High Density Glass for Portable Power

Flexible Glass
Flexible glass for energy storage.

Writing in Materials Letters (June 2009), Penn State researchers reported the highest known breakdown strength for a bulk glass ever measured. Breakdown strength, along with dielectric constant, determines how much energy can be stored in an insulating material before it fails and begins to conduct electricity. A bulk glass with high breakdown strength and high dielectric constant would make an ideal candidate for the next generation of high energy density storage capacitors to power more efficient electric vehicles, as well as other portable and pulsed power applications.

The highest dielectric breakdown strengths for bulk glasses are typically in the 4-9MV/cm range. The breakdown strength for the tested samples were in the 12MV/cm range, which in conjunction with a relatively high permittivity, resulted in energy densities of 35 J/cm3, as compared to a maximum energy density of 10 J/cm3 for polypropylene, the most common dielectric for pulsed power applications.

“For a bulk glass, this is extraordinary,” says Nick Smith, a Ph.D. candidate in materials science and engineering, who is lead author on the report and performed the testing. Smith used samples of 50 micron-thick commercial glass, which he etched for testing with hydrofluoric acid until the samples were only 10-20 microns thick. The resulting glass was so thin it could be flexed like a piece of plastic film. The thinner the glass, the more electric field can be applied before failure.

In addition to Smith, the authors are graduate student Badri Rangarajan, engineering science and mechanics, Michael T. Lanagan, professor of engineering science and mechanics, and Carlo G. Pantano, distinguished professor of materials science and engineering. This research was supported by the Office of Naval Research, the Materials Research Institute, the National Science Foundation, the Center for Optical Technologies, and Bayer MaterialScience LLC.

This article was featured in Focus on Materials - Summer 2009.