Crash Safety of Lithium-Ion Batteries Towards Development of a Computational Model

Battery packs for Hybrids, Plug-in Hybrids, and Electric Vehicles are assembled from a system of modules (sheets) with a tight sheet metal casing around them. Each module consists of an array of individual cells which vary in the composition of electrodes and separator from one manufacturer to another. In this paper a general procedure is outlined on the development of a constitutive and computational model of a cylindrical cell. Particular emphasis is placed on correct prediction of initiation and propagation of a tearing fracture of the steel can. The computational model correctly predicts rupture of the steel can which could release aggressive chemicals, fumes, or spread the ignited fire to the neighboring cells. The initiation site of skin fracture depends on many factors such as the ductility of the casing material, constitutive behavior of the system of electrodes, and type of loading. In the second part of the paper, a localized impact response of the entire battery pack is studied numerically from the point of view of predicting initiation and propagation of cracks in the steel casing. It was found that the weakest point occurs in the bolted connections between various parts of the casing. The calculations also revealed that failure of the joints occurred progressively and started quite early during simulation of the drop test.