Supercapacitors are not a strange term in the field of new energy. In fact, supercapacitors have been in the field for decades. Although its application form is different from that of batteries, it is always replaced by batteries in practical applications. In addition, it faces the disadvantages of high cost and technical difficulty. However, once the breakthrough in the technology of supercapacitors, it will have a great impetus to the development of the new energy industry. Therefore, despite the difficulties in the development process, the significance of overcoming it is significant.
The current status of supercapacitors
Supercapacitors have experienced more than 30 years of development since their birth. At present, miniature supercapacitors are widely used in small mechanical devices, such as computer memory systems, cameras, audio equipment, and auxiliary facilities for intermittent use of electricity. Large-sized columnar supercapacitors are used in the automotive field and natural energy harvesting, and it is expected that supercapacitors will have great potential in the future market in these two fields.
Long service life, strong environmental adaptability, high charge and discharge efficiency, and high energy density are the four distinctive features of supercapacitors, making it one of the most worthwhile topics in the world today. At present, the main research countries of supercapacitors are China, Japan, Korea, France, Germany, Canada and the United States. In terms of manufacturing scale and technical level, Asia is temporarily leading.
However, the development of supercapacitors has been shrouded in the shadow of batteries (mainly nickel-metal hydride batteries, lithium batteries). The development of nickel-metal hydride batteries and lithium batteries is greatly facilitated by the huge amount of financial support from the government and large investors, and it is easier to focus on the world. In contrast, supercapacitors are difficult to get strong financial support, and technological progress and development are subject to a large degree of constraints. This makes it a lot of cold in many areas.
The opportunity for the supercapacitor and the battery to level the gap
Although the manufacturing cost of supercapacitors is reduced by less than 10% per year, this technology still cannot expand production scale in the transportation industry and natural energy collection. Compared with the battery field, the technology of supercapacitors is too backward. To reduce the gap between the two in research and development, the first task should solve the following problems:
■ Increase the number of supercapacitor manufacturers and stimulate the development of related technologies through market competition;
■ Expand the production scale of high specific power supercapacitors and achieve annual production exceeding one million pieces;
■ Reduce the current manufacturing cost of supercapacitors by 50%;
■ Develop a supercapacitor sustainable development strategy, mainly for the exploration of more efficient electrode materials.
To achieve the above goals, manufacturers need to invest year by year in the supercapacitor market, mainly for the development and production of equipment. At the same time, the government's expansion of funding and technical support will also play a crucial role.
Analysis of application prospects of super capacitors
Super capacitors are an excellent battery! In the future, the energy storage density can be increased by another 10-100 times!
At present, the storage density of ordinary batteries is 0.02 kWh/kg, while the supercapacitor can reach 10 or 20 kWh/kg, which is 500-1000 times that of ordinary lead batteries! The future can be further improved! And the speed of charging and discharging is extremely fast, it only takes a few seconds!
In the past, a lead-acid battery of 50 kilograms can only store one kilowatt of electricity, and it will be broken after a long time, and the charging and discharging time is particularly long.
Now, if a supercapacitor battery is still 50 kilograms, it can store 500-1000 kWh, which is enough for the average car to run 5000 kilometers! Even a bus can run nearly 2,000 kilometers! If you press the standard of the current car, add 600 times of oil calculation, calculate the standard power consumption of 15 degrees per 100 kilometers, you can store 100 degrees of electricity, then you only need 5-10 kg of super capacitor battery. Yes! So, in this way, the car can already be used very well!
In the future, the graphene supercapacitor battery will be further invented, and the capacity will be further expanded ten times! That will be even better in the future!
In short, from the current technology point of view, it is already possible to have the development value of commercial electric vehicles! It is estimated that a super battery with a running distance of 600 kilometers can be installed on a single car. The cost is only about 1-2 million yuan. The charging will be simpler and faster, and it can be completed in a few seconds. It is non-polluting and can be used for life without intermediate replacement. It will be better in the future and it can be used completely! Moreover, there is another advantage that it can be converted into electric energy by the energy of the brakes and stored, and stored by wind energy and solar power, which is more energy-saving and the brake fluid is safer and more reliable.
