To increase the storage capacity of automotive cells manufactures are currently developing anodes based on silicon as active material. While silicon is promising due to its high specific capacity, it shows a strong volume change depending on state-of-charge. This not only deteriorates the cell’s lifetime but also leads to macroscopic cell expansion.
We develop an approach to perform coupled, three-dimensional electrochemical-mechanical computer simulations for silicon-based lithium-ion battery cells by accounting for the multiscale nature of the problem: To reduce mechanical stresses upon silicon expansion sub-micrometer-sized silicon particles are often embedded in a matrix particle. So we first determine the effective mechanical, state-of-charge dependent properties of this secondary particle using a large strain mechanical model. In a similar way we determine the effective electrode properties based on three-dimensional microstructure information (determined eg. by FIB-SEM or tomography imaging). The mechanical computations are performed with ITWM’s software tool ‘FeelMath’.
In a second step we employ our Battery and Electrochemistry Simulation Tool ‘BEST’ to conduct dynamic electrochemical (dis)charging simulations within the 3d microstructure to investigate the cell’s electrochemical performance. Furthermore, by directly coupling BEST with FeelMath we not only get transient information about the global cell properties, the distribution of lithium concentrations or local stress fields, but also about the evolution of structural changes in the expanding electrode. Furthermore, the resulting stress fields will serve as basis for mechanical degradation modeling.
This work received funding through the project DEFACTO (defacto-project.eu) from the European Union’s Horizon 2020 Programme (Grant Agreement No. 875247).