The battery breathing effect and its influence on adhesive layers in structural battery packs

In this work, two approaches to measure the deformation of a prismatic nickel-manganese-cobalt-battery (NMC) cell due to the battery-breathing-effect during charging is presented. One approach uses an optical system and the second approach uses a test rig with an external load on the cell. The measured deformations are then passed into a numerical model of the battery cell, which is integrated into the battery pack via adhesive bondlines. A structural methyl-methacrylate-adhesive (MMA) is characterized using ARCAN-specimens under different loading angles. From the tests, a Drucker-Prager equivalent stress is deduced which is used to calculate the stress distributions inside the structural adhesive layer on a bonded battery cell. The calculated equivalent stresses are compared to fatigue test data of butt-bonded cylinder specimens to predict the lifetime of the structural adhesive bondline of the battery cell. With the presented methods, the large influence of the battery breathing effect on the lifetime of structural adhesive cell bonds can be shown.