Research On Linear-like Polymer-based Dielectric Composite Materials And Films

Organic film capacitors with ultrahigh power density occupy an irreplaceable position in pulse power systems and power transmission.At present,the energy storage density of organic film capacitors is very low,which leads to a large volume of devices and further limits its application.The performance of capacitors is mainly determined by the polymer dielectric materials,so it is highly important to develop a linear-like polymer dielectric composite with high energy density and high charge-discharge efficiency.In this dissertation,the influence of materials composition and structural parameters on polymer energy storage properties was studied.The main results are as follows:1.Polyurea/Poly(vinylidene fluoride-chlorotrifluoroethylene)(PUA/P(VDF-CTFE))and Poly(vinylidende fluoride-trifluoroehtylene-chlorotrifluoroethylene)/PUA(P(VDF-Tr FE-CFE)/PUA)composite films based on linear materials and high dielectric ferroelectric materials were studied respectively.It is found that using blending method at low composite ratio can significantly improve the energy storage properties,but phase separation occurring at high composite ratio results in lower energy storage properties.As for the PUA/P(VDF-CTFE)composite,the breakdown strength of P(VDF-CTFE)composite film with 10%PUA(90/10)reaches 5020 k V/cm,which is 1.35 times of pure P(VDF-CTFE).Meanwhile,the charge-discharge efficiency increased significantly from10.6%to 46.1%under the electric field of 2500 k V/cm.As for the P(VDF-Tr FE-CFE)/PUA composite,the composite film with 20 vol.%PUA exhibits the highest energy density of 4.49 J/cm~3,while the charge-discharge efficiency is as high as 62%.2.PUA/P(VDF-CTFE)and P(VDF-Tr FE-CFE)/PUA composite films with the double-layer structure were prepared to solve the limitation of phase separation in the blending method.As for the PUA/P(VDF-CTFE)composite with a small difference in dielectric constant,the breakdown strength of composite film with the thickness ratio of1:1,is 6180 k V/cm,which is 35%higher than that of pure P(VDF-CTFE).The charge-discharge efficiency of the composite films is higher than 75%under the electric field of2000 k V/cm.As for the P(VDF-Tr FE-CFE)/PUA composite with a large difference in dielectric constant,the breakdown strength of composite film with the thickness ratio of1:1 is 4780 k V/cm,which is slightly lower than that of pure PUA.And the energy storage density is 4.78 J/cm~3,while the charge-discharge efficiency is 55%.3.To improve the dispersion of nanomaterials,Barium Titanate(BT)were surface modified by PUA with high insulation properties.It was found that the dielectric constant and breakdown strength were increased simultaneously.Then a dielectric gradient nanocomposite film was designed to alleviate the difference in dielectric constant.The result shows that the maximum breakdown strength of the three-layer film was up to 5970k V/cm,the energy density increased to 8.2 J/cm~3 with the charge-discharge efficiency of50%.4.A sandwich composite structure was proposed,with which high polarization nanomaterials as a middle layer and high charge-discharge efficiency linear materials as the outer layer.The optimized PMMA was used as the matrix to study the influence of different sandwich thickness on the energy storage properties.As a result,the breakdown strength of composite film with 14 vol.%BT is 5340 k V/cm,and the energy density increased to 7.48 J/cm~3 while the charge-discharge efficiency is as high as 77.2%.Finally,the composite film with high energy density and high efficiency is obtained.