Polaron-Based Electronic Conduction in Mixed Ionic-Electronic Conducting Lithium Garnets

Recent research has demonstrated that doped lithium garnet compositions with mixed ionic-electronic conducting (MIEC) properties can significantly enhance the performance of solid-state batteries with lithium metal anodes. However, the mechanisms that enable electronic conduction in these garnets are not well understood. In this study, we conduct first-principles calculations to investigate the polaron-based mechanism of electronic conduction in these MIEC garnets. We model polaron trapping on multivalent cation dopants in the lithium garnet structure and estimate the energy barriers for site-to-site polaron migration. By analyzing defect formation energies and cation charge transitions, we elucidate why certain cations and cation combinations greatly enhance the electronic conductivity in lithium garnets. Our computations lead to suggestions for new cation dopants and new strategies to further improve MIEC garnets in high-performance solid-state batteries. The study can serve as a general framework to guide the further development of novel MIEC materials for energy technologies.