Quantitative resolution of grain boundary impedance in Ce-doped Li7La3Zr2O12 through the distribution of relaxation time analysis and electrochemical performance in quasi solid-state batteries

Li7La3Zr2O12 (LLZO) garnets have many characteristics that make these materials a good solid electrolyte for Li-ion batteries, but their poor interfacial properties and limited ionic conductivity continue to limit their widespread applications. In this study, Ce-doped LLZO has been comprehensively analyzed through x-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), tunneling electron microscopy-energy dispersive spectroscopy (TEM-EDS), impedance spectroscopy with distribution of relaxation times, and testing of cell experimentally. XRD confirmed the dominant cubic phase with minor Ce-rich secondary phase, while SEM/TEM-EDS shows dense grains with flaky structure along with the homogeneous distribution of elements. Electrochemical testing of symmetric cell indicates lower polarization voltage and stability up to 700 h, while quasi solid-state battery with LiFePO4 as cathode leads to capacity retention of 72% after 24 cycles.