Mechanism Investigation of High-Performance Li–Polysulfide Batteries Enabled by Tungsten Disulfide Nanopetals

Understanding the reaction kinetics and mechanism of Li-polysulfide batteries is critical in designing advanced host materials for improved performance. However, up to now, the reaction mechanism within the Li-polysulfide batteries is still unclear. Herein, we study the reaction mechanism of a high-performance Li-polysulfide battery by in situ X-ray diffraction (XRD) and density functional theory (DFT) calculations based on a multifunctional host material composed of WS 2 nanopetals embedded in rGO–CNT (WS 2 -rGO–CNT) aerogel. The WS 2 nanopetal serves as a “catalytic center” to chemically bond the polysulfides and accelerate the polysulfide redox reactions, and the 3D porous rGO–CNT scaffold provides fast and efficient e – /Li + transportation. Thus, the resulting WS 2 -rGO–CNT aerogel accommodating the polysulfide catholyte enables a stable cycling performance, excellent rate capability (614 mAh g –1 at 2 C), and a high areal capacity (6.6 mAh cm –2 at 0.5 C). In situ XRD results reveal that the Li 2 S starts to form at an early stage of discharge (at a depth of 25% of the lower voltage plateau) during the discharge process, and β-S 8 nucleation begins before the upper voltage plateau during the recharge process, which are different from the conventional Li–S battery. Moreover, the WS 2 itself could be lithiated/delithiated during the cycling, making the lithiated WS 2 (Li x WS 2, 0 ≤ x ≤ 0.3) a real host material for Li-polysulfide batteries. DFT calculations suggest that Li x WS 2 (0 ≤ x ≤ 0.3) exhibits moderate binding/anchoring interactions toward polysulfides with adsorption energies of 0.51–1.4 eV. Our work reveals the reaction mechanism of the Li–polysulfide batteries and indicates that the lithiated host plays an important role in trapping the polysulfides.