A novel electrolyte of electric double-layer capacitors (EDLCs) for ultra-low temperature applications based on spiro-(1,1')-bipyrolidinium tetrafluoroborate (SBP-BF4) dissolved in acetonitrile (AN) and AN + dibutyl carbonate (DBC) mixtures has been developed. The physic-chemical properties and electrochemical characterizations at low temperature have been demonstrated on pure AN and AN/DBC mixed electrolytes. From 20 to -50 degrees C, AN electrolyte shows a slight superiority of the capacitance, but the novel DBC-mixed electrolytes exhibit much higher ion conductivity and better electrochemical performance at -60 degrees C, while AN electrolyte does not cycle at all due to the crystallization of AN and precipitation of SBP-BF4. The specific discharge capacitance of DBC mixtures maintain 92 F g (1) even at a high current density of 5 A g (1). At -60 degrees C, from electrochemical impedance spectroscopy measurement, the whole resistance for AN electrolyte rapidly increased about 60 times higher than that of 20 degrees C, while those for DBC mixtures remain relatively low within the whole temperature range. The cycle performance test indicates the DBC mixtures exhibit extremely stable capacitance, especially at ultra-low temperature. The capacitance for DBC-20% electrolyte is 95 Fg (1) even after 10000 cycles, which maintained 83% of the capacity of 20 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.