Poly (ethylene oxide) (PEO)-based polymer electrolytes have attracted considerable attention for solid-state batteries due to their excellent processability and interfacial compatibility. However, the incomplete understanding of decomposition byproducts fundamentally hinders the elucidation of degradation mechanisms and rational design of stable interfaces. In this work, we employed online mass spectrometry and gas chromatography-mass spectrometry (GC-MS) methods to investigate the interfacial reactions between PEO-based electrolytes and activated electrodes (e.g. lithium metal anode and LiCoO2 cathode), as well as the decomposition products of PEO under both electrochemical cycling and thermal runaway conditions. In addition to permanent gases (H2, CO2, O2, etc.), we successfully tracked the dynamic evolution of several cyclic ether compounds (1,4-dioxane, ethylene oxide, dioxolane, and 2-methyl-1,3-dioxolane) with voltage-/temperature-dependence, by exploiting the efficient gas chromatographic separation capability of GC-MS for complex gaseous products. These findings provide critical insights into the dynamic degradation behavior of PEO-based electrolytes, advancing our understanding of their decomposition pathways under varying operational conditions and establishing a material design framework for the rational development of next-generation polymer electrolytes.
