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.