A novel quaternary ammonium salt based on spiro-(1,1')-bipyrolidinium tetrafluoroborate (SBP-BF4) has been synthesized and dissolved in propylene carbonate (PC) with 1.5 mol L-1 (M) concentration for electric double-layer capacitors (EDLCs). The physic-chemical properties and electrochemical performance of SBP-BF4/PC electrolyte are investigated. Compared with the standard electrolyte 1.5 M TEMABF(4) in PC, the novel SBP-BF4/PC electrolyte exhibited much better electrochemical performance due to its smaller cation size, lower viscosity and higher conductivity. The specific discharge capacitance of activated carbon electrode based EDLCs using SBP-BF4/PC electrolyte is 120 F g(-1), the energy density and power density can reach 31 kW kg(-1) and 6938 W kg(-1), respectively, when the working voltage is 2.7 V and current density is 50 mA g(-1). The withstand voltage of activated carbon based EDLCs with SBP-BF4/PC electrolyte can reach to 3.2 V, where the stable discharge capacitance and energy density are 121 F and 43 Wh kg(-1), respectively. (c) 2014 Elsevier B.V. All rights reserved.