Developing laboratory tender X-ray emission spectroscopy to characterize next-generation lithium- sulfur batteries

X-ray emission spectroscopy (XES), based on radiative transitions from occupied valence electronic states, enables the study of the local electronic structure and chemical bonding of atoms in materials of various dimensions. While XES spectroscopy in the hard X-ray spectral region is heavily used at synchrotrons, the soft X-ray region remains significantly less explored due to numerous technical limitations. By using an appropriate spectrometer combined with a laboratory source of ionizing radiation, XES spectroscopy in principle allows the study of the local electronic structure of bulk materials (in both solid and liquid forms) with emission line energies in the soft X-ray spectral region. Consequently, XES spectroscopy brings this analysis from synchrotrons into smaller laboratories and potentially also into industrial labs. In the proposed project, we will attempt to develop and establish XES spectroscopy as an analytical tool for the laboratory analysis of the chemical state of sulfur in the cathodes of metal-sulfur batteries, which offer an extremely high energy density.

Batteries based on the use of a sulfur cathode theoretically enable an increase in energy density by an order of magnitude compared to lithium-ion batteries, and are therefore one of the most promising systems for applications requiring high energy density. To achieve the capacities necessary for commercial use, it is essential to improve the fundamental understanding of the electrochemical conversion mechanism of sulfur. Analytical techniques that enable non-destructive analysis of cathode materials during battery operation (operando methods) play a critical role in this. Currently, X-ray absorption spectroscopy using synchrotron light is most commonly employed to characterize electrochemical processes in the sulfur cathode. Limited access to large-scale experimental facilities represents a bottleneck for more routine analysis of electrochemical sulfur conversion. In the proposed project, we will develop a laboratory analytical method and use it to characterize the electrochemical conversion of sulfur in certain new types of metal-sulfur batteries that enable increased energy density and capacity.