In short, the future of electric vehicles will be born, you can use this technology to develop your own industry, to win a place for China!
Since battery technology has been overcome, it should be further improved, manufactured, and eventually sold to the user's own electric car! Then, you can make a very huge electric vehicle industry and get green development for China! It can completely eliminate urban automobile exhaust pollution, reduce the consumption of gasoline and diesel for hundreds of millions of tons, and reduce dependence on Middle East oil! Bring the wings of China's economic development!
We should continue to pay attention to this technology, this industry, timely cut into! In addition, it is the graphene industry, information technology transformation industry, new computer industry, intelligent software industry, modern agriculture, titanium alloy industry, upgrading and upgrading of traditional industries, etc. These will be the foundation of China's future development!
The predictability of supercapacitors in the future
Undoubtedly, supercapacitors rely on their own longevity, high charge and discharge efficiency and other significant features, only to find the right soil for their own development, the future development potential is huge.
For the development of the next decade, supercapacitors will be an important part of the transportation industry and natural energy collection. Among them, the supercapacitors used to assemble vehicles in the start-stop system will become their main sales channels in the future. The global market in 2016 will reach $270 million and will exceed $350 million in 2020.
Development Trend Analysis of Super Capacitor in Electric Vehicle
The supercapacitor-battery composite power system combines the advantages of supercapacitor and battery, which not only improves the instantaneous power characteristics of the electric vehicle, but also avoids large current discharge of the battery, prolongs the service life of the battery, and increases the driving range of the electric vehicle. It is an important development direction for super capacitors in the field of electric vehicles and has broad market prospects.
Due to the dual pressures of environmental pollution and the oil crisis, electric vehicles have gradually become an important green vehicle in people's lives. The power source is the source of energy for electric vehicles, but current battery technology cannot fully meet the requirements of electric vehicles.
A supercapacitor is an energy storage component between a battery and an electrostatic capacitor. It has a much higher energy density than a electrostatic capacitor and a much higher power density than a battery, and is not only suitable for a short-time power output source, but also It can also be used to improve the motion characteristics when the electric vehicle starts, accelerates and climbs, because it has higher power, higher specific energy and more energy storage. In addition, the super capacitor has the unique advantages of low internal resistance, high charge and discharge efficiency (more than 90%), long cycle life (tens of thousands to 100,000 times), no pollution, and other energy components (engine, battery, fuel cell). Etc.) Working together to form a joint is an effective way to achieve energy recycling and reduce pollution, which can greatly improve the driving range of electric vehicles on one charge. Therefore, super capacitors have broad application prospects in the field of electric vehicles and will be one of the important directions for the development of electric vehicles in the future.
At present, Japan, the United States, Switzerland, Russia and other countries are stepping up the development of supercapacitors, and research on the application of supercapacitors in electric vehicle drive and brake systems, and the production and application of supercapacitors in China is still in its infancy.
1. Mechanism and characteristics of super capacitor
Ultracapacitor is a new type of energy storage component developed recently. It is a physical secondary power source with super power storage capability and powerful pulsating power. It is different from conventional capacitors and has a capacity of tens of thousands of methods. . Supercapacitors are mainly divided into three categories according to the energy storage mechanism: (1) an electric double layer capacitor generated by charge separation at the interface between the carbon electrode and the electrolyte; 2 using metal oxide as an electrode, which is produced by oxidation-reduction reaction on the electrode surface and the bulk phase. Reversible chemisorption of a Faraday capacitor; 3 a capacitor that undergoes a redox reaction by using a conductive polymer as an electrode.
