Slot-die processing of lithium-ion battery electrodes—Coating window characterization

Slot-die coating is actually the most used coating method for the manufacturing of lithium-ion battery electrodes. An easy way of reducing production costs is to increase the line capacity. Thus, the relatively high-viscous slurries are coated at continuously increasing velocities. Facing these higher and higher velocities, the main processing challenge is to ensure that the surface quality stays constant. Therefore we investigated coating of high-viscous anode slurries consisting of large graphite particles. Systematically detected conditions for which coating defects occurred were discussed and compared with different theoretical limits for stable coating conditions. Thereby the uniformity of the stable wet film was analyzed and logged with a two dimensional laser sensor system.Even though the detected break-up lines are, in some regions, congruent with the applied viscocapillary models, the appearing coating defects are not as expected in the literature. Furthermore, large particles and agglomerations may provoke an additional film break-up at small film thicknesses regardless of the coating speed. For stable conditions the roughness of the film increases when the dimensionless gap width increases.

► Homogenous lithium-ion battery electrodes were slot-die coated at high velocities.
► Coating defects were found which match but could not be explained by the low-flow limit.
► The film-roughness increases when the dimensionless gap width increases.
► A range of coating parameters was found, that defines a “quality window”.