Thermal runaway of Li-ion battery with different aging histories

Safety issues associated with thermal runaway (TR) in batteries have attracted extensive research attention. However, understanding and predicting TR encounter significant challenges due to the complexities of chemical reactions, venting events, thermal stratification, multiphase interactions, and variable boundary conditions. These challenges are further complicated by intrinsic battery degradation, a phenomenon often insufficiently characterized and governed by multiple mechanisms. These primarily include the depletion of electrolyte and active materials, thickening of the solid-electrolyte-interphase (SEI), and formation of lithium plating and dendrites. Such degradation alters the battery's materials and structure, directly causing electrochemical performance penalties and potentially affecting its TR behavior. This study examines the TR behavior of commercial 18,650 cells with lithium nickel cobalt manganese oxide (NCM) cathodes, focusing on degradation associated typical usage scenarios: long-term cycling, low-temperature cycling, dynamic cycling with calendar aging. We employ Electrochemical Impedance Spectroscopy (EIS) to probe internal changes in the electrochemical properties of aged cells compared to fresh counterparts. The EIS results reveal pronounced SEI impedance and substantially increased charge transfer impedance in long-term cycled cells. TR tests were conducted using an Accelerating Rate Calorimeter (EV+ ARC, Thermal Hazard Technology) following the heat-wait-seek (HWS) strategy. Our findings indicate a significant impact of aging mechanisms on second-life battery safety. Specifically, cells subjected to low-temperature cycling demonstrated a considerably lower onset temperature for exothermic reactions, and shorter TR delay time, despite all aged cells showing similar state of health. Furthermore, the temperature corresponding to the cell voltage drop is consistently much lower for aged cells with dynamic cycling and calendar aging.