Synthesis and properties of garnet-type Li7-x-yLa3Zr2-yNbyO12-0.5x

The garnet-type oxide Li7La3Zr2O12 (LLZ) was found to have high lithium ion conductivity at room temperature by Weppner et al. in 20071). The ionic conductivity of a sintered pellet (92 % of theoretical density) was reported to be 2.44×10-4 S cm-1 at 25 °C. The Nb doped garnet of Li6.75La3Nb0.25Zr1.75O12 was recently reported by Ota et al.2) to exhibit a high lithium ion conductivity of 8x10-4 S cm-1 at room temperature. The new garnet-type solid electrolyte was found to be stable in molten lithium. However, the electrochemical properties of the interface between Li and LLZ have not been examined in detail. Kanamura et al.3) reported that the Li/LLZ/Li cell showed an unusual polarization behavior; the polarization potentials were steady with time up to the polarization current of 10 μA cm-2 but the potential increased suddenl