- Characteristics and advantages of supercapacitor
The supercapacitor stores energy in the separated charge. The larger the area used to store the charge, the denser the separated charge, and the greater its capacitance.
The area of the traditional capacitor is the flat area of the conductor. In order to obtain large capacity, the conductor material is rolled for a long time, and sometimes a special organizational structure is used to increase its surface area. Traditional capacitors use insulating materials to separate their two pole plates, usually plastic film, paper, etc. these materials are usually required to be as thin as possible.
In the traditional energy storage element, the power of the capacitor is high and the energy is low, while the battery is just the opposite. When they are used under the conditions of high temperature and high cycle, they will shorten their service life, and when they are used under the conditions of short-term and high power and energy, they are cumbersome and expensive. Supercapacitor overcomes the above shortcomings. Its power density is much higher than that of ordinary battery, and its energy density is also much higher than that of conventional capacitor. It has the following characteristics.
(1) The capacitance is large. The super capacitor uses activated carbon powder and activated carbon fiber as polarizable electrode, and the contact area with electrolyte is greatly increased. According to the calculation formula of capacitance, the larger the surface area of the two plates, the greater the electrical capacity. Therefore, the capacity of general electric double-layer capacitors can easily exceed 1F. Its emergence has suddenly increased the capacity range of ordinary capacitors by 3 or 4 orders of magnitude. At present, the maximum capacity of single supercapacitors can reach 5000f.
(2) The contradiction between high specific power and high specific energy output of storage equipment is properly solved. With high power density, the internal resistance of supercapacitor is very small, and the rapid storage and release of charge can be realized at the electrode / solution interface and in the electrode material body. Therefore, its output power density is as high as several kW / kg, which is unmatched by any chemical power supply and dozens of times that of general storage battery. Generally speaking, the specific power of an energy storage system with high specific energy is not high, while if the specific power of an energy storage system is high, its specific energy is not necessarily high, as is the case with many battery systems. The supercapacitor can provide high specific power of 1kW / kg ~ 5kW / kg, and its specific energy can reach 5W · H / kg ~ 20W · H / kg. Combined with the battery pack, it can form an energy storage system with high specific energy and high specific power output.
(3) The charging time is short and the charging and discharging cycle life is very long. The super capacitor can be charged in tens of seconds at the shortest time, and the longest charging time is less than ten minutes, which is much faster than the charging time of the battery. The super capacitor has no electrochemical reaction in the process of charge and discharge, so its cycle life can reach tens of thousands of times, which is far longer than the charge and discharge cycle life of the battery, up to 500000 times, or 90000 h, while the charge and discharge life of the battery is difficult to exceed 1000 times.
(4) It can provide high discharge current. For example, the rated discharge current of 2700f supercapacitor is not less than 950A, and the peak discharge current can reach 1680A.
(5) It can work normally in a wide temperature range (- 40 ℃ ~ + 70 ℃), while the battery is difficult to work in high temperature, especially low temperature environment.
(6) It can be used in parallel to increase the capacitance. For example, it can also be used in series after voltage equalization.
(7) Long storage life. After the super capacitor is charged, although there is also a small leakage current, the ion or proton migration movement inside the capacitor is generated under the action of electric field, there is no chemical or electrochemical reaction, no new substances are generated, and the electrode materials used are also stable in the corresponding electrolyte. Therefore, the storage life of the super capacitor can be regarded as almost unlimited.
(8) High reliability. There are no moving parts in the working process of the super capacitor, and there is little maintenance work, so the reliability of the super capacitor is very high.
- Application of super capacitor in automobile
Supercapacitors have a wide range of applications. Combined with high energy density materials such as fuel cells, supercapacitors can provide rapid energy release and meet high power requirements, so that fuel cells can only be used as energy sources. At present, the energy density of supercapacitors can be as high as 20kW / kg, which has begun to seize this part of the market between traditional capacitors and batteries.
