Electrical Double-Layer Capacitors Based on a Ternary Ionic Liquid Electrolyte Operating at Low Temperature with Realistic Gravimetric and Volumetric Energy Outputs.

We report on electrical double-layer capacitors (EDLCs) performing effectively at low temperature (down to -40 °C), owing to the tuned characteristics of both the ionic liquid (IL) electrolyte and carbonaceous electrodes. The transport properties of the electrolyte have been enhanced by adding a low-viscosity IL with the tetracyanoborate anion, [EMIm][TCB], to a mixture of [EMIm][FSI] with [EMIm][BF ], which was already successfully applied for this application. The formulated ternary electrolyte, [EMIm][FSI] [BF ] [TCB] , remained in the liquid state until it reached the glass transition at -99 °C and displayed a relatively low viscosity and high conductivity (η=23.