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Design of Functional Oxide and Nitride Nanomaterials for Flexible Electrochemical Energy Storage Devices

초록/요약

The Internet of Things (IoT) and communications technologies are undergoing significant advancements, and as a result, portable and flexible electronics are being hailed as crucial breakthroughs of the recent industrial revolution. These electronic devices can increase the potential of the next generation of electronic systems by protecting personal privacy and maintaining functionality in a variety of situations and perspectives. The utilization of rigid silicon components has led to significant advancements in fundamental traditional electronics. Nevertheless, these components are too hefty and are not well suited for flexible devices. However, flexible electronic circuits are stamped onto flexible carpets of silicon, plastic, paper, or cloth. This renders these devices bendable, rollable, twistable, and stretchable for use in emerging wearable and flexible applications. Although, due to the lack of efficient energy storage sources to power these modern electronics, it is difficult to take full advantage of flexible and wearable electronics in daily life applications. Batteries and supercapacitors are typical electrochemical energy storage devices that can store energy by a different mechanism including a faradaic or non-faradaic mechanism, for wearable, portable, and integrated electronics. However, numerous key questions have not been adequately addressed, as follows:  The detailed research on the stability of fabricated flexible supercapacitors under different bending states is not up to the mark. Thus, this is the bottleneck in the fabrication of reliable power sources for portable and flexible electronic applications.  There is a lack of active materials with low cost and simple synthesis methods to produce on a large scale active electrode materials and fabrication of flexible supercapacitors for commercialization of flexible supercapacitors.  The poor energy density of supercapacitors is a big barrier to their practical application, so there is a need to improve the energy density of supercapacitors by utilizing different strategies.  The weight of active electrode material and binder significantly reduces the mechanical properties of flexible supercapacitors during fabrication, making it a difficult research area to develop binder-free flexible supercapacitor devices. This dissertation fills the research gaps by developing efficient active electrode materials with improved mechanical properties using simple and low-cost methodologies. Also, new composite materials that can be used to make flexible supercapacitors without a binder during the synthesis steps have been suggested. In chapter 3, we developed a nanohybrid type active electrode material consisting of tungsten oxide (WO3) and nitrogen-doped graphene quantum dots (NGQDs). The synthesis approaches for the active electrode materials were cost-effective and facile (that is, hydrothermal and spray coating), which is an advantageous and adaptable approach for industrial application. The porosity network and large available surface area of active electrode material played important roles in improved electrode-electrolyte interactions, as revealed by the results of several techniques used to characterize the produced nanohybrid. The energy and power density offered by the fabricated flexible supercapacitor device was also outstanding with mechanical stability under bending conditions at different bending angles. The supercapacitor device has a charge storage capacitance of 178.82 Fg-1 and exhibited power and energy densities of 360.11 Wkg-1 and 15.79 Whkg-1, respectively, along with outstanding cyclic stability, with specific capacitance decreasing by 4.71 percent after 5000 cycles, according to electrochemical studies. In chapter 4, a lamellar flower-like alpha manganese vanadate (α-Mn2V2O7) was utilized for the first time to develop a hybrid flexible supercapacitor device by using binder a free synthesis route. This approach was utilized to enhance the energy density of the supercapacitor by utilizing an asymmetric scheme of fabrication in which one electrode was acting like a supercapacitor electrode material and the other was for the battery type behavior. Nickel foam (NF) was utilized as a charge collector in this study due to its mechanical properties. The capacitance contribution of α-Mn2V2O7 in the aqueous electrolyte is derived from diffusion-controlled (battery-type, 89.93%) and capacitive-controlled (10.07%) mechanisms, according to voltammetric analysis (0.5 M KOH). Furthermore, the constructed hybrid supercapacitor had a specific capacitance of 35.7 Fg-1 and an energy and power density of 28.4 Whkg-1 and 8.5 kWkg-1, respectively, at a scan rate of 5 mVs-1. Overall results showed that the proposed electrode materials can be utilized as an efficient flexible supercapacitor material with enhanced mechanical, energy, and power density characteristics. In chapter 5, the design of a lightweight supercapacitor device with enhanced mechanical characteristics was proposed. For this active electrode material was utilized as itself charge collector, instead of using separate conductive materials which will increase the weight and cost of the device and also effects the mechanical properties under different bending states. Additionally, titanium nitride (TiN) as an active electrode material is proven to be an effective material for energy storage applications, but it suffers from poor electrochemical stability due to quick corrosion issues. Here, a nickel (Ni) layer was introduced to cover the TiN surface, which results in the enhancement of stability and also increases the storage properties of the fabricated device. The electrochemical stability was tested over 10,000 charging/discharging cycles and it was observed that the presence of Ni was helpful to protect the TiN surface with the excellent value of specific capacitance up to 10.2 mFg-1.

