LiFePO4 batteries are widely regarded as safe. However, electric bus fires caused by overheating of LiFePO4 batteries have been reported. In this study, a pseudoadiabatic instrument was used to verify the thermal runaways of IFR 14500, A123 18650, A123 26650, and SONY 26650 cylindrical LiFePO4 lithium-ion batteries charged to 3.8 or 4.2V. At runaway maximum temperature lower than the auto-ignition temperature of electrolyte, both 14500 and 18650 LiFePO4 batteries were determined to be safer than 26650 batteries. The crucial temperatures for 26650 batteries are in the range of 240 - 280°C with a self-heat rate exceeding 100°C min−1. These high self-heat rates were not observed in 18650 and 14500 batteries. The effects of diameter on thermal runaway were visualized through the comparison of the runaway curves, crucial temperatures, maximum temperatures, maximum self-heat rates and total runaway energies of the batteries. The diameter effects on runaway hazards were investigated. The hazards of 26650 LiFePO4 batteries were caused by excessive heat because of internal short circuits above the crucial temperature, which were largely attributed to the collapse of the integrity of the separator. Therefore, the hazard of 26650 batteries is not caused by chemical activity.

中文翻译：

LiFePO 4电池被广泛认为是安全的。然而，已经报道了由LiFePO 4电池过热引起的电动公交车起火。在这项研究中，使用假绝热仪器来验证IFR 14500，A123 18650，A123 26650和SONY 26650圆柱形LiFePO 4锂离子电池充电至3.8或4.2V的热失控。在失控的最高温度低于电解液的自燃温度时，已确定14500和18650 LiFePO 4电池都比26650电池更安全。26650电池的临界温度在240-280°C的范围内，自热速率超过100°C min -1。在18650和14500电池中未观察到这些高的自热率。通过比较失控曲线，临界温度，最高温度，最大自热率和电池总失控能量，可以看到直径对热失控的影响。研究了直径对失控危害的影响。26650 LiFePO 4电池的危害是由于高于临界温度的内部短路引起的过热而引起的，这主要归因于隔膜完整性的破坏。因此，26650电池的危害不是由化学活性引起的。