Browsing by Author "Perera, K.S."
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Item An Ionic Liquid based Gel Polymer Electrolyte for Zn / Sri Lankan Natural Graphite Rechargeable Cells(Uva Wellassa University of Sri Lanka, 2019) Prasadini, K.W.; Perera, K.S.; Vidanapathirana, K.P.Ionic liquids (ILs) have been identified as viable substitutes for solvents such as ethylene carbonate, propylene carbonate and diethylene carbonate which are known to be toxic in gel polymer electrolytes (GPEs). Hence, at present, they have received a great attention towards the global focus on fabricating devices using low cost, environmental friendly materials. In this study, investigations were carried out to analyze the performance of IL based GPE in a Zn/Sri Lankan natural graphite rechargeable cell. As per the literature survey, this type of cell configuration has not been reported before. GPE was prepared using the conventional solvent casting method. Poly (vinylidene fluoride–co– hexafluoropropylene), zinc trifluoro methanesulfonate and 1–ethyl–3–methyl imidazolium trifluoromethanesulfonate were used as the polymer, the salt and the IL respectively. Cell of the configuration, Zn/IL based GPE/natural graphite was characterized using Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV) and Galvanostatic Charge Discharge (GCD) test. Open circuit voltage of the cell was about 1.0 V. This is quite sufficient for low power requirements. EIS results confirm that the GPE has a good ionic conductivity. The value of charge transfer resistance between the electrodes and the electrolyte obtained from EIS results is rather low. Cyclic voltammogramme obtained by cycling at 10 mV s-1 within the potential window 0.05 to 2.05 V has two reduction peaks and one oxidation peak. One reduction peak and the oxidation peak represent the movement of Zn ions. The other reduction peak is due to Zn ions. The specific charge of the cell was found to be 4.66 mA h g-1. The average discharge capacity of the cell was 3.00 mA h g-1 as per the GCD test. Over 1000 cycles, cell showed an efficiency of 92% confirming the stability of the cell to tolerate the continuous cycling. Further improvement is needed for commercial applications.Item Magnesium rechargeable cells based on PVdF gel polymer electrolyte(Uva Wellassa University of Sri Lanka, 2015) Jayathilake, Y.M.C.D.; Perera, K.S.; Vidanapathirana, K.P.Gel polymer electrolytes (GPEs) have received a keen interest as an excellent substitute for liquid electrolytes due to anticipation of several advantages such as no leakage, no corrosion and easy preparation. They are basically consisting of a salt solvent mixture encapsulated in a suitable polymer matrix (Osman, et al. 2012). Due to the satisfactory conducting and mechanical properties, they have been extensively considered as suitable electrolytes for various applications such as rechargeable cells (Kumar et al, 2003) super capacitors (Tripathi et al, 2013) and electrochromic devices (Wu et al, 2012). Plentiful of investigations have been carried out on applications with Li based GPEs but now attention has been focused towards other cation based GPE mainly due to some problems associating with lithium. As such non lithium based devices have come forward getting more interest. Use of magnesium in place of lithium would be very convenient as it possesses various important characteristics such as low cost, substantial abundance, more stability than lithium and low toxicity (Pandey et al, 2011). This paper reports about employing a magnesium based GPE in a magnesium rechargeable cell. Methodology Polyvinylidenefluoride (PVdF), Ethylene carbonate (EC), Propylene carbonate (PC) and Magnesium trifluromethane sulfonate (MgTf) purchased from Aldrich were used as received. Appropriate amounts of EC, PC and MgTf were mixed by magnetically stirring for about 2 hours. Required amount of PVdF was added and stirring was continued for another 10 minutes. Then, the mixture was heated at 120 C for 30 minutes. The resultant homogenous hot mixture was pressed in between two well cleaned glass plates to obtain a thin GPE film. A circular pellet of GPE was sandwiched in between two stainless steel (SS) electrodes and it was loaded inside a brass sample holder which is sealed by means of an O ring. Diameter and thickness of the sample were measured using a micrometer screw gauge. AC Impedance data were gathered by using Metrohm Autolab M101 impedance analyzer in the frequency range 0.01 Hz - 0.1 MHz. Temperature was varied from room temperature to 60 C by placing the sample holder inside a Sibata glass tube furnace. Cyclic Voltammetry studies were performed by placing an electrolyte sample in between two Mg electrodes. Three electrode electrochemical setup with a working electrode, a counter electrode and a reference electrode