Multi-Scale Analysis of Lithium-Sulfur Pouch Cells Using Imaging Methods

Lithium-sulfur batteries (Li-S) are promising energy storage technologies. Its high gravimetric energy density, the abundance of sulfur and low costs at high production volume, this battery type is especially applicable for automotive and aerospace applications. In recent years, the number of reported prototype cells has increased, as well as their accessible energy density. This underlines the progress of technology readiness of the Li-S system. However, despite this important breakthrough density and cycling stability have to be overcome in the Li-S research. Additionally, the influence of the cathode porosity as well as the surface of the carbon material and the electrolyte composition play an important role on the conversion of sulfur and the performance of prototype cells. Hard X-ray beamlines, as BAMline at the electron storage ring BESSY II in Berlin, Germany, have now been in service for over two decades. Several improvements have been implemented, allowing for operando tomography and fast radiographic measurements on the micrometer scale by using well-shaped synchrotron X-ray beam. In this study, operando X-ray imaging measurements on Li-S pouch cells are complemented by scanning and transmission electron microscopy and focused-ion-beam measurements on the nanometer scale delivering unique and multi-scale results about the morphology of sulfur inside the porous cathode material. Therefore, tiny pouch cells designs have been developed, allowing for operando tomography of stacked cells.