Investigation on the applicability of high Na-ion conducting Na3+x[ZrxSc2-x(PO4)3] glass-ceramic electrolyte for use in safer Na-ion batteries

Abstract

Various glass samples with general formula Na3+x[ZrxSc2-x(PO4)3] (x = 0, 0.25, 0.5 and 0.75 mol%) have been synthesized using the melt quenching technique. The as synthesized glass samples have been heat treated at and above their crystallization temperatures for different heat treating schedules (3, 5, 10, 15 and 20 h). The major crystalline phases such as Na3Sc2(PO4)3 (ICSD-27740) (NASICON), ZrO2 (ICSD-66781) and Zr2O(PO4)2 (ICSD-15084) have been observed in XRD traces of all the glass-ceramic samples. The glass-ceramic sample containing x = 0.5 mol% of ZrO2 (Na3.5Zr0.5Sc1.5(PO4)3) precipitates as only one major NASICON type phase (Na3Sc2(PO4)3) with high intensity which creates large number of vacancies with positive deficiency due to the partial replacement of the Zr4+ ions with Sc3+ ions. The impure crystalline phases (ZrO2 and Zr2O(PO4)2) which are precipitated in the glass-ceramic samples, expected to block the conduction pathways for the migration of Na+ ions between grains of glass network resulting in reduction in the bulk conductivity. The bulk conductivity ((σb = t/(Rb·A)) obtained by using bulk resistance (Rb) is the highest (σ = 9.47 × 10−4 S/cm) for the Na3.5Zr0.5Sc1.5(PO4)3 glass-ceramic sample (heat treated at 1023 K for 10 h), measured at 303 K and also retained its higher chemical stability when exposed to air even up to 60 days.