Characteristics of and factors influencing thermal runaway propagation in lithium-ion battery packs

The growing use of electric vehicles has made it imperative to use safe battery packs. Severe accidents may occur even due to minor faults in battery packs. One such issue is thermal runaway (TR) propagation in lithium-ion batteries (LIBs). In this study, cylindrical 18650 LIBs were employed to determine the factors responsible for TR propagation in battery packs. The main parameters studied were cycle aging, connection mode, arrangement, and state-of-charge (SOC). The results indicate that cyclic aging have little influence on the propagation process. When the positive of the battery are placed in the same direction, it is easier to cause the thermal runaway propagation of the battery pack than when the positive and negative are placed in the same direction. Meanwhile, parallel connections increased the probability of TR propagation. In addition, the SOC of the battery pack significantly affected TR propagation, with the highest probability at SOC values in the range of 40% to 60%. However, the probability of TR reduced at 80% and 100% SOC. Finally, our results indicate that the probability of TR propagation increased when the rate of increase in the temperature of adjacent cells was greater than 0.36 °C/s.