Abstract:

To investigate the effect of placement orientation on thermal runaway behavior of large-format NCM batteries, overheating-induced thermal runaway tests were conducted on 135 Ah prismatic NCM batteries under upright and inverted orientations. First, thermal runaway onset, temperature and voltage responses, and internal propagation behavior were compared. Jet temperature, mass loss, heat release, and smoke generation were then analyzed. Finally, eight characteristic parameters were selected from three aspects: thermal runaway onset, propagation, and jet hazards. A radar chart-based model was developed to assess runaway hazards. The results show that, compared with the upright orientation, the inverted orientation delayed runaway onset from 1 032.5 s to 1 093.0 s. However, after runaway occurred, the maximum surface temperature, maximum temperature rise rate, and propagation rate increased by 14.3%, 27.7%, and 27.6%, respectively. The maximum jet temperature also increased by 110.1 ℃. No significant differences were observed in total heat release or total smoke production between the two orientations. Although the inverted orientation increases runaway onset threshold, it significantly intensifies the hazards after runaway. Therefore, the overall runaway hazard is greater under the inverted orientation than under the upright orientation.

Key words: placement orientation, nickel cobalt manganese (NCM) battery, large-capacity, thermal runaway characteristics, jet flame, hazard assessment