In-line quality assurance in lithium-ion electrode manufacturing

In-line electrode quality assurance in Li-ion battery manufacturing is crucial for ensuring battery performance, safety, and longevity. As the demand for high-performance batteries grows, automated in-line quality control becomes essential. Continuous monitoring of electrode properties like coating thickness, uniformity, and material composition using techniques, such as optical inspection and laser scanning helps to detect defects early, reducing scrap and optimizing efficiency. This approach lowers production costs and improves the reliability of Li-ion cells.

In the scope of the BMBF-funded project IQ-EL, electrode inhomogeneity has been investigated by analyzing both the edge and middle parts of wet and dry electrodes using a high-precision confocal sensor (accuracy of 0.3 µm). Data was collected throughout the manufacturing process, enabling data-driven insights. A user-defined algorithm was developed to generate both 2D and 3D edge profiles, providing detailed characterizations of the electrode. Fig. 1 displays a 2D edge profile of an anode. An inline-sensor was used with a sensor span of approximately 4.780 µm (Fig. 2). Fig. 3a illustrates the surface profile of the electrode middle section, highlighting deviations in thickness of ~1.75 µm, substantially lower than the usual industrial threshold of ±10 µm to ±20 µm [2]. Such inhomogeneities can lead to an uneven distribution of current density, which may affect the overall performance and efficiency of the electrode. Fig. 3b shows the accuracy of the edge profile, which is a critical factor in determining the quality of the electrode. Excessive elevation at the electrode edges can create issues during the winding of the electrode foil, leading to cracking of electrode at the edge – these edge sections must be trimmed before the electrode is used in pouch cell production.

By measuring both the edge and middle sections of the electrode, the optimal parameter set for the slot-die coating process has been identified for various materials (graphite, NCM, LFP). Cell characterization additionally established criticality thresholds. 

Thickness inhomogeneities in electrode foils during the slot-die coating process were investigated in pilot-scale experiments. An algorithm was developed for automated data evaluation, which was also applied to commercial sensor data, ensuring a standardized data analysis of coating quality.