Iodide ion containing ionic liquid mixture based asymmetrical capacitor performance

Abstract Development of high efficiency energy storage systems is increasingly important as these systems enable utilize energy from renewable sources and reduce greenhouse gas evolution caused by fuel combustion technologies in the same time. Electricity storage in the supercapacitor containing neat 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) ionic liquid or mixture of ionic liquids (EMImBF4 with addition of 5 wt% 1-ethyl-3-methylimidazolium iodide (EMImI)) has been studied in the two- and three-electrode systems using high porosity carbon electrode material with specific surface area of 2090 m2 g-1, micropore surface area of 2060 m2 g-1 and total pore volume of 1.085 cm3 g-1. Based on electrochemical characterization data (cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge/discharge and constant power discharge), the asymmetrical capacitor with ionic liquid mixture of 5 wt% EMImI in EMImBF4 shows increase in cell capacitance 5 F g-1 and specific energy about 3.5 W h kg-1 as well as in specific power, compared with the data for symmetrical capacitor system based on neat EMImBF4. However, electrochemical stability, i.e. the potential region of ideal polarizability for the ionic liquid mixture based capacitor is lower and therefore the coulombic and energy efficiencies calculated are also smaller.