High-Temperature Spiro-(1,1′)-Bipyrrolidinium Tetrafluoroborate-Based Organic Electrolytes for Supercapacitors

Organic electrolytes based on different solvents (propylene carbonate, γ-butyrolactone, sulfolane, and benzonitrile) with high boiling points have been studied in supercapacitors. The cyclic voltammetry data, dependence of capacitance, internal resistance on voltage, and endurance tests indicate that a solution of spiro-(1,1′)-bipyrrolidinium tetrafluoroborate (SBP-BF4) in benzonitrile is one of the most reliable electrolytes in a voltage range of about 2.5 V up to temperature of 100-110°C . The high electrochemical stability of benzonitrile under such harsh conditions can be explained by the absence of an SEI film formation process on the electrode surface that doesn’t cause a noticeable internal resistance increase and capacity decrease when voltage is increased.