Flexible Energy Conversion and Storage Devices

Chunyi Zhi, PhD, is Associate Professor in the Department of Physics and Materials Science at City University of Hong Kong, China. He has published more than 150 papers and his research field is mainly about synthesis and functionalization of boron nitride nanotubes/nanosheets, polymer composites, as well as flexible/wearable energy storage devices and sensors etc.

Liming Dai, PhD, is Kent Hale Smith Professor in Department of Macromolecular Science and Engineering at Case Western Reserve University in Ohio.

Preface xiii

1 Flexible All-Solid-State Supercapacitors andMicro-Pattern Supercapacitors 1
Yuqing Liu, Chen Zhao, Shayan Seyedin, Joselito Razal, and Jun Chen

1.1 Introduction 1

1.2 Potential Components and Device Architecture for Flexible Supercapacitors 4

1.2.1 Flexible Electrode Materials 5

1.2.1.1 Carbon Materials 5

1.2.1.2 Conducting Polymers 6

1.2.1.3 Composite Materials 7

1.2.2 Solid-State Electrolytes 7

1.2.3 Device Architecture of Flexible Supercapacitor 8

1.3 Flexible Supercapacitor Devices with Sandwiched Structures 10

1.3.1 Freestanding Films Based Flexible Devices 10

1.3.2 Flexible Substrate Supported Electrodes Based Devices 14

1.4 Flexible Micro-Supercapacitor Devices with Interdigitated Architecture 18

1.4.1 In situ Synthesis of Active Materials on Pre-Patterned Surfaces 18

1.4.2 Direct Printing of Active Materials 21

1.4.3 Patterning ofWell-Developed Film Electrodes 24

1.5 Performance Evaluation and Potential Application of Flexible Supercapacitors 27

1.5.1 Performance Evaluation of Flexible Supercapacitors 28

1.5.2 Integration of Flexible Supercapacitors 29

1.6 Conclusions and Perspectives 32

References 32

2 Fiber/Yarn-Based Flexible Supercapacitor 37
Yang Huang and Chunyi Zhi

2.1 Introduction 37

2.2 Supercapacitor with Intrinsic Conductive Fiber/Yarn 40

2.2.1 Carbolic Fiber/Yarn-Based Supercapacitor 41

2.2.2 Metallic Fiber/Yarn-Based Supercapacitor 44

2.2.3 Hybrid Conductive Fiber/Yarn-Based Supercapacitor 48

2.3 Supercapacitors with Intrinsic Nonconductive Fiber/Yarn 51

2.3.1 Fiber/Yarn Modified by Carbon Materials 52

2.3.2 Fiber/Yarn Modified by Metallic Materials 54

2.4 Integrated Electronic Textiles 57

2.5 Conclusion and Outlook 61

References 62

3 Flexible Lithium Ion Batteries 67
Xuli Chen and YingyingMa

3.1 Overview of Lithium Ion Battery 67

3.1.1 General Principle 67

3.1.2 Cathode 70

3.1.2.1 LiCoO₂ with Layered Structure 70

3.1.2.2 LiMn₂O₄ with a Spinel Structure 70

3.1.2.3 LiFePO₄ with an Olivine Structure 70

3.1.3 Anode 71

3.1.3.1 Carbonaceous Anodes 71

3.1.3.2 Metal Alloy Anodes 71

3.1.4 Electrolyte 72

3.2 Planar-Shaped Flexible Lithium Ion Batteries 73

3.2.1 Bendable Planar Lithium Ion Batteries 73

3.2.1.1 Bendable Carbon-Based Planar Lithium Ion Battery 73

3.2.1.2 Thin Metal Material-Based Lithium Ion Battery 77

3.2.1.3 Polymer-Based Lithium Ion Battery 79

3.2.1.4 Special Structural Design-Based Flexible Lithium–Ion Battery 82

3.2.2 Stretchable Planar Flexible Lithium Ion Batteries 84

3.3 Fiber-Shaped Flexible Lithium Ion Batteries 87

3.3.1 Bendable Fiber-Shaped Lithium Ion Battery 87

3.3.2 Stretchable Fiber-Shaped Lithium Ion Battery 93

3.4 Perspective 94

References 95

4 Flexible Sodium Ion Batteries: From Materials to Devices 97
Shengyang Dong, Ping Nie, and Xiaogang Zhang

4.1 Introduction to Flexible Sodium Ion Batteries (SIBs) 97

4.2 The Key Scientific Issues of Flexible SIBs 98

4.2.1 Design of Advanced Active-Materials 99

4.2.2 Design of Flexible Substrates and Electrodes 99

4.2.3 Developing Novel Processing Technologies 101

4.3 Design of Advanced Materials for Flexible SIBs 101

4.3.1 Inorganic Anode Materials for Flexible SIBs 101

4.3.2 Inorganic Cathode Materials for Flexible SIBs 110

4.3.3 Organic Materials for Flexible SIBs 114

4.3.4 Other Major Components for Flexible SIBs (Electrolyte, Separators, etc.) 115

4.4 Design of Full Cell for Flexible SIBs 117

4.5 Summary and Outlook 121

References 123

5 1D and 2D Flexible Carbon Matrix Materials for Lithium–Sulfur Batteries 127
TianyiWang, Yushu Liu, Dawei Su, and GuoxiuWang

