Inhomogeneous lithium-storage reaction triggering the inefficiency of all-solid-state batteries

All-solid-state batteries offer an attractive option for developing safe lithium-ion batteries. Among the various solid-state electrolyte candidates for their applications, sulfide solid electrolytes are the most suitable owing to their high ionic conductivity and facile processability. However, their performance is extensively lower compared with those of conventional liquid electrolyte-based batteries mainly because of interfacial reactions between the solid electrolytes and high capacity cathodes. Moreover, the kinetic evolution reaction in the composite cathode of all-solid-state lithium batteries has not been actively discussed. Here, electrochemical analyses were performed to investigate the differences between the organic liquid electrolyte-based battery and all-solid-state battery systems. Combined with electrochemical analyses and synchrotron-based in situ and ex situ X-ray analyses, it was confirmed that inhomogeneous reactions were due to physical contact. Loosely contacted and/or isolated active material particles account for the inhomogeneously charged regions, which further intensify the inhomogeneous reactions during extended cycles, thereby increasing the polarization of the system. This study highlighted the benefits of electrochemo-mechanical integrity for securing a smooth conduction pathway and the development of a reliable homogeneous reaction system for the success of solid-state batteries.