Nitrogen-Doped Porous Carbon Structure from Melamine-Assisted Polyimide Sheets for Supercapacitor Electrodes

Nitrogen-doped porous carbon derived from various polymer precursors receives great attention for applications in supercapacitor electrodes due to its high specific area and fast ion transportation within the electrodes. The porous structure with high content of nitrogen atoms enhances the wettability and accelerates the diffusion of ions inside free-standing electrodes. These electrodes are fabricated by carbonization of nitrogen-rich carbon precursors such as polyimide and polyaniline. However, the porous structure and the high degree of nitrogen doping within electrodes are hard to maintain during the carbonization process. Herein, it is demonstrated that a new synthetic approach—nonsolvent-induced phase separation method—can prepare melamine-assisted polyimide sheet followed by carbonization process as nitrogen-rich supercapacitor electrodes with high porosity. A symmetric supercapacitor composed of the above-mentioned free-standing electrodes exhibits a specific capacitance of 176 F g⁻¹ at 1 A g⁻¹ (rate capability of 152 A g⁻¹ at 5 A g⁻¹) and long lifetime over 10 000 cycles with 99.2% capacitance retention. Also, the supercapacitor shows a high energy density of 6.3 W h kg⁻¹ and power density of 1.25 kW kg⁻¹. In conclusion the nitrogen-doped porous carbon sheet improves the energy density of a supercapacitor in comparison to electrodes prepared by conventional methods.