Strain rate dependent plasticity of lithium-ion pouch cells: Experiments and simulations

The safety of electric vehicles under crash event depends on the mechanical behavior of Lithium-ion cells under large deformation at high strain rates. Here, an extensive experimental campaign is performed on large-format pouch cells under out-of-plane indentation with two indenter shapes and speeds ranging from a few millimeters per minute up to ten meters per seconds, spanning six decades of strain rates. It reveals that the displacement at the onset of short circuit decreases with increasing strain rates, while a non-monotonic relationship is observed between the strain rate and the maximum force as well as the macroscopic cell tangent stiffness. Based on the experimental results, a phenomenological constitutive model is proposed making use of a Deshpande-Fleck yield locus and strain-rate dependent hardening. An internal variable is introduced to capture the softening at intermediate strain rates. The calibrated model is able to accurately reproduce the experimental data and is further validated on a hemispherical indentation performed at two meters per seconds.