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

Highlights: • Oxides adding can change the network structure and physical properties of A-Na₂O·2SiO₂ significantly. • The ionic conductivity of A-Na₂O·2SiO₂ increased ~5 times by adding 3 mol% Y₂O₃. • The conductivity of 3 mol% Y₂O₃-added A-Na₂O·2SiO₂ at 400 °C almost not changed after 500 h annealing • Conductivity degradation of A-Na₂O·2SiO₂ can be attributed to the crystallization. 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 SiO 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.