Flexible Temperature‐Invariant Polymer Dielectrics with Large Bandgap

Abstract

operate concurrently under high electric fields and elevated temperatures approaching or surpassing 150 °C. [2,4,8,[11][12][13] However, to date, the search for polymer dielectrics that provide appreciable energy densities at temperatures well above 100 °C has led to only marginal success. High temperature operation under high electric field is challenging for polymer dielectrics. For example, biaxially oriented polypropylene (BOPP), the state-of-the-art commercially available dielectric polymer used for energy storage, has a remarkable breakdown strength of ≈700 MV m −1 and ultralow loss, but can only operate continuously at temperatures up to 85 °C and for a short duration with significant derating at 105 °C. [14,15] Many heat resistant polymers have been designed and studied for high-temperature applications, but they are incapable of operating at an electric field similar to BOPP. [11,16,17] This is because their conjugated aromatic backbones that are able to withstand high temperature, built at the cost of largely reduced bandgaps, lead to high electrical conductivities and poor energy densities especially at elevated temperatures. Recent efforts for enhanced energy storage performance at high temperature via nanocomposites or coating modifications of polymer films, although encouraging, are prohibitively challenging for industrial-scale production due to requirements of (either) materials cost and (or) laborious multi-step synthesis and processing. [2,12,13,18,19] As a result, BOPP is still used today with cumbersome active cooling. The availability of flexible polymer dielectrics, capable of stable operation under ultrahigh electric field and elevated temperature is the limiting factor for high power density electrification and electronics.Due to hot carrier excitation, injection, and transport, assisted under thermal and electric extremes, polymers exhibit a nonlinear increase in electrical conduction, [20][21][22] leading to the reduction of the discharged energy density, largely increased energy loss and ultimately dielectric breakdown failure [23] . While the complexity of these processes makes the study of engineering conduction mechanism under critical electric fields far from fully understood, past studies revealed the dominant role of the bandgap in determining electrical conduction and intrinsic breakdown strength of the polymer dielectrics. [20,[24][25][26][27] However, careful evaluation of common high-temperature polymers reveals, unfortunately, an inverse Flexible dielectrics operable under simultaneous electric and thermal extremes are critical to advanced electronics for ultrahigh densities and/or harsh conditions. However, conventional high-performance polymer dielectrics generally have conjugated aromatic backbones, leading to limited bandgaps and hence high conduction loss and poor energy densities, especially at elevated temperatures. A polyoxafluoronorbornene is reported, which has a key design feature in that it is a polyolefin consisting of repeating units of fairly rigid fused bicycl...

Dielectric polymers for high-temperature capacitive energy storage

“…The bandgaps of Kapton® PI and Ultem® PEI calculated by density functional theory (DFT) are ~2.6 eV and ~3.2 eV, respectively. 153 However, it should be noted that, compared to inorganic crystals, the presence of amorphous domains and amorphous-crystalline interfaces in (semi)crystalline polymers significantly complicates the modeling of polymers. Regarding the prediction of the electronic structure of polymers, numerous factors, e.g., polymer chain configuration and the interaction between polymer chains, critically affect the electronic structures of polymers.…”

“…Recently, DFT computations reveal a typical inverse correlation between the T g values and bandgaps in high-temperature aromatic polymers including PI, PAI, PEI, PEEK, PEN and PET. 153 This result indicates that, although the T g values found in the aromatic polymers are highly desirable, the reduced bandgaps owing to high degrees of aromaticity in the aromatic polymers may significantly compromise their utilization as capacitive materials under high applied fields and elevated temperatures. Polyoxafluoronorbornene (POFNB) with a saturated fused bicyclic structure in the backbone was synthesized through a ring-opening metathesis polymerization of oxafluoronorbornene monomer using Grubbs 2 nd generation catalyst (Fig.…”

“…11b). 153 POFNB has a T g of 186 °C and a relatively low K of about 2.5 across the temperature range of 20-180 °C at 1 kHz. Interestingly, the nonplanar structure and nonconjugated polymer backbones of POFNB yield a wide bandgap of 4.9 eV, exceeding the current polymers with similar T g values.…”

Reviving the “Schottky” Barrier for Flexible Polymer Dielectrics with a Superior 2D Nanoassembly Coating

“…Polymer-film dielectrics represent the core framework of flexible electronics, [1][2][3][4][5] serving as insulators, [3] gate dielectrics, [1,[3][4][5] and capacitors. [6,7] To provide charge and energy storage for channel conductance and power conversion, they must be able to withstand enormous and ever-increasing operating electric fields (E). [4,6] Especially to enable ultra-compact and fast signal and power conversions, substantial effort has been devoted over the past several decades to tailoring materials properties in order to improve the breakdown strength (E BD ).…”

“…[4,6] Especially to enable ultra-compact and fast signal and power conversions, substantial effort has been devoted over the past several decades to tailoring materials properties in order to improve the breakdown strength (E BD ). Often the focus is on improving the bulk properties of polymer dielectrics, with promising progress coming from rational codesigns of new molecular structures, [6,7] bulk nanostructure engineering, [8] and processing optimization. [9,10] Performance-limiting phenomena related to the organic dielectric-metal electrode interface itself, on the other hand, continue to be debated even a century after Schottky injection was discovered as a principal mechanism of conduction and charge injection for insulators.…”