Enhanced ionic conductivity of NASICON-type NaTi₂(PO₄)₃ solid electrolytes with sodium-ion conduction: based on NaF-assisted synthesis

The ceramic composite electrolytes in the NaTi 2 (PO 4 ) 3 –NaF system were characterised by thermal analysis, X-ray diffraction, Fourier infrared absorption spectroscopy, scanning electron microscope, and impedance spectroscopy. X-ray diffraction confirmed that the ceramic composites have a Na Super Ionic Conductor (NASICON) structure. The scanning electron images showed that the addition of NaF significantly improved the microscopic morphology of the NaTi 2 (PO 4 ) 3 crystals and made the packing of crystal grains closer. The addition of NaF in a certain proportion is beneficial to the growth of crystals, making the crystal grains more compact and improving the density of the solid electrolytes. The ionic conductivity analysis was carried out by alternating current (AC) impedance spectroscopy. The conductivity can be effectively improved when a certain proportion of NaF is added to the ceramic composites. The maximum total conductivity is about 1.50 × 10 −5 S·cm −1 obtained when the molar ratio of NaF to NaTi 2 (PO 4 ) 3 reaches 0.4.