Electric vehicles (English: electric vehicle) or electric cars refer to all personal wheeled vehicles that can use electricity to drive electric motors as power. According to the classification of the power system, electric vehicles can be further divided into pure electric vehicles or battery electric vehicles (BEV), hybrid electric vehicles (HEV) and fuel cell vehicles (FCEV). The term "electric vehicles" in industry terms usually refers to plug-in electric vehicles (PIEVs), i.e. pure electric vehicles and plug-in hybrid vehicles (PHEVs), but in a broad sense, it can also include extended-range electric vehicles (REEVs), solar vehicles, and fuel cell vehicles.
Compared to traditional internal combustion engine vehicles (fuel vehicles), in terms of energy density, 1 kg (2.2 lb) of gasoline contains about 43 MJ (12 kW h) of chemical energy, while 1 kg of lithium-ion batteries can only store 0.15 kW h (0.54 MJ) of electrical energy, which is much lower than the same weight of fossil fuels. However, the size and weight of electric motors are also much lower than internal combustion engines, and they do not require auxiliary systems such as oil pipes, oil pumps and exhaust systems, which can save a lot of design space and weight. In addition, electric vehicle batteries can theoretically be charged in areas covered by the power grid, and the cost of electricity consumed is much lower than the cost passed on to consumers by the oil industry through mining, refining, transportation and sales. The potential for diffusion is enormous. However, because the history of large-scale development of electric vehicles is still relatively short, existing battery technology still has limitations, and the popularity of public charging stations is still far lower than that of gas stations (fuel vehicles have a first-mover advantage of almost a century in diffusion), the resulting range anxiety is currently the main obstacle to the diffusion of electric vehicles [ 1 ] .
Electric vehicles are new energy vehicles, with lower overall tailpipe emissions (pure electric vehicles are essentially zero-emission, but the power plants that power them may produce greenhouse gas emissions and air pollution ), quieter when driving, more responsive, superior energy conversion efficiency, and no dependence on gas stations (provided that there are reliable and convenient charging facilities or home energy). In addition, although the energy density of batteries is much lower than that of fuel, the energy conversion efficiency of the engine from the tank/battery to the wheels varies significantly, with gasoline vehicles having an energy conversion efficiency of 14~33%, diesel vehicles 28~42%, and electric vehicles over 86%.This means that although the energy density of fossil fuels is much higher than that of batteries, most of the energy is converted into useless work (noise, vibration, and exhaust kinetic energy, etc.) and wasted, and due to the problem of waste heat, the engine must be equipped with a cumbersome cooling system that takes up space and weight, while electric motors do not have this problem. In addition, because fuel combustion is not fully controlled, the internal combustion engine is not efficient at low speeds, and the vehicle must maintain idling speed when stopped to prevent stalling, so a gearbox and clutch are required to convert torque. The output power and torque of the electric motor are basically linearly related to the input electric power, and a single-speed drive can achieve the effect of a continuously variable transmission.
After the emergence of electric propulsion in the Second Industrial Revolution, rechargeable battery technology was mainly based on lead-acid batteries, nickel-chromium batteries, and mercury batteries. Their energy density, output voltage, and current could not meet the practical needs of vehicle driving.
Therefore, for a long time, electric vehicles were limited to electric locomotives that relied on overhead wires or third rails for power, to rail transport such as trams/trolleys and monorails, and to light one-person vehicles such as electric locomotives and electric bicycles that could only travel at low speeds and short distances. After entering the 2000s, the energy density of energy storage units represented by lithium batteries accelerated, partially solving the endurance problem that has plagued electric vehicles for nearly a century. New electric vehicle brands represented by Chinese new car manufacturers such as Tesla and BYD have emerged, and some traditional fuel vehicle manufacturers (mainly Germans and Koreans, and a small number of Japanese) are also accelerating their transformation into electric vehicle research and development and production. The economies of scale brought about by the advancement of manufacturing technology, the improvement of the industrial chain, and the increase in production have also significantly reduced the cost of electric vehicle components (especially batteries), and even the price of the entire vehicle can be the same or even lower than that of fuel vehicles.
At the same time, the construction of infrastructure such as charging stations, battery replacement stations and fuel cell support facilities (such as hydrogen refueling stations) for electric vehicles is also accelerating. In mainland China, the United States and European countries and regions such as Norway and Finland, policy support has been provided to varying degrees, including cash subsidies, low-interest loans and free land for factory construction. At the same time, some countries and regions have enacted legislation to phase out the sale of fossil fuel vehicles [2] in order to reduce air pollution and mitigate climate change. According to the International Energy Agency, by 2023, electric vehicles are expected to account for almost a fifth of global car sales.
Key TechnologyThe key to electric vehicle technology lies in the "three electric elements", namely the motor, the battery and the electronic control. Although other components of the vehicle are also important, as a vehicle, the most important aspects of electric vehicles are these three aspects that are closely related to the movement and operation of the vehicle.
