Analysis of internal cell temperature variations under different abuse test conditions using embedded temperature sensors

In this study, the internal temperature of commercially available 21,700-format cylindrical lithium-ion cells is in-situ monitored during three different abuse test conditions. Three typical abuse conditions, namely, nail penetration, over-temperature, and overcharge, were adopted to trigger the cells to thermal runaway. In the nail penetration and over-temperature tests, where the cells underwent thermal runaway, the peak difference between the cell core and surface temperature reached up to 186.6 °C and 331.8 °C respectively. Temperature differences up to 36.7 °C were observed in the overcharge tests, where the cell's internal protection devices prevented thermal runaway. After the abuse tests, post-mortem X-ray CT scans were used to investigate the cell structural integrity, including sidewall ruptures, active material ejection and jelly roll deformation. This study highlights that the core temperatures measured by embedded sensors are significantly higher than the cell surface during thermal runaway. In addition, the core-surface temperature difference is dependent on the triggering mechanisms and propagation of thermal runaway.