Effects of notch geometry on bursting fracture of a V-notched rectangular cup for Li-Ion secondary batteries

Abstract

A V-notched rectangular cup produced by a multi-stage deep drawing process is presented as a primary safety structure of the lithium-ion (Li-Ion) secondary batteries. The V-notched rectangular cup is required to sustain an inner pressure resulting from the elevated temperature induced by the chemical reaction of the electrolyte during normal operation, and it has to fail when the inner pressure reaches a critical pressure. The inner pressure below approximately 0.500 MPa is considered to be safe, and the battery that reaches the pressure above the critical limit must leak the excess inner pressure, without any explosion. In this study, a V-notched structure on the outer surface of a rectangular cup is proposed as the primary safety device. Predictions with respect to the bursting fracture pressure are presented, where geometric parameters such as the notch angle and depth are considered. The bursting behavior is predicted by adopting an implicit elasto-plastic finite element scheme combined with Cockcroft and Latham’s ductile fracture criterion. The predicted bursting fracture pressure is compared to the results from experimental investigations. It is confirmed that the bursting pressure of the V-notched rectangular cup is well matched with the variation of 5.88% between the predicted and experimentally measured results.