New All-Organic Layered Dielectric Film for High-Temperature Energy Storage

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1Research Background

With the rapid development of modern power electronics and electrical systems in high-temperature environments, the demand for high-performance dielectric materials is increasingly urgent. Polymer dielectric capacitors, due to their low dielectric loss, ease of processing, and high breakdown strength, have been widely used in medical defibrillation devices, flexible electronics, and pulsed power systems, accounting for more than half of the global high-voltage capacitor market. However, with the development of hybrid electric vehicles, oil exploration technologies, and aerospace power systems, there is a need for advanced dielectric films that possess superior energy storage performance in high-temperature environments. Existing biaxially oriented polypropylene (BOPP) shows a significant increase in energy loss above 80°C, making it unsuitable for high-temperature applications. To improve the energy storage performance of polymer dielectric films under harsh conditions, researchers have extensively studied linear aromatic polymers with high glass transition temperatures (Tg). Unfortunately, the energy storage performance of polymers such as polyimide (PI), polyetherimide, polyether ketone (PEEK), and polyarylether urea sharply declines at high temperatures. Therefore, suppressing the leakage current density of polymer dielectric films is crucial for enhancing energy storage density and efficiency at high temperatures. Additionally, increasing the energy storage density (Ue) is also very important, which can be calculated using the equation Ue = ∫EdD, where E is the applied electric field and D is the electric displacement (D = εε0). For linear polymer dielectric films, the equation simplifies to Ue = ½ε0E². Clearly, simultaneously increasing the dielectric constant ε and breakdown strength Eb is beneficial for enhancing Ue. However, there is an inverse relationship between ε and Eb, which strictly limits the increase of Ue.

2Results Overview

In this research, the researchers successfully designed and manufactured a novel all-organic layered dielectric film based on aramid nanofiber membrane (ANFm) and polyimide (PI) layers, achieved through a simple “dip and pull” technique. This PI-ANFm-PI (P-A-P) dielectric film exhibits a higher breakdown strength and lower leakage current density than the single-layer ANFm due to its flat surface and the formation of electron traps. The maximum discharge energy density (Ud) of the P-A-P dielectric film at 25°C is 3.68 J/cm³, with a charge-discharge efficiency (η) exceeding 80%. At 150°C, Ud is 1.76 J/cm³, and η is above 70%, significantly outperforming single-layer ANFm and pure PI dielectric films. These outstanding energy storage characteristics make the all-organic layered structure P-A-P film a promising candidate material for high-temperature energy storage.

3Illustrated Guide

Figure 1: Schematic diagram of the fabrication of single-layer ANFm and layered structure P-A-P film.

Figure 2: Digital photos of ANF/DMSO dispersion during deprotonation, ANF molecular chain in DMSO, transmission electron microscopy image of ANF in DI water, ANF diameter distribution diagram, atomic force microscopy image of ANF, XRD patterns of PPTA and ANF.

Figure 3: Cross-sectional morphology, surface morphology, AFM 3D images and surface roughness statistics of single-layer ANFm and layered structure P-A-P film.

Figure 4: Weibull statistics of breakdown strength of ANFm and P-A-P films at 25°C and 150°C, electric field distribution simulation diagram, and data on mechanical properties, current density, and Young’s modulus.

Figure 5: Molecular orbital energy levels of PI and ANF, schematic diagram of electron-hole pair formation, electrostatic force distribution and FTIR spectra, and hydrogen bond formation between ANF and PI molecular chains.

4Conclusion

This research effectively addresses the common challenges of local electric field distortion and mechanical performance degradation in organic-inorganic multilayer dielectric films by constructing a novel all-organic layered structure P-A-P dielectric film based on nanoscale ANF and PI. The surface of the P-A-P film becomes smooth after forming the outer layer of PI. Due to the enhanced Young’s modulus, eliminated grooves and pits, formed electron-hole pairs, and hydrogen bonds, the layered structure P-A-P film exhibits significantly improved breakdown strength and suppressed conduction loss. These advantages significantly enhance energy storage performance across a wide temperature range. For example, the maximum Ud of P-A-P-7 at 25°C is 3.68 J/cm³, with η exceeding 80%, and at 150°C, Ud is 1.76 J/cm³, with η exceeding 70%, clearly outperforming single-layer ANFm and pure PI films. This research provides an excellent strategy for developing advanced polymer dielectric films suitable for high-temperature energy storage by constructing a novel all-organic layered structure film based on nanoscale ANF and PI.

References:

https://doi.org/10.1021/acsanm.4c05899

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