Dopant-induced modulation of lithium-ion conductivity in cubic garnet solid electrolytes: a first-principles study

Area of Science:

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

Background:

• Cubic garnet Li7La3Zr2O12 (c-LLZO) is a key solid electrolyte for all-solid-state batteries.
• Doping c-LLZO with Ga, Al, or Fe stabilizes the structure and improves Li-ion conductivity.
• The impact of +3 charge dopants on Li-ion conductivity varies significantly, necessitating further investigation.

Purpose of the Study:

• To investigate the influence of Ga, Fe, and Al dopants on Li chemical potential and Li-ion conductivity in c-LLZO using DFT.
• To identify favorable dopant locations and determine optimal DFT+U parameters for Fe doping.
• To elucidate the relationship between dopant-induced charge distribution and Li-ion transport mechanisms.

Main Methods:

• Density Functional Theory (DFT) calculations, including DFT+U, were employed.
• Energetically favorable dopant sites in c-LLZO were identified.
• Analysis included projected density of states, charge density, and Bader charge analysis.

Main Results:

• Ga and Fe doping increase Li chemical potential (0.05-0.08 eV), lowering transfer barriers and enhancing conductivity.
• Al doping decreases Li chemical potential (0.08 eV), increasing attraction forces and reducing conductivity.
• Distinct charge distributions around dopants critically influence Li-ion chemical potential and conductivity.

Conclusions:

• Local charge distribution around dopants and Li atoms is crucial for Li-ion conductivity in c-LLZO.
• Ga and Fe doping enhance conductivity by creating more positive charge on adjacent oxygen, destabilizing Li ions.
• Al doping reduces conductivity due to increased attraction between Li ions and oxygen atoms.