Polar-fluoropolymer Blends for High Energy Density Low Loss Capacitor Applications
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Polar-fluoropolymer Blends for High Energy Density Low Loss Capacitor Applications Shan Wu1, 2, Minren Lin2, David S-G. Lu2 and Qiming Zhang1, 2, 3 1 Electrical Engineering Department, The Pennsylvania State University, University Park, Pennsylvania, USA. 2 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, USA. 3 Materials Science and Engineering Department, The Pennsylvania State University, University Park, Pennsylvania, USA. ABSTRACT Besides energy density, the electric loss at high electric fields is another major concern for many capacitor applications. This paper presents recent works in developing high energy density low loss polymer capacitors. In order to reduce the dielectric loss while maintaining high energy density in poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) and P(VDF-CTFE) (CTFE: Chlorotrifluoroethylene) based polymers, a polymer blend approach was investigated. We show that by blending P(VDF-CTFE) with a proper low loss polymer such as poly(ethylenechlorotrifluoroethylene) (ECTFE) can lead to marked improvement in the loss of dielectric films. In this study, P(VDF-CTFE) blends films with different wt% of ECTFE have been examined to find a balance between dielectric constant and the loss. In addition, crosslink in the blends has been employed to further improve the dielectric performance of the blends. The results indicate that these blends exhibit an excellent performance: relatively high dielectric constant (~ 6~7) and low loss (~ 0.01) at 1 kHz. For the crosslink blend films, the high field loss is reduced to below 5% with a discharged energy density 4.3 J/cm3 under a field of 300 MV/m. INTRODUCTION Polyfluoropolymers such as poly(vinylidene fluoride-hlorotrifluoroethylene) (P(VDFCTFE)) has been developed as an outstanding dielectric material for energy storage applications recent years [1-6]. P(VDF-CTFE) exhibits a dielectric constant of 12 measured at 1 kHz and room temperature. Under an electric field > 600 MV/m, a charged energy density of more than 30 J/cm3 can be reached, which represents a breakthrough in high energy density capacitor materials. On the other hand, the material shows a relatively high dielectric loss of 2.5%, while at high fields (>200 MV/m), the total electric loss can be 30%, which poses problems for several high energy density capacitor applications. Blends, which consist of more than one dielectric material, have been exploited for improving the dielectric properties of polymers when the constituent materials are properly selected [7, 8]. PVDF blends have been investigated in the past and the blends films show enhanced polymer properties [9]. Here we investigate a polymer blend approach to reduce the dielectric loss while maintaining high energy density in the P(VDF-CTFE) based polymers. Furthermore, by employing crosslink in the two polymers of the blends, we show that the electric loss at high field can be further reduced [10-12]. In this study, Poly(ethylenechlorotrifluoroethylene (ECTFE) is elected as the ot
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