Nonsolid TiOx Nanoparticles/PVDF Nanocomposite for Improved Energy Storage Performance

High Stability Hypha-Like Core-Shell Nanostructure by In Situ Induced Phase Inversion for Zinc Metal Batteries

Nanomaterials are widely used in many fields for their unique physical and chemical properties and especially demonstrate irreplaceability in energy storage systems. In this paper, a novel composite of copper sulfide with hypha-like core-shell nano-structure is synthesized by in situ phase inversion method, which serves as high stability negative electrode materials of zinc-ion batteries (ZIBs). The unique structure facilitates efficient electron and ion transport, enhances the kinetics of electrochemical reactions, and effectively suppresses the undesired expansion and decomposition of transition metal compounds. As a result, the half battery exhibits high specific capacity (250.2 mAh g-1 at 0.1 A g-1), reliable rate performance, and cycle stability (98.3 mAh g-1 at 1 A g-1 after 500 cycles). Additionally, when assembled with ZnxMnO2 positive to form a full battery, it demonstrates good cycling capacity at an intermediate current density of 2 A g-1, while maintaining excellent structural stability over 5,000 cycles (61% retention).

Significantly Enhanced the Energy Density of Dielectric Composites by Sandwich Structure with Highly Insulating Mica Nanosheets

Dielectric polymer composites exhibit great application prospects in advanced pulse power systems and electric systems. However, the decline of breakdown strength by loading of single high dielectric constant nanofiller hinders the sustained increase in energy density of the composites. Here, a sandwich-structured nanocomposite prepared with mica nanosheets as the second filler exhibits decoupled modulation of dielectric constant and breakdown strength. The traditional layered clay mineral mica is exfoliated into nanosheets and filled into polyvinylidene difluoride (PVDF), which shows a special depolarization effect in the polymer matrix. In Kelvin probe microscopy characterization and thermally stimulated depolarization current indicates that the mica nanosheets provided space charge traps for the polymer matrix and effectively suppressed the carrier motion. A sandwich structure composite material with mica nanosheets as the central layer has achieved a high energy density of 11.48 J cm-3, 2.4 times higher than the pure PVDF film. This is due to the fact that randomly oriented distribution of nanosheets in a polymer matrix provide better current blocking. This work provides an effective method to improve the energy density of dielectric polymer composites by synergistically introducing insulating nanosheets and high dielectric constant nanofillers.

Study of the in situ test setup and analysis methods for self-healing properties of metallized film capacitors

Metallized film capacitors (MFCs) are widely used in the power electronics industry due to their unique self-healing (SH) capability. SH performance is an essential assessment for MFC reliability verification in industrial production. The SH phenomenon of metallized films usually occurs rapidly in a very short period, and its real-time evolution details are often difficult to capture and analyze. In this paper, a test system for the SH performance of metallized films for capacitors was constructed. The system consists of three components: a voltage-current characteristic testing and current pulse capture device, a microscopic image real-time acquisition device, and an integrated analysis processing device. Through the voltage-current characteristic testing and current pulse capture device, the electrical parameters of the SH point, such as SH times, breakdown field strength, SH current, and SH energy, are obtained; through a microscopic image real-time acquisition device, the real-time spatial positioning of the SH point was obtained, and the interconnection between the morphology of the SH point and the electrical properties was established. The relationship between the SH point and the temperature distribution was further established using thermal imaging technology, which lays the foundation for a thorough and timely assessment and analysis of the failure mechanism and the real-time evolution of the metallized film SH process. This significantly improves the effectiveness of SH property research.

Electrospun Cellulose Nanocrystals Reinforced Flexible Sensing Paper for Triboelectric Energy Harvesting and Dynamic Self-Powered Tactile Perception

