Understanding the combustion characteristics and establishing a safety evaluation technique based on the overcharged thermal runaway of lithium-ion batteries

As an abusive method to trigger thermal runaway (TR), the overcharge method has been widely used to evaluate the safety status of lithium-ion batteries (LIBs). In this study, the combustion characteristics of LIBs were systematically studied by overcharging batteries at different charging rates (C-rates). The results indicated that a high C-rate could cause jet flames with temperatures as high as 1350 degrees C at a relatively low state of charge. Furthermore, certain maximum heat release rate (HRR) and mass loss rate (MLR) values of 192 kW and 1785 g/s were obtained at 1C, respectively. X-ray photoelectron spectroscopy results for sulfur showed that the valence of sulfur was related to the peak HRR. Moreover, a novel safety evaluation technique denoted as the relative overcharge safety status (OCSS) was presented to highlight the safety status of the overcharging battery. We found that the OCSS at different C-rates presented a linear relationship with the dimensionless time and obtained the safety threshold, safety boundary, and safety level to easily evaluate the TR risk. Therefore, the OCSS method may provide timely, real-time evidence for battery management systems when batteries are overcharged.

Automated summary

This study systematically investigates the combustion characteristics of LIBs at different charging rates. The results show that high charging rates can result in high-temperature jet flames at low state of charge, with specific maximum heat release rate and mass loss rate values. X-ray photoelectron spectroscopy results reveal a correlation between the valence of sulfur and the peak heat release rate. A novel safety evaluation technique is proposed to assess the safety status of overcharging batteries.