Engineering carbon nanosheets with hexagonal ordered conical macropores as high-performance sodium-ion battery anodes.

As one of the most promising candidates for sodium-ion battery anodes, hard carbons suffer from inferior rate performance owing to limited ion transfer rate and sluggish electrochemical kinetics. In this work, novel carbon nanosheets (CNS) with hexagonal ordered conical macropores are prepared. The CNS has a very thin thickness of approximately 370 nm, and the conical pores are penetrated through the whole nanosheet, forming well-connected ion transport freeway. In addition, the carbon microcrystal structure and interlayer spacing can be well tailored by adjusting the carbonization temperature, thereby controlling the sodium storage behavior of carbon electrodes. These structural merits endow CNS with accelerated ion transfer, minimized ion diffusion distance and fast electrochemical kinetics. Consequently, the CNS presents superior electrochemical performance. It delivers a high reversible capacity of 298 mAh g-1 at 0.1 A g-1; and after repeated charge/discharge for 500 times at 1 A g-1, its capacity remains 195 mA h g-1, with no rapid capacity loss. More importantly, CNS exhibits outstanding rate capability. Even under a very high current density of 2 A g-1, it still displays a large capacity of 210 mAh g-1, higher than most of state-of-the-art carbon anodes.