Sol-gel synthesis and determination of optimal sintering conditions of the Li6.75La3Zr1.75Nb0.25O12 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 Li6.75La3Zr1.75Nb0.25O12 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 Li6.75La3Zr1.75Nb0.25O12 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.