Thermal Runaway Behavior of Lithium Iron Phosphate Battery During Penetration

The nail penetration experiment has become one of the commonly used methods to study the short circuit in lithium-ion battery safety. A series of penetration tests using the stainless steel nail on 18,650 lithium iron phosphate (LiFePO₄) batteries under different conditions are conducted in this work. The effects of the states of charge (SOC), penetration positions, penetration depths, penetration speeds and nail diameters on thermal runaway (TR) are investigated. And the accelerating rate calorimeter is applied to reveal the thermal runaway mechanism. The experimental results show that the higher the SOC of the battery, the higher the possibility and risk of TR of the battery, and there seems to be a critical penetration depth where TR occurs. The battery exhibits higher average temperature at higher penetration speeds. Whether the battery get into TR is not related to the penetration speed. When the penetration location near the positive pole and negative pole,the risk of thermal runaway is much higher than the centre position of the battery. The larger the diameter of the nail, the lower the overall temperature of the battery. What’s more, the results of the penetration tests under the condition of parameter coupling shows that the average temperature of battery are greatly affected by the parameters of SOC, penetration position. The temperature of the LiFePO₄ battery is within 200°C when the TR occurs induced by the penetration, which is mainly due to the incomplete exothermic reaction inside the battery.