Thin and Dense Solid-solid Heterojunction Formation Promoted by Crystal Growth in Flux on a Substrate

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• Solid-state batteries require stable, highly conductive ceramic electrolytes.
• Direct growth of solid electrolyte layers on electrodes is challenging.

Purpose of the Study:

• To demonstrate the direct growth of cubic Li5La3Nb2O12 crystal layers on LiCoO2 substrates.
• To develop an ideal ceramic separator for all-solid-state batteries.

Main Methods:

• Conversion of an ultra-thin niobium substrate in molten LiOH flux.
• Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) for structural analysis.
• Utilizing a novel stacking approach for electrolyte-electrode integration.

Main Results:

• Successfully grew dense, well-defined Li5La3Nb2O12 polyhedral crystals.
• Identified tilted grain boundaries with specific symmetry (Σ3) showing minimal conductivity loss.
• Mitigated sub-phase formation at the interface by controlling reaction kinetics via Nb2O5 thin film.

Conclusions:

• The direct growth method yields a high-quality ceramic separator.
• The developed Li5La3Nb2O12 layer is suitable for all-solid-state batteries due to its dense interface and controlled grain boundaries.