Ionic conductivity and microstructural characteristics of NASICON-type solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ affected by synthesis and manufacturing processes for all solid-state battery

This study investigated the synthesis properties of Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) with respect to heat treatment, and analyzed the ion conductivity properties in relation to the fabrication methods. The LATP powders (LATP_600 and LATP_700) calcined at 600 and 700 °C showed various secondary phases such as LiTiPO₅ and AlPO₄ along with the LATP phase. However, calcination at 800 °C for 2 h (LATP_800) resulted in the formation of only the LATP phase. When sintering at the same temperature (800 °C) after various calcination temperatures, LiTiPO₅ did not occur in LATP_600–800, but did occur in LATP_700–800 and LATP_800–800. The ion conductivity characteristics of the LATP prepared by compression molding and tape casting methods revealed that the pellet LATP_800–800 and tape LATP_800–800 showed excellent total ion conductivity values of 7.7 × 10^− 4 S/cm and 9.7 × 10^− 4 S/cm at 25 °C. Specimens produced by compression molding showed abnormal grain growth (AGG), while those produced by tape casting exhibited a dense grain structure with suppressed AGG. Therefore, changing the specimen production method from compression molding to tape casting improved both the ion conductivity and microstructural properties of the synthesized LATP.