Flexible Supercapacitor Nanoarchitectonics E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
The 21 chapters in this book presents a comprehensive overview of flexible supercapacitors using engineering nanoarchitectures mediated by functional nanomaterials and polymers as electrodes, electrolytes, and separators, etc. for advanced energy applications. The various aspects of flexible supercapacitors, including capacitor electrochemistry, evaluating parameters, operating conditions, characterization techniques, different types of electrodes, electrolytes, and flexible substrates are covered. This is probably the first book of its type which systematically describes the recent developments and progress in flexible supercapacitor technology, and will be very helpful for generating new and innovative ideas in the field of energy storage material for wearable/flexible industry applications.
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Veröffentlichungsjahr: 2021
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Table of Contents
Cover
Title Page
Copyright
Preface
1 Electrodes for Flexible Integrated Supercapacitors
1.1 Introduction and Overview of Supercapacitors
1.2 Electrode Materials for Flexible Supercapacitors
1.3 Device Architecture of Flexible Supercapacitor
1.4 Integration of Flexible Supercapacitors
1.5 Conclusion
References
2 Flexible Supercapacitors Based on Fiber-Shape Electrodes
2.1 Introduction
2.2 Supercapacitors
2.3 Shape Dependent Flexible Electrodes
2.4 Fiber Shape Electrodes (FE/FSC)
2.5 Conclusion
References
3 Graphene-Based Electrodes for Flexible Supercapacitors
3.1 Introduction
3.2 Type of SCs
3.3 Fabrication Techniques for the Electrode Materials
3.4 Substrate Materials for the Flexible SCs
3.5 Graphene Nanocomposite-Based Electrode Materials
3.6 NSs for the Flexible SC
3.7 Conclusion
References
4 Polymer-Based Flexible Substrates for Flexible Supercapacitors
4.1 Introduction
4.2 Polymers-Based Flexible Materials for Flexible Supercapacitors
4.3 Synthesis and Fabrication Approach of the Polymer-Based Electrode
4.4 Physicochemical Characterization of Flexible Supercapacitors
4.5 Recent Findings on the Performance of Flexible Supercapacitors
4.6 Conclusion
References
5 Carbon Substrates for Flexible Supercapacitors and Energy Storage Applications
5.1 Introduction
5.2 Overview of the Energy Storage System
5.3 Capacitors Modeling
5.4 Industrial Applications of Capacitors
5.5 Conclusions
References
6 Organic Electrolytes for Flexible Supercapacitors
6.1 Introduction
6.2 Organic Electrolytes
6.3 Solid and Quasi-Solid-State Electrolytes
6.4 Ionic Liquids-Based Electrolytes
6.5 Redox Active Electrolytes
6.6 Conclusion
References
7 Carbon-Based Electrodes for Flexible Supercapacitors Beyond Graphene
7.1 Introduction
7.2 Materials Used to Prepare Flexible Supercapacitors
7.3 The Carbon-Based Electrode Used for Flexible Supercapacitors
7.4 Conclusion
References
8 Biomass-Derived Electrodes for Flexible Supercapacitors
8.1 Introduction
8.2 Biomass-Derived Carbon Materials
8.3 Incorporation of Biomass-Based Electrodes in Flexible Supercapacitors
8.4 Challenges for Using Biomass-Derived Materials
8.5 Conclusion
References
9 Conducting Polymer Electrolytes for Flexible Supercapacitors
9.1 Introduction
9.2 Components of a Supercapacitor
9.3 Configuration of a Supercapacitor
9.4 Conducting Polymer Electrolytes
9.5 Conclusion
References
10 Inorganic Electrodes for Flexible Supercapacitor
10.1 Introduction
10.2 Flexible Inorganic Electrode Based on Carbon Nanomaterial
10.3 Conclusion
References
11 New-Generation Materials for Flexible Supercapacitors
11.1 Introduction
11.2 Taxonomy of Supercapacitor
11.3 Fundamentals of Supercapacitor
11.4 Flexible Supercapacitor
11.5 Outlook and Perspectives
Acknowledgement
References
12 Asymmetric Flexible Supercapacitors: An Overview of Principle, Materials and Mechanism
12.1 Introduction: Why Store Energy?
12.2 Supercapacitor: A Green Approach Towards Energy Storage
12.3 Flexible Supercapacitors
12.4 Asymmetric Supercapacitor
12.5 Recent Advances in Flexible Asymmetric Supercapacitors
12.6 Conclusion
References
13 Aqueous Electrolytes for Flexible Supercapacitors
13.1 Introduction
13.2 Electrolyte Performance-Controlling Parameters for Designing Flexible Supercapacitors
13.3 Why Aqueous Electrolytes?
13.4 Acid Electrolytes
13.5 Alkaline Electrolytes
13.6 Neutral Electrolyte
13.7 Comparative Electrochemical Performances in Different Aqueous Electrolytes
13.8 Water-in-Salt Electrolytes for Flexible Supercapacitors
13.9 Conclusion and Future Prospects
Acknowledgements
References
14 Electrodes for Flexible Micro-Supercapacitors
14.1 Introduction
14.2 Electrode Configurations
14.3 Manufacturing Techniques
14.4 State-of-the-Art Electrode Materials
14.5 Conclusion and Outlook
Acknowledgement
References
15 Electrodes for Flexible Self-Healable Supercapacitors
15.1 Introduction
15.2 Self-Healable Nanomaterials
15.3 Nanomaterials-Based Interfaces for Supercapacitors
15.4 Conclusion
References
16 Electrodes for Flexible–Stretchable Supercapacitors
16.1 Introduction
16.2 Electrodes for Flexible/Stretchable Supercapacitors
16.3 Conclusion and Future Remarks
References
17 Fabrication Approaches of Energy Storage Materials for Flexible Supercapacitors
17.1 Introduction
17.2 Classification of Flexible Supercapacitors
17.3 Conclusion
References
18 Nature-Inspired Electrodes for Flexible Supercapacitors
18.1 Introduction
18.2 Energy Storing Mechanism of Supercapacitors
18.3 Flexible Supercapacitors
18.4 Essential Parameters of Supercapacitors
18.5 Natural Flexible Supercapacitors
18.6 Conclusion
References
19 Ionic Liquid Electrolytes for Flexible Supercapacitors
19.1 Introduction
19.2 Mobile Energy Storage Systems and Supercapacitors
19.3 Flexible Supercapacitors: Need and Challenges
19.4 Developments in the Design of a Supercapacitor
19.5 Electrolytes for Flexible Supercapacitors
19.6 Gel Polymer Electrolytes (GPEs)
19.7 Development in ILEs
19.8 Design Flexibility With IL Electrolytes
19.9 Electrolyte–Electrode Hybrid Design
19.10 Ionic Liquid Electrolytes and Problem of Leakage
19.11 Mechanical Stability of ILs
19.12 Conclusions
References
20 Conducting Polymer-Based Flexible Supercapacitor Devices
20.1 Introduction
20.2 Principles of Supercapacitor
20.3 Classification of Supercapacitors
20.4 Conducting Polymer-Based Flexible Supercapacitors
20.5 Electrolytes for Flexible Supercapacitors
20.6 Conclusions and Future Perspectives
Acknowledgements
References
Index
End User License Agreement
List of Illustrations
Chapter 1
Figure 1.1 Schematic illustration of charge storage in supercapacitors [13]. Cop...