Since the charge and discharge of the electric double layer capacitor is purely a physical process, the cycle number is high and the charging process is fast, so it is suitable for application in an electric vehicle. The double-layer supercapacitor is a new type of energy storage device that uses polarized electrolyte to store electrical energy. The principle structure is shown in Figure 1. When charging the electrodes, the surface charge of the electrodes in the idealized electrode state will attract the opposite ions in the surrounding electrolyte solution, causing these ions to adhere to the surface of the electrode to form an electric double layer, constituting the electric double layer capacitance. Since a supercapacitor has a much larger area for storing charge and a much smaller distance for charge isolation than a conventional capacitor, the capacitance of a supercapacitor unit is as high as several to tens of thousands of methods. Due to the special process, the equivalent resistance of the supercapacitor is very low, the capacitance is large and the internal resistance is small. The super capacitor can have a high peak current, so it has a high specific power, which is 50 to 100 times that of the battery, and can reach 10 kW/kg. This feature makes the super capacitor suitable for short-term high-power applications.
The supercapacitor has excellent charging and discharging performance. It can be charged to any voltage value at a very fast speed within the rated voltage range. When stored, all stored energy can be discharged, and there is no damage to the battery for rapid charging and discharging. problem. In addition, the super capacitor also has no pollution to the environment and high mechanical strength, good safety (fireproof, explosion-proof), maintenance-free during use, long service life (more than 10 years) and wide operating temperature range (30 °C ~ 45 °C) The advantages are the same, and there is a buffer function in the case of instantaneous high voltage and short circuit high current, and the energy system is relatively stable. The performance comparison between supercapacitor and lead-acid battery and common capacitor is shown in Table 1.
Application research status
Progress in applied research at home and abroad
Due to the superior performance of supercapacitors and the development of supercapacitors in recent years, supercapacitors have been widely used in the industrial field. At present, countries all over the world are scrambling to research and apply them more and more to electric vehicles. Supercapacitors have become a new trend in the development of electric vehicle power, and the composite power system composed of super capacitors and batteries is considered to be one of the best ways to solve the problem of electric vehicle power in the future.
Situation in Japan
Japan is a pioneer in the application of supercapacitors to hybrid electric vehicles. Supercapacitors are one of the important areas in the development of electric vehicles in Japan in recent years. Honda's FCX fuel cell-supercapacity hybrid is the world's first commercial fuel cell sedan, which was launched in 2002 in Japan and California. On June 24, 2002, Nissan produced a parallel hybrid truck equipped with a diesel engine, electric motor and super capacitor. In addition, a natural gas-super capacitor hybrid bus was introduced, which is 2.4 times more economical than the original natural gas vehicle. . At present, hybrid electric buses equipped with super capacitors have become a national research project in Japan.
The situation in Europe and America
The Swiss PSI Institute installed a 360 kW supercapacitor bank for a 48 kW fuel cell vehicle. The supercapacitor takes on all the transient power of the drive system during deceleration and start-up, assisting the fuel with a 15 kW rated pulse power of 50 kW. The battery works. The traction motor has a rated continuous power of 45kW and a peak power of 75kW. It uses a 360V DC power supply. The fuel consumption test conducted by the Volkswagen Bora test vehicle showed that its fuel consumption was less than 7L/100km, while the fuel consumption of the same quality BMW7 series was 10.7L/100km. In 1996, Eltran of Russia developed an electric vehicle with a supercapacitor as a power source. It uses 300 capacitors in series and can drive for 12km at a speed of 25km/h. The United States has made some progress in the research of supercapacitor hybrid vehicles. The supercapacitors developed by Maxwell have been well applied in various types of electric vehicles. The hybrid bus developed by the NASALewis Research Center in the United States uses supercapacitors as the main energy storage system.
China's current situation
At present, domestic research on electric vehicles with supercapacitors as the sole source of energy has made some progress. In July 2004, China's first “capacitor energy storage variable frequency drive trolleybus” was put into trial operation in Zhangjiang, Shanghai, and the bus used super capacitors. Compared with the characteristics of large power and fixed-point parking of public transportation, when the tram stops at the station, it can be quickly charged within 30s, and the power can be continuously supplied after charging, and the speed can reach 44km/h. In January 2005, Shanghai Jiaotong University signed an agreement with Yantai City, Shandong Province to jointly invest in the development of super capacitor bus. It plans to build a 12km demonstration line in Fushan District of Yantai and build an annual output of 10,000 new environmentally friendly super capacitors in Fushan High-tech Industrial Zone. The production base of the bus. The super capacitor electric bus developed by Harbin Institute of Technology and Jurong Group can accommodate 50 passengers with a top speed of 20km/h. However, the design and control of the super capacitor-battery composite power supply electric vehicle in China is basically in its infancy.
