Activated microporous carbon spheres for electric double-layer capacitor

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 CO 2 activation. A high specific area (>3400 m 2 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 MeEt 3 NBF 4 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 EMIMBF 4 . 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. • Size-tunable resin spheres were synthesized by the modification of the extension-Stöber method. • The AMCS with a high specific area of 3456.62 m 2 g –1 and diameter of 420 nm. • The method provides a simple, cost-effective, environment-friendly and easily scalable process for production. • The pouch cells of AMCS and N-AMCS as the active materials have a good long- term cyclability.