was employed for the study. Scan rate used was 5 mV/s. A cathode having Polypyrrole (PPy) polymerized in the presence of Dodecylbenzenesulfonate (DBS) was prepared as reported before (Perera et al, 2008). The cells in the configuration, Mg / GPE / PPy : DBS were assembled and their charge discharge behavior was monitored. Cells were subjected to charge and discharge between the potential values 0.5 V and 2.0 V. They were first discharged galvanostatically and then charged galvanostatically. When the required potential has reached, further potentiostatic charge was done till the current drops to 10%.Item Optimization and Structural Analysis of a Gel Polymer Electrolyte Based on Polyacrylonitrile to be used for Na Batteries(Uva Wellassa University of Sri Lanka, 2018) Perera, K.S.; Vidanapathirana, K.P.Today, an insurgence has arisen on non Li based batteries to meet the escalating energy demand. Na, Mg, and Zn are some of the suggested alternatives. Simultaneously, attention was focused on replacing liquid electrolytes due to their inherent drawbacks such as leakage, evaporation and high reactivity. One solution is employing quasi solid state gel polymer electrolytes (GPEs). Main objective of this study is preparing, optimizing and structural analyzing of a GPE to be used for Na batteries. GPE based on polyacrylonitrile (PAN) was prepared using the salt sodium thiocyanate (NaSCN) and the solvents, ethylene carbonate (EC) and propylene carbonate (PC). Materials were heated and the resultant was pressed between two glass plates to obtain a thin film. This procedure was repeated varying the polymer and the salt concentrations. The composition was fine tuned to obtain the highest room temperature conductivity. The structure analysis was done using X Ray Diffraction (XRD) technique. XRD measurements were carried out for two samples — with and without salt. The highest conductivity observed was 1.92 x 10-3 S cm-1 from the sample 202.5 PAN: 500 EC: 500 PC: 35 NaSCN (weight basis). When the polymer concentration was increased, conductivity increased first. However, further increase of polymer reduced the conductivity. This may be a result of interplay between dissociation of ion pairs and viscosity of the medium. Similarly, amount of charge carriers and their mobility governs the conductivity and results an optimum conductivity at a particular salt concentration. XRD results clearly suggest that crystalline phase in the PAN: EC: PC structure diminishes upon addition of the salt. It implies that the GPE is in amorphous phase and based on the conductivity value, it is suitable to be employed for Na rechargeable batteries. Keywords: Gel polymer electrolytes, X Ray Diffraction, Polyacrylonitrile, Sodium batteriesItem Sri Lankan Natural Rubber based Electrolyte for Electrochemical Double Layer Capacitors(Uva Wellassa University of Sri Lanka, 2019) Sanjaya, N.A.A.K.; Perera, K.S.; Vidanapathirana, K.P.Energy storage devices have received a global interest today to satisfy the increasing thirst for power. Solid polymer electrolytes (SPEs) play an important role being the ion conduction medium between the two electrodes of those devices. One crucial problem with many SPEs is their high cost due to use of commercial polymers. Recently, natural rubber (NR) has been recognized as a very suitable substitute for such expensive polymers. As NR is an insulator, several modification methods have been adopted to make it suitable for SPEs. Main objective of the present investigation was to check the suitability of NR based SPE to be used for an EDLC. This paper reports about a SPE prepared using methyl grafted NR (MG 49) and a Li salt with tetrahydrofuran following solvent casting method. A thin, bubble free film could be obtained. Samples were prepared varying the salt concentration. Impedance data were gathered at room temperature and the ionic conductivity was calculated for each sample. For the sample that showed the highest conductivity, impedance data were collected varying the temperature. For the electrochemical double layer capacitors (EDLCs), electrodes were prepared using Sri Lankan natural graphite. Performance of EDLCs were monitored using cyclic voltammetry and galvanostatic charge discharge tests. The highest ionic conductivity at room temperature was 3.62 × 10-5 S cm-1 at the salt concentration of 40 wt%. Single electrode specific capacity was depending on the potential window and the scan rate use for cycling. An initial single electrode specific capacity of 0.94 F g-1 was observed from EDLC. It reached a value of 0.55 F g-1 during 500 cycles. Single electrode specific discharge capacity dropped very fast at the beginning and then was constant around 0.05 F g-1. Investigations are in progress to improve the ionic conductivity of SPE and to improve the performance of EDLC.