High-Temperature Polyimide Dielectric Materials for Energy Storage

High-temperature energy storage with a new tri-layers polymer composites via hybrid assembly engineering

High-temperature energy storage polyimide dielectric materials: polymer multiple-structure design

Fluorinated polyimides (PIs) are among the most promising candidates for gate dielectric materials in organic electronic devices because of their solution processability and outstanding chemical, mechanical, and thermal stabilities. Additionally, fluorine (F) substitution improves the electrical properties of PI thin films, such as enhanced dielectric properties and reduced surface trap densities. However, the relationship between the fluorination density of PIs and crystal growth modes of vacuum-deposited conjugated molecules on PI thin films, which is directly related to the lateral charge transport along the PI-organic semiconductor interface, has not been systematically studied. Herein, five different soluble PIs with different F densities were synthesized, and the correlation between fluorination and thin-film properties was systematically investigated. Not only were their dielectric properties modulated, but the growth modes of the organic molecules deposited on the PI thin films also changed with increasing surface F density. This phenomenon was observed by both surface and crystallographic analyses, which resulted in extremely high operational stability of field-effect transistors and the successful fabrication of organic complementary circuits. We believe that the correlation between PI backbone fluorination and its thin-film properties will provide practical insights into the material design based on controlled molecular directed surface assembly on fluorinated polymer dielectrics.

High-temperature resistant polymer dielectrics present large application potentials in harsh-environment electrostatic capacitors. However, the widely used polymer films including polyimide often suffer poor mechanical strength or energy storage level especially at superimposed bending, electrical and thermal stresses during practical operation, owing to the inherent contradiction in synergistically strengthening both sides, which is a challenging problem that urgently needs to be solved. Here an all-organic synthesis route is exploited to synergistically realize high mechanical strength (378.3 MPa), breakdown strength (682 MV/m), energy density/efficiency (6.06 J/cm3 at η = 90%, the peak value reaches 10.29 J/cm3) at 150 °C in fabricated crystalline polyamide film, which respectively has an enhancement (81%, 88%, 2231%) than that of polyimide film, whose comprehensive performances present definite preponderance among existed polymer dielectrics. It is further demonstrated that, different from traditionally disadvantageous π–π and charge-transfer interactions, the particular coexistence of abundant and strong hydrogen bonds constraining large energy gap synergistically strengthens the anticorrelated mechanical and energy-storage performances, and the matched high film crystallinity establishing by Lewis acid and high temperature-assisted chain arrangement further strengthens both sides. Compared with nanocomposite strategy, such all-organic structure also endows it with large potential to match current production process toward large-scale fabrication of high-quality polymer dielectrics.

Polymer films are ideal dielectric materials for energy storage capacitors due to their light weight and flexibility, but lower energy density and poor heat resistance greatly limit their application in high-temperature energy storage. Unlike the traditional method of solely adding wide-bandgap inorganic fillers to enhance energy density, in this study we constructed trap-rich hybrid covalently cross-linked networks in polyetherimide (PEI) via reactive polyhedral oligomeric silsesquioxane (POSS)-functionalized boron nitride nanosheets (BNNS@POSS), which not only serve as interfacial layers for dielectric transitions and insulating barriers but also create deeper traps and higher energy barriers in the region of cross-linked chains. This strategy based on the co-modulation of interfaces and traps achieved the compatibility of high polarization and high breakdown strength and improved energy storage performance. Therefore, the composite film BNNS@POSS/PEI with the addition of 5 wt% BNNS@POSS achieved a maximum discharge energy density and charge-discharge efficiency at 150 °C of 6.16 J cm-3 and 89.92%, and maintained high values at 200 °C of 4.12 J cm-3 and 88.38%, respectively. Moreover, the glass transition temperature (Tg) of the composite dielectrics increased by 20.2 °C. This work provides a promising candidate material and development directions for research in the field of high-temperature energy storage capacitors.

