Hierarchical Design for Fabricating Cost‐Effective High Performance Supercapacitors

The salient feature of a supercapacitor is its ability to deliver much higher power density than a battery. A hierarchical design and a cost‐effective approach to fabricate high performance supercapacitors using functional carbon nano‐particles is reported. A special arc synthesis method is used to produce amorphous/crystalline composite with nitrogen and boron co‐doped high charge density carbon nanoparticles. Upon etch removal of the amorphous phase in the composite nanoparticle, a crystalline carbon framework emerges, consisting of a mixture of nano‐graphitic sheets mostly in the middle and single nanohorns distributed around the surface of the nanoparticle. These nanoparticles have large internal/external surfaces with subnano channels and sharp nano‐tips for high speed charge transport and local charge accumulation. To deliver high power density, the internal resistance of the device is reduced by assembling the nanoparticles via electro‐spraying and compacting them into dense films (without any binder) under 700 MPa of pressure before supercapacitor assembly. Taken together, the hierarchical processed supercapacitor has a very high (compared to literature values) power density of nearly 4.5 kW cm⁻³ and a respectable energy density of 2.45 mWh cm⁻³. Combining these carbon nanoparticles with large area spraying coating, it can lead to a cost‐effective production of high performance supercapacitors.