Sol-gel synthesis and determination of optimal sintering conditions of the Li_6.75La₃Zr_1.75Nb_0.25O₁₂ solid electrolyte

Solid electrolytes are widely used in electrochemical devices. Among these materials, electrolytes with the lithium-ion conductivity can be used in high-energy lithium and lithium-ion power sources. The perspective Li_6.75La₃Zr_1.75Nb_0.25O₁₂ solid electrolyte was synthesized by modified sol-gel synthesis method using the sparingly soluble Nb₂O₅ as one of the initial compounds. The influence of pressure and final sintering temperature on phase composition, density and lithium-ion conductivity was studied. Solid electrolyte obtained at 1150°C was single phase and had a cubic structure with the space group Ia-3d. Thus in the presented work, the cubic modification of Li_6.75La₃Zr_1.75Nb_0.25O₁₂ was obtained by thermal treatment for 1 h at 1150°C (versus 36 h at 1200°C in the literature). Moreover at this temperature the samples had the highest density and total lithium-ion conductivity (3.9·10^–5 Scm^–1 at 25°C). According to the SEM study ceramic samples have a dense structure with a particle size ∼1-3 μm. Solid electrolyte was also obtained by isostatic pressing at a pressure of 500 MPa but the values of density and total lithium-ion conductivity were comparable with that of the samples compressed statically. (paper)