Nb₂Se₂C, computationally by substituting the Nb layer of NbSe₂ with an Nb–C layer of Nb₂C. We investigated its catalytic activity toward lithium polysulfide (LiPS) adsorption and conversion, and compared it with NbSe₂ and Nb₂C using density functional theory (DFT) calculations. Adsorption energy analysis confirms that Nb₂Se₂C provides moderate and uniform binding across all LiPS species, ensuring stability and reversibility. In contrast, Nb₂C binds too strongly, impeding LiPS mobility, while NbSe₂ shows weak adsorption for smaller polysulfides. Notably, Nb₂Se₂C maintains moderate adsorption across LiPS species (S₈: −0.86 eV, Li₂S₆: −0.71 eV, Li₂S: −1.51 eV), preventing polysulfide accumulation. The Bader charge analysis further confirms its superior charge transfer ability, with negligible sulfur loss (S₈: −0.02|e| vs −1.33 |e|, for Nb₂C). Gibbs free energy (ΔG) profiles indicate Nb₂Se₂C promotes a relatively facile sulfur reduction step, with favorable steps from S₈ to Li₂S₈ (−2.55 eV) and minimal energy barriers, unlike Nb₂C, which exhibits high resistance (S₈ → Li₂S₈: +1.24 eV). Additionally, AIMD simulations conducted at 500 K confirm that all three materials are thermally stable. Overall, Nb₂Se₂C proves to be an excellent cathode host, efficiently suppressing the polysulfide shuttle effect, improving sulfur utilization, and optimizing Li–S battery performance.