Smart and Flexible Energy Devices

Ram K. Gupta, Tuan Anh Nguyen, Ram K. Gupta, Tuan Anh Nguyen

• Publisher: CRC Press
• Year: 2022
• Print ISBN:
  9781032033266
  9781032033242
• Edition: 1
• eBook ISBN:
  9781000543803
• Topic: Technology & Engineering
• Subtopic: Chemistry
• Index: Chemistry

The scientific community and industry have seen tremendous progress in efficient energy production and storage in the last few years. With the advancement in technology, new devices require high-performance, stretchable, bendable, and twistable energy sources, which can be integrated into next-generation wearable, compact, and portable electronics for medical, military, and civilian applications.

Smart and Flexible Energy Devices examines the materials, basic working principles, and state-of-the-art progress of flexible devices like fuel cells, solar cells, batteries, and supercapacitors. Covering the synthesis approaches for advanced energy materials in flexible devices and fabrications and fundamental design concepts of flexible energy devices, such as fuel cells, solar cells, batteries, and supercapacitors, top author teams explore how newer materials with advanced properties are used to fabricate the energy devices to meet the future demand for flexible electronics.

Additional features include:

• Addressing the materials, technologies, and challenges of various flexible energy devices under one cover

• Emphasizing the future demand and challenges of the field

• Considering all flexible energy types, such as fuel cells, solar cells, batteries, and supercapacitors

• Suitability for undergraduate and postgraduate students of material science and energy programs

This is a valuable resource for academics and industry professionals working in the field of energy materials, nanotechnology, and energy devices.

1 Smart and Flexible Energy Devices: Principles, Advances, and Opportunities

Tenzin Ingsel and Ram K. Gupta

Department of Chemistry, Kansas Polymer Research Center, Pittsburg State University, Pittsburg, Kansas, USA

DOI: 10.1201/9781003186755-1

CONTENTS

1. 1.1 Introduction
2. 1.2 Flexible supercapacitors
3. 1.2.1 Flexible supercapacitors based on carbon
4. 1.2.2 Flexible supercapacitors based on metal oxides and sulfides
5. 1.2.3 Flexible supercapacitors based on nanocomposites
6. 1.3 Flexible batteries
7. 1.3.1 Flexible Li-ion and Li-sulfur batteries
8. 1.3.2 Flexible metal–air batteries
9. 1.4 Flexible proton exchange membrane fuel cells
10. 1.5 Flexible solar cells
11. 1.5.1 Dye-sensitized flexible solar cells
12. 1.5.2 Perovskite-based flexible solar cells
13. 1.6 Conclusion
14. References

1.1 Introduction

Flexible devices are an essential group of electronics with versatile and innovative applications. Flexible electronics can function normally, even when subjected to various deformations such as stretching, bending, and twisting. Their potential applications range from wearable devices, renewable energy storage and production, medical care, consumer electronics, and many more. Electronics for flexible applications require reliable manufacturing to develop suitable materials, innovative technology, and tools to carry advanced research [1]. From a scientific perspective, materials that can power flexible devices remain a bottleneck for their development. For the past few years, multiple studies have been carried out to actualize power source materials that are mechanically flexible, strong, and suitable for versatile applications. Despite all the technological advances in the flexible device area, development in flexible energy conversion and storage systems is still in its infancy [2]. Ideal flexible energy conversion and storage device or power source materials for electronics exhibit suitable deformation properties; these include being bendable, stretchable, foldable and having operational safety and secure electrical functioning. Figure 1.1 illustrates an example of a futuristic, smart wearable glove that can sense, convert, and store various energy forms [3].

Figure 1.1 (a) Sensors and readout circuit schematics. (b) Piezoresistive multisensory. (c) Example of sensor response. (d) Example of patterned sensor configuration employed for application in each finger for characterization. Adapted with permission [3]. Copyright (2018) American Chemical Society.

