Revealing the Thermal Runaway Behavior of Lithium Iron Phosphate Power Batteries at Different States of Charge and Operating Environment

With the widespread use of Li-ion batteries, their safety issues have received increasing attention. Thermal abuse, electrical abuse, mechanical abuse, etc., can cause thermal runaway of batteries. Therefore, understanding Li-ion battery thermal runaway behavior and its suppression is of great practical significance. In this work, an experimental platform composed of a 202-Ah large-capacity lithium iron phosphate (LiFePO₄) single battery and a battery box is built. The thermal runaway behavior of the single battery under 100% state of charge (SOC) and 120% SOC (overcharge) is studied by side electric heating. Systematic studies are conducted to investigate the thermal runaway behavior of LiFePO₄ battery modules operating in different environments (open area and power battery box) and the suppression effect of spraying fire extinguishing media on thermal runaway. The results show that the decomposition of the solid electrolyte interphase (SEI) film in the battery is the key reason for thermal runaway, which is more intense in the overcharged state. To provide early warning of battery thermal runaway, it is suggested to collect the upper surface temperature of the battery in the battery management system. Moreover, the thermal runaway temperature of the Li-ion battery is lower in the power battery box than in the open area, but there is a risk of causing a chain reaction of the surrounding batteries. At this time, timely fire extinguishing agent spraying can effectively reduce the temperature of the thermal runaway battery and prevent the subsequent chain reaction.