Sodium ionic conductivity and stability of amorphous Na₂O·2SiO₂ added with M_xO_y (M = Zr, Y, and Sm)

Amorphous Na₂O·2SiO₂ (A-Na₂O·2SiO₂) is one of the promising sodium ionic conductors for solid-state sodium-ion battery electrolytes owing to its easy preparation and low production cost. However, Na₂O·2SiO₂ glass suffers from relatively low conductivity and poor thermal stability as a result of crystallization and other defects. Herein, we improved the ionic conductivity and thermal stability of A-Na₂O·2SiO₂ by adding this material with metal oxides (M_xO_y, M = Y, Sm, and Zr) at varying loadings. The physical properties and stability of the A-Na₂O·2SiO₂ added with different oxides were systematically investigated. The results indicated that oxide adding on A-Na₂O·2SiO₂ resulted in larger density values that increased with the adding content. Additionally, oxide adding changed the strength of the Si–O bond in A-Na₂O·2SiO₂, thereby affecting the overall network structure and uniformity. Among the different oxides prepared, added with 3 mol% Sm₂O₃, 3 mol% Y₂O₃, and 2 mol% ZrO₂ showed maximum hardness and elasticity modulus values. Additionally, oxide adding on A-Na₂O·2SiO₂ resulted in significantly improved ionic conductivity values. 3 mol% Y₂O₃-added A-Na₂O·2SiO₂ material showed the highest ionic conductivity value (5.2 × 10⁻³ S cm⁻¹) and optimum thermal stability, indicating that Y₂O₃-added Na₂O·2SiO₂ has high potential to be high-performance and stable sodium ionic conductors.