Effect of sodium salt in poly(ethylene oxide) electrolyte on initial discharge capacity of Na/poly(ethylene oxide)/S battery

Abstract

To investigate the effects of sodium salt in a poly(ethylene oxide) (PEO) electrolyte on the initial discharge properties of a Na/S cell, various concentrations of NaCF3SO3 from 0.1 to 2.0 m were added to the electrolyte. Scanning electron microscopy and differential scanning calorimetry results showed a continuous decrease in the crystallinity of the PEO electrolyte with increasing amounts of sodium salt. The ionic conductivity of the PEO electrolyte at 70 degrees C increased with increasing sodium salt concentration up to 0.33 m, at which point the highest ionic conductivity of 1.732 x 10(-4) S cm(-1) was obtained. However, the ionic conductivity decreased at 2.0 m sodium salt. The same trend was seen in the initial discharge capacity, in that the highest value of 435 mAh g(-1) was achieved at a sodium salt concentration of 0.33 m. These results demonstrate that 0.33 m of sodium salt is the optimum composition for Na/S batteries.