Abstract:

Lithium iron phosphate （LFP） battery features a long lifetime and high safety， which is widely used in electric commercial vehicles. However， thermal runaway accidents may still occur during its use. To inhibit the expansion of fire in LFP battery packs， an efficient， easy-to-operate and low-cost internal thermal runaway suppression technology is proposed， that is， injecting micro-positive pressure nitrogen into battery packs. The effect and feasibility of this technology are systematically analyzed by module thermal runaway tests of packs with/without micro-positive pressure nitrogen and the condensation test in the pack. The test results show that： （1） Under the condition of no suppression measures， the thermal runaway of all modules occurs within 140 s， and the battery burns continuously for 413 s， with a maximum surface temperature of 627.6 °C. The insulation resistance of the battery pack is 43.7 MΩ， reduced by 95%， and the internal relative humidity increasing by about 200%. （2） Under the condition of micro-positive pressure nitrogen suppression， only one battery explosion-proof valve of the battery module is opened， with the opening time 526 s later than that without nitrogen， and the maximum temperature on the battery surface is 148 ℃， so it is comprehensively judged that there is no thermal runaway in the battery module. Under the condition of micro-positive pressure nitrogen， there is no condensation in the pack， which effectively inhibits the respiration effect and reduces the risk of secondary disasters such as an insulation short circuit in the pack. This study provides new research ideas for the design and safety prevention and control technology of high-capacity lithium iron phosphate battery packs.

Key words: lithium iron phosphate battery pack, micropositive atmospheric, nitrogen environment, thermal runaway