Industrial Engineering 2016: Super Capacitors: Types, materials and applications- Amrita Jain-Manipal University*Corresponding Author:
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Supercapacitors or ultracapacitors are considered as one of the most upcoming and promising candidates for power devices in future generations. Because of its engaging properties, it is appropriate for some, advanced applications like hybrid electrical vehicles and comparative other force devices and systems. So as to utilize this device in power applications, its energy and power density should be increased. A lot of results from published work in the form of research and review papers, patents and reports are available this time. The reason for this article is to re-look the journey of the materials utilized for supercapacitors with center around the energy storage capability for practical applications. Moreover article also addresses the principal technological challenges which the research society is facing in the field of supercapacitors.
Since the Industrial Revolution, the social and economic prosperity of the nation has depended on the massive consumption of fossil resources (coal, gas, and oil) as a readily accessible carbon source. The worldwide energy demand from fossil fuels was estimated to be 13.731 billion tons of oil equivalent (BTOE) as of 2012 and is expected to approach 18.30 BTOE in 2035. The depletion and uneven distribution of natural resources has already caused economic problems (e.g., price fluctuations and unbalanced supply chains), resulting in issues in various domains such as energy generation and storage, industrial operations, and transportation. Furthermore, the massive worldwide consumption of fossil fuels has caused carbon accumulation in the natural cycle. CO2 from anthropogenic activities is the major contributor to the greenhouse gases causing significant environmental changes. A stastic guideline (i.e., adaptation and mitigation) to resolve the global-scale imbalance in carbon inventory was thus proposed by the United Nations (UN) in 2007. Those efforts, many studies have already considered how to restrict the consumption of fossil resources. As part of those mitigation strategies, the development of renewable energy sources (such as solar energy, tidal energy, geothermal energy, wind energy, and biofuels) has also been pursued extensively. People awareness on global climate change has also led to various types of political legislation (e.g., the renewable fuel standard and renewable portfolio standard) intended to motivate the expansion and commercialization of renewable energy options. Except for biofuels, most renewable energies are supplied as electricity (electric power). As such, there has been great demand for a reliable technical platform for electrochemical storage, including batteries, fuel cells, and electrochemical supercapacitors (SCs). In particular, SCs have drawn more attention than batteries because of their fast storage capability (i.e., low discharge time: SC: 1–10 s vs. lithium ion battery: 10–60 min) and enhanced cyclic stability (SC > 30,000 h vs. battery > 500 h). Exceed low energy density, recent advancements in SCs in terms of electrode materials and electrolytes hold significant potential to fill the gap between batteries and fuel cells and existing electrolytic-capacitor technology. An SC is a proficient energy storage system with attractive properties such as high energy and power densities, long lifetime, high reliability, excellent rate behavior, and environmental friendliness. Each type of SC (EDLCs, pseudo-capacitors, and hybrid capacitors) has different characteristics. Although the energy storage density in EDLCs is relatively small, the power density is higher than that of pseudo-capacitors. Cycle life is another important factor in evaluating SCs. Generally, tests for stability involve charging and discharging capacitors for a certain number of cycles and then comparing the capacitances before and after the field cycling stress. Most EDLCs use carbon-based electrodes, which have a long lifetime and can be cycled at a high rate, with the very small degradation in performance. EDLCs show good field cycling stability, with 10–20% degradation in capacitance after field cycling stress tests Pseudo-capacitors are profoundly different from EDLCs. They store energy through reversible faradic reactions, with capacitance 10–100 times larger than available with EDLCs But repeated reduction and oxidation processes can change the structure of PC electrodes, resulting in decreased field cycling stability. Moreover, the power density of pseudo-capacitors is smaller than that of EDLCs because faradic processes are slower than electrostatic processes. For example, the capacitance of a Co(OH)2-based capacitor decreased ~ 40% after field cycling. Both EDL and PC SCs use two electrodes made from the same type of material. To increase the operating voltage window and the power and energy density, hybrid capacitors have been developed. For example, EDLC/redox-type hybrid capacitors integrate the advantages of EDCLs and pseudo-capacitors by coupling both types of materials. As shown in MnO2–NPG/PPy-NPG capacitors have high energy and power densities and show good field cycling stability. New developments are making portable devices and electronics thinner and more power demanding, opening new commercial opportunities for SCs, which are lighter and more powerful than batteries. Because of all their exciting properties and probable usage in an increasing number of applications, the SC market is expected to top $11 billion by 2024.Nonetheless, SCs are not yet in extensive use. According to the developers, manufacturers, and suppliers of SCs, this lack of commercial success is due to their present low energy density and high cost-to performance ratio. Therefore, the development of materials and configurations to increase the energy density and reduce the costs of processing and preparation methods is necessary, and multiple ambitious research activities are currently being conducted.
Note: This work is partly presented at 3rd International Conference and Exhibition on Industrial Engineering, November 14-15, 2016 Dubai