Renewable graphene-like nitrogen-doped carbon nanosheets as supercapacitor electrodes with integrated high energy-power properties

The development of supercapacitors with integrated high energy-power properties coupled with long cyclic life is an urgent demand in the energy storage field. The key to the assembly of such devices is to design and fabricate novel high-performance electrode materials in conjunction with matched electrolytes. In this study, a renewable graphene-like nitrogen-doped carbon nanosheet (RGNC-NS) has been constructed by using simultaneous carbonization and auto-activation followed by ultrasonic-assisted liquid exfoliation from natural layered shrimp shells. The final RGNC-NS had an optimum integration of graphene-like nanostructures (∼5 nm thick), large specific surface area (1946 m² g^-1), and rich nitrogen doping (8.75 wt%), resulting in high conductivity (7.8 S cm^-1) and good surface wettability with an electrolyte. The RGNC-NS as a supercapacitor electrode exhibited an excellent rate capability with an ultrahigh capacitance of 322 F g^-1 at 0.5 A g^-1 and 241 F g^-1 at 100 A g^-1 (75% retention), as well as a long cyclic stability of 98.3% capacitance retention after 20 000 cycles at 10 A g^-1 in 6 M KOH. Moreover, the RGNC-NS in a mixed ionic liquid electrolyte displayed an integrated high energy-power density of 30 W h kg^-1 energy density at 64 000 W kg^-1 power density and 93.2% capacitance retention after 8000 cycles at 5 A g^-1.