At present, highly insulating polymers with large breakdown fields, such as polypropylene, are the dielectrics of choice in high-power capacitors. However, their energy densities are quite low because of small dielectric constants. Ferroelectric polymers from the PVDF family have significantly larger dielectric constants, yet their energy densities are still rather low. This can be traced to early saturation of their displacement fields with the applied electric field. However, an admixture of a small amount of another polymer, such as CTFE, results in a dramatic increase in the stored energy. We show that this highly non-linear increase in the energy density is due to the formation of disordered nanodomains with different copolymer concentrations, which undergo first-order non-polar to polar phase transitions with an increase of the applied field. The resulting energy density profile reproduces well the experimental data, while its variation with co-polymer concentration and distribution suggest avenues for additional substantial improvements in the stored energy. Most recently, we have identified a low-activation-energy pathway for these successive phase transformations, which provides further confirmation of the viability of the suggested energy storage mechanism. If time permits, we will also discuss the mechanisms of energy storage and release in novel polyurea-based dielectrics, which too can exhibit exceptionally high power densities.In collaboration with V. Ranjan, R. Dong, M. Buongiorno Nardelli, and L. Yu. 

Novel mechanisms for high power density energy storage in capacitor dielectrics

246th National Meeting (2013)

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