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The Electrochemical Society, Journal of The Electrochemical Society, 6(155), p. A442, 2008

DOI: 10.1149/1.2903882

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An Investigation of the Effect of Graphite Degradation on Irreversible Capacity in Lithium-ion Cells

This paper is available in a repository.
This paper is available in a repository.

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Abstract

The effect of surface structural damage on graphitic anodes, commonly observed in tested Li-ion cells, was investigated. Similar surface structural disorder was artificially induced in Mag-10 synthetic graphite anodes using argon-ion sputtering. Raman microscopy, scanning electron microscopy, and Brunauer-Emmett-Teller measurements confirmed that Ar-ion sputtered Mag-10 electrodes display a similar degree of surface degradation as the anodes from tested Li-ion cells. Artificially modified Mag-10 anodes showed double the irreversible charge capacity during the first formation cycle compared to fresh unaltered anodes. Impedance spectroscopy and Fourier transform infrared spectroscopy on surface-modified graphite anodes indicated the formation of a thicker and slightly more resistive solid electrolyte interphase (SEI) layer. Gas chromatography/mass spectroscopy analysis of solvent extracts from the electrodes detected the presence of new compounds with M(w) on the order of 1600 g mol(-1) for the surface-modified electrode with no evidence of elevated M(w) species for the unmodified electrode. The structural disorder induced in the graphite during long-term cycling may be responsible for the slow and continuous SEI layer reformation, and consequently, the loss of reversible capacity due to the shift of lithium inventory in cycled Li-ion cells. (C) 2008 The Electrochemical Society.