Best seen flexible polymeric dielectrics for use in extreme environments!
In the context of the rapid development of modern electronics industry, electrical energy is the basic condition to maintain its normal operation. At present, electricity is generated mainly from fossil energy consumption, but as a non-renewable fossil energy resources, its extensive use in the process will bring problems of environmental pollution and resource shortages. A ferroelectric capacitor having ultra high charge-discharge rate and high energy density light and concern. Having Typically, commercial biaxially oriented polypropylene film (BOPP) as is currently the most commonly used flexible energy storage material, the breakdown strength of about 700 MV / m, low loss, but only below 85 ℃ continuously working. When the temperature exceeds 105 ℃, significantly reducing the efficiency of energy storage and electrical properties under high electric field occurs. In many high temperature polymers (e.g.: PI, PEEK, PEI, PET, etc.), due to the large molecular chain having conjugated benzene ring, it has a good high temperature performance. However, this is at the expense of high temperature performance band gap on the implementation, resulting in the leakage current density surge breakdown field strength and reduce defects. Recently, by surface modification of the inorganic particles to increase the penetration resistance and high-temperature storage study properties of composite materials has yielded good results, but the preparation and limited cost and other factors, it can not achieve large-scale industrial produce.
Second, the research results
Recently, University of Connecticut USA Professor Yang Cao Task Force in polymer-based dielectric field made important progress. In the present study, in order to overcome the benzene ring Conjugate storage and leakage current properties at a high temperature polymer, of the first synthesizing bicyclic saturated backbone chain and having a band gap of 5 eV and greater flexibility polyfluoroalkyl (POFNB). at 150 ° C, POFNB conductivity than the best commercial two orders of magnitude lower temperature polymer, and its The energy density of 5.7 J / cm3 , which current performance is far superior dielectric reported. As used herein, a polymer dielectric having a design outstanding high temperature performance , the polymer may be used simultaneously at a high voltage and high temperature conditions of the electric and electronic systemsThe polymer storage dielectric. The work \”Flexible Temperature-Invariant Polymer Dielectrics with Large Band gap\” was published in top international academic journals Advanced Materials on.
III. Highlights herein:
1: π-π stacking of avoiding the effects of the conventional heat-resistant polymer is an aromatic ring, to control the temperature stable dielectric performance by increasing the bandgap of the polymer. 2: Use of the dielectric film, electrical and electronic equipment in the energy storage cooling system is no longer required.
Fourth, the research results discussed ideas and specific
POFNB polymer molecular chain structure exhibits a non-planar conformation , to avoid the conventional heat-resistant polymer molecular structure due to π-π stacking effect and structural constraints conjugated polymer chains and the charge mobility along the polymer chain. By this method the molecular design can be achieved while a large band gap (4.9 eV) and a higher glass transition temperature (186 ° C). By the density functional theory POFNB, BOPP, polyether ether ketone (PEEK), polyetherimide (PEI), and polyimide (PI) (DFT) of calculation results show that the band gap of the polymer followed PP> POFNB> PEEK> PEI> PI sequence of computed theoretical and experimental band gap has a better matching degree. Further, it was found PEEK, PEI, and PI in the aromatic ring helps to improve the energy level of π bond, reduce the band gap, and POFNB displays a greater band gap and a high glass transition temperature.
D-E curve sided POFNB exhibit very fine shape at normal temperature, which indicates POFNB energy loss is extremely low at normal temperature. Even when the electric field exceeds 700 MV / m is the case, POFNB still super high discharge efficiency (96.5%). When the test temperature was raised to 150 ° C, POFNB electric energy storage efficiency at 200 MV / m (Trade BOPP working field) is more than 94%. More importantly, this can eliminate cumbersome and bulky cooling systems are currently required BOPP energy storage system. Over the entire temperature range studied, POFNB exhibited at a high temperature stable energy density, which far exceeds the performance of the best films of flexible polymers and polymer composite reported so far. At 150 ° C, the energy consumption is much lower than conventional POFNB PI, PEI and PEEK heat-resistant polymers.
In order to better understand their highly stable energy density, the dielectric constant of POFNB studied in a wide frequency and temperature range. POFNB stable dielectric constant in the range of about 2.5 and a loss less than 0.5%. Even at temperatures as low -160 ° C, dielectric constant stability. POFNB dielectric constant temperature coefficient of 0.016% / ° C, the BOPP (0.061% / ° C), PEEK (0.085% / ° C), PEI (0.022% / ° C) polymer and the like is the lowest common – 1) and PI (0.042% / ° C). Importantly, the molecular design POFNB, the imide ring fused with the five-membered ring skeleton, the skeleton analogous to such elongated rigid bicyclic structure. Imide functionality further provides the connection to the benzene ring, a benzene ring such that the nitrogen to be sp2 hybridizedOf. Thus, the molecular structure to impart stability by flexible POFNB point at -160 ° C to 160 ° C is. In practical applications, the dielectric is a low loss and stable dielectric constant is difficult to achieve, POFNB dielectric film to ensure high stability and superior performance of the electronic energy storage device.
In addition to the polarization loss, the charge injection in a strong electric field and a high temperature, conduction losses in a high electric field is also dominant. At room temperature, POFNB conduct current exhibits high electric field is strongly suppressed, while at high temperature showed a more pronounced inhibition. When the temperature exceeds 100 ° C, the conductive POFNB much lower than all other high-temperature polymers and BOPP. With the best commercial high temperature compared to the dielectric polymer film, POFNB conductivity of 150 ° C at reduced by almost two orders of magnitude. The author uses the hopping model reveals the contribution of large band gap POFNB inhibition of current conduction. On the basis of the large band gap, POFNB charge in the form of a mobile can not jump, compared with PI, PEI and PEEK, even at 150 ° C POFNB conductivity remains at a low energy barrier on adjacent. This is because the increase in heat-assisted excitation energy POFNB can overcome the energy barrier between the local site. POFNB the unique
V. Study Summary
have a high temperature stability is characterized by a dielectric, which bicyclic olefins dense structure avoids π-π stacking effect of conventional heat-resistant polymer, and given its large band gap and flexibility. Transition temperature based on their large band gap and a high glass, POFNB dielectric with good high temperature stability. References: Flexible Temperature-Invariant Polymer Dielectrics with Large Bandgap Advanced Materials, 2020, 2000499. DOI:. 10.1002 / adma.202000499 full text link:. Https: //online library.Wiley.com/do i / 10.1002 / ah codes .202000499