Anode size – just geometry?

Summary:

Electric cars powered by batteries have become one way of reducing CO2 emissions in cities. However, to increase the acceptance of electric cars in society, the reliability and longevity of the battery must be guaranteed. To achieve these goals, the battery’s functioning must be fully understood. In this context, especially the accurate prediction of the state of charge of the battery needs to be improved. Thus, the utilization of the battery capacity should be increased, as well as the state of charge window for fast charging.
To this end, we investigate the oversized anode. The overhang of the anode leads to changes in the state of charge over time that are currently not considered in most models. If this phenomenon is not taken into account, a capacity test can lead to an incorrect estimation of the battery’s state of health. Further consequences include also incorrect predictions of the probability of lithium plating during fast charging.
To improve the predictions, the anode overhang was examined more closely. For this purpose, laser microscope images were taken after cell opening to visualize the deposits on top of the overhang. We identified a cover layer on top of the overhang, which makes the area it covers unusable for lithium intercalation. The usable anode area size identified is in alignment with the results of the electrical measurements. To analyse and understand this phenomenon, coin cells were built.
Coin cells are often used for laboratory tests due to their simple design, low material consumption, and low costs. To confirm comparability with conventional cell formats, the coin cell design and the influence of different electrode sizes on each other were evaluated. The effect of the lithium distribution on the electrode area was measured, and the results were used to understand the phenomena occurring in the original pouch cell.