Nitrogen, Sulfur, and Phosphorus Codoped Hollow Carbon Microtubes Derived from Silver Willow Blossoms as a High-Performance Anode for Sodium-Ion Batteries

Hard carbon materials have been considered as one of the most promising candidates as the anode in sodium-ion batteries. However, scale application of state-of-the-art hard carbon anodes is still hampered on account of their complicated, toxic, and time-consuming preparation techniques. In the present paper, silver willow blossoms composed of natural micrometer-scale fibers are employed to construct N, S, and P codoped hollow carbon microtubes (HCMTs) by direct high-temperature carbonization. The HCMT has a nanoscale wall with several micrometer-sized hollow cavities, which is facilitated to optimize the sodium-ion transfer. In addition, the temperature-dependent, tailorable interlayer spacing coupled with doped heteroatoms is able to provide sufficient energy storage sites. By combining these unique structural advantages, the HCMT exhibits impressive sodium storage performance. The HCMT sample pyrolyzed under 1300 °C is able to deliver a highly reversible capacity of 302 mAh g^–1, and after repeated charge/discharge for 100 times, the capacity retains 301 mAh g^–1, indicating no visible degradation. Moreover, under a large current density up to 1 A g^–1, a high capacity of 201 mAh g^–1 is still achieved, demonstrating good rate capability.