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.