下面为大家整理一篇优秀的paper代写范文- The Supercapacitor，供大家参考学习，这篇论文讨论了超级电容器。超级电容器是一种有效的储存能量的装置，近年来越来越受欢迎。与传统的化学电池不同，超级电容器是一种介于传统电容器和电池之间的装置。由于在储能过程中没有发生化学反应，所以储存过程是可逆的。因此，一个超级电容器可以被充电和放电成千上万次。超级电容器的优点包括足够的功率密度，充电和放电所需的短时间，以及长寿命周期。
1. INTRODUCTION
Supercapacitor is an efficient device for storage of energy, which has been increasingly popular in recent years. Different from traditional chemical batteries, supercapacitor is a device that goes between traditional capacitors and batteries. Since no chemical reaction occurs in the energy storing processes, the storage process is reversible. Therefore, a supercapacitor can be charged and discharged for hundreds of thousands of times, with the use of porous electrodes and electrolyte between them. The advantages of supercapacitor include adequate power density, short time required for charging and discharging, as well as long life cycles. Within ten minutes of charge a supercapacitor can store 95% of its designated capacity. Meanwhile, there is little “memory effect” in its life cycle. The efficiency of energy transfer is also higher with minimized losses, reaching 90% of power efficiency (Béguin&Frąckowiak, 2013). The reason why supercapacitors are super is the size of the porous electrodes. Special design enables supercapacitor to have much larger electrode surface areas, thus significantly increasing the capacity of it. In addition, supercapacitor is also environmentally friendly, as the production, usage, storage and disassembly processes of it have little influence on the environment, unless leakage of electrolyte occurs due to poor maintenance.
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There are three key factors that determine the performance of a supercapacitor, which are its electrodes, electrolytes as well as the operating environment. Although there has been extensive research down to improve the former two characteristics, there have not been equivalent effort made to study the performance of supercapacitors under varying operating conditions. Temperature is the most influential environmental factor for supercapacitor performances.There are many occasions where supercapacitors have to operate under cold and hot temperatures, since it is most widely applied to vehicles. As a result, many of the supercapacitors that are designed and tested for room temperature would not be applicable for outdoor use in winter and hot summers. The major reason for reduced performance is the influence of temperature on aqueous and non-aqueous electrolytes. Under low temperatures, the efficiency for electrolytes, even organic ones, will be significantly reduced with thousands of times of increased resistance. There have been some efforts in reducing the influence of temperature on supercapacitors in recent years. In this paper, the research by a group from Ilmenau University of Technology will be introduced. They designed a new supercapacitor using an innovative combination of graphene-based electrode andLi2SO4-based aqueous electrolyte (Vellacheri et al, 2014).This combination has effectively increased the performance of supercapacitors within a temperature range between -20°C and 45°C.
2. FEATURES
2.1 Cyclic Voltammogram Analysis
Figure 1.Cyclic Voltammograms of ElectrodeCells.
The design team has performed a series of tests to investigate the property of the newly designed battery. To see how are the charge-storage properties of the electrodes, symmetric two-electrode cells are fabricated after the graphene-based electrodes were made. These cells then underwent a series of cyclic voltammetry and galvanotactic charge and discharge. In figure 1, the cyclic voltammograms of the cells at different temperatures are shown. Room temperature (RT), 45°C, 0°C and -20°C were used, since they cover a range of the most frequent operating temperature of supercapacitors. The cyclic voltammograms all have shapes that are approximate to a rectangle. Similar results were obtained when the voltage of the experiment was increased in a range between 5 to 200 mV/s.
The near-rectangular shapes of the diagrams mean that the behavior of the electrode cells is almost ideal for a supercapacitor, due to the efficient transmission of charge in these electrodes as well as the efficient design of a double-layered charge system. These features of the cells would ensure that the electrode is easily accessible by ions, even when the temperature is far from RT. In addition to accessibility, electrical resistance is also a major factor of concern for the electrodes. The charge storage unit of a good supercapacitor must be low in electronical resistance, and high in the conductivity of ions, so that the supercapacitor would work smoothly. Building on these advantages, the electrodes tested also maintained stable capacitive currents, under different temperatures. Under temperature higher than RT, which is 45°C, an increase in capacitive current is observed, which is a result of higher rates of ion transmission under heat. The ions are then activated to reach more areas in the surface of the electrode cells. Similarly, the capacitive current dropped slightly under cold temperatures, due to the reduced icon activity.
