Alkali-Metal-Ion-Functionalized Graphene Oxide as a Superior Anode Material for Sodium-Ion Batteries

Although graphene oxide (GO) has large interlayer spacing, it is still inappropriate to use it as an anode for sodium-ion batteries (SIBs) because of the existence of H-bonding between the layers and ultralow electrical conductivity which impedes the Na+ and e(-) transformation. To solve these issues, chemical, thermal, and electrochemical procedures are traditionally employed to reduce GO nanosheets. However, these strategies are still unscalable, consume high amounts of energy, and are expensive for practical application. Here, for the first time, we describe the superior Na storage of unreduced GO by a simple and scalable alkali-metal-ion (Li+, Na+, K+)-functionalized process. The various alkali metals ions, connecting with the oxygen on GO, have played different effects on morphology, porosity, degree of disorder, and electrical conductivity, which are crucial for Na-storage capabilities. Electrochemical tests demonstrated that sodium-ion-functionalized GO (GNa) has shown outstanding Na-storage performance in terms of excellent rate capability and long-term cycle life (110 mAh g(-1) after 600 cycles at 1 Ag-1) owing to its high BET area, appropriate mesopore, high degree of disorder, and improved electrical conductivity. Theoretical calculations were performed using the generalized gradient approximation (GGA) to further study the Na-storage capabilities of functionalized GO. These calculations have indicated that the Na-O bond has the lowest binding energy, which is beneficial to insertion/extraction of the sodium ion, hence the GNa has shown the best Na-storage properties among all comparatives functionalized by other alkali metal ions.