EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Lithium-ion conducting argyrodite materials, Li6PS5X (X=Cl/Br/I), are among the most well-studied inorganic solid electrolyte due to their large ionic conductivity. One of the major remaining concerns with the use of these materials in solid-state battery is limited information on their actual stability window. This work presents a systematic study to understand the influence of cationic / anionic substitution on the oxidative electrochemical stability limit of argyrodites, Li6PS5X using a combination of cyclic voltammetry, optical absorption spectra, hard X-ray photoelectron spectroscopy as well as density functional theory calculations. Even though bandgap changes from Li6PS5Cl to Ge/Si- substituted Li6PS5I due to changing cation-anion interaction, the onset of oxidative degradation doesn’t change significantly as the valence band edges are mostly populated by sulfide anion having similar energy. Understanding the underlying mechanism of electrochemical degradation in terms of thermodynamic electrochemical stability and electronic structure would further help design electrochemically stable solid electrolytes.