In those applications that require high reliability and low energy requirements, supercapacitors can be used to replace batteries, or supercapacitors and batteries can be combined to be used in occasions with high energy requirements, so that smaller and more economical batteries can be used.
Super capacitor can absorb large current quickly. Compared with the principle of chemical charging, the working principle of super capacitor makes the performance of this product more stable. Therefore, the service life of super capacitor is longer. For devices that need fast charging, such as power tools and toys, supercapacitors are undoubtedly an ideal power supply.
The super capacitor has large enough capacity, low cost and no pollution to the environment. High power super capacitor is of great significance for the start, acceleration and uphill driving of electric vehicles: it can quickly provide high-power current when the vehicle starts and climbs; When the vehicle is running normally, it is quickly charged by the battery; When the vehicle brakes, the large current generated by the generator can be quickly stored, which can reduce the limitation of electric vehicle on large current charging of battery, greatly prolong the service life of battery and improve the practicability of electric vehicle. In view of the importance of electrochemical supercapacitors, industrial developed countries have attached great importance to them and become key strategic research and development projects in various countries.
2.1 application and development of super capacitor in pure electric vehicle
The influence of super capacitor on the dynamic performance of the whole vehicle mainly lies in the influence on the driving range. The capacity, energy density, discharge depth, power density and other performance parameters of supercapacitor will affect the energy consumption and driving range of vehicles.
At present, electric vehicles with low pollution and energy saving have attracted considerable attention in the world. Among the components of electric vehicles, supercapacitors have become one of the important directions of electric vehicle development because of their long service life and strong safety. This electric bus with capacitor as energy has no pollution, zero emission and good low temperature characteristics. It is suitable for the operation of public transportation in northern cities and has good market prospects and social benefits.
The application of supercapacitors to electric buses has become a very hot topic. Since the bus line stops are fixed and the charging time of the supercapacitor is very short, which can be completed within 1min, the charging time of the bus can be used, which will not affect the passenger’s travel time, and there must be two “braids” on the roof like the current tram, which also saves the cost of setting the tram track and looks more beautiful. One disadvantage of supercapacitor is its low energy density. It can only run 2025km at a time, but it has fast charging speed and can continue to run after charging.
2.2 application of super capacitor in hybrid electric vehicle
The power system of hybrid electric vehicle takes the fuel engine as the main power, and its electric energy storage system is usually the secondary power supply. The use of super capacity capacitor auxiliary starting device in the electric starting system of diesel locomotive shows prominent advantages, which are shown in:
(1) Due to the increase of starting power, the starting time of diesel generator set is shortened. The rotation acceleration of diesel engine increases, which improves the ignition quality of fuel.
(2) The maximum current load of the battery pack at startup is reduced, which helps to prolong the service life of the battery.
(3) The reliability of start-up is ensured, especially at low temperature and when the battery pack loses power or parameters deteriorate.
(4) Under the existing battery technology, the battery capacity can be effectively reduced.
But supercapacitors cannot completely replace batteries because of their low energy density. The working voltage of supercapacitor monomer is low, so it is necessary to connect multiple capacitor monomers in series to obtain a higher working voltage. However, multiple monomers in series have high requirements for the unity of monomers, and the capacity of the system will be doubled after being connected in series. At present, many processes in this field are still under development.
The characteristics of super capacitor just meet the special requirements of hybrid electric vehicle. Using the instantaneous high power characteristics of super capacitor, the special requirements of frequent engine start and instantaneous high power provided by battery are avoided. At the same time, the braking energy can be recycled, which can save energy and reduce emission pollution. It is especially suitable for hybrid electric vehicles that often drive in cities. In terms of recovering braking energy, at least 30% of the energy of the car is consumed due to heat dissipation and braking during driving, especially in cities, which often encounter red lights, which not only causes energy waste, but also increases environmental pollution. If the energy consumed by braking can be recovered for vehicle starting and acceleration, it can be said to kill two birds with one stone. Because the battery charging is completed through chemical reaction, it takes a long time, but the braking time is short, so the effect of energy recovery is poor. The unique characteristics of super capacitor are very suitable for energy recovery in the braking process, with low cost and broad application prospects.
