Ultra-high Dielectric Strength and Capacitive Energy Density of Thin Entangled Glassy Polymer Films

The influence of high-intensity electric fields on the stability of polymeric materials is a problem of interest in the design of next-generation energy storage and electronic devices, and for understanding the limits of stability of polymer films exposed to large electric fields generally. Here, we show that the dielectric strength of entangled glassy polymer films increases sharply as an inverse power-law of the film thickness h for “ultrathin” films below a micron in thickness. The dielectric strength enhancement in these polymer films can reach values as large as ≈ 2 GV/m in films thinner than 100 nm, but this large “finite-size” effect depends strongly on the polymer mass and sample aging time. Our enhanced dielectric breakdown with confinement can be consistently interpreted within a working model in which dielectric breakdown is taken to be an electric field-induced analog of previously reported mechanical yield enhancement in the same thickness range of glassy polymer films. As a proof of principle regarding applications, we utilized ultra-thin glassy polymer films of the type studied in our paper to fabricate polymeric nanocapacitors having ultra-high discharge energy densities (Udmax) as large as 27 J/cm3 and having efficiencies greater than 80 %. These efficiency values at comparable charge densities are significantly higher than those of competing ferroelectric polymer materials, and we anticipate that our observations will inspire the creation of practical high-energy density nanocapacitor devices for advanced energy storage applications.