We investigated various formulations containing synthetic graphite negative electrode material (IMERYS Graphite & Carbon) and tested the electrochemical performance of the resulting electrodes. Instead of applying the common laboratory-scale doctor blading process, the slurry was cast onto copper foil using the technically relevant comma-bar method on an industrial coating line. We investigated the effects of various parameters, such as formulation and preparation of the aqueous slurry (e.g. mixing conditions), binder and electrode additives, as well as coating conditions (e.g. continuous/intermittent and unpressed/pressed) on the homogeneity (e.g. thickness, mass and density distribution), adhesion (peeling strength) and electrochemistry (cycling behavior) of the resulting electrodes.
The experiments showed that the solid content and the mixing conditions as well as the coating mode (continuous/intermittent) and calendering process (unpressed/pressed) have a significant influence on the properties of the final electrodes. A higher solid content generally resulted in more homogeneous electrodes due to less sagging (gravity induced flow). Increased shear rates and mixing times, on the other hand, led to better electrochemical properties due to a more effective dispersion process. Furthermore, continuous coating allowed the preparation of more homogeneous electrodes than intermittent coating. Finally, calendering (which, of course, reduces the electrode thickness and increases the electrode density) resulted in improved adhesion and a more homogeneous thickness distribution, while negatively affecting the density distribution.
The methodology offers a useful way of further evaluating active material candidates that have been shown to be promising in laboratory-scale electrochemical experiments with regard to the electrode engineering and manufacturing on the pilot-scale and thus provides important information for the development of electrode materials.