The preload force effect on the thermal runaway and venting behaviors of large-format prismatic LiFePO4 batteries

In electrochemical energy storage systems, large-format LiFePO4 (LFP) batteries are usually formed the battery pack under preload force. However, the preload force effect on the safety of the batteries remains unclear. In this study, the TR and gas venting of the 280 Ah LFP batteries at 100% state of charge under four preload forces (0, 3, 6, and 9 kN) are investigated experimentally. The novelty compared to previous studies is that the fixture with a pressure sensor is used to set different preload forces before the experiment and monitor the expansion behavior of the LFP batteries during TR. The results quantitatively analyse the relationship between preload force and TR hazard of prismatic LFP battery. Two important results are presented: (I) the gas release inside LFP battery is horizontal and vertical at the same time, and the battery expansion behavior has a mitigating effect on gas pressure. (II) the TR hazard assessment model is pioneered to assess the TR hazard of batteries under four preload forces. The results show that the TR hazard is minimal at 3 kN. These results provide an effective guide to the setting of preload force and the emergency response to TR.