Synthesis and Li- ion Transport mechanism of Li_1.4M_0.4N_1.6(PO_04)_3 electrolyte

摘要

Li_1.4N_1.6M_0.4(PO_4)_3 with M = Al, Ga, N = Ti, Ge were prepared by annealing of the mixtures at 800℃. 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 A and c = 20.820 A, 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℃, 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 Li_1Ti_2(PO_4)_3 and 0.42 eV for N = Al and M = Ti doped compound.