Surface-Dominated Sodium Storage Towards High Capacity and Ultrastable Anode Material for Sodium-Ion Batteries

The development of sodium-ion batteries is hindered by the poor Na+ transport kinetics and structural instability of electrode materials during Na+ intercalation/deintercalation. In this work, surface-dominated Na storage is demonstrated on the oxygen-functionalized graphene nanosheets (FGS) with fast surface redox reaction and robust structural stability. The FGS samples with tunable oxygen contents and species are fabricated via a two-step thermal exfoliation method from graphite oxides. The surface-induced oxygen functional groups can serve as the surface-redox sites for the FGS electrode, attaining a high specific capacity of 603 mAh g(-1) at a current density of 0.05 A g(-1), excellent rate capability (214 mAh g(-1) at 10 A g(-1)), and ultrastable cycling stability (capacity retention close to 100% after 10 000 cycles at 5 A g(-1)). Even at a slow scan rate of 0.1 mV s(-1) for cyclic voltammetry, about 67.7% capacity is contributed from the surface adsorption/desorption and surface-redox reaction, suggesting surface-dominated Na storage for the FGS-700 (FGS sample obtained at 700 degrees C) electrode. The present work demonstrates that the surface oxygen functionalization is an effective strategy to develop high-performance graphene-based anodes due to the surface-dominated Na storage with improved reaction kinetics and suppressed structural variation.