Environmental pollution and energy crisis are two major challenges that the automobile industry must face. Electric vehicles cater to the development of the times due to their unique advantages of greenness and environmental protection; the performance of batteries will directly affect the safety and mileage performance of vehicles. This article looks forward to the future development trend of electric vehicle battery technology by analyzing the development and use of different types of batteries for electric vehicles.
Electric vehicles were first born in the early part of the 19th century. Because the technology was not mature enough at that time, it did not attract people's attention. General Motors of the United States used lead-acid battery technology to develop electric vehicles in 1996, and started the production of electric vehicle batteries in 1999. However, due to many technical problems, it was not recognized by the industry.
At the beginning of the 21st century, electric vehicles were further developed. At this time, the main power battery of the vehicle was upgraded to nickel metal hydride batteries, which significantly increased the cruising range of electric vehicles. During the same period, Japan’s Toyota Corporation also used nickel-metal hydride battery technology to develop a new generation of electric vehicles. This electric vehicle combines an electric motor with an internal combustion engine and is called a hybrid electric vehicle. Energy to achieve the purpose of reducing fuel consumption. The emergence of lithium-ion batteries in 2006 has enriched and further improved the battery technology of electric vehicles; the biggest advantage of lithium-ion batteries is that it has improved the safety of electric vehicle batteries, and has become a strong competitor of nickel-metal hydride batteries. partial advantage. Lithium-ion batteries are widely used in pure electric or hybrid vehicles because of their good safety performance.
Batteries are the key components of electric vehicles, and high-performance batteries are the premise and foundation for the stable operation of electric vehicles. Electric vehicle batteries have problems such as short battery life, long time required for a single charge, and potential safety hazards such as spontaneous combustion or even explosion, making it difficult to meet the needs of long-distance travel.
Electric vehicles use electric energy as the power source. Electric energy is only supplied by the battery of the vehicle. Batteries account for about 30% of the cost of the vehicle. Batteries and chips are the two most critical technologies for electric vehicles, and battery performance will directly affect the mileage of the vehicle. . Faced with the extreme cold weather test in the northern region in 2020, the performance of the cruising range of electric vehicles really surprised the car owners, and handed in an unqualified "answer sheet".
Currently, among the batteries available for electric vehicles, chemical batteries are the most widely used. Chemical batteries can be divided into two categories: batteries and fuel cells.
In the process of the development of electric vehicle technology, car companies have tried to use a variety of different types of batteries, but due to considerations of cost, technology and reliability, most batteries have been eliminated by the market, such as lead-acid batteries, manganese Lithium acid battery, etc. At present, the mainstream batteries on the market are mainly lithium-ion batteries, and a few car companies use nickel-metal hydride batteries, such as Toyota.
1) Li-ion battery
At present, lithium iron phosphate batteries have been widely used in domestic electric vehicles. Its advantages are safety and reliability, many cycle charging times, a cycle life of more than 1,800 times under standard charging conditions, and low cost of use. Good safety can make it stable at a high temperature of 390 ℃; it has now passed strict safety tests, and it is not easy to explode or burn due to overcharging, overheating, short circuit or in severe traffic accidents.
One of the more typical ones is the Denshi 500 electric vehicle jointly produced by BYD and Daimler Group. Under the same power supply performance, the amount of lithium iron phosphate is less than that of lithium batteries. For example, Tengshi Motors uses 144 lithium iron phosphate batteries. Compared with lithium batteries, the number of batteries is much smaller, and the burden on the BMS battery management system is smaller.
Lithium iron phosphate battery
At present, lithium iron phosphate batteries have been widely used in domestic electric vehicles. Its advantages are safety and reliability, many cycle charging times, a cycle life of more than 1,800 times under standard charging conditions, and low cost of use. Good safety can make it stable at a high temperature of 390 ℃; it has now passed strict safety tests, and it is not easy to explode or burn due to overcharging, overheating, short circuit or in severe traffic accidents.
Lithium iron phosphate battery
One of the more typical ones is the Denshi 500 electric vehicle jointly produced by BYD and Daimler Group. Under the same power supply performance, the amount of lithium iron phosphate is less than that of lithium batteries. For example, Tengshi Motors uses 144 lithium iron phosphate batteries. Compared with lithium batteries, the number of batteries is much smaller, and the burden on the BMS battery management system is smaller.
Blade battery
The blade battery is also called a super lithium iron phosphate battery. Because it is arranged like a blade and inserted into the battery pack, it is called a blade battery. The battery lengthens the battery cell of the power battery, so that the shape of a single cell is flat and narrow, and can be bundled to form a module through multiple "blades". Through technical improvement, compared with lithium iron phosphate batteries, the energy density of the battery is significantly improved. However, the difficulty of the blade battery lies in the production process, which requires extremely high precision and speed in the manufacturing process, and puts forward high requirements for the coating and rolling process of the pole piece.
BYD Blade LiFePO4 Battery
The blade battery uses the cells to directly form a battery pack, which reduces the module structure and single connection harness, improves the packaging efficiency, and further realizes integration. In addition, due to the special shape of blade batteries and the stability of materials, densely arranged blade batteries can serve as simple structural parts, further improving space utilization. Through this technology, the space utilization rate of the blade battery is increased from 40% of the original traditional battery to 60%, and its battery life reaches 600 km, and it also has the advantages of high safety and long life.
