INFLUENCE OF STATE OF CHARGE AND STATE OF HEALTH ON THE VIBRATIONAL BEHAVIOR OF LITHIUM-ION CELL PACKS

Electric mobility is one of the most important fields of development for automotive manufacturers to reduce fuel consumption and meet legislative requirements. As a result, specialists in the field of structural durability deal intensively with the effect of electric processes on the strength and durability of components like high voltage battery systems. Some literature sources refer to the influence of these effects on structural integrity while refraining from providing a detailed explanation. This paper investigates the effect of state of charge and state of health of lithium-ion cells on the vibrational characteristics of cell packs in high voltage battery systems. Previous studies have shown that cycling of cells causes volumetric expansion of lithium-ion cells, which leads to static loads being applied to the surrounding framework. If the volumetric expansion produces changes in vibrational behavior, a subsequent change in the loads applied to the surrounding frame, the mounting points, as well as to the adjacent components, is expected. To determine any possible changes in vibrational behavior, experimental modal analysis was performed on 14 cell packs at two different states of charge and various states of health. For this, the cell packs were suspended unrestrained and excited by an electrodynamic shaker from 30 Hz to 2000 Hz with a sine sweep. The results of the experimental modal analysis, which focused on the first two natural bending frequencies, revealed significant statistical spread. Due to the deviations in the results, no quantifiable influence of state of charge and state of health on the vibrational characteristics of the examined cell packs could be detected. The vibrational behavior of the cell packs appears to be more influenced by structural variations in the individual cells due to manufacturing tolerances and variations in the manufacturing process of the cell packs than by their state of charge or state of health.