Simulation of the water mass transport in electrodes during post-drying and moisture management of Li-ion battery production via the Two-Scale-Model

The moisture content of the material inside a lithium-ion battery (LiB) cell is a critical parameter for safety and performance of LiBs. Post-drying or final drying prior to filling the cell with electrolyte reduces the water content within the cell to an appropriate level, while moisture management aims to control the water content along the production chain. In both cases, the sorption of water in the composite structure of the porous electrode is the physical phenomenon that must be understood to design and adjust process parameters for post-drying and moisture management. It is our hypothesis that this sorption of water in the electrode can be simulated with a phenomenological mass transport model on two scales. Therefore, we introduce the Two-Scale-Model which couples the mass transport on micro scale (e.g., the polymeric binder phase of the electrode) and macro scale (e.g., the gas phase inside the electrode). Experimentally, a magnetic suspension balance refitted to measure vacuum drying curves with a customized sample holder provides validation data. The results of the Two-Scale-Model show that the mass transport on micro and macro scale can be characterized by the diffusion times of micro and macro scale. The Two-Scale-Model is theoretically validated by comparing its boundary cases with one-dimensional mass-transport models and experimentally validated by comparing the simulation results to experimental data. It is successfully applied to desorption of water from a LiB anode, which shows that the differentiation between micro- and macro-scale sorption is a feasible approach to describe the water mass transport in a LiB anode.