Vented gases and aerosols of automotive Li-ion LFP and NMC batteries in humidified nitrogen under thermal load

Chemical compounds were screened in a study on gases ventilated from Liion battery cells during thermal runaway in an inert environment. Automotive Li-ion pouch cells of lithium iron phosphate (LFP) and lithium nickel manganese cobalt oxide (NMC) cathode chemistry were exposed to heat-up in humidified nitrogen atmosphere until rupture caused by internally build up pressure. By means of analytic instruments such as Gas Chromatography-Mass Spectrometry and Fourier Transform Infrared Spectroscopy a screening of known and unknown constituent gaseous species was performed. Elemental metal contents in the aerosol phase were analyzed with Inductively Coupled Plasma Mass Spectrometry. Among the detected compounds there are several, to our knowledge, of potential toxic concern previously not reported to ventilate during thermal runaway of Li-ion batteries. Many of the compounds are irritating to the skin and the respiratory system. Whether the exposure of vented gases reach a dangerous dose in the case of real world accident involving Li-ion batteries cannot be concluded from this study. To assess first responders' occupational exposure risk, as well as victim exposure in e.g. a car accident, a full scale experiment is needed including propagation of thermal runaway in a stack of battery cells. Three of the detected compounds; ethyl ethylphosphonofluoridate, ethyl methylphosphonofluoridate, and methyl methylphosphonofluoridate are very similar to some organophosphorous chemical warfare agents. However, in order to perform a qualitative estimation of their quantities and possible toxicities in relation to a realistic scenario of a traffic accident, additional studies need to be performed. These include studies on a larger test system and quantity of tested material as well as in vitro studies to evaluate if they are potential enzyme inhibitors of acetylcholine esterase. This report includes description of the full experimental setup to safely perform such studies. A list of identified compounds together with toxicological assessment is given.