| It is well-known that the thin film capacitor with high energy density performs an important role in the field of advanced electronics and power system.Polymer dielectric composites are generally utilized as the main medium of thin film capacitors due to the excellent toughness,low cost and simple manufacture.The core issue with preparing high-performance composite was to have high dielectric constant,high breakdown strength and low dielectric loss at the same time.In this work,the multi-level structure design of polyimide dielectric composites is conducted to enhance high energy storage density and the impact of dielectric constant(?_r),breakdown strength(E_b)and dielectric loss(tan?)on energy storage density(U_e)is investigated and the research progress is as follows:(1)Polyimide/graphene oxide(GO@PI)with high?_r was produced and the effect of1,4-dibromobutane reducing agent on the energy storage performance of the system was discussed.The experimental structure showed that the introduction of GO filler could increase the dielectric constant(0.5GO@PI,?_r=4.5;1.5GO@PI;?_r=9.1).With the same content of fillers,the dielectric constant of the reduced r GO@PI composites was further increased(1.5r GO@PI;?_r=25.3),and the energy density of the reduced r GO@PI composites was decreased.(2)The influence of thickness ratio of PI layer and 0.5GO@PI(PI/GO@PI)on the energy storage performance of bi-layer composite materials was discussed.Compared with mono-layer 0.5GO@PI film(E_b=148.1 k V/mm),the results showed that the breakdown strength(E_b=293.9 k V/mm)of the PI/0.5GO@PI bi-layer composite was increased by 98%,so that the energy storage density was significantly increased.The dielectric loss tangent of PI/0.5GO@PI was kept at a low level(tan?<0.01).The existence of layer-by-layer interface and electric field redistribution in bi-layer composite were beneficial to increase the breakdown strength,which was constructed to achieve high energy density.(3)A series of multilayer composites composed of highly insulating PI layer and dielectric constant GO@PI composite layer were fabricated by layered coating method.The energy storage performance of multilayer composite was improved by changing the GO content in the dielectric layer and constructing different layer structures.The results showed that the PI/1.0GO@PI/PI tri-layer composite possessed a high E_b of 261.5 k V/mm,and its U_e reached 1.27 J/cm~3.Compared with the 1.0GO@PI mono-layer composite,the E_b and U_eof the tir-layer composite were increased by 97%and 144%,respectively,and the dielectric loss of the tri-layer composite was also less than 0.01.The energy storage density of the tri-layer composite increased due to the joint action of the insulating layer and the dielectric layer.(4)The tri-layer PI/graphene(PI/r GO@PI/PI)composites were prepared by the layered coating method.The insulating PI was used as the outer layer,and the reduced graphene oxide was used as the intermediate dielectric layer.?_r and U_e of the tri-layer composites was significantly increased originate from the existence of dielectric layer.When the mass ration of GO/1,4-dibromobutane was 1/5,the energy density of the PI/5r GO@PI/PI composite film(U_e=1.32 J/cm~3)with 1.0 wt.%GO filler was increased by about 3.9%in comparison with unreduced tri-layer PI/1.0GO@PI/PI.The results showed that the design of multilayer structure and GO by chemical reduction could improve the energy storage performance of polyimide multilayer composites. |
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