Effect of roll press on consolidation and electric/ionic-path formation of electrodes for all-solid-state battery

This study investigated unpressed and pressed electrodes with the synchrotron radiation X-ray computed laminography (CL) technique to clarify the relationship between the packing structure formation of an electrode processed with a roll press and the performance of all-solid-state batteries. Additionally, we evaluated the length and thickness of percolation paths constructed by the electrode particles using the 3-dimensional structure obtained by the X-ray CL measurement. The smallest packing fraction was in the cathode layers in both the pressed and unpressed electrodes. The cathode packing fraction had a non-uniform distribution shape as a function of the layer thickness. A similar distribution shape was maintained after pressing, except near the surface in contact with the pressing roller. Pressing caused the packing fraction of the cathode layer to become much larger than the unpressed one, especially near the surface where it significantly increased. The thickness of the percolation paths in the cathode layer also increased after pressing. Furthermore, we discovered that the cathode local path thickness, measured by using regions segmented by packing fraction values, had a linear relationship with the packing fraction. Consequently, the performance bottle neck is caused by the local layer that has the smallest packing fraction.