In-situ Preparation And High-temperature Dielectric Properties Of Oxide Nanosanwich Polyimide Composites

Polymer dielectrics are widely used in the field of dielectric energy storage due to their flexibility,lightweight,higher breakdown strength,ease of processing.Biaxially-oriented Polypropylene?BOPP?is the most important dielectric material for film capacitors.Although BOPP has excellent dielectric performance,its allowable operating temperature is lower than 105?,which is far from meeting the current high temperature demand for capacitor components in electric vehicles,aerospace and other fields.Therefore,it is urgent to develop polymer dielectric which can be used stably at high temperature??150??.In this paper,a unique process-Ion Exchange Method is utilized.After surface hydrolysis,ion exchange,heat treatment and reimination of polyimide?PI?,wideband gap oxides are grown on the upper and lower surfaces of PI in situ.The oxide nanosandwich composite with sandwich structure was prepared,which was obviously different and better than the previous sandwich structure polymer composite films.Through the analysis of FTIR,it can be seen that the absorption peak of PI surface groups before and after hydrolysis and before and after imination has changed significantly,which confirms the occurrence of hydrolysis and imination.Then,EDS,XPS and other characterization methods were used to confirm the material properties of the growth nanolayer and confirm that the metal ions all formed corresponding oxides.In addition,the SEM images of the composite also confirmed that the oxide layer was tightly bound to the polymer matrix.The oxide layer is dense without hole defects and its uniform thickness can be exactly regulated.Subsequently,the effects of the thickness and band gap of the oxide nanolayer on the dielectric properties and energy storage properties of the composite film were systematically studied.It can be found that the dielectric loss of oxide nanosandwich PI composite films decreases obviously when the dielectric constant increases with frequency.The dielectric properties of the composite films increased first and then decreased with the increase of oxide thickness.What notable is the Mg O?? 7.8 ev?nanolayer with wide band gap can significantly reduce the leakage current of the composite material at high temperature.At 250? and 125 MV/m,the leakage current density of Mg O nanosanwich PI composite decreases from 1.75×10-5 A/cm2 corresponding to PI to 7.65×10-8 A/cm2.The comprehensive improvement of dielectric properties has greatly improved the energy storage performance of the composite film.At 250?,the maximum discharge energy density of Mg O nanosanwich PI composite with efficiency above 90% reaches 4.65 J/cm³,which is 7.5 times that of PI.In addition,wide band gap ZrO₂??5.2 e V?and SrO??6.9 e V?can also significantly reduce the leakage current of PI under high temperature and high field,thus improving the energy storage efficiency and energy storage density of composite films at high temperature.By horizontally comparing the three oxide nanosanwich PI composite,it can be found that the high-temperature capacitance performance of composites is directly related to the band gap width of the oxide layer.Among them,the composites applied Mg O of widest band gap has the best insulation performance and the best energy storage performance.Wideband gap materials can greatly increase the energy level barrier between electrode and medium and effectively inhibit the injection of electrode charge at high-temperature and high electric field.In summary,the insulating layer nanosandwich polymer structure prepared by the ion exchange method achieves a significant increase in energy storage density and energy storage efficiency at high temperature,can omit the traditional cooling system,and is more conducive to light weight and miniaturization of devices.In addition,this work offers a new idea for the preparation of high-performance polymer dielectric used in special environments.