X-ray Photoelectron Spectroscopy Probing of the Interphase between Solid-State Sulfide Electrolytes and a Lithium Anode

All-solid-state lithium-ion batteries are considered as an alternative for next-generation energy storage systems. Solid-state electrolytes can improve the safety of lithiumion batteries by the replacement of the flammable organic liquid electrolytes and increase the energy density of the electrochemical cell by enabling lithium metal anodes. However, the solid-state electrolyte/electrode interphase, which governs the electron and mass transport properties, is poorly understood. In the present study, we report an X-ray photoelectron spectroscopy (XPS) investigation to gain a fundamental understanding regarding the formation of solid electrolyte interphase (SEI) layers between Li2S-P2S5 solid-state electrolytes and a lithium metal anode. We first identified the evolution of the interphase formation by stepwise deposition of lithium (in nanometer thickness) on Li2S, P2S5, Li7P3S11, and Li2P4S6, respectively. The components and growth of the interphase were monitored by XPS. The decomposition products at the interphase vary with the compounds, and their compositions were identified. The aging of the Li/solid electrolyte interface was also monitored by XPS. Our molecular-level insights into the interphase formation at the sulfide electrolyte/Li interface are crucial for improving the performance of all-solid-state Li-ion batteries.