source: EETimes article
PARIS—Researchers from Penn State University have found a way to prevent the dielectric breakdown and leakage of high-density supercapacitors as they are submitted to the high temperatures found in hybrid and electric vehicles, while increasing their energy density.
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.
Compared to BOPP, the new sandwich nanocomposite structure dubbed SSN-x (x being the percentage of barium titanate nanocomposites in the central layer) exhibits the same charge-discharge energy when operating at 150ºC as what BOPP would offer when running at 70ºC.
But the new SSN-x has several times the energy density of BOPP, claim the researchers, making it a promising material for electric vehicle and aerospace applications as the supercapacitors could be shrunk significantly while performing more stably at high temperatures. What’s more, the new composite material does not heat-up, making cumbersome and expensive cooling equipment unnecessary.
The researchers are now looking for industrial partners to perform manufacturability studies and figure out how the new material could be produced competitively at a larger scale.
featured photo: Boron nitride nanosheets (blue and white atoms)act as insulators to protect a barium nitrate central layer (green and purple atoms) for high temperature energy storage. (Photo credit: Wang Lab/Penn State)