5.1 Introduction 127

5.2 The Working Mechanism and Challenges of Li–S Batteries 128

5.3 Flexible Cathode Hosts for Lithium–Sulfur Batteries 129

5.4 Electrolyte Membranes for Flexible Li–S Batteries 138

5.4.1 Solid Polymer Electrolytes for Flexible Li–S Batteries 139

5.4.2 Gel Polymer Electrolytes for Flexible Li–S Batteries 142

5.4.3 Composite Polymer Electrolytes for Flexible Li–S Batteries 143

5.5 Separator for Flexible Li–S Batteries 144

5.6 Summary 148

References 149

6 Flexible Electrodes for Lithium–Sulfur Batteries 155
Jia-Qi Huang,Meng Zhao, Rui Xu, and Qiang Zhang

6.1 Introduction 155

6.2 Lithium–Sulfur Battery and Flexible Cathode 156

6.2.1 Lithium–Sulfur Battery 156

6.2.2 Flexible Cathode for Lithium–Sulfur Battery 156

6.3 The Flexible Cathode of Lithium–Sulfur Battery 157

6.3.1 Flexible Cathode Based on One-dimensional Materials 157

6.3.1.1 Flexible Cathode Based on CNTs 157

6.3.1.2 Flexible Cathode Based on Carbon Nanofibers 163

6.3.1.3 Flexible Cathode Based on Polymer Fibers 166

6.3.2 Flexible Cathode Based on Two-dimensional Materials 167

6.3.2.1 Flexible Cathode Based on Graphene Paper 167

6.3.2.2 Flexible Cathode Based on Graphene Foam 169

6.3.3 Flexible Cathode Based on Three-dimensional Materials 172

6.3.3.1 Flexible Cathode Based on Three-dimensional Carbon Foam Materials 172

6.3.3.2 Flexible Cathode Based on Carbon/Binder Composites Materials 174

6.3.3.3 Flexible Cathode Based on Three-dimensional Metal Materials 176

6.4 Summary and Prospect 177

References 178

7 Flexible Lithium–Air Batteries 183
Qing-Chao Liu, Zhi-Wen Chang, Kai Chen, and Xin-Bo Zhang

7.1 Motivation for the Development of Flexible Lithium–Air Batteries 183

7.2 State of the Art for Flexible Lithium–Air Batteries 184

7.2.1 Overview of Flexible Energy Storage and Conversion Devices 184

7.2.2 Overview of Flexible Lithium–Air Batteries 185

7.2.2.1 Similarities between Coin Cell/Swagelok Batteries with Flexible Battery 187

7.2.2.2 Differences between Coin Cell/Swagelok Batteries with Flexible Battery 188

7.2.3 Current Status of Flexible Lithium–Air Battery 190

7.2.3.1 Planar Battery 190

7.2.3.2 Cable-type Battery 199

7.2.3.3 Woven-type Battery Pack 202

7.2.3.4 Battery Array Pack 203

7.3 Challenges and FutureWork on Flexible Lithium–Air Batteries 206

7.4 Concluding Remarks 207

References 208

8 Nanodielectric Elastomers for Flexible Generators 215
Li-Juan Yin and Zhi-Min Dang

8.1 Introduction 215

8.2 Electro-Mechanical Principles 216

8.2.1 Electro-Mechanical Conversion 216

8.2.2 Equations of DE Generators 217

8.3 Increasing the Performance of Dielectric Elastomers from the Materials Perspective 218

8.3.1 Increasing the Relative Permittivity of DEs 219

8.3.1.1 Elastomer Composites 219

8.3.1.2 Elastomer Blends 222

8.3.1.3 Chemical Modification 223

8.3.2 Decreasing Young’s Modulus 225

8.3.3 Complex Network Structure 225

8.4 Circuits and Electro-Mechanical Coupling Methods 227

8.5 Examples of Dielectric Elastomer Generators 230

8.6 Conclusion and Outlook 231

Acknowledgments 232

References 232

9 Flexible Dye-Sensitized Solar Cells 239
Byung-Man Kim, Hyun-Gyu Han, Deok-Ho Roh, Junhyeok Park, KwangMin Kim, Un-Young Kim, and Tae-Hyuk Kwon

