Battery Safety
Thursday, November 9, 2023
3:15 PM - 3:45 PM
Li-ion Battery Safety: Effect of Aging Temperature

Compared to many other characteristics of Li-ion batteries, the safety behavior is a critical property that cannot be compromised. However, the safety behavior can change drastically depending on the previous aging conditions such as ambient temperature. In particular, cells aged at low temperature show a drastically reduced safety behavior due to Li plating [1,2]. Cells aged at higher temperatures with a pronounced solid-electrolyte-interface (SEI) layer on the anode show an increased onset of self-heating leading to improved safety [2,3]. The temperature-dependent aging behavior of commercial Li-ion pouch and 21700 cells is evaluated using an Arrhenius plot. Post-Mortem analyses of aged cells from both branches of the V-shaped Arrhenius plot confirmed two dominant aging mechanisms: Li plating and SEI growth for the low and high temperature range, respectively. Heat-wait-seek (HWS) tests under quasi-adiabatic conditions in an accelerating rate calorimeter (ARC) are a well-known method to evaluate the safety behavior of Li-ion batteries and can reveal critical temperatures such as the onset of self-heating. HWS tests on cells aged at different temperatures to different states of health (SOH) show the trend that more pronounced aging increases or decreases the onset of self-heating depending on the dominating aging mechanism. Typically, Li-ion battery safety increases with decreasing state of charge (SOC). This behavior is maintained for cells aged at higher temperatures, while cells aged at lower temperatures show the drastically reduced safety regardless of their SOC. In addition to the temperature measurement, several sensors for voltage, resistance, strain, and ultrasonic transmission and reflection were placed on the pouch cell to better understand the ongoing processes during the HWS tests. Furthermore, an externally coupled mass spectrometer provides information on the gases produced [2,4]. These HWS tests on commercial pouch and 21700 Li-ion cells aged at different temperatures in combination with the multi sensor study provide a comprehensive understanding of the influence of cell state, i.e. aging temperature, SOH, and SOC, on the safety behavior.

Max Feinauer
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