Dielectric And Energy Storage Properties Of Barium Titanate Nanofibers/Polyimide Multiple Composites

In recent years,polymer-based dielectric capacitors are the most promising candidate materials for many applications such as electric vehicle pulse weapon systems because of their high breakdown strength,flexibility,machinability and high mechanical properties,and it is urgent to have high energy storage density,charge and discharge speed,easy to process and shape,stable performance of the dielectric material to meet the needs of electronic components and equipment lightweight miniaturization.To improve the dielectric properties of BT-fiber/polyimide composites,by controlling the different sintering atmosphere to adjust the defects and ion concentration on the surface of BT-fiber.At the same time,the BT-fiber surface was modified with dopamine in order to reduce the dielectric loss.The FITR,TEM and HRTEM analysis were carried out on the fiber surface.BT-fiber with different surface defects can be obtained by controlling different sintering atmospheres:Air,nitrogen?N₂?and hydrogen?H₂?.And BT-fibers were introduced into PI matrix by solution blending to form composite films.The results show that the samples of BT-fiber treated with hydrogen atmosphere have higher dielectric constant and lower dielectric loss,compared with PI composites filled with BT-fiber treated with air and nitrogen.When the BT-fiber filler concentration was about 15 wt%,the composite film showed a high dielectric constant of 16?100 kHz?,while maintaining maximum energy storage density?Ue?value of 6.12 J/cm³.The effects of filler morphology and composition on the energy storage performance of composites were also studied.The precursor sol of barium titanate was mixed with two-dimensional layered boron nitride?BN?,and the composite-fiber?BN@BT-fiber?was prepared by electrostatic spinning technology,then it was polymerized with polyimide in situ.The results show that the dielectric properties and breakdown strength of the composite were improved obviously after the composite fiber was packed into the polyimide matrix.For example,the maximum energy storage density Ue is 7.1 J/cm³ at3438 kV/cm for the composite film with the filling content of 1 wt%of composite fiber BN@BT-fiber,which is about three times of pure PI?about 2.4 J/cm³ at 3628 kV/cm?.In order to significantly increase the energy storage density of the composite film,three kinds of composite structure fillers were designed and prepared.It is found that the interface effect between different fillers plays an important role in determining dielectric properties of composites,similar to that between matrix and fillers.Three kinds of BN and BT-fiber fillers with different interfacial bonding strength were successfully obtained by controlling the composite process?BN/BT-fiber<BN@BT-fiber<BN&BT-fiber?,then it was introduced into polyimide?PI?matrix to form a composite film,and the energy storage properties were greatly improved.the?BN&BT-fiber?polyimide composite material?3 wt%filler?with the embedded structure has the highest energy storage performance,including about 4343 kV/cm of excellent breakdown strength?E_b?and about 4.25 J/cm³ of high discharge energy density?Ue?.