The technical synergy between flexible sensing paper and triboelectric nanogenerator (TENG) in the next stage of artificial intelligence Internet of Things engineering makes the development of intelligent sensing paper with triboelectric function very attractive. Therefore, it is extremely urgent to explore functional papers that are more suitable for triboelectric sensing. Here, a cellulose nanocrystals (CNCs) reinforced PVDF hybrid paper (CPHP) is developed by electrospinning technology. Benefitting from the unique effects of CNCs, CPHP forms a solid cross-linked network among fibers and obtains a high-strength (25 MPa) paper-like state and high surface roughness. Meanwhile, CNCs also improve the triboelectrification effect of CPHP by assisting the PVDF matrix to form more electroactive phases (96% share) and a higher relative permittivity (17.9). The CPHP-based TENG with single electrode configuration demonstrates good output performance (open-circuit voltage of 116 V, short-circuit current of 2.2 µA and power density of 91 mW m-2 ) and ultrahigh pressure-sensitivity response (3.95 mV Pa-1 ), which endows CPHP with reliable power supply and sensing capability. More importantly, the CPHP-based flexible self-powered tactile sensor with TENG array exhibits multifunctional applications in imitation Morse code compilation, tactile track recognition, and game character control, showing great prospects in the intelligent inductive device and human-machine interaction.

Utilizing Linear Polymers to Optimize Remanent Polarization and Construct Multilayer Interfaces to Obtain High-Efficient Poly(vinylidene fluoride)-Based Energy-Storage Composites

Polyvinylidene fluoride (PVDF) has been widely studied as a ferroelectric polymer for energy dielectric applications. However, high-polarization PVDF has a low-efficiency issue, owing to high residual polarization. This study introduces highly insulating, low-loss linear polycarbonate (PC) into PVDF-based dielectrics. The PC layer optimizes the remanent polarization (Dr) of PVDF and maintains it within a small range, thus achieving a high charge-discharge efficiency. The multilayer structural design of PVDF-based dielectrics adjusts the interlayer electric field distribution. We have thoroughly studied the influence of the number and proportion of PC layers on the polarization and breakdown of the multilayer films as well as achieved collaborative regulation of dual parameters. Our results indicate that three layers of PC-PVDF-PC (CPC) films containing a large proportion of PC can polarize under high electric fields and maintain excellent charge-discharge efficiency, achieving an energy density and efficiency of 11.48 J/cm3 and 92.4%, respectively, under 610 kV/mm. The PVDF-based dielectrics prepared in this work are all organic films, and their flexibility and foldability are conducive to the preparation of flexible devices.

Enhancement of Energy Storage Performance of PMMA/PVDF Composites by Changing the Crystalline Phase through Heat Treatment

In today's contemporary civilization, there is a growing need for clean energy focused on preserving the environment; thus, dielectric capacitors are crucial equipment in energy conversion. On the other hand, the energy storage performance of commercial BOPP (Biaxially Oriented Polypropylene) dielectric capacitors is relatively poor; hence, enhancing their performance has drawn the attention of an increasing number of researchers. This study used heat treatment to boost the performance of the composite made from PMAA and PVDF, combined in various ratios with good compatibility. The impacts of varying percentages of PMMA-doped PMMA/PVDF mixes and heat treatment at varying temperatures were systematically explored for their influence on the attributes of the blends. After some time, the blended composite's breakdown strength improves from 389 kV/mm to 729.42 kV/mm at a processing temperature of 120 °C. Consequently, the energy storage density is 21.12 J/cm³, and the discharge efficiency is 64.8%. The performance has been significantly enhanced compared to PVDF in its purest state. This work offers a helpful technique for designing polymers that perform well as energy storage materials.

Quantum Dot Transfer from the Organic Phase to Acrylic Monomers for the Controlled Integration of Single-Photon Sources by Photopolymerization

This paper reports on a new strategy for obtaining homogeneous dispersion of grafted quantum dots (QDs) in a photopolymer matrix and their use for the integration of single-photon sources by two-photon polymerization (TPP) with nanoscale precision. The method is based on phase transfer of QDs from organic solvents to an acrylic matrix. The detailed protocol is described, and the corresponding mechanism is investigated and revealed. The phase transfer is done by ligand exchange through the introduction of mono-2-(methacryloyloxy) ethyl succinate (MES) that replaces oleic acid (OA). Infrared (IR) measurements show the replacement of OA on the QD surface by MES after ligand exchange. This allows QDs to move from the hexane phase to the pentaerythritol triacrylate (PETA) phase. The QDs that are homogeneously dispersed in the photopolymer without any clusterization do not show any significant broadening in their photoluminescence spectra even after more than 3 years. The ability of the hybrid photopolymer to create micro- and nanostructures by two-photon polymerization is demonstrated. The homogeneity of emission from 2D and 3D microstructures is confirmed by confocal photoluminescence microscopy. The fabrication and integration of a single-photon source in a spatially controlled manner by TPP is achieved and confirmed by auto-correlation measurements.

