High dielectric constant terpolymers for energy storage capacitors

Future pulsed power systems will need to be put on mobile platforms with limited space requiring much higher energy densities (5 - 10 J/cc) than is currently possible (2 J/cc). Achieving these energy levels with increased polypropylene film breakdown strength is a very difficult challenge. TRS is investigating an alternative approach using a relaxor ferroelectric terpolymer based on poly(vinylidene fluoride - trifluoroethylene - chlorofluoroethylene) (PVDF-TrFE-CFE) which exhibits a high dielectric constant (K > 50), and therefore can achieve stored energy densities in excess of 7 J/cc at lower electric fields than are currently used for biaxially oriented polypropylene (BOPP) capacitors. Relaxor ferroelectric terpolymer has been synthesized, solution cast, and metalized. The resulting film had a dielectric constant of 50, a loss of 0.025, a breakdown strength of 350 MV/m, and an energy density over 8 J/cc. In comparison commercial metalized BOPP film only stored 1 J/cc at the same field. The next stage of our work will be to evaluate the performance of capacitors wound from terpolymer film. Terpolymer-ceramic composite film has also been investigated as a way of further increasing dielectric constant and, therefore, energy density.