Enabling high-volumetric-energy-density supercapacitors: designing open, low-tortuosity heteroatom-doped porous carbon-tube bundle electrodes

In our work, we successfully design boron (B) and nitrogen (N) co- doped porous carbon tube bundle (B/N-PCTB) electrode materials which are directly derived from the biomass of dandelion fluff. The lowtortuosity, and open and porous structures contribute to electron transport along the tube wall and unimpeded ion diffusion inside the carbon tubes. The incorporation of heteroatoms into PCTBs can bring extra pseudocapacitance and double layer capacitance to enhance the overall capacitance. Benefiting from the hollow and open microstructure and heteroatom doping, the optimized B/N-PCTB electrode (active materials: 2.6 mg cm(-2)) possesses an impressive specific capacitance of 355 F g(-1) at 1 A g(-1). Even with an ultrahigh loading mass of 40 mg cm(-2), the electrode still has a relatively high specific capacity of 216 F g(-1) at 1 A g(-1). The assembled symmetric cell with an active material loading of 80 mg cm(-2) (cathode: 40 mg cm(-2); anode: 40 mg cm(-2)) shows a superior volumetric energy density of 12.15 W h L-1 at the power density of 699.84 W L-1. The facile yet high-performance porous carbon tube bundle is a promising material which can be applied in many other fields such as lithium ion batteries, hydrogen evolution reaction, and heavy metal ion adsorption.