Nanostructures and dielectric properties of PVDF-based polymer films with high energy density and low energy losses
- PDF / 67,113,564 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 74 Downloads / 179 Views
Nanostructures and dielectric properties of PVDF-based polymer films with high energy density and low energy losses Masahiko Ando1, Naoki Yoshimoto1, Yuichiro Yoshitake2, Shuji Kato2, Hidekazu Kodama3, Takeo Furukawa3, and Koji Tashiro4 1 Central Research Laboratory, Hitachi, Ltd., Omika 7-1-1, Hitachi, Ibaraki 319-1292, Japan 2 Hitachi Research Laboratory, Hitachi, Ltd., Omika 7-1-1, Hitachi, Ibaraki 319-1292, Japan 3 Kobayasi Institute of Physical Research, 3-20-41 Higashi-Motomachi, Kokubunji, Tokyo 185-0022, Japan 4 Toyota Technological Institute, 2-12-1 Hisakata,Tempaku, Nagoya 468-8551, Japan ABSTRACT Based on the investigation of mechanism for large dielectric losses in relaxor fluorinated polymers, polyvinylidene fluoride (PVDF) derivatives, a new nanostructure-controlled PVDF based polymer films with low dielectric loss, tanδ < 1% (0.6%), and high dielectric constant, εr = 13 at frequency of 1 kHz, was proposed for electrical energy storage applications. The high dielectric loss was mainly due to the electric-field induced α-β phase transition, and one dimensional extension of P(VDF-TrFE)-g-PEMA films was found to reduce the α phase component resulting in reduction of the dielectric loss while keeping the high dielectric constant. In-situ FTIR measurements suggested a possibility of further reducing the dielectric-loss. INTRODUCTION Polymers are presently the material of choice for energy storage applications because of their relatively high energy density, high electric breakdown field, low dielectric loss, fast speed, low cost, and high reliability. Among them, relaxer fluorinated polymers, polyvinylidene difluoride (PVDF) derivatives, are being actively explored as high dielectric materials1),2). However, their high dielectric constants are accompanied by large dielectric losses due to ferroelectric hysteresis with transformation of molecular conformations, resulting in poor chargedischarge efficiencies. In order to reduce the dielectric losses while keeping the high dielectric constant, here we propose a new nanostructure-controlled PVDF based polymer films with tanδ < 1% (0.6%) and ε = 13 at frequency of 1kHz. We investigated crystalline-structures vs. dielectric-properties relationship by characterizing the representative PVDF based copolymers and terpolymers with different crystalline phases developed for energy storage application1), 3). We found that the large dielectric losses from 101 to 105 Hz were mainly due to the α crystalline phase which is necessary to induce the high dielectric constant of the terpolymers. The large conformational changes during electric field-induced dipolar switching of β-phase through αphase should be the origin for the large dielectric losses. Based on these understandings, we have developed a model nanostructure to realize low tanδ with high ε, and verified it by making cast films composed of newly-synthesized PVDF graft polymers with one-directional extension processes4). Their nanostructures were characterized by using FTIR & XRD and it was found that surprisingly t
