Mechanical Anisotropy and Strain-Rate Dependency of a Large Format Lithium-Ion Battery Cell: Experiments and Simulations 2021-01-0755

In order to get a better understanding of the mechanical behavior of lithium-ion battery cells, especially for the mechanical anisotropy and dynamic effect, a series of tests for quasi-static indentation and dynamic impact tests has been designed. In the study, mechanical indentation tests with different indentation heads, different loading directions and different impact speeds were performed on a type of large format prismatic lithium-ion battery cells and jellyrolls of them. To mitigate thermal runaway, only fully-discharged cells and jellyrolls were used. The force-displacement response and open circuit voltage (OCV) were recorded and compared. It shows that jellyroll and battery cell have apparent mechanical anisotropy and strain-rate effect. The stiffness of jellyroll and cell in out-of-plane direction is much larger than that in two in-plane directions. Apparent strain-rate effect can also be observed in out-of-plane direction while the reaction force changes little in in-plane-direction indentation tests with different loading speeds. Furthermore, finite element models of jellyroll and battery cell were developed with LS-DYNA. A homogenized anisotropic material model is used to simulate the mechanical behavior of jellyroll. Mechanical anisotropy, strain-rate effect and failure criteria of the jellyroll material were considered in the model. Test results of jellyrolls were used for calibration and test results of battery cells were used for validation. The models could predict the load displacement relation and failure displacement in most loading cases. This study provides us a deeper understanding about the mechanical anisotropy and strain-rate effect of LIBs and a good guidance for numerical modelling and simulation.