Impact Testing of Cylindrical Battery Cells for Automotive Applications

The electrification of automobiles has forced auto makers to consider the effects of a vehicle crash on the large-format batteries carried onboard. Forces experienced during crash events can be severe and localized causing damage to the internal structures such as bus bars and individual battery cells. To ensure safety during crash events, it is important to understand the mechanical limitations of the battery cells, and design the battery pack accordingly, to avoid thermal runaway failure.

Analyzing the cell’s response to acute impact damage in different locations required the development of a custom test fixture to deliver well-defined mechanical impacts. The fixture developed guided an indenter to impact a precise cell location on a rigid baseplate. The indenter position, acceleration, and baseplate load were recorded throughout the drop. Data collected during testing was used to develop high-fidelity force-displacement curves, analyze plastic vs elastic deformation of the cell, and assess the cell’s mechanical limitations before failure.

Varying the impact location and energy over five unique cell locations revealed susceptible locations in the cell’s construction that resulted in thermal runaway at lower energies. Impacts along the radius of the cell, near the top and bottom edges of the cell, can result in thermal runaway with less than one fifth of the impact energy than the cell was able to withstand at the center along the radius. Similarly, impacts on the positive end cap resulted in thermal runaway with half the amount of energy absorbed by the negative end cap before thermal runaway occurred. The test results provided here are exemplary of those needed to guide crash safety design considerations when constructing a large-format battery pack for electric vehicles.