Synthesis, structure, transport properties, electrochemical stability window, and lithium plating/stripping of Mg and Nb codoped Li₇La₃Zr₂O₁₂ garnet-type solid electrolytes

In this work, the Mg and Nb codoped garnet-type solid electrolytes Li_7+x-yLa_3-xMg_xZr_2-yNb_yO₁₂ (0 ≤ x ≤ 0.4; 0.4 ≤ y ≤ 0.8) for all-solid-state Li-ion batteries were prepared by conventional solid-state method. The formation of a single-phase garnet structure (space group Ia3̅d) with lattice constant decreased from 12.94452(19) Å (x = 0, y = 0.4) to 12.92286(14) Å (x = 0.4, y = 0.8) have been observed. The La and Zr were substituted by Mg (24c) and Nb (16a), respectively, which greatly altered the conductivity of the sample. Additionally, a high-density structure was obtained through sintering at 1150 °C. The Mg and Nb codoped Li₇La₃Zr₂O₁₂ (LLZO) achieved Li-ion conductivity, ranging from 7.49 × 10^-4 S·cm^-1 (x = 0, y = 0.4) to 1.95 × 10^-4 S·cm^-1 (x = 0.4, y = 0.8) at 25 °C. The Li-ion 3D diffusion pathway was constructed by the bond valence sum mapping of Mg and Nb codoped LLZO. The Mg and Nb codoped LLZO retains remarkable electrochemical stability against lithium after 600 cycles at 0.1 mA·cm^-2. This work may inspire the rational design of garnet-based electrolyte materials to attain high performance in the energy storage field.