Subtle Local Structural Details Influence Ion Transport in Glassy Li⁺ Thiophosphate Solid Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Amorphous materials, particularly lithium thiophosphates (LPS), are key components in high-performance solid electrolytes for lithium-ion batteries.
• The local structure of these amorphous components significantly influences their electrochemical properties.

Purpose of the Study:

• To investigate the local structural variations in nominally identical 70Li₂S-30P₂S₅ glass samples.
• To correlate these structural variations with measured electrochemical properties, specifically activation energy and ionic conductivity.

Main Methods:

• Raman spectroscopy
• X-ray photoelectron spectroscopy (XPS)
• X-ray pair distribution function (PDF) analysis
• Electrochemical impedance spectroscopy (EIS)

Main Results:

• Significant variations (up to 13%) in the ratio of PS₄³⁻ tetrahedra to P₂S₇⁴⁻ units were observed in ostensibly identical samples.
• Higher concentrations of isolated PS₄³⁻ tetrahedra correlated with lower activation energies for ion transport.
• Measured ionic conductivity showed considerable variation across samples, consistent with structural differences.

Conclusions:

• Local structure heterogeneity in amorphous solid electrolytes is a critical factor affecting performance.
• Precise control and characterization of local structure are essential for reproducible and optimized solid electrolyte development.
• These findings emphasize the need to consider local structure in glass or glass-ceramic solid electrolytes for advanced lithium-ion batteries.