Sol-Gel-Driven Al and Ta Co-Doped Li7La3Zr2O12 Solid Ceramic Electrolyte for All-Solid-State Lithium Ion Batteries

Abstract

In this work, Al and Ta co-doped Li7La3Zr2O12 (Al-Ta LLZO) powder and pellets with a cubic garnet structure were fabricated and characterized by modified and optimized sol-gel synthesis. The Al-Ta LLZO pellets with a pure cubic structure and little second phases were obtained when the amount of Li addition was varied from 6.2 to 7.44 mol, while the Ta-only doped LLZO (Ta-LLZO) ones showed a mixed phase of cubic and pyrochlore phases for a low Li amount of 6.2 mol. In addition, the Al-Ta LLZO pellets had a very wide range of final sintering temperatures for pure cubic garnet phases. In contrast, the Ta-LLZO pellet had a pyrochlore-mixed cubic phase for a final sintering temperature above 1000 degrees C. The surface morphology of the two kinds of doped LLZO pellets became much denser and cleaner when the final sintering temperature was increased to 1100 degrees C. Especially, the Al-Ta LLZO pellets sintered at 1100 degrees C showed a theoretical density of 95.2% and an excellent lithium ion conductivity of 0.45 mS/cm. The results of this study suggest that modified sol-gel synthesis and co-doping can be an optimum method to obtain a pure cubic phase of LLZO powder and pellet for highly dense and conductive solid electrolyte ceramics.