Synthesis of Superionic Conductive Li_1+x+y Al_x Si_y Ti_2−x P_3−y O₁₂ Solid Electrolytes

Commercial lithium-ion batteries using liquid electrolytes are still a safety hazard due to their poor chemical stability and other severe problems, such as electrolyte leakage and low thermal stability. To mitigate these critical issues, solid electrolytes are introduced. However, solid electrolytes have low ionic conductivity and inferior power density. This study reports the optimization of the synthesis of sodium superionic conductor-type Li_1.5 Al_0.3 Si_0.2 Ti_1.7 P_2.8 O₁₂ (LASTP) solid electrolyte. The as-prepared powder was calcined at 650^◦ C, 700^◦ C, 750^◦ C, and 800^◦ C to optimize the synthesis conditions and yield high-quality LASTP powders. Later, LASTP was sintered at 950^◦ C, 1000^◦ C, 1050^◦ C, and 1100^◦ C to study the dependence of the relative density and ionic conductivity on the sintering temperature. Morphological changes were analyzed using field-emission scanning electron microscopy (FE-SEM), and structural changes were characterized using X-ray diffraction (XRD). Further, the ionic conductivity was measured using electrochemical impedance spectroscopy (EIS). Sintering at 1050^◦ C resulted in a high relative density and the highest ionic conductivity (9.455 × 10⁻⁴ S cm⁻¹ ). These findings corroborate with the activation energies that are calculated using the Arrhenius plot. Therefore, the as-synthesized superionic LASTP solid electrolytes can be used to design high-performance and safe all-solid-state batteries.