Influence of Lithium Metal Deposition on Thermal Stability: Combined DSC and Morphology Analysis of Cyclic Aged Lithium Metal Batteries

Safety properties of lithium metal batteries (LMBs) are key for potential commercialization. The few studies reported focus predominantly on pristine materials or as-assembled cells disregarding potential safety risks induced by cyclic aging and the associated formation of high surface area lithium deposits. Herein, LMBs using organic carbonate-solvent electrolyte were investigated to decipher the influence of the lithium metal deposition behavior on the thermal stability. For this purpose, cells were cycled to different states of health, states of charge and at varied current densities during charging before analyzing the thermal stability on material and cell level via differential scanning calorimetry. In combination with cryogenic-focused ion beam-scanning electron microscopy it is possible to correlate the lithium metal deposition morphology with the thermal stability. Therein, accumulation of highly porous lithium metal deposits during cycling leads to a significant increase of released heat caused by highly exothermic reactions between deposited lithium and the electrolyte. Consequently, a denser deposition morphology shifts the onset for exothermic decomposition reactions to higher temperatures. Overall, this study introduces the combination of different analytical techniques to evaluate LMB safety properties and reveals the safety-relevant impact of cyclic aging on thermal stability.