Li Jump Diffusion and Long-Range Transport in Garnet Single Crystals: Spanning the kHz-GHz Range

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Physics

Background:

• Garnet-type oxides are promising solid electrolytes for all-solid-state batteries due to their high ionic conductivity.
• Controlling lithium-ion (Li+) transport is crucial for enhancing energy storage performance.
• Large single crystals of garnets allow detailed investigation of Li+ dynamics.

Purpose of the Study:

• To investigate Li-ion dynamics in single-crystalline Li6.5La3Zr1.5Ta0.5O12.
• To correlate Li-ion transport mechanisms with electrical and nuclear magnetic resonance measurements.
• To understand the role of charge carrier concentration in determining ionic conductivity.

Main Methods:

• Utilized 7Li nuclear spin relaxation (NSR) and electrical conductivity spectroscopy.
• Probed ion dynamics across a wide frequency range (kHz to GHz).
• Investigated single-crystalline Li6.5La3Zr1.5Ta0.5O12 and compared with Li6La3ZrTaO12.

Main Results:

• Identified distinct activation energies for long-range transport (0.41–0.47 eV) and localized dynamics (approx. 0.22 eV).
• Observed higher Li+ mobility in Li6.5La3Zr1.5Ta0.5O12 compared to Li6La3ZrTaO12.
• Found that ionic conductivity is only slightly increased due to a potentially lower charge carrier concentration (Nc) in the higher mobility sample.

Conclusions:

• Li-ion transport in garnet electrolytes involves both long-range hopping and localized dynamics.
• Charge carrier concentration (Nc) is a critical parameter influencing practical ionic conductivity.
• Tailoring both mobility and carrier concentration is essential for optimizing solid electrolyte performance.