August 09 ElectroIndustry - 13

NANOTECHNOLOGY Energy Storage their intent to use them. Batteries will also be used in stationary power systems, portable electronics, and tools. Neither batteries nor ultracapacitors, however, is the perfect solution for energy storage. They are typically used together in systems. The battery has high-energy density capability, but limited ability to deliver power quickly enough. Conversely, the ultracapacitor has excellent power delivery, but limited energy density. Nanotechnology research has focused on these deficiencies in batteries and is developing new anodes, cathodes, electrolytes, and separators. Ultracapacitors may be used as a primary energy source, but more likely will be found in combination with batteries or fuel cells. These special capacitors • have very high power capability • show extended lifetimes (can be charged and discharged many more times than batteries since they do not depend upon a chemical reaction) • can be used over a wider temperature range than batteries • are lighter in weight • can use flexible packaging • require lower maintenance resulting from higher reliability • can be charged and discharged at very fast rates. Ultracapacitors do not depend on electrochemical reactions as batteries do, but depend only on electric fields of charged particles created by two electrodes. The ability of capacitors to quickly deliver power is why they are used exclusively in applications like camera flashes. Ultracapacitors, just like batteries, have their own drawbacks, and nanotechnology is being used to improve their characteristics in the hopes that they can be made with a much larger energy density. To compete with batteries, ultracapacitors must have a boosted storage capability that is achieved by increasing the surface area and therefore capacitance of the electrodes. At the Massachusetts Institute of Technology, CNTs have been used in electrodes to increase capacity by 25 times. Other improvement have come with the use of aerogels that have had nanomaterials added to them. Additionally, nanoelectrodes lead to better pore-size distributions that allow better electrolyte movement, and therefore increased charge and discharge rates. based electrodes. Although this leads to increased capacity, it comes at a cost. Increased electrode surface area also adds unwanted reduction-oxidation chemistry on the electrode material surface, and this leads to decreased performance and lifetime. Nanotechnology researchers have found a solution for this problem by applying a coating of amorphous carbon or inert inorganic material on the electrodes that is just a few nanometers thick. This stops the unwanted chemistry and increases the electrical conductivity of the electrodes at the same time. Researchers are exploring how shape, morphology, and assembly of nanoparticles in electrodes can most favorably impact capacity and charge/ discharge rates. It is fully expected that batteries of the future will almost all Batteries and battery technology are some of the most active research areas today, driven by the huge potential The future of green energy in demand for battery technology for electric the world depends upon these vehicles (EVs), hybrid EVs, and plug-in hybrid nanotechnology developments EVs. There has been a quick transition from taking place today nickel-metal-hydride batteries to lithium-ion batteries. One reason is the relatively low cost and weight of lithiumbased batteries. The use of nanomaterials speeds up the charge be nano-enhanced. The future of green energy in the world depends upon these and discharge as the distance for the nanotechnology developments taking lithium ion to move becomes set by the place today, and standards that support nanoparticle diameter. the mass manufacture of nano-enabled Increased surface area in electrodes can subassemblies will help to accelerate add capacity to a battery as the electrolyte these developments. ei can access more electro-active material. This is being done today with nanoAugust 09 • NEMA electroindustry 13

August 09 ElectroIndustry

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