Electrolyte filling and formation of Li-ion cells


© Fraunhofer IKTS
Overview of the results obtained in the Optilyt project on electrolyte penetration.
© Fraunhofer IKTS
Investigation of electrolyte filling at lab scale.

When it comes to industrial cell production, the filling and formation of Li-ion battery cells are two very time-consuming and cost-intensive process steps. Depending on the respective electrode design, cell format, separator and electrode additives, the wetting and formation times for the cell vary significantly. These cell-specific properties and processes are usually not very well scientifically understood. At the same time, knowledge about these processes taking place inside the cell is essential for optimizing the production process with regard to cost and cell quality.

The "Cell Design and Testing" working group has established analytical methods for characterizing this filling behavior, validated previously with partners for industrial cell formats and materials. These methods make it possible to monitor the wetting process in order to describe the permeation behavior of separators, electrodes and combinations of separators and electrodes with electrolytes in a systematic and quantitative way. For instance, the analysis of different separators in pouch cells has shown that ceramic materials, when compared with polyolefins, have a shorter wetting time and wet larger cell surfaces faster (see adjacent illustration).

The process of formation is being investigated in several funding projects. In connection with the institute’s own electrode production at pilot scale, the researchers identify the effects of electrode properties and process parameters of the formation on the long-term aging of a Li-ion cell. In this regard, cycle tests on lab cells have shown that the intercalation and SEI formation processes may run much faster, without negative implications for the quality of the cell.


Services offered


  • Analysis and optimization of electrolyte filling in the electrode-separator bond
  • Assessment of formation processes using DC measuring methods and electrochemical impedance spectroscopy with 3-electrode structure
  • Complementary material analyses (mercury porosimetry, REM in FIB cut, BET surface area, roughness analyses etc.)