Synopsis: Plastic Capacitors

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APS/V. Ranjan et al., Phys. Rev. Lett. (2012)

One of the biggest speed bumps hindering widespread adoption of electric vehicles is energy storage: conventional liquid fuels offer a stored energy per unit weight that is hard to beat. The two current approaches to overcoming this limitation are batteries, which use a chemical reaction to generate electricity, or capacitors, which directly store electricity then discharge it when needed. Capacitors take the lead in applications requiring quick delivery of energy. In essence, capacitors are made from two metal surfaces separated by a dielectric; the capacitance can be improved by bringing the surfaces closer together and by using a separator with high dielectric permittivity.

Computer simulations reported in Physical Review Letters by Vivek Ranjan of North Carolina State University, Raleigh, and colleagues predict that mixing a ferroelectric polymer with a pinch of another polymer could yield a sevenfold increase in stored energy compared to the pure dielectric. The calculations offer insights at the molecular level about how this occurs, showing the polymer atoms collectively rearrange from a nonpolar to polar state. Transition paths uncovered by the work have low activation energies and are accessible at technologically reasonable temperatures. The results point the way toward research into creating such optimized polymer dielectrics, which would make capacitive systems roadworthy for powering electric vehicles. – David Voss

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