The increasing demand for electrochemical energy storage devices such as battery cells both for electromobility and stationary applications [1] poses a need for improving the energy density and performance of current lithium-ion cells. One strategy is to use silicon-based anodes. The main challenge of this material is still the increased volume expansion during lithiation, which becomes more prominent with increasing silicon content and limits the performance and lifetime of silicon-based cells [2].

The integration of a pure silicon anode into the cell is one aspect of the EU-funded project greenSPEED [3]. Besides the physical tests and optimisation efforts, also a simulation approach using the finite-element method is pursued. The simulations aim to investigate the evolution of mechanical stresses in the cell due to pressure application and anode expansion for different cell geometries. Mechanical stresses are difficult to measure in real cells, which is why simulations can be a useful tool to get insight into these quantities.

A requirement for such simulations is knowledge about the mechanical behaviour of cell components. This information was obtained by performing mechanical tests and using the data to parameterise and optimise material models for the different cell components. In these tests, effects such as material orthotropy, strain rate dependency, and the influence of electrolyte were considered. These component models were applied to the different finite element meshes representing the cell structures, on which the various simulations were run. Information about the expansion behaviour of the investigated cell chemistry was obtained by dilatometry measurements [4] on bi-layer pouch cells.

Among the investigated cell geometries are bi-layer and multi-layer pouch cells as well as cylindrical cells. While bi-layer pouch cells exist already early in the project and can be used for a verification of the simulation results, the transfer to multi-layer pouch cells and cylindrical cells is done by a virtual upscaling approach since these cells do not yet exist physically. The simulations are thus used for a virtual assessment of the stress evolution during charging as consequence of anode expansion for the different cell geometries. They also enable an investigation of certain cell design aspects such as the tab design, which, according to simulations, is a hotspot of mechanical stresses in the pouch cells.

In this conference contribution, tools, toolchain and recent results of this simulation approach are presented.

Sources:
[1] https://www.grandviewresearch.com/industry-analysis/battery-market
[2] https://doi.org/10.1016/j.ensm.2024.103243
[3] https://greenspeed-project.eu/
[3] https://doi.org/10.1016/j.jpowsour.2022.232042