First-Principles Investigation of the Anchoring Behavior of Pristine and Defect-Engineered Tungsten Disulfide for Lithium-Sulfur Batteries

We used first-principles density functional theory (DFT) calculations to investigate the adsorption behavior of lithium polysulfides (LiPSs) on pristine, defective, and oxygen-doped tungsten disulfide (WS2). We elucidate strategies to activate the basal planes of WS2 by introducing substitutional dopants and quantify the LiPSs' absorption strength at the edge sites. The basal plane of pristine and monovacancy sites of WS2 is found to be inactive, but oxygen doping on the sulfur vacancy site of WS2 endows adequate adsorption strength to anchor LiPSs. The adsorption of polysulfides on the 50% WS2 edges also exhibits binding energies adequate to immobilize the higher-order polysulfides. The results directly corroborate the experimental observation of LiPSs' adsorption at the edge sites of pristine WS2. We explain that the adsorption of LiPSs is facilitated via charge transfer from the polysulfides to the WS2. The calculated density of states indicates that the LiPSs' adsorbed WS2 substrates exhibit semiconducting behavior with a slightly lower band gap compared to pristine WS2. Overall, our simulation results demonstrate that oxygen doping is an effective strategy to activate the basal plane of the WS2 nanosheet to effectively suppress LiPSs' migration for realizing Li-S batteries with improved performance.