Analyzing the impact of electrical aging on the lithium-ion cell’s mechanical behavior and safety is an important factor to assess the crash safety of electric vehicles during their lifetime. In this study, fresh and electrical aged state-of-the-art NCM pouch cells were investigated. Aged cells, which were cycled electrically to 90% state of health, under laboratory conditions in electric vehicle battery modules were used. The used charging/discharging strategy represents real customer behavior based on accelerated driving profiles. First, it is shown that electrical aging has a significant influence on the anodes’ and separators’ mechanical properties, which had a lower mechanical strength and stiffness under tension. Additionally, quasi-static cylindrical indentation and three-point bending tests were performed to investigate aging effects on cell level at varying state of charge (SOC). Aged cells with 0% SOC showed a right-shifted force–displacement curve and a 29% lower maximum force compared to fresh cells. Fully charged, aged cells reached a similar maximum force to fresh cells, but faster temperature increase and higher temperature peaks after internal short circuit. Inductively coupled plasma optical emission spectrometry analyses confirmed an increased lithium content on the anode surface, which is indicated in literature as a reason for the increased exothermic reaction of the aged cells. The results indicate a higher safety risk for the aged investigated pouch cells under mechanical loads based on their changed mechanical properties and thermal runaway behavior.

The knowledge about the influence of electrical aging on the behavior of lithium-ion cells under mechanical loads is of high importance to ensure a safe use of batteries over the lifetime in electric vehicles. In order to describe the mechanical behavior in relation to electrical aging, fresh and electrically aged NCM pouch cells were investigated under different mechanical crash loads. For the first time, the aged cells’ behavior under quasistatic lateral loading was taken into account. Aged cells showed lower maximum forces compared to the fresh cells. The reason of the changed mechanical cell behavior was explained with the different buckling behavior of fresh and aged cells by experimental images. Furthermore, quasistatic and dynamic crash tests in cell’s thickness direction were performed at varying state of charge (SOC) and compared to the results of a previously published study. Independently of the testing velocity, the electrically aged cells failed at increased deformation values. This observation was justified by an increased cell thickness due to an additional softer layer, formed on the aged graphite particle surface, which was observed by the means of scanning electron microscopy. Furthermore, the aged cells showed lower failure forces of up to −11% under quasistatic and dynamic loads at 0% SOC. It was also illustrated that electrical aging causes a deeper voltage drop after cell failure, which suggests a higher energy release after the internal short circuit. The investigations show that electrical aging has a significant influence on the mechanical properties of lithium-ion cells and must be taken into account in the safety assessment.

Automotive high-voltage busbars are critical electrical components in electric vehicle battery systems as they connect individual battery modules and form the connection to the vehicle’s powertrain. Therefore, a vehicle crash can pose a significant risk to safety by compromising busbar insulation, leading to electrical short circuits inside the battery. In turn, these can trigger thermal chain reactions in the cell modules of the battery pack. In order to ensure a safe design in future applications of busbars, this study investigated the mechanical behavior of busbars and their insulation. Our results indicated that crashlike compressive and bending loads lead to complex stress states resulting in failure of busbar insulation. To estimate the safety of busbars in the early development process using finite element simulations, suitable material models were evaluated. Failure of the insulation was included in the simulation using an optimized generalized incremental stress state dependent model (GISSMO). It was shown that sophisticated polymer models do not significantly improve the simulation quality. Finally, on the basis of the experimental and numerical results, we outline some putative approaches for increasing the safety of high-voltage busbars in electric vehicles, such as choosing the insulating layer material according to the range of expected mechanical loads.