Abstract: Lithium-ion batteries are susceptible to thermal runaway when exposed to external environmental influences during operation. This phenomenon, inherently unpredictable, can lead to severe and challenging-to-mitigate consequences, particularly as the State of Charge (SOC) markedly influences the onset and severity of thermal runaway. In this context, our investigation delves into the thermal runaway behaviors of lithium-ion batteries across a spectrum of SOC conditions, employing liquid nitrogen injection for cooling within a controlled environment. Moreover, this research extends to evaluating the impact of thermal insulation on battery enclosures, aiming to assess its contribution to enhancing the efficacy of liquid nitrogen cooling and the overall suppression capabilities against thermal runaway. The study elucidates a direct correlation between increased SOC and the magnitude of fire incidents, mass loss, and carbon monoxide generation during thermal runaway incidents. It was observed that the critical temperature threshold for initiating thermal runaway decreases with an elevation in SOC, whereas the peak temperature experienced during thermal runaway escalates. The duration to reach thermal runaway, time to peak temperature, and the differential in characteristic timescales exhibit a proportional relationship with SOC. Implementing thermal insulation treatments on battery enclosures demonstrated a notable extension in the cooling effects of liquid nitrogen, maintaining a prolonged cooling action on batteries undergoing thermal runaway. This significantly enhanced cooling duration effectively contributes to strategies aimed at delaying or even preventing thermal runaway, offering a viable approach to mitigating the risks associated with lithium-ion battery operations.

Key words: thermal runaway; liquid nitrogen fire extinguishing; lithium-ion battery; heat preservation treatment; thermal runaway suppression