Abstract: Over-charging is one of the important issues that cause fire in electric vehicles. In this paper, a fire test of lithium iron phosphate (LIP) battery electric vehicle was carried out by over-charging the battery. The temperatures inside the battery pack, under the chassis, on the car surface and inside the car, and the temperatures and radiative heat flux intensities all around the car, were measured during the test. The fire heat release rate was also measured by using the oxygen consumption principle. The results show that the development of LIP battery electric vehicle fire caused by over-charging is as follows: combustible gas was generated due to thermal runaway of the battery pack, the gas concentrated under the chassis and was later ignited, the flame quickly spread to the combustible materials around the chassis and tires, and then the fire caused the window glass to break one after another, the interior and passenger seats were ignited later, and then the whole vehicle burst into flame violently. The fire growth rate of the vehicle was between medium speed fire and fast speed fire, and the peak of fire heat release rate was measured to be about 5.5 MW. The maximum radiative heat flux intensity peaks at 0.5 m and 1.0 m away from the edge of the vehicle were 50~60 kW/m² and 20~22 kW/m², respectively, which might ignite the adjacent vehicles.

Key words: electric vehicle, lithium iron phosphate battery, overcharge, thermal runaway, fire spread, heat release rate