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      • Solid state electrochemical double layer capacitors with natural graphite and activated charcoal composite electrodes

        Hansika, P.A.D.,Perera, K.S.,Vidanapathirana, K.P.,Zainudeen, U.L. Techno-Press 2019 Advances in materials research Vol.8 No.1

        Electrochemical double layer capacitors (EDLCs) which are fabricated using carbon based electrodes have been emerging at an alarming rate to fulfill the energy demand in the present day world. Activated charcoal has been accepted as a very suitable candidate for electrodes but its cost is higher than natural graphite. Present study is about fabrication of EDLCs using composite electrodes with activated charcoal and Sri Lankan natural graphite as well as a gel polymer electrolyte which is identified as a suitable substitute for liquid electrolytes. Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and Galvanostatic Charge Discharge test were done to evaluate the performance of the fabricated EDLCs. Amount of activated charcoal and natural graphite plays a noticeable role on the capacity. 50 graphite : 40 AC : 10 PVdF showed the optimum single electrode specific capacity value of 15 F/g. Capacity is determined by the cycling rate as well as the potential window within which cycling is being done. Continuous cycling resulted an average single electrode specific capacity variation of 48 F/g - 16 F/g. Capacity fading was higher at the beginning. Later, it dropped noticeably. Initial discharge capacity drop under Galvanostatic Charge Discharge test was slightly fast but reached near stable upon continuous charge discharge process. It can be concluded that initially some agitation is required to reach the maturity. However, the results can be considered as encouraging to initiate studies on EDLCs using Sri Lankan natural graphite.

      • Optimization and application of a gel polymer electrolyte in solid state super capacitors with graphite electrodes

        Gunasekara, Buddhika P.,Perera, Kumudu S.,Vidanapathirana, Kamal P.,Vignarooban, K. Techno-Press 2021 Advances in materials research Vol.10 No.2

        The prime objective of the present study is to exploit a user friendly, inexpensive all solid state super capacitor using a suitable electrolyte and electrodes. A gel polymer electrolyte (GPE) consisted with polyvinylidene fluoride-co-hexafluopropylene (PVdF), ethylene carbonate (EC), propylene carbonate (PC) and zinc trifluoromethane sulfonate (Zn(CF<sub>3</sub>SO<sub>3</sub>)<sub>2</sub>-ZnTF) was prepared using solvent casting method and its properties were optimized by varying the composition. The composition of 16 PVdF : 22 ZnTF : 31 EC : 31 PC (weight %) exhibits the optimum room temperature conductivity of 3.09×10<sup>-3</sup> Scm<sup>-1</sup>. It is purely an ionic conductor having a negligible electronic conductivity. In addition, it was possible to obtain a thin, mechanically stable film. The electrodes were prepared using Sri Lankan natural graphite (NG) with a polymer binder. Eventhough there are reports about natural graphite based super capacitors, Sri Lankan natural graphite has not been considered for super capacitors at a large scale. The main reason for turning towards natural graphite is to reap the benefits of low cost as well as the safety. In order to optimize the electrode properties, the ratio between graphite and polymer binder (in weight basis) was changed. The polymer binder used was polytetrafluoroethylene (PTFE). Super capacitor fabricated with the electrode of the composition, NG : PTFE = 90:10 shows the maximum single electrode specific capacitance (2.58 Fg<sup>-1</sup>). The fabricated device retains for continuous charge discharge operation with a minimum performance reduction.

      • An ionic liquid incorporated gel polymer electrolyte for double layer capacitors

        Perera, Kumudu S.,Prasadini, K.W.,Vidanapathirana, Kamal P. Techno-Press 2020 Advances in energy research Vol.7 No.1

        Energy storage devices have received a keen interest throughout the world due to high power consumption. A large number of research activities are being conducted on electrochemical double layer capacitors (EDLCs) because of their high power density and higher energy density. In the present study, an EDLC was fabricated using natural graphite based electrodes and ionic liquid (IL) based gel polymer electrolyte (GPE). The IL based GPE was prepared using the IL, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (1E3MITF) with the polymer poly(vinyl chloride) (PVC) and the salt magnesium trifluoromethanesulfonate (Mg(CF<sub>3</sub>SO<sub>3</sub>)<sub>2</sub> - MgTF). GPE was characterized by electrochemical impedance spectroscopy (EIS), DC polarization test, linear sweep voltammetry (LSV) test and cyclic voltammetry (CV) test. The maximum room temperature conductivity of the sample was 1.64 × 10<sup>-4</sup> Scm<sup>-1</sup>. The electrolyte was purely an ionic conductor and the anionic contribution was prominent. Fabricated EDLC was characterized by EIS, CV and galvanostatic charge discharge (GCD) tests. CV test of the EDLC exhibits a single electrode specific capacitance of 1.44 Fg<sup>-1</sup> initially and GCD test gives 0.83 Fg<sup>-1</sup> as initial single electrode specific discharge capacitance. Moreover, a good stability was observed for prolonged cycling and the device can be used for applications with further modifications.

      • Electrochemical double layer capacitors with PEO and Sri Lankan natural graphite

        Jayamaha, Bandara,Dissanayake, Malavi A.K.L.,Vignarooban, Kandasamy,Vidanapathirana, Kamal P.,Perera, Kumudu S. Techno-Press 2017 Advances in energy research Vol.5 No.3

        Electrochemical double layer capacitors (EDLCs) have received a tremendous interest due to their suitability for diverse applications. They have been fabricated using different carbon based electrodes including activated carbons, single walled/multi walled carbon nano tubes. But, graphite which is one of the natural resources in Sri Lanka has not been given a considerable attention towards using for EDLCs though it is a famous carbon material. On the other hand, EDLCs are well reported with various liquid electrolytes which are associated with numerous drawbacks. Gel polymer electrolytes (GPE) are well known alternative for liquid electrolytes. In this paper, it is reported about an EDLC fabricated with a nano composite polyethylene oxide based GPE and two Sri Lankan graphite based electrodes. The composition of the GPE was [{(10PEO: $NaClO_4$) molar ratio}: 75wt.% PC] : 5 wt.% $TiO_2$. GPE was prepared using the solvent casting method. Two graphite electrodes were prepared by mixing 85% graphite and 15% polyvinylidenefluoride (PVdF) in acetone and casting n fluorine doped tin oxide glass plates. GPE film was sandwiched in between the two graphite electrodes. A non faradaic charge discharge mechanism was observed from the Cyclic Voltammetry study. GPE was stable in the potential windows from (-0.8 V-0.8 V) to (-1.5 V-1.5 V). By increasing the width of the potential window, single electrode specific capacity increased. Impedance plots confirmed the capacitive behavior at low frequency region. Galvanostatic charge discharge test yielded an average discharge capacity of $0.60Fg^{-1}$.

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