Deformation and failure of lithium-ion batteries treated as a discrete layered structure

Safety of lithium-ion batteries under mechanical loadings is currently one of the most challenging and urgent issues facing in the Electric Vehicle (EV) industry. The architecture of all types of large-format automotive batteries is an assembly of alternating layers of anode, separator, and cathode. The anode is composed of a very thin copper foil double-side coated with graphite powders, while the cathode is an aluminum foil with the active material coating. Each of the five components may develop a large plastic deformation until fracture. This study focuses on the effect of the properties of the coated materials on the local and global responses of a battery cell. Both anode and cathode coatings are described by the Drucker-Prager/Cap plasticity model, which is carefully calibrated through axial and lateral compression tests and closed-die compaction test. A separate experimental effort is put on finding the strength of the interface between the foils and the granular materials with a binder. The main new finding is that in the cases of plane-strain and axisymmetric loadings, the failure of cells proceeds in two stages. First, the shear bands localize along discrete lines. Then, fracture develops inside the shear bands due to large local strain gradient. The present model is applied to study the deformation and strength of large-format pouch cells subjected to local indentations by rigid punches. The prediction of the present model follows closely the measured load-displacement curve and captures with good accuracy the magnitude of the peak load and the corresponding critical displacement. In addition, an excellent correlation is achieved between the calculated profile of the through-thickness crack and the result of the micro CT scan. The present detailed computational model should be useful in the battery design process and will serve as an important new computational tool for assessing the safety of lithium-ion batteries against mechanical loading.