Effects of High Acceleration Mechanical Shocks on 94 Ah Large Format Lithium-Ion Battery Cells

Summary:

In regular operation and especially in the case of crashes, lithium-ion batteries have to withstand severe mechanical shock loads. To ensure their safety, they are tested according to various norms and regulations with procedures depending on the country of usage, the field of the application and the mass of the cell.
As there are only little pieces of literature available regarding the effects of mechanical shocks on cylindrical cells, but almost none for large format prismatic cells, a shock test series was conducted on prismatic cells with a nominal capacity of 94 Ah at 0 % SOC with a pneumatic shock test machine AVEX SM-110 by Benchmark Electronics Inc. As many standards do not exceed peak accelerations of 51 g for cells of this size and due to the expectation that the cells exhibit no damaging when undergoing typical standard test, as they were designed to withstand them, more severe shocks with 6 ms pulse width and 300 g peak acceleration were repeatedly conducted on different cells in various orientations. To gain an understanding of the electrical effects of the shocks during the tests, electrochemical impedance spectroscopy (EIS) was performed with a Gamry Interface 5000 P.
The results show visible jelly roll displacement and deformation for susceptible orientations up until the test had to be aborted due to safety concerns, but no signs of a thermal reaction. After 6 months of storage, no drop in voltage, which would indicate an internal short circuit, was observed. The impedance measurements showed small changes for low frequencies. High frequencies showed strong shifts but are also extremely cable dependent so observed changes could not unequivocally be attributed to the shocks. The results indicate a high safety level against shocks for this cell type.