2.2 Retention of Specific Capacitance
Figure 2.Galvanotactic Charge and Discharge Profile.
Some of the supercapacitors that performed exceptionally also experience a drastic drop in performance under cold temperatures. Figure 2 shows the galvanotactic charge and discharge profile of the supercapacitor. The experiment was performed under a density of current of 1mA/cm2. The reliability of the supercapacitor is shown through the symmetrical shape of the diagrams, as well as the constant slope of the graphs. Based on the profiles, specific capacitances of the electrodes are calculated. The value of specific capacitance at 45°C is the highest, 99F/g. at RT, the specific capacitance drops to 91F/g. the value further drops to 80F/g at 0°C and 74F/g at -20°C. Comparing the lowest value with the highest, a 25% drop is obtained.
Although this value is still no the not ideal situation, it is already an improvement compared to other temperature sensitive supercapacitors. The percentage of retention of 75% shows promising prospects for future improvements on the technology. In figure 3. Different current densities are added to the discussion. The graphs show the trend of specific capacitances under different current densities. Ideal charge storage properties are shown from the small IR drop and high specific capacitance in the curves. The electrodes designed can both maintain ion diffusion paths effective and ensure a high electrical conductivity, so that the performance of the supercapacitor under different temperatures are ensured. The energy densities of supercapacitors are also calculated for different operating temperatures, which are: 3.44, 3.16, 2.78 and 2.57 Wh/kg at 45°C, RT, 0°C and -20°C respectively. Although the value of 2.57 is still a 25% drop compared to the highest value, and a 20% drop compared to RT, it is already proven to be much better than most of the previously designed supercapacitors.
2.3 The Charge Storage Process
Figure 3. Influence of Temperature and Current Density.
To further understand the characteristics of the supercapacitor and temperature related aspects, a correlation between charge storage and temperature should be established, so that it can better adapt to practical situations. The process of charge storage in graphene-based electrodes happens by the repeated formation and deformation of an electrochemical double layer at the interface between electrode and electrolyte. This process happens both during charging and discharging. When the supercapacitor is being charged, the ions transmit from the electrolyte to the electrodes, forming the double layer at the interface between the two materials. This process is weakened, as seen in Figure 3, by the decreased temperature and the increased current density. The transmission of ions is thus hindered in some way under such circumstances.
Figure 4. Arrhenius-type Plots.
In Figure 4, an Arrhenius-type equation is used so that the charge storage situation is better understood. A plot of ln C (C is the charge stored during charging) and 1/T (T being the absolute temperature) is thus created. Ea (activation energy) is thus obtained from the slope of the plots. The calculated values of Ea for different current densities range from 0.82 to 1.88 kcal/mol (from 1 to 5 mA/cm2). These values are much smaller compared to the graphene-based supercapacitors with ionic liquid electrolyte, which mean that the supercapacitor designed using Li2SO4-based aqueous electrolyte has much more superior properties than other type. With a lower Ea, it is much easier for ions to form the electrochemical double layer, which is critical for the efficiency of charge storage.
2.4 Supercapacitor Cycle Life
Figure 5. Cycle Life Test
Another important aspect of supercapacitor is the cycle life, since it is a critical feature in practical application. To measure the cycle life of the supercapacitor, the specific capacitance after different numbers of cycles are plotted in figure 5. The current density used in the graph is 4mA.cm2, and the number of cycles measured are 5000. From the plots, no significant drop in specific capacitance is observed. Under different temperatures, the specific capacitance of the supercapacitor all remained stable, with a slight drop after 1000 cycles under 45°C. The long cycle life of the supercapacitor is contributed by the high electrochemical stability of graphene, even when the temperature is 45°C. In addition, the property of the Li2SO4-based aqueous electrolyte are compatible with the electrode, making the combination optimal for sustaining a long cycle life.
