Ionic conductivity of organosulfur melts for advanced storage electrodes

Organosulfur melts show promise as positive electrodes for advanced storage batteries. The attainable energy efficiency and power density of a secondary battery is directly related to polarization losses in the cell under load. One of the contributing factors to polarization of an organosulfur electrode is the rate of ionic transport in the melt. Among the sodium/organosulfur batteries under investigation in this laboratory is the sodium/beta-alumina/(tetraethylthiuram disulfide) cell, in which the product of cell discharge is the thiolate salt, sodium diethyldithiocarbamate (NaDEDC). Accordingly, the ionic conductivity of NaDEDC and related electrolytes in molten tetraethylthiuram disulfide (TETD) has been studied as a function of composition and temperature. The ionic conductivity of a NaDEDC/TETD melt of composition corresponding to 2% discharge of a Na/TETD battery was determined to be 2 x 10/sup -5/ ..cap omega..cm/sup -1/ at 130/sup 0/C which increases to 1 x 10/sup -3/ ..cap omega.. cm/sup -1/ for a melt corresponding to 28% discharge. The discharge data for Na/TETD batteries indicates that ionic conductivity of the positive electrode melt contributes negligible polarization after a few percent of cell discharge, indicating that ionic conductivity in the above range is acceptable for energy-efficient operation of these cells over nearly the entire compositional domain. The relationship between the equivalent conductivity of these melts and concentration is also discussed, as well as the implications of the measured viscosity of the pure TETD melt.