Figure 1.2 Schematic illustration of charge adsorption in porous carbon material...
Figure 1.3 (a, b) HRTEM images of multi-walled carbon nanotube (MWNTs) synthesiz...
Figure 1.4 Schematic diagram of the Origin (illustrating the transformations) of...
Figure 1.5 (a) Schematic presentation of graphene/carbon nanofiber (CNF) composi...
Figure 1.6 Photo of (a) the aqueous nitrogen-doped graphene (NG) enhanced polyac...
Figure 1.7 (a) Schematic structure and Fabrication method of stretchable pseudoc...
Figure 1.8 (a) Schematic illustration of the synthesis of urchin-like NiO–CuO ho...
Figure 1.9 (a) Photograph of prepared hybrid supercapacitor, (b, c) SEM images o...
Figure 1.10 (a) Optical images of CF/MWNT/V2O5 NW (CMV) electrode and wire-type ...
Figure 1.11 (a) Photographs of the screen-printed electrodes of several designs;...
Chapter 2
Figure 2.1 Schematic of charge-storage in supercapacitor [7].
Figure 2.2 Classification of electrochemical supercapacitors [9].
Figure 2.3 Types of flexible supercapacitors [9].
Figure 2.4 A flexible supercapacitor [15].
Figure 2.5 Flexible textile fiber FE for supercapacitor [21].
Figure 2.6 A flexible substrate paper electrode [24].
Figure 2.7 Yarn base flexible fiber electrode for supercapacitor [29].
Figure 2.8 Wrapped fiber shape FE/FSC [30].
Figure 2.9 Coaxial fiber-shape FE/FSC [33].
Figure 2.10 Parallel fiber shape FE/FSC [34].
Figure 2.11 SEM of twisted fiber-shape energy storage device [37].
Figure 2.12 Rolled fiber-shape flexible electrode/flexible supercapacitor [38].
Chapter 3
Figure 3.1 Diagram illustrating the fabrication of flexible SC device [Reprinted...
Figure 3.2 Schematic of electro-spinning set up [Reprinted from Zhu, N., Chen, X...
Chapter 4
Figure 4.1 (a) Scheme illustration of the fabrication process of PANi-GP paper. ...
Figure 4.2 Schematic illustration showing the procedure for the preparation of N...
Figure 4.3 Schematic illustration of the fabrication of ternary PEDOT: PSS/MnO
2
/...
Figure 4.4 GGO-PEDOT solution and film preparation (reproduced with permission f...
Figure 4.5 A schematic diagram for the electrode fabrication of GP/SWNTs/PPy (re...
Figure 4.6 (a) TEM micrograph of as-prepared graphene sheet (b) HRTEM of
f-
graph...
Figure 4.7 XRD patterns for (a) α-MnO
2
and α-Fe
2
O
3
electrodes (reproduced with p...
Figure 4.8 Schematic illustration for the structure of supercapacitor under diff...
Chapter 5
Figure 5.1 Images of (a) a common SCs and (b) an FSCs [3].
Figure 5.2 Various kinds of SCs. (a) a full-carbon Electrical Double Layer Capac...
Figure 5.3 Schematic presentation the structural changes within: (a) common elec...
Figure 5.4 (a) Images of zero-dimensional, one-dimensional, and two-dimensional ...
Figure 5.5 The types of models for the EDLCs on the surface with a positive char...
Figure 5.6 Schematic representation of an EDLC [7].
Figure 5.7 Schematic diagram of a PC [7].
Figure 5.8 Schematic diagram of a hybrid SC [7].
Figure 5.9 Equivalent circuit models [114].
Figure 5.10 Type of neuron body with several inputs and one output [114].
Figure 5.11 Schematic of the self-discharge method [167].
Figure 5.12 Schematic of SC fractional-order model [114].
Figure 5.13 Power electronics applications. (a) Wind turbines, (b) photovoltaics...
Figure 5.14 Different types of power conversion in power electronics converters ...
Figure 5.15 Trolley bus based on Ni(OH)
2
-AC SC [7].
Chapter 6
Figure 6.1 Capacitance of a nanoporous electrode as a function of the pore size ...
Figure 6.2 CV curves of Co
3
O
4
based symmetric supercapacitor in (a & b) 3M KOH a...
Figure 6.3 Nyquist plot of symmetric supercapacitor in (a) 3 M KOH and (b) 1 M T...
Figure 6.4 (a) CV curves measured with bending position in organic electrolyte a...
Figure 6.5 Liquid electrolyte uptake and leakage rates of the (a) (PEG-TBBPA) me...
Figure 6.6 Electrochemical performance of CNT@PDAA//PVDF-HFP/Et
4
NBF
4
-AN//CNT@PDA...
Figure 6.7 (a) CV curves of flexible solar cells with PVA-Li
2
SO
4
-BMIMI and PVA-L...
Figure 6.8 (a) Ragone plots and (b) Cyclic performances at a current density of ...
Figure 6.9 Comparison of (a) CV curves at the scan rate of 100 mV s
−1
, (b) GCD c...
Figure 6.10 Chemical structure of the redox-active mediators used with electroly...
Chapter 7
Figure 7.1 Schematic representation of the taxonomy of supercapacitors.
Figure 7.2 Schematic illustration of the preparation of PANI/GO/CNT ternary comp...
Figure 7.3 (a) Schematic fabrication method of the two-ply CNT/Co
3
O
4
@NiO/GN yarn...
Figure 7.4 (a) Pristine CNT paper with A4 size; (b) the deposition of MnO
2
on la...
Figure 7.5 Schematic diagram of the preparation of activated carbon from biomass...
Figure 7.6 Schematic diagram of the all-solid-state hybrid supercapacitor of C-N...
Figure 7.7 Schematic representation of flexible solid-state asymmetric supercapa...
Chapter 8
Figure 8.1 Schematic representation of flexible solid-state supercapacitor. (Rep...
Figure 8.2 (a) is CV of the NAC-400-Si/C HS full cell at various scan rates, (b)...
Figure 8.3 (a) polarization curves (b) galvanostatic charge/discharge curves at ...
Figure 8.4 Schematic representation of the synthesis of carbon from the deed lea...
