The state subsidies were halved and the local subsidies were cancelled. In 2019, the new policy on subsidies for new energy vehicles was finally introduced, and the new energy vehicles suffered the biggest decline in subsidies. So what kind of battery is good for plug-in new energy vehicles? How long can the new energy vehicle battery last? Let's have a look.
With the development of new energy vehicles, the innovation of new energy vehicle battery is more and more. New energy vehicle battery is a new type of vehicle battery which uses new energy technology to reduce greenhouse gas emissions.
New energy vehicle batteries can be divided into two categories, namely batteries and fuel cells. Batteries are suitable for pure new energy vehicles and can be classified as lead-acid batteries, nickel based batteries (Ni MH and Ni MH batteries, Ni Fu and Ni Zn batteries) and sodium? Zinc batteries?
Battery (sodium sulfur battery and sodium nickel chloride battery), secondary lithium battery, air battery, etc. Fuel cells are used in fuel cell new energy vehicles, which can be divided into alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC), proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC).
The battery pack of new energy vehicle is composed of multiple batteries stacked in series. A typical battery pack has about 96 batteries. For a lithium-ion battery charged to 4.2V, such a battery pack can generate a total voltage of more than 400V. Although the battery pack is regarded as a single high-voltage battery in the vehicle power system, charging and discharging the whole battery pack every time, the battery control system must consider the condition of each battery independently.
If the capacity of one battery in the battery pack is slightly lower than that of other batteries, the charging state will gradually deviate from other batteries after multiple charging / discharging cycles.
If the state of charge of the battery is not periodically balanced with other batteries, it will eventually enter a deep discharge state, which will lead to damage and eventually lead to battery failure. To prevent this, the voltage of each battery must be monitored to determine the state of charge. In addition, there must be a device to charge or discharge the batteries separately to balance the state of charge of these batteries.
What batteries do new energy vehicles use?
1. Lead acid battery
Representative enterprises or models: Chang'an Automobile, BAIC group, Great Wall Motor, Geely Automobile, SAIC General Motors and other traditional fuel vehicles generally use lead-acid batteries as vehicle power supply devices. At present, most low-speed electric vehicles on the market also use lead-acid batteries.
The first generation electric vehicle EV1 uses lead-acid battery, which was produced by General Motors in 1996. The lead-acid battery was invented by Gaston plante in 1859. It took 137 years from its invention to its application in electric vehicles. The so-called lead-acid battery uses lead oxide as positive plate, sponge lead as negative plate and sulfuric acid solution as electrolyte. At present, lead-acid battery is the most widely used battery in the automotive field. It is mainly used as the power supply for various electrical and electronic equipment in internal combustion engine vehicles.
There are two types of lead-acid batteries: closed type and non closed type. The closed type does not need maintenance, allows deep discharge, can be recycled, and is cheap. It has become the most traditional power supply device for fuel vehicles. For example, the maintenance free lead-acid battery used by Buick Welland. However, low energy and power of lead-acid battery is its fatal weakness.
Industry experts pointed out that the nominal voltage of a single cell lead-acid battery is 2.0V, which can discharge to 1.5V and charge to 2.4V; in practical application, six single cell lead-acid batteries are often connected in series to form 12V lead-acid batteries, and there are also 24V, 36V, 48V, etc. the service life is generally three years.
The power and density can be improved by increasing the surface area of the electrode, but it will increase the erosion rate and shorten the service life of the battery. Hu Zechun, an associate professor in the Department of electrical engineering at Tsinghua University, said: "the charging and discharging methods will also seriously affect its service life. Long term overcharging and excessive discharging will shorten the battery life. '
The reason why lead-acid batteries have been widely used in the past 50 years is that in addition to mature technology, mass production and low production cost, interchangeability and low price are also the dominant factors. Although new battery technology is constantly emerging, lead-acid battery is still used as a power source, mainly used in sightseeing vehicles, electric forklifts or some short distance buses.
2. Alkaline battery
Representative enterprises or models: FAW Toyota hybrid model, Changan Ford hybrid model, Lexus rx400h, Porsche Cayenne, etc., generally use Ni MH battery as power supply.
The so-called alkaline battery is composed of nickel base and alkaline solution electrolyte, mainly including nickel cadmium battery, nickel zinc battery and nickel hydrogen battery. Compared with nickel cadmium battery and nickel zinc battery, nickel hydrogen battery has higher specific energy and no pollution to the environment.
Industry experts pointed out that Ni MH battery is composed of hydrogen ion and nickel metal, with 30% more power reserve than Ni Cd battery, lighter than Ni Cd battery and longer service life. The disadvantage of Ni MH battery is that its price is much more expensive than Ni Cd battery and its performance is worse than lithium battery. It is reported that the second generation of electric vehicles developed by General Motors in 1999 were powered by Ni MH batteries, but they eventually withdrew from the market due to their lack of competitiveness. However, Japan's Toyota Motor Company uses Ni MH battery technology to build a hybrid electric vehicle (HEV), which combines internal combustion engine and electric motor.
Ni MH battery has become the most concerned battery in the field of battery technology research and market application of electric vehicles. Compared with lead-acid battery, Ni MH battery has increased three times in energy volume density and 10 times in specific power. The unique advantages of this technology include higher operating voltage, specific energy and specific power, better overcharge and discharge tolerance and thermal performance.
