The energy storage objective of a high energy density polymer dielectric materials, excellent charging-discharging efficiency and high power density for hybrid and electric vehicles has been finally achieved by a material scientists’ team working in the Penn State. The main role here is played by a 3D sandwich kind of framework that takes care of the intense electric region located in the ceramic/polymer composite from any kind of dielectric failure.
Figure 1: Enery storage density polymer dielectric materials
Qing Wang, the professor of materials science and team leader here, quotes, “Polymers are ideal for energy storage for transportation due to their light weight, scalability, and high dielectric strength. However, the existing commercial polymer used in hybrid and electric vehicles called BOPP, cannot stand up to the high operating temperatures without considerable additional cooling equipment. This adds to the weight and expense of the vehicles.”
There were two major challenges that obstructed path of this research. One, in the usual 2D polymer films like BOPP, the increment of dielectric constant (electric field strength) countered the charge-discharge efficiency and stability. Next, the strength of the field, lesser were the chances of energy storage in the material, it would dissipate all energy in form of heat. In order to solve this problem the team first tried a mixture of various materials by bringing a balance in the competing properties of these materials in 2D format. It led to increment of energy capacity of these materials but also led to breaking of the film on high temperatures as and when electrons left the electrodes and got injected in the polymer. This lead to generation of electric current.
Wang further goes on explaining that, “ That’s why we developed this sandwich structure. We have the top and bottom layers that block charge injection from the electrodes. Then in the central layer we can put all of the high dielectric constant ceramic/polymer filler material that improves the energy and power density.” The outer layer of this component contains boron nitride nanosheets inside a polymer matrix. These are excellent insulators, the central layer, on the other hand, has a high dielectric constant material known as barium titanate. Wang adds, “We show that we can operate this material at high temperature for 24 hours straight over more than 30, 000 cycles and it shows no degeneration.”