Glass-Type Polyamorphism in Li-Garnet Thin Film Solid State Battery Conductors

Ceramic Li₇La₃Zr₂O₁₂ garnet materials are promising candidates for the electrolytes in solid state batteries due to their high conductivity and structural stability. In this paper, the existence of “polyamorphism” leading to various glass-type phases for Li-garnet structure besides the known crystalline ceramic ones is demonstrated. A maximum in Li-conductivity exists depending on a frozen thermodynamic glass state, as exemplified for thin film processing, for which the local near range order and bonding unit arrangement differ. Through processing temperature change, the crystallization and evolution through various amorphous and biphasic amorphous/crystalline phase states can be followed for constant Li-total concentration up to fully crystalline nanostructures. These findings reveal that glass-type thin film Li-garnet conductors exist for which polyamorphism can be used to tune the Li-conductivity being potential new solid state electrolyte phases to avoid Li-dendrite formation (no grain boundaries) for future microbatteries and large-scale solid state batteries.