Impedance Spectroscopic Characterization of Polymer Lithium-ion Battery at Elevated Temperatures in Accelerated Rate Calorimeter (ARC)

In this work, we present a set of thermal characterization experiments of charged prismatic polymer lithium-ion battery (PLB). Cells at different state of charge (SOC) were tested inside an accelerated rate calorimeter (ARC) to determine the onset-of-thermal runaway (OTR) temperatures, and the thermally activated components were followed by monitoring the impedance (at 1 kHz) and the open circuit voltage (OCV) as a function of temperatures. An increase in the impedance was observed at around 133°C corresponding to the polyethylene separator shutdown. Above 140°C, the OCV dropped to zero indicating an internal short-circuit due to the separator meltdown, suggesting that the pinholes created in the separator at meltdown were large enough to create an internal short circuit. In addition, electrochemical impedance spectroscopy (EIS) at some SOCs was performed in the frequency range of 10 kHz-0.1 Hz at various temperatures (25-130°C). Results were modeled using an appropriate equivalent circuit, and parameters that affected the battery behavior at high temperatures would be identified.