Abstract: Supercapacitor electric vehicles (EVs) have established a new design concept for electric transportation vehicles due to their superior performance, low cost, and zero emissions. This paper reviews the basic principles and characteristics of supercapacitors and introduces their applications and development in pure electric vehicles and hybrid electric vehicles. Keywords: Supercapacitor; Pure electric vehicle; Hybrid electric vehicle; Application Currently, automobiles account for more than 90% of urban air pollution emissions, and countries around the world are searching for alternative fuels for automobiles. Due to the increasingly serious shortage of oil, people are gradually recognizing the importance of developing new types of vehicles that minimize exhaust emissions while using oil and other energy sources. Supercapacitors have high power density, short charging and discharging time, good high-current charging and discharging characteristics, long lifespan, and superior low-temperature characteristics compared to batteries. These excellent properties make them promising for applications in electric vehicles. For urban buses operating on routes within 20 kilometers, supercapacitor-powered electric vehicles can achieve a range of over 20 kilometers on a single charge, showing broad application prospects in urban public transportation. Electric vehicles belong to new energy vehicles and include three types: pure electric vehicles (BEVs), hybrid electric vehicles (HEVs), and fuel cell electric vehicles (FCEVs). It integrates the latest technologies from the fields of optics, mechanics, electronics, and chemistry, and is an integrated product of the latest achievements in engineering technologies such as automobiles, electric drives, power electronics, intelligent control, chemical power sources, computers, new energy, and new materials. Electric vehicles are not significantly different in appearance from traditional vehicles; the main difference lies in their power drive system. Electric vehicles use battery packs as energy storage power sources to provide electrical energy to the motor drive system, driving the motor and propelling the wheels forward. Although electric vehicles have lower climbing ability and lower speeds than traditional vehicles, they emit no pollution, have low heat radiation, low noise, do not consume gasoline, have a simple structure, and are easy to use and maintain. They are a new type of transportation, hailed as the "star of tomorrow," and are favored by countries around the world. 1. Introduction to Supercapacitors Supercapacitors , also known as electrochemical capacitors, are a new product that emerged in the late 20th century, with capacitances reaching farad levels. Based on the electrode materials used, there are currently three main types: high specific surface area carbon material supercapacitors, metal oxide supercapacitors, and conductive polymer supercapacitors. 1.1 Basic Principles Based on the different mechanisms by which electrochemical capacitors store electrical energy, they can be divided into electric double-layer capacitors (EDLCs) and pseudocapacitors. The energy storage mechanism of carbon-based supercapacitors mainly relies on the double layer formed near the carbon surface, hence the name electric double-layer capacitor. Metal oxides and conductive polymers, on the other hand, rely primarily on pseudocapacitors generated by redox reactions. The basic principle of an electric double-layer capacitor is to utilize the interfacial double layer formed between the electrode and the electrolyte to store energy—a novel type of electronic component. When the electrode and electrolyte come into contact, due to Coulomb forces, intermolecular forces, or interatomic forces, two stable layers of opposite charges appear at the solid-liquid interface, called the interfacial double layer. The size of the double-layer capacitance is related to the electrode potential and surface area. The electrodes of electric double-layer capacitors are typically composed of porous carbon materials with a high specific surface area. Carbon materials have excellent thermal and electrical conductivity, low density, good chemical corrosion resistance, and a small coefficient of thermal expansion. They can be prepared in various forms such as powder, granules, blocks, fibers, cloth, and felt through different methods. Pseudocapacitance occurs when electroactive materials undergo underpotential deposition on the electrode surface or in a two-dimensional or quasi-two-dimensional space within the bulk phase, resulting in highly reversible chemical adsorption/desorption or oxidation/reduction reactions, generating capacitance related to the electrode charging potential. Because pseudocapacitance occurs not only on the surface but also deep within the electrode, it can achieve higher capacitance and energy density than double-layer capacitance. For the same electrode area, pseudocapacitance can be 10 to 100 times greater than double-layer capacitance. Currently, pseudocapacitive electrode materials are mainly metal oxides and conductive polymers. 