Enhancement of Specific Capacitance in Carbon Supercapacitors Using Dual Redox Additive-Based Gel Polymer Electrolytes

In this report, supercapacitors (SCs) with high energy density were fabricated by using dual redox additive-based gel polymer electrolytes (GPEs) and activated carbon (AC) electrodes. The GPEs were prepared by using poly(vinylidene fluoride-co-hexafluoropropylene) as a host polymer, adiponitrile as a plasticizer, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as ionic liquid (IL), and diphenylamine (DPA) and copper iodide (CuI) as dual redox additives. The microstructural studies showed that plasticizers, ILs, and redox additives enhanced the amorphous nature of the host polymer matrix. The GPEs were thermally stable up to ∼200 °C. The electrical conductivity at room temperature and the electrochemical potential window of the dual redox additive-based GPE-IL + DPA + CuI are 3.3 × 10^–3 S cm^–1 and 6.4 V, respectively. The electrochemical performance of the SCs fabricated with the dual redox additive-based GPEs and AC electrodes was investigated by using cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopic techniques. It was observed that the dual redox additives enhanced the specific capacitance of the SC from 108.3 to 243.4 F g^–1 and specific energy from 5.1 to 11.5 W h kg^–1. The dual redox additive-based GPEs also showed good cyclic performance in specific capacitance with an initial 34% fading and Coulombic efficiency sustained by ∼100% for 5000 cycles.