The Electrical Conductivity of Sodium Polysulfide Melts

Abstract

The sodium polysulfide melt has been described by a macroscopic mode_. This model considers the melt to be composed of sodium cations, monosulfide anions, and neutral sulfur solvent. The transport equations of' concentral,_l.solution theory are used to derived the governing equations for this binaryelectrolyte melt model. These equations relate measurable transport propc_es to fundamental _,msport parameters, The focus of this research is to measure the electrical conductivity of sodium polysulfide melts and calculate one of fu,ndamenudtransport parameters from t_e experimental data, The conductance cells used in the conductivity measurements are axisymmetric cylindrical cells with a rrficroelectrcrteo The electrode effects, including double-layer capacity, charge transfer resistance, and concentration overpotential, were minimized by the use of tt_e alternating current at an adequately high frequency. The high cell constants of the conductance cells not only enhanced the experimental accuracy but also made the elecu'ode effects negligible, The elecuical conductivities of sodium poly_ulfide Na2S,_and Na2S5 were measured as a function of temperature (range: 300 to 360°C). Variations between experiments were only up to 2%. The values of the Arrhenius activation energy derived from the experimental data are about 33 kJ/mol. The fundamenta.l transport parameter which quantifies the interaction within sodium cations and monosulfide anions are of interest and expected to be positive. 'Values of it were calculated from the experimental conductivity data and most of them are positive. Some negative values were obtained ,, probably due to the experimental errors of transference number, diffusion coefficient, density or conductivity data.

Na-Mediated Stoichiometry Control of FeS2 Thin Films: Suppression of Nanoscale S-Deficiency and Improvement of Photoresponse

“…This outcome was probably due to the sodium polysulfide NaS x which has a low melting temperature, existing together with Na 2 SO 4 . 35 This compound might exist at the film surface in a liquid form during sulfurization, enhancing growth of the surface grains before it is completely eliminated during the washing step. 2.2.…”

Operational Strategies to Improve the Performance and Long‐Term Cyclability of Intermediate Temperature Sodium‐Sulfur Batteries

“…Extending the charging process beyond Na 2 S 8 will hamper the conductivity on account of the formation of the insulating S (S 8 ) phase [53] . Upon subsequent discharge, the conductivity decreases, signifying the electrochemical reduction of Na 2 S 8 to Na 2 S 5 and then to Na 2 S 4 [54] …”

“…[53] Upon subsequent discharge, the conductivity decreases, signifying the electrochemical reduction of Na 2 S 8 to Na 2 S 5 and then to Na 2 S 4 . [54] A cell containing 0.5 M Na 2 S 5 in TEGDME is subjected to EIS measurements throughout periodic intermediate stages (labeled C 1 to C 5 ) of galvanostatic charging, as illustrated in (Figure 5b) until C 3 , in line with the conductivity data. [24,25] Going beyond C 3 , the cell impedance increases, possibly due to the conversion of Na 2 S 8 into S 8 .…”

High and intermediate temperature sodium–sulfur batteries for energy storage: development, challenges and perspectives

“…5 Â 10 À30 U cm À1 , while that of for Na 2 S 5 and Na 2 S 3 are of the order 0.18 and 0.41 U cm À1 , respectively. 77,78 Diffusion coefficients (D) on poly-sulde melts at the single phase region (between Na 2 S 3 and Na 2 S 5 ) at 350 C linger between 1 Â 10 À5 cm 2 and 6 Â 10 À7 cm 2 s À1 for Na 2 S 5 . In the case of Na 2 S 4 , D was reported equal to ca.…”