Quantitative Evaluation of Vent-to-Thermal Runaway Transition and the Delay/Suppression Effects of Cooling Extinguishing Agents in Forced-Heated 18650 Cells

Single-cell-based experiments were conducted to evaluate the thermal runaway time of 18650 secondary batteries and the thermal runaway suppression on cooling with different extinguishing agents using the relative delay factor. Lithium-ion, lithium iron phosphate (LiFePO<sub>4</sub>), and sodium-ion batteries were tested using forced heating through an external controller. The gas venting observed in the battery vent was defined as the pre-runaway stage, in which water, foam, and liquid chemical agents were applied before thermal runaway. The cooling and suppression effects of each agent were analyzed and compared with the delay factor in the absence of treatment. The suppression performance was dependent on battery chemistry, and no single treatment showed consistent effectiveness across all cell types.