Structural analysis and electrical characterization of cation-substituted lithium ion conductors Li1−xTi1−xMxOPO4 (M = Nb, Ta, Sb)

Recent work has shown an increased interest in lithium titanium oxide phosphates as possible anode materials for lithium ion batteries. However, the intrinsic transport properties of these materials have not been studied yet. In this work, we employ X-ray diffraction and electrical impedance spectroscopy to characterize lithium titanium oxide phosphate LiTiOPO4. In order to better understand the transport of lithium ions, substitution with metal cations of different charges and different radii are used to elucidate changes in the crystal structure and their effects on the lithium ion conductivity. We show that substitution of the transition metal has a small influence on the ionic conductivity only, but comes with a noticeable impact on the activation energy. In addition to the experimental work, density functional theory calculations are employed to provide possible diffusion pathways and mechanism, and explain the decrease in the activation barriers for ionic motion.