Investigation of edge formation during the coating process of Li-ion battery electrodes

Abstract

In this manuscript, a method to reduce superelevations of lateral edges in cross-web direction during slot die coating of shear-thinning slurries for Li-ion battery electrodes (LIB) was developed. Therefore, the impact of the inner slot die geometry on the edge elevations was investigated. These elevations of the coating could be almost eliminated by optimizing the flow profile at the outlet of the slot die by modification of the internal geometry. This adaption is an essential step in optimizing the coating quality of slot die coating for battery electrodes to significantly reduce coating edges and, hence, the resulting production reject during the coating step of the industrial roll-to-roll process. It was also shown that lateral edges of the coating can be influenced explicitly by process parameters such as volume flow and gap between slot die and substrate. This correlation has already been shown for other shear-thinning material systems in previous works, which is now confirmed for this material system. At the beginning, the influence of different internal geometries on the formation of the edge elevations was shown. Finally, for the shear-thinning electrode slurry used in this work, optimal dimensions of the previously determined inner geometry for the slot die outlet were found. The optimization was performed for a state-of-the-art electrode area capacity (approximately 2.2 mAh cm−2). The results enable a significant reduction of defects and reject in the coating step of large-scale production of LIB electrodes in the future, adding to a more sustainable battery production.

Impact of Electrode Defects on Battery Cell Performance: A Review

“…Elevated coating edges for example detrimentally affect downstream processes such as coil winding or calendering, leading to cracks in the electrode layer as well as deformation or tearing of the current collector (Figure 2d). [16] The coating step is followed by the drying of the electrode layer, typically using convective methods such as heated laminar air flows. This step, additionally to being a production bottleneck, is the most energy intensive step since significant quantities of solvents must be removed from the electrode while the structure is being formed.…”

“…High precision is required to reach the desired electrode loading while ensuring a uniform coating geometry. Elevated coating edges for example detrimentally affect down‐stream processes such as coil winding or calendering, leading to cracks in the electrode layer as well as deformation or tearing of the current collector (Figure 2d) [16] …”

Optimization of Edge Quality in the Slot‐Die Coating Process of High‐Capacity Lithium‐Ion Battery Electrodes

“…As already known in literature, the influence of the dimensionless gap G * mitigates the formation of edge elevations. [1,10,15] A decreasing dimensionless gap G * results in a decreasing draw ratio of coating speed and average flow velocity below the die lips. This counteracts the neck-in flow and surface tension mechanism in edge formation and leads to decreasing fluid flow inwards the center of the coating.…”

“…In addition, experiments with different coating gaps can be compared using the known dimensionless coating gap G * from Reproduced with permission under the terms of the Creative Commons CC BY license. [1] Copyright 2021, the Authors. Published by Springer Nature.…”

CFD model of slot die coating for lithium-ion battery electrodes in 2D and 3D with load balanced dynamic mesh refinement enabled with a local-slip boundary condition in OpenFOAM

“…Current research has shown that adjustments to the (inner) slot die geometry influence the formation of edge elevations. 13 This motivates the establishment of more advanced methods to investigate the complex interactions of the various influencing parameters, which have an effect on edge elevations. One way to meet these requirements is to implement a CFD-simulation model and deriving novel solution approaches.…”