(Invited) Changes in Thermal Stability of Cyclic Aged Commercial Lithium-Ion Cells
Authors: Lian Torleif , Vie Preben J. S. , Gilljam Martin , Forseth Sissel 
Published: February 2020

It is well-known that lithium-ion cells can have safety issues. A large number of battery fire incidents have been reported. Of the more famous ones are fires in the APU battery of Boeing Dreamliner [1], fires in the Chevrolet Volt battery [2] and the Samsung Galaxy Note 7 recall (2016).
Thermal stability is one of several factors affecting the safety aspects of lithium ion cells. The thermal stability for uncycled cell materials and cells is well-documented, but the effect of cyclic ageing on thermal stability is far less studied [3-6] and only in 18650 sized cells.
In this presentation, we describe a systematic approach on how different temperature and current loads are affecting the thermal stability during cyclic aging of three different sized commercial cylindrical lithium-ion power cells. The cells were heated in an Accelerating Rate Calorimeter (ARC) with a heat-wait-seek procedure and temperature steps of 5 °C. Decrease in thermal stability was found in all three cyclic ageing test series as a function of relative high current and low temperature (5 °C) even though the cells were tested within the limits specified by the cell manufacturers. The decrease in thermal stability was minor for one of the test series but rather large and potentially dangerous for the other two test series. As a result, one of the cells with decreased thermal stability experienced severe disintegration of the cell can during the ARC test. A picture of the disintegrated cell that was cycled at 5 °C and 1C/1C condition is presented in Figure 1.
New and potentially dangerous safety related alterations have been found in cyclic aged lithium-ion batteries. The decrease in thermal stability could be dangerous and should be an end of life criteria. An uncycled cell in a battery module may withstand the heat from a neighboring thermal runaway cell, while a cycled cell may be driven into thermal runaway. It is of vital importance to develop new diagnostic tools capable of detecting a dangerous drop in thermal stability in cyclic aged lithium-ion cells.

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Friesen, A., et al., Al2O3 coating on anode surface in lithium ion batteries: Impact on low temperature cycling and safety behavior. Journal of Power Sources, 2017. 363: p. 70-77

Figure 1