During an accident of an electric vehicle, the battery pack can be damaged by the intrusion of an external object, causing large mechanical deformation of its lithium-ion battery cells, which may result in an electrical short circuit and subsequently the possible thermal runaway, fire, and even explosion. In reality, the external objects can come in different directions, for example, an out-of-plane indentation that perpendicularly punches the large surface of the pouch cell and an in-plane loading that compresses the thin edge of the cell. In this study, the mechanical deformation of a large-format lithium-ion pouch cell under in-plane loads is investigated via three different types of tests — in-plane compression of fully constrained cells, in-plane compression of cells sandwiched by foams, and in-plane indentation by a round punch. A special apparatus is designed to apply different boundary conditions on the cell, and the deformation history, especially the formation of the buckles of the cells, are monitored by two digital cameras. Post-testing structural analysis is carried out by a cross-sectional cutting and polishing procedure, which gives clear evidence of buckling of all the component layers.
