How about a cylindrical lithium battery 21700?

Compared with soft packs and square lithium batteries, the 1,8650 cylindrical lithium battery is the earliest commercialized, with the highest degree of automation and the lowest current cost. Tesla has been holding for many years, basically maintaining a three-point situation with soft bags and square batteries.

Since Tesla announced the adoption of the Model 3 21700, the cylindrical battery family has also had one more star member. This article takes a look at several technical points related to cylindrical batteries. If there is no special statement in the following, the cylindrical battery specifically refers to 18650.

Cylinder battery structure

Pay attention to the power battery and you will find that the cylindrical 18560 battery is the most studied and technically discussed battery variety. The monomer is mainly composed of positive, negative, diaphragm, positive and negative electrode collector, safety valve, overcurrent protection device, insulator and shell. The shell, with more early steel shells, is currently dominated by aluminum shells.

Monomer overflow protection device, the design of each manufacturer is not the same, depending on the security requirements, the price to be different, can be customized. General safety devices mainly include PTC positive temperature coefficient resistors and fuse devices.

PTC, when there is an excessive current, resistance heating, and temperature accumulation, it also promotes the increase of PTC resistance. When the temperature exceeds a threshold, it suddenly increases, which is equivalent to isolating the faulty core from the overall loop to avoid further thermal runaway. happen.

The fuse device is a fuse in principle. When a large current is encountered, the fuse is fused and the circuit is disconnected.

The difference between the two protection devices is that the former can be restored, and the latter's protection is one-time. Once the failure occurs, the system must consider that the replacement problem core can work properly.

Cylinder core characteristics

Cylinder cores, especially 18650, due to their own structural characteristics, and due to the standardization of their models, the level of automation of cylindrical core production is the highest among the three main core forms. This makes it possible to achieve a high degree of consistency and a corresponding increase in yield. Data show that Samsung, Panasonic and other major foreign manufacturers can reach 98 % of the good quality, and our manufacturers can also exceed 90 %.

Advantage

1) As mentioned above, the monomer is more consistent;

2) The mechanical properties of the monomer itself are good. Compared with the square and soft-pack batteries, the closed cylinder, with an approximate size, can obtain the highest bending strength;

3) The technology is mature and the cost is low, but at the same time, the space for cost optimization has also been consumed;

4) Monomer energy is small, and when an accident occurs, the form is easy to control, but this is also becoming the reason for its replacement.) Those who can not kill you will also make you strong.

Disadvantages, 1) In the context of electric vehicles, the number of cylindrical monomers in the battery system is very large, which makes the complexity of the battery system greatly increase. Whether it is a mechanism or a management system, compared to the other two types of batteries, the cost of the system is higher. Cylinder battery;

2) Under the condition of uneven temperature environment, the probability of alienation of a large number of core characteristics increases. Of course, Tesla chose 18650 at the beginning of its design, and it is believed that it is only a helpless choice because 10 years ago, it was able to mass-produce qualified power batteries., Only cylindrical batteries. The safety and thermal management requirements of the battery are instead the research and development power of its powerful electronic control system.

3) The space for the increase in energy density is already very small. In the 2016 news, Chaowei has a single capacity of 4050 mAh, and the core is 306 Wh/kg of energy, and no higher record has been seen since then. In the established space, only the materials of death and death, recognized as a difficult road.

Tesila's Model3 battery system is on fire.

Tesla Model 3 fully launched 21700 ternary lithium batteries, opening a new phase of cylindrical battery capacity enhancement. The Tesla Model 3 21700 battery system has an energy density of about 300 Wh / kg, which is more than 20 % higher than the 18650 battery energy density used by the original Model S, 35 % higher monomer capacity, and a system cost reduction of about 9 %.

21700 Related manufacturers and models

At present, there are only a handful of companies in the world that can mass-produce 21700 batteries. In addition to the mass production of 21700 batteries jointly developed by Panasonic and Tesla, Samsung SDI has also demonstrated related 21700 products. It is understood that the product has not yet been mass-produced.

Domestic 21700 manufacturers, news data show that the manufacturers who started 21700 are Bic, lishen, Yiwei Lithium, Tianpeng Power Supply, Far East Foster, Lions New Energy and so on.

With the publicity of the two products of Nanjing Jinlong and Beiqi, on August 16, the Ministry of Industry and Information Technology of the State issued the new vehicle product publicity of the "Road Motor Vehicle Production Enterprise and Product Notice"(299th batch). Among them, two pure electric vans (models NJL5040XXYBEV25 and BJ5040XXYCJ06EV) produced by Nanjing Jinlong Bus Manufacturing Co., Ltd. and Beiqi (Changzhou) Automobile Co., Ltd. were the first to carry 21700 triple lithium ion batteries.

From 18650 to 21700, how do you think of the rise?

Ever since I saw this picture on the Internet, I 've been looking for a chance to put it in the article for no other reason. The summary of ascension than energy in the picture can be said to be very comprehensive. Along the lines of the graph, if the energy ratio of the core is increased by chemical methods, the future of the 18650 is not bright.

The challenges faced by the development of lithium-ion batteries in 18650. In the face of the current situation in which people continue to improve their specific energy, if they maintain the same size and increase the energy density, the 18650 faces many challenges:

1) The supply chain of new materials such as NCA, Silicon and other new materials is not yet mature, the cost is high, and the supply is difficult to stabilize. For example, materials with higher energy density 811 have a gap between their own stability and the process control distance. The result is that 811 The 1,8650 is much more expensive in the short term. However, the performance is much worse;

2) The new material process has high environmental requirements, high investment in fixed assets, and huge energy consumption;

3) Low single battery capacity, high technical requirements and high cost for PACK group;

4) The single core is at most suitable for positive single and negative bipolar ear structures, and has a significant impact on energy density;

5) When high energy density and high ratio charging are required at the same time, the design space is very small. In 18650, 523 + graphite system was used. According to the new national standard, 1C achieved 2.4 AH has reached the design limit.

Larger diameter cylindrical lithium-ion batteries will become an inevitable trend. There are data as shown in the figure below. Larger size electric cores are compared with 18650 in the polar ear design and winding rate. Large-size electric cores show obvious advantages.

The page contains the contents of the machine translation.