Evaluating ionic conductivity in DMSO − NaCF3SO3 electrolytes: the role of charge carrier concentration and mobility

Understanding the factors that influence conductivity changes in electrolyte systems due to salt doping is important for optimizing their performance. This work quantitatively evaluated key transport parameters, namely diffusivity (D), mobility (µ), and concentration (n) of charge carriers, and the Stokes drag coefficient (F_d) using the Nyquist plot fitting method. A liquid electrolyte system with varying concentrations of sodium trifluoromethanesulfonate (NaCF₃SO₃) in dimethyl sulfoxide (DMSO) was prepared. The conductivity increased from 1.00 × 10⁻² S cm⁻¹ (L1 electrolyte containing 0.6 M NaCF₃SO₃) to 1.14 × 10⁻² S cm⁻¹ (L3 electrolyte containing 1.0 M NaCF₃SO₃), driven by an increase in n from 6.70 × 10²⁰ cm⁻³ (L1 electrolyte) to 7.43 × 10²⁰ cm⁻³ (L3 electrolyte), indicating increased ion dissociation within the electrolyte. The conductivity decreased to 1.03 × 10⁻² cm⁻³ (L4 electrolyte containing 1.2 M NaCF₃SO₃) due to decrease in both µ and D, from 9.54 × 10⁻⁵ to 6.94 × 10⁻⁶ cm² V⁻¹ s⁻² and from 2.47 × 10 to 1.79 × 10⁻⁶ cm² s⁻¹, respectively, due to the higher availability of free ions in the electrolyte. The F_d values also increased, indicating increased viscosity and reduced ion movement. These findings suggest that the conductivity variations for DMSO − NaCF₃SO₃ liquid electrolytes are primarily influenced by µ, D, and F_d, rather than n.