Praperation And Mechanism Investigation Of Polyetherimide-based Composites With Excellent Energy Storage Performance

Polymer-based dielectrics are widely used as advanced pulse capacitors owing to their highest power density devices compared with other energy storage devices,such as electrochemical capacitors and batteries.With the rapid development of power electronic technology,polymer dielectrics with high energy storage density,low loss and excellent temperature stability are urgently required.Therefore,preparing polymer dielectric with excellent energy storage property at high temperature has become a hot research focus.Filling nanofillers with different properties into polymer matrix is one of the most common methods in enhancing their polarization or breakdown strength.Nevertheless,it is still challenging to lift the polarization and the breakdown strength of polymer dielectrics without sacrificing one of them.Importantly,at high temperature,the increased carrier injection and the unavoidably reduced barrier of the dielectrics always result further degradation of their energy storage performances.To address the abovementioned problems,polyetherimide(PEI)with high glass-transition temperature was selected as polymer matrix to prepare PEI-based composites.The two-dimensional calcium niobate(CNO)nanosheets with high dielectric constant and the nanofiller with porous organometallic framework structure(ZIF-8)were selected as fillers,respectively.in-situ polymerization has been used to prepare PI-based composites.It is expected to obtain the PEI-based composites dielectric with excellent energy storage properties.The energy storage characteristics and mechanism of PEI based composite media are studied by means of scanning electron microscopy(SEM),X-ray diffraction(XRD)and finite element analysis(FEA).Results show that the addition of CNO nanosheets can significantly increase the polarization of PEI.The introduction ZIF-8 nanoparticles could substantially suppress the movement of polymer chains,finally contributes to enhance the breakdown strength of the composites.In other words,the addition of both CNO and ZIF-8 benefits to enhance the energy storage properties of PEI.the multiphase PEI-based composites were prepared through using the CNO nanosheets and ZIF-8 nanoparticles as fillers(PEI/CNO/ZIF-8).The results show that the polarization and the breakdown strength of the PEI/CNO/ZIF-8composites are enhanced.The energy storage density of the composite dielectric reached 3.1 J/cm~3as the filler loading is 1 wt%,with a high efficiency of 85.4%.Furthermore,the PEI/CNO/ZIF-8 composites present excellent energy storage performances even at high temperature.When the temperature is 150℃,the breakdown field strength of the composite dielectric reached 380 kV/mm,and the energy storage density is 3.2 J/cm~3,and the energy storage efficiency could be kept at a high level(>80%).In general,CNO has a high dielectric constant.At the same time,there is a strong interaction between the negative surface of CNO and the positive groups on the PEI molecular chain,which is conducive to improving the interface polarization of the composite film.The synergistic effect of the two can improve the polarization performance of the composite film.There are a lot of exposed metal sites on the surface of ZIF-8 particles,which interact with the monomer of synthetic PEI in the process of in-situ polymerization,effectively reduce the internal free volume of materials,block the movement of molecular chains,inhibit carrier migration,and improve the insulation performance of composite films.In the three-phase composite film,CNO and ZIF-8compete with each other on the PEI molecular chain,and can achieve a balanced state under the appropriate filling amount.The polarization performance and insulation performance of PEI based composite film are improved synergistically,and finally the energy storage characteristics of PEI based composite film are greatly improved under actual working conditions.