Figure 8.5 (a and d) CV measurements of Neem leaf derived carbon at various rate...
Figure 8.6 (a) Schematic representation of the fabrication process of the wrinkl...
Figure 8.7 (a–c) low and high magnified SEM images of the AWCM, showing the wrin...
Figure 8.8 (a) Schematic representation of a flexible supercapacitor. (b) Image ...
Chapter 9
Figure 9.1 Components of a supercapacitor. Adapted from Ref. [23].
Figure 9.2 Schematic illustration of (a) a dry solid-state polymer electrolyte (...
Figure 9.3 Outline of solid hydroxide ion conducting electrolytes for supercapac...
Chapter 10
Figure 10.1 (a, b) SEM images of a four layered buckled graphene film on PDMS su...
Figure 10.2 Schematic illustration of the structure of the ASC. The digital imag...
Figure 10.3 Bending and Twisting of electrodes and specific capacitance of NiCo2...
Figure 10.4 Schematic illustration of the process for fabricating the transparen...
Figure 10.5 (a) Schematic drawing of electrodeposition of MnO2 onto the SWNT coa...
Figure 10.6 (a) Schematic illustration of a flexible supercapacitor using the te...
Chapter 11
Figure 11.1 Structural comparison of flexible supercapacitor with conventional s...
Figure 11.2 Classification of supercapacitor electrode.
Figure 11.3 Various approaches to enhance energy density.
Figure 11.4 Fabrication of the 3D porous structures of RGO/cellulose composites.
Figure 11.5 (a) The photographs of M-RGO/PA66-nano and the scheme for assembling...
Figure 11.6 SEM images of (a), (b) bare CNF, (c), (d) NiCo2O4/CNF composite.
Figure 11.7 (a) Digital photograph of whatman filter paper (white color) and aft...
Figure 11.8 (a) CV curves of CSCC-4 at scan rates from 5 to 100 mV s−1; (b) GCD ...
Figure 11.9 (a) Photograph of a light-emitting-diode (LED) power under four diff...
Chapter 12
Figure 12.1 Schematic representation of a symmetric supercapacitor showing its c...
Figure 12.2 Ragone Plot for various electrochemical energy storage devices. Repr...
Figure 12.3 Classification of supercapacitors on the basis of electrode material...
Figure 12.4 Schematic representation of a flexible solid-state supercapacitor. R...
Figure 12.5 An overview of recent development in the area of flexible solid-stat...
Figure 12.6 Innovative cell designs for flexible supercapacitors: sandwich type,...
Figure 12.7 Schematic illustration of the fabrication and energy storage mechani...
Figure 12.8 Electrochemical characterization distinguishing between ideal and pr...
Figure 12.9 Three discharging curves showing different shapes with the same star...
Chapter 13
Figure 13.1 Various features to be considered for achieving the desired performa...
Figure 13.2 Effect of electrolytes on the performance of supercapacitors. Reprod...
Figure 13.3 Various types of electrolytes used for fabrication of flexible super...
Figure 13.4 Schematic representation of pressure dependence on different electro...
Figure 13.5 Schematic representation demonstrating the correlation among the rea...
Figure 13.6 Cyclic voltammograms of pristine-CNT and functionalized-CNT in 1 M H...
Figure 13.7 (a) Schematic showing capacitive and faradic charge-storage processe...
Figure 13.8 (a) Cyclic voltammograms at different potential scan rates of 1, 10 ...
Figure 13.9 Illustration on the effect on capacitance and fate of MnO
2
birnessit...
Figure 13.10 Ragone plot of Mn
3
(PO
4
)
2
-based symmetric and asymmetric ESs in diff...
Figure 13.11 Cyclic voltammograms of activated carbon electrode displaying the v...
Figure 13.12 (A) Diagram representing the mobility/diffusion of hydrated H
+
, K
+
,...
Figure 13.13 (a) Cyclic voltammograms of activated porous calcium carbide-derive...
Figure 13.14 Cyclic voltammograms recorded at voltage scan rate was 0.5 mV s
−1
f...
Chapter 14
Figure 14.1 (a) Schematic diagram of a sandwich-type flexible µSC. (b) Schematic...
Figure 14.2 Schematic diagram showing the arrangement of two-electrode fiber µSC...
Figure 14.3 (a) Schematic diagram showing a typical interdigitated µSCs configur...
Figure 14.4 Schematic diagram showing the three typical fabrication routes of in...
Figure 14.5 Schematic diagram showing the fabrication process of using laser scr...
Figure 14.6 (a) Schematic of the laser reduction of GO fiber for formation of RG...
Figure 14.7 Schematic diagram showing the fabrication process for laser-assisted...
Figure 14.8 (a) Schematic diagram showing the fabrication process of screen prin...
Figure 14.9 Morphology of inkjet-printed graphene patterns. Scanning electron mi...
Figure 14.10 (a) Schematic diagram showing the 3D printing fabrication process. ...
Figure 14.11 (a) Schematic of thermal engineering of electrode-electrolyte inter...
Figure 14.12 (a) Digital photograph of transferred MXene µSC on scotch tape with...
Figure 14.13 Schematic of AgNWs-MoS2 based µSC and its supercapacitive performan...
Figure 14.14 Schematic of transfer of PPy nanowires-based µSC on different subst...
Figure 14.15 (a) Capacitative contributions, (b) Phase angle versus frequency an...
Figure 14.16 (a) Morphology of PPy-wrapped MnO2 nanoflakes, (b) cyclic voltammog...
Figure 14.17 Schematic of work function difference and kinetic approach of posit...
Chapter 15
Figure 15.1 Shows different design of supercapacitors (a) coin (b) cylindrical a...
Figure 15.2 Illustrates the schematic working of an electric double layer superc...
Figure 15.3 Illustrating the pairing of carbon and Li insertion electrodes in a ...
Figure 15.4 Shows self-healing supercapacitor. (a) Schematic illustration of fab...
Figure 15.5 An illustration of reversibility of H-bonds in a self-healing SC.
Figure 15.6 (a) Schematic diagram showing synthesis procedure of nanoparticles o...
Figure 15.7 (a, b) Schematic fabrication of symmetric devices of supercomputers,...
Figure 15.8 (a) CV curves of GN/PANI/CNT, GN/PANI, PANI/CNT-2 and GN within the ...
Chapter 16
Figure 16.1 Ragone plot of various energy sources [Reprinted with permission fro...
Figure 16.2 (a) Schematic representation of the conventional and (b) flexible/st...
Figure 16.3 Classification of various types of electrodes for flexible/stretchab...
Figure 16.4 (a) CV curves of the VGO electrode at the bent and flat states, (b) ...
Figure 16.5 (a) Schematic representation of the flexible supercapacitor along wi...
