Microelectrodes for local conductivity and degradation measurements on Al stabilized Li₇La₃Zr₂O₁₂ garnets

The attractiveness of Li₇La₃Zr₂O₁₂ (LLZO) cubic based garnets lies in their high ionic conductivity and the combination of thermal and electrochemical stability. However, relations between composition and conductivity as well as degradation effects are still not completely understood. In this contribution we demonstrate the applicability of microelectrodes (Ø = 20–300 μm) for electrochemical impedance spectroscopy (EIS) studies on LLZO garnets. Microelectrodes allow to obtain local information on the ionic conductivity. A comparison between the overall performance of the sample (3.3 × 10⁻⁴ S cm⁻¹) and local measurements revealed differences in conductivity with a maximum of the locally measured values of 6.3 × 10⁻⁴ S cm⁻¹ and a minimum of 2.6 × 10⁻⁴ S cm⁻¹. One reason behind these conductivity variations is most probably a compositional gradient in the sample. In addition, microelectrodes are very sensitive to conductivity changes near to the surface. This was used to investigate the effect of moisture in ambient air on the conductivity variations of LLZO. Substantial changes of the measured Li-ion transport resistance were found, particularly for smaller microelectrodes which probe sample volumes close to the surface.