Effect of Al3+ and Sn4+ Doping at the B-site on the Electrochemical Properties of LLTO Ionic Conductors

Abstract

Perovskite-type Li_0.35La_0.55TiO₃ (LLTO) solid electrolytes have gained significant attention as promising candidates for all-solid-state batteries due to their high ionic conductivity, excellent chemical stability, and strong application potential. In modifying B-site doping in LLTO, the ionic radius of the dopant metal plays a crucial role in determining lattice stability, ionic conductivity, and other properties of the solid electrolyte. Al³⁺ and Sn⁴⁺ are considered attractive dopants due to their low cost and ionic radii being close to that of Ti⁴⁺, minimizing lattice distortion after doping. To investigate the differences in their mechanisms, LLTO samples doped with varying proportions of Al³⁺ and Sn⁴⁺ were successfully synthesized via the high-temperature solid-state method. The Li_0.35La_0.55Ti_0.96Al_0.04O₃ sample doped with Al³⁺ exhibited a maximum ionic conductivity of 1.06 × 10^–4 S/cm with an activation energy of 0.372 eV. In contrast, the Li_0.35La_0.55Ti_0.94Sn_0.06O₃ sample doped with Sn⁴⁺ achieved a higher ionic conductivity of 2.7 × 10^–4 S/cm with an activation energy of 0.357 eV. These results indicate that LLTO doped with Sn⁴⁺ exhibits superior ionic conductivity compared to LLTO doped with Al³⁺. This suggests that doping with elements of slightly larger ionic radii may be more effective in enhancing the performance of LLTO oxide ceramic solid electrolytes.