Roles of Alkaline Earth Ions in Garnet‐Type Superionic Conductors

Abstract The roles of alkaline earth ions in garnet‐type superionic conductors Li 7.1 La 3 Zr 1.95 M 0.05 O 12 (M=Mg, Sr, Ba) are further investigated. In contrast to previous reports, the alkaline earth ions are specifically allocated to the octahedral sites (Zr 4+ sites) instead of dodecahedral sites (La 3+ sites) in the present work. The alkaline‐earth‐ion‐doped Li 7.1 La 3 Zr 1.95 M 0.05 O 12 garnets exhibit enhanced room‐temperature conductivities with the increasing ionic radii of alkaline‐earth ions. Ba‐doped Li 7.1 La 3 Zr 1.95 Ba 0.05 O 12 provides the highest conductivity of 1.13×10 −3 S cm −1 at room temperature, whereas Mg‐ and Sr‐doped garnets show conductivities of 4.32×10 −4 and 8.91×10 −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 9 V vs. Li/Li + , and stability against metallic lithium by means of symmetric galvanostatic cycling.