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

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.