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AFRL selects XG Sciences to develop graphene nanoplatelet-based high-energy ultracapacitors; potential benefit for automotive applications

Hybrid supercapacitor electrodes from xGnP. Source: Lawrence Drzal. Click to enlarge.

The Air Force Research Laboratory (AFRL) recently selected XG Sciences, a spin-off company from Michigan State University, to develop ultrahigh-energy ultracapacitors for use in space energy storage systems.

XG Sciences supplies exfoliated graphite nanoplatelets (xGnP) that can be formulated into inks and pastes for fabrication of electrodes for ultracapacitors, batteries, and fuel cells. XG Sciences’ technologies were developed in large part at the Composite Materials and Structures Center in the Michigan State University College of Engineering.

Representation of a typical xGnP nanoplatelet. Click to enlarge.

Each particle consists of several sheets of graphene with an overall thickness ranging from an average of about 5 nm to about 15nm, depending on grade. Particle diameters can range from sub-micron to 50+ microns.

The project is supported by the Air Force Research Laboratory under Contract Nº FA9453-12-M-0032.

Our Air Force contract will target development of ultracapacitors capable of delivering the high specific energy necessary for advanced space applications. Our graphene-based energy storage materials deliver significant improvements over traditional carbon charge storage materials due to their highly accessible surface area, low resistance current carrying capability, and tailorable particle size. We believe that this research will also help advance the state-of-the-art in ultracapacitors for automotive and industrial applications.

—Rob Privette, XGS VP Energy Markets

The primary disadvantage of the current generation of supercapacitors is the relatively low energy density, notes XGS Chief Scientist and MSU professor Dr. Lawrence Drzal. A solution to increasing energy density rests in utilizing electrode materials with higher specific capacitance in organic electrolytes coupled with a reduction in the amount of inactive binder.

While activated carbons are considered excellent electrode materials for supercapacitors, they tend to suffer from low electrical conductivity and high resistance to ion transport resulting from complex pore structures. The net result, notes Drzal, is that supercapacitors of activated carbons produce small specific capacitance, thereby restricting their successful application as high power density supercapacitor electrode materials. Graphene, however, offers the potential to utilize carbon but in a structure that overcomes the limitations of activated carbon.

In a 2010 paper published in the journal ACS Applied Materials & Interfaces, Drzal and Sanjib Biswas used graphene nanosheets prepared by direct exfoliation to build a multilayer film that exhibited superior high-frequency capacitative properties with a knee frequency close to 398 Hz and a nearly rectangular cyclic voltammogram at 1000 mV/s for high-power supercap applications.

A major benefit in our approach is that nanomaterials of a desired architecture along with graphene’s attractive physical and chemical characteristics can be synthesized into an architecture consisting of large and small graphene nanosheets into a highly dispersed and aligned network in a bulk macroscopic configuration designed to maximize device performance.

Monolayers of large-sized nanosheets function as a series of highly electrically conducting current collectors within the mesoporous network of small-sized graphene nanosheets for improved rate capability of EDLC electrode with a specific capacitance of 80 F/g at a high discharge current density of 10 A/g. These inexpensive graphene nanosheets and the ease of the process to produce the aligned nanostructure make this new material and method highly advantageous for high power supercapacitor applications

—Biswas and Drzal 2010



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