Lithium Ion Conductivities of NASICON-type Li_1+xAl_xTi_2−x(PO₄)₃ Solid Electrolytes Prepared from Amorphous Powder Using a Mechanochemical Method

Abstract

Amorphous (a-LATP) powders with various nominal compositions of Li_1+xAl_xTi_2−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).