Polymer electric storage

A team of Penn State materials scientists is developing ferroelectric polymer-based capacitors that can deliver power more rapidly than conventional batteries.

Qing Wang, associate professor of materials science and engineering, and his research team, developed a polymer of polyvinylidene fluoride and trifluoroethylene which, with the addition of chlorotrifluoroethylene had a very high dielectric permittivity at room temperature.

In a further modification of the ferroelectric polymer, the researchers added nanoparticulate ceramics to further improve the energy density.

Because ceramics often have higher permittivities than the polymers, they believed that combining polymers with high breakdown strength with ceramics of high permittivity would produce a composite material with a large energy storage capacity.

Unfortunately mixing nanoparticles of ceramic with polymers is not simple. The ceramic particles tend to clump and aggregate. If the two materials are not matched for electrical properties, their interface will break down at high electric fields and the ability of the composite to store energy will decrease, rather than increase.

Wang and his team fine-tuned the dielectric particles to the polymer matrix by adding functionalised groups to the materials to match them. They also tried to control the mixing so that uniformly dispersed particles are spread through the matrix.

Wang said: 'Matching the permittivity and uniformly dispersing the ceramic nanoparticles is not easy. Both problems have to be tackled and solved at the same time for the material to have the desired characteristics.'

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