Biomass-derived three-dimensional honeycomb-like hierarchical structured carbon for ultrahigh energy density asymmetric supercapacitors

Porous carbon materials derived from various biomasses have aroused intense interest from the scientific community due to their low cost, abundant resources, eco-friendliness and easy fabrication. Herein, three-dimensional honeycomb-like hierarchical structured carbon (HSC) has been fabricated by one-step carbonization/activation of abundant and low cost bacterial cellulose for ultrahigh energy density supercapacitors. Benefitting from its interconnected honeycomb-like hierarchical and open structure with a high specific surface area, the prepared HSC exhibits a superhigh specific capacitance of 422 F g(-1) at 2 mV s(-1) with remarkable rate performance (73.7% at 500 mV s(-1)) in 6 M KOH aqueous electrolyte. Meanwhile, the symmetric supercapacitor could deliver a high energy density of 37.3 W h kg(-1) in 1 M Na2SO4 aqueous electrolyte. To evaluate the practical application, an asymmetric supercapacitor fabricated with NiCoAl-layered double hydroxide as the positive electrode and HSC as the negative electrode achieves a conspicuously high energy density of 100 W h kg(-1) and could still retain 33 W h kg(-1) even at a high power density of 36.8 kW kg(-1), which is highly comparable with or even higher than those of the previously reported asymmetric supercapacitors in aqueous electrolytes. Furthermore, our asymmetric supercapacitor exhibits excellent cycling stability along with 113% capacitance retention after 10 000 cycles. Such spectacular results will shed new light on biomass-derived carbon materials for the next generation of ultrafast energy storage devices with high energy density and excellent long cycle life.