Laser Anode Patterning Leads to More Sustainable, Higher Performance Batteries
A breakthrough from the Fraunhofer Institute for Laser Technology in the way batteries are manufactured holds promise for lithium-ion batteries.
The development of high-performance battery cells has become crucial in light of sustainability. However, despite their ability to enable sustainable technologies, batteries still pose many risks.
Fraunhofer Institute for Laser Technology demonstrates a laser hole patterning system integrated into a roll-to-roll battery production web at Hannover Messe 2023 in Hannover, Germany. Image used courtesy of Dale Wilson
Lithium-ion (Li-ion) battery manufacturing can negatively impact the environment from the sourcing of raw materials through production. Hence, if the industry truly wants to enable a sustainable future through battery technology, it must first reconcile how to ensure battery production is a sustainable endeavor.
To that end, researchers from the Fraunhofer Institute for Laser Technology have demonstrated a laser-powered method for Li-ion battery production, enabling unprecedented levels of sustainability.
Traditional Electrode Manufacturing
Traditionally, manufacturing electrodes for lithium-ion batteries involves a roll-to-roll wetting and drying process, which coats the electrode materials on a conductive substrate, such as copper foil, and then dries them to remove the solvent.
During wetting, the electrode materials are mixed with a solvent to form a graphite paste slurry coated onto the substrate. This process is meant to wet the electrode materials and facilitate their deposition onto the substrate, ensuring that the electrode materials are evenly distributed on the substrate and have good adhesion, which is essential for achieving high energy and power density.
Schematic of a traditional Li-ion drying process. Image used courtesy of Kumberg et al.
After the coating process, the electrodes are dried to remove the solvent. The drying process is usually conducted in a controlled environment with low humidity and high temperature to promote fast solvent evaporation. Here, drying occurs within a furnace at continuous temperatures ranging from 160 to 180 degrees Celsius.
These gas-powered continuous furnaces, which carry the copper foil on a conveyor belt, can be as long as 100 meters and dry up to 100 meters of foil per minute. However, they consume a lot of energy and occupy a lot of space.
While the roll-to-roll process has seen success, it is not a sustainable option for the future.
A major reason for this is that the high temperatures required for the furnace drying process consume a significant amount of energy. As these are traditionally gas-powered furnaces, their continued use results in increased production costs, high energy consumption, and, ultimately, high carbon emissions.
Additionally, this technique is not space-efficient, requiring large physical areas ranging from 60 to 100 meters in length. For these reasons, traditional roll-to-roll electrode manufacturing does not present a sustainable solution for battery manufacturing in the long term.
Lasers Pave the Way
To overcome these challenges, the researchers at Fraunhofer have developed a laser-based drying process that significantly reduces energy consumption and space requirements.
Instead of using a high-temperature furnace, the newly proposed process utilizes a diode laser with a wavelength of 1 micrometer to illuminate the electrode over a large area. The graphite paste from the wetting process absorbs the laser’s energy, causing the graphite particles to get hot and the liquid to evaporate, resulting in efficient drying.
The electrode layer applied to the copper foil. Image used courtesy of Fraunhofer
According to the researchers, a major benefit of the diode laser system is a significant increase in energy efficiency over conventional furnaces. Additionally, the process is at least 60 percent more space efficient.
Beyond the drying process, the researchers developed a new laser-based method for modifying the electrode structure. Using a high-power ultrashort pulse laser with one millijoule of pulse energy, the researchers successfully introduced a hole structure into the battery electrode, which serves as Li-ion highways, reducing the distance they have to travel and shortening the charging process. This, in turn, prevents defects from occurring and increases the number of potential charging cycles, ultimately extending the battery's lifetime.
Fraunhofer Professor Arnold Gillner explained to EE Power at Hannover Messe in Germany that the system uses a kW class laser to drill 50-60 um diameter holes into the anode material on a pitch of 500 um. While these holes do not completely penetrate the 200-um thick anode metal, they do increase the charging rate of Li-ion batteries for EVs by improving ion diffusion.
When EE Power asked if this process was new, Gillner explained that mechanical methods have also been employed to press indentations into the anode. However, this compacts the material around the holes, negating many advantages of creating depressions in the anode.
The fast pulses of the laser can ablate the anode material to prevent material compaction and minimize localized heating. Because the laser ablation is designed to be incorporated into a roll-to-roll processing web, the system must create these holes very rapidly, Gillner told us.
In the demonstration model at the show, the laser beam was split into a pattern of 24 individual beams. Gillner explained that a production system could also be scanned across the web to cover a large area. In addition, the kW laser primary source could be “split into many hundreds of beams” to further increase coverage and production rates, he said.