Insight into the effects of S-vacancy and O-doping in monolayer VS2 as lithium-ion battery anodes from first-principles calculations

First-principles calculations are executed to probe the effects of S-vacancy and O-doping on the structure and electrochemical performances of monolayer VS2 as an anode material for lithium-ion batteries (LIBs). According to the defect formation energy, the formation of S-vacancy in monolayer VS2 is an endothermic reaction while the O-doping formation is an exothermic reaction. The difference in electronic structure arrangement near the defects results in varied adsorption energies of Li ions at the same site from that of pristine VS2. Two defects can significantly reduce the diffusion energy barrier of Li ions on the VS2 monolayer surface, 0.016 (for S-vacancy) and 0.117 eV (for O-doping), compared with pristine VS2 without defects (0.233 eV). In addition, these two defects are beneficial to the intercalation and de-intercalation of Li on the surface of VS2, so they can provide excellent rate performance for LIBs. All the Pristine, O-doped, and S-vacancy VS2 monolayers can stably adsorb the upper and lower Li layers, with theoretical capacities of 1397, 1419, and 1442 mAh/g, respectively. As a result of defect engineering, VS2 can become an ideal anode material for the LIBs due to its low diffusion barrier, high Li capacities, and high electrical conductivity.