Slot Die Coating Rheology in Battery Electrode Slurry Manufacturing
Slot die slurry throughput depends on high-shear thinning during extrusion and rapid low-shear yield stress recovery to prevent edge bead defects.
Three-Interval Thixotropy Test
Meaning
Multi-step rotational or oscillatory rheological profiles evaluate how a material recovers its structure over time after experiencing high shear. The three-interval thixotropy test measures slurry behavior through consecutive phases of low shear, destructive high shear, and a final low-shear recovery period. This sequence simulates the transitions a slurry undergoes from static storage to intense slot-die extrusion and finally to static drying on the foil.
Analyzing the rate of viscosity recovery helps engineers predict the risk of post-deposition running or sag.
Shear Profiling
Establishing the baseline viscosity of the material at rest requires negligible deformation forces. The second interval applies a high shear rate to simulate the flow behavior during passage through the pump and the narrow slot die.
Recovery Dynamics
Dynamic measurement in this step immediately reduces the shear rate back to the baseline level, tracking how quickly the slurry recovers its original structure. If the structure rebuilds too slowly, the wet film will sag or drip after coating, but if it rebuilds too quickly, the surface ripples will not level out. Measuring this recovery profile provides a quantitative value for the recovery time, which is directly used to configure the drying zone parameters and the gap between the die and the foil.
Formulation Utility
Tuning the binder and active material concentrations based on these test results allows for the design of a slurry that is easy to coat yet quick to stabilize on the foil. This testing method is a standard tool for qualifying new raw materials and checking batch-to-batch consistency in electrode manufacturing.