Figure 16.6 Fabricating process for RuO2/PEDOT:PSS/graphene ternary flexible ele...
Figure 16.7 Schematic illustration of the flexible and transparent multifunction...
Figure 16.8 SEM (a–d) and AFM (e) images of layered buckled graphene on PDMS [Re...
Figure 16.10 (a) A representative photograph of MXene/BC composite paper, (b–c) ...
Figure 16.11 (a–d) various digital images of the electrodeposited PANI@MGTF@GP f...
Chapter 17
Figure 17.1 Diagrammatic representation of supercapacitor (a) EDLC type, (b) Pse...
Figure 17.2 Diagrammatic representation of electro-chemical deposition process.
Figure 17.3 Diagrammatic representation of a three electrode electro-chemical de...
Figure 17.4 Diagrammatic representation of the preparation process of NiCo
2
O
4
na...
Figure 17.5 Schematic diagram of the fabrication process of supercapacitor by co...
Figure 17.6 Schematic diagram of the spray deposition arrangement used to fabric...
Figure 17.7 Synthesis of different forms of materials by sol–gel method.
Figure 17.8 Diagrammatic representation of the fabrication processes of nanoporo...
Chapter 18
Figure 18.1 Schematic representation of (a) an electrical double-layer capacitor...
Figure 18.2 A stretchable supercapacitor based on kirigami structure. Adapted fr...
Figure 18.3 (a) Chemical structure of the Juglone molecule extracted from waste ...
Chapter 19
Figure 19.1 Performance comparison using a Ragone plot presenting different ener...
Figure 19.2 A schematic presentation of EDLC based supercapacitor, electrode sep...
Chapter 20
Figure 20.1 The schematic diagram of the fabrication process: 3D reduced graphen...
Figure 20.2 The SEM images of vertically aligned CNT arrays (a) and side-view of...
Figure 20.3 The schematic representation of supercapacitor devices: interdigital...
Figure 20.4 The photographs of solid-state supercapacitor devices assembled from...
Figure 20.5 The galvanostatic charging and discharge curves of two individual su...
Figure 20.6 The schematic representation of the fabrication of micro-supercapaci...
Figure 20.7 The morphology of electroactive sponges: SEM and TEM (inset) images ...
List of Tables
Chapter 1
Table 1.1 Several common conducting polymers.
Chapter 3
Table 3.1 Summary of graphene-based flexible electrode for SCs [Reprinted (adapt...
Chapter 4
Table 4.1 Pore structure of GNPC and NPC materials from BET analysis [45].
Table 4.2 Summary of the supercapacitive behavior of various electrode for flexi...
Chapter 5
Table 5.1 Separators and electrolytes applied in FSCs [3].
Table 5.2 Various flexible substrates are used to fabricate flexible solid-state...
Table 5.3 Summary of different materials used in EDLC electrode [7].
Table 5.4 Summary of different materials used in PC electrode [7].
Table 5.5 Summary of different materials used in hybrid SC electrode [7].
Table 5.6 Comparison of EDLCs, PCs, and hybrid capacitors [4].
Table 5.7 Recently-published review papers on SCs [108].
Table 5.8 Summary of the fabricated FSCs [4, 6, 115, 116].
Table 5.9 Comparison of models in terms of SC electrical behavior [114].
Chapter 6
Table 6.1 Electrochemical performance of organic electrolyte based flexible supe...
Table 6.2 Electrochemical performance of gel polymer electrolyte (GPE) based fle...
Table 6.3 Electrochemical performance of ionic liquid based flexible supercapaci...
Table 6.4 Electrochemical performance of redox active electrolyte based flexible...
Chapter 7
Table 7.1 Carbon nanotube (CNT)-based materials used to design flexible supercap...
Table 7.2 Activated Carbon-based materials used for preparation of flexible supe...
Chapter 8
Table 8.1 Biomass-derived electrodes for flexible supercapacitor performance.
Chapter 11
Table 11.1 Graphene based electrode for flexible supercapacitor and their perfor...
Table 11.2 Metal Oxide based electrode for flexible supercapacitor and their per...
Table 11.3 Conductive polymer based electrode for flexible supercapacitor and th...
Chapter 13
Table 13.1 Bare and hydrated ionic radii of some commons ions.
Table 13.2 Electrochemical performances of various flexible supercapacitors in d...
Chapter 14
Table 14.1 Comparison of the key features, advantages and disadvantages of fabri...
Chapter 16
Table 16.1 Electrochemical and flexibility properties of some flexible/stretchab...
Chapter 17
Table 17.1 Classification of Flexible Supercapacitors.
Chapter 19
Table 19.1 Basic properties of acetonitrile and propylene carbonates.
Guide
Cover
Table of Contents
Title Page
Copyright
Preface
Begin Reading
Index
End User License Agreement
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Flexible Supercapacitor Nanoarchitectonics
Edited by
Inamuddin, Mohd Imran Ahamed, Rajender Boddula and Tariq Altalhi
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Preface
The tremendous demand for energy for miniaturized portable and wearable electronic devices has inspired intense research on lightweight, flexible energy storage devices for commercial applications such as smartwatches, mobile phones, flexible displays, electronic skin and implantable medical devices. The speedy progress in flexible electronics has sparked wide-ranging endeavors in exploring coordinating power sources as flexible supercapacitor devices. Flexible supercapacitors are flexible, wearable devices that deliver high-power density, high specific capacitance, fast charge/discharge processes, long cycle life, low cost, and environmental friendliness. They hold enormous potential to meet the rapidly expanding market for portable and wearable electronics. Designing flexible supercapacitors requires essential architectures such as electrodes, electrolytes, and substrate materials that become robust, flexible, and durable under mechanical deformations without sacrificing the electrochemical performance. These flexible supercapacitors are promising energy technologies that can supplement or even substitute batteries in portable and flexible electronics; however, research and development (R&D) studies need to be conducted for their large-scale commercialization. Therefore, awareness and knowledge of flexible supercapacitors is crucial for advanced energy research.
This book presents a comprehensive overview of flexible supercapacitors using engineering nanoarchitectures mediated by functional nanomaterials and polymers as electrodes, electrolytes, separators, etc., for advanced energy applications. Various aspects of flexible supercapacitors, including capacitor electrochemistry, evaluating parameters, operating conditions, characterization techniques, different types of electrodes, electrolytes, and flexible substrates are covered. Since it is probably the first book of its type to systematically describe the recent developments and progress in flexible supercapacitor technology, it will help readers understand fundamental issues and solve problems. This book is the result of the commitment of top researchers with various backgrounds and expertise in the flexible power sources field. Those working in science, research, industry, or academia will benefit from the information archived herein relating to the fields of flexible power sources, solid-state electrochemistry, advanced energy storage material science, energy, electronics, advanced materials, and wearable science. It will be a very helpful reference source for generating innovative ideas in the field of energy storage material for wearable/flexible industry applications and also useful in resolving current industry issues. A summary of the information included in the 21 chapters is given below.
