Bamboo-derived hard carbon/carbon nanotube composites as anode material for long-life sodium-ion batteries with high charge/discharge capacities

Hard carbon derived from bamboo for the anode material of sodium-ion batteries has a three-dimensional (3D) open framework structure and has naturally incorporated K-ions into its carbon structure, increasing the d-interlayer spacing of hard carbon materials for facilitating Na⁺ transport. In this work, bamboo-derived hard carbon was prepared via two carbonization temperatures at 700 and 1000 °C for an hour and employed as an anode for sodium-ion batteries (SIB). X-ray diffraction (XRD) and Fourier transform (FT)-Raman spectroscopic results indicated the disordered structure with d-spacing (d₀₀₂) around 0.36–0.37 nm, which is a benefit for sodium ion insertion/desertion. Herein, the composition between carbon-nanotube (CNT) and bamboo-derived hard carbon (BB) was synthesized by a ball mill with various contents of CNT (1 wt%, 5 wt% and 10 wt%). At the optimal CNT content of 5 wt%, the sample exhibited excellent performance and outstanding stability. As the anode, the half-cell SIB using BB(700)w@5%CNT (with a carbonization temperature of 700 °C and CNT loading of 5 wt%) delivered a high initial specific capacity of 268.9 mAh·g⁻¹ at 0.1C and capacity retention of 78.6% after 500 cycles at 1.0C. The full cell SIB fabrication BB(700)w@5%CNT in combination with Na₃V₂(PO4)₃ as the cathode demonstrated a high specific capacity of 127.6 mAh·g⁻¹ at 0.2C with its capacitive retention remaining of 78% at 1.0C after 1000 cycles. The attained storage performance indicates that hard carbon-CNT composite anode material enhanced the conductive path of electron transport and provided long-term cycling stability. The good electrochemical performance as well as the low cost and environment-friendliness of the bamboo-derived hard carbon proves its suitability for future sodium-ion batteries.