Operando SANS and Synchrotron Radiography Characterization of the Carbon Cathode from Lithium Sulfur Batteries

In recent years lithium sulfur (Li-S) battery research became an important route to go beyond traditional lithium ion batteries. Among various battery systems, Li-S batteries have comparatively high theoretical energy density and lower cost, making Li-S batteries very promising for next generation secondary batteries. However, the current energy density achieved, and significant capacity decay with cycling, do not fulfill the needs for industrialization. To overcome the drawbacks of Li-S batteries and improve their performance, better understanding of the reaction mechanism and how this relates to capacity decay is necessary. A great deal of ex-situ characterization research has been conducted that has shed light on the working mechanism. Considering the complexity of the solution and interfacial chemistry, with multiple intermediate lithium polysulfides and the inherent multi-electron reaction pathways, we developed advanced operando techniques to provide new information on the dynamic processes occurring at the electrode interface. In this presentation operando small angle neutron scattering (SANS) results will be shown, specifically shedding light on the precipitation process of S 8 and Li 2 S as a function of state of charge. We address the question of whether precipitation of S 8 and Li 2 S in the charged and discharged states, respectively, occurs in the pore or on the surface of the carbon cathode. This is a question that enjoyed very little discussion, due to the challenges in directly measuring the precipitation. Operando radiographic evidence will also be shown regarding the distribution of precipitates in the electrode. These results will increase the understanding of the charge / discharge mechanism of Li-S batteries and will contribute to the advancement of this battery chemistry.