Research Symposium-2015

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Browsing Research Symposium-2015 by Author "Amiyangoda, A.G.T.R."

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    Investigation on Structural Modification of Sri Lankan Vein Graphite for Ion Intercalation
    (Uva Wellassa University of Sri Lanka, 2015) Amiyangoda, A.G.T.R.; Rathnayake, R.M.N.M.; Karunarathne, R.I.C.N.; Wijayasinghe, H.W.M.A.C.
    Rechargeable batteries have become the main energy source for the portable electronic devices. Synthetic graphite have been used as anode electrode material in rechargeable batteries. Presently these rechargeable batteries are expensive mainly due to high cost of materials, such as synthetic graphite and metal oxides, used in their electrodes. It is suggested that the cost of these batteries can be reduce by introducing cheaper natural graphite for their anode electrode. Sri Lankan natural vein graphite can be classified into four distinct structural verities. They are Shiny-Slippery- Fibrous Graphite (SSF), Needle-Platy Graphite (NPG), Coarse Striated-Flaky Graphite (CSF) and Coarse Flakes of Radial Graphite (CFR). Development of Sri Lankan natural vein graphite to the anode of Li-ion rechargeable batteries, through purification and surface modification have been investigated recently. Furthermore, natural graphite has to be structurally modified by expanding interlayer distance to facilitate the intercalation of larger Na ions for the application in rechargeable Sodium Ion Batteries (SIB) (Wei, 2011). The present study investigated the possibility of expanding the interlayer distance of Sri Lankan natural vein graphite for accommodating Na-ion intercalation by converting into Graphite Oxide (GO). Materials and methods Purified samples from all four structural varieties of Sri Lankan vein graphite, were used in this study. Raw graphite samples were oxidized to Graphite Oxide (GO) by using improved hummers method (Madusanka Y.N., Amareweera T.H.N.G.,Wijayasinghe H.W.M.A.C., 2013). In this method 96% H2SO4 (Sigma-Aldrich) and 85% H3PO4 (Sigma-Aldrich) were added to purified vein graphite. Then KMnO4 (Belgolabo) was added little by little to the mixture with in two hours and stirred. Sample was allowed to cool until room temperature. Solution was poured into 30% H 2O2 in an ice bath and the sample was vacuum filtered using Fisher brand filter papers using distilled water. The d.c. electrical conductivity of raw graphite and prepared GO samples were measured using the standard four probe method. Fourier Transform Infrared (FTIR) spectra of raw graphite and GO samples were employed to study the structural modification. Further the X-ray diffractometry was used to confirm the formation of GO.For the Na-ion intercalation study, the modified graphite oxide was tape casted by the doctor blade method to fabricate electrodes. GO was the active material, carbon black was selected as the conductive additive and the binder was polyvinylidene fluoride (PVDF). All the materials were weighed using a chemical balance and placed in a small beaker. Then excessive amount of acetone and dimethylformamide (1:1 ratio) were added to the beaker, covered with an aluminum foil and stirred for 12 hours. Mixture was poured on to a copper foil pasted on a glass to form a very thin layer. It was allowed to dry. The electrodes were fabricated by cutting the copper foil to required shape. A half-cell was assembled using the fabricated GO anode with a gel electrolyte and sodium metal as the reference electrode. Assembling and testing of the cell was conducted inside a N2 filled glove box. Discharging current of the half-cell under 0.5 kΩ load over time was measured and it was recorded using a computer interfaced program.