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CFP2022-1018

Nowadays lithium ion batteries (LIB) became one of the key technologies for energy storage in different kind of applications because of their high energy density and their advanced stage of development. Therefore, LIB’s are not simply rated by their performance parameters but also by issues of safety. With respect to the interaction of electrical and chemical hazards as well as emergence of fire and explosions, the thermal runaway represents the main risk potential related to the extended use of LIB’s. For safety studies a thermal runaway can be provoked by different events which can be analyzed via temperature and voltage monitoring, as well as measurements of gaseous products and post mortem studies.
The safety assessment of Lithium Ion Batteries is examined using various standards before the battery is approved on the respective market. The requirements of the standards for the individual tests can be very different. Therefore, it is necessary to identify the crucial parameters to unify a particular test. In order to understand the crucial parameters of a crush test, this study presents the results of different punch diameters and punch speeds in a custom-made battery cell investigation chamber. This chamber allows the determination of parameters which influence the response of battery cells to internal short circuits. The response is analyzed via measurement of cell voltage, temperatures, as well as camera recording, and FTIR spectroscopy to identify and quantify infrared active gas species.
The similarities and differences of the various test procedures on the electrical, thermal and chemical response of the cells are explained and the changes in the mechanical behavior discussed. For the increase of the punch diameter there is a stronger initial voltage drop, a faster decrease of the measured cell surface temperature and a linear increase of the force as well as of the deformation required for the thermal runaway, while the battery cell exhibits a much stiffer behavior when the crush speed is increased. The influence on the reproducibility of the results is emphasized in order to develop a general proposal for more comparable and reliable tests. It is shown that due to the strong differences in the mechanical behavior of the cell, the prescribed standards should be adapted in order to be able to obtain more reproducible and comparable results.

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