However, the application of Ni MH battery also has some limitations, such as capacity reduction at low temperature and poor charging tolerance at high temperature. In addition, the price is also the main factor restricting the development of Ni MH battery, and the raw material such as nickel is very expensive. Although Ni MH batteries store more energy than lead-acid batteries, over discharge will cause permanent damage, and the state of charge must be limited to a small range. Most of the energy stored in batteries is not actually used. For example, Toyota Prius can only use 20% of the energy of batteries. 'industry experts said.
3. Lithium ion battery
Representative enterprises or models: honda hybrid, Buick hybrid, etc., such as Honda Accord hybrid, Buick LaCrosse hybrid.
Lithium ion batteries can be divided into lithium ion batteries and lithium polymer batteries. The cathode materials of lithium-ion batteries mainly include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, etc., while the anode materials mainly include graphite, lithium titanate, etc. The performance of Li ion batteries with different cathode materials is also different.
4. Lithium iron phosphate battery
Representative enterprises or models: BYD pure electric vehicles (Qin, Qin EV, Tang, etc.), Yutong new energy bus, Xiamen Jinlong new energy bus, etc.
At present, the lithium-ion battery which is widely used in electric vehicles is lithium iron phosphate battery. BYD new energy uses lithium iron phosphate batteries. It has a covalent structure of phosphorus and oxygen, so that oxygen atoms will not be released, so it has good thermal stability and safety, and the price is relatively cheap. These factors make LiFePO4 battery the first choice for small electric vehicles and PHEV power batteries.
Industry experts pointed out that LiFePO4 battery is a kind of lithium-ion battery which uses LiFePO4 as cathode material. It is characterized by no cobalt and other precious elements, low price of raw materials, rich in phosphorus and iron. Its working voltage is 3.2V, electric capacity is 170mAh / g per unit weight, high discharge power, fast charging, long cycle life and high stability in high temperature and high heat environment.
However, among the lithium-ion batteries, the specific energy, specific power and operating voltage of lithium phosphate batteries are relatively low, so lithium cobalt oxide and lithium manganese oxide batteries have more advantages in the application of large-scale pure electric vehicles. 'industry experts said.
5. Ternary lithium battery
Representative cars or models: Tesla, Geely Dihao, BAIC ev200, JAC iev5, arize 7e, Roewe erx5, etc.
Tri lithium battery is a kind of lithium battery with nickel cobalt lithium manganate as cathode material. According to Professor Ouyang Minggao of Tsinghua University, the so-called "ternary" means that the positive electrode is ternary and the negative electrode is graphite. Ternary lithium battery has the advantages of high energy density and better cycle performance than normal lithium cobalt oxide. At present, with the continuous improvement of formula and structure, the nominal voltage of the battery has reached 3.7V, and the capacity has reached or exceeded the level of lithium cobalt oxide battery.
The electric vehicle produced by Tesla company is the choice of ternary lithium battery. Kurt Kelty, technical director of Tesla battery, gives the reasons for the choice: higher energy density, better stability and consistency; can effectively reduce the cost of the battery system; small size, controllability and safety can be continuously improved.
However, some people in the industry pointed out that 'three element lithium batteries mainly include nickel cobalt aluminum lithium battery, nickel cobalt manganese lithium battery and so on. Due to the unstable high temperature structure of nickel cobalt aluminum, the high temperature safety is poor, and the high pH value is easy to make the monomer flatulence, which leads to danger. At present, the cost is high. '
It is reported that if there is a short circuit inside the existing ternary lithium battery or if the cathode material meets with water, there will be an open fire. Therefore, the general ternary lithium battery will have a layer of steel shell protection, because Tesla's battery pack is composed of about 7000 18650 batteries, so although Tesla has carried out a full range of protection for the battery pack, there are still fire hazards in extreme collision accidents.
The lithium iron phosphate battery is much more stable. Even if the battery board is punctured or short circuited, it will not explode and burn, and it will not catch fire when it is exposed to high temperature of 350 ℃ (the ternary lithium battery can't bear it at 180-250 ℃). Therefore, in terms of safety performance, LiFePO4 battery is slightly better. "People in the industry told reporters.
Compared with Ni MH battery, Li ion battery has higher working voltage and higher specific energy, which is three times of Ni MH battery. Lithium ion batteries are small in size, light in weight, long in cycle life, low in self discharge rate, no memory effect and no pollution; the numerical range of single performance index of lithium ion batteries is large, because there are many electrode combinations in lithium ion batteries, and there are some differences in their performance. "Associate Professor Hu Zechun explained.
Of course, there are also problems when lithium-ion batteries are widely used in electric vehicles, mainly due to a variety of performance limitations, including the safety, cycle life, cost, working temperature and material supply of lithium-ion batteries. It is reported that at present, lithium-ion batteries are mainly small capacity and low-power batteries, while large capacity and high-power lithium-ion batteries have not been produced on a large scale. In addition, the immature technology of battery management system (such as equalization charging technology) is also one of the important reasons why lithium-ion battery has not been widely used in electric vehicles.
How long can the new energy vehicle battery last?
New energy batteries can generally be used for about 3 to 6 years
Many prospective car owners are concerned about whether the battery, like the mobile phone battery, will not be able to carry electricity for a long time? At present, no one has used new energy electric vehicles for a long time, so there is no such problem