Stability of Nb-Doped Cubic Li₇La₃Zr₂O₁₂with Lithium Metal

The garnet-type Nb-doped cubic lithium ion-conducting solid Li6.75-xLa3Zr1.75Nb0.25O12–0.5x (LLZ-Nb) was prepared with 0.46 wt% Al2O3 using a sol-gel precursor. LLZ-Nb sintered at 1,150°C for 36 h exhibited a bulk conductivity of 6.13 × 10−4 S cm−1 and a grain boundary conductivity of 7.76 × 10−3 S cm−1 at 25°C. The cell resistance of Li/LLZ-Nb/Li was gradually increased with storage time over 5 months. The increase in cell resistance was attributed to both the grain boundary and interfacial resistance between LLZ-Nb and the lithium electrode. The Li/LLZ-Nb/Li cell showed a short-circuit for 280 s polarization at 0.5 mA cm−2 and no short-circuit for 41 h polarization at 0.1 mA cm−2. LLZ-Nb was stable in saturated LiOH and LiCl aqueous solution.