Solid-state electric double layer capacitors fabricated with plastic crystal based flexible gel polymer electrolytes: Effective role of electrolyte anions

• Flexible EDLCs with succinonitrile based gel electrolyte membranes are reported.
• Anionic size of salts in gel electrolytes plays important role on capacitive performance.
• Li-triflate incorporated gel electrolyte shows better performance over LiTFSI-based gel.
• Highest specific capacitance, energy and power are 240 F g−1, 39 Wh kg−1 and 19 kW kg−1, respectively.

Flexible gel polymer electrolyte (GPE) thick films incorporated with solutions of lithium trifluoromethanesulfonate (Li-triflate or LiTf) and lithium bis trifluoromethane-sulfonimide (LiTFSI) in a plastic crystal succinonitrile (SN), entrapped in poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP) have been prepared and characterized. The films have been used as electrolytes in the electrical double layer capacitors (EDLCs). Coconut-shell derived activated carbon with high specific surface area (∼2100 m2 g−1) and mixed (micro- and meso-) porosity has been used as EDLC electrodes. The structural, thermal, and electrochemical characterization of the GPEs have been performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), impedance measurements and cyclic voltammetry. The high ionic conductivity (∼10−3 S cm−1 at 25 °C), good electrochemical stability window (>4.0 V) and flexible nature of the free-standing films of GPEs show their competence in the fabrication of EDLCs. The EDLCs have been tested using electrochemical impedance spectroscopy, cyclic voltammetry, and charge–discharge studies. The EDLCs using LiTf based electrolyte have been found to give higher values of specific capacitance, specific energy, power density (240–280 F g−1, ∼39 Wh kg−1 and ∼19 kW kg−1, respectively) than the EDLC cell with LiTFSI based gel electrolyte. EDLCs have been found to show stable performance for ∼104 charge–discharge cycles. The comparative studies indicate the effective role of electrolyte anions on the capacitive performance of the solid-state EDLCs.

Figure optionsDownload as PowerPoint slide