Commercial Cokes and Graphites as Anode Materials for Lithium - Ion Cells
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David J. Derwin *, Kim Kinoshita **, Tri D. Tran +, Peter Zaleski
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*Superior Graphite Co., 6540 S. Laramie Ave. Chicago, IMl.60638 * * Energy and Environmental Division Lawrence Berkeley National Laboratory, Berkeley, Ca. 94720 +Chemistry & Materials Science Department, Lawrence Livermore National Laboratory, Livermore, Ca. 94550
Abstract Several types of carbonaceous materials from Superior Graphite Co. were investigated for lithium ion intercalation. These commercially available cokes, graphitized cokes and graphites have a wide range of physical and chemical properties. The coke materials were investigated in propylene carbonate based electrolytes and the graphitic materials were studied in ethylene carbonate / dimethyl solutions to prevent exfoliation. The reversible capacities of disordered cokes are below 230 mAh / g and those for many highly ordered synthetic (artificial) and natural graphites approached 372 mAh / g (LiC 6). The irreversible capacity losses vary between 15 to as much as 200 % of reversible capacities for various types of carbon. Heat treated cokes with the average particle size of 10 microns showed marked improvements in reversible capacity for lithium intercalation. The electrochemical characteristics are correlated with data obtained from scanning electron microscopy (SEM), high resolution transmission electron microscopy (TEM), X - ray diffraction (XRD) and BET surface area analysis. The electrochemical performance, availability, cost and manufacturability of these commercial carbons will be discussed.
INTRODUCTION The carbonaceous materials (both graphite and coke) that will be discussed were supplied by Superior Graphite Co., a leading producer of quality graphite, carbon and related materials for 80 years. Currently producing graphite related products at three different plants, Superior Graphite Co. has been able to be a leader in the graphite industry by expanding their operations from graphite mining to graphite processing and finally to the development of engineered graphitic materials. Utilizing Superior Graphite Co.'s unique high temperature furnaces (at the Hopkinsville KY and Russelville, Ark. plants) and advanced process technologies with raw material supplies (at the Chicago plant), several
575 Mat. Res. Soc. Symp. Proc. Vol. 496 01998 Materials Research Society
different types of carbon were examined and processed under a variety of conditions. Working in conjunction with Lawrence Berkeley National Laboratory and Lawrence Livermore National Laboratory, this study focused on how different carbon based materials, by varying processing steps, could produce low cost materials suitable for application in lithium - ion cells.
EXPERIMENTAL The cokes and graphites used in this study have been divided into two classes (graphitized and non graphitized) based on the highest heat treatment temperature to which the carbon was exposed to. This distinction was made because different electrolytes were used to evaluate these two classes of materials to minimize the irreversible capac
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