A novel Bi-doped borosilicate glass as sealant for sodium sulfur battery. Part 1: Thermophysical characteristics and structure

A novel Bi-doped borosilicate glass has been developed as sealant for sodium sulfur battery. The thermophysical characteristics like thermal expansion coefficient, glass transition and softening temperatures, viscosities and densities of the Bi-doped and undoped glasses are systematically studied. It is found that the thermal expansion match between the Bi-doped glasses and alpha-alumina/beta-alumina is satisfactory. The Bi-doped glass has a viscosity around 105 Pa s in 800–850 °C range, which is suitable to allow a good bonding with the sealed parts. The FTIR analysis indicates that the substitution of Bi2O3 for SiO2 makes the glass network less rigid. Bi2O3 builds the glass network as [BiO6] unit. [BO4] unit enters the glass network and induces the overlapped vibrations of [BO4] unit and [SiO4] tetrahedron. The Bi-doped glass sealant exhibits superior chemical compatibility with alpha-alumina and beta-alumina.