Standardizing XPS and HAXPES Analyses of LLZO Solid-State Electrolytes and Their Reactive Compounds

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Surface contamination of Lithium lanthanum zirconium oxide (LLZO) is a major obstacle for its application in high-performance solid-state batteries.
• Developing reliable methods to characterize and mitigate these surface issues is critical for advancing battery technology.

Purpose of the Study:

• To establish comprehensive baseline reference data for Li₇La₃Zr₂O₁₂ (LLZO) surfaces using X-ray photoelectron spectroscopy (XPS) and hard X-ray photoelectron spectroscopy (HAXPES).
• To develop robust procedures for calibrating and charge-correcting XPS/HAXPES energy scales for accurate cross-laboratory comparisons.
• To unambiguously identify surface contaminants and reaction layers on LLZO under various synthesis and treatment conditions.

Main Methods:

• Detailed dual-beam lab-based XPS and HAXPES analyses were performed on LLZO surfaces.
• Reference samples including Li, Li₂O, LiOH, Li₂CO₃, La₂O₃, ZrO₂, and La₂Zr₂O₇ were analyzed to establish binding energy positions and chemical shifts.
• Procedures for energy scale calibration and charge correction were developed and proposed.

Main Results:

• Baseline reference data, including precise binding energy positions and chemical shifts for LLZO surface species, were established.
• The study demonstrated the capability of lab-based HAXPES to nondestructively probe compositional inhomogeneities in LLZO surfaces up to 20-30 nm depth.
• Reliable methods for identifying surface contaminants and reaction layers were proposed, crucial for understanding LLZO surface chemistry.

Conclusions:

• The established reference data and methodologies significantly enhance the ability to characterize LLZO surface contamination and reaction layers.
• Lab-based HAXPES is a powerful complementary technique to XPS for detailed, in-depth surface analysis of LLZO.
• This work provides essential foundational data and protocols for improving the performance and reliability of LLZO-based solid-state batteries.