Preparation And Properties Of Barium Titanate/Boron Nitride/Polyimide Composites

Flexible nanodielectric materials are receiving tremendous attention and research interest due to the increasing concern on power energy storage.To fulfill newly emerging applications of high-Ue capacitors,such as hybrid electric vehicles and electrical weapon systems,advanced dielectric materials with superior integrated performance including high energy and power density,good processability,environmentally friendly and flexible storage of energy are highly demanded.Ceramic polymer composites,which combine the advantages of ceramic materials and polymer materials,are thought to be promising electronic materials.Through the optimization of the preparation process,it is expected to obtain a high energy storage density composite material with excellent mechanical properties through simple forming process.In this paper,firstly,high quality and yield boron nitride nanosheets?BNNS?were successfully obtained by ultrasonic exfoliation of the original hexagonal boron nitride?h-BN?in aqueous urea solution.After casting and thermal amidation method,the boron nitride/polyimide?BNNS/PI?dual phase composite films with high breakdown strength and barium titanate/boron nitride nanosheets/polyimide?BaTiO₃/BNNS/PI?three-phase composite films with high energy density are respectively fabricated.The detailed research contents are as follows:?1?Using aqueous urea solution as solvent,the BNNS was prepared by liquid phase ultrasonic exfoliation of h-BN,and the mechanism of exfoliation was also discussed.It was found that the grafting of amino groups on the surface of boron nitride had a great influence on the exfoliation.By means of transmission electron microscopy?TEM?,atomic force microscopy?AFM?and scanning electron microscopy?SEM?,the morphology of the prepared BNNS was found to be less than400 nm and the lateral dimension was about 3 nm.Based on the analysis of X electron diffraction?XRD?and photoelectron spectroscopy?XPS?,it is further shown that the obtained BNNS had few layers and basically stable structure,and the existence of amino groups is explained in terms of mechanism.?2?Using BNNS and the polyimide precursor polyamic acid?PAA?,BNNS/PI hybrid films were prepared through casting and thermal amidation,and the thermal and dielectric properties of the films were preliminarily studied.It was found that the addition of BNNS could improve the thermal stability of PI films effectively by TG/DTA analyzer.The dielectric properties analysis showed that with the increase of BNNS content,the dielectric constant of the BNNS/PI composite films increased,dielectric loss and electrical conductivity decreased,breakdown strength increased first and then decreased.The breakdown strength reached the maximum when the mass fraction was 12 wt.%.?3?In order to further improve the dielectric constant of film materials,the barium titanate nanoparticles with high dielectric constant were added into BNNS/PAA.With the addition of 12 wt.%BNNS fixed,after casting and thermal amidation,BT/BNNS/PI three-phase composite films were prepared.The results showed that,when the BT content reached 15 wt.%,compared with PI,the dielectric constant of the three-phase composite film increased by 50%,the breakdown field strength increased by 49%,and the energy storage density increased by 400%finally.This demonstrated that the two nanomaterials could improve the energy storage density effectively.