Structural dynamics of lithium-ion cells—part II: Investigation of large-format prismatic cells and method evaluation

A recently introduced test bench for experimental modal analysis of lithium-ion cells is used to investigate the structural dynamics of large-format prismatic cells for battery electric vehicles. To our knowledge, it is the first experimental investigation of the structural dynamics of a single lithium-ion prismatic cell in literature. Significant differences in the sensitivity of the natural frequencies on the state of charge (SOC), compared with previous pouch cell investigations, can be observed, likely due to different boundary conditions through the cell casing. The natural frequencies follow the staged characteristic of anode swelling due to lithium-intercalation with an hysteresis behavior. Linear characteristic is seen in the temperature sensitivity, which is known from thermal swelling of the separator. Mode shape analysis indicates displacement of the jelly roll inside the new cells due to an initially present gap, while aged cells show significantly changed dynamics. Mode shapes and SOC sensitivity indicate a potentially stressful situation for the jelly rolls in the case of vibrational load, especially for new and unconstrained cells. The obtained natural frequencies and mode shapes can be used to design vibrational abuse experiments for maximum stress, so as to better understand if vibration can be harmful to lifetime and safety.