Comparison of Thermal Runaway Characteristics of Lithium-Ion Batteries at Different Heating Rates

Lithium-ion battery fire test methods specify different conditions for initiating thermal runaway, including an external heating rate and a target time to visible flame occurrence. This study examined the temperature responses produced by two heating rates using the same external heating method and cell arrangement. Five NMC pouch cells were tested in each experiment, with five replicate tests per condition. Case 1 used a set heating rate of 8.5 °C/min. Based on the mean time to first visible flame occurrence in Case 1, a rate of 30 °C/min was selected for Case 2 to target flame occurrence within 7–9 min. The measured heating rates were 8.50 ± 2.08 and 28.98 ± 3.83 °C/min, respectively. The mean time for the heating source to reach 200 °C decreased from 1531.8 to 372.0 s, whereas its maximum temperature rises were similar (921.5 ± 34.6 and 924.4 ± 5.1 °C). At 1.8 m above the floor, the maximum temperature rise increased from 88.26 °C in Case 1 to 318.54 °C in Case 2. These results show that heating rate affected the timing and upper-region distribution of the temperature response more strongly than the near-source peak rise under the conditions tested. The findings apply to the external heating configuration examined here and do not represent a direct comparison with an overcharge test.