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

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

TitleAn Investigation of the Effect of Graphite Degradation on Irreversible Capacity in Lithium-Ion Cells
Publication TypeJournal Article
Year of Publication2008
AuthorsLaurence J Hardwick, Marek Marcinek, Leanne Beer, John B Kerr, Robert Kostecki
JournalElectrochemical Society
Volume155
A442
Issue6
PaginationA442-A447
Keywordschromatography, electrochemical electrodes, electrochemical impedance spectroscopy, Fourier transform spectra, graphite, infrared spectra, lithium, mass spectra, Raman spectra, scanning electron microscopy, secondary cells, sputtering, surface structure
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 Mw on the order of 1600gmol−1 for the surface-modified electrode with no evidence of elevated Mw 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.

DOI10.1149/1.2903882