Hard carbon derived from sepals of Palmyra palm fruit calyx as an anode for sodium-ion batteries

Hard carbons with large interlayer spacing, disordered structures and interconnected porosity at low cost, are considered as promising anode materials for sodium-ion batteries (NIB). In this work, we report the synthesis of hard carbon anode materials from sepals of palm fruit calyx (bio-waste) that are prepared by carbonization at moderate temperature between 500 °C and 900 °C. Electron microscopy studies show that the resultant hard carbon is highly porous with interconnected porous network. X-ray diffraction and Raman spectroscopic analyses indicate that the carbonized materials possess disordered structure with large interlayer spacing (0.37 nm). The electrochemical studies reveal that hard carbon which is pyrolyzed at 700 °C (WHC-700) shows better performance, delivering 397 mAh g−1 and 280 mAh g−1, initial discharge and charge capacities, respectively. Specific capacities of about 275 mAh g−1 and 175 mAh g−1 are achieved for WHC-700 material at a current density of 30 and 200 mA g−1, respectively. The sepals of Palmyra palm fruit calyx (bio-waste material) yield hard carbon material at moderate carbonization temperature with optimum microstructural properties and larger interlayer spacing. These attributes are responsible for their good electrochemical performance as an anode material for NIBs.