Ta-Doped Li₇La₃Zr₂O₁₂for Water-Stable Lithium Electrode of Lithium-Air Batteries

Garnet-type high lithium ion conductivity solid electrolytes with nominal compositions of Li 7-x La 3 Zr 2-x Ta x O 12 (x = 0–0.7) were prepared by using a sol-gel precursor and are proposed as the protective layer for a water-stable lithium electrode for lithium-air rechargeable batteries. The Li 6.75 La 3 Zr 1.75 Ta 0.25 O 12 (LLZ-0.25Ta) composition sintered at 1,180°C for 36 h showed the highest relative density of 96.7% and resistance to water permeation. The LLZ-0.25Ta was stable in contacting with lithium metal and also in a saturated LiOH/10 M LiCl aqueous solution. The total and bulk conductivities of the sintered LLZ-0.25Ta pellet were 5.20 × 10 −4 and 6.55 × 10 −4 S cm −1 at 25°C, respectively. The Li/LLZ-0.25Ta/Li cell showed a stable cell resistance of 310 Ω cm 2 at 25°C for 4 months. However, polarization experiments on the Li/LLZ-0.25Ta/Li cell suggest a lithium dendrite short-circuit after 100 s at 0.5 mA cm −2 and after 2000 s of polarization at 0.1 mA cm −2 at room temperature.