1.2 Differences from Traditional Capacitors and Batteries: The operating mechanisms of electrochemical capacitors and batteries differ fundamentally. For double-layer supercapacitors, charge storage is a non-Faraday process, meaning ideally no electron migration occurs across the electrode interface, and charge and energy storage is electrostatic. However, for batteries, a Faraday process essentially occurs, involving electron migration across the double layer, resulting in changes in oxidation state and the chemical properties of the electroactive materials. In general, charge storage processes have the following important differences: For non-Faraday processes, charge accumulation is accomplished electrostatically, with positive and negative charges residing at two separate interfaces. The intervening layer is a vacuum or molecular insulator, such as a bilayer, the mica film in an electrolytic capacitor, an air layer, or an oxide film. For Faraday processes, charge storage is accomplished through electron migration. The electroactive material undergoes chemical or oxidation state changes, which obey Faraday's law and are related to the electrode potential, potentially creating a quasi-capacitance. This energy storage is indirect. In terms of specific energy and specific power, supercapacitors fall between batteries and traditional capacitors, with significantly higher cycle life and charge/discharge efficiency. Due to their long lifespan, often exceeding that of the equipment using them, supercapacitors require no maintenance throughout their lifespan. Furthermore, they have relaxed environmental requirements after use, producing no pollution, hence they are also known as green energy. The advantages of supercapacitors for automotive energy storage devices include: supercapacitors are green energy and do not pollute the environment; chemical batteries, on the other hand, cause secondary pollution. Supercapacitors offer superior cycle life (approximately 100,000 cycles) compared to chemical batteries (200-1000 cycles) and are more prone to damage. They also boast faster charging speeds (0.3s-15min) and longer charging times (3-10 hours). Supercapacitors have higher charge/discharge efficiency (98%) than chemical batteries (70%). They also exhibit higher power density (1000-10000W/kg) compared to chemical batteries (300W/kg). Supercapacitors are completely maintenance-free, operate over a wide temperature range of -40°C to +70°C, and exhibit minimal capacity variation. Lead-acid battery electric vehicles experience a 90% reduction in range at 1°C, while supercapacitors only experience a 10% reduction. Supercapacitor-powered electric buses demonstrate high regenerative braking energy recovery efficiency, achieving up to 70% recovery during normal braking, compared to only 5% for chemical battery systems. Finally, they offer lower relative cost. While supercapacitors are twice as expensive as lead-acid batteries, their lifespan is approximately 100 times longer than that of chemical batteries, resulting in significantly lower overall operating costs for supercapacitor-powered electric vehicles compared to chemical batteries. 2. Application of Supercapacitors in Electric Vehicles Globally, approximately 500 billion transport vehicles operate on fixed routes via public transportation systems annually, with public transport vehicles remaining the most common mode of transportation. Sales in 2000 were 183,000 vehicles, and are projected to reach 220,000 vehicles annually over the next five years. The United States alone saw 40,000 vehicles sold. It is estimated that by 2010, the number of public transport vehicles will reach 650,000. If these vehicles are not modified and continue to use diesel or gasoline, the required fuel consumption will become a heavy burden, and the resulting air pollution will be significant. It is estimated that fuel cells will not be able to achieve large-scale production within the next decade. Leaving aside the exorbitant cost of fuel cells, my country's existing and soon-to-be-promoted projects using ethanol gasoline and natural gas vehicles are also plagued by high costs. Because the production cost of fuel ethanol is higher than that of gasoline, relevant national departments are formulating subsidy plans to bring the price of ethanol gasoline down to par with gasoline of the same octane rating. Research and discussion are underway regarding the fact that natural gas engines are several times more expensive than diesel engines of the same displacement. Officials from the Beijing Public Transport Corporation, which was among the first in China to mass-produce natural gas engines, acknowledged that currently, natural gas vehicles mainly meet the operational needs of the Chang'an Avenue route. Supercapacitors, however, solve this problem. They offer sufficiently large capacity, low cost, and no environmental pollution. High-power supercapacitors are crucial for the starting, acceleration, and hill-climbing of electric vehicles: they rapidly provide high-power current during startup and hill climbing; they quickly charge the battery during normal driving; and they rapidly store the large current generated by the generator during braking. This reduces the limitations of high-current charging of the battery, significantly extending battery life and improving the practicality of electric vehicles. Given the importance of electrochemical supercapacitors, developed industrial nations have given them high priority, making them a key strategic research and development project. 