Synthesis and Li- ion transport mechanism of Li1.4[M 0.4N1.6](PO4)3 electrolyte

Abstract

Li1.4N1.6M0.4(PO4)3 with M = Al, Ga, N = Ti, Ge were prepared by annealing of the mixtures at 800°C. X-ray diffraction showed the formation of NASICON phase with space group R-3c along with a minor impurity second phase. Rietveld refinement of the X-ray data was performed to identify the structural variation. The compound with N = Ti and M = Al exhibited lattice parameters a = 8.5015 Å and c = 20.820 Å, slightly lower than for the undoped Ti compound (N = M = Ti). Measurements of σionic were carried out on sintered pellets by impedance spectroscopy at 30°C, highest ionic conductivity 2.57 × 10-4 S/cm among the prepared samples was observed when N = Al and M = Ti, two orders of magnitude higher than for the undoped case. Bond valence approach was applied to visualize the migration pathways of Li+ ion and barrier energies were estimated. Obtained Li site energy landscapes indicate the continuous Li transport pathway accessible with activation energy of 0.45eV for undoped Li1Ti2(PO4)3 and 0.42 eV for N = Al and M = Ti doped compound. ©The Electrochemical Society.