Dry Electrode Manufacturing in a Calender: The Role of Powder Premixing for Electrode Quality and Electrochemical Performance

The dry manufacturing of battery electrodes has the potential to significantly reduce costs and the environmental impact of battery production but deteriorates the electrode quality due to drawbacks in the processability of the materials. By varying the mixing intensity of the powder mixtures, this work investigates the impact of blend homogeneity on the flow properties and the processability of the dry mixtures. Furthermore, the electrochemical performance of dry laminated electrodes made of LiNi0.6Mn0.2Co0.2O2 is investigated with respect to their initial mixture homogeneities and compared to slurry-based electrodes. An improvement of the powder flowability is observed for mixtures with a homogeneously distributed PVDF binder, which acts as a temporary lubricant in dry electrode manufacturing due to its ability to shear, resulting also in filament formation. Capacity and rate performance of electrodes made of homogeneous mixtures are the highest with 169 mAh/g at C/20 and 70 mAh/g at 3C compared to 169 and 49 mAh/g for the slurry-based electrodes, respectively. Cyclic voltammetry indicates lower overpotentials for incompletely homogenized electrodes due to the existence of carbon black aggregates that establish better long-range conductivity. Overall, electrodes from highly homogenized powders show the best electrochemical performance in terms of C-rate capability due to their favorable electrode thickness and porosity resulting from better processability in combination with a sufficiently distributed carbon binder domain.