Performance of perovskite-type Li-ion solid electrolyte Li_2x−ySr_1−xTi_1−yNb_yO₃

All-solid-state lithium batteries are recognized as the next-generation energy storage batteries due to their high energy density and high security, to which researchers have paid more attention. All-solid-state lithium batteries are composed of solid materials, and the Li-ion solid electrolytes do not contain flammable and explosive organic solvents, which can enhance the safety of the battery. As important components, Li-ion solid electrolytes are widely studied in all-solid-state lithium batteries, which currently include Li-superionic solid electrolyte (LISICON), Na-superionic solid electrolyte (NASICON), garnet-type solid electrolyte, perovskite-type solid electrolyte, sulfide-type solid electrolyte, and polymer solid electrolyte. Li-ion solid electrolytes generally have the advantages of high Li-ion conductivity, low electronic conductivity, wide operating temperatures, wide electrochemical windows, and inhibition of lithium dendrite growth. Among the solid electrolytes, the perovskite-type solid electrolytes have a wide tolerance factor that allows most elements to dope into the ABO₃ structure. Additionally, the perovskite-type Li-ion solid electrolytes are summarized into two types: (1) the three-component Li_3xLa_2/3−xTiO₃ (LLTO, 0 < x < 1/6) and (2) the four-component (Li, Sr)(A, B)O₃ (A = Zr, Hf, Ti, Sn; B = Nb, Ta). In this paper, the four-component Li_2x−ySr_1−xTi_1−yNbyO₃ (x = 3y/4, y = 0.25, 0.5, 0.6, 0.7, 0.75, 0.8) solid electrolytes were prepared by conventional solid-state reaction method. X-ray diffraction (XRD), scanning electron microscopy, alternating current impedance, and potentiostatic polarization methods were adopted to study the crystal structure, micromorphology, ion conductivity, and electronic conductivity, respectively. XRD analysis show the synthesized samples exhibit a cubic perovskite structure when y≤0.70 with almost no impurity phase formed. Li_0.35Sr_0.475Ti_0.3Nb_0.7O₃ exhibits the highest ion conductivity of 3.62×10⁻⁵ S·cm⁻¹, electronic conductivity of 2.55×10⁻⁹ S·cm⁻¹ at 20 ℃, and activation energy of only 0.29 eV. The LiFePO₄/Li half-cell was fabricated using Li_0.35Sr_0.475Ti_0.3Nb_0.7O₃ as a separator, exhibiting a capacity of 93.9 mA·h·g⁻¹ and a retention capacity of 90.72% after 100 cycles.