Operando X-ray photoelectron spectroscopy of solid electrolyte interphase formation and evolution in Li₂S-P₂S₅...

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Solid-state electrolytes, such as lithium sulfide-phosphorus pentasulfide (Li₂S-P₂S₅) compounds, are critical for enabling stable lithium metal anodes in next-generation batteries.
• The instability of many solid-state electrolytes against metallic lithium and the poorly understood chemical evolution at their interfaces during cycling impede the rational design of advanced battery materials.

Purpose of the Study:

• To develop and apply advanced operando X-ray photoelectron spectroscopy (XPS) and real-time in situ Auger electron spectroscopy (AES) mapping.
• To investigate the formation and evolution of the solid-electrolyte interphase (SEI) at the Li/Li₂S-P₂S₅ interface during electrochemical cycling.
• To measure individual overpotentials associated with specific SEI constituents.

Main Methods:

• Operando X-ray photoelectron spectroscopy (XPS) for probing interfacial chemistry under electrochemical conditions.
• Real-time in situ Auger electron spectroscopy (AES) mapping for spatially resolved analysis of interphase evolution.
• Electrochemical cycling to simulate battery operation and drive interfacial reactions.

Main Results:

• Electrochemical driving of Li⁺ to the surface of Li₂S-P₂S₅ results in phase decomposition into Li₂S and Li₃P.
• Oxygen contamination within the electrolyte leads to the formation of Li₃PO₄ and subsequently Li₂O phases.
• The spatially non-uniform distribution of these phases and their varying ionic conductivities significantly impact the overall SEI properties and performance.

Conclusions:

• The study elucidates the complex chemical evolution and phase segregation occurring at the Li/Li₂S-P₂S₅ interface during cycling.
• Understanding these interfacial phenomena, including the role of oxygen contamination, is essential for the rational design and optimization of solid-state electrolytes for lithium metal batteries.