21700 battery

The use of ternary 21700 battery is the technical reason for frequent car burns

Tesla uses ternary lithium-ion batteries. Before last year, more than ten cars had caught fire and burned. In May this year, four cars burned one after another, causing three deaths and one injury. From January to June this year, there were six spontaneous combustion accidents of new energy vehicles abroad

Why do electric vehicles have frequent combustion accidents?

1. The use of ternary 21700 battery is the technical reason for frequent car burns

Tesla uses ternary lithium-ion batteries. Before last year, more than ten cars had caught fire and burned. In May this year, four cars burned one after another, causing three deaths and one injury. From January to June this year, there were six spontaneous combustion accidents of new energy vehicles abroad. The ternary lithium-ion batteries used in these vehicles are all from "famous families", and the manufacturing process should not be the main problem. The main cause of the accident is fire after severe collision and spontaneous combustion for no reason, which has to be found from the inherent insecurity of ternary lithium-ion batteries.

Like the gasoline tank, the battery pack is a component containing high-energy substances and is the material basis for the safety of electric vehicles. The electrolyte in lithium-ion batteries is made of flammable solvents. The positive electrode oxidant and the negative electrode reductant are separated by only a micron-thick diaphragm, and internal short circuits generate heat. In order to pursue high specific energy, companies now use thinner diaphragms, which are more prone to internal short circuits. During charging and discharging, the internal resistance of the battery generates heat, and more heat is generated at high rates. When a certain temperature is reached, the oxidant on the positive electrode is easy to react chemically with the electrolyte, especially the ternary material will also decompose the primary ecological oxygen, which is a state that is much more active than oxygen and is very easy to react chemically with reducing substances. A large amount of chemical reaction heat causes thermal runaway, which will produce a large amount of gas, causing the air pressure to rise, and then battery rupture, combustion, explosion and other accidents.

Therefore, the temperature at which thermal runaway occurs is different for different oxidants on the positive electrode. The lower the thermal runaway temperature of the positive electrode material, the worse the safety of the battery. The safety of ternary positive electrode batteries is lower than that of lithium iron phosphate batteries and other batteries.

Since the ternary lithium-ion battery has the "three elements of combustion" inside and can self-ignite even when isolated from the air, the fire of the ternary lithium-ion battery is difficult to extinguish and spreads rapidly, making it difficult for drivers and passengers to escape and get rescued. At present, my country's ternary lithium-ion battery needle puncture test cannot be completely passed, but it is allowed to be used in passenger cars and even commercial vehicles. According to incomplete statistics, there were 21 electric vehicle fires in my country from January to September this year.

2. Focusing on the development of pure electric vehicles is the reason for frequent fires

In recent years, the "three vertical" development route of electric vehicles led by the Ministry of Science and Technology has changed again and again, from pure electric vehicles, hybrid electric vehicles, fuel cell electric vehicles, to pure electric vehicles, plug-in electric vehicles, fuel cell electric vehicles, and then to pure electric vehicles, extended-range electric vehicles, and fuel cell electric vehicles. Among them, hybrid vehicles changed to plug-in after about two years; after maintaining for about 5 years, they changed to extended-range this year; what remains unchanged are pure electric vehicles and fuel cell electric vehicles.

At present, fuel cell vehicles have many problems to solve and are still far from marketization. Pure electric vehicles are the focus, but long-range pure electric vehicles under high subsidies need to solve five major anxieties. First, there is mileage anxiety: even if you carry more batteries, you still worry about power outages; the car body is heavy and does not save electricity; the air conditioning seriously shortens the mileage. Second, safety anxiety: there are many batteries and high specific energy, which is dangerous and prone to combustion and explosion accidents. Third, charging anxiety: charging piles must be dense, and it is still difficult to meet the requirements even if it costs money and land. Fourth, price anxiety: the battery consumption is large, the price is high, and the competitiveness is low. Fifth, battery anxiety: the battery life is shorter than the whole vehicle, and the second and third sets of batteries require users to pay extra.

