Abstract <p>Lithium-based materials play a crucial role in modern energy storage systems because of their excellent electrochemical characteristics. Ongoing advancements in lithium batteries have significantly enhanced energy density, safety, and cycling stability. Among various emerging technologies, all-solid-state batteries have gained considerable attention as they eliminate the use of liquid electrolytes, thereby improving both safety and durability. Nevertheless, their performance is often limited by low ionic conductivity. NASICON-type electrolytes, such as Li_1.3[X]Ti_1.7(PO₄)₃ (where X represents divalent, trivalent, or tetravalent cations), exhibit outstanding chemical stability and high Li⁺ ion mobility. In this work, Li_1.3[X]Ti_1.7(PO₄)₃ compounds were synthesized using melt-quenching, grinding, uniaxial pressing, and sintering techniques. The structural and morphological properties were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrical characteristics were investigated through impedance spectroscopy in the frequency range of 10 Hz–20 MHz and the temperature range of 303–723 K. The heat-treated samples crystallized into the LiTi₂(PO₄)₃ phase, and variations in lattice parameters were found to depend on the ionic radius of the dopant. Doping affected the M1–M2 bottleneck, influencing Li⁺ transport pathways. Appropriate dopant incorporation led to enhanced porosity and improved ionic conductivity. Notably, Al-doped LTP achieved a high ionic conductivity of 0.82 × 10^–4 S/cm at 550°C, marking a substantial enhancement in Li⁺ conduction. These results indicate that LTP-based solid electrolytes are strong contenders for next-generation energy storage applications, particularly all-solid-state lithium batteries, owing to their excellent thermal stability, high ionic conductivity, and ease of synthesis.</p>