Clearly, within the battery community lithium lanthanum titanate (LLTO) is the most prominent Li + conductor of the perovskite family. The studies of Bezou et al. and Inaguma et al. are commonly referred to as the first ones reporting an A-site deficient perovskite structure for Li 3x La 2/3-x TiO 3 (0.04 < x < 0.17) and bulk ionic conductivity of ∼ 10 -3 S/cm at room temperature. It has been widely acknowledged and theoretically confirmed 119 that the diffusion proceeds via a vacancy mechanism where Li + migrates through a bottleneck made up of four O-ions which expands in size during the diffusion process (Figure ).