Flexible high-temperature dielectric materials from polymer nanocomposites

Abstract

Dielectric materials, which store energy electrostatically, are ubiquitous in advanced electronics and electric power systems. Compared to their ceramic counterparts, polymer dielectrics have higher breakdown strengths and greater reliability, are scalable, lightweight and can be shaped into intricate configurations, and are therefore an ideal choice for many power electronics, power conditioning, and pulsed power applications. However, polymer dielectrics are limited to relatively low working temperatures, and thus fail to meet the rising demand for electricity under the extreme conditions present in applications such as hybrid and electric vehicles, aerospace power electronics, and underground oil and gas exploration. Here we describe crosslinked polymer nanocomposites that contain boron nitride nanosheets, the dielectric properties of which are stable over a broad temperature and frequency range. The nanocomposites have outstanding high-voltage capacitive energy storage capabilities at record temperatures (a Weibull breakdown strength of 403 megavolts per metre and a discharged energy density of 1.8 joules per cubic centimetre at 250 degrees Celsius). Their electrical conduction is several orders of magnitude lower than that of existing polymers and their high operating temperatures are attributed to greatly improved thermal conductivity, owing to the presence of the boron nitride nanosheets, which improve heat dissipation compared to pristine polymers (which are inherently susceptible to thermal runaway). Moreover, the polymer nanocomposites are lightweight, photopatternable and mechanically flexible, and have been demonstrated to preserve excellent dielectric and capacitive performance after intensive bending cycles. These findings enable broader applications of organic materials in high-temperature electronics and energy storage devices.

Sandwich-structured polymer nanocomposites with high energy density and great charge–discharge efficiency at elevated temperatures

“…Several conduction mechanisms exist in polymeric materials, including the hopping conduction, the Schottky charge injection (thermionic emission) and the PooleFrenkel (P-F) emission (20,25). Hopping conduction is commonly observed in amorphous polymers such as c-BCB, as we previously demonstrated (8). The other two mechanisms are related to the thermal excitation of charge carriers and hence are considered as the major contributions to the high-temperature conduction loss.…”

“…2A). The volume fraction of BNNSs in the outer layers is fixed at 10 vol % according to the materials optimization (8), and the content of BT NPs in the middle layer has been systematically varied. This series of sandwich-structured nanocomposites are hereafter termed as SSN-x, where x stands for the volume fraction of BT NPs in the central layer.…”

“…More recently, the solution-processed polymer nanocomposites based on cross-linked divinyltetramethyldisiloxane-bis(benzocyclobutene) (c-BCB) and boron nitride nanosheets (BNNSs) have been successfully developed as high-temperature dielectric materials (8), which outperform all of the existing polymer dielectrics in terms of the operating temperatures and the charge-discharge efficiency [η, η is given by the ratio of the discharged energy density (U e ) versus the stored energy density]. Notably, η of c-BCB/BNNS at 150°C reaches up to 97% at 200 MV m −1 , the typical field strength applied on DC bus capacitors in electric vehicles (9), which matches the η value of BOPP operating at 70°C.…”

Direct and indirect measurements on electrocaloric effect: Recent developments and perspectives

“…168 Moreover, a colossal electrocaloric effect was reported very recently in ferroelectric polymer nanocomposites by taking advantage of the significantly enhanced breakdown field 134,136,169 due to the presence of the boron nitride nanosheets (BNNSs). 170 The electrocaloric properties of nanocomposites even surpass those of the recently reported giant magnetocalorics, 12 which demonstrates the interest and potential role of electrocaloric effect in next-generation refrigeration. For instance, composites combining relaxor terpolymer P(VDF-TrFE-CFE), Ba 0.67 Sr 0.33 TiO 3 ceramics, and BNNSs show a huge electrocaloric temperature change of over 50 K at room temperature under a ultrahigh electric field of 2500 kV/cm, 134 while relaxor composites based on P(VDF-TrFE-CFE) and PMN-PT 136 are also demonstrated to be comparable to this performance (see Table I).…”

Perovskite Srx(Bi1−xNa0.97−xLi0.03)0.5TiO3 ceramics with polar nano regions for high power energy storage

“…To address serious concerns on air pollution and climate change, researchers are actively searching for new environmentally friendly energy storage technologies nowadays [3][4][5][6][7]. Compared with chemical batteries [8] and electrochemical capacitors [9], dielectric capacitors have merits of high power density (~GW/kg for ceramic capacitors), short charge/discharge time (~ns) and high cycling reliability (> 10 6 cycles) [3,10].…”