Chapter 1 discusses the types of electrode materials and the role they play in the high performance of flexible supercapacitors. Device preparation is described as well as the integration of flexible supercapacitors in various applications.
Chapter 2 highlights flexible fiber-shaped electrodes for flexible supercapacitors. Supercapacitors have an incredible impact on electrochemical devices in energy storage systems. To meet the rapid consumer demand for wearable and portable devices a new class of energy devices employ flexible fibrous electrodes/supercapacitors. These fiber-shaped flexible electrodes have garnered great attention for use in miniaturized microscale devices and the modern textile industry.
Chapter 3 discusses recent developments in graphene-based flexible supercapacitors, the structural morphology of flexible graphene-based electrodes and methods used to fabricate them, and the electrochemical performance of the devices.
Chapter 4 mainly discusses the preparation of polymer-based electrode materials. Also highlighted are the various prominent characterization techniques to elucidate the intercorrelation between physicochemical and performance properties of polymer-based electrode materials. The new reinforced polymer-based electrode materials for flexible supercapacitor applications are also discussed.
Chapter 5 thoroughly reviews the energy storage system and types of capacitor modeling. The structure, types of flexible supercapacitors and industrial applications are introduced.
Chapter 6 discusses the types of electrolytes for flexible supercapacitors and their salient features. Various electrolytes such as polyethylene glycol, polyvinylidene fluoride, ionic liquid and redox-active materials-based electrolytes are discussed along with their effect on the performance of flexible supercapacitors.
Chapter 7 discusses the preparation and properties of carbon-derived composite materials such as CNT-conducting polymer, CNT-metal oxide, activated carbon-conducting polymer, and activated carbon-metal oxide. The main focus of this chapter is to provide an overview of the latest progress in the development of flexible supercapacitors beyond graphene.
Chapter 8 highlights the various synthesis processes for making biomass-derived electrode materials, their recent developments and the associated challenges for the near future. After a brief general introduction, the chapter moves on to discuss various electrode materials used for flexible supercapacitors; biomass-derived carbon materials and their different activation processes like physical, chemical and other activations; and carbonization processes using the hydrothermal method, pyrolysis method, etc. The possible incorporation of biomass-based electrodes in flexible supercapacitors and the challenges for using biomass-derived materials in the near future are also discussed in detail.
Chapter 9 portrays the importance and applicability of conducting polymer electrolytes, especially in flexible supercapacitors. The components of supercapacitors and their configurations are discussed in detail along with the role of conducting polymer-based electrolytes and their significance in the performance of flexible supercapacitors. The essential enhancing parameters of such electrolytes, including their consequences and electrochemical activity, are also elaborated.
Chapter 10 discusses the various inorganic electrode materials used in flexible supercapacitors. These flexible inorganic-based electrodes have great potential in the field of stretchable, lightweight and intrinsic fast charging and discharging performance.
Chapter 11 focuses on different new generation materials used for flexible supercapacitor electrodes. Also, in order to predict future trends, the direction towards developing new materials exhibiting superior electrochemical performance and their feasibility in practical applications are discussed.
Chapter 12 briefly describes flexible supercapacitors and their flexible components with a concise outline of innovative cell designs. Additionally, there is an overview of the principle behind the energy-storage mechanism and the anode and cathode materials used for asymmetric supercapacitors.
Chapter 13 provides detailed insights into the gradual development and latest accomplishments achieved with aqueous electrolyte-based flexible supercapacitors. Advantages of low production costs, eco-friendliness, non-flammability, and many other attractive factors have motivated scientists to design these smart devices to meet the high rising energy demands of modern society.
Chapter 14 presents systematic evaluations of different kinds of micro-supercapacitor configurations, possible strategies of fabrication, and state-of-the-art electrode materials. Discussions on designing asymmetric micro-supercapacitors and the influence of electrolytes on enhancing charge-storage properties are also provided. Finally, the challenges of current technologies and possible solutions are highlighted.
Chapter 15 discusses the categories of supercapacitors and their mode of action. Different types of nanomaterials, including metallic, non-metallic and graphene-based hybrid, are discussed in detail for their self-healable properties to modify the electrodes in supercapacitors. The major focus is given to those nanomaterials that increase the self-healing properties of supercapacitors with enhanced capacitance.
Chapter 16 discusses the recent advancements for the fabrication of flexible and stretchable electrode supercapacitors using metal oxides, 2D materials, carbon, conductive polymers, and various hybrid nanocomposites. Moreover, possible applications of flexible/stretchable supercapacitors using these electrode materials, along with upcoming opportunities and challenges in this emerging field, are also discussed.
Chapter 17 discusses the classification of flexible supercapacitors and various superconducting materials. Additionally, different fabrication methods, namely, electrochemical deposition, chemical bath deposition (CBD), inkjet printing spray deposition, sol-gel technique, and direct writing method are discussed in detail.
Chapter 18 deals with the fundamental aspects of flexible supercapacitors with naturally inspired electrodes for energy storage systems. The mechanisms and principle behind energy storage in supercapacitors along with its essential parameters are presented. The use of common and naturally occurring materials and their electrochemical behavior is also discussed.
Chapter 19 focuses on advances in the field of high-performance ionic liquid electrolytes for flexible supercapacitors. After a brief discussion of the fundamentals, developments in the field of ionic liquids are presented. Design perspectives like electrolyte-electrode hybridization, challenges in encapsulation and mechanical stability are also presented.
Chapter 20 describes various types of conducting polymer-based flexible supercapacitors. Special emphasis is given to the fabrication methods employed for flexible supercapacitor devices. The different electrolytes, which play a significant role in flexible supercapacitors, are also discussed. The chapter concludes with perspectives on flexible supercapacitors.
Inamuddin, Mohd Imran Ahamed, Rajender Boddula and Tariq Altalhi
March 2021
1Electrodes for Flexible Integrated Supercapacitors
Sajid ur Rehman1,2and Hong Bi1*
1School of Chemistry and Chemical Engineering, Anhui University, Hefei, China
2High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China
Abstract
Supercapacitor, as a new type of energy storage device lying in-between battery and traditional capacitor, owns many advantages such as fast charge and discharge time, high power density, environmental-friendly and long cycle life. It has become one of the hot research topics in the field of energy storage. Electrode materials play a vital role in flexible supercapacitors, the common electrode materials include carbon materials, conducting polymers and transition metal oxides. In order to exploit flexible high-performance supercapacitors, new high-performance electrode materials need to be developed. Metal oxides are promising supercapacitor electrode materials due to their low cost, good chemical stability, high theoretical specific capacitance and environmental friendliness. However, cycling stability and rate performance of metal oxides based supercapacitor still can’t meet the requirements of practical applications. Therefore, the research on electrode materials are not limited to single-component material, and nanocomposites can synergistically enhance the intrinsic properties of each component to exhibit more outstanding electrochemical properties. In this chapter, we discuss the electrode materials for flexible supercapacitors in detail and also describes the device preparation as well as the integration of the flexible supercapacitors in various applications.
