Activated microporous carbon spheres for electric double-layer capacitor

Abstract

Supercapacitors (SC) are essential energy storage devices for renewable energies. In this study, activated microporous carbon spheres (AMCS) and nitrogen-doped AMCS (N-AMCS) were synthesized using a modified extended Stöber method followed by CO2 activation. A high specific area (>3400 m2 g−1) was obtained for AMCS and N-AMCS, and the diameters of the sphere could be tuned from 400 nm to 1.0 µm. The SC study revealed that the AMCS and N-AMCS achieved specific capacitances of 232.75 and 263.59 F g−1, respectively, in 6 M potassium hydroxide (KOH). The SC pouch cells were filled with aqueous, organic, and ionic liquid electrolytes. In 1 M MeEt3NBF4 in acetonitrile, the energy densities of AMCS and N-AMCS were 27.96 and 31.20 Wh kg−1, respectively, at the current density of 0.5 A g−1, whereas the energy densities of AMCS and N-AMCS were 69.19 and 117.69 Wh kg−1, respectively, in EMIMBF4. In addition, in the aqueous electrolytes, AMCS and N-AMCS had capacitance retentions of 94% and 97%, respectively, after 10,000 cycles, while the capacitance retentions of 82% and 97% were achieved with AMCS and N-AMCS, respectively, after 50,000 cycles.