Resolving transport effects in highly coherent LLZO electrolytes and interfaces in thin-film-based solid-state batteries by electrochemical impedance spectroscopy

Li7La3Zr2O12 (LLZO) and its doped compounds are among the most promising solid-state electrolytes for the new generation of Li metal batteries. LLZO can host fast Li-ionic transport in its structure along with preferential crystalline planes and orientations. The materials’ electrical properties and degradation effects strictly depend on structural and microstructural features. To realize the commercialization of Li metal batteries, the high ionic conductivity of the solid-state electrolyte (SSE) material is crucial. In this MSC project, we will use electrochemical impedance spectroscopy (EIS) to characterize LLZO epitaxial thin-film materials. LLZO thin films are deposited by pulsed laser deposition (PLD). Deposition conditions and substrates are used to tune the crystallographic and microstructural features such as grain boundaries and size. We use EIS with micro-and reference electrodes to map the electrochemical of the films. The analysis of the EIS data includes the formulation of basic equivalent circuit modelling by fitting and Arrhenius plots. The model is formulated by complex impedance spectra fittings to extract the resistance and capacitance parameters that control the ionic transport in the film. We will thus compare polycrystalline and highly coherent films. We characterise the effective ionic conductivity that accounts for the bulk and grain boundary contributions and conductivity along different crystallographic orientations. To verify the consistency of these values and estimate degradation effects, we will fit complex electric modulus formalism to extract the effective ionic conductivity of the different microstructural features.