Impact of NaCF3SO3 on charge transfer mechanism in gellan gum–based solid polymer electrolytes

Abstract

Concentration (n), mobility (µ), and diffusivity (D) of charge carriers are the three main properties that profoundly influence not only the ionic conductivity but also the overall performance of solid polymer electrolytes (SPEs). In this work, SPEs incorporating gellan gum (GG) as the host polymer and varying concentrations of sodium trifluoromethanesulfonate, NaCF₃SO₃ (10 to 50 wt.%), were prepared using the solution casting technique. The characteristics of n, µ, and D within the electrolyte samples at room temperature were determined by evaluating the Nyquist plot with equations derived from an electrical equivalent circuit. The conductivity started at (4.27 ± 0.29) × 10⁻⁸ S cm⁻¹ for the free-salt sample (L0 electrolyte) and gradually increased to an optimal value of (1.06 ± 0.99) × 10⁻⁶ S cm⁻¹ in the sample containing 40 wt.% NaCF₃SO₃ (L4 electrolyte). Increasing the NaCF₃SO₃ concentration from 10 to 40 wt.% in GG led to an increase in n from (6.81 ± 0.03) × 10¹⁶ cm⁻³ to (5.61 ± 0.31) × 10¹⁸ cm⁻³ due to enhanced ion dissociation. Conversely, the µ and D decreased from (1.15 ± 0.03) × 10⁻⁵ cm² V⁻¹ s⁻² to (1.19 ± 0.05) × 10⁻⁶ cm² V⁻¹ s⁻² and from (2.97 ± 0.08) × 10⁻⁷ cm² s⁻¹ to (3.06 ± 0.13) × 10⁻⁸ cm² s⁻¹, respectively, attributed to increased collisions between free ions. The value of Stokes drag coefficient (F_d) increased from (1.40 ± 0.02) × 10⁻¹⁴ kg s⁻¹ to (1.35 ± 0.05) × 10⁻¹³ kg s⁻¹ due to the low charge carriers mobility in the electrolyte system. Although the L4 electrolyte exhibits low conductivity at room temperature, its conductivity increased by three orders of magnitude to 1.87 × 10⁻³ S cm⁻¹ at 75 °C, highlighting its potential as a promising natural-based polymer electrolyte. This work provides a detail mechanism of charge transport that influences the conductivity variation within the natural-based polymer electrolyte system, offering important insights for fundamental understanding.