Pristine NASICON Electrolyte: A High Ionic Conductivity and Enhanced Dendrite Resistance Through Zirconia (ZrO) Impurity-free Solid-Electrolyte Design.

Sodium batteries are considered a promising candidate for large-scale grid storage at tropical climate zone, and solid-state sodium metal batteries have a strong proposition as high energy density battery. The main challenge is to develop ultra-pure solid-state ceramic electrolyte and compatible metal interface. Here, a scalable and energy-efficient synthesis strategy of sodium (Na) Super Ionic CONductor, NaZrSiPO (x = 2, NZSP) solid electrolyte, has been introduced with the complete removal of unreacted zirconium oxide (ZrO) impurities. Additionally, the reaction mechanism for the formation of pure phase NZSP is reported for the first time. The NZSP prepared by utilizing the Zr precursor, i.e., tetragonal zirconium oxide (t-ZrO) derived from the Zr(OH) gets quickly and completely consumed in the synthesis process leaving no unreacted monoclinic ZrO impurities. The synthesis process only needs a minimum stay of 4 h, which is three times less than the conventional synthesis method. The elimination of ZrO impurities results in a 2.5-fold reduction in grain boundary resistivity, showcasing a total ionic conductivity of 1.75 mS cm at room temperature and a relative density of 98%. The prepared electrolyte demonstrates remarkable resistance to dendrite formation, as evidenced by a high critical current density value of 1.4 mA cm.