After the subsidy stops, the longer the mileage and the higher the original subsidy, the harder it is to sell the car. At present, it is only appropriate to make micro-sized electric vehicles with low power consumption and small contradictions between safety and mileage.

The pursuit of long mileage by pure electric vehicles leads to excessive installation of batteries and reduced safety. This technical development route is the reason for the frequent occurrence of hot cars.

3. Subsidizing long-mileage pure electric vehicles with heavy money is the policy reason for frequent car fever

Since the electric vehicle mileage index and subsidies are linked to pure electric mileage, a nationwide "artificial ternary wind" has been forced out; subsidies are linked to battery specific energy, resulting in an increasing use of nickel in ternary batteries, and the ratio of nickel, cobalt and manganese is gradually moving from 333, 523, and 622 to 811, and the higher the energy density, the greater the risk.

Unreasonable subsidy policies are the reason for frequent car fever.

4. Mileage as the main aspect of the contradiction is the ideological reason for frequent car fever

The main contradiction of electric vehicles is the opposition between safety and mileage. Mileage is considered the main aspect of the contradiction, and safety is considered the secondary aspect of the contradiction. This is a mistake in the ideological method and the root cause of problems in the development route, policy, and technology.

In summary, the development route and policy of new energy vehicles in my country mislead the large and urgent use of ternary lithium-ion batteries, exacerbating the contradiction between safety and mileage, and the consequence is frequent electric vehicle burns. Moreover, the heavy body, high power consumption, and high actual emissions deviate from the original intention of electric vehicles to save energy and reduce emissions.

Range-extended technology can solve the contradiction between safety and mileage

In the past ten years, my proposition can be summed up in two sentences. Principle: Use safe and mature batteries to develop energy-saving and emission-reducing electric vehicles; Technical route: Take micro-sized pure electric vehicles as a breakthrough, and develop pure electric drive range-extended vehicles for large and medium-sized vehicles. Micro-sized pure electric vehicles can use lead-acid batteries as low-speed vehicles, or lithium-ion batteries as high-speed vehicles, which is determined by the market; range-extended electric vehicles can solve the five major anxieties of pure electric vehicles, and marketization is the most feasible.

It is gratifying that my proposition has been gradually accepted. The Ministry of Science and Technology included range-extended vehicles in the "New Three Verticals" in January this year; the National Development and Reform Commission included range-extended vehicles in the category of pure electric vehicles in the "Automotive Industry Investment Management Regulations (Draft for Comments)" issued in July. Once the subsidies for new energy vehicles stop and the industry enters the marketization stage, it is expected that micro-sized pure electric vehicles and range-extended electric vehicles will develop rapidly.

The author divides the development of range-extended vehicle technology into three generations.

The first generation of extended-range electric vehicles is to add a range extender to a pure electric vehicle, simply to increase the mileage, and the range extender generates electricity when the electricity is used up. Take the BMW i3 as an example. If a range extender is installed, the price will increase by 15%. The 0.7L displacement engine and the vehicle's fuel consumption per 100 kilometers in extended-range mode are 5.35L. The battery of this small car is heavy, the range extender has high power and consumes a lot of energy, and the range extender is simply connected in series with the battery, so the fuel consumption is high.

The second generation of extended-range electric vehicles has optimized the power system in technology, with a smaller engine, optimized engine energy efficiency, fewer batteries and lower costs, and lighter vehicles are more energy-efficient. Its advantages are that the battery pack will not be overcharged or over-discharged, the life span is extended, and the safety is high; the lithium iron phosphate battery has a suitable specific energy and further improved safety; there are fewer batteries and the impact of subsidy reduction and cancellation is small; it saves more than 50% of fuel when driving with extended range than fuel vehicles, which saves a lot of money; it can be driven without external charging, without building charging piles, and can travel long distances; if charging conditions are available, the fuel saving rate within 100 kilometers in the city is more than 80%; the production and refueling facilities of fuel vehicles can be used, which is convenient for development; there is no anxiety about mileage, safety, charging, price, and battery.