2.5 Electrochemical Behavior
Figure 6. Electrochemical Behavior
To understand the electrochemical behavior of the supercapacitor, electrochemical impedance spectroscopy has been done at various temperatures as indicated in Figure 6. From the Nyquist plots, charge transfer resistance and diffusion controlled kinetics are shown in separated sections of the graphs, which are either high or low frequencies. In the high frequency region, which is represented by the semicircle part of the graphs, the diameter of the semicircle indicates the variation of the supercapacitor performances. With smaller circles, the variation of the performance is also smaller, leading to higher stability and reliability. The low frequency region is represented by the straight-line parts of the graphs. From the diameter of the circles, the position as well as the slope of the lines, the charge transfer resistances are calculated to be 0.95 Ω, 1.24 Ω, 1.62 Ω and 2.06 Ω at RT, 45°C, 0°C and -20°C respectively. The vertical shape of the plots is another indicator of the supercapacitor performance, with the line being more vertical, the supercapacitor is also more ideal. Consistency of the specific capacitances during the charge and discharge processes also reaffirms the performance. As the temperature dropped from RT to -20°C, the ESR increased 3.2 times, which is a relatively minimal influence on the power density of the supercapacitor. Overall, the combination of graphene and Li2SO4 proves to be an ideal set of supercapacitor design.
3. APPLICATIONS
3.1 Supercapacitors in Mobile Devices
Supercapacitors can also be applied in mobile devices, which will enable devices such as mobile phones to be fully charged within minutes. Such an application will solve the problem of the increasingly high dependence of people on their mobile phones with limited power capabilities. Since the design of the mobile phones are growingly sleeker in recent years, the room left for battery is increasingly limited. In addition, a common lithium battery will degenerate after two years of use. Compared to batteries, supercapacitors are much more durable, as shown from the above discussions. Even after 5000 times of charge and discharge cycles, supercapacitors are still fully functional. Once batteries are replaced by supercapacitors, mobile devices will not need to be charged in a daily basis. Mobile devices using supercapacitors are easily charged in seconds, with increased durability (Monteiro, Garrido, & Fonseca, 2011). The supercapacitor will not degenerate even after thousands of cycles. Taking an average of 10 times of charge and discharge cycles, supercapacitors can be used for decades. Since the supercapacitors are using physical processes in operation, the efficiency is also much larger than chemical batteries. However, the technology is still far from mass production due to its cost. More research is needed to lower the cost of supercapacitors and make it accessible to the market.
3.2 Applications in Solar Energy
The increased range of temperature makes supercapacitors more applicable for outdoor usage, since the performance is insured even when the temperature goes below 0 degrees or above 40 degrees. EDLC supercapacitors can be fully charged within a very short period of time. However, the current supercapacitors in the market are too expensive to be applied in a wider range. Therefore, most of the supercapacitors are used as an auxiliary energy source. As a small PV (photovoltaic) system, the current consumption of Solar Lamp’s regulator should be smaller than 1% of its working current. Therefore, low energy consuming components should be selected for the regulator. Adding a supercapacitor to the PV system will ease the pressure on the battery and increase the life of the system (Narayanan, Kumar, Deepa, & Srivastava, 2015).
The output power of solar battery is highly dependent on weather conditions, which are highly fluctuating over time. Such instability in the charging current has posed a threat on the battery life, increasing the cost of the system directly. The increased production and use of battery will also lead to more environmental pollutions. Therefore, a medium system is effective in mitigating the influence of instability on the battery, through the use of supercapacitors. Since supercapacitors can be charged and discharged at a much faster rate, without causing much damage to itself, the control system will use supercapacitors to generate a steady output current to the batteries. When the sunlight is instable, the supercapacitors will be charged first, so that the batteries are not directly influenced. Such a system will enable the supercapacitors to power the road lamps even when there is no sunlight, increasing the period of lighting.
3.3 Automotive Industry
Currently, supercapacitors are most widely used in the automotive industry. The increased range of operating temperature make supercapacitors part of the practical solutions in hot and cold areas of the world. In addition to the reduced influence of temperature, supercapacitors can also be charged as discharged within minutes. In the automotive industry, the intelligent start and stop control system brings a wide platform of application for supercapacitors. For motors which use hybrid powers, the discharge process will lead to drastic drops of charge, due to the frequent start and stop of the vehicles. The energy drawn from the battery during normal driving is relatively lower, while the energy required for acceleration is higher. With the traditional battery technology, a balance must be achieved between power density and cycle life. As a result, compromises have to be made.
