05 Apr 2023
System will be presented this month at Hannover Messe alongside many other photonics-related launches.Fraunhofer Institute for Laser Technology (ILT) in Aachen, Germany, have developed innovative laser-based technologies for producing lithium-ion batteries that, compared to those produced conventionally, can be charged more quickly and have a longer lifetime.
Furthermore, laser-based drying is a significantly more efficient means of coating water-based electrodes. Using a demonstrator, Fraunhofer ILT will present its forward-looking laser technologies for battery cell production at the Fraunhofer booth at Hannover Messe 2023, which runs between 17-21 April.
Scientists at the ILT have developed two laser-based manufacturing technologies that not only save energy in production, but also make it possible to create battery cells with higher power density and a longer service life.
One of the key steps in producing lithium-ion batteries is the manufacture of graphite-based electrodes. For these electrodes, a copper foil is coated with a graphite paste using roll-to-roll processes and then dried in a continuous furnace at 160 to 180 degrees Celsius. As well as consuming a great deal of energy, the gas-powered continuous furnaces – which feeds the copper foil on a conveyor belt – take up a lot of space: They are between 60 and 100 meters long and dry up to 100 meters of foil per minute when operating on an industrial scale.
The ILT researchers developed a system in which a diode laser carries out the drying process. The laser beam has a wavelength of 1 micrometer and is amplified by special optics that illuminate the electrode over a large area. The optics were specially designed for the drying system by Fraunhofer’s industry partner Laserline.
Samuel Fink, group leader for Thin Film Processing at Fraunhofer ILT, explains the principle behind the process: “In contrast to the hot-air drying process, our diode laser projects a high-intensity beam onto the copper foil, which is coated with graphite paste.
The jet-black graphite absorbs the energy. The resulting interaction causes the graphite particles to heat up and the liquid to evaporate.” The Fraunhofer technology provides a number of benefits: Compared to power-guzzling continuous furnaces, the diode laser is very energy-efficient, and the system gives off little heat to the environment.
Furthermore, the laser drying system takes up much less space than conventional furnaces. “Drying with the diode laser will reduce the energy required by up to 50 percent and the space needed for a drying system on an industrial scale by at least 60 percent,” said Fink.
In addition to these benefits, the team at Fraunhofer ILT has been able to improve the power density and lifetime of the lithium-ion batteries. Once again, thanks to laser technology: in this case, a high-power ultrashort pulse laser (USP) with 1 millijoule of pulse energy introduces a hole structure, referred to as channels, into the battery electrode.
These channels serve as a highway for the ions – they significantly reduce the distance the ions have to travel and shorten the charging process. At the same time, this prevents defects from occurring, which in turn increases the number of charging cycles and ultimately extends the lifetime of the battery.
One of the challenges the ILT scientists faced was how to process larger areas to achieve the high throughput required for industrial production. The Fraunhofer team solved this problem by using a multi-beam arrangement with parallel process control. Four scanners, each with six beamlets, process the foil in parallel. They cover a width of 250 millimeters and process the graphite layer continuously. The multi-beam optics were developed and implemented in close collaboration with Pulsar Photonics, a Fraunhofer ILT spin-off, founded in 2013.
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