Investigating Chemo-Mechanical Phenomena in All-Solid-State Lithium Metal Batteries Using In Situ Curvature Measurements

With increasing interest in the use of solid electrolytes (SE) for lithium-ion and lithium metal batteries, it is important to understand their chemo-mechanical properties and failure mechanisms. A key failure mechanism in the garnet-type solid electrolyte lithium lanthanum zirconium oxide (LLZO) are short circuits caused by Li penetration through the SE once a critical current density (CCD) is reached. Such Li penetration is known to cause fracturing of the SE, highlighting the need to investigate the combined chemo-mechanical phenomena that affect the performance and lifetime of all-solid-state batteries. The unique challenge of evaluating the mechanical driving forces behind this mechanism and how the stresses within the SE evolve during Li plating require careful in situ measurements. This work investigates the evolution of such phenomena within the LLZO using in situ curvature measurements, in both a traditional symmetric Li cell configuration and a novel anode-free configuration. Data was then analyzed in the context of a Finite Element Model (FEM) to quantitatively evaluate stress evolution in the solid electrolyte. Results show that Li metal plating within a surface flaw leads to an accumulation of stress prior to short-circuiting. The combined results of experiments and the FEM suggest that it is critical to minimize surface defects and flaws during the manufacturing of LLZO.