36 enables a smaller battery to be created. Viscosity control is essential to achieve a homogeneous coating thickness and minimal deviations. Battery slurry with higher viscosity increases resistance to sedimentation on standing and delivers a thicker electrode film on coating. The higher viscosity may also render the coating process harder to control, possibly leading to irregularity and variable layer density, which in turn brings about a variable ion-transfer rate and hence unpredictable battery life (and unpredictable recharge cycle time). Electrode density has an effect on cycle performance and irreversible capacity loss in lithium-ion batteries. It needs to be monitored and controlled within appropriate ranges, based on the requirements in the calendaring process. The density measurement provides the weight of the slurry, and the noise in the signal shows how homogeneous it is. There isn’t a direct relationship, but when the particles are larger the noise tends to be louder. These data points allow a realtime, stochastic curve to be generated from a measurement every second. The viscosity of the polymeric binder solution affects coating performance. It influences the ease with which the powders are dispersed within it, the power required for mixing and the speed of application of uniform coating. The Porous Electrode Theory (PET) suggests the relevance of positive electrode density on the overall performance of lithium-ion battery cells, validated by experiments. Cells with a high positive electrode density show a slightly higher discharge capacity at low current rates, but at high current rates the cells with a low positive electrode density give better performance. A machine-learning framework uses the data from the sensors to build a model for the process, delivering 21 types of high-level data to the equipment suppliers. Many of these measurements are derived from the underlying stochastic curve and ML model, and are based on more advanced processing to integrate with the equipment data systems to control the process. Electrode coating A second type of sensor uses the same resonant technique for measuring the thickness of the coating, as this is directly proportional to viscosity and speed. This measurement is vital as accurate control of the layer thickness improves efficiency and increases the lifetime of the cells, as the differences in the layers has an impact on the lifetime of the battery pack. With a focus on the viscosity of the material being laid down, the system can compensate for any changes by varying the speed. The next stage is the electrolyte filling, and that has a quality assurance and traceability issue. All of the sensors generate traceability data with a QR code that provides the exact solid content and thickness that is essential under failure analysis, so you are not just banking on lab samples. This can then be added into tracking documents such as a battery passport, which holds all of the direct data on the construction and validation of a cell, rather than using samples from a batch. This helps improve the overall lifetime of a battery pack by ensuring all the cells in the pack have a similar performance level. This can be used for environmental measurements, such as raising an alert if moisture rises and the coating is affected. Measuring temperature highlights any changes in the slurry due to environmental issues through temperature-compensated viscosity. The sensors must have the resolution and stability to detect changes in moisture and temperature throughout the year, from day to night, so continuous monitoring is key, rather than a batch taken in the morning or evening. Camera monitoring for Z-folding Pouch cells are manufactured by stacking electrode-coated cell sheets. In the Z-folding process, the pre-cut anode and cathode sheets are inserted into the separator foil from both sides. The separator foil is supplied as a rolled-up, continuous web material. This Z-shaped arrangement of the electrode sheets and separator foil gives the process its name. Tech focus | Battery cell manufacturing January/February 2025 | E-Mobility Engineering Dissolving versus extruding a slurry (Image courtesy of the University of Braunschweig, IPAT/Mattis Batzer)
RkJQdWJsaXNoZXIy MjI2Mzk4