Main articles: Electric motor and Traction motor Different brands of electric vehicles have different motor designs. For example, pure electric vehicles produced by Tesla typically use asynchronous motors, while the Nissan Leaf and Chevrolet Bolt use permanent magnet synchronous motors [12], and some pure electric vehicles and plug-in hybrid vehicles produced by BYD use brushless DC motors. Compared with gasoline and diesel engines, electric motors can produce higher torque and do not need to rely on gearboxes and clutches to cope with torque changes during acceleration and idling. The acceleration response speed is also better than that of fuel vehicles (fuel vehicles usually have a certain lag due to the operation of the gearbox). The engine of an electric vehicle can also be combined with regenerative braking to recover the generated torque in the form of electrical energy and store it in a flywheel, battery or supercapacitor, thereby recovering energy while enhancing the braking effect, effectively extending the vehicle's mileage.
Because the energy conversion efficiency of electric motors far exceeds that of various traditional internal combustion engines based on the principle of piston engines, and the generated heat dissipation is very small, there is no need for a large cooling system to cool the engine, which can save a lot of space and weight for other parts of the vehicle. At the same time, when electric vehicles use a two-wheel drive design, they do not need a drive shaft to distribute torque to the front and rear wheels. If it is four-wheel drive, the unified electronic control design of the front and rear motors can be used, and there is no need for a drive shaft, which saves additional space for the chassis and cockpit. Some specially designed electric vehicles (such as Yangwang U8) can even use four motors to drive four wheels separately, so that each wheel can operate independently and can deal with complex terrain more flexibly.
The biggest advantage of electric motors over traditional internal combustion engines is environmental protection and economy. Although the prices of the Although the cost of electricity varies in different regions, in general, the operating cost of electric motors per 100 kilometers is still better than that of cars. In addition, electric vehicles are energy efficient, with lower noise pollution during operation. The electricity used is not based on fossil fuels like fuel vehicles, but can be partially or even fully renewable. Many electric vehicle users can even use private photovoltaic charging.
In addition, electric vehicles do not require combustion and do not produce tail gas emissions. Even if the greenhouse gases and air pollution caused by power plants are taken into account, the carbon footprint produced is much smaller than the petroleum industry on which fuel vehicles rely. There are many organizations and individuals who oppose electric vehicles, who often sow fear, confusion and doubt and consider the pollution caused by the production of electric vehicles and energy generation as the environmental cost of electric vehicles, but often avoid talking about the environmental cost caused by the manufacture of fuel vehicles and the extraction/refining of oil, which is only higher in comparison.
Nissan Leaf battery
BYD's CTB blade battery was introduced at the 2023 International Motor Show in Germany Main article: Electric vehicle battery Electric vehicle batteries (EVBs) are usually batteries that can be connected to the electricity grid for charging and replenishing energy. They are generally designed to have a large capacity with a high kilowatt-hour specification, so the most common are lithium batteries with a higher energy density. Unlike automotive batteries that are responsible for starting, starting, and ignition (SLI) in traditional fuel vehicles, electric vehicle batteries must be able to continuously produce higher power for a long period of time, so they must be deep-cycle batteries that can be deeply discharged, therefore needing a higher power-to-weight ratio. Because current battery technology is still at a disadvantage in terms of specific energy compared to traditional liquid fossil fuels (gasoline and diesel), the range anxiety caused by this has become the biggest obstacle to the spread of electric vehicles, although future solid-state batteries have the potential to overcome this limitation.
Early electric vehicles used lead-acid batteries, followed by nickel-cadmium batteries, nickel-metal hydride batteries, and occasionally molten-salt batteries such as zinc-air batteries and nickel-chloride batteries [ 13 ] . However, due to their low endurance, battery-powered electric vehicles were essentially abandoned from the market after the popularity of gasoline-powered vehicles in the 1920s. Since the late 1990s, the popularity of various portable electronic products (such as laptops, tablets, PDAs, smartphones, etc.) and personal light vehicles (such as electric motorcycles, electric bicycles, and electric scooters, etc.) has led to the improvement of battery technology and performance.
Lithium batteries have high capacity, high power density, and almost no memory effect. They can be charged/discharged in any power state. Electric vehicles have also benefited from this. Currently, the most commonly used electric vehicle batteries are lithium-ion batteries and lithium-ion polymer batteries. By 2018, electric vehicles with a full electric range of over 400 kilometres (250 mi) (such as the Tesla Model S) have been commercialized, and battery-derived technologies have also been applied to different vehicle sectors [14].
The manufacturing and procurement costs of raw materials (lithium ore and other rare earth elements) of lithium batteries have always been a problem (although as of 2019, the unit cost of battery cells for electric vehicles has decreased by 87% compared to 2010 [15]), and when damaged or short-circuited, they are prone to thermal runaway and fire, which poses a major safety risk. At present, the fastest growing electric vehicle battery is the lithium iron phosphate battery represented by BYD's blade battery. Although the energy density is not as high as that of lithium-ion batteries, it has advantages in safety, battery life and deep charge/discharge performance. charging, and is also widely used in photovoltaic energy storage and other fields.
Because the energy capacity and output power of electric vehicle batteries far exceed that of traditional vehicles, they can also be used to support many built-in electrical appliances that are difficult to equip as standard in traditional vehicles, such as beverage refrigerators, entertainment screens, and electric heated seats, that is, the so-called "three major elements" of new energy vehicles, namely "refrigerators, color TVs, and large sofas". In addition, many new electric vehicles also support V2G functions, which can be used as backup power to directly power other electrical appliances and power tools during power outages, outdoor travel, and emergencies.