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목차

Chapter 1. Introduction 1
1.1. Research motivation 1
1.2. Problem statement 2
1.3. Research Objectives 5
1.4. Dissertation outline 5
1.5. Related publications 8
Chapter 2. Literature review 9
2.1. Electrochemical Energy Storage Devices 9
2.2. Supercapacitors 12
2.2.1. Electrical double-layer capacitors (EDLC) 17
2.2.1.1. Helmholtz model 17
2.2.1.2. Gouy–Chapman model or diffuse model 17
2.2.1.3. Stern modification 18
2.2.2. Pseudocapacitors 20
2.2.3. Hybrid Supercapacitors 21
2.3. Flexible Supercapacitors 24
2.3.1. Tungsten Oxides (WO3) for Flexible Supercapacitors 25
2.3.2. Graphene Quantum Dots (GQDs) for Flexible Supercapacitors 27
2.3.3. Manganese Vanadate (MnV) for hybrid supercapacitor 30
2.3.4. Titanium Nitride (TiN) for flexible supercapacitor 31
2.4. Flexible Charge Collector 31
2.5. Flexible Electrolyte 32
Chapter 3. 2D WO3/NGQDs Nanohybrid for Flexible and Transparent Supercapacitor Fabrication 36
3.1. Introduction 36
3.2. Material and Methods 38
3.2.1. Materials 38
3.2.2. CVD Graphene Synthesis 39
3.2.3. Synthesis of 2D WO3 40
3.2.4. Synthesis of nitrogen-doped graphene quantum dots (NGQDs) 40
3.2.5. Fabrication of Supercapacitor Device 40
3.2.6. Characterizations of prepared electrode materials 43
3.3. Results and Discussion 44
3.3.1. Morphological and structural characterizations 44
3.3.2. Electrochemical Performance of Fabricated Supercapacitor 51
3.4. Conclusion 62
Chapter 4. Binder Free Synthesis of Manganese Vanadate for Excellent Electrochemical and Flexible Asymmetric Supercapacitor Application 64
4.1. Introduction 64
4.2. Experimental Materials and methods 66
4.2.1. Materials 66
4.2.2. Hydrothermal Synthesis of Manganese Vanadate 67
4.2.3. Synthesis of Negative electrode materials 68
4.2.4. Preparation of Hybrid Flexible Supercapacitor Device for Electrochemical Testing 68
4.2.5. Electrochemical Testing of fabricated Supercapacitor devices 69
4.2.6. Instrumental Tools for Phyical and Chemical Characterization 70
4.3. Results and discussion 70
4.4. Conclusion 87
Chapter 5. Synergic Effect of Ni layer on TiN for Long-Lasting Electrochemical Flexible Supercapacitor Application 89
5.1. Introduction 89
5.2. Material and Methods 92
5.2.1. Materials 92
5.2.2. Titanium nitride and nickel thin film deposition 92
5.2.3. Fabrication of Flexible supercapacitor device 95
5.2.4. Characterization Tools 95
5.2.5. Electrochemical Performance analysis 95
5.3. Results and discussion 96
5.4. Conclusion 116
Chapter 6. Conclusion 117
References 119

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