NASICON-type Li_1.5Al_0.5Ge_1.5(PO₄)₃ Containing Amorphous Phase for Solid Li-Ion Conductor (Supporting Information)

Amorphous Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP), which is an oxide-based solid electrolyte with a NASICON-type structure, was sintered at various temperatures to investigate its ionic conductivity and potential windows. The LAGP sheet sintered at 600 °C exhibited a slightly diminished ionic conductivity in comparison to that sintered at 800 °C; however, it effectively suppressed the current density value for oxidative decomposition around 5 V vs. Li⁺/Li. The crystal structure of the sintered LAGP sheets was confirmed using X-ray diffraction (XRD) and Raman spectroscopy. The results showed that the LAGP sheet sintered at 600 °C contained both crystalline and amorphous phases of LAGP. It was considered that the oxidation resistance of the solid electrolyte was improved by sintering at 600 °C owing to the mixture of crystalline and amorphous phases of LAGP.