A first principle comparative study of the ionic diffusivity in LiAlO₂ and NaAlO₂ polymorphs for solid-state battery...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Materials Science

Background:

• Lithium aluminates are key battery electrode coating materials, with well-understood ion diffusion in their tetragonal phase.
• High-pressure lithium aluminate phases and sodium aluminate polymorphs lack detailed ionic diffusivity studies.
• Atomistic investigations are needed to understand diffusion mechanisms in various aluminate phases.

Purpose of the Study:

• To conduct a comparative density functional theory study on lithium and sodium aluminates.
• To investigate structural properties and activation energies for vacancy hops in different aluminate phases.
• To elucidate the factors influencing ionic conductivity in these materials.

Main Methods:

• Density functional theory (DFT) calculations.
• Analysis of structural properties and activation energies for single vacancy hops.
• Electronic structure calculations, including the electron localization function.

Main Results:

• Lithium aluminate shows poor ionic conductivity due to Al-O bond covalency.
• Orthorhombic beta-sodium aluminate exhibits significantly lower diffusion barriers compared to lithium aluminate.
• The reduced covalency of Na-O bonds, verified by electronic structure tools, correlates with improved ionic conductivity.

Conclusions:

• Ionic conductivity in aluminates is strongly influenced by the degree of covalency in metal-oxygen bonds.
• The electron localization function serves as a valuable indicator for ion diffusion pathways and conductivity.
• Orthorhombic beta-sodium aluminate presents a promising candidate for enhanced ionic conductivity in battery applications.