Effect of Nonmetallic Doped VS2 on Polysulfide Anchoring and Catalysis in Lithium–Sulfur Batteries: A First-Principles Study

The sluggish conversion kinetics of lithium polysulfide (LiPSs) and the notorious shuttle effect caused by the dissolution of highly soluble LiPSs in the electrolyte have become major obstacles to the practical application of lithium-sulfur batteries. Thus, searching for bifunctional catalyst materials that can effectively capture and convert LiPSs to inhibit their shuttling effect has become the key to developing efficient lithium-sulfur batteries. In this paper, the potential of a series of doped VS2 monolayers with nonmetallic atoms replacing S atoms as cathode catalytic materials for lithium-sulfur batteries is discussed through first-principles calculations. The nonmetallic doping system focused herein exhibits unique structural stability and intrinsic conductivity advantages compared to conventional metal doping strategies that may induce problems such as lattice distortion. The study results show that among a series of nonmetallic atoms doped VS2 monolayers, O-VS2 and Se-VS2 were considered the best candidates. The adsorption strength of soluble LiPSs on both the top and bottom surfaces of O-VS2 and Se-VS2 was sufficient to inhibit the shuttle effect, while the structure of LiPSs remained unchanged. This was necessary to decrease the capacity decay. The projected density of states (PDOS) calculation indicates that O-VS2 and Se-VS2 maintain the metallic properties of VS2, even after the adsorption of LiPSs. Importantly, O-VS2 and Se-VS2 exhibit significant catalytic activity for sulfur reduction reactions (SRR) during discharge and for the decomposition of Li2S during charging. The suitable d and p band center positions and the more charge accumulation by adsorbed LiPSs are responsible for the high redox kinetics of O-VS2 catalyzed polysulfide conversion. Furthermore, the energy barrier for Li ions diffusion on the Se-VS2 surface is smaller than that on the VS2, and the energy barrier for diffusion on the O-VS2 surface is smaller than that on the graphene surface, which facilitates Li ions diffusion on the surface. Overall, O-VS2 and Se-VS2 can be considered an effective catalyst with strong adsorption behavior, enhanced electronic conductivity, and improved redox kinetics of polysulfides. This study provides new insights for the further development of high-performance lithium-sulfur batteries.