Soluble starch-derived porous carbon microspheres with interconnected and hierarchical structure by a low dosage KOH activation for ultrahigh rate supercapacitors.

The developed porous structure and high density are essential to enhance the bulk performance of carbon-based supercapacitors. Nevertheless, it remains a significant challenge to optimize the balance between the porous structure and the density of carbon materials to realize superior gravimetric and areal electrochemical performance. The soluble starch-derived interconnected hierarchical porous carbon microspheres were prepared through a simple hydrothermal treatment succeeded by chemical activation with a low dosage of KOH. Due to the formation of interconnected spherical morphology, hierarchical porous structure, reasonable mesopore volume (0.33 cm g) and specific surface area (1162 m g), the prepared carbon microsphere has an ultrahigh capacitance of 394 F g @ 1 A g and a high capacitance retention of 62.7 % @ 80 A g. The assembled two-electrode device displays good cycle stability after 20,000 cycles and an ultra-high energy density of 11.6 Wh kg @ 250 W kg. Moreover, the sample still exhibits a specific capacitance of 165 F g @ 1 A g at a high mass loading of 10 mg cm, resulting in a high areal capacitance of 1.65 F cm. The strategy proposed in this study, via a low-dose KOH activation process, provides the way for the synthesis of high-performance porous carbon materials.