Chemical Imaging of Cathode–Electrolyte Interphase in Sulfide Solid-State Batteries

The cathode–electrolyte interphase critically impacts the performance of solid-state batteries, yet its chemical evolution remains poorly understood, especially in sulfide systems. Here, we employ scanning transmission X-ray microscopy (STXM) to directly map the NMC–argyrodite interphase. We show that sulfide oxidation primarily occurs at the electrolyte surrounding NMC particles, while the bulk electrolyte remains electrochemically stable. This interfacial oxidation, accompanied by Ni reduction, leads to the formation of S0 and SOx2– species that drive high- impedance interphase growth. Our results provide direct evidence of cathode–electrolyte interactions and a clear visualization of interfacial degradation.