This paper focuses on high voltage supercapacitors with non-aqueous solutions. We used two types of electrolyte solutions: tetraethyl ammonium tetra fluoroborate (Et4NBF4) in adiponitrile (ADN) and a mixture of Et4NBF4 with tetraethyl ammonium hexa-fluorophosphate (Et4NPF6) in ADN. We show that supercapacitors based on activated carbon electrodes with electrolyte solutions comprising a mixture 0.7 M Et4NBF4 and 1 M Et4NPF6 in ADN display 100% efficiency over 10,000 cycles at 3.5 V and a current density of 2.5 mA cm(-2) at room temperature. These supercapacitors works well even at 60 degrees C. (C) 2016 The Electrochemical Society.