Nitrogen-Doped Carbon Membrane Derived from Polyimide as Free-Standing Electrodes for Flexible Supercapacitors

Nitrogen-doped carbon materials have attracted great interest in the energy storage due to the better electrochemical performances than the pristine carbon materials. In this work, a heterocyclic polyimide containing benzopyrrole and benzimidazole rings is carbonized to fabricate the free-standing and flexible carbon membrane (CarbonPI ) with a high packing density (0.89 cm(-3)), in which the location of nitrogen atoms in the doped configurations is easily controlled. XPS analysis indicates that quaternary nitrogen is the predominant nitrogen-doped configurations. The high content of nitrogen effectively improves the wettability of the electrode materials. The CarbonPI membrane exhibits excellent volumetric capacitance (159.3 F cm(-3) at 1 A g(-1)), high rate capability (127.5 F cm(-3) at 7 A g(-1)), and long cycle life. TEM images reveal the very slight change of the microstructure of graphitic nanosheet of CarbonPI during the long charge/discharge cycles.