Abstract: In this paper， NASICON-type sodium-ion solid electrolyte Na₃Sc₂（PO₄）₃ was synthesized by solid-state reaction method using scandium oxide， sodium carbonate and ammonium dihydrogen phosphate as raw materials. The effects of scandium oxide content on sintering properties， phase composition， microstructure and ionic conductivity were studied. The electrolytes were characterized using X-ray diffraction （XRD）， scanning electron microscopy （SEM）， and electrochemical performance was tested by electrochemical impedance spectroscopy （EIS）. The results indicate that a proportional NASICON-type Na₃Sc₂（PO₄）₃ is obtained when the scandium oxide content is 21.49% （mass fraction）， at which the synthesized materials exhibits a dense microstructure， high crystallinity， uniform grain size， and the largest unit cell volume. Consequently， it demonstrates the highest room-temperature ionic conductivity of 8.79×10^-6 S/cm. An excess of scandium oxide inhibites grain growth and forms the sodium-deficient Na_2.63Sc₂（PO₄）₃ phase. The sodium vacancies increase， the lattice distortion occurs， the porosity increases， and the ionic conductivity decreases. The lack of scandium oxide causes cell shrinkage and glass phase covering grain boundaries， hindering ion migration， which is also not conducive to ion transport and reducing ion conductivity. Therefore， precise stoichiometric control is critical for optimizing the structure and enhancing the ionic conductivity of NASICON-type Na₃Sc₂（PO₄）₃ electrolytes.

Key words: sodium-ion battery; solid electrolyte; Na₃Sc₂（PO₄）₃; scandium oxide; ionic conductivity; microstructure