Li₇La₃Zr₂O₁₂-Based Solid Electrolytes Codoped with Ta⁵⁺ and Al³⁺ Ions for Lithium Power Sources

Abstract— Li₇La₃Zr₂O₁₂-based compounds are today the most promising solid electrolytes for high-energy lithium and lithium–ion power sources. The solid electrolytes Li_7–x–3yAl_yLa₃Zr_2−xTa_xO₁₂ (x = 0.3–0.6, y = 0.05–0.20) were prepared by the sol–gel method. The effect of doping of Li₇La₃Zr₂O₁₂ in Zr and Li sublattices with tantalum (Ta⁵⁺) and aluminum (Al³⁺) on the crystal structure, morphology, and electrical conductivity of this compound was examined. The compounds obtained had the cubic structure (space group Ia-3d). The resistance of the solid electrolytes obtained was determined by the electrochemical impedance method. The compounds Li_6.25Al_0.15La₃Zr_1.7Ta_0.3O₁₂, Li_6.3Al_0.10La₃Zr_1.6Ta_0.4O₁₂, Li_6.2Al_0.10La₃Zr_1.5Ta_0.5O₁₂, and Li_6.25Al_0.05La₃Zr_1.4Ta_0.6O₁₂ have the maximal lithium-ion conductivity (~2.0 × 10^–4 S cm^–1 at 20°C). The heat treatment at 1150°C for 1 h is optimum for forming highly conducting and dense ceramic membranes. Symmetrical cells with Li electrodes show stable behavior in cycling. The solid electrolytes obtained can be used in lithium power sources.