Green needle coke-derived porous carbon for high-performance symmetric supercapacitor

The synthesis of low-cost and high-performance electrode material is one of the key challenges in the supercapacitor development. Herein, we report to prepare the porous carbon materials by thermal treatment using coal-based green needle coke. The as-synthesized porous carbon thermally treated at 750 °C achieves the best ideal electric double-layer capacitive performance, which is superior to the ones treated at other temperatures. Because of the high conductivity and free ion diffusion pathway possessed in porous carbon, high specific capacitance (274.9 F/g at 1A/g), and ideal coulomb efficiency (98.9% after 1000 circles at 5 A/g) of the sample observes in 3-electrode testing systems. The operational voltage window can be expanded to 0–1.8 V in 1 M Na2SO4 electrolyte for the 2-electrode system. Moreover, a symmetric button-type supercapacitor has assembled using the as-synthesized porous carbon supported on Ni-foam as both the positive and negative electrodes. The device delivers a high capacitance of 147.7 F/g, capacitive retention rate of 75.8% at 12 A/g, and a prominent energy density of 20.51 Wh/kg at power density of 1031.42 W/kg. Notably, the constructed supercapacitor shows outstanding cycling stability with capacity retention of 95.6% and coulombic efficiency of 98.5% after running 5000 cycles at 1 A/g.