Unraveling the Catalytic Potential of 2D Nb<sub>2</sub>Se<sub>2</sub>C for Lithium Polysulfide Conversion: A DFT Study
Shrish Nath Upadhyay, Jayant K. Singh
Abstract
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.