Preparation and Electrical Properties of Aluminum-Substituted Lithium Titanium Phosphates By a Novel Sol-Gel Method

The development of solid state electrolytes is regarded as the key point for the next generation of Li batteries. Among the candidates of possible lithium-ion-conductive solid electrolytes, Al-substituted LiTi₂(PO₄)₃ (LATP) were widely investigated as promising materials because of their relatively high ionic conductivity, chemical stability and mechanical strength. Preparation difficulties prevented practical applications of LATP and systematic studies on the processing of such materials are scarce. Moreover, published electrical properties showed a rather large scatter. In this study, LATP powders were easily prepared in kg-level and at low cost by a novel sol-gel method with high phase purity, densification activity and conductivity. So far, the highest ionic conductivity was obtained with Li_1.5Al_0.5Ti_1.5(PO₄)₃. Electrical and microstructural properties of LATP samples with nonstoichiometry in Li and Ti position were also analyzed. Slight Li deficiency or Ti excess is beneficial for the conductivity of the samples. Moisture existing in ambient air is found to mislead the conductivity testing results. Reliable data should be tested in dry atmosphere. At 25 °C the conductivity of Li_1.5Al_0.5Ti_1.5(PO₄)₃ is more than 1 × 10^-3 and 5 × 10^-4 S/cm in ambient atmosphere and dry argon, respectively.