Structural and transport properties study of fluorine doped Li${}_{6.4}$Al${}_{0.2}$La${}_3$Zr${}_2$O${}_{12}$ electrolyte

Cubic Li${}_7$La${}_3$Zr${}_2$O${}_{12}$ due to its high ionic conductivity seems to be a promising solid electrolyte material for all solid state lithium ion batteries. Multiple ion doping is an effective way to enhance the structural and transport properties of Li${}_7$La${}_3$Zr${}_2$O${}_{12}$ electrolyte. In this work, the effect of F${}^{-}$ doping at O${}^{2-}$ site in Li${}_{6.4}$Al${}_{0.2}$La${}_3$Zr${}_2$O${}_{12}$ electrolyte has been investigated with the help of XRD, SEM, TEM, Raman and impedance spectroscopy. The formation of a garnet-like cubic phase and partial substitution of F${}^{-}$ at the O${}^{2-}$ site is confirmed by the XRD pattern. The SEM images show the formation of highly dense microstructure. The optimum relative density of 91% has been obtained for the sample with x = 0.2. The formation of a pure cubic phase with the Ia $\overline{3}$ d space group is also confirmed by Raman spectra and TEM data for this sample. While the impedance spectroscopy result shows that 0.2 mol of F${}^{-}$ doping at O${}^{2-}$ site in Li${}_{6.4}$Al${}_{0.2}$La${}_3$Zr${}_2$O${}_{12}$ electrolyte material gives optimum ionic conductivity of 3.18 × 10${}^{-4}$ S/cm with activation energy of 0.24 eV. The modulus and dielectric studies confirm the presence of a well-defined relaxation process for the sample with x = 0.2. All of the studies suggest that partial substitution of fluorine at oxygen site helps in improving the structural and transport properties of Li${}_{6.4}$Al${}_{0.2}$La${}_3$Zr${}_2$O${}_{12}$ garnet structured solid electrolyte.