PIL/IL gel polymer electrolytes: The influence of the IL ions on the properties of solid-state supercapacitors

Abstract

In this work we evaluated the influence of different gel electrolytes prepared with a synthesized poly(ionic liquid) – PIL matrix (PILTFSI) and two ionic liquids (ILs) 1-methyl-3-butylimidazolium bis(fluorosulfonyl)imide (MBIMFSI) and 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (DPITFSI) on the electrochemical properties of solid-state supercapacitors. The synthesized PIL/IL gel electrolytes exhibited a conductivity of 3.2 × 10−3 S cm−1 (MBIMFSI) and 5.0 × 10−4 S cm−1 (DPITFSI) at 25 °C and electrochemical windows of 2.8 V and 3.0 V, respectively (obtained by linear sweep voltammetry). By using galvanostatic charge/discharge measurements carried out in a synchronous 2–3 electrode experiment, which allows the simultaneous registration of the voltage of the cell and the potential (versus a reference) of the positive and negative electrodes, we was able to evaluate in details the influence of each gel systems (focusing of the different ions of the IL) on the work voltage and capacitance of the cells. We have demonstrated that the working voltage of the cell (including the work potential of each electrode) should be determined using the complete cell instead of the electrochemical window of the electrolyte obtained with blocking electrodes. Additionally, we showed which gel was able to give to the supercapacitor the best performance, and we have described for the first time the asymmetry on the double layer formation in such PIL/IL solid-state supercapacitors prepared with a symmetrical configuration (same material and same mass in both electrodes).