Comparative study of thermal runaway and cell failure of lab-scale Li-ion batteries using accelerating rate calorimetry

The safety of Li-ion batteries (LIBs) has long been a critical issue for their widespread application. The ever-increasing requirements for large-scale applications such as electric vehicles and stationary energy storage systems have spurred great interest in ensuring high standards of safety, which requires an understanding of the thermal runaway features of cells and modules. In this study, we evaluated the thermal runaway of pouch-type LIB cells with cell capacities of 33–3300 mA h by using accelerated rate calorimetry (ARC) and lab-made hotbox ramping measurements. The large-capacity cells (1000 and 3300 mA h) exhibited distinct stage behaviors of the self-heating rate in the ARC profiles and large exothermic reactions accompanied by an abrupt open-circuit voltage drop (internal short circuit) in the ramping test. The small-capacity cell (33 mA h) showed an incomplete thermal runaway feature. These findings were attributed to the large proportion of inactive components relative to the active components, which is discussed in terms of the heat capacity. The data sensitivity factor is also suggested as a reliable measure of thermal runaway evaluation of LIB cells.