Ion-conducting membranes are crucial in electrochemical storage and energy conversion technologies such as fuel cells, alkaline ion batteries, and redox-flow batteries. The purpose of the membrane is to prevent direct contact between the electrodes while allowing selective ions to pass through. The characteristics of the ion-conducting membranes include excellent mechanical and thermal stability, chemical resistance, high ionic conductivity, and selectivity. Polymers and polymer-based precursors make up the majority of the materials that have been used as ion-conducting membranes. However, most polymer-based membranes have issues related to poor chemical resistance, recyclability, and thermal and mechanical stability. In addition, as more sustainable materials are being sought to create a sustainable society, new environmentally friendly and economically viable materials are in high demand. The clay-based material could be an alternative for ion-conducting applications due to its porous structure, high surface area, tunable interlayer spacing, excellent thermal and mechanical stability, and high ion conductivity. Clay minerals are primarily used in water treatment, pharmaceutics, ceramics, paints, and coating industries. Furthermore, clay minerals have been used as a filler material in energy storage and conversion system to improve the thermal stability and ion conductivity in electrodes, electrolytes, and separators.Herein, we report a novel approach to making non-polymeric hybrid clay membranes using environmentally benign materials such as clay and zwitterion (i.e., sulfobetaine). These membranes with improved ionic conductivity will find immense potential in applications in energy storage and conversion systems. Such membranes have been synthesized by intercalating sulfobetaine molecules into the interlayer spacing of the bentonite clay matrix. Sulfobetaine is a zwitterion composed of quaternary ammonium cations and sulfonate anions. Leveraging the unique structure-property features that exist in zwitterions helps to alter the interlayer spacings in the clay matrix, thereby enabling ion diffusion through the silicate layers. Furthermore, it helps in the formation of a self-supporting membrane. The functionalized membrane's crystal structure and chemical composition were investigated using XRD, XPS, and ATR-FTIR. XRD was used to identify the layered structure of the silicates in clay and the increased interlayer spacing (1.15 nm to 1.8 nm) of the hybrid clay membrane. Data from XPS and ATR-FTIR confirmed the successful functionalization of clay with sulfobetaine. Furthermore, the ionic conductivity of the hybrid clay membrane was characterized using a non-aqueous lithium electrolyte solution, and found a conductivity of . This is one of the first reports showcasing how zwitterions can impart conductivity in clay silicate motifs. It suggests an easy and novel approach to transport lithium-ion through silicate layers, thereby making it suitable for use as membranes in batteries and supercapacitors. The current study demonstrates an easy and versatile approach to developing cost-effective and eco-friendly membranes from sustainable materials such as clay, which, when functionalized, has the potential to be a highly efficient ion-conducting material with applications in energy storage, devices, and technologies.

Guest Editorial: Situational awareness of integrated energy systems

Ceramic/polymer composites can be chemically stable, mechanically strong, and flexible, which make them candidates for electric devices, such as pressure or temperature sensors, energy storage or harvesting devices, actuators, and so forth. Depending on the application, various electrical properties are of importance. Polymers usually have low dielectric permittivity, but increased dielectric permittivity can be achieved by the addition of the ceramic fillers with high dielectric constant. With the aim to enhance dielectric properties of the composite without loss of flexibility, 5 wt% of BaTiO3‐Fe2O3 powder was added into a polyvinylidene fluoride matrix. The powder was prepared by different synthesis conditions to produce core/shell structures. The effect of the phase composition and morphology of the BaTiO3‐Fe2O3 core/shell filler on the structure and lattice dynamics of the polymer composites was investigated. Based on the results of the thermal analysis, various parameters of ceramic/polymer composites were determined. Differences in the phase composition and morphology of the filler have an influence on the formation of various polyvinylidene fluoride allomorphs and the degree of crystallinity. Furthermore, the dielectric performances of pure polyvinylidene fluoride and the polymer/ceramic composites were measured.

Over the last few decades several innovative ideas have been explored in the energy storage areas, ranging in size, capacity, design complexity, and targeted applications. Some of them are designed for large scale power system applications, others for smallor medium-scale renewable energy or hybrid power systems, while the others are designed to perform short-term energy storage ride through for critical infrastructure (communication systems, hospitals, military facilities, etc.). Energy storage has become an enabling technology for renewable energy applications, grid integration and enhancing power quality and stability in the power transmission and distribution, having a great potential to improve power grid quality and stability and to provide an alternative to fossil fuel-based energy generation. The major constraints for renewable energy penetration are the availability, intermittency, and variability, which can be addressed through energy storage. The energy storage choice depends on specific usage requirements, often incorporating several energy storage systems in order to increase system reliability, capacity, and supply security. In the electric power system, the renewable energy promise lies in its potential to increase grid efficiency, reliability, or in optimizing power flows and supporting variable power supplies. The parameters used in comparisons of various energy storage technologies include efficiency, energy capacity and density, run time, costs, system's response time, lifetime in years and cycles, self-discharge, and maturity of each energy storage technology. The most common energy storage technologies include compressed air, pumped hydro, batteries, fuel cells, flywheels, and super-capacitors. The last four are suitable for the medium scale applications. The chapter discussed energy storage technologies and gives an up to date comparative summary of their performances. After completing this chapter, the readers are able to understand the role, importance, configurations and topologies of energy storage systems, operation principles, characteristics, performances, and operation of major energy storage systems used in power systems, buildings, and industrial facilities. Another benefit is that readers are able to understand the critical role and necessity of energy storage systems in power and renewable energy systems, the differences between large-, mediumand small-scale energy storage systems, and how a system is selected on specific applications based on system characteristics and performances. Major energy storage technologies discussed in this chapter are compressed air energy storage, pumped hydropower storage systems, batteries, flywheels, hydrogen energy storage, fuel cells, supercapacitors, and superconducting energy storage systems. Thermal energy storage systems are covered in detail in the next chapter. This chapter provides comprehensive reviews of the energy storage technologies and gives an up to date comparative summary of their performances, characteristics, and applications.

