Preparation And Dielectric Properties Of Poly (1-butene) Based Composite Films Modified By Inorganic Fillers For High Energy Storage

The energy storage capacitors with ultra-high energy storage density,microsecond charge discharge rate and cycle stability are widely used in military,power and electronic industries and civil fields.At present,polymer-based composite dielectrics are often used as diaphragm materials for energy storage capacitors.However,in the process of actual application,there are still some problems to be solved,such as poor dispersion between the filler and the polymer matrix,weak interface interaction and so on.In this paper,a series of composite films were prepared by solution casting method with poly（1-butene）（PB-1）as matrix.The effects from the morphology and size of inorganic fillers and inorganic-organic interface on the structure,morphology and properties of PB-1 based composite films were designed and studied.The corresponding dielectric mechanism was analyzed,and the relationship between polarization characteristics and energy storage performance was discussed.PB-1 is a polycrystalline polymer.The key to solve the problem of the film processing is to control the crystal type and shorten the conversion cycle.PB-1-based films were prepared by controlling the dissolution temperature and introducing organic phase（polypropylene）or inorganic phase（MWCNTs）.The processing technology of PB-1-based films with good crystallization and dielectric properties was optimized.The results showed that during the crystallization of PB-1solution,the dissolution at 130℃was more conducive to the formation of crystalline form II in the PB-1 solution crystallization system,and the conversion period from crystal form II to crystal form I was 168 h.Both polypropylene and MWCNTs can be used as heterogeneous nucleating agents to shorten the PB-1transition period effectively.In addition,compared with the biaxial stretching process,the solution casting method was easier to achieve the dispersion of the inorganic particles and the PB-1 matrix.In order to increase the dielectric constant of the PB-1 matrix films and reduce the dielectric loss of the conductive filler.In this paper,MWCNTs were selected as fillers and modified with dopamine to form MWCNTs coated by poly dopamine layer（PDA）.Then the PDA modified MWCNTs/PB-1 binary composite films were prepared by solution casting method.The introduction of MWCNTs,the modification of PDA and the different filling amount all have impacts on the structure and dielectric performance of the PDA modified MWCNTs/PB-1 binary composite films.When the content of MWCNTs was 0.67 vol.%,the dielectric constant of the composite film reached 43.9 with dielectric loss 0.19 at 1 k Hz,which was 20 times of that of the pure film.The binary composite film prepared with 0.33 vol.%MWCNTs coated by PDA showed the best energy storage characteristics.When the electric field was 320 MV·m^-1,the effective energy storage density and the charge-discharge efficiency were 2.14 J·cm^-3 and 93.0%,respectively.The multi walled carbon nanotube nanocomposite particles coated with barium zirconate titanate（BZT）were synthesized by sol-gel hydrothermal method,which surface was also modified by PDA.The filler was compounded with PB-1 matrix to prepare ternary composite films via solution casting method.The dielectric properties of PB-1 composite films were improved by the synergistic effect between the charge storage behavior of BZT ferroelectric phase and the charge transport behavior of MWCNTs conductive phase.At 1 k Hz,the dielectric constant of the PDA modified 10 vol.%BZT-0.5 vol.%MWCNTs/PB-1 ternary composite film was25.43,which was 12.7 times of the pure PB-1 film,and its dielectric loss was only0.0077.What’s more,the maximum energy storage density of the composite film could reach 4.57 J·cm^-3 and the largest charge-discharge efficiency was 83.5%under the electric field of 210 MV·m^-1.The high dielectric constant barium zirconate titanate nanofibers（BZT NF）prepared by electrospinning and the boron nitride nanosheets（BNNS）with two-dimensional structure and high breakdown strength were filled to the PB-1matrix,simultaneously.The ternary composite films were prepared by the solution casting method.The energy storage properties of PB-1 composite films were significantly improved,which is attributed to the increase of breakdown field strength and dielectric constant.When the contents of BNNS and BZT NF were 2.0vol.%and 2.5 vol.%,the effective energy storage density and charge-discharge efficiency of the composite film could reach 7.34 J·cm^-3 and 94.9%,under an electric field of 440 MV·m^-1.