Laser drying in battery cell production

A laser-assisted roll-to-roll drying process can make electrode drying in battery cell production more economical. It combines conventional oven-based convection drying with laser drying.

Electrode-drying using the roll-to-roll process (R2R) has so far been one of the most cost- and CO2-intensive production steps in the manufacture of lithium-ion batteries. A laser-assisted R2R drying process, which was developed as part of the IDEEL research cooperation, could change this in the future. It combines conventional, oven-based convection drying with laser drying based on high-power diode lasers and reduces the drying time by over 60 percent while maintaining the same quality of results.

The high energy and time consumption and the considerable amount of space required made drying the active paste (slurry) applied to a current conductor film using the roll-to-roll process (R2R) one of the most cost- and CO2-intensive production steps in the entire battery production process. Against this background, the IDEEL (Implementation of Laser Drying Processes for Economical & Ecological Lithium Ion Battery Production) research project, which was completed on December 31, 2024 after a three-year term, looked for alternative drying processes using highly efficient large-area laser irradiation. The project was supported by the Federal Ministry of Education and Research as part of the Battery 2020 funding program and was carried out under the leadership of Laserline GmbH. Other project partners included the Production Engineering of E-Mobility Components (PEM) at RWTH Aachen University, Coatema Coating Machinery GmbH, Optris GmbH & Co. KG, the Fraunhofer Institute for Laser Technology (ILT), the Münster Electrochemical Energy Technology (MEET) Battery Research Center at the University of Münster and the Fraunhofer Research Fabrication Battery Cell FFB.

The initial focus of the IDEEL research cooperation was the development and gradual optimization of a suitable laser drying process. To this end, new materials for anode and cathode coating were designed specifically for laser use and aqueous formulations based on graphite, lithium iron phosphate and silicon graphite were successfully tested (PEM at RWTH Aachen University, MEET Battery Research Center at the University of Münster). A highly efficient diode laser system with an electrical efficiency of more than 50 percent and new processing optics with coaxial thermographic coupling and a rectangular laser spot over 0.5 meters wide (Laserline) served as the heat source. A highly integrative thermographic camera with industrial PC-compatible data output was developed for contactless, automatic process monitoring and control, which ensures constant adherence to the target temperature even with changing web speeds and coating thicknesses (Optris, Laserline, Fraunhofer ILT). Based on these system components, a modular laser drying unit with a specialized air concept and tailor-made double-chamber wide-slot nozzles for the fast and safe application of water-based battery pastes (Coatema) was developed as a demonstrator. Within this demonstrator, the laser-based R2R drying process was scaled up to industry-typical feed rates and at the same time the optimum process configuration was determined and validated (Fraunhofer ILT, Fraunhofer FFB).

As the drying process requires mass transport by air removal in addition to heating, a hybrid configuration with hot air and laser modules was implemented as the most technically and economically promising approach. In this R2R process configuration, laser drying is connected upstream and used for rapid heating and pre-drying of the slurry, while the downstream convection oven extends the temperature holding time and finalizes the through-drying of the active paste. This approach makes it possible to utilize the advantages of the new process in existing systems as well, which can then be retrofitted with laser modules. The development of technical optimization potential is thus combined with the sustainable use of capital goods. With this in mind, the project participants developed an innovative hybrid drying system that achieves a web speed of 30 meters per minute for the first time and reduces drying times by more than 60 percent. The laser booster at the start of the process also halves the required oven length, which saves valuable process space and significantly reduces the need for energy-intensive drying rooms. This reduces the operating costs of the drying process by 20 to 30 percent overall, while the reduced kiln operation and simultaneous use of the system until the end of its service life also significantly optimizes the CO2 balance. The new approach therefore enables more economical and climate-friendly processes, which also significantly improves the overall economic and ecological balance of battery production.

The new hybrid process is also not expected to have any disadvantages in terms of process results. Experimental studies by the Fraunhofer ILT, the PEM at RWTH Aachen University, the MEET Battery Research Center and the Fraunhofer FFB have shown that the results of hybrid drying are not inferior to those of established convection drying. Despite the increased throughput rate, the quality of the results is at least equivalent in terms of adhesion, residual moisture, electrical conductivity and electrochemical properties. The industrial relevance of the newly developed process has thus been fully demonstrated. Accordingly, the hybrid process developed as part of the IDEEL project will be incorporated into the work of the Fraunhofer FFB, which is to be expanded into a development center for modern battery cell production for Germany and its European partners. (OM-4/25)