Lithium-Sulfur Batteries: New insights and developments

Kurzfassung

The identification and quantification of species involved in the electrochemical reactions of lithium-sulfur (Li-S) batteries are still unclear and controversial aspects of the investigation of these cells. However, a deeper understanding of the system is crucial to improve the capacity and cycling stability of the cell. In this work, the reduction process of sulfur in a Li-S battery was studied using UV-Vis spectroscopy under argon atmosphere. Absorbance maxima of dissolved sulfur and polysulfide species were determined at various concentrations. Reference solutions of polysulfides reduce the λmax in the UV-region with decrease of polysulfide order. This tendency is also observed between 25–75% depth of discharge due to the progressive reduction of polysulfides in the electrolyte. Because the application of UV-Vis spectroscopy alone does not provide a complete overview insight intoof the distribution of all species during cycling, we present a comparison between the output of a physicochemical model with experimental data obtained from UV-Vis spectroscopy and other characterization methods. The model affirms that the highest concentration of polysulfide is observed when all sulfur has been dissolved. In the tested cells, this occurs at around 37% DOD (450 Ah∙kgS−1). A significant concentration of polysulfides is confirmed at the end of discharge which is of significant importance for improving the cycling stability of Li-S cells.