A comprehensive study of thermal runaway behavior and early warning subjected to internal short-circuit

The thermal runaway (TR) caused by internal short-circuit (ISC) of Li-ion batteries (LIBs) poses a significant threat by elevating the risk of fires or explosions. To this end, this paper investigates the evolution in voltage, temperature, and vent gas of eight types of batteries subjected to penetration by integrating the effects of state of charge (SOC), nail position, and nail speed. The batteries undergo TR triggered by the shrinkage of the separator and reactions between the cathode and electrolyte. The primary vent gases included electrolyte vapors, CO₂, CO, H₂, CH₄, C₂H₄, C₂H₆, and C₃H₆, with electrolyte vapors constituting over 90 % of the total. The elevated SOC significantly increases the risk of TR without affecting the main gas components. TR reactions intensify when penetration occurs near the electrodes. However, nail speed has virtually no effect on the thermal and electrochemical behavior of LIBs. Based on these findings, we propose a sensitive detection method based on characteristic gas capture. Since mature sensors for electrolyte vapors are not yet commercially available, we choose H₂, CO, CO₂, CH₄, and smoke gas sensors for early detection. Nail experiments with a 20 Ah hard-case battery reveal that H₂ is captured first, even at a battery temperature of only 23.8 °C. The results provide valuable insights for process safety evaluation, fire prevention, and practical engineering applications in LIBs rescue.