Dielectric fluoropolymer films for high-voltage applications

Combined high-dielectric constants with high charge/discharge efficiencies


Dielectric materials are electrical insulators that can be polarized by an applied electric field, which makes them useful for energy storage within electrical capacitors. Many capacitors use films made from thermoplastic dielectric polymers. Polymers such as polypropylene (PP) and polyethylene terephthalate (PET) are used for high-voltage applications such as kilo-volt range dielectrics. However, dielectric polymers, as is typical of most electrical insulating materials, undergo significant losses in dielectric strength, or insulating resistance, when subjected to stresses, such as applied AC or DC electrical stresses.

Also, dielectric materials exhibit many other electrical variabilities, such as charge/discharge efficiency, dielectric constant, and dielectric loss over a specific range of electric frequencies and voltage ranges. These electrical properties must frequently be balanced in designing components for the applications and environments in which they are used, such as dielectric materials. For example, some dielectric polymers, such as PP and PET, have excellent charge/discharge efficiencies but have relatively low dielectric constants. To date, attempts to provide dielectric materials having high dielectric constants and high charge/discharge efficiencies have failed.

With the foregoing in view, the Army has developed novel classes of modified fluoropolymers for use in dielectric materials, including dielectric films, for applications that include high-voltage capacitors, resonators, antennas, oscillating circuits, separators, and batteries.  Additionally, these materials may find use as actuators, transducers, and sensors that exhibit higher charge/discharge efficiency and low dielectric loss without sacrificing overall energy density or compromising other electrical properties. These fluoropolymers are modified by removing hydrogen atoms with electron beam irradiation and reacting the radicals with a gas.

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