  We have studied lithiation of graphene oxide (GO) as a function of oxygen
coverage using first principles calculations. Our results show that the
lithiation potentials and capacities in GO can be tuned by controlling the
oxygen coverage, or the degree of reduction. We find a range of coverages where
the lithiation potentials are above the solid electrolyte interface (SEI)
formation threshold, but with capacities comparable to, or larger than
graphite. We observe that in highly oxidized and mildly reduced sheets,
lithiation occurs through the formation of Li-O bonds, whereas at low coverages
that are typical of reduced-GO (rGO) (O:C - 12.5 %), both Li-O bonds and LiC6
configurations are observed. The covalent Li-O bond is much stronger than the
bonds formed in the LiC6 ring and the lithiation potentials for epoxides at
high and medium coverages are generally large (> 1 eV). For these
congifurations, as in the case of Li4Ti5O12 anodes, there will be no formation
of SEI, but with the additional advantage of having higher lithium storage
capacity than Li4Ti5O12. In reduced GO sheets, the presence of residual oxygen
atoms allows for formation of covalent Li-O bonds that lead to storage
capacities and lithiation potentials higher than that of graphite. Finally, our
calculations show high lithiation potentials for the edges of graphene
nanoribbons, which will impede the formation of SEI and hence lead to large
reversible capacity.

Materials Science