9.1 Introduction 239

9.2 Materials and Fabrication of Electrodes for FDSCs 242

9.2.1 Photo-electrode 242

9.2.1.1 Flexible Substrate for Photo-electrode 242

9.2.1.2 Nanostructured-photoactive Film 243

9.2.1.3 Fiber-type FDSCs 249

9.2.2 Counter-electrode 251

9.3 Sensitizers in FDSCs and Thin Photoactive Film DSCs 254

9.3.1 State-of-the-Art Review of Sensitizers in FDSCs 254

9.3.2 Sensitizers in Thin Photoactive Film DSCs 258

9.4 Electrolyte and Hole-Transporting Materials for FDSCs 270

9.5 Conclusion and Outlook 276

References 278

10 Self-assembly in Fabrication of Semitransparent and Meso–Planar Hybrid Perovskite Photovoltaic Devices 283
Ravi K.Misra, Sigalit Aharon,Michael Layani, Shlomo Magdassi, and Lioz Etgar

10.1 Introduction 283

10.1.1 Semitransparent Perovskite Solar Cells Through Self-assembly of Perovskite in One Step 285

10.1.1.1 Cell Architecture and Morphology 286

10.1.1.2 Transparency and Photovoltaic Performance of the Cells 288

10.1.1.3 Recombination Behavior of the Charges in Cells 291

10.1.2 Mesoporous–Planar Hybrid Perovskite Devices Through Mesh-assisted Self-assembly of Mesoporous-TiO2 292

10.1.2.1 Cell Architecture and Morphology 293

10.1.2.2 Photovoltaic Performance of the Solar Cells 297

10.1.2.3 Study of Recombination Behavior through Charge Extraction 300

10.2 Summary and Future Perspective 302

References 302

11 Flexible Organic Solar Cells 305
Lin Hu, Youyu Jiang, and Yinhua Zhou

11.1 Introduction 305

11.1.1 Working Principle 306

11.1.2 Performance Characterization of OSCs 307

11.1.3 Device Structure 308

11.1.3.1 Conventional Device Structure 308

11.1.3.2 Inverted Device Structure 308

11.2 Active Layer 308

11.2.1 Donor Materials 310

11.2.1.1 Poly(Phenylenevinylene) (PPV) and Polythiophene (PT) Derivatives 310

11.2.1.2 D–A Conjugated Polymers 311

11.2.2 Acceptor Materials 313

11.2.2.1 Fullerene Derivatives 313

11.2.2.2 Non-fullerene Acceptors 315

11.3 Flexible Electrode 317

11.3.1 Conductive Polymer (PEDOT:PSS) 317

11.3.2 Metal Nanowires and Grids 318

11.3.3 Hybrid Carbon Material 319

11.4 Interfacial Layer 320

11.4.1 Hole Transporting Layer (HTL) 320

11.4.2 Electron Transporting Layer (ETL) 320

11.5 Tandem Organic Solar Cells 321

11.5.1 Interconnecting Layer 322

11.5.2 Low Bandgap Polymer Sub-cell 324

11.6 Fabrication Technology for Flexible Organic Solar Cells 326

11.7 Summary 328

References 329

12 Flexible Quantum Dot Sensitized Solar Cells 339
Yueli Liu, Keqiang Chen, Zhuoyin Peng, andWen Chen

12.1 Introduction 339

12.2 Basic Concepts 340

12.2.1 Quantum Dots (QDs) 340

12.2.1.1 Quantum Size Effect 341

12.2.1.2 Multiple Exciton Generation 341

12.2.1.3 Ultrafast Electron Transfer 342

12.2.1.4 Large Specific Surface Area 343

12.2.2 Quantum Dots Sensitized Solar Cells (QDSSCs) 344

12.2.2.1 Schematic of the Structure and Charge Circulation of QDSSCs 344

12.2.2.2 Evaluation of the Photovoltaic Performances of QDSSCs 345

12.3 Development of the Flexible QDSSCs 347

12.3.1 Choosing of the Types of QDs 347

12.3.1.1 Cd-based QDs 347

12.3.1.2 Pb-based QDs 348

12.3.1.3 Cu-based QDs 349

12.3.2 Fabrication of the Flexible Photo-anode Films 350

12.3.3 TiO2-Based Photo-anodes 351

12.3.3.1 Photo-anodes of TiO2 Nanoparticles 351

12.3.3.2 Photo-anodes of TiO2 Nanoarray Structures 352

12.3.3.3 Designing of Novel TiO2 Architecture as Photo-anodes 354

12.3.4 ZnO based Photo-anodes 354

12.3.5 Other Metal Oxide Based Photo-anodes 355

12.3.6 Development of the Sensitization Method 355

12.3.6.1 In situ Sensitization Techniques 356

12.3.6.2 Ex situ Techniques 358

12.3.6.3 Co-sensitization Techniques 360

