Sintering behavior and electrochemical properties of garnet-like lithium conductor Li6.25M0.25La3Zr2O12 (M: Al3Â + and Ga3Â +)

The sintering behavior and electrochemical properties of garnet-like Li6.25M0.25La3Zr2O12 (M: Al3 + and Ga3 +) were investigated. The sintering of Li6.25Al0.25La3Zr2O12 progressed at 1050 °C. On the other hand, the densification of Li6.25Ga0.25La3Zr2O12 pellets progressed at lower temperatures above 950 °C to yield relative densities of 93.9% after sintering at 1000 °C. The temperatures at which the sintering of Li6.25M0.25La3Zr2O12 progressed are in good agreement with the temperatures where the liquid phases of Li-M-O compounds form. The sintering of these compounds was consistent with the change in the lattice parameter due to the replacement of Li+ for Al3 +/Ga3 + in the structure. These results suggest that the cation diffusion between the grains and the grain boundaries due to the replacement of Li+ for Al3 +/Ga3 + in the garnet-like structure improves the grain growth of these compounds. Dense pellets of Li6.25Ga0.25La3Zr2O12 were obtained by sintering at 1000 °C for 12 h without the use of mother powders, and the bulk and total conductivities obtained at 25 °C were 1.6 × 10− 3 and 9.6 × 10− 4 S cm− 1, respectively. The activation energies for the bulk and total conductivities were 0.25 and 0.32 eV, respectively. Li6.25Ga0.25La3Zr2O12 was stable in contact with lithium metal, even for a long period of 1 month.