Ionic conductivity prediction model for composite electrodes and quantification of ionic conductivity reduction factors in sulfide-based all-solid-state batteries

In recent years, all-solid-state batteries have been considered as suitable candidates for application in electric vehicles from the viewpoints of safety, rapid recharging, and energy density. Thus, vigorous efforts have been made to develop solid electrolytes (SE) with high ionic conductivity. However, it has been reported that the ionic conductivity of all-solid-state batteries decreases significantly when the electrodes are composed of a composite containing active materials. In this paper, we clarify the reason for the decrease in ionic conductivity both experimentally and via simulations. In addition, we propose a prediction model for the ionic conductivity of composite electrodes. First, to clarify the reason for the decrease in the ionic conductivity of SE, SE layers with controlled porosity are prepared. It is found that the contact ratio between the SE is the most significant factor in decreasing the ionic conductivity. In addition, a path-resistance-separation model is proposed to predict the overall ionic conductivity by separating the path inside the composite into macroscopic pathways that avoid the active material and microscopic pathways that avoid voids. The proposed model is expected to be used for improving the efficiency of all-solid-state battery design.