Enhanced Li capacity at high lithiation potentials in graphene oxide

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. 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. In highly oxidized and mildly reduced sheets, lithiation occurs through formation of Li-O bonds, whereas at low coverages, typical of reduced-GO (rGO) (O:C similar to 12.5%), both Li-O bonds and LiC6 configurations are observed. The covalent Li-O bond is much stronger than the bonds in the LiC6 ring and the lithiation potentials for epoxides at high and medium coverages are generally large (>1 eV). For these configurations, as for Li4Ti5O12 anodes, there is no formation of SEI, but with the additional advantage of higher lithium storage capacity. In rGO, the presence of residual oxygen atoms allows formation of covalent Li-O bonds leading 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 impede the formation of SEI and lead to large reversible capacity. (C) 2011 Elsevier B.V. All rights reserved.