All Solid Lithium Metal‐Polymer Battery End‐of‐Life: an Investigation of Symmetric, Battery, and Bilayer Cells

ABSTRACT Li metal as a negative electrode material is very promising to reach higher energy density batteries beyond Li‐ion. Batteries using a solid polymer electrolyte (SPE), such as poly(ethylene oxide), can cycle over several thousand cycles, but their end‐of‐life mechanism remains unclear. Failure modes may originate from both positive and/or negative active electrode materials and at the active material/electrolyte interfaces. For the Li metal negative electrode, X‐ray computed tomography (XRCT) is a powerful and accurate tool to visualize and quantify the heterogeneity of the Li electrodeposits induced by the oxidation (pitting) and reduction (stripping) electrochemical steps. This work investigates the impact of cycling on symmetric cells and reveals the direct link between the heterogeneities induced by Li microstructure and the electrochemical signature of cell shortcut. To go further in the investigation, full batteries and bilayer positive cells were analyzed using the same approach, but major differences were highlighted compared to symmetric cells. This work highlights the importance of studying full batteries to understand the behavior of Li metal during long‐term cycling. A failure mechanism occurring in Li metal batteries is proposed in light of these new findings.