In terms of providing instantaneous high power for the cold start of the engine, the cold start of the engine puts forward special requirements for the battery. The battery must provide instantaneous high power before the engine can start. However, the general battery does not have this characteristic, unless the starting ignition battery is used, but the starting ignition battery is not suitable for long-term low current working environment, and it often fails at low temperature, so it is not suitable. It is found that this problem can be solved if the super capacitor and battery are combined in the engine starting system to give full play to the unique characteristics of super capacitor and form a new starting system.
- Precautions for use of super capacitor
Precautions for the use of supercapacitors include:
(1) Supercapacitors have a fixed polarity. The polarity shall be confirmed before use.
(2) Super capacitors should be used under nominal voltage. When the capacitor voltage exceeds the nominal voltage, it will lead to electrolyte decomposition, while the capacitor will heat, reduce capacity, increase internal resistance and shorten service life. In some cases, it can lead to capacitor performance collapse.
(3) Supercapacitors cannot be used in high-frequency charging and discharging circuits. High-frequency fast charging and discharging will lead to internal heating, capacity attenuation and internal resistance increase of the capacitor, which will lead to the collapse of the performance of the capacitor in some cases.
(4) The service life of supercapacitor and the external ambient temperature have an important impact on the service life of supercapacitor. Capacitors should be kept away from heat sources as far as possible.
(5) The voltage drop when the supercapacitor is used as the backup power supply. Because the supercapacitor has the characteristics of large internal resistance, there is a voltage drop at the moment of discharge, △ v = IR.
(6) For the ambient gas in use, the supercapacitor shall not be located in places with relative humidity greater than 85% or containing toxic gas. These environments will lead to corrosion of leads and capacitor shell, resulting in open circuit.
(7) For the storage of supercapacitors, supercapacitors should not be placed in high temperature and high humidity environment, but should be stored in the environment with temperature of – 30 ℃ ~ + 50 ℃ and relative humidity of less than 60%, so as to avoid sudden rise and fall of temperature, because this will lead to product damage.
(8) For the use of super capacitor on double-sided circuit board, when super capacitor is used on double-sided circuit board, it should be noted that the connection can not pass through the accessible place of the capacitor. Due to the installation mode of super capacitor, it will lead to short circuit.
(9) When the capacitor is welded on the circuit board, do not touch the capacitor shell on the circuit board, otherwise the weldment will penetrate into the threading hole of the capacitor and affect the performance of the capacitor.
(10) After installing the super capacitor, do not tilt or twist the capacitor forcibly, which will lead to looseness of the capacitor lead and performance degradation.
In addition, avoid overheating the capacitor during welding. If the capacitor is overheated during welding, the service life of the capacitor will be reduced. For example, if a printed circuit board with a thickness of 1.6mm is used, the welding process shall be 260 ℃ and the time shall not exceed 5S. After the capacitor is welded, the circuit board and capacitor need to be cleaned, because some impurities may cause short circuit of the capacitor.
When capacitors are used in series, there is a problem of voltage balance between monomers. Simple series will lead to overvoltage of one or several monomeric capacitors, which will damage these capacitors and affect the overall performance. Therefore, when capacitors are used in series, they need the technical support of the manufacturer.
The appearance of supercapacitor solves the contradiction between power density and energy density in energy system. With the further development of supercapacitor technology, it will replace the current frequently replaced battery, and the household energy storage system may also be realized. As an energy storage system with huge energy storage, fast charging and discharging speed, wide working temperature range, safe and reliable operation, no maintenance and low price, if it can be widely used in power system, it will promote technological progress and achieve greater economic benefits.