Two-Dimensional Metal-Organic Framework Incorporated Highly Polar PVDF for Dielectric Energy Storage and Mechanical Energy Harvesting

Here, we introduce a 2D metal-organic framework (MOF) into the poly(vinylidene fluoride) (PVDF) matrix, which has been comparatively less explored in this field. Highly 2D Ni-MOF has been synthesized in this regard via hydrothermal route and has been incorporated into PVDF matrix via solvent casting technique with ultralow filler (0.5 wt%) loading. The polar phase percentage of 0.5 wt% Ni-MOF loaded PVDF film (NPVDF) has been found to be increased to ~85% from a value of ~55% for neat PVDF. The ultralow filler loading has inhibited the easy breakdown path along with increased dielectric permittivity and hence has enhanced the energy storage performance. On the other hand, significantly enriched polarity and Young's Modulus has helped in improving its mechanical energy harvesting performance, thereby enhancing the human motion interactive sensing activities. The piezoelectric and piezo-tribo hybrid devices made up of NPVDF film have shown improved output power density of ~3.26 and 31 μW/cm² compared to those of the piezoelectric and piezo-tribo hybrid devices comprising of neat PVDF (output power density ~0.6 and 17 μW/cm², respectively). The developed composite can thus be considered an excellent candidate for multifunctional applications.

TiO2 Nanoparticle/Polyimide Nanocomposite for Ultrahigh-Temperature Energy Storage

With the development of electronic technology, there is an increasing demand for high-temperature dielectric energy storage devices based on polyimides for a wide range of applications. However, the current nanofillers/PI nanocomposites are used for energy harvesting at no more than 200 °C, which does not satisfy the applications in the oil and gas, aerospace, and power transmission industries that require an operating temperature of 250-300 °C. Therefore, we introduced a nanocomposite based on nonsolid TiO₂ nanoparticles and polyimide (PI) with high energy storage performance at an ultrahigh temperature of 300 °C. The synergy of excellent dielectric properties and a high breakdown strength endowed the nanocomposite with a low loading content of 1 wt% and a high energy storage density of 5.09 J cm^-3. Furthermore, we found that the nanocomposite could stably operate at 300 °C with an outstanding energy storage capability (2.20 J cm^-3). Additionally, finite element simulations demonstrated that the partially hollow nanostructures of the nanofillers avoided the evolution of breakdown paths, which optimized the breakdown strength and energy storage performance of the related nanocomposites. This paper provides an avenue to broaden the application areas of PI-based nanocomposites as ultrahigh-temperature energy-storage devices.

Optimizing nanostructures to achieve enhanced breakdown strength and improved energy storage performances in dipolar polymers

Polymer dielectrics have attracted ever-increasing attention for electrical energy storage applications in recent years. Typically, polymer-based nanocomposite films are adopted to obtain polymer dielectrics with high energy density but sometime suffer from the inhomogeneous distribution of fillers. In this work, enhanced breakdown strength, suppressed dielectric loss and improved energy storage performances of PVDF film are concurrently achieved via the regulation of the sub-nano free volume, without introduction of any kinds of fillers and also minimizing the uneven distribution of the local electric field. The most improved breakdown strength is up to 488 MV m^-1, with an enhancement of 60% compared with that of pristine PVDF, which enables the irradiated PVDF film to exhibit an improved polarization strength and charged energy density, giving rise to a maximum polarization strength of 3.55 μC cm^-2 and a charged energy density of 9.75 J cm^-3. More importantly, the irradiated PVDF film exhibits a superior discharged energy density of 7.91 J cm^-3 which is 261% that of the pristine PVDF film, while maintaining the charge-discharge efficiency above 80%. In addition, the alteration of experimental breakdown strength with the increase of irradiation dose is found to be inversely correlated with the size variation of free volume holes, and the theoretical simulation of local electric field distribution further proves that the breakdown strength enhancement originates from the size shrinkage of free volume holes. The adjustment of free volume provides a potentially effective way to regulate the dielectric properties and energy storage performances of dipolar polymers.