Vacancy-Suppressed Garnet Electrolytes for Durable Solid-State Batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Cubic-garnet solid electrolytes (SEs) show promise for all-solid-state batteries (ASSBs) due to high ionic conductivity and lithium metal stability.
• Intrinsic lithium and oxygen vacancies in garnet SEs, formed during sintering, cause interfacial issues and short circuits.

Purpose of the Study:

• Quantify intrinsic vacancies in Li$_{6.5}$La$_{3}$Zr$_{1.5}$Ta$_{0.5}$O$_{12}$ (LLZTO).
• Develop a strategy to suppress vacancies and create lithium-stuffed garnet SEs for improved ASSB performance.

Main Methods:

• Tuning lithium content in green pellets and bedding powder during sintering.
• Characterization of vacancy concentrations and lithium occupancy.
• Electrochemical testing of symmetric and hybrid cells.

Main Results:

• Achieved vacancy-suppressed, lithium-stuffed LLZTO with Li occupancy > 6.5 pfu and O vacancy < 0.02 pfu.
• Demonstrated enhanced chemical and air stability of the optimized SE.
• Exhibited high critical current densities (1.00 mA cm$^{-2}$ at 30°C, 1.75 mA cm$^{-2}$ at 60°C).

Conclusions:

• Controlling intrinsic vacancies is crucial for enhancing the structural and electrochemical integrity of garnet electrolytes.
• Optimized Li-stuffed LLZTO shows excellent cycling stability (>3000 h in symmetric cells, 2000 cycles in hybrid cells with 90% retention).
• This work advances the practical application of garnet SEs in ASSBs.