A special electric generator can be used to solve the problem. During the braking process, the generator can fully charge the supercapacitor within seconds. Then, the fully charged supercapacitor will provide power for all the systems in the vehicle. Once the supercapacitor runs out of energy, batteries will be used instead. In addition to supplying power for other systems in the vehicle, supercapacitors can also charge the battery through slow discharge. With the coordination of the two, there is no longer need for an engine as ideal energy recycling is achieved. Such a system will result in a reduction in oil consumption of as high as 10% (Eddahech, Briat, Ayadi, & Vinassa, 2014). Although supercapacitors have undergone continuous improvements over the years, with increasing power density, it still cannot replace batteries. The biggest disadvantage of supercapacitors is its speed of auto-discharge, which is much faster than batteries. Without a battery, a supercapacitor powered vehicle would not be started after being parked for a few days. The features and disadvantage of supercapacitors make it perfect for a hybrid power system currently.
Thus, a dual system is designed to resolve the conflicting needs of sudden acceleration and normal driving. The major system is in charge of providing the best mileage, while the auxiliary energy system will provide temporary energy supply when the cars are accelerating and climbing. Taking advantage of the supercapacitor to be charged and discharged rapidly, the braking energy can be restored in them and reused in driving. With the use of supercapacitors, therefore, the energy can be recycled and stored in the auxiliary energy system, significantly increasing the energy efficiency of the system. Due to the low power density, supercapacitors are not ready to replace batteries in the major system. Although supercapacitors are not able to act as the major source of power currently, it is obviously advantageous acting as the auxiliary energy source. A combination of battery and supercapacitor system will result in a notable increase in the usage life of battery. Compared to batteries, supercapacitors are able to absorb the motion energy created in the braking and acceleration of vehicles, which will further increase the mileage of the vehicles.
However, a balanced design of different components is necessary to achieve the best improvements in performance. Without a proper design, the large amount of energy stored in the power system will lead to increased risks of explosion. The safety concerns are also increased due to the rapid discharge rate and the inner resistance which is too low. The low operating voltage has also limited the application of supercapacitors. These problems should not be overlooked. There have been cars developed in recent years using supercapacitors. The features of energy saving and fast discharge speed makes vehicles using supercapacitors adaptable to different types of markets and satisfying varying needs of consumers.
4. CONCLUSIONS
Inexpensive and reliable energy sources have been the pursuit of researchers for decades. The new type of supercapacitor introduced in this paper is a significant step forward in the field. The Cyclic voltammetry and galvanotactic charge and discharge plots have shown an almost ideal energy storing device. The property of temperature endurance under both high and low temperatures have further widened the range of application for the technology. Under the temperature of -20 degrees Celsius, the rate of efficiency retention is calculated to be 80%, which is better that most of the other supercapacitors in the current market. Based on the advantages of this design and other intrinsic features of supercapacitors, applications in the mobile devices, solar energy and automobile industry are promising. The use of supercapacitors will revolutionize the mobile phone industry, due to the significantly reduced charging time and the much longer “battery” life. In the solar panel field, the temperature endurance is further highlighted, using supercapacitors as regulators of current to increase the life of the entire system, directly protecting the environment. Similarly, in the automotive industry, the use of supercapacitors will not only increase the durability of batteries, but also the efficiency of energy use. Disadvantages of supercapacitors include the higher cost of production and lower power density, which is expected to be overcome in future research and development.
REFERENCES:
Béguin, F., &Frąckowiak, E. (2013). Supercapacitors: Materials, systems, and applications. Weinheim: Wiley-VCH.