Topology of supercapacitors used in electric vehicles
Pure super capacitor electric vehicle
Directly using supercapacitor as the only energy source for electric vehicles, this method is simple, practical, low cost, and achieves zero emissions, so it is suitable for short-distance, fixed-line areas, such as tractors at train stations or airports. School and kindergarten delivery carts, park tour buses and electric buses.
Composite power electric vehicle
Supercapacitors can be combined with batteries, fuel cells, etc. to form a composite power system, but fuel cells are not yet available for practical use because of their high cost. Therefore, there are more researches on supercapacitor-battery composite power supply systems at home and abroad, and its topology is summarized as shown in Figure 2. The structure of Figure 2a is the simplest, but since there is no DC/DC converter, the battery and the super capacitor will have the same voltage, so that the super capacitor outputs and receives power only when the battery voltage changes rapidly, thus reducing the load balancing effect of the super capacitor. . Both Figure 2b and Figure 2c use a bidirectional OC/OC converter. The bidirectional DC/DC tracking in Figure 2b detects the terminal voltage of the battery to regulate the terminal voltage of the supercapacitor to match the two. Since the change in the battery terminal voltage is gentler than the terminal voltage of the super capacitor, for DC/DC, Figure 2b is easier to control than Figure 2c. Although theoretically more flexible, the control strategy for DC/DC is very precise and difficult to maintain.
Control strategy for composite power system
Speed constraint control strategy
When the vehicle starts, the supercapacitor should store more energy, and the super capacitor should be discharged to ensure the acceleration performance of the electric vehicle. When the vehicle is driving at a high speed, the super capacitor should store less energy to brake. More energy is received during the process. The energy stored in the supercapacitor is proportional to the square of the terminal voltage. Since the terminal voltage of the supercapacitor has a relatively large variation range, how to control the depth of discharge during discharge, in order to prepare for secondary discharge during driving or regenerative braking to recover charging, But you need to repeat the test in the experiment to get it.
Current constraint control strategy
During the driving process of the electric vehicle, the load current changes relatively much due to frequent acceleration, deceleration, and ups and downs. When the load current is too large to exceed the maximum discharge or charging current that the battery can withstand, in order to avoid the battery pack. Over-discharge or over-charge, need to be discharged or charged by the super capacitor, in order to improve the working state of the battery pack and extend its service life.
In order to avoid damage to the battery caused by excessive feedback current, a constant charging current braking mode can be adopted, that is, the battery charging current is the controlled object. This is a more practical control strategy for electric vehicles with battery single-supply systems. Since the battery voltage does not change significantly during regenerative braking, the rise in armature current is not too great. In the supercapacitor-battery composite power system, the super capacitor terminal voltage will change greatly during the single regenerative braking process. As the supercapacitor terminal voltage rises during the braking process and the motor back electromotive force decreases, The armature current will rise sharply, which may cause damage to the power device or even the motor. Therefore, a constant power strategy can be used when charging the super capacitor, that is, the charging power of the super capacitor during the regenerative braking process is controlled.
When the super capacitor voltage is low, charging with a large current is used. When the capacitor voltage rises, the charging current command value decreases, which can balance energy recovery and system device protection.
Integrated control strategy
The speed constraint control strategy can improve the dynamic performance of the vehicle. When the current constraint control strategy is adopted, the battery current can work within the specified range and protect the battery. These two control strategies have their own advantages and disadvantages, and adopt comprehensive control strategies. The comprehensive application of the speed constraint control strategy and the current constraint control strategy can take into account their advantages, not only can protect the battery, extend the service life of the battery, but also improve the dynamic performance of the vehicle.