Evolution at the Solid Electrolyte/Gold Electrode Interface during Lithium Deposition and Stripping

Quasi-binary thiophosphate-based solid electrolytes (SEs) are attracting substantial interest for lithium batteries due to their outstanding room temperature ionic conductivities. This work describes reactions occurring at the solid electrolyte (SE)/Au interface during Li deposition and stripping for two exemplary SE materials: beta-Li3PS4 (beta-LPS) and Li10GeP2S12 (LGPS). We used in situ Raman spectroscopy, along with X-ray photoelectron spectroscopy ()CPS) and scanning electron microscopy (SEM) to evaluate potential dependent changes in the chemistry of these materials at active electrode interfaces. For beta-LPS, a partially reversible conversion of PS43- to P2S64- was found along with the formation of Li2S during Li deposition and stripping. In contrast, LGPS exhibited only irreversible changes at potentials below 0.7 V vs Li+/Li. The different behaviors likely relate to differences in the structures of the two SE materials and the availability of easily bridged anion components in close proximity. The work shows that SE integrity at interfaces can be altered by applied potential and illustrates important speciations for the interfacial structures that mediate their electrochemical activities.