In this study, the lithium ion battery (LIB) additive 1,3-propane sultone (PS) was investigated using capillary electrophoresis (CE) connected to a quadrupole time-of-flight mass spectrometer (Q-TOF MS). In the first part, PS was thermally aged with the organophosphates dimethyl phosphate (DMP), diethyl phosphate (DEP) or triethyl phosphate (TEP) at 60°C for one month. It was observed that PS reacted with traces of water, with organophosphates, with decomposition products of the organophosphates and polymerized to long-chain decomposition products. Due to the large number of in part similar decomposition products, it was not possible to baseline separate them from each other. The structures of the decomposition products were identified and the deviations of the detected m/z-ratios of the decomposition products to the calculated m/z-ratios were lower than 3.0ppm. Moreover, one of the most interesting aspects was the formation of DEP in the aged samples of TEP and PS. In the second part, PS was mixed with DMP, DEP or TEP in the LIB electrolyte and aged at 60°C for one month. In these samples, decomposition products were determined, formed by reaction of PS with carbonates, organophosphates and DMP, DEP or TEP. In these electropherograms, the decomposition products were baseline separated. In this study, the high reactivity of PS with different electrolyte compounds from the electrolyte was shown in battery research for the first time.