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

Perovskite-type Li0.35La0.55TiO3 (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 Li0.35La0.55Ti0.96Al0.04O3 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 Li0.35La0.55Ti0.94Sn0.06O3 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.