MoS2 nanosheets as interlayer in Li-S batteries

Abstract

This work has investigated the use of MoS2 nanosheets acting as an interlayer to effectively block polysulfide shuttling (movement from cathode to the anode) in Li-S batteries. In the first part of the work we exfoliated bulk MoS2 into a few layered MoS2 flakes, resulting in increased surface area and improved electric properties, to achieve a better interlayer performance by effectively trapping polysulfide (PS) in the cathode. This was done through solvothermal lithium intercalation followed by water sonication, creating a reaction between water and intercalated lithium to promote exfoliation. In the second part was explored the electrochemical characterization of distinct Li-S test cells (each with different interlayers), and compared to a standardized Li-S test cell. The afore mentioned interlayers were spread either on to the cathode or the separator. Furthermore, carbon black, bulk and exfoliated MoS2, were compared as active materials of the interlayers. Bulk MoS2 exfoliation into thinner flake, resulted in a size reduction up to 56 times and a decrease in the number of layers. The results of optical spectroscopy suggest effects of quantum confinement. Furthermore, with XRD, was analytically demonstrated successful intercalation and exfoliation. Then, through Raman and SEM analysis demonstrated evidence of thinner MoS2 structures. On another hand, exfoliated MoS2 was spread on a sulfur cathode creating the interlayer that successfully trapped polysulfides. This was showed through a 4 percentage points increase in sulfur utilization for the first cycle, and an improvement of sulfur loss by cycle of 0.02% retaining a good 99.4% coulombic efficiency. In addition a ΔE decreased of 45%, a result of improved battery kinetics. Nonetheless a simple carbon black DL interlayer was also made using a different solvent. However was observed a increase of sulfur utilization by 9% in the first cycle and the same degradation of sulfur per cycle as the standard battery with an impressive CE of 99.7%.