Operando SAXS-WAXS for multi-scale analysis of lithium metal pouch cell batteries with gel polymer electrolyte.

Operando small- and wide-angle X-ray scattering (SAXS/WAXS) were first applied on half-pouch cells composed of a Li metal foil, an in-situ crosslinked gel polymer electrolyte and a Cu grid, where lithium plating and stripping cycles were applied. Spatially resolved WAXS revealed significant heterogeneity with possible salt concentration gradients and degradation products formation between the lithium and polymer. On the other hand, no changes of the polymer structure at the nanoscale are found in SAXS at first. Observations were confirmed by post-mortem analysis, revealing lithium deposition heterogeneities. Next steps will be the study of the cathode- electrolyte interfaces, using the same setup with NMC 811 coated aluminum grids. Such advanced characterization techniques and the understanding they bring to the degradation mechanisms are crucial for the further development of semi-solid electrolyte systems, and therefore their possible commercialization.