Microstructural Tuning of Solid Electrolyte Na₃Zr₂Si₂PO₁₂ by Polymer-Assisted Solution Synthesis Method and Its Effect on Ionic Conductivity and Dielectric Properties

NASICON-type Na3Zr2Si2PO12 (NZSP) has emerged as a promising solid-state electrolyte for all-solid-state Na batteries. The ionic conductivity of NZSP is found to be dependent on the processing of the material. Multistep mixing and sintering at elevated temperatures (1200 °C) for long hours have been shown to be detrimental to the electrolytic properties of NZSP because of the precursor imbalance in the compound and thereby the formation of unwanted secondary phases. In the present work, a straightforward polymer-assisted solution synthesis (PASS) route is proposed for development of highly conducting single-phase NZSP. Because of the capping effect, the polymer not only prevents an imbalance of precursors in the system but also allows achievement of high density in the system. Furthermore, the presently reported PASS method confers better control over the microstructure and conductivity of the NZSP samples. The role of polymer and sintering condition on the phase purity and microstructure and hence on the conductivity is thoroughly studied by X-ray diffraction (XRD), field-emission scanning transmission electron microscopy (FE-SEM), energy-dispersive X-ray (EDAX), X-ray photoluminescence spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS) and discussed. The detailed ionic conduction mechanism is further studied using frequency-dependent ac impedance analysis. The suitability of the presently reported NZSP as a solid-state electrolyte is examined by cyclic voltammetry and galvanostatic sodium stripping–plating experiments.