In the typical Li–S battery, lithium metal is used as the negative electrode and it is separated from the positive sulfur-based composite electrode by an ion conducting liquid. All three components should be designed with an integrated approach that focuses on improved cycling stability, cycling efficiency, and high sulfur utilization.[1] All three properties are in correlation with the chemical environment, which includes the type and the structure of the host matrix, the amount of sulfur present, the electrolyte, any additives, the separator, and the lithium surface. Recently, certain improvements in terms of cycling stability have been achieved when acting on some of these parameters. For instance, changes in the morphology and composition of the host substrate showed remarkable improvements in the stability and efficiency of Li–S cells. However, the origin of some of the changes is not well understood and is still the subject of lengthy debates.[2] Among the factors that negatively affect the development of Li–S batteries is a lack of in situ techniques; the techniques developed for Li-ion batteries cannot directly be used for the characterization of Li–S cells.[3, 4] If appropriately designed, in situ analytical techniques could be very helpful in improving our understanding of the reaction mechanisms occurring in Li–S cells. In particular, such techniques could be able to qualitatively and quantitatively determine the amount of polysulfides dissolved in different parts of Li–S cells. Our recent work regarding the development of new insitu techniques proposed the use of a four-electrode-modified Swagelok cell that could determine quantitatively the amount of polysulfide that diffused from the cathode to electrolyte in the separator.[5] The use of a four-electrode cell clearly demonstrated the differences between the cathode composites and the electrolytes that were detected as different amounts of soluble polysulfides in the separator.