The second generation of extended range is a fusion of fuel vehicles and electric vehicles. It changes the limitations of the first generation of simply extending the driving range and achieves energy conservation and emission reduction. This technology has been used in many vehicles, such as the 12-meter extended-range bus of Hualong New Energy Automobile Co., Ltd., which uses lithium iron phosphate batteries, with a fuel consumption of 12L per 100 kilometers in urban bus mode and 16.3L per 100 kilometers in highway mode; the extended-range truck of Canada's PlanB can reduce pollutant emissions by 70%, with a fuel consumption of 17L per 100 kilometers; the e-POWER power system of Nissan NOTE is a series hybrid, with a three-cylinder 1.3L displacement engine, a 1.5kWh battery, and a fuel consumption of only 2.9L per 100 kilometers; the extended-range low-speed vehicle of Shandong Dezhou Fulu Group uses lead-acid batteries, a single-cylinder 0.2L engine, an oil-electric efficiency of 299g/(kW·h), and a fuel consumption of only 1.8L per 100 kilometers.

However, the second-generation extended-range electric vehicles also have shortcomings because the range extender generates electricity to charge the battery, the battery supplies power to the motor, and the current flows through the battery pack. First, at least 10% of the energy is lost during the battery charging and discharging process; second, although the battery usage is less than that of pure electric vehicles, the battery usage still needs to be about 40% of that of pure electric vehicles because the power needs to meet the maximum speed requirements, and the car price is significantly higher than that of fuel vehicles; third, there are more batteries and the body is heavier, which has the potential to reduce weight and save energy; fourth, the battery is always working at high load, and its life is affected.

At present, Jiangsu Duke New Energy Automobile Company in my country has proposed "engine power generation directly drives electric vehicles", referred to as "power generation direct drive electric vehicles", which can be called the third generation of extended range technology. The electricity generated by the generator on the car does not need to pass through the battery to directly drive the motor, which overcomes the shortcomings of the second generation of extended range, and has all the advantages of the second generation, and can reduce the battery charging and discharging 10% of the energy loss. Its advantages are: further reduction of batteries, reduction of vehicle weight, and reduction of power consumption; fewer opportunities for high current working of batteries, and longer life; less battery usage, further reduction of costs; and high fuel saving rate, the total cost of the vehicle's entire life cycle is much lower than that of fuel vehicles of the same level. Moreover, this technology is applicable to various vehicles and helps to save energy and reduce emissions.

Some people may say that the extended-range model still needs to burn oil, which is not the ultimate goal. In this regard, the author would like to point out two points. First, if my country's automobile fuel consumption is reduced to less than half of the current level, 200 million tons of crude oil will be saved each year, which will effectively improve the environment, improve energy security, and also allow my country to take a big step forward from a large automobile country to a powerful automobile country. Second, pure electric vehicles may not be the ultimate goal. They have many batteries, heavy bodies, and high power consumption. Tesla's punishment in Singapore shows its disadvantages. For new energy vehicles, their energy conservation and emission reduction throughout their life cycle should be assessed.

Moreover, the future extended-range electric vehicles can burn ethanol instead of oil, which is both energy-saving and does not increase CO2 emissions. Therefore, the author believes that the extended-range model is not a "transition to pure electric vehicles", but the main force of future vehicles.

In short, the main contradiction of electric vehicles is the contradiction between safety and pure electric mileage. Electric vehicles should reduce battery usage, improve safety, and reduce vehicle prices, rather than one-sidedly pursuing long mileage, installing more batteries, or desperately increasing specific energy and increasing danger. The solution is to miniaturize the product and develop extended-range electric vehicles (or miniaturization + extended-range), which is the best technical route to cope with the decline of subsidies and move towards marketization. It is worth mentioning that extended-range electric vehicles and lithium iron phosphate batteries are an excellent match, solving the main contradiction between safety and mileage, and are most suitable for marketization.

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