2.1 Application and Development of Supercapacitors in Pure Electric Vehicles The main impact of supercapacitors on the overall vehicle power performance lies in their effect on driving range. The performance parameters of supercapacitors, such as capacity, energy density, depth of discharge, and power density, all affect the energy consumption and driving range of a vehicle. The Institute of Electromagnetic and Electronic Technology at Harbin Institute of Technology has developed an electric bus using supercapacitors as energy storage devices. This type of electric bus can travel 25 kilometers continuously after only 15 minutes of charging, with a top speed of 52 kilometers per hour. It is reported that three projects undertaken by the institute, including the provincial "15th Five-Year Plan" major science and technology project—"Electric Vehicles Powered by Capacitors"—have passed the provincial science and technology department's appraisal. This research has reached the international advanced level in terms of driving range and top speed of electric vehicles powered by capacitors. The development of this supercapacitor electric bus is the first of its kind in China, and its performance indicators have reached the advanced level of similar international products. This project has achieved breakthroughs and innovations in vehicle control technology, electric drive technology, and capacitor management and balancing technology. It is understood that electric vehicles, which are less polluting and save energy, have attracted considerable attention internationally. Among electric vehicle components, supercapacitors have become an important direction in electric vehicle development due to their long service life and high safety. Electric buses powered by capacitors are pollution-free, emission-free, and have good low-temperature performance, making them suitable for public transportation in northern cities and possessing good market prospects and social benefits. Applying supercapacitors to electric buses has become a hot topic. Since bus routes and stops are fixed, and supercapacitors can be charged in a very short time (less than one minute), they can be charged while the bus is stopping at the station. This does not affect passenger travel time and avoids the need for two overhead wires on the roof like current trams, saving on track installation costs and improving aesthetics. One drawback of supercapacitors is their low energy density; a single charge only allows for one ride. However, their fast charging speed allows them to run continuously after a full charge. Compared with lead-acid batteries, this is much better. Lead-acid batteries take 5-8 hours to charge, so it is enough to build a supercapacitor electric bus charging station in a suitable location along the line. The cost of building such a charging station is much smaller than building a gas station, and it is also cheaper than building a gas station or lead-acid battery charging station of the same scale. 2.2 Application in hybrid vehicles Although pure electric vehicles have the above advantages, due to the limitation of battery capacity, the driving range and climbing and acceleration performance of the vehicles are not as good as those of ordinary cars. Although people have made great efforts in the research and development of batteries, it is difficult to achieve the driving range of 400-500 kilometers on a full tank of gas as ordinary cars [91]. To fully meet the desires of users, it is difficult to achieve this with the performance of existing battery storage devices alone, so hybrid electric vehicles have emerged. Hybrid electric vehicles (HEVs) are specifically designed and developed for urban public transportation. They can run on both electricity and gasoline, making them the most realistic industrial product for electric vehicles in the short term. Compared to traditional vehicles of the same type, these vehicles can reduce exhaust emissions by 50%-70% and fuel consumption by more than 30%, meeting increasingly stringent environmental requirements. They combine the energy-saving and low-emission characteristics of electric vehicles with the convenience of gasoline vehicles. Hybrid electric vehicles are mainly classified into two types according to their energy synthesis methods: series hybrid electric vehicles (SHEVs) and parallel hybrid electric vehicles (PHEVs). In a series hybrid system, the engine drives a generator, and the generated electricity is used to drive the wheels with an electric motor. That is, all the kinetic energy generated by the engine is first converted into electrical energy, which is then used to propel the vehicle. A parallel hybrid system uses both an engine and an electric motor to drive the wheels, utilizing these two power sources as needed. Because the power sources are parallel, it is called a parallel hybrid system. In addition, there is a series-parallel hybrid system, which can maximize the advantages of both series and parallel systems. Currently manufactured hybrid electric vehicles primarily use internal combustion engines as their power source, with their electrical energy storage systems typically being secondary power sources. However, these secondary power sources have many shortcomings and require significant improvement. These problems can be solved by using supercapacitors. The use of ultra-large capacity capacitors in the electric starting systems of internal combustion locomotives has shown significant advantages, including: 1. Reduced starting time of the diesel-generator set due to increased starting power. Increased diesel engine acceleration improves fuel ignition quality. 