Operando Resonant Inelastic X-ray Scattering: An Appropriate Tool to Characterize Sulfur in Li-S Batteries

Application of new analytical tools providing insight into the mechanism of lithium-polysulfide formation in the cathode and their interaction with the host matrix and electrolyte is essential for further development of Li-S batteries. In this work, resonant inelastic X-ray scattering (RIXS) measurements at the sulfur K-edge were performed on the Li-S battery in operando mode to study the lithium-polysulfide formation during the discharge process. The relative amounts of each sulfur compound in the cathode during the discharge process were determined from the linear combination fit using reference spectra measured on standard sulfur compounds. Because of resonant excitation condition the sensitivity for the lithium-polysulfide detection was significantly enhanced, while the sulfate signal from the electrolyte was heavily suppressed. In addition, the influence of self-absorption effects in the analysis was minimized due to fixed excitation energy. Consequently, a full quantitative analysis could be performed for the conventional Li-S battery consisting of sulfur-carbon composite cathode free from any additives and a LiTFSI based electrolyte.