Indentation of small format Lithium-ion pouch cells: Experiments and modeling

Abstract

Lithium-ion pouch cells are widely used in applications such as cell phones and electric vehicle battery packs. Here, a series of indentation experiments is performed on 4Ah pouch cells. The experimental program includes hemispherical indentation with six different indenter tip radii as well as indentation with cylindrical indenters with three rod diameters. Aside from varying the shape and size of the indenters, the location and direction of loading is varied including out-of-plane and in-plane loading of the rectangular-prismatic pouch cells. It is found that the force–displacement curves obtained for hemispherical indenters scale linearly with the indenter tip radius, while a scaling with the square root of the radius is observed for the experiments with cylindrical indenters. Finite element simulations are performed of all experiments using an enhanced Deshpande-Fleck plasticity model with two stage hardening. Despite the orthotropic nature of the jelly-stack, it is found that the simulations with an isotropic plasticity model provide reasonable predictions of the force–displacement curves for all experimental configurations. This surprising result is explained through the exceptionally high slenderness of the metallic current collector foils comprised in a pouch cell that respond through early buckling failure instead of contributing to the in-plane compressive load carrying capacity.