CONTENTS
CHAPTER 1. INTRODUCTION 1
1.1 Current Scenario 1
1.2 Energy crisis and environment challenges 2
1.3 Advances in energy storage 3
CHAPTER 2. LITERATURE SURVEY 4
2.1 Introduction to supercapacitors 4
2.2 Electrode materials for supercapacitors 5
CHAPTER 3. PRESENT STATUS AND DEVELOPMENT 9
3.1 Material used and its properties 11
3.2 Actual device and testing 12
CHAPTER 4. APPLICATIONS 13
CHAPTER 5. CONCLUSION 15
References
List Of Figures:
Figure Figure Name Page No.
1 Energy Crisis
2 Consequences of using fossil fuels
3 Future energy sources and their status
4 Ragone Plot
5 Comparison between capacitor, ultracapacitor and batteries
6 Classification of supercapacitors
7 Discharging and charging status in EDL supercapacitor.
8 Types of carbon materials for supercapacitor electrodes
9 Scheme of material preparation
10 SEM Characterization images
11 Prepared supercapacitors
12 Applications
CHAPTER 1.
Introduction
1.1 Current Scenario:
The usage of energy is increasing with the increase in human population. Remarkable actions have been taken to create advances for boosting the use of renewable energies, for example, hydroelectric, wind, and solar energy. As the ordinary fossil energies are not economical energy sources. One of the main problems is that the accessibility of these renewable energies is irregular and firmly relies on the environmental circumstances. The disturbances caused in the regions of these renewable sources is also a significant issue. In such manner, the improvement of profoundly proficient, stable and nature-friendly energy storage methods is fundamental for impetuous practical utilization of renewable energy.1
Supercapacitors (SCs), otherwise called electrochemical capacitors or ultracapacitors, are developing as a vital class of energy storage devices. [2,3] SCs have specifications in terms of working that overcome any limitation between ordinary capacitors and batteries. In contrast with ordinary capacitors, SCs have higher energy density. Moreover, the unique charge storage system of SCs makes them store and deliver a large amount of charge in a small timeframe, and in this way can give higher power than batteries. SCs can possibly be utilized as a part of a large number of applications, including backup power units, electric automobiles and hybrid vehicles, also, modern energy storage assemblies. [3,4] The SCs market was above US$270 million during the year 2009, and was foreseen on rising at a normal yearly progress rate of about 21% through 2014. To deal with the increased interest for portable electronic devices, for instance, wearable gadgets, cell phones, and versatile applications, the change of high execution and strong power sources with astounding flexibility, light-weight and security is essential.[5,6] However, previous works have provided a fair amount of information about the liquid based SCs with aqueous medium electrolytes or ionic liquids as electrolyte. These SCs have two critical drawbacks that most distant point their applications for flexible electronic devices. Moreover, the device manufacturing includes high-cost packaging materials and system to avoid potential release of electrolytes, as an extensive bit of the electrolytes are extremely unsafe and damaging. Second, it is difficult to make versatile supercapacitors commercially, using liquid electrolyte due to the packaging issue.[1,7,8]
Figure 1: Energy Crisis
Image source: Web/Google image search
Flexible solid state SCs rose as an additional class of charge storing devices and have drew in a broad attention. Contrary to common SCs, the solid state SCs have a couple of basic central focuses including small size, reduced weight, accuracy, cyclic stability, and an additional range of working temperatures. They hold magnificent abilities to be used as a charge storing devices for various uses and wearable devices.[9]
1.2 Energy Crisis and Environment Challenges
Energy is an unavoidable subject in current society, running from fundamental day by day life to cutting-edge science and innovation.
Figure 2: Consequences of using fossil fuels.
Image source: https://www.ecotricity.co.uk/our-green-energy/energy-independence/the-end-of-fossil-fuels
With continually expanding energy request and ceaselessly crumbling natural issues, energy has turned into a bottleneck and is upsetting the advancement of mankind society. Amazingly, current power supplies are mostly constrained to the non-renewable fossil fuels. To manufacture a maintainable future, energy source should be non-fossil-based, in a perfect world, it ought to be solid, moderate and limitless. [1] Figure 3, demonstrates a very much considered guide for the future energy situation, which exhibits the improvement pattern of energy advances with the objective of supplanting fossil-based energy by renewable energy [2]. Hence, it is necessary to explore characteristic and renewable energy sources to substitute fossil fuel sources, advising us to search for greener and more efficient energy technologies to meet the increasing energy requests.
