Effect of Zr⁴⁺ on Lithium-Ion Conductivity of Garnet-Type Li_5+xLa₃(Nb_2−xZr_x)O₁₂ Solid Electrolytes

Garnet-type structured electrolytes are considered a key technology for the next generation of lithium-ion batteries such as all-solid-state batteries. Cubic Garnet-type solid oxides with composition Li5+xLa3(Nb2−xZrx)O12 (x between 0 and 1.5) were synthesized by solid-state reaction and sintered by spark plasma sintering. Powder characterization indicates the formation of solid solution with high chemical homogeneity and spherical particles. High relative densities (>96%) were obtained by spark plasma sintering at 950 °C for 10 min and pressure application of 50 MPa. Although the formation of secondary phase La2Zr2O7 was identified by the X-ray diffraction patterns of Zr-doped pellets, it has been eliminated for x = 0.75 and 1 by conventional heat treatment at 850 °C for 1 h. High ionic conductivity values were attained for x ≥ 0.75, reaching a maximum value in the order of 10−4 S.cm−1 at 25 °C with activation energy of 0.38 eV. The results indicated that Zr4+ promoted significant increasing of the lithium-ion conductivity by lowering the activation energy