Microscopic Study of Solid–Solid Interfacial Reactions in All-Solid-State Batteries

The sulfide-based solid-state electrolyte has garnered attention as a potential material for next-generation all-solid-state batteries. However, during cycling, interfacial reactions between the sulfide solid-state electrolytes and the cathode can occur, which is a serious issue that needs to be addressed. Therefore, resolving interfacial reactions has become a crucial issue in the development of solid-state batteries. A sulfide-based all-solid-state battery paired with LiFePO 4 has shown poor first-cycle discharge capacity and efficiency, which have been attributed to LiFePO 4 /Li 6 PS 5 Cl interfacial reactions. Thus, in this study, the microscopic LiFePO 4 /Li 6 PS 5 Cl interface reactions were visualized using nano-beam X-ray fluorescence (nano-XRF) mapping and nano-beam X-ray absorption spectroscopy (nano-XAS). The mapping evolution of the Fe valence state of LFP in a different state of charge was observed. The nano-XRF and nano-XAS tools at the nanoscale allowed for the decoupling of the interfacial reactions on the cathode/sulfide, which can shed light on new directions for an in-depth understanding of the interfacial phenomena of solid-state batteries. This study paves the way for the development of all-solid-state batteries with improved performance and stability.