Sintering temperature, excess sodium, and phosphorous dependencies on morphology and ionic conductivity of NASICON Na3Zr2Si2PO12

Abstract

The phase pure NASICON Na3Zr2Si2PO12 materials were synthesized through solid-state synthesis method at different temperatures ranging from 1100 to 1280 °C to understand the effect of final sintering temperature on the material properties. The structural and morphological characterizations were carried out using powder X-ray diffraction and scanning electron microscopy. The electrical characterizations were performed using AC impedance spectroscopy. The highest ionic conductivity of 1.13 mS cm−1 at 20 °C was observed for the NASICON sample, which was sintered at 1100 °C for 12 h using 10 wt% excess sodium precursor NaNO3. The density of the samples appeared to be similar irrespective of the final sintering temperatures. The decrease in conductivity with increase in sintering temperature might be due to the loss of volatile components at high temperature. It is shown by our systematic studies that adding excess Na content alone, rather than adding excess Na and P contents to compensate for the volatile loss, is ideal in synthesizing dense NASICON materials, while keeping the sintering temperature at 1100 °C for 12 h via the solid-state synthesis method. A promising electrochemical stability was observed during the galvanostatic stripping-platting experiment for one of the compositions. This class of materials forms the basis for a sodium-ion electrolyte for all-solid-state sodium-ion secondary battery.