Gallium-Doped Li 7 La 3 Zr 2 O 12 Garnet-Type Electrolytes with High Lithium-Ion Conductivity.

Owing to their high conductivity, crystalline Li _7-3x Ga _x La ₃ Zr ₂ O ₁₂ garnets are promising electrolytes for all-solid-state lithium-ion batteries. Herein, the influence of Ga doping on the phase, lithium-ion distribution, and conductivity of Li _7-3x Ga _x La ₃ Zr ₂ O ₁₂ garnets is investigated, with the determined concentration and mobility of lithium ions shedding light on the origin of the high conductivity of Li _7-3x Ga _x La ₃ Zr ₂ O ₁₂ . When the Ga concentration exceeds 0.20 Ga per formula unit, the garnet-type material is found to assume a cubic structure, but lower Ga concentrations result in the coexistence of cubic and tetragonal phases. Most lithium within Li _7-3x Ga _x La ₃ Zr ₂ O ₁₂ is found to reside at the octahedral 96h site, away from the central octahedral 48g site, while the remaining lithium resides at the tetrahedral 24d site. Such kind of lithium distribution leads to high lithium-ion mobility, which is the origin of the high conductivity; the highest lithium-ion conductivity of 1.46 mS/cm at 25 °C is found to be achieved for Li _7-3x Ga _x La ₃ Zr ₂ O ₁₂ at x = 0.25. Additionally, there are two lithium-ion migration pathways in the Li _7-3x Ga _x La ₃ Zr ₂ O ₁₂ garnets: 96h-96h and 24d-96h-24d, but the lithium ions transporting through the 96h-96h pathway determine the overall conductivity.