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, Nb 2 Se 2 C, computationally by substituting the Nb layer of NbSe 2 with an Nb–C layer of Nb 2 C. We investigated its catalytic activity toward lithium polysulfide (LiPS) adsorption and conversion, and compared it with NbSe 2 and Nb 2 C using density functional theory (DFT) calculations. Adsorption energy analysis confirms that Nb 2 Se 2 C provides moderate and uniform binding across all LiPS species, ensuring stability and reversibility. In contrast, Nb 2 C binds too strongly, impeding LiPS mobility, while NbSe 2 shows weak adsorption for smaller polysulfides. Notably, Nb 2 Se 2 C maintains moderate adsorption across LiPS species (S 8: −0.86 eV, Li 2 S 6: −0.71 eV, Li 2 S: −1.51 eV), preventing polysulfide accumulation. The Bader charge analysis further confirms its superior charge transfer ability, with negligible sulfur loss (S 8: −0.02|e| vs −1.33 |e|, for Nb 2 C). Gibbs free energy (Δ G ) profiles indicate Nb 2 Se 2 C promotes a relatively facile sulfur reduction step, with favorable steps from S 8 to Li 2 S 8 (−2.55 eV) and minimal energy barriers, unlike Nb 2 C, which exhibits high resistance (S 8 → Li 2 S 8: +1.24 eV). Additionally, AIMD simulations conducted at 500 K confirm that all three materials are thermally stable. Overall, Nb 2 Se 2 C proves to be an excellent cathode host, efficiently suppressing the polysulfide shuttle effect, improving sulfur utilization, and optimizing Li–S battery performance.