This review summarizes the current state of polymer composites used as dielectric materials for energy storage. The particular focus is on materials: polymers serving as the matrix, inorganic fillers used to increase the effective dielectric constant, and various recent investigations of functionalization of metal oxide fillers to improve compatibility with polymers. We review the recent literature focused on the dielectric characterization of composites, specifically the measurement of dielectric permittivity and breakdown field strength. Special attention is given to the analysis of the energy density of polymer composite materials and how the functionalization of the inorganic filler affects the energy density of polymer composite dielectric materials.

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New layered 1:1 mixed Ba 2+ /Ti 4+ metal phosphonates, BaTi(O 3 PC 6 H 5 ) 3 and SrTi(O 3 PC 6 H 5 ) 3 , have been prepared via a hydrothermal route, in which mixed metal oxides, BaTiO 3 and SrTiO 3 , were reacted with phenyl phosphonic acid. The mixed-metal phosphonates were combined with polystyrene (PS) via a solution route and cast as thin films for dielectric permittivity measurements. The composites exhibit an enhancement in the dielectric permittivity as a function of weight loading relative to the parent mixed metal oxide-PS composites.

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In this work, we have investigated the dielectric integrity of P(VDF-HFP)/CCTO and PS/CCTO composites. An attempt has been made to understand the effect of filler preparation method (sol-gel vs. solid state) and loading on dielectric permittivity, loss, DC breakdown, and energy density of the resulting composites. The composites show high dielectric permittivity with increasing addition of CCTO fillers, presumably due to the giant dielectric permittivity exhibited by these fillers. DC breakdown measurements performed by embedding spherical electrodes into composite films show low breakdown strength at very high filler loadings (40 vol. %) possibly due to percolative effects of fillers. Nonetheless, at lower filler loadings (<20 vol. %), the composites show high permittivities and lower reduction in breakdown strength leading to high calculated energy densities of 12 J/cc. With an optimized filler loading, we have achieved a composite system capable of storing large electric energy desirable for pulse power application.