Direct visualization of sulfur cathodes: new insights into Li-S batteries via operando X-ray based methods.

As the need for the development of "beyond lithium" ion battery technologies continuous unabated, lithium sulfur batteries have attracted widespread attention due to their very high theoretical energy density of 2,600 Wh kg-1. However, despite much effort, the detailed reaction mechanism remains poorly understood. In this study, we have combined operando X-ray diffraction and X-ray microscopy along with X-ray tomography, to visualize the evolution of both the morphology and crystal structure of the materials during the entire battery cycling (discharging/charging) process. The dissolution and reformation of sulfur clusters is clearly observed during cycling. In addition, we demonstrate, for the first time, the critical role of current density and temperature in determining the size of both the resulting sulfur clusters and Li2S particles. This study provides new insights about promising avenues for the continued development of lithium sulfur batteries, which we believe may lead to their broad deployment and application.