Figure 3: Future energy sources and their status
Image Source: https://www.eia.gov/energyexplained/?page=us_energy_home
1.3 Advances in energy storage:
Energy conversion and storage assumes the key part in accomplishing worldwide energy supportability. To date, various energy change and capacity advances, for example, sunlight based cell, flywheel, compacted air, power device, supercapacitor, and battery, have been produced with the objective of using supportable energy sources, for example, sun oriented, geothermal, tidal or biomass energy[3].Supercapacitors and batteries have been ended up being the best electrochemical energy transformation and capacity gadgets for viable applications. Quickly, supercapacitors store charge at the cathode/electrolyte interface by means of electrical twofold layers or reversible faradaic responses, while batteries straightforwardly change over substance energy into electrical energy by exothermal redox responses [4]. Inventive materials configuration lies at the heart of creating propelled energy storage gadgets. Encourage leaps forward in anode materials configuration hold the way to cutting-edge energy storage devices. Normally, energy storage materials are delivered by applying renewable assets through basic, ease and naturally agreeable methods, with controlled morphologies, rich porosity, changed surface science and proper functionalities. To change such science dream into reality, more endeavors ought to be committed to planning and testing superior, maintainable electrode materials.[1]
CHAPTER 2.
Literature survey
This chapter is divided into two sections. The first section introduce the technological and current progress on supercapacitors. The second section reviews the materials focusing on the development of electrode materials.
2.1 Introduction to Supercapacitors:
A supercapacitor (SC) (also known as electric double layer capacitor (EDLC) or ultracapacitor is a high-limit capacitor with capacitance values considerably higher than different capacitors (yet brings down the voltage restraints) that overcomes any issues between electrolytic capacitors and rechargeable batteries.
Figure 4: Ragone Plot.[1]
They regularly store 10 to 100 times more charge for each unit volume or mass than electrolytic capacitors, can acknowledge and convey charge considerably speedier than batteries, and endure numerous more charge and discharge cycles than rechargeable batteries.
Figure 5: Comparison between Capacitor, Ultracapacitor and Batteries.[10]
Based upon the capacity system or cell design, electric double layer capacitors (EDLCs), pseudocapacitors, and hybrid capacitors can be recognized. EDLCs depend on high particular surface-territory (41000 m2g1) nanoporous materials as dynamic cathode materials, prompting an immense capacitance in correlation with electrostatic capacitors. The cathodes are typically made of nanoporous carbon materials on account of their accessibility, existing mechanical generation, and nearly ease. Pseudocapacitors depend on leading polymer or metal oxide based terminals and some of the time functionalized permeable carbons, consolidating electrostatic and pseudocapacitive charge storage devices. These materials can hold considerably higher particular capacitance values when contrasted with EDLCs, with the charge storing component depending on quick redox responses happening on the terminal surface however not in the mass like in batteries.However, as on account of batteries, redox responses can prompt mechanical changes making the electrodes to expand and shrink, offering poor mechanical strength. Hence, brings down the cycle life is an essential lack of pseudocapacitive materials. The long last, hybrid capacitors are made out of an EDLC cathode and a pseudocapacitive or battery as anode, joining the properties of both frameworks and prompting an intermediate performance.[10]
Figure 6: Classification of Supercapacitors
Image source: https://en.wikipedia.org/wiki/Supercapacitor
An electric double layer is a structure showing up when a charged electrode is put into a fluid. The adjusting counter charge for this charged surface will frame on the fluid, getting close to the surface and forming a double layer of charge. At the point when a supercapacitor is charged, electrons are compelled to go from the positive cathode to the negative terminal through an outer circuit. As a result, cations inside the electrolyte move in the negative anode and anions in the positive terminal shaping an EDL that remunerates the outside charge unbalance. Amid the release, electrons go from the negative cathode to the positive anode through an outer circuit, and both sorts of particles in the pores get to be distinctly blended again until the cell is released.
Figure 7: Discharging and charging status in EDL supercapacitor.[1]
Particles don’t move in the mass electrolyte an indistinguishable route from they do inside the pores of an anode material. The versatility of particles into the pores is extraordinarily impacted by the pore size, which if too little makes the pores difficult to reach, not adding to double layer capacitance [10,12].
2.1.1 Electrode Materials for Supercapacitors:
Carbon based materials are widely used in many applications. As they feature relatively low cost and an established industrial production processes, their availability is quite high. This section details carbons for supercapacitors, from the most widespread types to the newest developments. These materials show electrolytic double layer capacitance. This type of capacitance is very suitable for cyclic stability, maintaining the performance of the SC for thousands of cycles.
