Fraunhofer Institute for Solar Energy Systems ISE
In addition to electrode production and cell finalization, our research focus is on cell assembly, which plays a key role in battery cell production. This involves going through various processes to produce a finished battery cell from the individual materials (electrodes, separator, housing, current collector tabs and electrolyte). In addition to the materials used, the manufacturing processes, their precision and process atmospheric conditions have a significant influence on the performance of the battery cells, such as ageing, safety and energy density.
In our pilot line for battery cell production, the materials pass through seven stations from start to finish. Electrodes are first separated from electrode tracks or individual electrodes by means of punching. The separated electrodes and separator material (available as a web or individual sheets) are then assembled into a cell stack either in a continuous Z-folding process or by means of individual sheet stacks. The positional accuracy is maintained by automatic placement in a cell stack holder. The current collector tabs are then connected to the current collectors of the electrodes using ultrasonic welding. In the next step, the composite films, which serve as the housing material, are cut to size and deep-drawn in a subsequent step to create the half-shells for the cell stack. Once the cell stack has been inserted, the housing is sealed on three sides using a heat-sealing process. The cell stack is then filled with electrolyte in a vacuum chamber and sealed under a specific absolute pressure using impulse sealing. The gas produced during the forming process of the battery cell can also be drained in the vacuum chamber. A new battery cell has been created.
With our pilot line and our infrastructure, we cover these technical requirements for cell assembly:
- Optimum setting of system and process parameters depending on the materials used
- High production accuracy, especially during stack formation
- Low particle load in the atmosphere (clean room class ISO 7)
- Dry atmosphere (up to -55 °C dew point)
