Thermal runaway and fire behaviors of a 300 Ah lithium ion battery with LiFePO4 as cathode

Abstract

A series of thermal runaway (TR) tests are conducted on the 300 Ah large-scale lithium iron phosphate (LiFePO4) batteries under external heating. The combustion process of the battery can be divided into four stages, and the aggressive cylindrical flame is observed. Due to the battery's large size, the TR expanding process within the battery body is clearly observed based on the temperature rate curves of different surfaces. The flaming combustion accelerates the occurrence of TR but has little influence on the peak surface temperature. The cooling effect of safety valve opening on each thermocouple is influenced by the electrolyte distribution inside the cell. A real-scale scenario is considered to evaluate the fire-induced toxicity of an electric bus that a 10 cell pack combusts in a garage with fresh air renewal. The fractional effective dose is much greater than the critical value of 1, indicating the catastrophic toxicity. The air renewal rate required for safety is calculated to provide advice for the ventilation management of garage. The battery fire is compared with the pool and gas fires of common fuels. It is found that this large-scale LiFePO4 battery has the higher specific capacity and superior safety performance in the aspect of heat release features after comparing with previous LIB samples.