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Ionic liquid (IL) based gel polymer electrolytes (GPEs) are being investigated extensively at present as substitutes for conventional GPEs based on a polymer, a salt and solvents. The main reason behind this is the drawbacks in usage of solvents. IL based GPEs have been employed for energy storage devices such as batteries and super capacitors due to their interesting mechanical, physical and electrochemical properties. This study focused on synthesis preparation and characterization of an IL based GPE consisting of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-co-HFP), zinc trifluoro metha -nesulfonate (Zn(CF3SO3)2 - ZnTF) and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (1E3MITF). Thin film samples were prepared using solvent casting method. The optimized composition was found to be 1 PVdF-co-HFP: 1 1E3MITF: 3 ZnTF (by weight basis). This mechanically stable, thin film has the maximum room temperature conductivity of 7.42×10-3 S cm-1. Conductivity variation with temperature follows Vogel - Tamman - Fulcher (VTF) behavior confirming the relation of conductivity mechanism with the free volume theory. The IL based GPE is a purely an ionic conductor having a considerable anionic contribution. It shows stability up to 2.5 V which is very much convenient from a practical point of view. Oxidation and reduction of Zn takes place at the potentials of 0.5 V and –0.5 V, respectively. In addition, Zn platting and stripping occurs only on the Zn electrodes but not on the stainless steel (SS) electrodes. Impedance measurements taken for the GPE continuously for a long period of time exhibited a satisfactory stability with Zn electrodes.

This paper is based on fabrication and characterization of a gel polymer electrolyte and evaluation its potential candidacy for electrochemical double layer capacitors. Gel polymer electrolyte samples consist of polyvinylidenefluoride (PVdF), zinc chloride (ZnCl2), ethylene carbonate (EC) and propylene carbonate (PC) Salt and polymer concentrations were varied to obtain the best conductivity. The maximum room temperature conductivity of 8.6 × 10-4 Scm-1 was obtained with the composition, 6.875PVdF:1 ZnCl2: 12.5 EC : 12.5 PC (by weight). DC polarization test results proved that gel polymer electrolyte is predominantly an ionic conductor. The electrochemical double layer capacitor was assembled having two identical graphite electrodes with the gel polymer electrolyte. Cyclic voltammetry measurements were taken in different potential windows and at various scan rates using three electrode setups. The results proved the dependency of the potential window as well as the scan rate on the performance of the capacitor. Continuous charge discharge cycling for 50 cycles showed that the device is rather stable in spite of the decrement of specific capacity that occurred at the beginning. The initial specific capacity was about 8.68 Fg-1. The present study showcases the value of Sri Lankan natural graphite in energy applications.

Supercapacitors (SCs) are promising alternative energy storage devices due to their relatively fast rate of energy storage and delivery. Redox capacitors in the family of SCs are based on conducting polymer (CP) or transition metal oxide electrodes. In this study, symmetric redox capacitors have been fabricated utilizing the CP, polyaniline (PANI) as electrodes and a gel polymer electrolyte (GPE) based on polyvinylidenefluoride (PVdF) as the electrolyte. Investigations have been carried out to study the effect of polymerization current density of PANI electrodes on the performance of redox capacitors. Polymerization current density was varied from 4 mA cm−2 to 9 mA cm−2 and the performance of redox capacitors was evaluated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) test and galvanostatic charge discharge (GCD) test. EIS results showed that redox capacitor having electrodes prepared using the current density 7 mA cm−2 has the lowest charge transfer resistance and CV test elucidated that the same redox capacitor has maintained around 80% of maximum specific capacity from its initial value after 200 cycles. GCD results exhibited the highest specific discharge capacity of 421.4 F g−1, specific power density of 935.6 W kg−1 and specific energy density of 8.0 Wh kg−1 after 200 cycles for the same capacitor.

In this study, a gel polymer electrolyte (GPE) consisting with polyacrylonitrile (PAN), ethylene carbonate (EC), propylene carbonate (PC) and magnesium trifluromethane sulfonate (Mg(CF3SO3)2) was prepared using the hot pressed method. The starting materials were heated at 130 oC for 2 hours and the resulting hot viscous mixture was pressed in between two well cleaned glass plates. The composition was fine-tuned by varying the salt and the polymer concentration in order to obtain a mechanically stable, thin and flexible film with a high ionic conductivity. It was found that the composition, 105 PAN : 150 MgTF : 400 EC : 400 PC gives the maximum conductivity of 1.06 x 10-2 Scm-1. DC polarization test done with blocking electrodes confirmed the ionic nature of the sample while the results obtained with non-blocking electrodes proved that the anionic contribution for the conductivity is dominant. The sample was used in redox capacitors having two identical polypyrrole electrodes doped with dodecylbenzesulfonate. Cyclic Voltammetry, Galvanostatic Charge Discharge and Electrochemical Impedance Spectroscopy techniques were used to evaluate the performance of the redox capacitors. The specific capacitance was high at low scan rates. The electrolyte was quite stable when use in the redox capacitors. Further, redox capacitor was having a good cycleability which is one of the important key issues to be considered for practical applications.

To supplement the ever increasing power demand in the present day world, supercapacitors have emerged as one of the suitable power storage devices. Redox capacitors have received a considerable attention due to factors such as high cycle ability, satisfactory specific capacitance and good stability. There are many reports on redox capacitors based on liquid electrolytes but these have several drawbacks. In this study, a magnesium chloride (MgCl2) based gel polymer electrolyte was prepared and characterized for its suitability to be used in a redox capacitor. The composition, 0.1 polyacrylonitrile (PAN):0.4 ethylene carbonate (EC):0.4 propylene carbonate (PC):0.125 MgCl2 (weight ratios) exhibits the highest room temperature conductivity of 4.08×10-4 S cm-1. Conductivity variation of this sample with the temperature shows Arrhenius behavior. The ionic transference number is 0.84. This shows that the GPE is an ionic conductor. Redox capacitors were fabricated with two polypyrrole (PPy) electrodes. They were characterized using Cyclic Voltammetry technique, Impedance Spectroscopy and Galvanostatic Charge Discharge test. Cycling at the scan rate of 10 mV/s within the potential window of -1.4 V to +1.4 V showed a specific capacitance of 120.35 F/g. Impedance data showed the electrochemical behavior of the device having resistive and capacitive behavior. Galvanostatic charge discharge test results exhibit average power density and energy density of 341 W/kg and 5 Wh/kg respectively.