Effect of SBPBF₄ addition in Acetonitrile- and Linear Carbonate-based Electrolytes: Improving Voltage Stability and Reducing Gas Evolution in Supercapacitors

Abstract

Electric double-layer capacitors (EDLCs), or supercapacitors, are high-performance energy storage devices known for their superior power density, rapid charge-discharge capabilities, and long cycle life. The electrolyte composition, specifically the choice of solvent and salt, plays a critical role in determining the voltage range, energy efficiency, and cycle lifespan of EDLCs. This study explores the novel electrolyte spiro-1,1-bipyrolidinium tetrafluoroborate (SBPBF₄), selected for its high solubility and outstanding electrochemical stability at elevated voltages. SBPBF₄, with its unique cyclic structure among quaternary ammonium salts, offers advantages particularly suited for high-voltage applications.This study investigates SBPBF₄ in low-viscosity solvents, namely acetonitrile (AN) and dimethyl carbonate (DMC), chosen for their complementary properties that could further enhance SBPBF₄’s performance. A central focus is on the electrolyte's impact on stability and gas generation in both symmetrical AC//AC and hybrid LTO//AC configurations. Findings indicate that SBPBF₄ enhances float durability and minimizes gas generation, an effect attributed to the resistance of the SBP⁺ cation to Hofmann elimination. This resistance interrupts degradation cycles typically triggered by interactions between residual water and solvents, stabilizing the electrolyte and preventing reductive decomposition at the negative electrode surface. Understanding these mechanisms is essential for optimizing low-viscosity solvent-based electrolytes and ensuring reliable operation in EDLCs and hybrid supercapacitors.