Heteroatom-doped hierarchically porous carbons derived from cucumber stem as high-performance anodes for sodium-ion batteries

Sodium-ion batteries (SIBs) are regarded as one of the most promising alternatives to lithium-ion batteries (LIBs) for large-scale energy stationary applications due to the abundant reserve of sodium. However, it is still challenging to develop low-cost and high-performance anode materials for SIBs. Herein, heteroatom-doped hard carbons with hierarchically porous and disordered structures are prepared via pyrolysis of natural biomass cucumber stem. The electrochemical performances of the biomass carbon are significantly influenced by the carbonization temperatures due to the different microstructures and heteroatomic contents. The biomass carbon carbonized at 1000 °C delivers the highest reversible capacity of 337.9 mAh g⁻¹ while used as the anode material for SIBs. Furthermore, the biomass carbon achieves a sheet-like morphology with macroscopically open structure after the hydrothermal activation of KOH. It is worth noting that the activated carbon exhibits a high reversible capacity (458.6 mAh g⁻¹), an excellent rate capability (102.6 mAh g⁻¹ at 10 A g⁻¹) and a cycling stability (198.6 mAh g⁻¹ at 0.2 A g⁻¹ over 500 cycles). The enhanced electrochemical properties of the activated carbon can be attributed to the larger surface area and highly developed nanopores, which could significantly facilitate the transport and storage of sodium ions.