Keywords: Flexible electrodes, carbon, metal oxides, supercapacitors, EDLC, pseudo-capacitors, hybrid electrodes, electrolytes
1.1 Introduction and Overview of Supercapacitors
In today’s world, coal, oil, natural gas and other traditional nonrenewable fossil energy are gradually exhausted, as the demand and consumption of energy are increasing day by day, which have been difficult to maintain for the sustainable development of human society and economy. Supercapacitor, also known as an electrochemical capacitor, is a new type of energy storage device between the battery and traditional capacitor, which is based on the principle of electric double-layer capacitance (EDLC) or pseudocapacitance. Because of its fast charge and discharge rate, high power density, environment-friendly and long cycle life, it has attracted increasing attention [1].
Supercapacitor is mainly composed of current collector, electrode active material, diaphragm and electrolyte (see Figure 1.1) [2]. Among them, electrode materials play an important role in improving electrochemical performance. The collector usually has good conductivity, does not react with the electrolyte, can exist stably in it, and has little contribution to the specific capacity of the capacitor. Different metal materials, such as nickel foam and aluminum foam, are used according to the electrolyte. An ideal electrode material should have the characteristics of large specific surface area, good conductivity, unique porous structure, high catalytic activity, good chemical stability and low manufacturing cost [2, 3]. Supercapacitors are commonly categorized into three sets based on the mechanism of charge storage: (1) EDLCs that store charge statically at interface of carbon electrode with large specific surface area; (2) Faraday pseudocapacitors that store electric energy electrochemically through electron transfer during reversible redox reaction, usually based on metal oxides and conducting polymer; (3) hybrid supercapacitor composed of special hybrid electrode or asymmetric electrode, which has significant carbon double-layer capacitance and pseudocapacitance of conducting polymer or transition metal oxide [4, 5].
Figure 1.1 Schematic illustration of charge storage in supercapacitors [13]. Copyright © 2013 Elsevier Ltd. Reproduced with permission from Elsevier.
Starting from the theory of interface double electric layer proposed by Helmholtz, a German physicist, EDLCs began to be developed gradually. When two electrodes are inserted into the electrolyte, the positive and negative ions in the electrolyte will move towards the two poles rapidly under the action of the electric field, and attach to the electrode surface, forming a compact double electric layer [6]. As shown in Figure 1.1 [7], in the charging process, the applied electric field releases electrons, and the direction of electrons is from the negative electrode to the positive electrode. At this time, the ions present in the electrolyte will transport towards the respective electrodes respectively, so as to adsorb on the electrode surface and form a stable voltage. In the process of discharge, electrons flow through the conductor to generate current, at this time, the anion and cation on the electrode surface will be released into the electrolyte. In this process, the electrode material will not react with the electrolyte, only the adsorption and desorption of anions and cations in the electrolyte on the electrode surface [8, 9].
Hybrid supercapacitor (HSC) includes a composite symmetrical supercapacitor, battery supercapacitor mixer and asymmetric supercapacitor (ASCs). The structure of ASCs is shown in Figure 1.5 [10], which is usually assembled by two different materials as anode and cathode. In the process of charging and discharging, oxidation–reduction (Faraday) reaction usually takes place at the positive electrode, while adsorption and desorption of the negative electrode mainly take place at the double electric layer. In fact, EDLC can achieve fast and stable charge storage but provide relatively low specific capacitance, while the pseudocapacitor can obtain high specific capacitance but has poor multiplier performance and low cycle stability. The hybrid supercapacitor, which combines the advantages of EDLC and pseudocapacitor, has become a new hotspot in capacitor research area. It can achieve high energy and power density as well as good cycle stability in one device. However, the performance of all these supercapacitors depends on the properties of their active materials, the fabrication of electrodes, the selection of electrolytes and the geometry of devices [11, 12].
Throughout the development of supercapacitors, electrode materials have always played an important role in the electrochemical performance. Generally, the ideal electrode material should have the characteristics of large specific surface area, good conductivity, unique porous structure, high mechanical strength, good chemical stability and low manufacturing cost. Among them, carbon materials, metal oxides, conductive polymers and other electrode materials are the main research objects.
1.2 Electrode Materials for Flexible Supercapacitors
1.2.1 Carbon Materials
As electrode material of flexible supercapacitors (FSCs), carbon-based materials are beneficial due to their low cost, large specific surface area, stable electrochemical performance, better electrical and thermal conductivity, and mature synthesis process. At present, the commonly used carbon materials include activated carbon [14], carbon nanotubes [15], graphene [16], and carbon aerogel [17]. Their specific surface area, pore size and distribution, conductivity and heteroatom doping have certain effects on the electrochemical performance of [18].
1.2.1.1 Activated Carbon
Activated carbon is the first electrode material used in supercapacitors. Due to its advantages of low price, wide source of raw materials and stable physical and chemical properties, it has been widely used in commercial supercapacitors. So far, it still has a broad market [19]. After activated by KOH, the specific surface area of activated carbon can reach as high as 2,000 m2 g–1. However, the specific surface area of the active carbon electrode material is not directly proportional to the specific capacitance. The main reason is that the activated carbon has not been fully explored in terms of specific surface area, and the diameters of various electrolyte ions are required to be different for different pore diameters in the activated carbon, so some micropores do not play the role of storing electric charge, resulting in the available effective specific surface area becoming smaller, affecting its electrochemical performance [20]. As shown in Figure 1.2 [21], when the porous carbon has large pores (>50 nm), the electrode surface can rapidly adsorb electrolyte ions. Because the pore size is large, its specific surface area is reduced, resulting in a small effective adsorption area and poor capacitance performance. When the pore is a mesopore (2–50 nm), the inner surface of the pore can also rapidly adsorb electrolyte ions, and the mesopore also results in a large specific surface area and specific surface area. When the porous carbon is microporous (<2 nm), the size of ions is larger than that of the pore size, so, it cannot enter into the inner part of the pore, and the ion adsorption is reduced, resulting in the reduction of effective adsorption area. Therefore, in order to improve the electrochemical properties of the materials, in addition to improving the specific surface area of the activated carbon, the doping of hetero-atoms, pore size control and the addition of surface functional groups can also be used. Zhou et al. [22] reported N-doped porous carbon with pore size classification by activating m-aminophenol formaldehyde resin with KOH, which has a high specific surface area of 1,847.5 m2 g−1 and thus a specific capacitance of 114 F g−1. Bleda Martine et al. [23] obtained oxygen-containing functional groups on the activated carbon through HNO3 peroxidation and subsequent heat treatment in N2 atmosphere, which not only improved the wettability of the surface of the activated carbon to the electrolyte but also generated additional pseudocapacitance to improve the specific capacitance.
