Dielectric Polymer Materials for High-Density Energy Storage

Zhi-Min Dang

• Publisher: William Andrew
• Year: 2018
• Print ISBN: 9780128132159
• eBook ISBN: 9780128132166
• Topic: Technology & Engineering
• Subtopic: Engineering General
• Index: Technology & Engineering

Dielectric Polymer Materials for High-Density Energy Storage begins by introducing the fundamentals and basic theories on the dielectric behavior of material. It then discusses key issues on the design and preparation of dielectric polymer materials with strong energy storage properties, including their characterization, properties and manipulation. The latest methods, techniques and applications are explained in detail regarding this rapidly developing area. The book will support the work of academic researchers and graduate students, as well as engineers and materials scientists working in industrial research and development.In addition, it will be highly valuable to those directly involved in the fabrication of capacitors in industry, and to researchers across the areas of materials science, polymer science, materials chemistry, and nanomaterials.- Focuses on how to design and prepare dielectric polymer materials with strong energy storage properties- Includes new techniques for adjusting the properties of dielectric polymer materials- Presents a thorough review of the state-of-the-art in the field of dielectric polymer materials, providing valuable insights into potential avenues of development

1

Introduction

Zhi-Min Dang^1,2, ¹Tsinghua University, Beijing, China, ²Xi’an University of Science and Technology, Xi’an, China

Abstract

This book is named Dielectric Polymer Materials for High-density Energy Storage. It is well known that the film dielectric capacitor has a very high-power density but a low energy density, which limits its application as an energy storage device. Recently, the dielectric polymer materials have attracted wide attention internationally, and more excellent works show some advanced dielectric polymer materials with both high energy density and high-power density by designing different composition, microstructure, and preparation processing so that some materials are used to produce the high-density energetic film capacitors. In this chapter, we will simply introduce the request for high-performance dielectric polymer materials in order to develop the high-density energetic film capacitors. Furthermore, some research achievements are reviewed simply on the basis of present works, including different methods in order to solve key science issues. The detail contents can be introduced in each chapter subsequently.

Keywords

Dielectric polymer materials; high-density energy storage; capacitor; development; review

Acknowledgment

The authors gratefully acknowledge support from the National Basic Research Program of China (973 Program) (No. 2015CB654603) and the National Natural Science Foundation of China (Nos. 51425201, 51622701, 51377010). Z. M. D. also thanks the Postgraduate Education Reform Project of Tsinghua University (53812000216) for financial support.

1.1 Film Dielectric Capacitors

Though fossil fuels made an important contribution to the rapid development of society in recent years, it resulted in severe climate change so that we must find a sustainable route to replace the use of fossil fuels [1,2]. As a result, scientists pay more effort to explore renewable energy from the sun and wind in order to produce “green” power energy directly from nature. It is also well known that the power energy will be one very crucial consumption mode among many kinds of energies because the power energy can be transmitted over a large scale over a long distance via a transmission system, and this kind of energy can be stored by employing different types of energy-storage equipment. The development of power energy storage technology will accelerate its wide use in many fields. For example, many countries have worked out a timetable to prohibit the use of oil fuel automobiles. The development of electric vehicles or hybrid electric vehicles with low CO₂ emissions becomes the first choice in many countries. Therefore, one of the great challenges in the 21st century is unquestionably energy storage. In order to make good use of “green” power from the beginning, the manufacture of the power energy storage device/equipment with high energy density is a crucial. Due to the requirement of energy storage techniques, advanced batteries and capacitors with high energy density are researched by global scientists widely. In the present state, we need to improve their performance further to meet the higher requirements of future systems, ranging from portable electronics to hybrid electric vehicles and large industrial equipment, by developing new materials and improving our understanding of nanoscale interfaces in advanced functional materials [3–5].

Among the currently available power energy storage devices, each kind of device has its advantages and disadvantages. Fig. 1.1 shows the plot of energy against power density, also called a Ragone plot [1], for the most important energy storage systems. These systems can often be classified in two categories. They include all kinds of batteries and capacitors. It is well known that the batteries often have a high energy density, but a low power density due a low discharge rate, which is often limited to the electrode chemical reaction. Comparison to the lithium ion battery, though the dielectric capacitors possess the highest power density because of their fast charge–discharge capability [5,6], the energy density of the dielectric capacitors is very low. Fig. 1.2 shows a schematic picture, in which a narrow bottle neck limits the charge–discharge rate of batteries. However, an open bottle structure of dielectric capacitors supports a very short charge–discharge rate. Therefore, if a high-energy density polymer material can be realized, polymer film capacitors would remarkably help to reduce the volume, weight, and cost of the electric power system in hybrid electric vehicles.

