Graphene inducing graphitization: Towards a hard carbon anode with ultrahigh initial coulombic efficiency for sodium storage

Hard carbons exhibit great potential as anode materials for Sodium-ion batteries (SIBs). However, the large initial irreversible capacity is still a major obstacle in their practical application. It is widely known that lower surface area and fewer defects may increase the initial Coulombic efficiency (ICE) for carbon anode in SIBs. In this study, a graphene-induced graphitization strategy is proposed for synthesizing less defective hard carbon. This strategy is realized through the assembly of phenolic resin (PF) and graphene oxide (GO) taking advantage of their hydrogen bonding interaction. Thus, aromatic ring near graphene has a strong tendency to be arranged along the graphene layer during pyrolysis process, a significant transition from sp(3) to sp(2) hybridization carbon occurs, endowing hard carbon with fewer defects and lower surface area. The structural advantages of the hard carbon contribute to the superior ICE (90.4%), the highest ever reported, and excellent reversible specific capacity of 343 mA h g(-1) at 30 mA g(-1) even after 100 cycles.