Ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate-based gel polymer electrolyte for electrochemical capacitors

A novel ionic liquid gel polymer electrolyte (ILGPE) based on low viscosity ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate (EMImTCB) entrapped in poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymer has been prepared for its application as an electrolyte in electrochemical double layer supercapacitors. The ILGPE shows excellent thermal stability up to 310 °C, a wider electrochemical window of ∼3.8 V (vs. Ag) and a high ionic conductivity of ∼9 × 10−3 S cm−1 at room temperature. The solid-state electrochemical double layer capacitors (EDLCs) have been fabricated with MWCNT electrodes and ILGPE films. The EDLC cells have also been fabricated with pure ionic liquid EMImTCB for comparison. The performance characteristics have been evaluated by impedance spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge studies. The ILGPE based EDLCs show comparable capacitance values (∼34.4 F g−1) and the values of the resistive parameters as compared to the pure ionic liquid based capacitor cells. The solid-state EDLC cell shows a specific energy of ∼3.5 W h kg−1 and a specific power of ∼4.2 kW kg−1 of MWCNT. The performance studies on EDLCs indicate the excellent potential of the ionic liquid EMImTCB based gel polymer films as electrolytes.