Global demand for lithium-ion secondary batteries have been increasing due to new market growth from electric vehicles and power storage systems. Lithium-ion batteries possess high power density, energy density and long cycle life without memory effect and little self-discharge, and have been primary energy storage system for commercial electronics. However, recent accidents regarding battery safety, such as Samsung Note 7 issue, has raised doubt among public about lithium-ion batteries as option for energy storage. Separator is one of the primary component for lithium-ion battery safety. Commercial separators like PE or PP not only possess outstanding mechanical and electrochemical performance, but also have thermal shutdown function that provide safety measure by pore—blocking with melted polyolefin materials. Nevertheless, polyolefin materials suffered serious shrinkage at elevated temperature, which cause internal short-circuited of batteries ; also, polyolefin materials have relatively low electrolyte uptake, and could be major obstacle for future lithium-ion battery application. Hence it’s necessary to design new type of separator that guarantee battery safety and demonstrate better electrochemical performance In this study, we proposed a brand-new method to design composite separator with high thermal stability, electrolyte uptake ability and thermal shutdown function. Polyimide(PI) nanofiber film was used as substrate and produced by electrospinning technique, and ultra-thin Low-Density-Polyethylene(LDPE) layer was laid upon PI by simple spin-coating method. Spin-coating method provided unique advantages such as ultra thin coating layer (less than 1 micron), uniform coating structure and simple process, and was yet been applied for construction of composite film as lithium-ion battery separator. Coating parameter was tuned to obtain the optimized composite separator. Field-emission scanning electron microscope (FE-SEM) was used to investigate morphologies of separators ; Contact angle measurement was conducted to verify electrolyte affinity of different separators ; A.C. impedance method was used to measure conductivities and verify thermal shutdown of separators, and electrolyte uptake of different separators were measured by electrolyte soaking method in an argon-filled glovebox. The composite film had sub-micron average pore size, and possessed excellent physical properties, for instance, high porosity(73%), electrolyte uptake(1300%), ion conductivity(4.3*10-4 S/cm), air permeability(gurley value=0), and thermal stability(no shrink up to 150。C). Thermal shutdown function of composite film was also confirmed by impedance measurement at elevated temperature. It was noticed that physical properties between pristine PI and composite film were similar owning to ultra-thin coating layer, which mitigate performance loss from LDPE coating. Afterward, full cell battery tests were conducted with CR2032 type coin cell (Cathode : LFP, anode : MCMB, electrolyte : 1 M LiPF6 in EC/EMC/DMC=1:1:1+1%VC, 1C=2.4mAh/g). The first cycle charge-discharge curves, rate capability and cyclic performance were conducted. The composite film showed flatter first cycle charge-discharge plateau, better capacity retention at higher C-rate (Composite film :102 mAh/g at 1C, 79% retention, Celgard 2500 : 73 mAh/g, 51% retention , w.r.t. 0.1C), and higher discharge capacity at 0.5C 50th cyclic test. The higher porosity and electrolyte uptake of composite film facilitated ion conduction and were the main cause for enhanced battery performance. With enhanced thermal stability and electrochemical performance, we expected this type of composite separator to be promising for future lithium-ion battery application. Figure 1

Current status of polymer nanocomposite dielectrics for high-temperature applications

