Significance of in situ X-ray tomography for analysing buried interfaces in solid-state batteries: A case study on a Li/Li symmetric cell with a polymer-based electrolyte

Advanced in -situ characterization methods are crucial for comprehending how solid-state batteries evolve during cell cycling and to identify responsible factors for cell failure. In this study, we advocate for the use of laboratorybased in -situ X-ray tomography as a screening technique to non -invasively monitor the structural evolution of the cell of interest. The detected features of interest can be subsequently analysed by spectroscopic, microscopic and spectrometric techniques. To illustrate the proposed approach, we study the evolution of a Li symmetric cell while cycling from the pristine state up to cell failure. Pre-screening with in -situ X-ray tomography provides 3D images of the interface and suggests the occurrence of electrolyte thickening, puncturing and contact loss. These observations are consistent with impedance measurements conducted while cycling. Post-mortem XPS-analysis identifies lithium salt and organic compound accumulation on the electrolyte after cycling, providing a possible explanation for the observed electrolyte thickness increment. SEM images give visual proof of the interfacial contact loss, and Auger mapping gives further confirmation of the XPS data. This case study illustrates that prescreening using laboratory -based in -situ X-ray tomography, combined with in-depth analysis techniques, helps to advance our understanding of buried interfaces in solid-state batteries and to identify responsible factors for cell failure.