Ternary lithium battery
Compared with lithium iron phosphate batteries, many electric vehicles generally use ternary lithium batteries, mainly because ternary lithium batteries have the advantages of high energy density, light weight, good low-temperature charging performance and longer cruising range; its energy density It is 200 Wh kg-1, that is, under the same conditions, the cruising range of the ternary lithium battery is longer than that of the lithium iron phosphate battery. At the same time, the ternary lithium battery also has the characteristics of good low temperature performance and high discharge rate. But the disadvantage of ternary lithium battery is poor stability.
Ni-MH battery
Ni-MH battery
Models using nickel-metal hydride batteries are often hybrid vehicles, a typical representative of which is the Toyota Camry Hybrid. A major advantage of Ni-MH batteries is that they are more stable than ternary lithium batteries, and their energy density is about 70 to 100 Wh kg-1. The battery cell voltage is usually 1.2 V, which is only 1/2 of that of lithium batteries. 3 or so. Therefore, when the system voltage is constant, the volume of the battery pack is much larger than that of the lithium battery. Moreover, the capacity of Ni-MH batteries will decay during the cycle charge and discharge process, so Ni-MH batteries should actively avoid excessive charge and discharge in the setting of the control system.
2) Fuel cells
Fuel cells are one of the ideal clean energy sources in the future. This type of battery is a chemical device that directly converts the chemical energy of fuel into electrical energy. Its principle is to send fuel and air into the fuel cell separately, and through chemical reaction, generate electricity to drive the vehicle. Moreover, the fuel cell reacts with fuel and oxygen as raw materials, and there are very few harmful gases in the tail gas emissions.
Fuel cells
However, in practical applications, many technologies of fuel cell vehicles need to be solved urgently. At present, fuel cell vehicles are mainly concentrated in the field of commercial vehicles. The disadvantage of this battery is that the volume of the fuel cell is several times larger under the same energy as the chemical battery. The power is only 115 kW. If the domestic fuel cell stack reaches 115 kW, the volume will be very large, and it is difficult to accommodate the space of ordinary passenger cars. Therefore, limited to my country's current fuel cell technology, it is still mainly used in commercial vehicles.
The development of human society is inseparable from innovation, and the automobile industry is developing rapidly in continuous innovation and transcendence. New energy vehicles have become a new trend in the development of the automotive industry. At present, most car companies are also transforming to new energy vehicles, trying to create new energy products for consumers that are better than fuel. As the most important component of new energy vehicles, the market demand for power batteries is also rapidly expanding. At present, the charging time is long and the energy density of the battery is low.
How to break through the "bottleneck" that restricts the development of electric vehicle batteries has become the focus of continuous development and research in the industry. Battery makers are also working to make batteries lighter and smaller without reducing their power reserves.
1) Supercapacitor
Supercapacitor
A supercapacitor is a new type of storage device, also known as an electric double layer capacitor. The capacitor can realize free conversion between electric field energy and electric energy. The basic principle is to use a porous electrode made of activated carbon material, and an electrolyte solution is filled between the two electrodes. When a voltage is applied across the electrodes, the electrolyte solution can form a collector layer, which is equivalent to two capacitors connected in series. In addition, the surface area of activated carbon is relatively large, and the distance between the electrolytes is small, resulting in a large capacitance of the supercapacitor. The device has the advantages of high power density, long cycle life, wide working temperature limit, maintenance-free, green and environmental protection, showing good development prospects.
2) Graphene battery
Graphene battery (Image Credit: Lightboxx/Shutterstock.com)
Graphene batteries are generally considered by the industry to be the future main battery that is most likely to replace ternary lithium batteries. It is a new generation of batteries developed by utilizing the activity characteristics of lithium ions between the surface of graphene and electrodes. Graphene is a material that is characterized by good electrical conductivity, light weight, good strength and toughness, and is a very good special new material. In terms of charging efficiency, graphene batteries are dozens of times higher than traditional batteries; their service life is twice that of lithium batteries and four times that of hydrogenated batteries; and their weight is only about 50% of traditional batteries. Huawei has announced a battery fast charging technology in this field, which can fully charge a 3,000 mAh graphene battery in just 5 minutes. Because its use cost is too high, it is difficult to popularize and use at present.
3) Lamination technology improves performance
Automotive power batteries will develop in the direction of long batteries and large modules. Traditional winding batteries can no longer meet the shape requirements of vehicle-grade power batteries. They are replaced by batteries with laminated process characteristics. The size of the sheet cell is flexible, and it is not limited by the structure of the winding needle. The stacking makes the interface of the pole piece more flat. Compared with the same type of winding process battery, the energy density of laminated battery can be increased by 5%, the cycle life can be increased by 10%, and the cost can be reduced by 15%. It is suitable for wide application in the field of power cells.
To sum up, the development and popularization of electric vehicles is an inevitable trend in the development of the automobile industry. With the rapid development of national science and technology, many new technologies, new processes, and new materials have been continuously developed and applied in the field of electric vehicles. The battery of electric vehicles in the future The technology will surely break through shortcomings such as short cruising range, long charging time, and unstable performance, and usher in a brilliant spring for the electric vehicle industry.
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