This paper details the influence of adding ester co-solvent to ethylene carbonate (EC) based electrolyte in the view of supercapacitor applications. The incorporation of ester solvents with methoxy or fluorinated groups allows a good compromise to be reached between electrochemical performance in a wide temperature range and safety issue. The use of spiro-(1,1′)-bipyrrolidinium tetrafluoroborate (SBPBF4) instead of tetraethylammonium tetrafluoroborate (TEABF4) allows the increase of electrolyte conductivity at low temperature thanks to its higher solubility. An improvement of capacitance stability is also obtained with the use of SBPBF4.