Migration of Lithium Ions and Effects of Defects in the Garnet-Type Li₇La₃Zr₂O₁₂Solid Electrolyte

As a garnet-type solid electrolyte in solid-state lithium-ion batteries, the cubic phase of Li₇La₃Zr₂O₁₂ (LLZO) has attracted significant attention due to its high ionic conductivity. Using ab initio density-functional theory, we performed calculations to explore the migration pathways and activation energies of the lithium ions (Li⁺) in cubic LLZO, both with and without defects. Our calculations show that the two types of defects, lithium vacancies and interstitials, have distinct effects on the migration of lithium ions. The vacancies and interstitials have been suggested to be formed under O-rich and O-poor conditions, respectively. The vacancy-mediated migration of Li⁺ involves energy barriers in the range of 0.39 eV to 0.48 eV across various pathways, which are considerably lower than the 0.78 eV required to activate migration of Li⁺ in defect-free LLZO. On the other hand, migration of interstitial Li⁺ exhibits a higher barrier of 1.18 eV, reflecting the tighter constraints within the lattice. These insights not only deepen our understanding of Li⁺ migration mechanisms but also provide valuable guidance for enhancing ionic conductivity in cubic LLZO.