Early warning of thermal runaway for larger-format lithium iron-phosphate battery by coupling internal pressure and temperature

Understanding the gas production mechanism during thermal runaway is crucial for safety protection and early warning. However, few studies have investigated gas production behavior and characteristics during the early stages of thermal runaway owing to issues such as high temperature, corrosive environments, and difficult sealing. This study presents the internal pressure incubation behavior of prismatic batteries detected by external sensors through customized battery cover plates. The interplay between temperature and pressure during thermal abuse is analyzed to inform strategies for early detection and prevention. Experimental results reveal that the actual pressure threshold under heating conditions is 11–50 % lower than the threshold at ambient temperature. Additionally, venting in one type of experimental valve occurred 42.7 % earlier due to inferior heat transfer within the battery compared to the other type. To enhance early warning capabilities, we propose using the second derivative of pressure concerning temperature (d2P/dT2) and the ratio representing the relative changes in pressure and temperature L as early warning indicators. The results indicate that the (d2P/dT2) consistently increased after exceeding 0.1 in one type of experiment, while fluctuating in the other. Furthermore, the dimensionless number L exhibited a distinctive U-shaped distribution as the temperature increased. Theoretical analysis reveals that the L is highly sensitive to early-stage internal pressure fluctuations and the increased gas production rate caused by rising temperatures. These findings offer a reliable and robust approach to monitoring and implementing early warning systems for thermal runaway.