First-principles Insight into Li and Na Ion Storage in Graphene Oxide*

The structural, electronic, and adsorption properties of Li/Na ions on graphene decorated by epoxy groups are investigated by first-principles calculations based on density functional theory. Our results show that the concentration of epoxy groups remarkably affects the structural and electronic properties of graphene. The bandgaps change monotonically from 0.16 eV to 3.35 eV when the O coverage increases from 12.5% to 50% (O/C ratio). Furthermore, the highest lithiation potential of 2.714 V is obtained for the case of graphene oxide (GO) with 37.5 % O coverage, while the highest sodiation potential is 1.503 V for GO with 12.5% O coverage. This clearly demonstrates that the concentration of epoxy groups has different effects on Li and Na storage in GO. Our results provide a new insight into enhancing the Li and Na storage by tuning the concentration of epoxy groups on GO.