Lithiated graphite electrode

Due to its layered structure, graphite is the carbonaceous material most sensitive to the detrimental effects of interactions with solution species. Co-intercalation of solution species such as solvent molecules together with the Li ions may lead to exfoliation and destruction of their structure, as indeed happens in solutions of PC, y-BL, THF and other solvents [356-358], Lithiated graphite electrodes behave reversibly only in solutions in which highly passivating, stable surface layers are formed on the pristine material before any Li intercalation takes place. 

Figure 25 illustrates three cases of lithiated-graphite electrodes in solutions [87], (Typical chronopotentiograms are also presented.)... 

Figure 25 Typical chronoamperograms and schematic view of the structure of lithiated graphite electrodes in three classes of electrolyte solutions (as indicated). 1. Reversible behavior 2. partially reversible behavior, low capacity (x < 1 in LijC6 3. irreversible behavior, the electrode is deactivated and partially exfoliated before reaching intercalation stages. Note that in reality the graphite particles are usually flakes, the electrode s structure is porous and the surface films are also formed inside the electrode among the particles, and thus have aporous structure [87]. (With copyrights from Elsevier Science Ltd., 1998.)...

B. Markovsky, A. Rodkin, G. Salitra, Y. Talyosef, D. Aurbach, H.-J. Kim, The Impact of Co2-l- Ions in Solutions on the Performance of LiCo02, Li, and Lithiated Graphite Electrodes, J. Electrochem. Soc. 2004, 151, A1068-A1076. 

Figure 14 Typical impedance spectra measured from LiNi02, LiCo02, LiMn204, and lithiated graphite electrodes in EC-DMC/LiAsF solutions (Li as R.E. and C.E. elecfaodes). The potential of the measurements is indicated near each spectrum. A model that provides an excellent fit with these spectra is also presented. The assignment of its various elements to features of the experimental spectra is also shown. Reproduced with pennission from Elsevier Science. (See [95].)...

Markervich, E., Salitra, G., Levi, M.D., and Aurbach, D. (2005) Capacity fading of lithiated graphite electrodes studied by a combination of electroanalytical methods, Raman spectroscopy and SEM. J. Power Sources, 146, 146-150. 

Figure 12 compares typical Nyquist plots obtained from a noble metal electrode covered by surface films (deposited at low potentials in a Li salt solution), Li metal, and lithiated graphite electrodes. The figure also shows the expected structure of surface films formed on these electrodes and toe relevant equivalent circuit analogs for toe impedance behavior of the three electrodes. The surface films formed on aU three types of electrodes should have a multilayer stmcture, and they comprise toe compact inner part and a porous outer (solution side) part. Hence, toe simplest analog for describing ion transport under an electrical field through different... 

Figure 12. A schematic illustration of impedance spectra, relevant equivalent circuit analogs, and the structure of the surface films for lithium, lithiated graphite electrodes, and noble metal electrodes polarized to low potentials In Li salt, nonaqueous solutions. Reprinted from reference 219 with permission from Bsevier Sdenoe.

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