Preparation and characterization of Li5ReSi4O12 (Re = Nd, Gd) solid electrolyte

Dense Li5ReSi4O12 (Re = Nd, Gd) ceramic materials with densities of 3.0–3.1 g/cm3 were synthesized by a solid-state reaction method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The conductivity of Li5NdSi4O12 was 1.2 × 10−2 mS/cm at 550 °C and 2.5 × 10−4 mS/cm at 350 °C, respectively, with activation energy of 0.84 eV. Li5GdSi4O12 with activation energy of 0.90 eV had conductivities similar to Li5NdSi4O12, suggesting that neither rare earth ion significantly affected the properties of Li5ReSi4O12.

Research highlightsIt is the first time to report two new Li-ion solid conductors, Li5NdSi4O12 and Li5GdSi4O12, which may be used as solid electrolytes for high-temperature electrochemical devices. The conductivity of the two silicates is over 1.2 × 10−2 mS/cm at 550 °C, which is higher than other high-temperature Li-ion solid electrolytes (e.g. LiSmSiO4). We found that both of the silicates had close density, conductivity and activation energy, suggesting that neither rare earth ion significantly affected the properties of Li5ReSi4O12 (Re = Nd, Gd).