Yttrium Contenting Compositionally Complex Medium-Entropy Li-Garnet Electrolyte with Improved Ionic Conductivity.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• High-entropy materials offer tunable properties for advanced applications.
• Lithium-garnet electrolytes are promising for solid-state batteries but require conductivity enhancement.

Purpose of the Study:

• To design and synthesize a novel medium-entropy lithium-garnet electrolyte with enhanced ionic conductivity.
• To investigate the underlying mechanisms responsible for the improved ionic transport.

Main Methods:

• Compositional tuning using a medium/high-entropy design concept with specific dopants (Y, Nb, Ta, Hf).
• Neutron powder diffraction and Rietveld refinement for structural analysis.
• Density functional theory and Born-Oppenheimer molecular dynamics simulations for ion transport investigation.
• Fabrication and testing of lithium metal symmetric cells.

Main Results:

• A record ionic conductivity of ~5.7 × 10⁻⁴ S/cm was achieved in Li₆.₆La₃ZrNb₀.₃Ta₀.₃Hf₀.₃Y₀.₁O₁₂.
• Stable long-term cycling performance (0.1 mA/cm² for >200 h) in Li metal symmetric cells.
• Structural analysis revealed competing conduction mechanisms and the critical role of Y content.
• Computational simulations confirmed high Li-ion mobility and hopping transitions.

Conclusions:

• The medium-entropy design strategy is effective for developing high-performance lithium-garnet electrolytes.
• Appropriate Yttrium content is crucial for optimizing ionic conductivity through specific site occupancy and vacancy engineering.
• The findings provide fundamental insights into ion transport mechanisms in garnets, guiding future electrolyte development for advanced batteries.