Novel Polar-fluoropolymer Blends with Tailored Nanostructures for High Energy Density and Low Loss Capacitor Application
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Novel Polar-fluoropolymer Blends with Tailored Nanostructures for High Energy Density and Low Loss Capacitor Applications Shan Wu1, Minren Lin1, David S-G. Lu1, Lei Zhu2 and Q. M. Zhang1 Department of Electrical Engineering and Materials Research Institute The Pennsylvania State University, University Park, PA 16802 2 Department of Macromolecular Science and Engineering Case Western Reserve University, Cleveland, OH 44016 1
ABSTRACT Dielectric polymers with high energy density with low loss at high electric fields are highly desired for many energy storage and regulation applications. A polar-fluoropolymer blend consisting of a high energy density polar-fluoropolymer of poly(vinylidene fluoridechlorotrifluoroethylene) (P(VDF-CTFE)) with a low dielectric loss polymer of poly(ethylenechlorotrifluoroethylene) (ECTFE) was developed and investigated. We show that the two polymers are partially miscible which leads to blends with high energy density and low loss. Moreover, by introducing crosslinking to further tailor the nano-structures of the blends a markedly reduction of losses in the blend films at high field can be achieved. The crosslinked blend films show a dielectric constant of 7 with a dielectric loss of 1% at low field. Furthermore, the blends maintain a high energy density and low loss (~3%) at high electric fields (> 250 MV/m). INTRODUCTION The dielectric capacitors, which can charge and discharge high electric energy by applying and removing high electric field, play an significant role in electronics and electric devices [1-3]. It was found that a very high energy density could be obtained in novel defect modified ferroelectric poly(vinyledene fluoride) (PVDF) copolymers by reducing or eliminating the remnant polarization. For example, P(VDF-CTFE) and P(VDF-HFP) can release a discharge energy density more than 25 J/cm3 [4-6], attracted a lot of attentions for energy storage capacitor applications. However, the relatively high loss of these new materials severely limiting the performance of the capacitor, for example, the temperature rise, instability, and short lifetime will be induced by the losses at high electric fields. A novel blends approach with tailored nanostructure for high energy density low loss capacitor applications was developed and investigated in this proceeding. According to some former studies of PVDF based polymer blends, there are few polymers, which are miscible with P(VDF-CTFE) [7-9], have a low loss. In this proceeding, poly(ethylene-chlorotrifluoroethylene) (ECTFE) with a very low loss of 0.18% can mix well and form high quality transparent blend films with P(VDF-CTFE). Blend films with a much-reduced loss (~1%) while maintaining relatively high dielectric constant (K ~ 7) can be achieved. Moreover, it is developed that chemical crosslinking the blend in the melt can further improve the mixing of two polymers at much smaller level to nano scale, thus leading to a dramatic cut off of high field losses in the blend.
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EXPERIMENT In this study, P(VDF-CTFE) 91/9 mol% copolymer an
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