Microscopic Degradation Mechanism of Argyrodite-Type Sulfide at the Solid Electrolyte-Cathode Interface

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Interfacial engineering is crucial for solid-state battery performance, particularly for sulfide electrolytes and oxide cathodes.
• Surface coatings like LiNbO3 are used but can degrade under harsh conditions (high temperature, high potential).

Purpose of the Study:

• To investigate the interfacial degradation mechanism in sulfide-based solid electrolyte/LiNbO3-coated oxide cathode systems.
• To understand the role of the solid electrolyte interface in cell performance degradation.

Main Methods:

• Utilized half-cells with argyrodite Li6PS5Cl and LiNbO3-coated LiNi0.5Co0.2Mn0.3O2.
• Exposed cells to 60 °C and potentials of 4.25 and 4.55 V vs Li/Li+.
• Employed transmission electron microscopy/electron diffraction (TEM/ED) and X-ray absorption spectroscopy (XAS) for analysis.

Main Results:

• TEM/ED showed the argyrodite structure transforming into an amorphous phase with LiCl and Li2S formation.
• XAS confirmed a decrease in PS4 units and an increase in P-S-P domains in the solid electrolyte.
• P-O bond formation was observed at higher potentials (4.55 V vs Li/Li+).

Conclusions:

• The interfacial degradation, particularly on the solid electrolyte side, is a key factor limiting all-solid-state battery performance.
• Delithiation and high potentials induce structural and chemical changes at the interface, compromising battery function.