As the core component of electric vehicle, battery has always been regarded as an important symbolic technology and a bottleneck restricting the development of electric vehicle. Its performance directly determines the cruising range of electric vehicles, and various incidents of spontaneous combustion of electric vehicles also worry consumers.
When it comes to buying electric cars, most consumers may think of policies such as "preferential treatment", "unlimited number" and "unlimited number" for the first time. However, if you really want to buy an electric car and drive comfortably, it is not enough to know the preferential policies. As the core component of electric vehicle, battery has always been regarded as an important symbolic technology and a bottleneck restricting the development of electric vehicle. Its performance directly determines the cruising range of electric vehicles, and various incidents of spontaneous combustion of electric vehicles also worry consumers. Therefore, before buying an electric car, you must understand its "heart". Starting from this issue, EasyPoint will popularize a series of basic knowledge about new energy vehicles, hoping to help consumers buy new energy vehicles in the future.
Because there are many kinds of batteries for electric vehicles, most of them have been eliminated by the market, so we first have a general understanding of the basic characteristics of these batteries through a table, and then explain several common batteries on the market at present.
Lead-acid batteries are widely used at present, and their main advantages are stable voltage and low price. Disadvantages are low specific energy (that is, energy stored per kilogram of battery), short service life and frequent daily maintenance. The life of old batteries is about 2 years, so it is necessary to check the height of electrolyte regularly and add distilled water. However, with the development of science and technology, the life of lead-acid batteries has become longer and the maintenance has become simpler. Lead-acid batteries are the same, because of their low energy density, so they are very large. In addition, because its composition is sulfuric acid electrolyte, the environmental pollution after abandonment is more serious. Its biggest disadvantage is that its driving ability is relatively low, and it can not meet people's daily needs when applied to pure electric vehicles. At present, lead-acid batteries are mostly used in low-speed electric vehicles, especially old scooters and electric bicycles.
Lithium iron phosphate battery is a kind of lithium ion battery, which is characterized by not containing precious metal elements such as cobalt, and the raw materials are phosphorus and iron, which is not only rich in resources, but also relatively low in price. The safety of lithium iron phosphate battery is second to none among lithium batteries. It decomposes at 700℃~800℃, but it is not as violent as the chemical reaction of ternary lithium material, and it will not release oxygen molecules, so it is safe. Because of this, it has also become one of the main categories of electric vehicle batteries. In addition, it has the advantages of high charging and discharging efficiency and no pollution to the environment. However, it also has its own shortcomings. Because the energy density of the battery is low, it is relatively large. The battery capacity is small, which leads to its relatively low driving ability. After scrapping, its recyclable value is very low. Moreover, due to the poor low-temperature performance, the research shows that a battery with a capacity of 3500mAh will be scrapped if it works in an environment of-10.
Tesla MODEL S adopts ternary lithium battery with higher energy density than lithium iron phosphate battery, which means that ternary lithium battery with the same weight has a longer cruising range than lithium iron phosphate battery. However, when the temperature of ternary lithium battery itself is 250-350℃, its internal chemical components begin to decompose, so higher requirements are put forward for the battery management system and the cost of the battery is relatively high. Simply put, ternary lithium materials are more likely to catch fire than lithium ferrous phosphate materials. However, in recent years, due to the increasing demand of consumers for driving range, car companies have paid more and more attention. They try their best to avoid its defects by taking certain technical and design measures.
Japanese manufacturers choose lithium manganate battery because its comprehensive performance is relatively balanced and technically not as radical as ternary lithium battery. Because precious metal cobalt is not needed, the cost is much lower and there is no patent restriction. This sounds like an electrification continuation of Japan's economic application strategy. Lithium manganate is a cathode material with low cost, good safety and good low temperature performance. However, the material itself is not stable, and it is easy to decompose to produce gas. Therefore, it is often used to mix with other materials to reduce the cost of batteries. However, its cycle life decays quickly, it is easy to bulge, its high temperature performance is poor and its life is relatively short. Mainly used in large and medium-sized batteries and power batteries, the nominal voltage is 3.7V Although the energy density is not as good as that of ternary lithium batteries, other comprehensive properties are quite excellent.
The high cost and safety of lithium batteries are the main reasons why Toyota mainly uses Ni-MH batteries in vehicles. After 90' s, Ni-MH battery developed gradually. For example, many hybrid vehicles, such as Toyota Prius, use this battery as an energy storage element. Its main advantage is that it can adapt to large current discharge and is more suitable for occasions requiring high power output. Its high energy density increases the cruising range. Ni-MH battery has stable discharge and less heat generation. Its main disadvantage is that it has "memory effect", that is, the capacity of the battery will be attenuated during cyclic charging and discharging, and overcharge or overdischarge may aggravate the capacity loss of the battery. Therefore, for manufacturers, the control system of Ni-MH battery will actively avoid overcharge and overdischarge, such as artificially controlling the charging and discharging interval of the battery within a certain proportion of the total capacity to reduce the capacity decay speed.