All-organic Film Research Articles

Tri-layer high-temperature all-organic films with superior energy-storage density and thermal stability

Tri-layered all-organic composites exceed the upper energy-storage-density limits of commercial bench-mark BOPP (∼1.4 J cm−3) and representative ferroelectric polymer-based composites (<4 J cm−3) at elevated temperature.

Massively Parallel Aligned Poly(vinylidene fluoride) Nanofibrils in All-Organic Dielectric Polymer Composite Films for Electric Energy Storage

It is a formidable challenge to combine the performance advantages of linear and nonlinear polymer dielectrics for developing all-organic film capacitors with high energy density and low loss. In this work, massively parallel aligned poly(vinylidene fluoride) (PVDF) nanofibrils were in situ fabricated for the first time in the polyethylene (PE) matrix via a multistage stretching technology involving hot stretching and solid-state stretching at an elevated temperature. The largely enhanced interfacial area of PVDF nanofibrils could effectively induce interfacial polarization, imparting PE composite films with a high dielectric constant of 4.50. More interestingly, the nanoconfinement effect of PVDF nanofibrils greatly restricted the migration of free electrons and impurity ions, and an impressive breakdown strength of 624 MV m–1 was obtained. As a result, the as-prepared PE/PVDF composite films exhibited an attractive discharged energy density of as high as 6.4 J cm–3, which was more than 10 times of the conventional counterparts, and outperformed the current linear dielectric polymers. The ingenious structure design of in situ nonlinear dielectric nanofibrils provides a promising approach to maximize the advantageous polarizations and minimize the disadvantageous polarizations in the linear and nonlinear polymer dielectric blends, achieving all-organic polymer dielectric composite films with high energy density and low loss.

Dielectric and energy storage properties of all-organic sandwich-structured films used for high-temperature film capacitors

Dielectric polymers with ultrahigh power density are widely utilized in the fields of modern electronics and power systems. This article proposes the all-organic sandwich-structured films with ferroelectric polymer poly (vinylidene fluoride-hexafluoropropylene) and linear polymer poly (ethylene terephthalate) (PET) as the energy storage dielectrics for film capacitors. The morphological characterizations, thermal, dielectric, and energy storage performances have been investigated to evaluate the comprehensive properties of the sandwich-structured films. Excellent interlaminar interfaces are observed between poly(vinylidene fluoride-hexafluoropropylene) and PET layers. Compared with pure PET films, the sandwich-structured films exhibit improved thermal stability and dielectric constant, but some degradation in loss factor and breakdown strength. With the increase of ambient temperature, the sandwich-structured films still show improved and stable dielectric properties and insulating strength up to 125 °C. The sandwiched all-organic film shows an improved energy density (Ud) as high as 8.2 J/cm3 and concurrently an immense charge-discharge efficiency of 86.4%. This strategy offers a feasible idea to enhance the thermal, dielectric, and energy storage capability of dielectric films with a layered architecture, which facilitates the evolution of flexible film capacitors.

Self-healable PEDOT-based all-organic films with excellent electrochromic performances

PEDOT-based all-organic films after breaking up can be intrinsically self-healed through thermal stimulation (no more than 130 °C), and maintain excellent electrochromic properties.

Excellent Energy Storage Performance of Ferroconcrete-like All-Organic Linear/Ferroelectric Polymer Films Utilizing Interface Engineering.

Ferroelectric polymers are regarded as the preferred material in dielectric energy storage devices because of their high dielectric constant. However, their relatively low breakdown strength and efficiency restrict their practical application. This work combines coaxial spinning and hot pressing to compound the highly insulating linear poly(methyl methacrylate) (PMMA) and ferroelectric poly(vinylidene fluoride) (PVDF) to obtain a PMMA/PVDF all-organic film with a ferroconcrete-like structure. Further, improvements in the energy storage performance over those of the pristine polymer were achieved via modulation of the PMMA to PVDF ratio. The 45% PMMA/PVDF film had an energy storage density of 17.7 J/cm3 and an energy efficiency of 73% at 640 kV/mm. Moreover, 51% PMMA/PVDF exhibited the best energy storage density (U = 20.7 J/cm3, η = 63% at 630 kV/mm). This work, therefore, provides a new idea for the design of all-organic polymer films for the field of energy storage.

