(492c) Dry Mixing and Its Impact on Powder Properties for Dry Coating of Lithium-Ion Battery Electrodes

In the context of climate change and the expansion of electromobility, the demand for lithium-ion batteries (LIB) is increasing rapidly. Electrode and cell production is associated with high energy consumption of approx. 40 kWh per kWh of battery capacity produced. As one of the largest energy consumers and cost drivers in the common electrode production, the drying process of the wet-coated electrodes offers a high potential for improving the economic efficiency, sustainability, and carbon footprint of the battery manufacturing process. A solvent-free processing of battery electrodes via a dry coating process represents a promising method to achieve these goals.

In this regard, the dry mixing of the powdered electrode components at the beginning of the process chain have a crucial impact on the performance of the dry coated battery electrodes. Within this process step, it is important to structure the electrode materials to achieve a well-tuned powder flowability being important for the following process steps (powder metering and film formation). While for wet film coating the binder is pre-dissolved in the solvent during slurry production, in the dry mixing process the binder must be homogeneously distributed in the powder mixture and the conductive additives must be well dispersed within the powder mixture. Furthermore, the binder together with the mixed powder must be able to build a network (e.g. by PTFE fibrillation) during the film formation while maintaining a sufficient electrical conductivity of the resulting electrode.

The impact of the mixing process in a high-intensity mixer on powder mixtures consisting of cathode-active material, carbon conductive additives and binder (PTFE), was investigated. Process-structure-property relationships were identified through various powder characterization methods (flowability coefficient, dynamic angle of repose, electrical resistance, Hausner ratio, particle size distribution). Figure 1A shows particle size distributions as a function of the specific mixing energy (here corresp. mixing time). With increasing specific mixing energy, the particle size distribution becomes narrower, shifts towards smaller particle sizes, and gets monomodal for high specific mixing energies. This represents the fibrillation, which is greatest at low mixing energies and the fibrils are broken up with increasing time. The fibrillation process is also presented in the photos in Figure 2, showing that after the premixing of active material and carbon additive, the addition of binder causes fibrillation. A special post-treatment leads to a more homogeneous product. The increasing flowability of the mixture during the mixing process consequently increases its bulk density. Its electrical resistance decreases due to improved particle contacts (see figure 1B). The fibrillated powders were also evaluated for their functionality in a dry coating process with powder metering and film formation via a multi-roll calender.