2. Reduced maximum current load on the battery pack during starting, helping to extend battery life. 3. Improved starting reliability, especially at low temperatures and when the battery pack is depleted or its parameters deteriorate. 4. Effective reduction in battery capacity within existing battery technology. However, supercapacitors cannot completely replace batteries because of their relatively low energy density. The operating voltage of a single supercapacitor cell is low, so multiple cells must be connected in series to achieve a higher operating voltage. However, connecting multiple cells in series requires high uniformity among the cells, and the system's capacity is reduced exponentially after series connection. Many of the technologies involved in this area are still under development. The characteristics of supercapacitors perfectly meet the specific requirements of hybrid electric vehicles. Utilizing the instantaneous high-power characteristic of supercapacitors avoids the need for frequent engine starts and the requirement for batteries to provide instantaneous high power. Simultaneously, it can recover and reuse braking energy, thereby saving energy and reducing emissions, making it particularly suitable for hybrid electric vehicles that frequently travel in urban areas. Regarding braking energy recovery, at least 30% of a car's energy is consumed during driving due to heat dissipation and braking, especially in urban driving where red lights are frequent. This not only wastes energy but also increases environmental pollution. If the energy consumed during braking could be recovered and used for starting and accelerating the car, it would be a win-win situation. However, since battery charging is a chemical reaction that takes a long time, while braking time is short, the energy recovery effect is not ideal. Flywheel batteries, currently under research, are difficult to put into practical use in the short term due to their high precision requirements and manufacturing difficulties. Supercapacitors, with their unique characteristics, are very suitable for energy recovery during braking, and they are also relatively inexpensive, showing broad application prospects. Regarding providing instantaneous high power for engine cold starts, cold starts place special demands on batteries; the battery must provide instantaneous high power for the engine to start. However, ordinary batteries do not possess this characteristic, unless a starting ignition battery is used. But starting ignition batteries are not suitable for long-term low-current operating environments and often fail at low temperatures, making them unsuitable. Research has found that combining supercapacitors and batteries in an engine starting system, leveraging the unique characteristics of supercapacitors to create a new type of starting system, can solve this problem. As a new type of energy storage element, supercapacitors have filled the gap between traditional electrostatic capacitors and chemical power sources. With their advantages of low cost and high performance, coupled with their pollution-free nature, they have become increasingly important to people. With the deepening of research on electric vehicles, the advantages of supercapacitors in this field have become more and more obvious. The high performance of supercapacitors determines their very broad market prospects, while low cost determines their significant economic benefits. Although supercapacitors have the defect of low specific capacity, it is believed that through improvement, they will definitely drive a qualitative leap in the automotive industry. 3 Conclusion For the mining of thin coal seams with relatively large resources in China, the current coal mining machinery and mining technology are relatively mature. When choosing to apply them, we should make a practical choice based on the local coal seam occurrence and select the appropriate coal mining machinery according to local conditions, so as to give full play to its huge investment benefits and role. References: [1] Cui Shumei, Zhang Fan, Song Liwei, et al. Research on the power performance of supercapacitor electric vehicles. Micro Motor, 2005, 38(4): 37-40. [2] Ye Zi. Electric vehicle exhibition plays the "new energy" card (N). China Trade News, 2007-8-7. [3] Zhang Zhian, Deng Meigen, Yang Bangchao, et al. Recent research progress on electrode materials for electric double-layer capacitors (J). Electronic Components and Materials, 2003, 22(11): 1-5. [4] Xiong Qi, Tang Donghan. Research progress on supercapacitors in hybrid electric vehicles (J). Journal of Sun Yat-sen University, 2003, 42(6): 130-133. Click to download: Application of supercapacitors in electric vehicles