An Electrochromic Hydrogen-Bonded Organic Framework Film.

Hydrogen-bonded organic frameworks (HOFs) possess various merits, such as high porosity, tunable structure, facile modification, and ready regeneration. These properties have yet to be explored in the context of new functional HOF materials. The facile and inexpensive electrophoretic deposition (EPD) method applied in this study generated a transparent HOF film at room temperature in just 2 min and is applicable to other HOFs. The resulting film exhibited reversible electrochromism with the advantage of long cycle life (>500 cycles). More strikingly, this all-organic film could be readily regenerated (through rinsing with DMF and redeposition) and showed tunable electrochromic behavior (through low-cost postsynthetic modification) with the ability to undergo successive color changes, which is difficult to achieve with conventional electrochromic materials. An electrochromic device was manufactured to further demonstrate the application potential of the film.

Design on polarization distribution in all-organic polymer hybrids for high density energy storage

Polymer-based dielectric capacitors have attracted increasing attention in advanced electronics and pulsed power systems due to their high power density and ultrafast charge–discharge speed. However, most of recent achievements focus on polymer-based nanocomposites employing high-k inorganic nanofillers, generating mismatched filler/matrix interfaces that need careful modification. Herein, all-organic hybrid polymers have been explored to achieve ultrahigh energy storage density. Ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) with large polarization was introduced into poly(vinylidene fluoride) (PVDF) with smaller polarization forming blend films, and next sandwich structures constructed by PVDF and P(VDF-TrFE)/PVDF blend films were elaborately designed. A high discharge energy density (Ue) of 23.6 J/cm3 at 636 MV/m has been achieved in 30/70 (volume ratio) P(VDF-TrFE)/PVDF blend film, which is 55% and 130% higher than that of PVDF and P(VDF-TrFE), respectively. Further, by designing sandwich structured all-organic films with 50/50 (volume ratio) P(VDF-TrFE)/PVDF blend film as middle layer to provide high electric displacement and PVDF as two outer layers to withstand high electric field, high Ue = 20–24 J/cm3 and charge–discharge efficiency (>65%) have been achieved. In-depth understanding on the microscopic mechanism for achieving high Ue is gained via finite element analysis showing that the volume fraction of ferroelectric phase in the hybrid system and the mesoscopic layer/layer interfaces are crucial. This work thus provides a promising alternative strategy for high-density energy storage via all-organic films design.

Sandwich-structured all-organic composites with high breakdown strength and high dielectric constant for film capacitor

Currently, energy storage capacitors with high breakdown strength and dielectric constant are highly desired in microelectronics and electric power systems. All-organic film capacitors have been studied owing to their high breakdown strength and low dielectric loss. In this study, poly(vinylidene fluoride) (PVDF) with high breakdown strength was used as outer layers and poly(vinylidenefluoride-ter-trifluoroethylene-ter-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)) with high dielectric constant was used as the interlayer to prepare sandwich-structured composites. These PVDF/P(VDF-TrFE-CTFE)/PVDF composites with various contents of terpolymer were manufactured through a layer-by-layer solution-casting method. At 1 kHz, the maximum dielectric constant of the sandwich-structured composites reaches up to 18.61 when the content of terpolymer is 45 vol%. The discharged energy density increases with the increasing content of terpolymer at the same electric filed. At 660 kV/mm, the composite with 25 vol% terpolymer delivers the maximum discharged energy density, which is 20.86 J/cm3.

β-Cyclodextrin toughened polyimide composites toward all-organic dielectric materials

Flexible all-organic dielectric materials are highly required for miscellaneous applications in modern flexible electronics and energy storage devices but are often hindered by the poor mechanical performance, especially the poor toughness. In this work, because of the special chemical structures and properties, β-cyclodextrin (β-CD) was used to toughen the polyimide (PI) matrix and improve the dielectric properties. Dynamic mechanical analysis (DMA) indicated that β-CD was miscible with PI matrix. The obtained PI/β-CD composite films exhibited a high dielectric permittivity of 8.11, breakdown strength of 217 MV/m, maximum energy density of 1.46 J/cm3, tensile strength > 160 MPa, toughness > 56 J/g, T 5% > 300 °C and T g > 280 °C, which are much better than other all-organic dielectric materials, such as PVDF and its derivatives. These PI/β-CD composite films would be promising materials for all-organic film capacitors.