Preparation and characterization of 1-ethyl-3-methylimidazolium chloride–based gel polymer electrolyte in electrochemical double-layer capacitors

Abstract

Electrochemical double-layer capacitors (EDLCs) have recently received an enormous attraction due to their ability to produce higher power density without compromising the durability. Producing cheaper, safer, and more durable devices obviously brings more benefits to the modern world applications. This investigation was carried out to optimize an ionic liquid (IL)–based gel polymer electrolyte (GPE), to fabricate an EDLC using the optimized electrolyte with natural graphite electrodes, and to characterize the performance of the device. Electrolyte was prepared with the IL, 1-ethyl-3-methylimidazolium chloride (1E3MICl); the polymer poly(vinylidenefluoride)-co-hexafluoropropylene (PVdF-co-HFP); and the salt, zinc chloride (ZnCl₂). The electrochemical properties of the electrolyte were evaluated by electrochemical impedance spectroscopy (EIS), DC polarization test, and linear sweep voltammetry (LSV), and the EDLC was characterized by EIS, cyclic voltammetry (CV), and galvanostatic charge–discharge (GCD) test. The optimum composition was found to be 26% PVdF-co-HFP:52% ZnCl₂:22% 1E3MICl (weight percentages) with the room temperature conductivity of 1.85 × 10⁻³ S cm⁻¹ and ionic transference number of 0.72. EDLC exhibited a single-electrode specific capacitance of 4.92 F g⁻¹ with 65% retention over 1000 cycles as per CV test. In the GCD results, the EDLC was able to held discharge capacitance of 3 F g⁻¹ for complete 1000 cycles. The durability of the EDLC with this IL-based GPE shows a great potential in the energy applications with further enhancements.