µKoBatt – μ-friction stir welding for cell-internal contacting of large-format lithium-ion cells

The aim of the BMBF-funded research project "µKoBatt" is to enable micro friction stir spot welding (µFSSW) as a process for cell-internal contacting of lithium-ion battery cells in a battery production environment. The focus here is on the design and manufacture of a pilot system for µFSSW for the battery production environment and the integration of µFSSW in battery production by developing suitable methods for process monitoring and quality assurance. With µFSSW it will be possible to increase the maximum number of foils that can be welded, thereby increasing the performance of the batteries.

Motivation

The increasing demand for high-performance electrical storage systems presents manufacturers of lithium-ion battery cells with the challenge of being able to produce energy-dense, large-format cells in a short time and in large quantities. The limitations in lithium-ion battery design freedom and long production times are defined by the manufacturing processes used in the battery production process chain.

One key point in production is cell-internal contacting, as over 80% of the total production costs have already been incurred up to this point. The industrially established joining processes for cell-internal contacting (ultrasonic and laser beam welding) are reaching their technical limits in terms of the number of electrode foils that can be welded simultaneously, which means that the reliable and efficient production of large-format battery cells is currently only possible to a limited extent. Welding foil stacks with many layers either requires longer welding times or results in defective connections, which can affect the quality of the cell.

Preliminary work has shown that even 100-layer foil stacks made of pure aluminum and copper can be welded with arresters using micro friction spot welding (μFSSW). However, the investigations were carried out on substitute geometries with uncoated foils and in a conventional welding machine that is not suitable for use in a battery production environment.

Research objective

The research project will build on the previously performed feasibility studies. The overall objective of the research project is to enable μFSSW for the cell-internal contacting of large-format cell bodies in a battery production environment. This includes not only tailoring the μFSSW process for cell-internal contacting, but also the overall integration of a new pilot welding system into the battery production environment. To this end, the cause-and-effect relationships within the process chain will be analyzed.  At the end of the project, it will be possible to carry out a welding process integrated into the battery process chain with process monitoring for the reliable production of novel large-format lithium-ion battery cells by μFSSW.

Approach

Use

As part of the research project, the existing knowledge of µFSSW for the cell-internal contacting of large-format battery cells will be expanded, enabling a TRL of 6 ("prototype in operational environment") to be achieved and transferred to industry.

In addition to the advantages of the μFSSW, such as high weld quality, operating safety, environmental friendliness, automation capability and low energy requirements, the process has the unique selling point of being able to join large stacks of film with minimal or no increase in process time. Overall, this enables the low-waste and cost-efficient production of energy-dense cells and thus a resourceful use of materials in production as well as efficient implementation in electrically powered vehicles. The high process robustness also allows greater production tolerances before welding, which enables more resilient production and independence from the foreign raw materials market.

The rapid manufacturability of innovative large-format cells as well as the diverse focus areas of the project consortium will improve the competitiveness of German companies.

Acknowledgement

The project is funded by the Federal Ministry of Education and Research (BMBF) as part of the program to increase efficiency and exploit synergy effects in battery cell production for electromobility (SynBatt) under the funding code 03XP0545 and is supervised by Project Management Jülich (PtJ). We would like to thank the BMBF and the PtJ for their cooperation.