Numerically Characterizing Nail Penetration Testing for Safety Evaluation of Li-Ion Cells

Multi-physics modeling was performed for better understanding the nature of nail penetration testing. Nail penetration test is a mechanical abuse technique used to evaluate battery safety performance by inducing battery internal short circuits (ISC).  With specified battery chemistries and form factors, it has shown nail penetration results are affected by a number of test parameters, including battery sizes, short resistances caused by mechanical failure, nail penetration locations, speeds, depths, nail materials and diameters etc.  Due to the lack of sufficient understanding of relationships between testing parameters and outcomes, nail penetration test could give inconsistent results and is not able to provide desired reliability.

3D multi-physics modeling of nail penetration process was carried out to quantify testing parameter influence.  This objective is not feasible to be achieved by testing approaches, not only since nail penetration is a high dynamic process involving multi-physical behaviors, but measurement data is insufficient.  The model applied in this study is able to estimate battery dynamic responses under nail penetration tests by integrating a series of physical-based sub-models. The initial consequence of nail punch damage, short circuits, was addressed as an input variable.

Utilizing this model, outcome difference between a nail penetration test and a real ISC case scenario was identified. Simultaneous battery behaviors along nail movement in the battery were captured.  Parameter studies were conducted to quantify the effect of selected testing parameters, e.g. nail penetration speeds, depths and locations. The numerical results provide in-depth insights for understanding the nature of nail penetration testing and improve safety testing reliabilities.