Eddahech, A., Briat, O., Ayadi, M., & Vinassa, J. (2014). Modeling and adaptive control for supercapacitor in automotive applications based on artificial neural networks. Electric Power Systems Research, 106, 134-141. doi: 10.1016/j.epsr.2013.08.016
Monteiro, J., Garrido, N., & Fonseca, R. (2011). Efficient supercapacitor energy usage in mobile phones. Paper presented at the 318-321. doi: 10.1109/ICCE-Berlin.2011.6031796
Narayanan, R., Kumar, P. N., Deepa, M., & Srivastava, A. K. (2015). Combining energy conversion and storage: A solar powered supercapacitor. Electrochimica Acta, 178, 113-126. doi: 10.1016/j.electacta.2015.07.121
Vellacheri R., Al-Haddad, A., Zhao, H, Wang, W., Wang, C., Lei, Y. (2014). High performance supercapacitor for efficient energy storage under extreme environmental temperatures. Nano Energy (2014) 8, pp. 231–237
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1. INTRODUCTION
Supercapacitor is an efficient device for storage of energy, which has been increasingly popular in recent years. Different from traditional chemical batteries, supercapacitor is a device that goes between traditional capacitors and batteries. Since no chemical reaction occurs in the energy storing processes, the storage process is reversible. Therefore, a supercapacitor can be charged and discharged for hundreds of thousands of times, with the use of porous electrodes and electrolyte between them. The advantages of supercapacitor include adequate power density, short time required for charging and discharging, as well as long life cycles. Within ten minutes of charge a supercapacitor can store 95% of its designated capacity. Meanwhile, there is little “memory effect” in its life cycle. The efficiency of energy transfer is also higher with minimized losses, reaching 90% of power efficiency (Béguin&Frąckowiak, 2013). The reason why supercapacitors are super is the size of the porous electrodes. Special design enables supercapacitor to have much larger electrode surface areas, thus significantly increasing the capacity of it. In addition, supercapacitor is also environmentally friendly, as the production, usage, storage and disassembly processes of it have little influence on the environment, unless leakage of electrolyte occurs due to poor maintenance.
http://www.51due.net/writing/research-paper/sample32341.html
There are three key factors that determine the performance of a supercapacitor, which are its electrodes, electrolytes as well as the operating environment. Although there has been extensive research down to improve the former two characteristics, there have not been equivalent effort made to study the performance of supercapacitors under varying operating conditions. Temperature is the most influential environmental factor for supercapacitor performances.There are many occasions where supercapacitors have to operate under cold and hot temperatures, since it is most widely applied to vehicles. As a result, many of the supercapacitors that are designed and tested for room temperature would not be applicable for outdoor use in winter and hot summers. The major reason for reduced performance is the influence of temperature on aqueous and non-aqueous electrolytes. Under low temperatures, the efficiency for electrolytes, even organic ones, will be significantly reduced with thousands of times of increased resistance. There have been some efforts in reducing the influence of temperature on supercapacitors in recent years. In this paper, the research by a group from Ilmenau University of Technology will be introduced. They designed a new supercapacitor using an innovative combination of graphene-based electrode andLi2SO4-based aqueous electrolyte (Vellacheri et al, 2014).This combination has effectively increased the performance of supercapacitors within a temperature range between -20°C and 45°C.
2. FEATURES
2.1 Cyclic Voltammogram Analysis
Figure 1.Cyclic Voltammograms of ElectrodeCells.
The design team has performed a series of tests to investigate the property of the newly designed battery. To see how are the charge-storage properties of the electrodes, symmetric two-electrode cells are fabricated after the graphene-based electrodes were made. These cells then underwent a series of cyclic voltammetry and galvanotactic charge and discharge. In figure 1, the cyclic voltammograms of the cells at different temperatures are shown. Room temperature (RT), 45°C, 0°C and -20°C were used, since they cover a range of the most frequent operating temperature of supercapacitors. The cyclic voltammograms all have shapes that are approximate to a rectangle. Similar results were obtained when the voltage of the experiment was increased in a range between 5 to 200 mV/s.
The near-rectangular shapes of the diagrams mean that the behavior of the electrode cells is almost ideal for a supercapacitor, due to the efficient transmission of charge in these electrodes as well as the efficient design of a double-layered charge system. These features of the cells would ensure that the electrode is easily accessible by ions, even when the temperature is far from RT. In addition to accessibility, electrical resistance is also a major factor of concern for the electrodes. The charge storage unit of a good supercapacitor must be low in electronical resistance, and high in the conductivity of ions, so that the supercapacitor would work smoothly. Building on these advantages, the electrodes tested also maintained stable capacitive currents, under different temperatures. Under temperature higher than RT, which is 45°C, an increase in capacitive current is observed, which is a result of higher rates of ion transmission under heat. The ions are then activated to reach more areas in the surface of the electrode cells. Similarly, the capacitive current dropped slightly under cold temperatures, due to the reduced icon activity.
2.2 Retention of Specific Capacitance
Figure 2.Galvanotactic Charge and Discharge Profile.
