Microstructure and ionic conductivity of Li0.5-xLa0.5(Ti1-xNbx)O3 solid-state electrolytes

Abstract

Solid electrolytes are critical in the development of solid-state batteries, which have advantages in terms of safety and stability. Lithium Lanthanum Titanate (Li3xLa2/3-xTiO3) is regarded as one of the most favored candidate solid electrolytes. However, the doping dependences of ionic conductivity and microstructure are still poorly understood. In this work, nominal Li0.5-xLa0.5(Ti1-xNbx)O3 (LLTN, x = 0, 0.01, 0.03, 0.05 and 0.07, labelled as LLTN0, LLTN1, LLTN3, LLTN5, LLTN7, respectively) ceramics are synthesized to investigate the above doping effects. The bulk ionic conductivity of LLTN5 sample reaches as high as 0.71 × 10−3 S/cm, which is approximately two times higher than the bulk ionic conductivity of the undoped sample at room temperature. The XRD refinement and Raman results indicate that niobium doping increases the lattice cell along the c-axis and stretch the TiO bond, which extends the tunnels for Li-ions diffusion. This work suggests that it is effective to enlarge the lattice cell for the improvement of the Li-ion conductivity in LLTO.