Ion-exchange membranes (IEMs) are at the core of many energy storage and conversion devices, such as fuel cells and redox flow batteries, being responsible for the migration of ionic species, separating the fuel stocks, and providing support to the electrode assemblies. For practical applications they are required to possess not only high ionic conductivity, but also specificity, thermal stability, long lifetime, and electrical insulation. The preparation of polymeric materials with such high-performance properties is still challenging and can lead to high prices, hindering their widespread use in energy conversion technologies. This is even more arduous when considering polymers to be used in anion conducting membranes, due to the need for the extra chemical stability and ability to withstand alkaline conditions at high temperatures for long periods of time [1].Polyketones are known to be high performance thermoplastic polymers with applications ranging from fire-retardants film coatings, packaging, and fibers, resulting from their high thermal and chemical stability. They can be obtained in high yields by copolymerization of inexpensive and readily available feedstocks such as ethylene and carbon monoxide. Our group proved that polyketones with alternating 1,4-dicarbonyl repeating units constitute an ideal starting point to access a wide class of modified polymers by simple Paal-Knorr cyclization, to gain pyrrole-N-bound functional groups stemming from the aliphatic backbone [2].This is a new account on our research on the ion conducting polymeric materials derived from polyketone, obtained by reaction with variously functionalized amines, and their easy conversion to anion exchange materials. The effect of reaction conditions on their thermal properties and chemical stability in alkaline media has been studied, and their conductivity in a wide range of frequencies assessed by broadband electric spectroscopy to shed light on the conduction mechanisms.The proposed conducting polymers combine the thermal stability of the aliphatic polyketone structure with the chemical flexibility given by the groups derived from functionalized amines branching out, proving to be highly tailorable, with possible applications in current energy conversion technologies. Acknowledgements: The authors wish to thank the Research Projects of Relevant National Interest (PRIN 2017) of the Italian Ministry of Education, University and Research “Novel Multilayered and Micro-Machined Electrode Nano-Architectures for Electrocatalytic Applications (Fuel Cells and Electrolyzers)” (Prot. 2017YH9MRK) and the SID2020 Project of the Department of Industrial Engineering, University of Padova “A New frontier in Hybrid Inorganic-Organic Membranes for Energy Conversion and Storage Devices” (Prot. BIRD201244) for funding.

Preparation and characterization of fluorine-containing benzimidazole polyimide films with a micro-branched crosslink structure

Polyimides (PI) reinforced with cross‐linked organosilicon nanophase (ON), formed by the sol‐gel procedure, were characterized by wide‐angle and small‐angle x‐ray diffraction, thermogravimetric analysis, dynamic mechanical analysis, thermally stimulated depolarization current and dielectric relaxation spectroscopy. The ON proved to possess a rather loose inner structure characterized by the mean‐square electron density fluctuations. Thermal stability and thermomechanical properties of nanocomposites in the glassy state remained nearly the same as those of the pristine PI, while a significant reinforcement effect was observed for the rubbery PI matrix. Both a looser molecular packing of PI chain fragments adjacent to the ON and a loose inner structure of the spatial aggregates of ON were believed to be responsible for a non‐additive decrease of the experimental values of dielectric permittivity for the nanocomposites. The data obtained suggested a reasonably good potential of PI reinforced with the ON as low dielectric permittivity materials. In Commemoration of the Contributions of Professor Valery P. Privalko to Polymer Science.

This work employed polymer active agent polyvinylpyrrolidone (PVP) treated barium titanate (BT) nanoparticles (PVP@BT) as functional nanofillers to fill polyimide (PI) matrix to fabricate PI nanocomposite films. The microstructure, dielectric properties, and heat resistance of PI, PI/BT, and PI/PVP@BT dielectric nanocomposite films were investigated. Fourier transform infrared spectrometer (FTIR) indicated that PVP has been successfully coated on the surface of BT nanoparticles. Due to the enhanced aggregation of monomers on the PVP@BT nanoparticles, higher molecular weight and viscosity of PI/PVP@BT nanocomposite films were achieved. Compared with PI/BT nanocomposite films, the dispersion of PVP@BT nanoparticles in PI/PVP@BT nanocomposite films was better, as verified by field emission scanning electron microscope and high‐resolution transmission electron microscopy. Filling a small amount of PVP@BT nanoparticles into the PI matrix improved the dielectric properties of the resultant nanocomposite films. The dielectric constant of the nanocomposite films with 10 wt% filler loading was up to 7.1 at 1000 Hz, which was 2.5 times higher than that of pure PI (2.9). PI nanocomposite film dielectric loss was generally lower than 0.015. Thermogravimetric analysis (TGA) tests verified that both pure PI and PI nanocomposite films showed excellent thermal stability. This work can be expected to provide a new strategy for designing and manufacturing PI dielectric nanocomposite films for energy storage applications.