Modeling the dielectric breakdown strength and energy storage density of graphite-polymer composites with dielectric damage process

Authors: Xiaodong Xia; Bai-Xiang Xu; Xiazi Xiao, and George J. Weng

Recent experimental data has demonstrated significant influences of graphite volume concentration on the dielectric breakdown and energy storage behavior of graphite-polymer composites, but no existing homogenization theory has been established to illustrate such dependence in the context of alternating current (AC) loading. In this paper we develop a novel homogenization scheme to connect the microstructural parameters of constituent phases and the AC frequency to the dielectric breakdown strength and energy storage density of the overall composite. The major microstructural features covered are the graphite volume concentration, imperfect bonding effect, graphite aspect ratio, percolation threshold, filler-dependent electron tunneling, Maxwell-Wagner-Sillars polarization, and frequency-dependent electron hopping and dielectric relaxation. A thermodynamic framework is developed to describe the evolution of a dielectric damage parameter with respect to the electric field. We highlight the developed theory with validation through the experimental data of graphite/PVDF composite over a wide range of graphite volume concentration and AC frequency. The results indicate that the dielectric breakdown strength of the graphite-polymer composite decreases with respect to the graphite volume concentration, while the energy storage density increases with it.

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