Which is better for electric vehicle, ternary lithium or lithium iron phosphate battery?

Electric vehicle batteries currently have two mainstream designs. One is represented by Tesla, using ternary lithium battery + high IQ battery management system to give full play to the advantages of large energy density of ternary lithium battery. Another is represented by many cars, using lithium iron phosphate battery + relatively simple battery management system, making full use of the advantages of lithium iron phosphate battery.

Electric vehicle batteries currently have two mainstream designs. One is represented by Tesla, using ternary lithium battery + high IQ battery management system to give full play to the advantages of large energy density of ternary lithium battery; one is represented by many cars, using lithium iron phosphate battery + Relatively simple battery management system, making full use of the advantages of lithium iron phosphate battery.

Which one is better?

The author believes that batteries suitable for electric vehicles should have the following characteristics: safety, large charge and discharge current, slow capacity decay, and high energy density.

These two types of batteries can be roughly evaluated with such scores on these four items.

Design analysis of electric vehicle ternary lithium / lithium iron phosphate battery (Figure)

Make up for the shortage of ternary lithium battery with high IQ power management system

1. Insufficient supplemental discharge current

Tesla uses the NCR18650A battery, with a typical capacity of 3070mAH. Panasonic also has a NCR18650B with a typical capacity of 3350mAH. However, it does not release the Datasheet. It is only used by the NCR18650A used by Tesla. The discharge of 2C (1C discharge current refers to It is 1 hour to discharge the battery of this capacity from full discharge current, such as NCR18650A's 1C discharge is 3350mA), it can also discharge more than 3100mAH, and it is not known.

The discharge results at different currents, the best effect at 2C discharge

It is said that Matsushita will introduce 18650 batteries with a capacity of 4000mAH next year. It is said that there is no improvement in performance under high current. When the capacity is increased, the 1C current of the corresponding battery pack is relatively increased. With the high energy density of the ternary material (which can exceed 200WH/Kg), the 2C discharge current of the battery pack can already satisfy the motor of the sports car. For example, the 85KWH battery of Tesla, from the measured data, the short-term 3C discharge should not be a problem. That is corresponding to 342 horsepower, very objective.

2, to make up for the lack of capacity attenuation

It can be seen that the battery used by Tesla cars is cycled from 0% to 100% at the same charge and discharge current. After 900 cycles, the capacity has been attenuated to 55%. If it is from 0% to 50% each time, even 3000 times. The cycle capacity can still be maintained at 70%. The battery management system tries to keep the battery under low stress and works in a cycle of 0%-50% or 25%-75%, so it can guarantee that there is no obvious endurance attenuation for 300,000 km.

3, security

No matter which brand of ternary material lithium battery, there will be an open flame after internal short circuit or positive electrode material water contact. Even if the 18650 battery has steel shell protection, it still cannot withstand extreme impact. But as long as it can be done, it is not easier to burn than the diesel locomotive fuel tank in extreme accidents. I think Tesla's battery management system has already solved the battery safety problem.

With a high-intelligence battery management system, Tesla has been able to pull the total score of ternary material lithium batteries from 270 to 350 points.

Lithium iron phosphate

Its biggest disadvantage is its low energy density (110WH/Kg), and its capacity attenuation is very high at low temperatures (about 55% at 25°C at -10°C). The advantages are also quite obvious, especially for car companies in China. China's lithium mine reserves are abundant. As of 2011, the world's proven reserves are 13 million tons, and China's reserves are 3.5 million tons. The iron oxide phosphate reserves of the positive electrode material are abundant, and the price of the lower test space after mass production is still large. China is extremely lacking in cobalt mines, with half of the world's reserves in Congo, 21% in Australia and only 1% in China. The use of lithium cobalt oxide or a battery of ternary materials with cobalt, the cost of producing electric vehicles in China's car companies is very passive.

lithium iron phosphate battery can be easily discharged at 20C, so the hybrid car configuration small battery first considers lithium iron phosphate battery. The 3000-time capacity of the 0%-100% cycle is attenuated to 80%, and the long-term storage decay speed of full power is not exaggerated. Puncture, short circuit, high temperature of 350 °C will not explode and burn. These advantages make it difficult for China, especially Chinese car companies with R&D and production of lithium iron phosphate, to choose other types of batteries.

Ternary lithium battery + excellent battery management system will win

Sometimes the product does not necessarily sell well, the author is more optimistic about Tesla's battery technology: battery management as the core. After watching Musk's interview, the author knows that Tesla's top-level goal of electric vehicles is to reduce carbon emissions and make profits from clean energy. Opening patents will lower the threshold of this program, and more manufacturers will follow suit. The more vendors involved, the more Tesla is happy, which is consistent with their purpose.

I often listen to domestic electric vehicles and talk about "curving overtaking". Automobiles are a comprehensive industry, including machinery, electronics, automation, materials, basic science, management, finance, law, education, medical care, etc. Together, they constitute the overall level of the automotive industry, and can even be said to be the epitome of the country's comprehensive strength. China's current situation is lagging behind developed countries. The automobile industry must also lag behind the developed countries. With the advantage of certain components and the operating advantages of certain companies, it can only shorten the gap with others, and it is far from overtaking. The author certainly looks forward to seeing overtaking in my lifetime, which requires the efforts of us and the next generation.

As long as Tesla does not go into the research and development of lithium iron phosphate electric vehicles, I believe that in the long run, the solution of using excellent battery management system + ternary material lithium battery will go further, exceeding the application of lithium iron phosphate.

After 20 years, electric energy will definitely replace fuel

If compared with the internal combustion engine car, no matter which kind of battery is extremely inconvenient, there are still some immature batteries. For example, Tesla is working on the development of aluminum air battery vehicles. Since 1970, 2 trillion barrels of crude oil that is easily exploited in the world has been used up halfway. The remaining 1 trillion barrels are not used up in 25 years. If oil technology fails to cut mining costs sharply in the past 25 years, after 25 years, the price of crude oil per barrel will exceed 500 US dollars, or even 1000 US dollars. It can be contrasted that in 2008, Brent crude oil in the North Sea fluctuated around 10 US dollars. This year's price fluctuated around 100 US dollars. When the fuel car is opened in the future, when the oil price is 5 Yuan per kilometer, whether lithium battery car or fuel cell car or will develop a suitable for their own characteristics of the functional program.

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