Study On High Energy Density Tri-layer Polymer Matrix Composite With Oriented Functional Fillers

Energy storage capacitors have great application prospects in modern electronic and electrical systems because of their merits of rapid charge and discharge and no chemical reaction.High dielectric constant polymer composites are important materials for preparing energy storage capacitors.Conductor/polymer composites achieve high dielectric constants at low conductor contents(<1 wt%)and maintain good processability and mechanical properties of the polymer.However,they tend to exhibit high dielectric losses(>1,@100 Hz)and low breakdown strengths,resulting in low energy densities.Therefore,how to preparing high energy density composites based on conductor/polymer composites is still a significant challenge.Our research reported in this thesis mainly includes following two parts.Firstly,an oriented carbon nanotube bundles(ACBs)and epoxy resin(EP)were used as the basic composition.With DSC tests,the curing efficiency was characterized through calculating the degree of solidification.An evaluation which was then used as standard to design orthogonal experiments,the best microwave curing process for ACB/EP composites was obtained.After that,a high-k composite(m-ACB/EP)having a higher dielectric constant and a low percolation threshold(fc)was prepared with microwave curing technique.The spatial distribution,electrical and dielectric properties of ACB in m-ACB/EP composites were in-depths studied,and compared with those of composites(t-ACB/EP)prepared using traditional thermal curing process.Results show that the composites prepared by different curing processes have different spatial structures.Among them,m-ACB/EP has dielectric anisotropy which is not possessed by t-ACB/EP,and.fc values of m-ACB/EP in X?Y?Z direction are lower than those of t-ACB/EP.When the ACB content(f)is 0.6 wt%,the conductivity of m-ACB in Z direction is three orders of magnitude higher than that of t-ACB/EP,Moreover m-ACB/EP has a dielectric constant of 797.6(@100 Hz),which is about 10.6 times of t-ACB/EP.Secondly,new high-k tri-layer A-B-A composites with high energy density was designed using layer curing process.Layer A is an ACB/EP composite prepared with microwave curing,in which ACBs tends to be oriented along Z-axis;layer B is polydopamine-modified barium titanate nanofiber(PDA@BTnf)/EP composite,of which PDA@BTnf tends to align in the X-Y plane.The effects of the orientation of functional fillers and thickness ratio of A and B layers on dielectric properties,breakdown strength and storage density of composites were systematically investigated,and compared with those single-layer composites(ACB/EP·ACB/PDA@BTnf/EP)and double-layer composite([ACB/EP]2).Compared with ACB/PDA@BTnf/EP,A-B-A composite with the same composition has the highest dielectric constant(1080.9,@100Hz),the maximum increase in breakdown strength(150%),besides the dielectric loss and energy density inscrease are 60%and 1780%.