From Synthesis to Battery Cell Integration of Al-doped Li7La3Zr2O12 Solid Electrolyte

The main aim of this work is to study the capability of synthesizing a garnet type Al-doped Li7La3Zr2O12 ceramic achieving a Li-ion conductivity in the order of 0.1 mS cm-1 at room temperature and to integrate the material as an electrolyte in a full battery cell. Nebulized spray pyrolysis is chosen as the synthesis method resulting in nanocrystalline starting powder. Further heat treatment using conventional sintering and field assisted sintering, after powder calcination, are used to achieve the cubic garnet modification, which exhibits high ionic conductivity. The synthesis and processing temperatures can be reduced to below 1000 °C, which is an advantage compared to conventional solid state reaction routes because Li loss from the garnet structure increases with increasing temperature. The processing parameters and their influence on the Li loss during calcination, which influences the electrochemical performance, are optimized and the influence of the calcination atmosphere is studied using high temperature X-ray diffraction. The solid electrolyte is characterized by means of scanning electron microscopy and transmission electron microscopy combined with energy dispersive X-ray spectroscopy for microstructural imaging and elemental mapping of powders and ceramics. The material properties like phase composition, density, grain size and microstrain are studied and their possible influence on the electrochemical performance is determined. AC-impedance spectroscopy is utilized for temperature dependent conductivity measurements as well as the determination of the area specific resistance of the interface between the solid electrolyte and Li metal in a symmetrical cell configuration. The highest total Li-ion conductivity achieved is 0.77 mS cm-1 and the best area specific resistance is calculated to 30.7 Ω cm2, both values are amongst the best reported in the literature to date. Al-doped Li7La3Zr2O12 is integrated in full battery cells using a melted Li metal anode and different cathodes, e.g., a thin film LiCoO2 cathode resulting in a full all-solid-state battery operational at room temperature and a slurry-based cathode resulting in a hybrid cell containing a small amount of liquid electrolyte; both battery cells present novel approaches towards an industrially applicable solid‑state battery cell