Experimental study on thermal runaway evolution and toxicity hazard of lithium-ion batteries in a tunnel under longitudinal air flow

The widespread adoption of lithium-ion batteries (LIBs) for energy storage has introduced significant fire risks, particularly in confined and restricted environments such as tunnels. This study investigated thermal runaway (TR) behavior in a model tunnel at ventilation speeds ranging from 0 m/s to 2.5 m/s, using LiFePO4 (LFP) and LiNi(x)Co(y)MnzO(2) (NCM) batteries. The experiments identified two critical phases (e.g., safe venting and uncontrollable TR) that govern flame propagation within the tunnel. NCM batteries exhibited a maximum ceiling temperature exceeding 127 degrees C at wind speeds below 2.0 m/s, while LFP cells surpassed this threshold even without ventilation. Furthermore, CO emissions from LFP battery TR were significantly reduced (similar to 90 %) with an increase in ventilation speed to 2.0 m/s. However, mitigating the toxic CO emissions from NCM battery TR required substantially higher ventilation speeds. The maximum ceiling temperature rise due to longitudinal airflow was characterized using a power function. These results contribute to a deeper understanding of the hazards posed by battery TR in confined spaces and offer insights into enhancing the resilience of critical urban infrastructure.