Highly porous carbon spheres for electrochemical capacitors and capacitive flowable suspension electrodes

In flowable and conventional electrochemical capacitors, the energy capacity is largely determined by the electrode material. Spherical active material, with high specific surface area (SSA) represents a promising material candidate for film and flow capacitors. In this study, we synthesized highly porous carbon spheres (CSs) of submicrometer size to investigate their performance in film and suspension electrodes. In particular, we studied the effects of carbonization and activation temperatures on the electrochemical performance of the CSs. The CSs activated at optimum conditions demonstrated narrow pore size distribution (<3 nm) with high SSA (2900 m²/g) and high pore volume (1.3 cc/g), which represent significant improvement as compared to similar materials reported in literature. Electrochemical tests of CSs in 1 M H₂SO₄ solution showed a specific capacitance of 154 F/g for suspension electrode and 168 F/g for film electrode with excellent rate performance (capacitive behaviors up to 100 mV/s) and cycling performance (95% of initial capacitance after 5000 cycles). Moreover, in the film electrode configuration, CSs exhibited high rate performance (78 F/g at 1000 mV/s) and volumetric power density (9000 W/L) in organic electrolytes, along with high energy density (21.4 Wh/L) in ionic liquids.