Effect of Nb substitution on structural, electrical and electrochemical properties of LiTi₂(PO₄)₃ as electrolyte materials for lithium ion batteries

The NASICON (Na Super Ionic CONductors)-type materials are good ionic conductors when serving as solid electrolytes for lithium–ion batteries. In this paper, Nb-doped LiTi2(PO4)3 has been synthesized by solid-state reaction method and the structural, vibrational and dielectric studies are systematically investigated. The X-ray diffraction conforms that the Nb-doped LiTi2(PO4)3 compound has NASICON structure, i.e. rhombohedral with space group R-3c. The average crystallite size and lattice constant are increased with dopant concentration. The grain sizes of the synthesized compounds are investigated by scanning electron microscope and it is found to be in the range of 5 μm. From Fourier-transform infrared spectroscopy spectra, stretching vibrations of P-O-P bond are identified in the region of 700–750 cm−1. AC electrical study is carried out by exploiting the impedance and dielectric spectroscopy. The activation energy increases with dopant concentration since ion diffusion becomes easy as the volume fraction of the grain increases. Non-Debye behavior of conductivity relaxation is reflected in the modulus analysis.