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 (LiFePO 4 ) 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 LiFePO 4 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.

中文翻译：

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磷酸铁锂电池在渗透过程中的热失控行为

钉钉实验已成为研究锂离子电池安全短路的常用方法之一。在这项工作中，使用不锈钢钉在 18,650 磷酸铁锂 (LiFePO 4 ) 电池上进行了一系列不同条件下的渗透测试。研究了荷电状态 (SOC)、穿透位置、穿透深度、穿透速度和钉子直径对热失控 (TR) 的影响。并应用加速量热计揭示热失控机制。实验结果表明，电池的SOC越高，电池发生TR的可能性和风险就越大，TR发生的地方似乎存在临界穿透深度。电池在更高的穿透速度下表现出更高的平均温度。电池是否进入TR与穿透速度无关。当穿透位置靠近正极和负极时，热失控的风险远高于电池中心位置。钉子的直径越大，电池的整体温度越低。此外，参数耦合条件下的渗透测试结果表明，电池平均温度受SOC、渗透位置等参数影响较大。LiFePO 4 电池在渗透引起TR发生时的温度在200°C以内，这主要是由于电池内部放热反应不完全所致。热失控的风险远高于电池的中心位置。钉子的直径越大，电池的整体温度越低。此外，参数耦合条件下的渗透测试结果表明，电池平均温度受SOC、渗透位置等参数影响较大。LiFePO 4 电池在渗透引起TR发生时的温度在200°C以内，这主要是由于电池内部放热反应不完全所致。热失控的风险远高于电池的中心位置。钉子的直径越大，电池的整体温度越低。此外，参数耦合条件下的渗透测试结果表明，电池平均温度受SOC、渗透位置等参数影响较大。LiFePO 4 电池在渗透引起TR发生时的温度在200°C以内，这主要是由于电池内部放热反应不完全所致。参数耦合条件下的渗透测试结果表明，电池平均温度受SOC、渗透位置等参数影响较大。LiFePO 4 电池在渗透引起TR发生时的温度在200°C以内，这主要是由于电池内部放热反应不完全所致。参数耦合条件下的渗透测试结果表明，电池平均温度受SOC、渗透位置等参数影响较大。LiFePO 4 电池在渗透引起TR发生时的温度在200°C以内，这主要是由于电池内部放热反应不完全所致。