Purification of Vein Graphite by Alkali Roasting for Anode Material in Lithium Ion Batteries
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Date
2013
Journal Title
Journal ISSN
Volume Title
Publisher
Uva Wellassa University of Sri Lanka
Abstract
Unique vein graphite deposits with highly crystallized and high purity graphite are present in
the mineralization zone of the central highlands of Sri Lanka This graphite has been identified
as a potential candidate for the lithium ion rechargeable batteries (Balasooriyaet al., 2007).
Recent attention has been made towards the purification of vein graphite in order to prevent the
anode ageing and decomposition of the electrolyte in lithium ion batteries (Amaraweera et al.,
2013). Alkali roasting for purification of graphite has found to be a very effective method to
remove sulfide and silicate impurities at low temperatures (Lu et al., 2002). Therefore, this
study focused on studying the effectiveness of alkali roasting for the purification of vein
graphite in Sri Lanka
Methodology
Graphite powder (<53 µm) from Needle Platy Graphite (NPG) and Shiny Slippery Fibrous
(SSF) morphological types from Bogala and Kahatagaha mines were used for this study. The
graphite was treated in aqueous solutions containing 5, 10, 15, 20, 25, 30 and 35 vol. % NaOH
(Solid: liquid, 1:2) separately and roasted at 250 C under air for one hour. Then, the roasted
sample was acid leached in 10 vol. % H2SO4. After that, the solid was filtered, washed to
neutral and vacuum dried at 100 C for 15 hours. Minimum concentrations of NaOH for the
purity enhancement were identified for each graphite type. Roasting treatments were repeated at
150 C, 200 C, and 300 C, using the data obtained previously to identify the effect of roasting
temperature on purity enhancement.
Carbon percentages of the treated graphite samples and untreated graphite samples were
determined by heat treating at 950 C for 3 hours in Muffle Furnace, according to ASTM – C
561 and weighing the residues. Pellets of treated and untreated graphite powder (D =12 mm and
L = 5 mm) prepared by cold uniaxial pressing at 100 Mpa were used to measure D.C
conductivity by four-probe method at room temperature.
Description
Keywords
Science and Technology, Mineral Sciences, Materials Sciences, Graphite Industry, Graphite