Experimental study on thermal runaway and venting gas explosion hazards in prismatic lithium-ion batteries at different states of charge

This study experimentally investigates the thermal runaway (TR) behavior and the flammability characteristics of vent gases released from large-capacity lithium-ion batteries at varying states of charge (SOC). A 280Ah commercial prismatic cell with LiFePO₄ cathodes is induced into TR through external heating in a sealed chamber. Vent gases are periodically sampled and analyzed using gas chromatography coupled with mass spectrometry. Results demonstrate that TR severity intensifies above 50 % SOC. During the 25 %, 50 %, and 75 % SOC tests, the maximum cell temperature increased sequentially by 35 % and 258.3 %, while gas emissions rose by 79.3 % and 644.7 %, respectively. Furthermore, 15, 19, and 36 gaseous components are detected under the three conditions. At higher SOCs, a notable characteristic of the gas composition is the reduction in CO₂ and the elevation in H₂. The lower flammability limit for 25 % and 50 % SOC (10 %–15 %) is slightly higher than that for 75 % SOC (5 %). The upper flammability limit for 25 % and 50 % SOC (55 %–65 %) is significantly higher than that for 75 % SOC (4.7 %–6.6 %), with the highest deflagration risk of the gas mixture at 50 % SOC. These findings provide critical insights for thermal safety assessment, secondary explosion mitigation, and explosion-proof design for industrial battery systems.