Sol-gel processing of Li1.5Al0.5Ti1.5(PO4)3 solid electrolyte thin films via polymeric complex precursor

Thin films of crack-free lithium ionic conductive Li1.5Al0.5Ti1.5 (PO4)(3) (LATP) solid electrolyte could be fabricated by a modified Pechini-type polymeric precursor method with controlled amount of citric acid (CA), pH, and viscosity of precursor at low temperatures between 600 and 700 A degrees C. It turned out that the increase in molar ratio of citric acid to total metal salts (M) in the precursor gave drastic change of thermal reactions and crack-free LATP thin films could be obtained from the precursor with CA/M = 5. In addition, the formation of LATP crystal phase required the viscosities more than 0.100 Pa s. It was also found that the pH control of the coating solutions was a key step to obtain homogeneous thin films. FT-IR measurements revealed that the change of pH in the precursors gave structural changes in precursor complexes. The LATP thin film of 200 nm in thickness prepared from the solution at CA/M = 5, 0.100 Pa s, and pH = ca. 10, sintered at 650 A degrees C showed an ionic conductivity of ca. 0.029 S/cm at 300 A degrees C.