Effect of Nb–Sm co-doping on the ionic conductivity of Li₇La₃Zr₂O₁₂ electrolytes

Li-conducting oxide material Li₇La₃Zr₂O₁₂ is a promising solid electrolyte due to its relatively high conductivity. In this work, Li_7−x+yLa₃Zr_2−x−yNb_xSm_yO₁₂ (0 ≤ x ≤ 0.4, 0 ≤ y ≤ 0.1) was prepared using a solid-state synthesis method, and the effects of Nb–Sm co-doping on the structure, microstructure, and conductivity of Li₇La₃Zr₂O₁₂ were investigated. Results showed that the co-doping of supervalent cation Nb and low-valent cation Sm was able to facilitate the formation of cubic garnet modification. The optimized composition Li_6.7La₃Zr_1.5Nb_0.4Sm_0.1O₁₂ showed the highest relative density at 94.3%, and reached the highest total conductivity of 1.06 × 10⁻³ S/cm at 30 °C, with the lowest activation energy of 0.39 eV. Based on SEM and above results, it can be found that the Nb–Sm co-doping can enhance sinterability and increase density, leading to lower impedance and higher conductivity. Although a small amount of impurity phase LaNbO₄ was observed in the XRD patterns, its overall influence on ionic conductivity was negligible.