Preparation And High-Temperature Energy Storage Performance Of Multidimensional Filler/Polymer-Based Nanocomposites

Polymer film capacitors play a crucial role in modern electronic devices,and are widely used in fields such as oil and gas exploration and electric vehicles(working temperature>120℃).However,due to the low dielectric constant and poor thermal conductivity of polymers,they are prone to failure in high temperature environments.This means that in order to meet their use in high temperature conditions above 120℃,additional refrigeration systems must be installed,which occupies a large amount of equipment volume and weight.This contradicts the actual application requirements of current electronic devices for lightweight and miniaturization,and therefore a new generation of polymer-based film capacitors with excellent high-temperature energy storage performance needs to be developed.In contrast to the current method of improving the high-temperature energy storage performance of polymers by adding single-dimensional inorganic fillers,this work aims to synergistically enhance the high-temperature energy storage performance of polyimide(PI)based composite films by combining the advantages of different dimensional inorganic fillers.The specific research work is as follows:(1)TO/PI:One-dimensional nanofibers with high aspect ratios and high dielectric constants can significantly improve the dielectric constant of composite films at low filling levels.In this work,we first prepared one-dimensional titanium dioxide(TO)nanofibers with high dielectric constants using electrospinning technology.To improve the interfacial compatibility between the TO nanofibers and the PI matrix,dopamine hydrochloride was used to modify the TO nanofibers.Based on our previous research,the modified TO nanofibers were combined with PI at an optimal volume ratio of 1.5 vol.%,resulting in the formation of a1.5TO/PI composite film.The results showed that at 25℃,the addition of TO nanofibers increased the dielectric constant of the PI film from 3.2 to 3.8 in the 1.5TO/PI composite film,but also decreased the breakdown field strength of the composite film.When the composite film was subjected to high temperature,the decrease in breakdown field strength was more pronounced.Although the addition of TO nanofibers significantly increased the dielectric constant of PI,this increase could not compensate for the decrease in discharge energy density of the composite film due to the reduced breakdown strength.At 200℃,the composite film only achieved a breakdown strength of 198 MV/m and a discharge energy density of 0.54 J/cm~3,which was lower than the 383 MV/m and 1.57 J/cm~3 of pure PI film.(2)AO/TO/PI:Zero-dimensional nano-particles are easy to prepare and have a high viscosity percolation threshold.Adding an appropriate amount of high thermal conductivity and insulation inorganic nanoparticles to the composite material can improve the thermal stability of the composite film without affecting the processing performance of the composite material.Therefore,based on the research work on the TO/PI composite film,we added two layers of AO/PI protective layers containing high thermal conductivity and insulation AO on the outside of the composite film to prepare a three-layer structure AO/TO/PI composite film.The results showed that the addition of high insulation AO enhanced the charge blocking ability of the composite film at high temperatures,increased the breakdown strength of the composite film,and allowed the TO nanofibers to better play a role in improving polarization.The AO also built an efficient thermal conduction network,accelerating the heat dissipation of the PI polymer at high temperatures.These improvements in performance make the composite film have excellent high-temperature energy storage performance.Among them,the 7AO/1.5TO/PI composite film with AO filling of 7 vol.%can achieve a breakdown strength of 375 MV/m at200℃,which is 89.4%higher than the 1.5TO/PI composite film without AO.At the same time,the 7AO/1.5TO/PI composite film obtained a high energy storage density and efficiency of 2.31J/cm~3 and 81%at 200℃,respectively,which is a 47.1%and 38.5%increase in energy storage density and efficiency compared to pure PI.(3)AONS/TO/PI:Two-dimensional nanosheets have a large specific surface area and can serve as charge-blocking materials to suppress the growth of electric trees.Additionally,the sheet-like structure is more conducive to constructing thermal conductive pathways.Therefore,we used aluminum oxide nanosheets(AONS)as a new outer protective material and prepared AONS/TO/PI composite films.The results showed that the addition of high-specific-surface-area AONS effectively reduced the high-temperature electrical conductivity loss of the composite film,resulting in a higher energy storage density.Specifically,the 7AONS/1.5TO/PI composite film with a 7 vol.%AONS loading exhibited a breakdown strength of 388 MV/m at200℃,while achieving a super high energy storage density of 3.42 J/cm~3 and an efficiency of83%,which were respectively 117%and 42%higher than those of pure PI polymer.