Thermal Runaway of Lithium-Polymer-Cell Batteries

This study examines heat release rates (HRR) and smoke emissions from battery failures resulting from direct fire, mechanical damage, and overcharging across various states of charge. All experiments in this work used a battery comprising three or six lithium-polymer (Li-Poly) cells, each with a nominal voltage of 3.7 volts. Measurements were taken to characterize the critical components influencing HRR and smoke emission calculations in each experiment. The HRR was characterized using oxygen consumption calorimetry, carbon dioxide generation calorimetry, and radiative heat exposure (RHE) measurements with a heat flux gauge. The HRR measured with all three methods showed both quantitative and qualitative agreement, with the median and maximum measurements differing by no more than 10% in most cases. A larger difference in peak HRR was observed when fully charged batteries were exposed to direct fire, with the RHE-derived measurement showing more variable local extrema than the calorimetry-derived methods. As the maxima were higher and the minima were lower, this difference was attributed to the sensor response time; however, further research is needed to verify these findings. Speciated gas and particulate measurements were collected from plumes generated during battery failure. The mass-specific extinction coefficient of particulates, derived from an optical laser and gravimetric measurements of a filter sample, is not a universal constant for battery fires because the resulting smoke is test-specific and time-dependent, evolving throughout the thermal runaway process. Hydrocarbons and gaseous carbonates released during thermal runaway are inversely related to total heat release, meaning more are released when the batteries are not fully ignited. The results presented here provide a more accurate understanding of the limitations of existing methodologies and have implications for improving standard test methods.