Due to the rapidly increasing demand for lithium-ion batteries (LIB) it is crucial to lower the need of production energy per kWh of battery capacity produced. One of the most energy consuming process steps is the drying of wet-coated electrodes. Eliminating this step offers a high potential to improve carbon footprint and sustainability as well as decrease cost and space demand for large dryers. A promising method to achieve these targets is a dry coating process for LIB.
The mixing step at the beginning of the process chain for dry coating of electrodes has a crucial influence on resulting powders and their suitability for the coating process. The main goal is to achieve a uniform distribution of the binder, conductive agent and active material, simultaneously optimizing the product’s micro- and macrostructure for the subsequent stages of powder dosing and film formation.
In order to understand correlations between process parameters and product, an anode pre-mix of graphite as active material, carbon black and PTFE binder was continuously mixed at different intensities in a twin-screw extruder. The shear stress and specific energy input acting on the material have been varied to obtain different powder structures by changing extrusion parameters (rotational speed, throughput). This results in products with different properties (e.g. particle size distribution, flowing behavior, electrical conductivity and porosity) and different behavior in the calender gap during film formation. An increase of extrusion torque (specific energy input) leads to a higher stress on the material and larger granules with higher conductivity and lower packing density after extrusion. These granules show better electrical conductivity due to the enhanced particle contact but are disadvantageous in film formation behavior due to their granule size. In order to optimize the dry coating process, systematic investigations were carried out and finally a suitable extrusion parameter set was chosen to obtain homogeneous electrodes with a good electrochemical performance.