While commercial solutions exist based on Biaxially Oriented Polypropylene (BOPP) typically used in hybrid and electric vehicles, they cannot stand up to the high operating temperatures without considerable additional cooling equipment. The researchers managed to increase a polymer's dielectric constant while reducing its propensity to leak energy in the form of heat.
To do so, they developed a sandwich structure with top and bottom layers that block charge injection from the electrodes and a central layer hosting a mix of high dielectric constant ceramic/polymer filler materials.
The outer layers are composed of boron nitride nanosheets in a polymer matrix, excellent insulators that strap a central layer made up of barium titanate. By blocking the charge injection from the electrodes, the unique three-dimensional sandwich-like structure effectively protects the dense electric field in the polymer/ceramic composite from dielectric breakdown.
In their paper "Sandwich-structured polymer nanocomposites with high energy density and great charge–discharge efficiency at elevated temperatures" published in the Proceedings of the National Academy of Sciences (PNAS), the scientists reported high temperature operation for 24 hours straight over more than 30,000 cycles, without degradation.