Nanotek Instruments (Dayton, OH), parent company of Angstron Materials Inc., received U.S. Patent 7,623,340 for its development of a new high-performing class of graphene meso-porous nanocomposites. According to inventors Lulu Song, Aruna Zhamu, Jiusheng Guo and Bor Z. Jang, a supercapacitor featuring such a nanocomposite exhibits an exceptionally high capacitance value.
FIG. 1 shows an atomic force microscopic picture of a sample of NGPs. In practice, NGPs are obtained from a precursor material, such as minute graphite particles, using a low-cost process, but not via flattening of carbon nanotubes (CNTs). These nano materials could potentially become cost-effective substitutes for CNTs or other types of nano-rods for various scientific and engineering applications.
The new nanocomposite provides a superior supercapacitor electrode material for uses that include hybrid electric vehicles (EVs), transportation and energy storage. The technology is based on the company’s breakthrough discovery of nano graphene platelets (NGPs). Angstron, the world leader in production of NGPs, will make the nanocomposite material.
The NGP-based nanocomposite exhibits high levels of capacitance and electrical conductivity as well as demonstrating chemical stability and low mass density. Both NGPs and NGP-based nanocomposites can be mass produced cost-effectively when compared to carbon nano-tubes and fibers. Supercapacitors containing this advanced material offer the potential to supplement a battery used in an electric car to provide bursts of power needed for rapid acceleration. Until now, this critical requirement has been the largest technical hurdle to making battery-powered cars commercially viable.
In addition, supercapacitors must also be able to store sufficient energy to provide an acceptable driving range. The new NGP-based material makes it possible for a supercapacitor to meet weight and cost targets while combining adequate energy and power with a long cycle life. Angstron will provide the meso-porous NGP nanocomposites in two forms: NGPs coated with a thin layer of conducting polymer or surface functional groups and NGPs bonded by a conductive binder, coating, or matrix material such as a polymeric carbon.
The platelets in these products are comprised of a sheet of graphite plane or multiple sheets of graphite plane with a thickness less than 10 nm and an average length, width, or diameter smaller than 500 nm. The binder or matrix material bonded to the platelets to form the nanocomposite material create a surface area greater than 500 m.sup.2/gm.
Angstron Materials leads the industry as the only advanced materials company to offer large quantities of both pristine graphene and oxidized graphene. Multi-layer graphene, both pristine and oxidized versions, are collectively referred to as nano graphene platelets (NGPs). NGPs offer improved performance properties including very high
Young’s modulus, strength and surface area, superior thermal and electrical conductivity, lower density and less weight. NGPs are also resistant to gas permeation. As a result, Angstron is able to work with companies to develop products for batteries, fuel cells, supercapacitors, light weight structural components as well as electromagnetic interference (EMI), radio frequency interference (RFI), electrostatic discharge (ESD), lightning strike and other functional and structural composite applications.
In addition to its ability to provide sample materials and scale-up, Angstron partners with customers to help manufacturers identify optimal designs, experience with research and development to help manufacturers harness the advantages of nano compositions and manufacturing processes. Available in a wide range of geometries, NGP products are easily surface functionalizable for polymer and common solvent applications and offer high loading potential for nanocomposite applications. Angstron combines real world technology to make next generation products in the aerospace, automotive, energy, marine, construction, electronics, medical, and telecommunications markets.
Electrochemical capacitors (ECs), also known as ultracapacitors or supercapacitors, are being considered for uses in hybrid electric vehicles (EVs) where they can supplement a battery used in an electric car to provide bursts of power needed for rapid acceleration, the biggest technical hurdle to making battery-powered cars commercially viable. A battery would still be used for cruising, but capacitors (with their ability to release energy much more quickly than batteries) would kick in whenever the car needs to accelerate for merging, passing, emergency maneuvers, and hill climbing.
The EC must also store sufficient energy to provide an acceptable driving range. To be cost- and weight-effective compared to additional battery capacity they must combine adequate specific energy and specific power with long cycle life, and meet cost targets as well. Specifically, they must store about 400 Wh of energy, be able to deliver about 40 kW of power for about 10 seconds, and provide high cycle-life (>100,000 cycles).
ECs are also gaining acceptance in the electronics industry as system designers become familiar with their attributes and benefits. ECs were originally developed to provide large bursts of driving energy for orbital lasers. In complementary metal oxide semiconductor (CMOS) memory backup applications, for instance, a one-Farad EC having a volume of only one-half cubic inch can replace nickel-cadmium or lithium batteries and provide backup power for months. For a given applied voltage, the stored energy in an EC associated with a given charge is half that storable in a corresponding battery system for passage of the same charge. Nevertheless, ECs are extremely attractive power sources.
ECs are also gaining acceptance in the electronics industry as system designers become familiar with their attributes and benefits. ECs were originally developed to provide large bursts of driving energy for orbital lasers. In complementary metal oxide semiconductor (CMOS) memory backup applications, for instance, a one-Farad EC having a volume of only one-half cubic inch can replace nickel-cadmium or lithium batteries and provide backup power for months. For a given applied voltage, the stored energy in an EC associated with a given charge is half that storable in a corresponding battery system for passage of the same charge. Nevertheless, ECs are extremely attractive power sources.
Compared with batteries, they require no maintenance, offer much higher cycle-life, require a very simple charging circuit, experience no "memory effect," and are generally much safer. Physical rather than chemical energy storage is the key reason for their safe operation and extraordinarily high cycle-life. Perhaps most importantly, capacitors offer higher power density than batteries.
FIG. 2 Schematic of two basic forms of meso-porous NGP nanocomposites: (A) comprising NGPs coated with a thin layer of conducting polymer or surface functional groups; and (B) comprising NGPs bonded by a conductive binder, coating, or matrix material that can be a conducting polymer or carbon (e.g., polymeric carbon).
Instead of trying to develop much lower-cost processes for making carbon nanotubes (CNTs), researchers (Jang, et al.) at Nanotek Instruments, Inc., have worked diligently to develop alternative nano-scaled carbon materials that exhibit comparable properties, but are more readily available and at much lower costs. This development work has led to the discovery of processes for producing individual nano-scaled graphite planes (individual graphene sheets) and stacks of multiple nano-scaled graphene sheets, which are collectively called nano-sized graphene plates (NGPs). NGPs could provide unique opportunities for solid state scientists to study the structures and properties of nano carbon materials. The structures of these materials may be best visualized by making a longitudinal scission on the single-wall or multi-wall of a nano-tube along its tube axis direction and then flattening up the resulting sheet or plate.
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