The performance of the cylindrical lithium battery 21700 from a technical point of view

From a technical point of view, there are 21,700 cylindrical lithium batteries. Compared with soft packs and square lithium batteries, 18650 cylindrical lithium batteries were the earliest commercialization, the highest degree of processing automation, and the lowest cost of power lithium-ion batteries at that time. With Tesla's years of gripping, it has basically maintained the state of the three points nationwide with soft packs and square batteries. Since Tesla announced 21,700 Model 3s, this cylindrical battery family has added another star. The following are some technical aspects of cylindrical batteries. Cylinder battery refers specifically to 18650, which is not specified below. Cylindrical cell structure If we attach importance to power lithium-ion batteries, we will find that the cylindrical 18560 battery is the battery with the most discussions, the most types, and the most technical reviews. The monomer is mainly composed of positive electrode, negative electrode, gap, positive and negative collector, safety valve, overcurrent protection device, insulation, shell, etc. The shells were mostly steel shells in the early days, and aluminum shells were important at that time. Individual over-current protection equipment has different plans from different manufacturers. According to different safety requirements, the price is different and can be customized. Generally, safety equipment mainly includes PTC positive temperature coefficient resistance and fuse equipment. PTC, when the current is too large, the resistance heats up, and the temperature accumulates more, which promotes the increase of the PTC resistance value. When the temperature later exceeds a certain threshold, it suddenly rises, which is equivalent to isolating the faulty battery from the entire circuit to prevent heat Further losses. In principle, a fuse is a fuse that blows when the circuit breaks due to excessive current. The difference between these two types of protection devices is that the former is recoverable, while the latter is disposable. In the event of a failure, the system must consider replacing the faulty unit to make it work normally. Cylindrical cell features Cylindrical batteries, especially the 18650 type, have the highest level of automation among the three important battery modes due to their structural features and standardization of models. This makes a high degree of consistency possible and yields increase. Data shows that the product quality rate of leading foreign manufacturers such as Samsung and Songyu can reach 98%, while the product quality rate of Chinese manufacturers can exceed 90%. Advantages: 1) As mentioned above, the monomer has good consistency; 2) The mechanical properties of the monomer itself are good. Compared with square and soft-packed batteries, the closed cylinder can obtain the highest bending strength under similar standards; 3) The technology is outdated and the cost is low, but at the same time it almost consumes the cost of optimization space; 4) The single energy is very small, when When things happen, the way is easy to control, but this has also become the reason why it is replaced (what makes you destroyed, what does not kill you, will make you stronger, as the saying goes) 1) In the environment of electric vehicles, the battery The large number of cylindrical batteries in the system adds to the complexity of the battery system. Regardless of whether this mechanism is still a processing system, it is related to the other two batteries. 2) In the case of uneven temperature environment, the probability that many batteries have different characteristics increases. Of course, the reason why Tesla chose 18650 at the beginning of the plan was considered an impossible choice, because 10 years ago, qualified power lithium-ion batteries could be processed in large quantities as long as they were cylindrical batteries. The safety and heat treatment requirements of the battery are the driving force for the research and development of its strong electronic control system. 3) There is little room for energy density to rise now. In the 2016 news, Chaowei's single-cell capacity has reached 4050mAh, and the battery specific capacity has reached 306Wh/kg, which is no higher record. In a given space, as long as it is a wooden door material, it is recognized. Tesla's Model 3 battery system caught fire at 21700. Tesla Model 3 was completely powered by 21,700 ternary lithium batteries, opening a new stage of cylindrical battery advancement capabilities. The energy density of the 21700 battery system of Tesla Model 3 is about 300Wh/kg, which is more than 20% higher than the 18650 battery energy density used in the original ModelS, and about 35% higher than the single capacity, and the system cost is reduced by about 9%. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.