The following subsections will explore principles of different flexible energy storage and conversion devices, their recent advances, and growth opportunities. The first section will cover flexible supercapacitors based on carbon material, metal oxides, sulfides, and nanocomposites. A few concepts to look forward to in the flexible supercapacitors include two common types of supercapacitors based on their energy storage mechanism and wearable textile-based supercapacitors; in addition, comparisions are made in energy and power density of pristine carbon materials and nanocomposites comprised of carbon and metal oxides. The flexible battery section discusses flexible lithium-ion, lithium-sulfur, and metal-air. Some recent progress in flexible battery technologies is explained, where unique electrode design prototypes pave the way for their large-scale production and practical applications. The flexible fuel cell part presents motivation for exploring their advantages. For the flexible solar cell part, third-generation low-cost, flexible dye-sensitized solar cells and perovskite solar cells are reviewed.

1.2 Flexible supercapacitors

1.2.1 Flexible supercapacitors based on carbon

Supercapacitors (SC) are energy storage devices known for their relatively simple assembly, high power density, quick charge-discharge rates, and high cyclic performance. Such properties make supercapacitors suitable for their use in flexible electronics. Supercapacitors can be divided into two categories based on how the charge is stored in the device. In electrical double-layer capacitors (EDLCs), electrical energy is stored via ion adsorption and desorption at the electrode/electrolyte interface. In pseudocapacitors, power is mainly generated and accumulated by redox reactions occurring at the surface [4,5]. Different types of materials are suitable for supercapacitors functioning via these two distinct charge-storage principles. Carbon-based materials are widely known to be applied in EDLCs, while pseudocapacitors use metal sulfides, metal oxides, and conducting polymers. EDLCs and pseudocapacitors have their advantages and disadvantages. For instance, EDLCs have high cycling stability, but only moderate capacitance. On the other hand, pseudocapacitors have poor cycling stability but high capacitance. This brings us to hybrid supercapacitors, which are made up of selectively chosen and synthesized nanomaterials for nanocomposites that show enhanced energy density without compromising their power density and cyclic life. This is a perfect segue into the subsections on discussions about flexible supercapacitors based on carbon, metal oxides, metal sulfides, and nanocomposite materials [2].

When it comes to carbon-based materials for flexible supercapacitors, carbon materials of different morphology and structure, such as graphene, carbon nanotubes (CNTs), and carbon fiber, are widely investigated [6]. Due to their high conductivity, large surface area, and desirable mechanical properties, such carbon materials are fit for applications in flexible devices. Graphene is a two-dimensional structure with monolayers of carbon atoms where the carbon bonds are sp² hybridized. Graphene represents a distinguished group of carbon materials because of its outstanding electrical and thermal conductivity, mechanical flexibility, and relatively low production cost [7]. Supercapacitors based on graphene can deliver a decent specific capacitance of about 550 F/g, theoretically. However, due to the restacking of graphene sheets during the fabrication process and the cutback in their specific surface area, the specific capacitance delivery is lower than the theoretical limit. Laser reduction of graphene oxide generated graphene with heavily reduced restacking of graphene sheets [8]. The supercapacitor device was constructed by employing two identical laser-reduced graphene film (LSG) electrodes sandwiched with a polymer gel electrolyte. An extremely thin device was obtained with a thickness of less than 100 μm. The LSG electrode showed a high specific surface area and high specific capacitance of 204 F/g, with high energy and power density. The LSG electrode displayed outstanding cycle stability. The device proved highly flexible, with its bending having no adverse effect on the electrochemical performances [9].

Carbon-based materials have also been used as capacitive sensors, a subset of strain sensors where mechanical strain gets converted to electrical output [10]. In fact, in an ideal capacitive strain sensor, a strain is proportional to the capacitance. Equation 1.1 represents the strain-capacitance relationship.

