Argyrodite-based solid electrolytes are promising candidates for next-generation solid-state lithium batteries due to their high ionic conductivity, favorable mechanical properties, and low-temperature processability. However, interfacial degradation driven by surface inhomogeneities and degradation with lithium metal limits their long-term performance and cycling stability. Studying the nature and evolution of the solid electrolyte/Li interface is crucial to understand the impact of degradation on overall cell performance. Here, we investigate the potential-dependent interfacial evolution of Li6PS5Cl0.5Br0.5 in an anode-free cell using in operando Raman microscopy. We directly observe the formation of Li2S as the dominant degradation product, along with Li2Sx species during lithium plating and stripping. Notably, these products persist across cycles, indicating irreversible interfacial reactions. Post-mortem X-ray photoelectron spectroscopy (XPS) confirms the presence of sulfur-containing species, while operando electrochemical impedance spectroscopy (EIS) reveals substantial impedance buildup, attributed to the insulating nature of the interphase and formation of voids. Raman mapping further uncovers spatial heterogeneities in decomposition across the interface, and post-mortem SEM highlights pronounced morphological changes. This study establishes in operando Raman microscopy as a powerful tool to elucidate interfacial dynamics in solid-state batteries and provides mechanistic insights essential for designing solid electrolytes with enhanced interfacial stability and electrochemical performance.