Roles of Alkaline Earth Ions in Garnet-Type Superionic Conductors

The roles of alkaline earth ions in garnet-type superionic conductors Li7.1La3Zr1.95M0.05O12 (M=Mg, Sr, Ba) are further investigated. In contrast to previous reports, the alkaline earth ions are specifically allocated to the octahedral sites (Zr4+ sites) instead of dodecahedral sites (La3+ sites) in the present work. The alkaline-earth-ion-doped Li7.1La3Zr1.95M0.05O12 garnets exhibit enhanced room-temperature conductivities with the increasing ionic radii of alkaline-earth ions. Ba-doped Li7.1La3Zr1.95Ba0.05O12 provides the highest conductivity of 1.13x10(-3)S cm(-1) at room temperature, whereas Mg- and Sr-doped garnets show conductivities of 4.32x10(-4) and 8.91x10(-4)S cm(-1) at room temperature, respectively. The obtained ionic conductivities are comparable to other promising superionic conductors that are already known. Moreover, the alkaline-earth-ion-doped garnets demonstrate a wide electrochemical stability window of 9V vs. Li/Li+, and stability against metallic lithium by means of symmetric galvanostatic cycling.