Porous carbon nanosheets derived from expanded graphite for supercapacitors and sodium-ion batteries

Two-dimensional carbons have attracted extensive interest in the field of energy storage and conversion owing to their unique nanostructure, high aspect ratios, and abundant surface-active sites. In this work, carbon nanosheets with developed porosity and high specific surface area were fabricated from expanded graphite (EG) by a siliconization/chlorination strategy. The worm-like macroporous structure and nanosheet morphology of EG are inherited by the resultant carbon nanosheet. The siliconization/chlorination strategy creates abundant micropores in EG, endowing the as-obtained carbon nanosheet with a high specific surface area of 1229 m² g⁻¹ and a total pore volume of 0.75 cm³ g⁻¹. With high specific surface area, nanosheet morphology, and macroporous structure, the EG-based carbon nanosheet presents excellent performance when used as electrode materials of supercapacitors and sodium-ion batteries. When used as an electrode of supercapacitors, it delivers a specific capacitance of 210 F g⁻¹, retains 62% of the initial capacitance with increasing current density from 0.1 to 30 A g⁻¹, and maintains 98.6% of the initial capacitance after 5000 cycles. When used as the anode of sodium-ion batteries, it presents a reversible capacity of 198 mAh g⁻¹ at 0.1 A g⁻¹ and maintains 65 mAh g⁻¹ after 1000 cycles at 5 A g⁻¹. The proposed strategy could be extended to other sp² carbon materials for a highly porous structure.