The proliferation of solar, wind and even tidal electric generation and the rapid emergence of hybrid electric automobiles are building the pressure for those with know-how to advance high-capacity electrical storage. Now a team of Penn State materials scientists is developing ferroelectric polymer-based capacitors that can deliver power more rapidly and are much lighter than conventional batteries.

Qing Wang, associate professor of materials science and engineering, and his research team reported on Aug. 20 at the 236th national American Chemical Society meeting in Philadelphia in two papers, on the development of power density tunable polymers and polymer ceramic nanocomposites as electric storage materials for capacitors.

Wang believes that eventually, properly tuned polymer capacitors could replace batteries. Traditional materials are ceramic materials that have high weight and are very fragile. But the researchers, have developed a polymer of polyvinylidene fluoride and trifluoroethylene which, with the addition of chlorotrifluoroethylene, has a very high dielectric permittivity at room temperature.

Permittivity is a measure of how much charge is stored in a material for a given electric field and is an indicator of how effective a material will be when storing energy in a capacitor. The researchers found that by altering the amounts of the various chemical components of the polymer, they could tune the dielectric property and energy density.

Hybrid cars are a good target for ferroelectric polymer capacitors because they convert mechanical energy generated when, for example coasting downhill, to electricity and charge batteries for use at other times. But conventional batteries are often heavy, and may not be able to deliver the power needed for quick acceleration.

Wang and his researchers modified this ferroelectric polymer by adding nanoparticulate ceramics to further improve the energy density. Because ceramics often have higher permittivities than the polymers, they believed that combining polymers with the high breakdown strength with ceramics of high permittivity would produce a composite material with a large energy storage capacity.

Breakdown strength is a measure of the maximum electric field that an insulating material can withstand before it begins to conduct electricity. The higher the breakdown strength, the better a material is for a capacitor.

The National Science Foundation and the Office of Naval Research funded this research.

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