Figure 1.1 Power density again energy density of all kinds of power energy storage equipment [1].

Figure 1.2 Schematic energy storage and release processes, (A) battery and (B) dielectric film capacitor.

High-power and high-energy density capacitors are one of the major enabling technologies for the development of commercial, consumer, and military systems with ever-increasing demands for compact, reliable, and efficient electrical power systems [1,6–8]. Electrostatic capacitors would supply higher power density, lower loss, and higher operating voltage than do other types of capacitors such as electrolytic capacitors and supercapacitors. Examples of important applications include high-frequency inverters, insulated-gate bipolar transistor snubbers, power factor correction, and pulsed-power generation. However, the low energy density of these dielectric capacitors (<2.0 J/cm³) leads to high capacitor volume and weight. For instance, DC bus capacitors in power inverters of electrical vehicles occupy ~35% of the inverter volume and ~23% of the inverter weight [6,9]. Therefore, it is imperative to develop novel technologies that can significantly increase the energy density of electrostatic dielectric capacitors.

In this book, we focus on introducing all kinds of dielectric polymer materials with a high energy storage density, which can be used to design and fabricate advanced film dielectric capacitors with both high-power and high-energy density at the same time.

1.2 Key Science Issues

Though a very high-power density of polymer dielectric capacitors, the dielectric capacitors are limited by energy densities that are at least an order of magnitude lower than those of electrochemical devices such as batteries [10] and electrochemical capacitors [11,12]. For instance, the energy densities of most commercially available electrochemical capacitors to date are in the range of 18–29 J/cm³ [13], while that of the best commercial capacitor film represented by biaxially-oriented polypropylenes (BOPP) is only about 1.2 J/cm³ [14,15]. Since dielectric capacitors can occupy more than 25% of the volume and weight-to-power electronics and pulsed-power systems, dramatic enhancement of the energy density of dielectric capacitors would be essential to realize their full potential as an enabling technology.

The energy density of dielectric capacitors is governed by the dielectric material that separates the opposite static charges between two electrodes and is given in Eq. (1.1).

$U=\int \mathit{EdD}$ (1.1)

(1.1)

where U represents the total stored energy density, E represents the applied electric field, and D is the electric displacement. A schematic picture is shown in Fig. 1.3. For linear dielectrics, the energy storage density of the capacitor is given in Eq. (1.2).

$U=\frac{1}{2}{\epsilon }_0{\epsilon }_{\mathrm{r}}{E}^2$ (1.2)

(1.2)

where ${\epsilon }_0$

is the vacuum permittivity and k is the dielectric constant (the ${\epsilon }_r$

also often denotes the dielectric constant in many reports). Therefore, U is strongly dependent on both k and E, with E limited by the breakdown strength (E_b). Compared with ceramic and electrolytic capacitors, polymer capacitors are easily processed at a low temperatures or with an organic solvent so that they can be operated under high voltages and fail gracefully with an open circuit, making them the preferred high-energy density capacitors [16–19]. However, the state-of-the-art dielectric polymers such as BOPP often have a low value of k (c.2.2), which substantially limits U value to, e.g., less than 4 J/cm³ even though the dielectric material has a high breakdown level. To raise k, a...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• 1. Introduction
• 2. Fundamentals of Dielectric Theories
• 3. Preparation, Structure and Properties of Fluorine-containing Polymers
• 4. Manipulating Dielectric Properties by Modifying Molecular Structure of Polymers
• 5. High Energy Storage Dielectric Polymer Materials With Hierarchical Microstructures
• 6. Core-Shell Structural Fillers to High Energy Storage Dielectric Polymer Materials
• 7. Multiphase/Multicomponent Dielectric Polymer Materials With High Permittivity and High Breakdown Strength
• 8. Electrospinning Functional Fillers/Polymer Composites With High Energy Storage
• 9. Thermally Conductive Dielectric Polymer Materials for Energy Storage
• 10. Charging and Discharging Characteristics of Dielectric Polymer Materials
• 11. Dielectric Polymer Materials with High Thermal Stability
• 12. Processing of Polymeric Dielectrics for High Energy Density Capacitors
• 13. Future Perspectives
• Index