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

Abstract 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 ( d 002 ) 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 Na 3 V 2 (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.