Densification and lithium ion conductivity of garnet-type Li_7-xLa₃Zr_2-xTa_xO₁₂ (x=0.25) solid electrolytes

The garnet-type Li₇La₃Zr₂O₁₂ ceramic is one of promising solid electrolytes for all-solid-state secondary lithium batteries. However, it faces problem of volatilization of lithium during sintering, which may cause low density and deterioration of ionic conductivity. In this work, the effects of sintering temperature and addition on the density as well as the lithium ion conductivity of Li_7-xLa₃Zr_2-xTa_xO₁₂ (LLZTO, x=0.25) ceramics prepared by solid state reaction have been studied. It is found that optimization of the sintering temperature leads to a minor increase in the ceramic density, yielding an optimum ionic conductivity of 2.9×10^-4 S·cm^-1 at 25℃. Introduction of Li₃PO₄ addition in an appropriate concentration can obviously increase the density, leading to an optimum ionic conductivity of 7.2×10^-4 S·cm^-1 at 25℃. This value is superior to the conductivity data in most recent reports on the LLZTO ceramics.