Herbert Diess, the former CEO of the Volkswagen Group, described the battery as the "heart of the electric car and the key to the future of mobility." This is also reflected in the price: According to the German Federal Ministry for Economic Affairs and Climate Action (BMWi), the battery accounts for up to 40 percent of the added value of an electric vehicle. No wonder, then, that 40 battery gigafactories are currently under construction or in planning in Europe alone.
Now, the industry needs to reduce the already significantly lower battery costs of just under 100 US dollars per kilowatt hour even further. Prof. Arnold Gillner, head of the Business Development department at Fraunhofer ILT, named two important tasks in January 2023 at the Laser Symposium Electromobility LSE'23: "In addition to reducing energy consumption in the production of batteries, it is important to increase their energy density through new materials in the long term."
In the ILT’s own Battery Lab, the Fraunhofer team has access to state-of-the-art technology and a wide range of equipment for laser-based battery production on an area of almost 140 square meters to research new materials and processes. There are electrical and mechanical test stands that allow users to directly evaluate the laser processes both of today's standard lithium-ion batteries with liquid electrolytes and future solid-state batteries.
The Battery Lab has an argon-powered glove box system that integrates vacuum-based PVD coating technology and a high-temperature furnace. This makes it possible to coat solid-state cell materials sensitive to air and then assemble them into test cells.
Drying with diode laser halves energy consumption
At the Hannover Messe in 2023, the Aachen researchers demonstrated how energy consumption can be drastically reduced when the graphite electrodes of lithium-ion batteries are dried. Until now, continuous ovens operated with gas have dried the copper foils coated with graphite paste at a temperature of 160 to 180 degrees Celsius in a roll-to-roll process. The researchers from Aachen are replacing this high-energy process with a system using a diode laser that heats the electrode over a large area using special optical system. Samuel Fink, group leader for thin-film processes at Fraunhofer ILT, says: "Drying with the diode laser reduces energy requirements by up to 50 percent and the space required for an industrial-scale drying system by at least 60 percent."
The researchers also have their sights set on energy density: In Hanover, the institute presented a high-power ultrashort pulse laser that splits the infrared pulsed laser beam into 24 partial beams to structure the battery electrodes. The multi-beam optical system was developed and implemented in close collaboration with Pulsar Photonics GmbH, a Fraunhofer ILT spin-off founded in 2013.
Channels are formed that act as ion highways, shortening the distance travelled by the ions and, thus, accelerating the charging process. This prevents defects from occurring, increases the number of charging cycles and extends the service life of the battery. The process is not new, but the Fraunhofer researchers have succeeded in transferring it from laboratory scale to a scalable, industry-ready process. "In the next step, we will scale the technology from the prototype to an industrial production line," explains Matthias Trenn, team leader Surface Structuring at Fraunhofer ILT.
Inspirations from the Arctic
Using lasers to weld batteries is a central aspect of industrial battery production and, thus, also for the Aachen researchers. The spectrum of their projects ranges from a joining process suitable for large-scale production for current busbars of fast-charging and discharging batteries, a system for laser welding of large cylindrical lithium-ion cells for high-performance applications (40 to 50 ampere hours), to integrated solutions such as for Aurora Powertrains from Finland.
The Lapland-based start-up has developed a waterproof and dustproof battery with IP67 classification for its electric snowmobile eSled, which has a high energy density of more than 190 Wh/kg. The customized laser technology developed at Fraunhofer ILT connects the aluminum cell conductor with the copper conductor for this purpose.
"Because the aluminum is on top in production, the advantage of absorption at green or blue laser wavelengths is not as considerable as it is with copper," says Dr. Alexander Olowinsky, head of department Joining and Cutting at Fraunhofer ILT, explaining the details of the laser solution. "The single mode infrared laser with a small beam diameter is the more elegant, faster and significantly more cost-effective solution, because the beam quality is currently even worse with green or blue due to the system."