$\mathrm{C}={\mathrm{\epsilon }}_0{\mathrm{\epsilon }}_{\mathrm{r}}\mathrm{S}/\mathrm{d}\dots$(1.1)

Where ε₀ is the vacuum dielectric constant (F/m), ε_r denotes the dielectric constant of the electrolyte, S is the size of the electrode accessible to ions (m²), and d is the thickness of the dielectric layer [10]. A carbon-based capacitive strain sensor was fabricated as knittable fiber. The core was made up of rubber and played a role as a dielectric layer, and carbon nanotube served as the active material [11]. The fiber supercapacitor device effectively absorbed shear and tensile stresses and converted them to capacitance during deformation. The device showed high capacitance, strain linearity, and high sensitivity to mechanical force. Figure 1.2 shows a schematic image of the twisted and stretchable fiber, as well as the actual fiber sewn into a glove, where it shows high structural reversibility (stretched up to 60%) [11]. The fiber was also helically wrapped around a glass tube to demonstrate no fiber damage or delamination. The scanning electron microscopes (SEM) further displayed the surface microstructure of the fiber-based sensor. Such design can potentially be applied in wearable energy devices, such as flexible solar cells, batteries, and supercapacitors, among many others.

Figure 1.2 (a) Schematic image of a twisted sandwich-structured fiber device composed of two CNT electrodes with silicon rubber as the core. Digital images of (b) the fiber sewn into a glove and enlarged images of (c) before and (d) after subjecting the test sample to 60% tensile strain with a scale bar (8 mm). (e) Photograph of helically wrapped fiber on a glass tube with scale bar (50 mm). Microstructural mapping of fiber during its relaxation after an applied strain at low magnification (f) and high magnification (g). Adapted with permission [11]. Copyright (2016) American Chemical Society.

A textile-based EDLC was fabricated where an activated carbon was screen printed onto a carbon fiber cloth. The carbon cloth was knitted with patterns and acted as a current collector, as shown in Figure 1.3 [12]. The textile EDLC showed suitable capacitance, performance, and mechanical stability to be stret...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• Preface
• Editors
• Contributors
• Chapter 1: Smart and Flexible Energy Devices: Principles, Advances, and Opportunities
• Chapter 2: Innovation in Materials and Design for Flexible Energy Devices
• Chapter 3: Basics and Architectural Aspects of Flexible Energy Devices
• Chapter 4: Characterization Techniques of Flexible Energy Devices
• Chapter 5: Micro- and Nanofibers-Based Flexible Energy Devices
• Chapter 6: 3D Printed Flexible Energy Devices
• Chapter 7: Environmental Impact of Flexible Energy Devices
• Chapter 8: Metal Oxide-Based Catalysts for Flexible and Portable Fuel Cells: Current Status and Future Prospects
• Chapter 9: Flexible Fuel Cells Based on Microbes
• Chapter 10: Flexible Silicon Photovoltaic Solar Cells
• Chapter 11: Flexible Solar Cells Based on Metal Oxides
• Chapter 12: Inorganic Materials for Flexible Solar Cells
• Chapter 13: Efficient Metal Oxide-Based Flexible Perovskite Solar Cells
• Chapter 14: Flexible Solar Cells Based on Chalcogenides
• Chapter 15: Perovskite-Based Flexible Solar Cells
• Chapter 16: Quantum Dots Based Flexible Solar Cells
• Chapter 17: A Method of Strategic Evaluation for Perovskite-Based Flexible Solar Cells
• Chapter 18: Flexible Batteries Based on Li-Ion
• Chapter 19: Flexible Batteries Based on Na-ion
• Chapter 20: Flexible Batteries Based on K-ion
• Chapter 21: Flexible Batteries Based on Zn-Ion
• Chapter 22: Fabrication Techniques for Wearable Batteries
• Chapter 23: Carbon-Based Advanced Flexible Supercapacitors
• Chapter 24: 2D Materials for Flexible Supercapacitors
• Chapter 25: Flexible Supercapacitors Based on Metal Oxides
• Chapter 26: Recent Advances in Transition Metal Chalcogenides for Flexible Supercapacitors
• Chapter 27: MOFs-Derived Metal Oxides-Based Compounds for Flexible Supercapacitors
• Chapter 28: Textile-Based Flexible Supercapacitors
• Chapter 29: Current Development and Challenges in Textile-Based Flexible Supercapacitors
• Chapter 30: Flexible Supercapacitors Based on Nanocomposites
• Chapter 31: Textile-Based Flexible Nanogenerators
• Index