Exfoliation of the graphene

The extent of the irreversible capacity depends on both the anode material and the electrolyte composition. Empirical knowledge indicates that the PC presence, which is well-known for its tendency to cause the exfoliation of the graphene structures, is especially apt to induce such irreversible capacities. On the other hand, reformulation of the electrolyte may lead to significant reduction in the irreversible capacity for given electrode materials. 

When the electrolyte solutions are not too reactive, as in the case of ethereal solutions, there is no massive formation of protective surface films at potentials above Li intercalation potential, and most of the solvent reduction processes may occur at potentials lower than 0.3 V vs. Li/Li+. Hence, the passivation of the electrodes is not sufficient to prevent cointercalation of solvent molecules. This leads to an exfoliation of the graphite particles into amorphous dust (expholiated graphene planes). This scenario is demonstrated in Figure 2a as the reduction of the 002 diffraction peak21 of the graphite electrode, polarized cathodically in an ethereal solution. 

Figure 3.7 Experimental setup diagram (left) and exfoliation of the graphite anode (right). Liu, N., Luo, E, Wu, H., Liu, Y, Zhang, C., and Chen, J. One-step ionic-liquid-assisted electrochemical synthesis of ionic-liquid-functionalized graphene sheets directly from graphite [91]. Copyright Wiley-VCHVerlag GmbH Co. KGaA. Reproduced with permission.

The relatively low cost of graphite in comparison to CNTs makes exfoliated graphite an attractive material (20). The use of graphite nanoplatelets is advantageous because of the chemistry of the graphene and graphene-Uke sheets compared to clay nanoplates. 

Bulk graphite oxide is best prepared from purified natural graphite using the Hummers method Hummers, W. S. Offeman, R. E. J. Am. Chem. Soc. 1958,80,1339. For the mechanical exfoliation of bulk graphene oxide into sheets within an aqueous medium, see Stankovich, S. Dikin, D. A. Dommett, G. H. B. Kohlhaas, K. M. Zimney, E. J. Stach, E. A. Finer, R. D. Nguyen, S. T. Ruoff, R. S. Nature 2006,442, 282. 

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