Redox activity of argyrodite Li6PS5Cl electrolyte in all-solid-state Li-ion battery: An XPS study

Argyrodite Li6PS5Cl is a good candidate as solid electrolyte for bulk all-solid-state Li-ion batteries due to its high ionic conductivity and its good processability, although it shows some interface reactivity towards electrode active materials. In this work we have cycled LiCoO2/Li6PS5Cl/Li4Ti5O12 full cells and analyzed the interfacial mechanisms by surface-sensitive characterization techniques: Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS). We show that Li6PS5Cl has an electrochemical redox activity in the positive electrode. It is partially oxidized into LiCl, P2S5 and polysulfides Li2Sn upon charge, with some reversibility upon discharge. Li6PS5Cl also reacts with LiCoO2 upon cycling, leading to the formation of phosphates at the interface.