Analysis of Deformations in Crush Tests of Lithium Ion Battery Cells

Abstract

Several mechanical tests have been conceived, especially by car manufacturers and related institutions, to assess the hazard level and the general behavior of batteries under severe abuse conditions. No experiments have been reported in the literature for investigating the detailed mechanisms of internal cell deformation and configuration leading to internal shorts due to lateral mechanical deformation. This work aims at determining the maximum deformation inside a lithium-ion battery cell before the onset of the short circuit. Hence, static crushing tests were carried out by means of a hydraulic test machine on pouch type li-ion cell. A semi-spherical punch was used on whole healthy samples, for which it was possible to measure the voltage in real time during the test; a semi-cylindrical punch was used on previously sectioned batteries, for which it was possible to observe the deformations suffered by the various layers that alternate inside the battery. The optical setup used is based on a telecentric lens with in-line illumination and 6X magnification, which permits to reduce the field of view to 1.2 × 1.5 mm. The system has allowed, even with difficulties related to large displacements and loss of focus, to apply the Digital Image Correlation technique to identify the deformation field inside the battery cell. Large local strains were detected, which are responsible of metallic and polymeric layers failure and determine the short circuit.