Research and Demonstration Center for the Production of Large-Area Lithium-Ion Cells

Abstract

Electro mobility is a significant future trend justified by the efficiency as well as by the low emissions of electric drives compared to conventional internal combustion engines. One of the key issues to be solved in this context is the battery technology. In order to reduce battery costs advanced methods for the bulk production of lithium-ion cells need to be developed. Therefore, funded by the Federal Ministry of Education and Research (BMBF), the Institute of Machine Tools and Industrial Management (iwb) built up a demonstration center for the production of lithium-ion cells (DeLIZ). State of the art cell stacking technologies, such as flat winding, single sheet stacking and z-folding, have inherent drawbacks considering the final cell quality and the process yield. On the one hand, decollating and handling of nonrigid sheet type structures are complicate issues in the single sheet stacking process. On the other hand, the flat winding process affects the cell quality negatively by the applied process loads. Consequently, this paper evaluates different cell stacking methods taking into account aspects of automation and process quality. Furthermore, an innovative z-folding process is presented as a result of these investigations. Due to the increased stacking speed and the optimized separator handling, the developed z-folding process is supposed to show a higher operating efficiency than conventional stacking processes. Besides that, the cell production is improved by laser based tailoring of the electrodes, providing a more flexible cutting process which is free of tool wear and shows a reduced burr. Since each process step of the cell-assembly has a major impact on the quality of the finished lithium-ion cells, an overall quality management system is developed. After the identification of the important quality parameters, process latitudes can be defined. Furthermore, sensors for the measurement of these parameters can be selected and integrated into the demonstration center. The evaluation of the process data allows the optimization of the cell quality, the performance and safety as well as the energy efficiency and the process stability of the production system.