Tesla has been the headline news at home and abroad recently, and there are overwhelming negative news about Model 3 delays and closures. However, with the disclosure of more information and the exposure of Model3P80D parameters, the biggest change is the use of a new 21700 battery instead of the original battery.

What is 18650 battery

5 batteries in 18650 compared with 18650

In order to make the 21700 battery easier to understand and more interesting to discuss with your friends, let’s briefly review Tesla’s current 18650 battery. After all, the principle is the same.

As a cylindrical battery, 18650 has a different appearance from ordinary AA batteries. This makes it widely applicable to various electronic products. And compared with the traditional AA5 battery, the volume is larger and the capacity can be maintained better.

I have to mention its naming, cylindrical battery, they have a very simple naming rule, 18650, for example, the first two display, how many millimeters in diameter this battery is, the number represents the height and shape of the battery (number 0 ( Cylindrical), or 18650 batteries with a diameter of 18 mm and a height of 65 mm cylindrical batteries. The standard was originally introduced by Sony, but it did not really become popular in the beginning, because the shape can be changed according to needs.

With the development of glare flashlights, notebook computers, etc., 18650 ushered in its own product peak period. In addition to foreign manufacturers such as Panasonic and Sony, various small domestic workshops also began to produce such batteries. However, compared with the average capacity of foreign manufacturers above 3000ma, the capacity of domestic products is not superior, and many domestic batteries have poor quality control, which directly ruined the reputation of 18650 batteries.

Why use 18650 battery

IPhoneX’s battery is one of these stacked batteries

Tesla chose 18650 because of its mature technology, relatively excellent energy density, and stable quality control. In addition, as an emerging car manufacturer, Tesla did not have any battery production technology before, so it is more cost-effective to directly purchase mature products from excellent manufacturers than to research or find a factory to produce stacked batteries.

700Wh 18650 battery pack

However, compared with stacked batteries, 18650 is smaller and has lower personal energy! This means that more single batteries are needed to form a suitable battery pack to increase the vehicle’s cruising range. This creates a technical challenge: how to manage thousands of batteries?

For this reason, Tesla has created a set of top-level BMS battery management system to manage thousands of 18650 batteries (due to the complexity of the management system, this article will not repeat it, and I will explain it to you later). Under the precise management system, it has excellent 18650 battery quality control and high individual consistency, which also makes the whole system maintain high controllability and stability.

But because the BMS battery management system is too heavy, it leads to another fatal problem: how to solve the heat dissipation problem of the battery system?!

If you disassemble the current smartphone battery, you will find that the battery shell is not very hard, but is protected by a very thin aluminum plate. The advantage of this is that it can be made very thin, so you don’t have to worry too much about heat dissipation. But the disadvantage is that it is easy to break, even bend by hand, and smoke.

18650 metal protective sleeve

But the 18650 battery is different. For safety reasons, the surface of the battery is coated with steel or aluminum alloy to prevent the battery from exploding. But it is this rigid structure that brings huge challenges to heat dissipation, especially when 8000 batteries are put together.

Tesla BMS system

Tesla uses the engine exhaust manifold to cool the batteries with liquid to ensure that the temperature difference between each battery does not exceed 5 degrees. But this cooling method raises another problem: weight and cost!

Because if the energy density of the 18650 battery is compared with the energy density of the stacked battery, the advantage of the 18650 is obvious. But if you add the weight of the BMS battery management system to the 18650 battery pack, the energy density of the stacked batteries will exceed 18650! This proves how complicated the BMS system is. So to solve the weight and cost issues, the simplest solution is to replace the relatively outdated 18650 battery.

What are the advantages of the 21700 battery

Since the cylindrical battery products are already very mature, it is possible to increase the diameter of 3mm and the height of 50mm on the basis of the original 18650, directly increase the volume and bring a larger Mah. In addition, due to its large size, the 21700 battery has a multi-stage ear, which slightly increases the charging speed of the battery. In addition, the larger the battery size, the number of batteries in the vehicle will be relatively reduced, thereby reducing the complexity of the BMS system, thereby reducing weight and cost.

Electric mountain bike with 21,700 batteries

But Tesla is not the first company to use 21,700 batteries. As early as 2015, Panasonic took the lead in using batteries in its electric bicycles. Later, Tesla saw that the use of this battery was very effective, so it proposed to purchase upgrades like Panasonic. With the two long-term cooperation, it is natural for Model 3 to use 21700.

model can use 21700

According to Musk, I don’t think it will be used in the near future, but it will definitely be used in the next version. After all, this battery has played a very positive role in production cost and price!

In addition, the main problem facing electric vehicles is when will battery technology achieve a qualitative leap. But if you look closely, it raises two very difficult questions: which one to choose between long battery life and fast charging. Musk seems to have chosen fast charging because he has made it clear that he does not want to see the sum of model and ModelX exceed 100 kWh.

Tesla model chassis

There is another problem to be solved, and that is the design of the chassis. The size of the 18650 lithium battery is different from the size of the 21700 battery, which directly leads to a change in the design of the chassis where the battery pack is installed. In other words, Tesla will have to redesign the chassis of existing models to accommodate 21,700 batteries.

The latest Model3P80D data

Model3P80D is currently the fastest known Model3 model, equipped with electric motors at the front and rear, realizing a four-wheel drive system by fly-by-wire. 0-100km/h acceleration in 3.6 seconds, comprehensive road conditions range of 498 kilometers! The capacity of 21,700 battery packs is 80.5 KWH, which is the origin of the P80D name.

BAIC New Energy van equipped with 21,700 yuan of lithium

In fact, the 21700 battery is not an advanced technology. If you open Taobao, you can find the 21700 battery. It is also suitable for portable devices such as flashlights and e-cigarettes just like the 18650 battery. In addition, the two domestic trucks of BAIC and King Long used 21,700 battery packs as early as last summer. From this point of view, it is not a black technology, and domestic manufacturers are also producing it, but the Model3 attribute of the theme pushes it to the forefront. What I care more about is when Model 3 will be delivered in China!