Optical investigation of graphite electrode wetting


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High reject rates and production fluctuations in battery cell manufacturing lead to increased material and energy consumption. The best possible transparency of the individual manufacturing steps and their physical backgrounds can uniform and increase the quality of the manufactured cells. In the manufacturing of lithium ion cells, the electrolyte filling and the associated electrode wetting of the lithium ion cell is a quality-critical process. In order to increase the gravimetric energy density and to reduce the cell price, the electrolyte quantity in the cell is minimized. However, insufficiently wetted electrodes result in higher internal resistance and capacity losses. A precise examination of the electrode wetting is therefore necessary. Physically, the electrolyte flow in the battery electrodes is based on the Washburn equation for capillary flows in porous media. In literature there are already several analytical and simulative methods to investigate this wetting step. We present a revised optical approach with a contrast medium solution to investigate graphite electrode wetting in more detail. This allows the fluid movements to be precisely resolved in terms of location and time. Thus, digital image processing can be used to determine the velocity vectors of wetting and identify non-wetted areas. Thus, the presented method can be used to spatially describe the graphite electrode wetting and the capillary electrolyte movements as a function of the process frame conditions. With the help of the presented experiments future product and process technical questions can be derived and answered.

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