Thermal Runaway Evolution, Propagation Mechanism and Multi-Dimensional Fire Investigation Methodology for 18650-Type NCA Lithium-Ion Batteries

To address the critical industry challenges of insufficient thermal safety and reliability in the stacking design of lithium-ion battery (LIB) modules, as well as the lack of accurate traceability methods for LIB fire accidents, this study takes commercial 18650-type lithium, nickel cobalt aluminum (NCA) LIBs as the research object. First, we systematically investigated the thermal runaway (TR) behavior of single cells under thermal and electrical abuse conditions, identified the significant discrepancies in TR behavior between the two abuse scenarios, quantitatively revealed a positive correlation between TR risk and state of charge (SOC), and determined that the core feature is that the maximum heat release occurs in the negative electrode of the battery. Subsequently, we quantitatively analyzed the influences of the initial TR trigger position and module stacking structure on the TR propagation characteristics within the module, and obtained the key conclusions that center-triggered TR exhibits a faster propagation rate and that the vertical stacking structure significantly aggravates the TR chain reaction. Finally, based on the TR process, this paper summarizes the burn mark characteristics caused by different triggers of thermal runaway in LIBs. The results of this study provide critical fundamental data for optimizing the thermal safety design of LIB modules, and offer a scientific basis for the formulation of LIB fire rescue schemes and the implementation of fire investigation.