Electrolytic Characteristics of Fluoroethylene Carbonate for Electric Double-Layer Capacitors at High Concentrations of Electrolyte

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The use of partially fluorinated compounds as alternative solvents can increase the solubility of electrolytes and improve the performance of electric double-layer capacitors (EDLCs). The solubility of triethylmethylammonium tetrafluoroborate (TEMABF₄) in fluoroethylene carbonate (FEC) was 3.0 M (M = mol dm⁻³) or more at 25°C. The molar concentration of FEC in 2.5 M TEMABF₄ solution was higher than that of propylene carbonate (PC) in 2.0 M TEMABF₄ solution. The kinematic viscosity and ionic conductivity of 2.0 M TEMABF₄ solution in FEC were slightly lower than those of the counterpart in PC at room temperature. The use of TEMABF₄ at the high concentrations in FEC slightly increased the gravimetric capacitance of coin cells.