Calendar aging of Li-O2 cells under different storage environments probed by operando mechanical pressure

Storage-induced degradation of the Li metal negative electrode in Li-O 2 cells remains largely unexplored, particularly from a mechanical point of view. In this work, we study how different storage atmospheres affect Li-O 2 cells during five days of rest and directly measure the resulting Li expansion using operando mechanical pressure measurements. Cells with 1 M LiTFSI in TEGDME as the electrolyte were stored under different atmospheric conditions. Electrochemical impedance spectroscopy, SEM imaging, mass change measurements, and performance tests were used to correlate mechanical pressure changes with interfacial changes and electrochemical performance. Cells stored in Ar show stable pressure, nearly constant thickness and impedance, and Coulombic efficiencies similar to the pristine cell, indicating a relatively stable SEI and limited electrolyte decomposition. Storage in dry air or static O 2 leads to moderate pressure build-up and impedance growth, together with reduced reversibility. Ambient air and flowing O 2 cause a large mechanical pressure rise, substantial Li thickening, significant electrolyte loss, considerable impedance growth, and loss of reversibility. SEM/EDS/XPS show a porous interphase that becomes more C-rich under O 2 flow, attributed to accelerated TEGDME decomposition. Finally, we show that controlling gas transport and engineering the electrolyte composition can effectively mitigate storage-induced degradation in Li-O 2 cells.