Some of the supercapacitors that performed exceptionally also experience a drastic drop in performance under cold temperatures. Figure 2 shows the galvanotactic charge and discharge profile of the supercapacitor. The experiment was performed under a density of current of 1mA/cm2. The reliability of the supercapacitor is shown through the symmetrical shape of the diagrams, as well as the constant slope of the graphs. Based on the profiles, specific capacitances of the electrodes are calculated. The value of specific capacitance at 45°C is the highest, 99F/g. at RT, the specific capacitance drops to 91F/g. the value further drops to 80F/g at 0°C and 74F/g at -20°C. Comparing the lowest value with the highest, a 25% drop is obtained.
Although this value is still no the not ideal situation, it is already an improvement compared to other temperature sensitive supercapacitors. The percentage of retention of 75% shows promising prospects for future improvements on the technology. In figure 3. Different current densities are added to the discussion. The graphs show the trend of specific capacitances under different current densities. Ideal charge storage properties are shown from the small IR drop and high specific capacitance in the curves. The electrodes designed can both maintain ion diffusion paths effective and ensure a high electrical conductivity, so that the performance of the supercapacitor under different temperatures are ensured. The energy densities of supercapacitors are also calculated for different operating temperatures, which are: 3.44, 3.16, 2.78 and 2.57 Wh/kg at 45°C, RT, 0°C and -20°C respectively. Although the value of 2.57 is still a 25% drop compared to the highest value, and a 20% drop compared to RT, it is already proven to be much better than most of the previously designed supercapacitors.
2.3 The Charge Storage Process
Figure 3. Influence of Temperature and Current Density.
To further understand the characteristics of the supercapacitor and temperature related aspects, a correlation between charge storage and temperature should be established, so that it can better adapt to practical situations. The process of charge storage in graphene-based electrodes happens by the repeated formation and deformation of an electrochemical double layer at the interface between electrode and electrolyte. This process happens both during charging and discharging. When the supercapacitor is being charged, the ions transmit from the electrolyte to the electrodes, forming the double layer at the interface between the two materials. This process is weakened, as seen in Figure 3, by the decreased temperature and the increased current density. The transmission of ions is thus hindered in some way under such circumstances.
Figure 4. Arrhenius-type Plots.
In Figure 4, an Arrhenius-type equation is used so that the charge storage situation is better understood. A plot of ln C (C is the charge stored during charging) and 1/T (T being the absolute temperature) is thus created. Ea (activation energy) is thus obtained from the slope of the plots. The calculated values of Ea for different current densities range from 0.82 to 1.88 kcal/mol (from 1 to 5 mA/cm2). These values are much smaller compared to the graphene-based supercapacitors with ionic liquid electrolyte, which mean that the supercapacitor designed using Li2SO4-based aqueous electrolyte has much more superior properties than other type. With a lower Ea, it is much easier for ions to form the electrochemical double layer, which is critical for the efficiency of charge storage.
2.4 Supercapacitor Cycle Life
Figure 5. Cycle Life Test
Another important aspect of supercapacitor is the cycle life, since it is a critical feature in practical application. To measure the cycle life of the supercapacitor, the specific capacitance after different numbers of cycles are plotted in figure 5. The current density used in the graph is 4mA.cm2, and the number of cycles measured are 5000. From the plots, no significant drop in specific capacitance is observed. Under different temperatures, the specific capacitance of the supercapacitor all remained stable, with a slight drop after 1000 cycles under 45°C. The long cycle life of the supercapacitor is contributed by the high electrochemical stability of graphene, even when the temperature is 45°C. In addition, the property of the Li2SO4-based aqueous electrolyte are compatible with the electrode, making the combination optimal for sustaining a long cycle life.
