Observation of Interfacial Degradation of Li₆PS₅Cl against Lithium Metal and LiCoO₂ via In Situ Electrochemical Raman Microscopy

Sulfide‐based Li + conducting solid electrolytes, such as argyrodite, Li 6 PS 5 Cl, for all‐solid‐state batteries can have comparable ionic conductivities with liquid electrolytes. However, the interface between sulfide containing solid electrolytes and Li metal and Li‐ion positive electrodes has been found to be unstable, leading to poor cell performance and cycling. Understanding the in situ evolution of interfacial layers between the electrolyte and both electrodes is of paramount importance for designing stable and long‐life solid‐state batteries. Here, in situ Raman microscopy was used to study the interface between Li 6 PS 5 Cl electrolyte and metallic Li and LiCoO 2 . Under potential control, Raman microscopy identified the appearance of degradation products (Li 2 S, P 2 S x and polysulfides) at the electrode/solid electrolyte interface.