Enhancement of the lithium ion conductivity of Ta-doped Li₇La₃Zr₂O₁₂ by incorporation of calcium

Fast ion conducting garnet materials have been identified as promising electrolytes for all solid-state batteries. However, reliable synthetic routes to materials with fully elucidated cation site occupancies where an enhancement in lithium conductivity is observed remains a challenge. Ca-Incorporation is developed here as a promising approach to enhance the ionic conductivity of garnet-type Li_7−xLa₃Zr_2−xTa_xO₁₂ phases. Here we present a new sol–gel synthetic strategy as a facile route to the preparation of materials of a desired stoichiometry optimized for Li⁺ conductivity. We have found that the ionic conductivity of Li_6.4La₃Zr_1.4Ta_0.6O₁₂ is increased by a factor of four by the addition of 0.2 mol of Ca per formula unit. Ca is incorporated in the garnet lattice where it has no effect on the sinterability of the material and is predominately located at the La sites. We anticipate that the ease of our synthetic route and the phases presented here represents a starting point for the further realization of solid state electrolyte compositions with similarly high Li+ conductivities using this methodology.