2.5 Electrochemical Behavior
Figure 6. Electrochemical Behavior
To understand the electrochemical behavior of the supercapacitor, electrochemical impedance spectroscopy has been done at various temperatures as indicated in Figure 6. From the Nyquist plots, charge transfer resistance and diffusion controlled kinetics are shown in separated sections of the graphs, which are either high or low frequencies. In the high frequency region, which is represented by the semicircle part of the graphs, the diameter of the semicircle indicates the variation of the supercapacitor performances. With smaller circles, the variation of the performance is also smaller, leading to higher stability and reliability. The low frequency region is represented by the straight-line parts of the graphs. From the diameter of the circles, the position as well as the slope of the lines, the charge transfer resistances are calculated to be 0.95 Ω, 1.24 Ω, 1.62 Ω and 2.06 Ω at RT, 45°C, 0°C and -20°C respectively. The vertical shape of the plots is another indicator of the supercapacitor performance, with the line being more vertical, the supercapacitor is also more ideal. Consistency of the specific capacitances during the charge and discharge processes also reaffirms the performance. As the temperature dropped from RT to -20°C, the ESR increased 3.2 times, which is a relatively minimal influence on the power density of the supercapacitor. Overall, the combination of graphene and Li2SO4 proves to be an ideal set of supercapacitor design.
3. APPLICATIONS
3.1 Supercapacitors in Mobile Devices
Supercapacitors can also be applied in mobile devices, which will enable devices such as mobile phones to be fully charged within minutes. Such an application will solve the problem of the increasingly high dependence of people on their mobile phones with limited power capabilities. Since the design of the mobile phones are growingly sleeker in recent years, the room left for battery is increasingly limited. In addition, a common lithium battery will degenerate after two years of use. Compared to batteries, supercapacitors are much more durable, as shown from the above discussions. Even after 5000 times of charge and discharge cycles, supercapacitors are still fully functional. Once batteries are replaced by supercapacitors, mobile devices will not need to be charged in a daily basis. Mobile devices using supercapacitors are easily charged in seconds, with increased durability (Monteiro, Garrido, & Fonseca, 2011). The supercapacitor will not degenerate even after thousands of cycles. Taking an average of 10 times of charge and discharge cycles, supercapacitors can be used for decades. Since the supercapacitors are using physical processes in operation, the efficiency is also much larger than chemical batteries. However, the technology is still far from mass production due to its cost. More research is needed to lower the cost of supercapacitors and make it accessible to the market.
3.2 Applications in Solar Energy
The increased range of temperature makes supercapacitors more applicable for outdoor usage, since the performance is insured even when the temperature goes below 0 degrees or above 40 degrees. EDLC supercapacitors can be fully charged within a very short period of time. However, the current supercapacitors in the market are too expensive to be applied in a wider range. Therefore, most of the supercapacitors are used as an auxiliary energy source. As a small PV (photovoltaic) system, the current consumption of Solar Lamp’s regulator should be smaller than 1% of its working current. Therefore, low energy consuming components should be selected for the regulator. Adding a supercapacitor to the PV system will ease the pressure on the battery and increase the life of the system (Narayanan, Kumar, Deepa, & Srivastava, 2015).
The output power of solar battery is highly dependent on weather conditions, which are highly fluctuating over time. Such instability in the charging current has posed a threat on the battery life, increasing the cost of the system directly. The increased production and use of battery will also lead to more environmental pollutions. Therefore, a medium system is effective in mitigating the influence of instability on the battery, through the use of supercapacitors. Since supercapacitors can be charged and discharged at a much faster rate, without causing much damage to itself, the control system will use supercapacitors to generate a steady output current to the batteries. When the sunlight is instable, the supercapacitors will be charged first, so that the batteries are not directly influenced. Such a system will enable the supercapacitors to power the road lamps even when there is no sunlight, increasing the period of lighting.
3.3 Automotive Industry
Currently, supercapacitors are most widely used in the automotive industry. The increased range of operating temperature make supercapacitors part of the practical solutions in hot and cold areas of the world. In addition to the reduced influence of temperature, supercapacitors can also be charged as discharged within minutes. In the automotive industry, the intelligent start and stop control system brings a wide platform of application for supercapacitors. For motors which use hybrid powers, the discharge process will lead to drastic drops of charge, due to the frequent start and stop of the vehicles. The energy drawn from the battery during normal driving is relatively lower, while the energy required for acceleration is higher. With the traditional battery technology, a balance must be achieved between power density and cycle life. As a result, compromises have to be made.
