In this study, we present the positive effect of 1,10-phenanthroline as an electrolyte additive that is strongly adsorbed on activated carbon electrodes, thereby adding effective redox activity to their initially capacitive interactions with electrolyte solutions. We obtain a stable capacitance of 320 F/g for the negative electrode and 190 F/gelectrode for full symmetric supercapacitor cells, operating up to 3.4 V in nonaqueous media, during many thousands of cycles. This corresponds to a specific capacity of 180 (mA h)/gelectrode. The high voltage and capacity of these systems can pave the way for developing high-energy-density pseudocapacitors that may be able to compete with battery systems. We explored the mechanisms of the electrode interactions using electrochemical tools, including impedance spectroscopy.