How to Improve the Quality of Thermal Safety Tests for Lithium-Ion Batteries by Thermal Runaway Criteria Definition and Temperature Sensor Positioning

Lithium-ion battery safety testing is essential for understanding cell behavior under abuse conditions. However, despite recent advances in test standardization, the quantitative assessment of safety-relevant temperatures remains sensitive to thermal runaway criteria and temperature sensor positioning. To address this issue, 20 commercially available 18650-type cells of the same type were investigated by thermal stability and lateral heating tests, using multiple temperature sensor positions and thermal runaway criteria. Thermal runaway criteria based on changes in vent gas temperature were introduced, providing a robust and precise alternative for thermal runaway identification. Both safety tests revealed pronounced intra- and inter-cell variability, which posed a significant risk of misinterpreting test results. Statistical analysis revealed that increasing the number of measurement positions enabled identification of the actual temperature of safety-relevant events with significantly higher accuracy, thus reducing the required sample size.