Spiro-(1,1′)-bipyrrolidinium tetrafluoroborate salt as high voltage electrolyte for electric double layer capacitors

• The high voltage electrolyte salt SBP-BF4 was synthesized.
• SBP-BF4/PC and TEMA-BF4/PC were used as electrolyte and compared.
• The highest withstand voltage for carbon/SBP-BF4–PC system has been observed.

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 TEMA-BF4 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 g−1 and 43 Wh kg−1, respectively.