Mixed glass former effect in borate and thioborate sodium-ion conducting glass systems
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As alternative energy sources continue to increase their production, there becomes a higher demand for cost-effective, safe, and energy efficient grid storage. Solid-state batteries are becoming of increased attention due to the demands for grid storage of alternative energy production, especially on days when these sources are under producing. As these solid-state batteries are being developed, many aspects of these batteries are being researched to optimize safety, cost-effectiveness and energy density. Current lithium-ion batteries have been scrutinized due to their safety concerns utilizing a flammable, liquid electrolyte. These concerns may be limited by replacing these organic, liquid electrolytes with an inorganic solid-state electrolyte. Of particular interest are glassy electrolytes. Glassy solid-state electrolytes prove to be an advantageous competitor due to the relatively low manufacturing costs and increased safety. In addition, properties of these electrolytes (i.e ionic conductivity, density, glass transition temperature, etc.) can be modified due to the mixed glass former effect (MGFE) which occurs when varying the ratio of glass formers from one binary system to the other through a ternary system. Physical and electrochemical properties vary in a non-linear, non-additive trend as the composition, and subsequently the structure, is changed. The structure and physical properties of three glass systems, 0.2Na2O + 0.8[xBO3/2 + (1-x)GeO2], 0.6Na2S + 0.4[xBS3/2 + (1-x)GeS2], and 0.6Na2S + 0.4[xBS3/2 + (1-x)SiS2], have been examined in an attempt to understand the MGFE. By examining an oxide and a sulfide system, it will be seen how substituting one anion for another affects the structure and the physical properties of these glassy solid-state electrolytes. The glass structure was examined through Raman, infrared and NMR spectroscopies. Glass transition temperature was obtained through differential scanning calorimetry. Ionic conductivities were obtained using impedance spectroscopy. Densities were obtained using the Archimedes method.