High power supercapacitors using polyacrylonitrile-based carbon nanofiber paper

Porous carbon nanofiber paper has been obtained by one-step carbonization/activation of PAN-based nanofiber paper at temperatures from 700 to 1000 °C in CO₂ atmosphere. The paper was used as supercapacitor electrode without any binder or percolator. At low temperature, e.g., ?900 °C, nitrogen enriched carbons with a poorly developed specific surface area (S_BET ? 400 m²/g) are obtained. In aqueous electrolytes, these carbons withstand high current loads without a noticeable decrease of capacitance, and the normalized capacitance reaches 67 μF/cm². At 10 s time constant, the values of energy and power densities are 3-4 times higher than for activated carbons (AC) presenting higher specific surface area. By carbonization/activation at 1000 °C, subnanometer pores are developed and S_BET = 705 m²/g. Despite moderate BET specific surface area, the capacitance reaches values higher than 100 F/g in organic electrolyte. At high power densities, the nanofiber paper obtained at 1000 °C outperforms the energy density retention of ACs in organic electrolyte. The high power capability of the carbon nanofiber papers in the two kinds of electrolytes is attributed both to the high intrinsic conductivity of the fibers and to the high diffusion rate of ions in the opened mesopores.