Gel Polymer Electrolyte Based Electrical Double Layer Capacitors: Comparative Study with Multiwalled Carbon Nanotubes and Activated Carbon Electrodes

We report the comparative studies on gel polymer electrolyte based flexible electrical double layer capacitors (EDLCs) fabricated with two different electrodes, namely multiwalled carbon nanotubes and activated carbon (charcoal, AC). The gel electrolyte comprising lithium trifluoromethanesulfonate (Li-triflate or LiTf)/ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf)/poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) exhibits ionic conductivity on the order of 10–3 S cm–1 at room temperature, which is suitable enough to be used in EDLCs. A mixture of ethylene carbonate (EC) and propylene carbonate (PC) has also been incorporated to enhance the flexibility of the electrolytes. The comparative studies on EDLCs have been performed from the electrode and electrolyte points of views using impedance analysis, cyclic voltammetry and galvanostatic charge–discharge tests. The MWCNT-based EDLC shows the specific capacitance value of 32 F g–1, whereas the activated charcoal offers the substantially higher value of 157 F g–1. These result in the higher specific energy of AC-based EDLCs as compared to the devices with MWCNTs electrodes. However, the MWCNTs electrodes, due to their mesoporous nature, exhibit high rate capability and hence high specific (pulse or continuous) power relative to the predominantly microporous AC electrodes. The charge–discharge cyclic performance of MWCNT-based EDLC is also excellent (for >5 × 104 cycles) with respect to that for AC-based device, limited to 4000–5000 cycles.