12.3.7 Interfacial Engineering in QDSSCs 360

12.3.7.1 Surface Passivation by Large-bandgap Semiconductors 361

12.3.7.2 Surface Passivation by Metal Oxides 361

12.3.7.3 Surface Passivation by Molecular Dipoles 362

12.3.7.4 Surface Passivation by Dye Molecules 362

12.3.7.5 Surface Passivation by Molecular Relays 362

12.3.7.6 Combined Interfacial Engineering Methods 363

12.3.8 Optimization of the Counter Electrodes 363

12.3.8.1 Noble Metal Counter Electrodes 365

12.3.8.2 Carbon Counter Electrodes 365

12.3.8.3 Metallic Compound Counter Electrodes 366

12.3.8.4 Polymer Counter Electrodes 370

12.4 Conclusion and Future Outlook 370

Acknowledgments 371

References 371

13 Flexible Triboelectric Nanogenerators 383
Fang Yi, Yue Zhang, Qingliang Liao, Zheng Zhang, and Zhuo Kang

13.1 Introduction 383

13.1.1 Motivation for the Development of Flexible Triboelectric Nanogenerators 383

13.1.2 Basic Working Mechanism and Working Modes of Flexible Triboelectric Nanogenerators 385

13.2 Materials Used for Flexible Triboelectric Nanogenerators 387

13.3 Flexible Triboelectric Nanogenerators for Harvesting Ambient Energy 388

13.3.1 Harvesting Biomechanical Energy 388

13.3.2 HarvestingWind Energy 391

13.3.3 HarvestingWater Energy 392

13.4 Flexible Triboelectric Nanogenerators for Self-Powered Sensors 393

13.4.1 Self-Powered Touch/Pressure Sensors 393

13.4.2 Self-Powered Motion Sensors 397

13.4.2.1 Sensing Motion of Human Body 397

13.4.2.2 Sensing Motion of Objects 399

13.4.3 Self-Powered Acoustic Sensors 399

13.4.4 Self-Powered Liquid/Gas Flow Sensors 402

13.5 Flexible Triboelectric Nanogenerators for Self-Charging Power Units 405

13.5.1 Self-Charging over a Period of Time to Power Electronics 406

13.5.2 Sustainably Powering Electronics 406

13.6 Flexible Triboelectric Nanogenerators for Hybrid Energy Cells 409

13.7 Service Behavior of Triboelectric Nanogenerators 411

13.8 Summary and Prospects 414

References 415

14 Flexible Thermoelectric Materials and Devices 425
Radhika Prabhakar, Yu Zhang, and Je-Hyeong Bahk

14.1 Introduction 425

14.2 Thermoelectric Energy Conversion Basics 426

14.3 Flexible Thermoelectric Materials 429

14.3.1 Conducting Polymers 431

14.3.2 Graphene and Carbon Nanotube Based TE Materials 434

14.4 Flexible Thermoelectric Energy Harvesters 435

14.4.1 Energy Management 439

14.4.2 Architecture of Thermoelectric Modules 440

14.5 Transverse TE Devices 441

14.5.1 Simulations of Transverse TEG 444

14.6 Thermoelectric Sensors 446

14.7 Summary and Outlook 447

References 448

15 Carbon-based Electrocatalysts forWater-splitting 459
Guoqiang Li and Weijia Zhou

15.1 Introduction 459

15.2 Nonmetal-doped Carbon for HER 460

15.2.1 Nitrogen-doped Carbon-based Catalysts for HER 460

15.2.2 Other Heteroatom (B, S)-doped Carbon-based Catalysts for HER 462

15.2.3 Dual- or Treble-doped Carbons in Metal-free Catalysis 463

15.2.4 Metal-doped Carbon for HER 464

15.3 Metals Embedded in Carbon for HER 466

15.3.1 Core–Shell Structure for Carbon Nanotube and Nanoparticle 468

15.3.2 Metal Organic Frameworks for HER 471

15.4 Electrochemistry 474

15.4.1 Overpotential/Onset Potential and Calibration 474

15.4.2 Current Density and Electrochemical Surface Area 475

15.4.3 Tafel Plot and Exchange Current Density 476

15.4.4 Electrochemical Impedance 476

15.4.5 HER Durability and H2 Production 477

15.4.6 Activation 477

15.5 Outlook and Future Challenges 479

15.5.1 HER Mechanism for Carbon-based Catalysts 479

15.5.2 Electrochemistry, Especially for Activation Process 480

15.5.3 OER in Acidic Electrolyte 480

References 480

Index 485

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