Synthesis of Li5+xLa3HfxNb2-xO12 (x = 0.2-1) ceramics with cubic garnet-type structure

Using solid state electrolyte instead of liquid electrolyte has been considered as a preferred alternative to the conventional liquid electrolyte. The safety and stability of electrolyte directly affects the lithium ion batteries. Lithium garnets Li5La3M2O12(M = Nb, Ta) in cubic phase exhibits higher ionic conductivity and good stability. How to continue to enhance the ionic conductivity of electrolyte is one of the key issues in development of solid state batteries. In this research, the synthesis and transport properties of the Li5+xLa3HfxNb2-xO12 (x = 0.2-1) samples with cubic garnet-structure type were reported by a solid state reaction for the first time. The optimized conditions to synthesize the Li5+xLa3HfxNb2-xO12 (x = 0.2-1) ceramics is 1100 °C for 30 h with 10% excess lithium salt. The lattice constants of Li5+xLa3HfxNb2-xO12 (x = 0.2-1) materials increase with increasing x due to the substitution of larger ionic radii Hf4+ for the smaller Nb5+ in the garnet structure. The Li5+xLa3HfxNb2-xO12 ceramics exhibits higher ionic conductivity than that of Li5La3Nb2O12 electrolyte.