Figure 1.2 Schematic illustration of charge adsorption in porous carbon materials with different sizes in double-layer capacitors [24]. Copyright 2016. Reproduced with permission from John Wiley & Sons.
1.2.1.2 Carbon Nanotubes
Carbon nanotubes (CNTs) are a kind of tubular carbon material made of single or multi-layer graphite curled. Its structure is very perfect, with seamless porous structure connected by hexagonal carbon atoms [25]. CNTs can be categorized into single-walled carbon nanotubes (SWCNTs, single layer) and multi-walled carbon nanotubes (MWCNTs, two or more layers). Single-walled carbon nanotubes have a higher specific surface area, but it is more difficult to prepare and purify. CNTs have excellent physical and chemical properties. Due to its unique hollow porous structure, large specific surface area, and good conductivity, it is considered to be an ideal electrode material for supercapacitors [26–29]. As shown in Figures 1.3(a, b) carbon nanotubes can form a network structure when they are entangled with each other. Most of the pore diameter is more than 2 nm, which is conducive to the penetration of electrolyte ions. Therefore, their specific surface area utilization ratio is high. Popvo et al. [30] have synthesized the MWCNTs at different temperatures and study the influence on supercapacitance properties. As shown in Figures 1.3(c, d), they found an increase in double-layer capacitance because of the larger surface area as well as the improvement in pseudocapacitance owing to the larger oxygenated groups grown on the exterior of nanotubes.
Figure 1.3 (a, b) HRTEM images of multi-walled carbon nanotube (MWNTs) synthesized at different temperatures, (c–d) CV curves at 20 mV s−1 rate in 1 M H2SO4 aqueous electrolyte, respectively [30]. Copyright 2016. Reproduced with permission from John Wiley & Sons.
1.2.1.3 Graphene
Graphene is a kind of two-dimensional crystal plane material [31, 32] which is composed of sp2-hybridized carbon atoms tightly stacked and connected, in which the covalent bond between carbon atoms is formed, presenting a hexagonal ring honeycomb shape. It has a unique two-dimensional (2D) structure and many attractive characteristics and is widely used in electrochemical energy storage devices, as shown in Figure 1.4 [33]. Graphene is one of the allotropes of carbon, and it is also the basic unit of other dimensional carbon materials. A single layer of graphene has only one carbon atom thickness (0.335 nm).
Graphene has a large specific surface area, better electrical and thermal conductivity, excellent mechanical strength and chemical stability. Its surface is easy to show a three-dimensional (3D) fold structure, which is conducive to the transmission of electrons on the surface and the diffusion of ions in the material. It has great potential to apply it to electrode materials of supercapacitors. In fact, graphene itself is easy to aggregate, making its specific surface area far away from the theoretical value, thus limiting its electrochemical performance [34–36]. Therefore, it is very important to modify the surface of graphene or composite it with other materials. Si et al. [37] combined Pt particles with graphene, which made Pt nanoparticles deposit on graphene sheets. Pt played a role of separation, prevented the aggregation of graphene sheets face to face, mechanically peeled off graphene effectively. As a result, the embedded Pt@graphene had a highly expanded layered structure and retained the characteristics of 2D graphene hexagonal carbon network with large specific surface area. The specific surface area of Pt@graphene composite was 862 m2 g−1, and the specific capacitance of Pt@graphene composite was increased to 269 F g−1. Zhu et al. [38] reported that porous graphene oxide prepared by KOH chemical activation has a specific surface area of up to 3,100 m2 g−1, accompanied with high conductivity and low hydrogen and oxygen content, and the sp2-bonded carbon has a continuous highly curved three-dimensional network, forming a hole with a width of 0.6–5 nm. Using organic and ionic liquid electrolytes, the double electrode supercapacitor made of this kind of carbon can obtain 3.5 V working voltage and 167 F g−1 specific capacitance (5.7 A g−1 current density), and the energy density can reach 70 Wh kg−1. In addition, the electrochemical properties of graphene can also be improved by combining graphene with other pseudocapacitor materials (such as transition metal oxides (NiO, MnO2, etc.) or conducting polymers (polyaniline, polypyrrole, etc.).
Figure 1.4 Schematic diagram of the Origin (illustrating the transformations) of graphene from graphite and peculiar structure of graphite and graphene [33]. Open access article under Creative Commons CC BY license copyright © 2020, Elsevier.
1.2.1.4 Carbon Aerogels
Carbon aerogel is a lightweight, porous, amorphous three-dimensional carbon nanostructured material. Because of its large specific surface area, abundant mesoporous and wide range of density variation, it is considered as an ideal electrode material for supercapacitors. In 1989, Pekala used resorcinol and formaldehyde as raw materials and sodium carbonate as catalyst. It is found that the carbon aerogel has the specific surface area of 400–800 m2 g−1 and the ultrafine pore size (<100 nm), and the specific capacitance of the 5 mol L−1 KOH solution is 45 F g−1. Subsequently, the research on carbon aerogels in supercapacitors has attracted more and more attention. Lin et al. [39] synthesized a series of carbon aerogels with a bimodal (microporous and mesoporous) structure by using iron-based ionic liquids as a solvent ionic thermal carbonization method and pore-forming agent. It has a high specific surface area up to 1,200 m2 g−1 and pore volume of 0.8 cm3 g−1, and a specific capacitance reaching as high as 245 F g−1. Carbon aerogels have certain advantages in the application of supercapacitors, but their shortcomings have seriously restricted their industrialization, such as expensive raw materials, long-time synthetic process, high equipment cost and difficulty to achieve a large-scale production.
1.2.1.5 Graphene Hydrogel
The effective specific area of graphene is greatly reduced due to the stacking and agglomeration of graphene layers. Therefore, the researchers have envisaged the connection and integration of 2D structure and designed various kinds of graphene, such as graphene hydrogel, aerogel, foam and sponge, to develop and utilize the properties of graphene in various 3D network structures. Its preparation methods are various, mainly including self-assembly, template oriented, new 3D printing and ultrasonic-assisted technology. Although the structures and properties of these 3D graphene materials are different, they all have the common characteristics of high specific surface area and porosity, low bulk density, high conductivity and so on. Therefore, they have been widely studied and applied in adsorption, catalysis, sensing, energy storage and conversion, biomedicine and other fields [40].
