Research on thermal runaway characteristics and mechanism of NCM811 Lithium-ion batteries under cross-seasonal and wide-temperature condition at-10 °C ∼ 33 °C: A case study in Qingdao, China

Multiple heat sources and extreme ambient temperatures pose more severe challenges to the safety performance of lithium-ion batteries (LIBs), and the kinetic characterization of thermal runaway (TR) of LIBs at extreme temperatures has yet to be improved. Through the establishment of a dual heat source coupled stimulation experimental platform, this study investigates the TR mechanism and flame jet dynamics of LIBs under broad temperature ranges corresponding to spring, summer, autumn, and winter (-10 degrees C similar to 30 degrees C). The results indicate that the increase in ambient temperature leads to a gradual reduction in the TR onset time (t(onset)), in the order of Tonset-Winter>Tonset-Spring>Tonset-Autumn>Tonset-Summer; for example, with 100% SOC (State of Charge), Tonset-Winter = 2528 s, Tonset-Summer = 2211 s, which was accelerated by 14.3%. However, TR maximum temperature (T-max) showed the opposite trend, Tmax-summer = 687.2 degrees C, Tmax-winter = 796.5 degrees C, which decreased by 15.9%. When SOC >= 75%, the average warning time for TR disaster of LIB (from venting to the beginning of TR) is 254 s less than that of winter in the summer with higher temperature, which makes the adoption of emergency measures and escape more urgent. When SOC >= 50%, the TR process was accompanied by flame generation, and the flame eruption process was the most intense at 100% SOC, with a maximum flame area of about 4400 cm(2), and its flame temperature was likewise the highest at 986.4 degrees C. Carbon and metal oxides were detected in the TR ejecta, and the lower the ambient temperature, the finer the ejecta particles were. The results of the study provide an important scientific reference for improving the theory of TR of LIBs, guiding the investigation of TR and fire in new energy vehicles, and formulating relevant standards.