Constructing Conductive Graphitic Structure on Hard Carbon as an Efficient Free-Standing Anode for Sodium-Ion Batteries

Hard carbon as a candidate anode for sodium-ion batteries, its rate capability is still a big challenge due to poor conductivity. In this work, conductive graphitic carbon structure was constructed on hard carbon (HC/NF-1, HC/NF-2, and HC/NF-3) by a simple hydrothermal and catalytic graphitization method, and used as a freestanding anode for sodium-ion batteries. The graphitic carbon consists of ∼84 graphitic layers. HC/NF-2 displays high reversible capacity (285.6 mAh·g−1 at 0.1 A·g−1), excellent rate capability (107.1 mAh·g−1 at 5.0 A·g−1), and long-term cycle performance (166.2 mAh·g−1 at 1.0 A·g−1 after 1000 cycles). The remarkable electrochemical performances of HC/NF-2 are mainly attributed to the construction of graphitic carbon, which significantly improves the conductivity of hard carbon and accelerates the migration of electrons. In addition, HC/NF-2 with a suitable thickness of solid-phase hard carbon provides more sodium storage sites and shortens the sodium ions diffusion pathway during discharge/charge cycles. Importantly, the macroporous Ni foam used as a current collector can effectively expand the contact area between the electrolyte and electrode. These results indicate this work can provide a reference for designing other composite carbon-based material for high-performance energy storage systems.