Failure in lithium-ion batteries under transverse indentation loading

Deformation and failure of constrained cells and modules in the battery pack under transverse loading is one of the most common conditions in batteries subjected to mechanical impacts. A combined experimental, numerical and analytical approach was undertaken to reveal the underlying mechanism and develop a new cell failure model. When large format pouch cells were subjected to local indentation all the way to failure, the post-mortem examination of the failure zones beneath the punches indicates a consistent slant fracture surface angle to the battery plane. This type of behavior can be described by the critical fracture plane theory in which fracture is caused by the shear stress modified by the normal stress. The Mohr-Coulomb fracture criterion is then postulated and it is shown how the two material constants can be determined from just one indentation test. The orientation of the fracture plane is invariant with respect to the type of loading and can be considered as a property of the cell stack. In addition, closed-form solutions are derived for the load-displacement relation for both plane-strain and axisymmetric cases. The results are in good agreement with the numerical simulation of the homogenized model and experimentally measured responses.