Metal oxides have good specific capacitance and conductivity, making them suitable for electrode fabrication focused on high energy and high power supercapacitors [4]. There are several different metal oxide materials used for electrode fabrication such as RuO2, IrO2, MnO2, NiO, Co2O3, SnO2, V2O5 or MoOx. The most studied ones are ruthenium and manganese oxides [13].
Apart from metal oxides conducting polymer electrodes also have high electrical conductivity, up to 104S cm-1 as in doped polyacetylene, high electroactivity, which is the ability of an electrode coated with a polymer film to reversibly change its oxidation-reduction state in a solution under the application of an external electric field, the ability to form passive layers on metal surfaces, and the semiconductor band structure[11].
The polymer electrode exhibits a current peak at redox potential of the polymer, while metal oxide electrodes can exhibit a series of redox reactions. These properties of both metal oxides and conducting polymers produce pseudocapacitance reducing the cycle life of the supercapacitor.
CHAPTER 3.
PRESENT STATUS AND DEVELOPMENT
3.1 Material Used and its properties:
In this work porous carbon from the biomass is used as the electrode material for the supercapacitor.
Figure 8: Types of Carbon materials for supercapacitor electrodes
This carbon is attained after carbonization and activation process. Carbonization is the way toward creating amorphous carbon by the chemical conversion of the carbon source after heating whereas, activation provides high surface area. This can be done by partially controlling the oxidation of carbon precursor by a physical or chemical activation. In case of physical activation high temperature is provided in oxidizing environment like CO2 etc, whereas chemical activation is achieved with the help of chemicals like KOH. The main aim behind every activation process is the increase in porosity.
Figure 9: Scheme of material preparation
Nanopores can be classified according to their size, namely into micropores (2 nm), mesopores (2–50 nm), and macropores (450 nm). The pore size of the material plays important role in retaining the charge as the mesopores and macropores can hold charge for lesser duration as compared to micropores where the ions are squeezed into the pores causing higher duration of charge retention.
Figure 10: SEM Characterization images
The morphology of the material is studied using Scanning electron microscope (SEM). In this study it was observed that the final material consists micropores(<2 nm), mesopores(2-50nm) and macropores(>50nm) in a crumpled sheet-like structure. Although all types of pores are present in this material but the micropores and mesopores are dominating as evident from the SEM images. This type of morphology has very high surface area and is a potential electrode material for supercapacitor.
3.2 Actual Device Parameters:
The electrical properties of a supercapacitor are mostly controlled by different parameters, for example, electrode materials, electrolytes, separators, and current collectors. Electrode is prepared by covering a metallic current collector with an around 100 μm thin layer of porous carbon material. This active material is blended with a binder in order to frame slurry. The thickness of the slurry ought to be controlled for making the covered layer of active material adequately thin to be conductive all through the material.
Figure 11: Prepared Supercapacitors
As the resistance of the supercapacitor cells must be low, special considerations must be paid to the contact resistance between the electrode material and the current collector.
A generally utilized estimation is the particular capacitance, which is the inherent capacitance of a cathode material communicated in F/g. Though, this is an extremely valuable factor for the material, a higher specific capacitance does not really imply that the material will be a good supercapacitor electrode. There are different variables significantly affecting capacitance, for example, electrical conductivity (both that of materials and between terminal particles), which represents electron and particle move into the layer [13].
CHAPTER 4.
APPLICATIONS
Figure 12: Applications
Image source: https://static.wixstatic.com/media/6bbeef_4fd99faaf5ba4f9aac365bf5d1027c65.jpg
• Maintenance free applications
• Public transportation
• HEVs, start-stop system
• Back-up and UPS system
• System of energy recuperation
• Consumers electronics
• An excellent example of the use of an ultracapacitor can be found in electrical smart meters, emergency radios and flashlights.
CHAPTER 5.
Conclusion
Supercapacitors are a very useful technology for various applications requiring high power ratings, long cycle life, and reliability. Those requirements are specified by the renewable energy systems such as wind power conversion and solar systems. The first requires high power burst for blade pitch adjusting or enhancing low voltage ride-through capability. The second requires output power smoothing, which is classically done with the batteries that do not last more than few years [14].
In this work an attempt has been made to achieve these goals by using an economical and eco-friendly electrode material for a productive utilization of the biomass waste materials. This biomass-derived activated carbon indicates a good performance in terms of capacitance for supercapacitor applications.
References
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