Synergistic Effect of Calcination and Sintering on the Reduction of Grain Boundary Resistance of LATP Solid Electrolyte

The NASICON-type Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP) solid electrolyte is a promising candidate for next-generation lithium-ion batteries due to its high stability in air and moisture, as well as high bulk ion conductivity. However, the grain boundary resistance of LATP limits its overall ionic conductivity, which remains a major obstacle to the commercialization of all-solid-state batteries. In this study, we made efforts to solve the problem by promoting the minimization of voids and the formation of well-defined grain boundaries by controlling the temperature of two heat treatments during the synthesis process. The crystallization temperature was confirmed through thermogravimetric analysis/DTA analysis, and the degree of crystallization was confirmed using XRD analysis. The formation of grain boundaries and the presence of voids were evaluated by cross-sectional SEM images after sintering. After sintering, the LA_900 °C sample, characterized by a high degree of crystallization and well-formed grain boundaries without voids, demonstrated a low bulk and grain boundary resistance, which was confirmed by electrochemical impedance spectroscopy analysis. The result was an ionic conductivity of 1.72 × 10^-4 S/cm. These results provide valuable insights into the facile synthesis of LATP.