The thermal runaway analysis on LiFePO4 electrical energy storage packs with different venting areas and void volumes

With increasingly more electrochemical energy storage systems installed, the safety issues of lithium batteries, such as fire explosions, have aroused greater concerns. In this study, the thermal runaway behaviors of two different structures of lithium–iron-phosphate battery packs were compared. A fire explosion occurred in battery pack I, which had a small venting area and void volume, but battery pack II with a large venting area and the void volume kept safe. To explain these phenomena, a new experimental method coupling multiple measurements was proposed in this study to survey the velocity, composition, and temperature of venting gas. The venting gas velocity had two peaks, with its maximum value reaching about 270 m/s. Besides, the venting gas was mainly composed of hydrogen and carbon dioxide, accounting for around 30.33% and 38.86%, respectively. With the experimental data used as boundary conditions in a mathematical model, the diffusion behaviors of the venting gas within these two battery packs were derived. By comparing the flammable gas concentration with their lower explosion limits and upper limits, this study found that the high concentration of hydrogen and ethylene might bear the main responsibility for the fire explosion in battery pack I.