Impact of sintering temperature and ascertaining hopping bottlenecks for ions in sodium superionic conducting electrolyte for sodium-ion batteries

Recently, sodium super-ionic conducting (NASICON) type solid electrolytes have gained attention for next generation batteries because of their high ionic conductivity, low cost, excellent chemical and electrochemical stability. Therefore, in the present study, NASICON-type solid electrolyte Na3Zr2Si2PO12 is synthesized by so-lution assisted-solid state reaction (SA-SSR) route. The electrolytes are sintered at three different temperatures, 1200 degrees C, 1250 degrees C and 1300 degrees C. The sintered electrolytes are characterized by various experimental techniques. The Rietveld refinement of X-ray diffraction pattern of prepared electrolytes revealed the monoclinic crystal structure. The 3-dimension hopping channel for sodium ion migration through triangular bottleneck area is identified. From complex impedance spectroscopy measurement, the highest bulk and grain boundary conduc-tivity are found, & SIM; 4.05 mS cm  1 and & SIM; 0.31 mS cm  1, respectively, for the sample sintered at 1250 degrees C. The optimized electrolyte shows wide electrochemical stability (-6.5 V) which is suitable for high voltage battery application. Using optimized electrolyte, sodium half-cell is fabricated with sodium metal as anode, and Na3V2P3O12 (NVP) as cathode. The assembled cell delivers maximum discharge capacity & SIM; 101.6 and & SIM; 84.5 mAh g  1 at the current density 10 and 40 mA g  1, respectively with good capacity retention (-95.02%) upto 50 cycles.