Graphene hydrogel is a 3D solid structure cross-linked by 2D graphene, which can be prepared by freeze-drying or supercritical drying to remove moisture. It has both the intrinsic properties of graphene nanosheet and 3D porous material and shows better performance than the graphene nanosheet in the electrochemical application. Graphene hydrogel has interconnected porous structure, large specific surface area, low mass density and strong mechanical properties, making it widely used in electrode materials of the supercapacitor. As a high volume capacitor material, the large pores interconnected in the frame become unimpeded ion transmission channels, which is conducive to shortening the diffusion distance from the external electrolyte to the internal surface, thereby enhancing the ion transmission; while the graphene sheet in the frame is conducive to promoting the electron transmission on the electrode surface [12, 39]. Huang et al. [41] reported the elastic carbon aerogels and graphene as 3-D Matrix for supercapacitance properties. The schematic diagram as illustrated in Figures 1.5(a, b) demonstrates the interconnected macropores which exhibit high elasticity, improved surface area along with charge-transfer efficiency owing to the excessive interconnections between graphene flakes and carbon nanofiber ribs, which reveals prominent capacitive performance as supercapacitor electrode as shown in Figures 1.5(d–e). Xu et al. [42], using hydroquinone as both reductive and functionalized molecules, synthesized functional graphene hydrogels through a simple one-step reduction method, showing excellent electrochemical properties. Graphene hydrogel as a negative electrode can effectively prevent the aggregation of graphene nanosheets, provide large active surface area, and promote the transmission of electrolyte ions. Gao et al. [43] used graphene hydrogels with 3D interconnected pores as negative electrodes, and vertically aligned MnO2 nanosheets loaded on nickel foam as positive electrodes, successfully produced asymmetrical supercapacitors with high energy and power density. The potential window could reach 2.0 V, and the energy density achieved 23.2 wh kg−1 while the power density was 1.0 kW kg−1.
Figure 1.5 (a) Schematic presentation of graphene/carbon nanofiber (CNF) composite aerogels (GCA) by co-assembly and carbonization. (b) Illustration of the pre-oxidation process of polyacrylonitrile (PAN) nanofibers and hydrogen bondings between GO and pre-oxidized PAN. (c) SEM image showing the graphene/carbon composite aerogel (GCA). (d) CV curves at different scan rates in 6 M KOH aqueous electrolyte. (e) Galvanostatic charge/discharge curves at different current densities [41]. Open access article under Creative Commons CC BY license copyright © 2016, Springer Nature.
1.2.2 Conducting Polymers
In 2000, the Nobel Prize in chemistry was awarded to Heeger A.J., MacDiarmid A.G. of the United States and Yingshu Shirakawa of Japan for their contributions to the field of conducting polymers [44]. Through their research, they have proved that people usually think that insulating polymer materials can also have conductivity under certain conditions, breaking the traditional concept that polymers are insulators. Since then, more and more attention has been paid to this field, and researchers have developed many conductive polymers such as polyacetylene, polyaniline, polypyrrole, thiophene and their derivatives. Their structures are shown in Table 1.1.
Common conductive polymer electrode materials are prepared by chemical oxidation and electrochemical oxidation. Conductive polymers have been widely used as electrode materials for supercapacitors because of their low cost, good conductivity and wide electrochemical window. When oxidation occurs, the conductive polymer can be p-doped with anions, while in the reduction process, it will be n-doped with cations. The simplified charging process equation is as follows:
The discharge time is contrary to the above process. The conducting polymer will be p-type or n-type doped, so it can store more charge and obtain higher Faraday pseudocapacitance.
There are three kinds of devices for supercapacitor assembled only by conducting polymer materials [45] namely, polyaniline, polypyrrole, polythiophene and derivatives of polythiophene, as well as composites of these materials with carbon nanotubes and inorganic battery materials. Various treatments of the conducting polymer materials to improve their properties are considered and comparisons are made with other supercapacitor materials such as carbon and with inorganic battery materials. Conducting polymers are pseudo-capacitive materials, which means that the bulk of the material undergoes a fast redox reaction to provide the capacitive response and they exhibit superior specific energies to the carbon-based super-capacitors (double-layer capacitors: type I (symmetric), using the same p-type doped conducting polymer for positive and negative materials; type II (asymmetric), p-type doped conducting polymer with different electric activity ranges for positive and negative materials; type III (symmetric), for two electrodes the same polymer is used, in which p-type doping is used as positive electrode and n-type doping is used as negative electrode. In addition, a conductive polymer can be used as a positive electrode and a carbon material as a negative electrode to construct an asymmetric device. Among them, the type III device based entirely on conductive polymer is the most attractive, because it is highly conductive in the charged state and has high capacitance performance, but due to the difficulty of n-type doping, the performance of these types of conductive polymer supercapacitor devices is not as good as expected [46]. Wang et al. [47] demonstrated the excellent performance of N-graphene doped polyacrylic acid/polyaniline composites flexible solid-state carbon cloth supercapacitors. Figure 1.6(a) shows the image of aqueous nitrogen-doped graphene (NG) enhanced polyacrylic acid/polyaniline (NG-PAA/PANI) composites suspension containing 32 wt.% PANI and 1.3 wt.% NG. Figure 1.6(b) demonstrates the flexibility of the carbon cloth electrode and Figure 1.6(c) shows the SEM image of carbon fiber. The optimal performance of electrode (CC@ NG-PAA/PANI) has been achieved with a high capacitance of 521 F g−1 at 0.5 A g−1.
Table 1.1 Several common conducting polymers.
Polymers
Structural formula
Polyacetylene
Polyaniline
Polypyrrole
Polythiophene
Carbon materials generally have excellent cycle stability, but the capacity of conducting polymers usually starts to decrease in less than 1,000 cycles. This is because, in the process of charge and discharge test, ions are continuously doped/de-doped (embedded/de-embedded) into the doped polymer under the action of electric field, its physical structure will change, which to a certain extent, aggravates the expansion and contraction of the skeleton chain, destroys the stability of the material, leading to its cycle stability decay. In addition, some conducting polymers undergo incomplete reversible redox reactions [48, 49]. Therefore, the specific capacitance and cycle stability of the conductive polymer can be greatly improved by forming a composite electrode material between the conductive polymer and other materials such as carbon materials (graphene, carbon nanotubes, etc.) and metal oxides (NiO, CoO, etc.). Zhang et al. [49] synthesized graphene and polypyrrole composites (GNS/PPy) by in-situ polymerization of pyrrole monomers in the presence of graphene under acidic conditions. The specific capacitance of GNS/PPy was 482 F g−1 at the current density of 0.5 A g−1, and the attenuation of specific capacity was less than 5% after 1,000 charge–discharge cycles, indicating that the composite had excellent cycling stability.
Figure 1.6
