Precision under inert gas
The development of solid-state batteries is regarded as one of the most promising approaches to energy storage for the future. For a research facility dedicated to materials development, IEF-Werner, in collaboration with MBRAUN, designed an automation solution for the assembly of battery cells: A robot-based single-sheet stacker positions anode, cathode and separator foils with high precision and reproducibility under inert gas conditions.
In battery research, electrode and separator foils are often still processed manually – with the individual sheets being stacked on top of one another using tools such as tweezers. This is time-consuming and prone to errors. However, reproducible quality is crucial, particularly when developing new cell concepts. “Our task was to automate the previous manual process for our client MBRAUN whilst ensuring the required high precision,” explains Sandro Schwer, project manager at IEF-Werner. The aim was to position the anode, cathode and separator precisely on top of one another, without any misalignment in position or angle.
High demands on stacking accuracy
The requirements for positioning accuracy are high: the individual layers must be aligned with an accuracy of ±0.1 millimetres and ±0.1 degrees relative to one another. Even the slightest deviations can mean that the resulting cell stack cannot be processed further.
This is particularly critical because the stacked cells are later sealed into aluminium foil during the rest of the process. Only precisely aligned layers can ensure a stable and functional cell structure. Furthermore, variations in thickness of just a few micrometres and differences in the size of the individual sheets complicate the stacking process.
In addition to pure positioning accuracy, process quality also plays a decisive role in electrode stacking: imprecise alignment of the anode, cathode and separator can impair cell performance, worsen current distribution or, in the worst case, cause internal short circuits. Reproducible and particle-free stacking is therefore essential for the efficiency, service life and safety of modern battery cells.
Robot-based single-sheet stacker
At the heart of the system is a robot-based handling system that automatically separates the foils and places them on a stacking table. The materials are supplied via magazines, which are manually loaded by operating staff. Depending on the cell design, these may contain, for example, several layers of anode, cathode and separator.
A specially developed gripper removes the individual sheets and positions them with precision. A multi-vacuum gripper is used for this purpose, which handles the sensitive materials gently. To prevent contamination and cross-contamination between anode and cathode materials, the different materials are processed using separate gripping tools. This reliably prevents the transfer of the finest particles between the individual layers. Depending on the application, Cartesian handling systems may be used as an alternative to the robot.
Integration into the glovebox
Integrating the system into a glovebox presented a particular challenge. Battery production requires specific process conditions, as many materials are sensitive to moisture, oxygen and other components of the air. All handling therefore takes place in an inert gas atmosphere, for example using argon or nitrogen. “Even small amounts of water or oxygen can trigger undesirable chemical reactions and impair the quality of the cell components,” explains Schwer.
In terms of design, this means that all components used must be suitable for operation in this environment. At the same time, a design that is as compact as possible is crucial. Unlike a conventional cleanroom, the glovebox or mini-environment approach encloses only the actual process area. This keeps the volume requiring cleaning very small, whilst ensuring consistently high-purity and stable process conditions within the system.
Compared with conventional cleanroom solutions, this approach leads to a significant reduction in energy consumption as well as in capital and operating costs. At the same time, research applications benefit from constant and reproducible conditions, as well as the safe handling of sensitive materials.
Flexible for different cell concepts
The system is designed as a pilot system and enables the implementation of various cell configurations. In this way, a range of stacking configurations and different formats can be processed. However, this must be carried out on a single-type basis within each process.
The solution therefore particularly supports the development and testing of new materials and cell architectures. The automated stacking ensures reproducible conditions and enhances the reliability of the test results.
Although the system is currently being used in a laboratory setting, the concept is already geared towards future scaling. The partial automation of the stacking process enables insights to be gained that can be applied to future production lines in both low- and high-volume settings. “The automated and precise assembly of cell stacks is a key prerequisite for ensuring that new battery technologies can be manufactured economically in the future,” explains the IEF project manager.
Significance for the future
The development of solid-state batteries is being driven forward intensively worldwide. This opens up a new field of application with great potential for automation specialists. “Being active in this field of technology right now is strategically important for us,” emphasises Schwer. “This allows us to build up expertise at an early stage and secure a further pillar for future concepts.”
