Investigating the internal short-circuit in 18650 cells under thermal abuse conditions

The occurrence of an Internal Short-Circuit (ISC) in 18650 lithium-ion cells under thermal abuse conditions remains elusive. Equipped with Current Interrupt Devices (CID), the cell's voltage drop may introduce ambiguity, and potentially obscure the precise determination of an ISC. Therefore, comprehensive investigations were undertaken to rigorously explore the ISC and thermal runaway (TR) relationship. In this paper, and for the first time, a three-electrode 18650 lab-scale cell is tested in an Accelerated Rate Calorimeter (ARC) to analyze the potentials' variation under adiabatic conditions. Results have shown that the cell's voltage drop coincides with the positive potential drop (Ewe). Furthermore, tests on cells without CID have indicated that the accelerated TR is triggered following the massive ISC. Moreover, for a long time, the ISC has been associated with the melting of the separator. Hence, this study includes tests on identical lab-scale cells utilizing three types of separators: polyethylene, trilayer, and coated polypropylene. TR tests, conducted under adiabatic and ambient conditions, didn't reveal a significant impact of the separators. Given that the novel preliminary test developed in this study has demonstrated that the loss of their mechanical integrity happens at around the same temperature, the outcomes of the TR tests were comparable.