Role of Oxygen Functional Groups in Electrochemical Sodium Ion Intercalation into Oxygen-Functionalized Graphitic Carbon Materials (Supporting Information)

Graphene-like graphite (GLG) is capable of reversible intercalation/deintercalation of sodium ions while the interlayer distance is almost the same as that of graphite, and elucidation of this factor will provide important insights into the design guidelines for anode materials for sodium-ion batteries. We focused on oxygen-containing functional groups in GLG and investigated their effect on the sodium ion intercalation potential using density functional theory calculations. It was found that the intercalation potential of sodium ions increased significantly in models containing lactones and ketones, leading to the formation of the low-stage intercalation compounds at higher potentials compared to sodium metal deposition reaction. In addition, it was suggested that the introduction of these functional groups changed the electronic state of the materials to increase electron acceptability, which contributed to the increase in potential. Furthermore, the negatively charged oxygen atoms interacted electrostatically with sodium ions, which to some extent had a positive effect on increasing the reaction potential. From these results, it was concluded that the oxygen-containing functional groups in GLG play a crucial role in the performance as anode materials of sodium-ion batteries.