Transference number calculations for sodium polysulfides
Transference number calculations for sodium polysulfides Transference numbers of sodium cations and sulfur anions in sodium polysulfide melts are calculated from previously determined experimental data. Concentrated electrolyte theory assuming a binary electrolyte consisting of sodium anions, sulfide cations, in a neutral sulfur solvent is used to relate the transference numbers to fundamental solution transport properties. Slopes of open-circuit potential measurements vs. melt composition on sodium-sulfur cells with and without transference are used to determine the sulfur anion and sodium cation transference numbers. The transference number of sodium cations is calculated from previous experimental data for two temperatures, 573 and 633 K, and range from 0.88 to 0.93 for sodium sulfide mole fractions between 0.20 and 0.34. These values for transference numbers presented here are more accurate than previous interpretations of these data where unity sodium cation transference numbers were assumed. The results of this work are shown to be important in the design of sodium-sulfur cells.
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