Aimed at improving batteries for future mobility applications, the techniques were developed by researchers at the Fraunhofer Institute for Laser Technology (ILT) in Aachen, Germany.
As well as boosting the power density of the batteries, the team said the laser-based technologies can save energy during production.
One of the key steps during production of lithium-ion batteries is the manufacturing of electrodes using graphite. For these electrodes, a copper foil is coated with a graphite paste using the roll-to-roll process, then dried in a continuous furnace at 160-180ºC.
The gas-powered furnaces consume a large amount of energy, the team said, and take up a lot of space – they are 60-100m long, and dry up to 100m of foil per minute when operating on an industrial scale.
To improve on that process, the Fraunhofer researchers developed a system in which a diode laser does the drying. The laser, with a wavelength of one micrometre, is combined with an optical system that illuminates the electrode over a large area, designed by industrial partner Laserline.
“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,” said Samuel Fink, group manager for thin film processing at Fraunhofer ILT.
Compared to power-guzzling continuous furnaces, the researchers said the diode laser is very energy efficient and emits very little heat to the environment. The system also takes much less space than conventional furnaces.
“Drying with the diode laser will reduce the energy required by up to 50% and the space needed for a drying system on an industrial scale by at least 60%,” Fink predicted.
The team reported improvements on power density and service lifetime of lithium-ion batteries with another technique.
In the process, a high-power, ultrashort pulse laser (USP) with one millijoule of pulse energy created channels in the battery electrodes. These channels serve as Li-ion highways for ions, significantly reducing the distance ions have to travel and shortening the charging process. This also prevents defects from occurring, the researchers said, which increases the number of potential charging cycles and ultimately extends the lifetime of the battery.
The laser-based process for producing the hole structures and the positive effect on the battery cell are well-known in theory, but the Fraunhofer researchers said they transferred the principles from the laboratory to a “scalable, industry-ready process” that uses USP radiation in the femtosecond range to modify the electrodes.
“The short interaction time of the laser pulses is sufficient to ablate the material, but also prevents the holes from melting, which means that the battery does not lose power,” said Matthias Trenn, team leader for surface structuring at Fraunhofer ILT.
One of the challenges was working out how to use the process on larger areas to achieve the high throughput required for industrial production. The team said they solved the problem by using a multi-beam arrangement for parallel process control. Four scanners, each with six ‘beamlets’, processed in parallel. They covered a width of 250mm, processing the graphite layer continuously.
The multi-beam optics were developed and implemented in collaboration with Pulsar Photonics, a Fraunhofer ILT spin-off founded in 2013.
The research demonstrated that laser technology can be used as a digital production process to improve the quality of battery cells and significantly increase sustainability during manufacturing, the Fraunhofer announcement said. “The next step is to scale up the technology from the prototype to an industrial production line,” said Trenn.
Fraunhofer ILT will demonstrate the laser technologies at Hannover Messe 2023 (17-21 April).
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