Metals News
Does the power battery want to be "continuous" or "safe"?
The content below was translated by Tencent automatically for reference.

SMM News: now the length of the range of pure electric vehicles, as a prerequisite for judging the quality of a car seems to be a normal thing, many car companies often use this model range as high as 500km, surpassing the publicity of a number of domestic competitors to attract the attention of consumers. It is undeniable that for most consumers, the improvement of mileage can reduce or even eliminate "mileage anxiety", but the accompanying safety problems are also worthy of consumer consideration and attention.

1. Forced into the 811 era.

With the further tightening of the subsidy policy, the government has put forward higher requirements for battery energy density and range. In early 2018, four ministries issued the Circular on adjusting and perfecting the Financial subsidy Policy for the Popularization and Application of New Energy vehicles (hereinafter referred to as the "Circular"). The notice requires that the subsidy coefficient be linked to energy density in 2018. Passenger cars need to get the maximum subsidy system energy density > 140Whkg; non-fast charging pure electric buses to get the highest subsidy also need > 140Wh/kg.

By 2019, the adjusted "notice" shows that the battery energy density limit for double subsidy equipment must not be less than 160Whkg, and this limit will reach 260Wh/kg by 2020. On the one hand, the demand of consumers and the requirement of policy, how to improve the energy density of power batteries has become the hottest topic in recent years. In addition, due to the high technical barriers of Ni-Co-Al NCA batteries, and Japanese enterprises monopolize the material market of NCA, Chinese battery manufacturers can only choose the route of Ni-Co-mn NCM under the comprehensive technical conditions, process, cost and other factors.

According to the different proportion of nickel, cobalt and manganese, Ni-Co-mn ternary lithium batteries can be subdivided into 111, 523, 622 and 811 types. Now, the main types in the market are 523 and 622 types, and the monomer energy density is in 200Wh/kg. On the other hand, the 811 battery has exceeded 300 Wh / kg in one fell swoop, which is equivalent to increasing the energy density by nearly 50%, making the NCM811 battery the best choice for many Chinese battery manufacturers.

So 2018 is also known as the 811 yuan year of Chinese batteries. In May of that year, Bick Battery was the first to announce the mass production of the 3.0Ah cylindrical 18650 battery NCM811. Subsequently, Penghui Energy also disclosed that the 2.8Ah and 3.0Ah cylindrical 18650 batteries of the company's NCM811 materials have been mass-produced. Of course, in addition to Beek and Penghui Energy claims to have mass production capacity, several domestic battery factories also announced the future layout of the high nickel 811 last year.

Among them, Ningde Times and BYD, the two giants of power batteries, are not fast. Ningde era has achieved mass production and loading this year, but BYD's final mass production and application time has not yet been announced. But Ningde was not the first company to lay out and mass-produce the 811s, but it was the first battery factory to load the 811s, and the first model to go on sale was the X1 PHEV, which was launched in March by BMW, Ningde's earliest partner.

Advantages and disadvantages of 2.811

So what exactly is an 811 battery? In addition to the high energy density, what are its advantages and disadvantages? NCM811, cathode material is nickel, cobalt and manganese, and the content ratio is 80% to 10%. Because the main role of nickel in lithium ion battery is Lago capacity, which makes the energy density of battery higher, 811 battery has become the highest energy density lithium battery.

However, nickel is also an element with high metal activity, so the greater its specific gravity, the lower the safety of the battery. The main manifestation is the capacity loss of cyclic charging and the accelerated attenuation of high temperature environmental capacity. in the long run, the service life of 811 battery will decrease, and the risk of spontaneous combustion caused by thermal out of control will increase significantly.

Secondly, cobalt, as the key material of ternary lithium battery, can not only improve the stability of the battery, but also increase the cycle life of the battery, which plays a vital role in the ternary lithium battery. However, in the 811 battery, the proportion of cobalt accounts for only 10%, the safety hazard can not be underestimated.

However, the price of cobalt is the most expensive of the three elements, and after the development of the ternary lithium battery market in recent years, lithium, cobalt and other metal resources are tight, especially cobalt. Its transaction price rose from 25.5-280000 yuan / ton in 2016 to 534000 yuan / ton at the end of 2017, a sharp increase of 97.8%. The transaction price of nickel has been hovering around 100000 yuan / ton, and the ex-factory price of manganese is even lower. The basic cost is only 13000 yuan per ton. It can be seen that the 811 route can not only increase the energy density, but also effectively reduce the cost by increasing the content of nickel and reducing the content of cobalt.

It is reported that the unit cost of the ternary cell produced by 811 materials can be reduced by about 7% compared with the 523 cell. After calculating the cost of the battery package, the comprehensive unit Wh cost can be reduced by more than 8%.

It is worth mentioning that the first car launched by Tesla in 2013 used Panasonic's nickel-cobalt-aluminum 80% to 15% 5% lithium-ion battery, while China's new energy vehicles were generally using lithium iron phosphate batteries, which is why Tesla has maintained an absolute lead in mileage for many years.

3. How can security be improved?

In this way, the advantages and disadvantages of the 811 battery are so obvious that public opinion has made two different voices about it. One believes that the 811 battery is currently the highest energy density battery, pure electric vehicles want to break through the 500km, 600km or higher endurance bottleneck, the development of 811 is the only way; the other is that the current battery package protection technology is not enough to ensure the safety of 811 batteries with poor thermal stability, and it is unwise for battery factories and mainframe factories to go all out to 811. Is there no way to solve the problem?

Ouyang Minggao, academician of the Chinese Academy of Sciences and executive vice chairman of the China Electric vehicle Association, has made a detailed analysis on the safety of high nickel power batteries. He believes that there are three main technical ways to improve the safety of high nickel batteries.

First of all, the battery pack and cathode materials need to be further studied. For example, if single crystal particles are used to replace polycrystalline cathode materials, the thermal stability and safety of the battery can be improved to a certain extent.

Secondly, the thermal spread is blocked, that is, the heat insulation material is added to the dominant heat transfer path to form the effect of "firewall". The technology has been used on BMW's X1 PHEV, which uses 811 batteries.

Finally, there is the management of the heat out of control. At present, Ningde era in this regard has been able to achieve 15 minutes in advance will be able to cause heat out of control of the internal short circuit warning.

By doing all this, perhaps the safety and durability of the 811 battery can be greatly improved. However, as far as the current situation is concerned, the 811 battery has clearly not yet reached its most mature state, and consumers are worried that their excessive launch on the market will further dampen the enthusiasm for buying pure electric vehicles. This is not a good deal in the long run.

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