Conductivity behavior of Na5YSi4O12 and its typical structural analogues by solution-assisted solid-state reaction for solid-state sodium battery

Solid-state electrolytes for sodium batteries have been studied for many years, however, have not advanced much since at ambient temperature solid-state electrolytes still exhibit a magnitude huge gap in ionic conductivity than the commercial organic liquid electrolytes. In this paper, the solid-state electrolyte Na5YSi4O12 (NYS) is synthesized employing the solution-assisted solid-state reaction (SASSR) method with the ionic conductivity (σt) reaching up to 1.52 mS cm-1 sintered at 1050°C for 6h, demonstrating a significant progress improvement over the conventional solid-phase reaction method. On this basis, Y3+ is further substituted with the other Lanthanides including Yb3+, Dy3+, Gd3+, Eu3+, and Sm3+ to form the solid electrolytes Na5MSi4O12(M= Yb3+, Dy3+, Gd3+, Eu3+, and Sm3+). The conductivity evolution is found increasing with the increase in the ionic radius of the substituted elements. The X-ray diffractometer analysis reveals a wider sodium ion transport channel and larger ionic radius which lead to higher sodium ion concentration. However, the sintering temperature and impurity phase are reduced with an increase in ionic radius. Notably, among the six solid-state electrolytes, Na5SmSi4O12(NSS) exhibits the highest conductivity of 2.41 mS cm-1 and the lowest sintering temperature of 950°C. The low sintering temperature and high ionic conductivity make NSS a fast sodium conductor that can meet industrial needs.