In this research the impact of combined mechanical loads on lithium-ion 18650 cells is examined. During regular operation lithium-ion cells are exposed to mechanical loads such as vibrations. A recently published research investigating the failure mechanisms of lithium-ion cells that can be caused by vibrations show, that 18650 cells are very stable against vibrational loads . Another mechanical load that can possibly affect lithium-ion cells are shocks that can be caused e.g. by an accident with an electric vehicle or the drop of a power tool. A variety of publications investigate the failure mechanisms caused by such events [2-4]. In the present work we want to investigate if vibrational loads can cause detectable damage in 18650 lithium-ion cells when these cells are exposed to shocks prior to the vibration. A scenario where this could happen in a real application, is e.g. a power tool dropped from a scaffolding (shock event) and then going back to normal operation (vibrational loading). We investigated five different cell types in the present study. The potential risk of an inner mandrel has been reported in . Therefore, we chose cells with and without mandrels for our experiments. Prior to the shocks, performance parameters are measured for every cell in a predefined checkup routine and computer tomography (CT) images of the cells are taken. After the characterization the cells are exposed to a predefined number of shocks applied by a drop in a special experimental setup designed for such drop tests. Between the drops and the vibrational loads another checkup is performed. Then sinusoidal vibrational loads are applied to the cells on an electro mechanical shaker. During the vibration the cells are monitored with electrochemical impedance spectroscopy (EIS). The vibrational loads are applied until a change in the EIS spectrum can be observed or until a certain test duration is exceeded. After vibration another checkup is performed, if the cell is still able to be operated safely. CT images are also taken to investigate changes in the cells internal structure. The research reveals potential safety issues that are prone to combined mechanical loads as they can occur in real applications. Pretests show that a possible failure mechanism is damaging or breaking of internal current collectors.
 P. Berg, M. Tillinger, A. Jossen, The Impact of Automotive Random Vibrations on 18650 Lithium-Ion Cells, Kraftwerk Batterie 2019, Aachen, Germany, 2019
 G. Kermani, E. Sahraei, Review: characterization and modeling of the mechanical properties of lithium-ion batteries, Energies 10 (2017) 1730
 L. Greve, C. Fehrenbach, Mechanical testing and macro-mechanical finite element simulation of the deformation, fracture, and short circuit initiation of cylindrical Lithium ion battery cells, J. Power Sources 214 (2012) 377–385
 X. Zhang, T. Wierzbicki, Characterization of plasticity and fracture of shell casing of lithium-ion cylindrical battery, J. Power Sources 280 (2015) 47–56