Lithium Ion Conductivities of NASICON-type Li1+xAlxTi2−x(PO4)3 Solid Electrolytes Prepared from Amorphous Powder Using a Mechanochemical Method

Amorphous (a-LATP) powders with various nominal compositions of Li1+xAlxTi2−x(PO4)3 (x = 0, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6) in the Li2O-Al2O3-TiO2-P2O5 (LATP) system, were prepared directly from a mixture of Li2O, γ-Al2O3, anatase-type TiO2, and P2O5 as the starting powder, using mechanical milling (MM) at room temperature. Crystalline LATP (c-LATP) powder with a NASICON-type structure was formed by the heat treatment of mechanochemically prepared a-LATP powder. In addition, heat-treated c-LATP (x = 0.5, 0.6) powders included an impurity phase of crystalline Li5AlO4. The sintered c-LATP (x = 0) pellet without Al3+ doping exhibited a low electrical conductivity on the order of 10−7 S cm−1 at room temperature. On the other hand, the sintered Al3+-doped c-LATP (x = 0.3, 0.4, 0.45, and 0.5) pellets showed high electrical conductivities on the order of 10−4 S cm−1 at room temperature. The sintered c-LATP (x = 0.45) pellet exhibited the highest lithium ion conductivity (2.9 × 10−4 S m−1) at 25°C and the lowest activation energy (30 kJ mol−1).