Research On High-energy-density Dielectric Films With Low Dielectric Loss

Organic film capacitors are energy storage devices with ultra-high power density.Compared with other types of capacitors,they have advantages of easy processing,stable performance and resistance to cyclic aging.And as a result,they are more and more widely used in new-energy vehicles,aerospace,laser pulse weapons,etc.However,with the developing trend of miniaturization and light-weight of electronic power systems,higher requirements are put forward for energy storage film capacitors,such as higher energy-storage density,higher breakdown field strength,and lower dielectric loss.Recently,biaxially oriented polypropylene(BOPP)is widely used to manufacture film capacitors,but its low energy storage density is difficult to meet the increasing development needs.Organic composite material with high energy storage density and low dielectric loss is developed to solve the problems,hoping to achieve the goal of engineering applications.Common polymer dielectric materials include polar materials and non-polar materials.Polar dielectric materials show high dielectric constant but high dielectric loss,and non-polar materials show low dielectric loss but low energy storage density.In order to optimize polymer materials with low dielectric constant and high dielectric loss,two strategies are proposed,including“increasing the dielectric constant of low-loss materials”and“reducing the dielectric loss of high energy-storage materials”.Poly(vinylidene fluoride-trifluoroethylene-fluorochloroethylene)with high dielectric constant and polyetherimide with low dielectric loss are used in the paper.Solution mixing and interlayer strategy are used to manufacture composite and composite films are manufactured by solution casting method.The composite films with different electrical properties are manufactured by controlling the volume ratio of materials.Systematical test and analysis are made to analyse their performance.The specific research content shows as follows:(1)In the paper,comparative experiments are set up to systematically study the influence of processing conditions,including solvent type,solution concentration and dissolution temperature.Microscopic characterization and electrical test are made to analyse performance of films.It's found that the best organic solvent to dissolve PEI is N,N dimethylacetamide(DMAc).When solution concentration of 12 wt.%-15 wt.%and dissolution temperature of 60?-80?are adopted,PEI films prepared by casting method show excellent dielectric response and energy-storage characteristics.(2)During the experiment,PEI was used as the matrix to compound P(VDF-TrFE-CFE)and manufacture single-layer films.Obvious phase separation can be observed referring to appearance of the solution and surface morphology of films,corresponding to sharp decline in electrical properties.Subsequently,P(VDF-TrFE-CFE)was used as the matrix to composite PEI and manufacture single-layer films.At a low composite ratio,dielectric loss of the film is 7.9%,which accounts for 70%of pure P(VDF-TrFE-CFE)and dielectric constant remains at a high level.Finally,in view of the compatibility of the two-phase composite,PMMA was used to manufacture a three-phase organic composite.The surface morphology of films prove that phase separation is significantly optimized.(3)During the experiment,P(VDF-TrFE-CFE)/PEI interlayer composite films were prepared by solution casting method.SEM cross-sectional morphology and microstructure were characterized to prove that double-layer composite films were successfully manufactured.According to electrical performance tests,the dielectric constant of the PEI-based interlayer film is increased by 50%,the breakdown field strength is as high as 653 k V/mm,the discharge energy density can reach 3.84 J/cm~3 and the dielectric loss of the film is still less than 1%.Subsequently,PEI/P(VDF-TrFE-CFE)double-layer films were prepared.The microscopic characterization of films proves that the double-layer structure was successfully manufactured.The electrical test results show that the dielectric loss of the composite film is reduced by 88.5%,the breakdown field strength is higher than 600 k V/mm,the charge and discharge efficiency is significantly improved and double-layer films exhibit excellent energy storage characteristics.According to the film composite ratio and processing method designed in the paper,dielectric films with high energy-storage density and low loss can be manufactured,which provides a new strategy for engineering applications.