A special electric generator can be used to solve the problem. During the braking process, the generator can fully charge the supercapacitor within seconds. Then, the fully charged supercapacitor will provide power for all the systems in the vehicle. Once the supercapacitor runs out of energy, batteries will be used instead. In addition to supplying power for other systems in the vehicle, supercapacitors can also charge the battery through slow discharge. With the coordination of the two, there is no longer need for an engine as ideal energy recycling is achieved. Such a system will result in a reduction in oil consumption of as high as 10% (Eddahech, Briat, Ayadi, & Vinassa, 2014). Although supercapacitors have undergone continuous improvements over the years, with increasing power density, it still cannot replace batteries. The biggest disadvantage of supercapacitors is its speed of auto-discharge, which is much faster than batteries. Without a battery, a supercapacitor powered vehicle would not be started after being parked for a few days. The features and disadvantage of supercapacitors make it perfect for a hybrid power system currently.
Thus, a dual system is designed to resolve the conflicting needs of sudden acceleration and normal driving. The major system is in charge of providing the best mileage, while the auxiliary energy system will provide temporary energy supply when the cars are accelerating and climbing. Taking advantage of the supercapacitor to be charged and discharged rapidly, the braking energy can be restored in them and reused in driving. With the use of supercapacitors, therefore, the energy can be recycled and stored in the auxiliary energy system, significantly increasing the energy efficiency of the system. Due to the low power density, supercapacitors are not ready to replace batteries in the major system. Although supercapacitors are not able to act as the major source of power currently, it is obviously advantageous acting as the auxiliary energy source. A combination of battery and supercapacitor system will result in a notable increase in the usage life of battery. Compared to batteries, supercapacitors are able to absorb the motion energy created in the braking and acceleration of vehicles, which will further increase the mileage of the vehicles.
However, a balanced design of different components is necessary to achieve the best improvements in performance. Without a proper design, the large amount of energy stored in the power system will lead to increased risks of explosion. The safety concerns are also increased due to the rapid discharge rate and the inner resistance which is too low. The low operating voltage has also limited the application of supercapacitors. These problems should not be overlooked. There have been cars developed in recent years using supercapacitors. The features of energy saving and fast discharge speed makes vehicles using supercapacitors adaptable to different types of markets and satisfying varying needs of consumers.
4. CONCLUSIONS
Inexpensive and reliable energy sources have been the pursuit of researchers for decades. The new type of supercapacitor introduced in this paper is a significant step forward in the field. The Cyclic voltammetry and galvanotactic charge and discharge plots have shown an almost ideal energy storing device. The property of temperature endurance under both high and low temperatures have further widened the range of application for the technology. Under the temperature of -20 degrees Celsius, the rate of efficiency retention is calculated to be 80%, which is better that most of the other supercapacitors in the current market. Based on the advantages of this design and other intrinsic features of supercapacitors, applications in the mobile devices, solar energy and automobile industry are promising. The use of supercapacitors will revolutionize the mobile phone industry, due to the significantly reduced charging time and the much longer “battery” life. In the solar panel field, the temperature endurance is further highlighted, using supercapacitors as regulators of current to increase the life of the entire system, directly protecting the environment. Similarly, in the automotive industry, the use of supercapacitors will not only increase the durability of batteries, but also the efficiency of energy use. Disadvantages of supercapacitors include the higher cost of production and lower power density, which is expected to be overcome in future research and development.
REFERENCES:
Béguin, F., &Frąckowiak, E. (2013). Supercapacitors: Materials, systems, and applications. Weinheim: Wiley-VCH.
Eddahech, A., Briat, O., Ayadi, M., & Vinassa, J. (2014). Modeling and adaptive control for supercapacitor in automotive applications based on artificial neural networks. Electric Power Systems Research, 106, 134-141. doi: 10.1016/j.epsr.2013.08.016
Monteiro, J., Garrido, N., & Fonseca, R. (2011). Efficient supercapacitor energy usage in mobile phones. Paper presented at the 318-321. doi: 10.1109/ICCE-Berlin.2011.6031796
Narayanan, R., Kumar, P. N., Deepa, M., & Srivastava, A. K. (2015). Combining energy conversion and storage: A solar powered supercapacitor. Electrochimica Acta, 178, 113-126. doi: 10.1016/j.electacta.2015.07.121
Vellacheri R., Al-Haddad, A., Zhao, H, Wang, W., Wang, C., Lei, Y. (2014). High performance supercapacitor for efficient energy storage under extreme environmental temperatures. Nano Energy (2014) 8, pp. 231–237
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