Mixed glass former effect of 0.5 Na2S + 0.5[xSiS2 + (1-x) PS5/2] and 0.67 Na2S + 0.33[xSiS2 + (1-x) PS5/2] glass systems

Watson, Deborah
Major Professor
Steve W. Martin
Committee Member
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Materials Science and Engineering

With the growing interest in using renewable energy resources such as wind and solar to generate and harvest electricity, there is a demand to develop new electrical energy storage systems to accommodate the growth. All solid state sodium batteries may be one potential solution for this demand as sodium has a high natural abundance and low cost compared to lithium, making it a great candidate for solid state batteries in large grid scale applications. In order for this goal to be realized, research into electrolyte materials to allow the use of high energy dense sodium metal is imperative.

This research studies two mixed glass former yNa2S + (1-y)[xSiS2 + (1-x)PS5/2] systems (y= 0.50 & 0.67) as potential models for glassy electrolytes. The mixed glass former effect is a nonlinear, non-additive change in the physical properties of the glass that may lead to an increase or decrease in the properties. The y = 0.50 system exhibits a negative MGFE in the glass transition temperature (Tg). The structural analysis via Raman, Infrared and 29Si and 31P magic angle spinning nuclear magnetic resonance showed the non-equal sharing of Na+ between the P and Si glass formers in the y = 0.50 where the Na+ preferentially associates with P short range order (SRO) structures over Si SRO structures. The immediate depolymerization is what leads to a minimum in Tg(s). In the y = 0.67 system a weak negative MGFE is observed in the Tg, density while exhibiting a positive MGFE in the ionic conductivity. The SRO of these glasses contain fully depolymerized, non-networking structures and an excess of Na2S which lead to a negative MGFE in these properties.