Material Behavior Characterization of a Thin Film Polymer Used in Lithium-Ion Batteries

Abstract

The use of lithium-ion batteries in the automotive industry has become increasingly popular. As more hybrid and electric vehicles take to the road an understanding of how these batteries will behave structurally will be of greater concern. Impact testing can give a valuable overview of the strengths and weaknesses of a battery's design, however, these tests can be time consuming, expensive, and dangerous. Finite element analysis can deliver a reliable low cost approximation of physical testing results. The accuracy of FE results depends greatly on the mathematical representation of the material properties of Li-ion battery components. In this study, the material properties of thin film polymer used as a separator between an anode and a cathode of a lithium ion battery are tested experimentally under various temperatures, strain rates, and solvent saturations. Due to the anisotropy of the material, two similar sets of experiments were conducted on the material in perpendicular directions. It was found that temperature and strain rate have a nearly linear effect on the stress experienced by the material. Additionally, saturating the separator material in a common lithium ion solvent resulted in its softening with a positive effect on its toughness. Two viscoplastic constitutive equations developed for modeling polymeric materials were employed to model the experimental data.