Coupled-Physics Modeling of a Lithium-Ion Battery Cylindrical Cell Microstructure

Safety of consumer vehicles is an extremely important consideration for the automotive industry. An emerging market in the automotive industry today is the electric and hybrid-electric vehicle market. As environmental concerns grow, such vehicles will become a necessity for manufacturers to remain within increasingly stringent emissions regulations. A recent problem with the high-voltage lithium-ion batteries used in many of these vehicles is that of thermal runaway following a severe collision. This paper represents our early attempt to look at one aspect of this extensive project — a coupled-physics model of battery cell microstructure. In this case, couple-physics refers only to thermal-structural coupling and the microstructure being studied here is the laminate-level structure. A 2-D finite element model of a lithium-ion cell was therefore developed. This 2-D model of the cell, also called a jellyroll, is a cross-section cut of one cell within a battery pack. Each battery cell is an assembly of alternating thin sheets of functional materials (anode, separator and cathode), which are rolled into a cylindrical shape. The cross-section then takes the form of a layered spiral. The typical cell is made of an aluminum cathode with coating, copper anode with coating, and a non-linear, viscoelastic polymer separator. Once the 2-D jellyroll FE model was created, some initial structural element simulations were run to validate the geometry setup and model integrity. Next, thermal-structural coupled-field simulations were run to investigate stress propagation resulting from thermal loads as well as the same loading cases performed with the structural-only model. Different loading conditions, including uniaxial stress-strain state, hydrostatic pressure test, and thermo-mechanical loading were simulated. The results from the simulations performed in the project set the groundwork of future models involving electrical properties and models of 3-D cells and the full battery pack.