Hierarchical Design for Fabricating Cost‐Effective High Performance Supercapacitors

Abstract

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 fi lms (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. IntroductionAdvances in the development of renewable energy sources and energy storage systems have propelled the need to design and fabricate ever higher charge-density nanoparticles (HCDN). To this end it is desirable to design a nanostructure with a large surface area for a given total volume or mass. Equally important is the consideration of surface reactivity and the availability of nanoscale channels for atomic/charged species to access HCDN were part of our design consideration. Below we start with the study of HCDN synthesis and characterization at each length scale, and then followed by a discussion on supercapacitor fabrication and its performance. Results and Discussion HCDN Fabrication and Structural AnalysisThe fi rst goal is to synthesize a HCDN with near spherical shape consisting of doped crystalline frame-work having numerous internal nano-channels and sharp tips for the transport and accumulation of charges. To achieve such an architecture the following two-step processing sequence was taken to synthesize the unique HCDN: First, a composite nanoparticle was synthesized consisting of fi ne lamella layers of crystalline carbon sandwiched between amorphous layers of nitride and/ or carbide materials. Second, the amorphous layers of the composite nanoparticle were selectively etched away by heating the sample in air at 450˚C to produce the desired structure.DC arcs have been extensively used in nano carbon studies. [10][11][12][13][14] To perform the fi rst step, we used a DC arc that was confi gured as a high temperature furnace where a hole in the cathode serves as a crucible which can be fi ll...

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