Migration of lithium ions and effects of defects in garnet-type solid-state electrolyte Li7La3Zr2O12

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 migrating lithium ions in cubic LLZO, both with and without defects. The defect configurations considered in this study are selected from our previous work, where we identified thermodynamically stable defects under different chemical conditions. Our results reveal that various types of defects significantly impact Li-ion migration. Lithium vacancy (VLi) exhibits an activation energy of approximately 0.06 eV per migrating Li-ion, and lanthanum vacancy (VLa) show 0.07 eV per migrating Li-ion, while zirconium antisite on the Li site with a lanthanum vacancy (ZrLi + VLa) defect configuration results in a similarly low activation energy of 0.10 eV per migrating Li-ion. The Schottky-type (2VLi + VO) defect, the two Li vacancies with lanthanum antisite (2VLi+ LaLi), and the combined (LaLi + VO + VZr) defect configurations, yields low activation energies in the range of 0.11–0.20 eV per migrating Li-ion. In contrast, Li-ions in defect-free LLZO require higher activation energy of 0.46 and 0.60 eV per migrating Li-ion for two distinct migration routes. Interstitial and Frenkel-type migrations exhibit significantly higher activation energy of 3.10 and 2.05 eV, respectively, reflecting the tighter constraints within the lattice. These findings highlight the critical role of specific defect configurations in influencing Li-ion migration behavior and activation energies in cubic LLZO.