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

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 ͑SEI͒ 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.