Operando X-ray photoelectron spectroscopy of solid electrolyte interphase formation and evolution in LiS-PS solid-state electrolytes.

Solid-state electrolytes such as LiS-PS compounds are promising materials that could enable Li metal anodes. However, many solid-state electrolytes are unstable against metallic lithium, and little is known about the chemical evolution of these interfaces during cycling, hindering the rational design of these materials. In this work, operando X-ray photoelectron spectroscopy and real-time in situ Auger electron spectroscopy mapping are developed to probe the formation and evolution of the Li/LiS-PS solid-electrolyte interphase during electrochemical cycling, and to measure individual overpotentials associated with specific interphase constituents. Results for the Li/LiS-PS system reveal that electrochemically driving Li to the surface leads to phase decomposition into LiS and LiP. Additionally, oxygen contamination within the LiS-PS leads initially to LiPO phase segregation, and subsequently to LiO formation. The spatially non-uniform distribution of these phases, coupled with differences in their ionic conductivities, have important implications for the overall properties and performance of the solid-electrolyte interphase.