Quantification of heat energy leading to failure of 18650 lithium-ion battery abused by external heating

Abstract

The presence of unavoidable extreme thermal fields, as well as frequent incidents of Lithium-ion battery (LIB) fires, emphasizes the importance of understanding the contribution of external heat energy to the degradation and failure of the LIB. In this study, we quantified the heat energy from the external heat source, heat transferred, and heat causing the safety vent crack to better understand the relationship between external thermal stress and LIB behavior during external heating tests. For experior data purposes, a series of external heating testing was performed with the NCA and LCO LIBs with 25–100% SOC. The external heat energy (qh) required to crack the safety vent varied between 92.70 and 232.80 kJ/m3 and 142.62–172.14 kJ/m3 for NCA and LCO, respectively. During venting at 25–100% SOC, the heat transferred for NCA and LCO were 56.77–136.07 kJ/m3 and 86.56–102.81 kJ/m3, respectively, representing 58.45–78.46% and 57.00–61.63% of the qh. Around 117.71–224.76 kJ/m3 and 181.10–218.59 kJ/m3 were produced by side reactions in NCA and LCO before the safety vent crack. The LIB's internal heat energy for breaking the safety disc (qsv) was estimated to be 174.49–360.83 kJ/m3 in NCA and 269.00–321.40 kJ/m3 in LCO. The qrec to qh ratio indicates that less qh may be required for the higher SOC LIB to enter stage II while the produced qgen reaches a maximum of 2 and 1.5 times that of qh for 100% NCA and LCO, respectively. During the breakout of the disc, the qsv exceeds the qh to about 2.4 and 1.9 times for 100% NCA and LCO, respectively. The findings of this study provide fundamentals on the thermal behavior of LIBs which can be used to understand the difference in hazard in transporting different types of LIBs, and decide how to implement designs for resisting thermal runaway propagation.