Ultrasonic-ethanol assisted exfoliation for synthesis of biomass waste-derived porous carbon for high-rate supercapacitors

As an energy storage device with performance and mechanism different from batteries, supercapacitor is widely used in microelectronics and electric vehicle industries, but it is difficult to apply on a large scale due to its poor energy density and rate performance caused by low specific surface area utilization and proportion of mesopores. Herein, scallion peel is used as raw material and a pretreatment method of ultrasonic-assisted ethanol extraction is proposed to prepare a highly ordered hydrophilic sheet-like porous carbon (PC) with a high content of mesopores. The optimized PC shows excellent specific capacitance (421.62 F g(-1) at 1 A g(-1)), good conductivity and high-rate performance (capacitance retention is 84.2% from 0.5 to 50 A g(-1)). In addition, the specific capacitance still retains 94.0% after 10,000 cycles at 5 A g(-1). When the power density of the assembled supercapacitor is 27,058.61 W kg(-1), the energy density in the aqueous electrolyte (6 M KOH) remains 12.53 Wh kg(-1). The result shows that this pretreatment of the precursor results in the optimization of the pore structure and surface properties of the sample, so the electrochemical performance of PC has improved. This work not only promotes the multi-level utilization of biomass waste, but also provides a new idea for the synthesis of PC for high-rate supercapacitors.