Thermal runaway difference between fresh and retired lithium iron phosphate batteries under overheating

Safety is an important factor restricting the cascade utilization of lithium-ion batteries (LIBs). In this paper, the safety characteristics of fresh and retired lithium iron phosphate batteries are investigated by means of a heating-triggered thermal runaway (TR). The results show that under the heating condition of 200 W, the internal short circuit (ISC) can directly cause the TR of a new battery and lead to an explosion with an overpressure of 98.9 kPa. However, there is still a buffer time of 13.1-22.3 min between the ISC and TR for the retired battery with states of health (SOHs) of 80% - 60%, and the retired battery cannot explode. The large-scale ISC onset time, TR onset time, and TR onset temperature of the 70% SOH battery are 27.4 min, 40.5 min, and 179.9 °C, respectively, which are the smallest among retired batteries, indicating that the 70% SOH battery may be more likely to trigger TR. The findings can provide guidance for the safe application of retired batteries.