A German team has developed a new laser drying solution for lithium-ion batteries

Researchers at Germany's Fraunhofer ILT have announced that they have developed two innovative laser-based technologies for the production of lithium-ion batteries. According to the introduction, the two manufacturing techniques not only save energy in production, but also have the potential to produce batteries with higher power density and longer service life.

The researchers note that the manufacture of graphite electrodes is one of the key steps in the production of lithium-ion batteries. In the previous electrode preparation process, the usual operation is to apply graphite paste evenly on the copper foil using the roll-to-roll process, and transfer the electrode into the gas furnace at 160℃-180℃ (mainly through the conveyor belt to transport the copper foil) for drying. As well as consuming a lot of energy, gas-powered continuous furnaces also take up a lot of space, with transmission belts typically 60-100 meters long and drying 100 meters of copper foil per minute when operating on an industrial scale.

(Photo credit: Fraunhofer ILT)

Researchers at the Fraunhofer ILT Institute for Laser Technology have developed a system in which diode lasers can be used to carry out the drying process. The laser beam, which has a wavelength of 1 micron (1μm), is amplified by special optics to illuminate electrodes over a large area. The optical system was designed specifically for drying systems by Laserline, Fraunhofer's industry partner.

Samuel Fink, head of Fraunhofer ILT's film processing group, explains the principle behind the process: "In contrast to the hot-air drying process, our diode laser delivers a high-intensity beam of light onto a copper foil coated with graphite paste to complete the drying process. The black graphite absorbs the energy and the resulting interaction causes the graphite particles to heat up and the solution to evaporate in the process."

The technology offers many benefits: diode lasers are very energy efficient compared with power-hungry furnaces, and they release very little heat into the environment. In addition, laser drying systems take up significantly less space than traditional furnaces - using diode laser drying will reportedly reduce energy by up to 50 percent and reduce the space required for an industrial-scale drying system by at least 60 percent.

It also improves the power density and longevity of lithium-ion batteries. A high-power ultra-short pulsed laser (USP) with a pulse energy of 1 millijoule (mJ) introduces a channel-like hole structure in the battery electrode. These channels act as "superhighways" for ions -- they greatly shorten the distance they travel, and thus the charging process. At the same time, this prevents defects from occurring, thus increasing the number of charging cycles and ultimately extending the battery life.

One of the challenges encountered by the Fraunhofer ILT researchers was how to deal with larger areas to achieve the high throughput required for industrial production. However, the team has solved this problem by using a multi-beam arrangement with parallel process control: they use four scanners, each with six beams, to process the foil in parallel. They emit a beam that covers layers of graphite 250mm wide and is able to process these layers continuously. Developed and implemented in close collaboration with Fraunhofer ILT subsidiary Pulsar Photonics, this multi-beam optical system extends the life of the graphite negative electrode, improves the cycle life of chemical storage batteries, and reduces the cost of lithium batteries.